Proceedings Volume 9517

Smart Sensors, Actuators, and MEMS VII; and Cyber Physical Systems

Proceedings Volume 9517

Smart Sensors, Actuators, and MEMS VII; and Cyber Physical Systems

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Volume Details

Date Published: 1 July 2015
Contents: 14 Sessions, 84 Papers, 0 Presentations
Conference: SPIE Microtechnologies 2015
Volume Number: 9517

Table of Contents


Table of Contents

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  • Front Matter: Volume 9517
  • Harvesting
  • Materials and Processes
  • Resonators
  • Optical Devices
  • Modeling
  • Devices
  • Characterization
  • Systems
  • Chemical Sensors
  • Poster Session
  • Energy Harvesting and Low Power Design
  • Embedded Systems Applications
  • Networking and Embedded Computing
Front Matter: Volume 9517
Front Matter: Volume 9517
This PDF file contains the front matter associated with SPIE Proceedings Volume 9517 including the Title Page, Copyright information, Table of Contents, Introduction, and Conference Committee listing.
Vibration energy harvesting: fabrication, miniaturisation and applications
S. P. Beeby, D. Zhu
This paper reviews work at the University of Southampton and its spin-out company Perpetuum towards the use of vibration energy harvesting in real applications. Perpetuum have successfully demonstrated vibration-powered condition monitoring systems for rail and industrial applications. They have pursued applications were volume is not a particular constraint and therefore sufficient power can be harvested. Harvester reliability and longevity is a key requirement and this can be a challenging task in high shock environments. The University of Southampton has investigated the miniaturization of the technology. MEMS electromagnetic harvesters were found to be unsuitable although miniaturized devices fabricated using bulk components did perform well. Screen printed piezoelectric harvesters were also found to perform well and were ideally suited to a low profile application where device thickness was limited. Screen printing was not only used to deposit the active piezoelectric material but also an inertial mass ink based on tungsten. This enables the device to be printed entirely by screen printing providing a low-cost route to manufacture. Finally, details of a simulation tool that can take real world vibrations and estimate vibration energy harvester output was presented. This was used to simulate linear and nonlinear harvesters and in many applications with a characteristic resonant frequency the linear approach was found to be the optimum. Bistable nonlinear harvesters were found to work better with more random vibration sources.
Influence of process parameters on properties of piezoelectric AlN and AlScN thin films for sensor and energy harvesting applications
Stephan Barth, Hagen Bartzsch, Daniel Gloess, et al.
This paper reports on the deposition of AlN and AlXSc1-XN films by pulse magnetron sputtering. The influence of process parameters on the film properties and the evaluation of the films for micro energy harvesting are presented. For AlN it is shown, that film stress can be varied in a considerable range between compressive and tensile stress while maintaining good piezoelectric properties. Additionally, the effect of doping AlN with Sc regarding piezoelectric and mechanical properties is presented. The films show the expected increase of piezoelectric properties as well as the softening of the material with higher Sc concentrations. Above a threshold concentration of around 40% Sc in the AlXSc1-XN films, there exists a separation into two phases, an Al-rich and a Sc-rich wurtzite phase, which is shown by XRD. At Sc concentrations higher than 50%, the films are not piezoelectric, as the films are composed primarily of the cubic ScN phase. Sc doping allows to significantly increase the energy generated in test setup. Up to 350 μW power have been generated under optimum conditions.
From MEMS to macro-world: a micro-milling machined wideband vibration piezoelectric energy harvester
J. Iannacci, G. Sordo
In this work, we discuss a novel mechanical resonator design for the realization of vibration Energy Harvester (EH) capable to deliver power levels in the mW range. The device overcomes the typical constraint of frequency narrowband operability of standard cantilevered EHs, by exploiting a circular-shaped resonator with an increased number of mechanical Degrees Of Freedom (DOFs), leading to several resonant modes in the range of vibrations of interest (i.e. multi-modal wideband EH). The device, named Four-Leaf Clover (FLC), is simulated in Ansys Worbench™, showing a significant number of resonant modes up to vibrations of around 2 kHz (modal eigenfrequencies analysis), and exhibiting levels of converted power up to a few mW at resonance (harmonic coupled-field analysis). The sole FLC mechanical structure is realized by micro-milling an Aluminum foil, while a cantilevered test structure also including PolyVinyliDene Fluoride (PVDF) film sheet is assembled in order to collect first experimental feedback on generated power levels. The first lab based tests show peak-to-peak voltages of several Volts when the cantilever is stimulated with a mechanical pulse. Further developments of this work will comprise the assembly of an FLC demonstrator with PVDF pads, and its experimental testing in order to validate the simulated results.
Low-profile and wearable energy harvester based on plucked piezoelectric cantilevers
Michele Pozzi, Heather J. A. Almond, Glenn J. T. Leighton, et al.
The Pizzicato Energy Harvester (EH) introduced the technique of frequency up-conversion to piezoelectric EHs wearable on the lateral side of the knee-joint. The operation principle is to pluck the piezoelectric bimorphs with plectra so that they produce electrical energy during the ensuing mechanical vibrations. The device presented in this work is, in some ways, an evolution of the earlier Pizzicato: it is a significantly more compact and lighter device; the central hub holds 16 piezoelectric bimorphs shaped as trapezoids, which permits a sleek design and potentially increased energy output for the same bimorph area. Plectra were formed by Photochemical Machining of a 100-μm-thick steel sheet. To avoid the risk of short-circuiting, the plectra were electrically passivated by sputtering a 100 nm layer of ZrO2. Bench tests with the steel plectra showed a very large energy generation. Polyimide plectra were also manufactured with a cutting plotter from a 125μm-thick film. Besides bench tests, a volunteer wore the device while walking on flat ground or climbing stairs, with a measured energy output of approximately 0.8 mJ per step. Whereas most of the tests were performed by the traditional method of discharging the rectified output from the EH onto a resistive load, tests were performed also with a circuit offering a stabilised 3.3 V supply. The circuit produced a stable 0.1 mA supply during running gait with kapton plectra.
Materials and Processes
High temperature performance of sputter-deposited piezoelectric aluminum nitride thin films
M. Gillinger, M. Schneider, A. Bittner, et al.
Aluminum nitride (AlN) is a promising material for sensor applications in harsh environments such as turbine exhausts or thermal power plants due to its piezoelectric properties, good thermal match to silicon and high temperature stability. Typically, the usage of piezoelectric materials in high temperature is limited by the Curie-temperature, the increase of the leakage current as well as by enhanced diffusion effects in the materials. In order to exploit the high temperature potential of AlN thin films, post deposition annealing experiments up to 1000°C in both oxygen and nitrogen gas atmospheres for 2 h were performed. X-ray diffraction measurements indicate that the thin films are chemically stable in a pure oxygen atmosphere for 2 h at annealing temperatures of up to 900°C. After a 2 h annealing step at 1000°C in pure oxygen. However, a 100 nm thin AlN film is completely oxidized. In contrast, the layer is stable up to 1000°C in pure nitrogen atmosphere. The surface topology changes significantly at annealing temperatures above 800°C independent of annealing atmosphere. The surface roughness is increased by about one order of magnitude compared to the "as deposited" state. This is predominantly attributed to recrystallization processes occurring during high temperature loading. Up to an annealing temperature of 700°C, a Poole-Frenkel conduction mechanism dominates the leakage current characteristics. Above, a mixture of different leakage current mechanisms is observed.
Wafer bonding technology for new generation vacuum MEMS: challenges and promises
V. Dragoi, E. Pabo
Various MEMS devices are incorporated into consumer electronic devices. A particular category of MEMS require vacuum packaging by wafer bonding with the need to encapsulate vacuum levels of 10-2 mbar or higher with long time stability. The vacuum requirement is limiting the choice of the wafer bonding process and raises significant challenges to the existing investigation methods (metrology) used for results qualification. From the broad range of wafer bonding processes only few are compatible with vacuum applications: fusion bonding, anodic bonding, glass frit bonding and metal-based bonding. The outgassing from the enclosed surfaces after bonding will affect the vacuum level in the cavity: in some cases, a getter material is used inside the device cavity to compensate for this outgassing. Additionally the selected bonding process must be compatible with the devices on the wafers being bonded. This work reviews the principles of vacuum encapsulation using wafer bonding. Examples showing the suitability of each process for specific applications types will be presented. A significant challenge in vacuum MEMS fabrication is the lack of analytical methods needed for process characterization or reliability testing. A short overview of the most used methods and their limitations will be presented. Specific needs to be addressed will be introduced with examples.
3D integration approaches for MEMS and CMOS sensors based on a Cu through-silicon-via technology and wafer level bonding
L. Hofmann, S. Dempwolf, D. Reuter, et al.
Technologies for the 3D integration are described within this paper with respect to devices that have to retain a specific minimum wafer thickness for handling purposes (CMOS) and integrity of mechanical elements (MEMS). This implies Through-Silicon Vias (TSVs) with large dimensions and high aspect ratios (HAR). Moreover, as a main objective, the aspired TSV technology had to be universal and scalable with the designated utilization in a MEMS/CMOS foundry. Two TSV approaches are investigated and discussed, in which the TSVs were fabricated either before or after wafer thinning. One distinctive feature is an incomplete TSV Cu-filling, which avoids long processing and complex process control, while minimizing the thermomechanical stress between Cu and Si and related adverse effects in the device. However, the incomplete filling also includes various challenges regarding process integration. A method based on pattern plating is described, in which TSVs are metalized at the same time as the redistribution layer and which eliminates the need for additional planarization and patterning steps. For MEMS, the realization of a protective hermetically sealed capping is crucial, which is addressed in this paper by glass frit wafer level bonding and is discussed for hermetic sealing of MEMS inertial sensors. The TSV based 3D integration technologies are demonstrated on CMOS like test vehicle and on a MEMS device fabricated in Air Gap Insulated Microstructure (AIM) technology.
Design and fabrication of indium phosphide air-bridge waveguides with MEMS functionality
We present the design and fabrication of a dual air-bridge waveguide structure integrated with MEMS functionality. The structure is designed to function as a tunable optical buffer for telecommunication application. The optical buffer structure is based on two parallel waveguides made of high refractive index material with subwavelength dimensions. They are suspended in air, and are separated by a sub-micron air gap. Due to the fact that the size of the waveguides is much smaller than the wavelength of light that propagates in the structure, a significant fraction of the optical mode is in the air gap between the waveguides. By changing the size of the air gap using MEMS techniques, we can vary this fraction and hence the effective refractive index of the waveguide structure, thus generating tunable optical delay. The optical buffer structure was grown on an InP substrate by molecular beam epitaxy, and the device layer was made of InGaP. An InGaAs layer was sandwiched between the device layer and the substrate to serve as a sacrificial layer. The sub-micron waveguides, their supports in the form of side pillars with tapered shapes in order to minimize optical losses, and the MEMS structures were patterned using electron beam lithography and plasma etching. Electrodes were integrated into the structure to provide electrostatic actuation. After the sample patterning, the waveguide structure was released using HF etch. Our simulations predict that by varying the waveguide separation from 50 nm to 500 nm, we could achieve a change in propagation delay by a factor of two.
Electrothermal piezoresistive cantilever resonators for personal measurements of nanoparticles in workplace exposure
Hutomo Suryo Wasisto, Wenze Wu, Erik Uhde, et al.
Low-cost and low-power piezoresistive cantilever resonators with integrated electrothermal heaters are developed to support the sensing module enhancement of the second generation of handheld cantilever-based airborne nanoparticle (NP) detector (CANTOR-2). These sensors are used for direct-reading of exposure to carbon engineered nanoparticles (ENPs) at indoor workplaces. The cantilever structures having various shapes of free ends are created using silicon bulk micromachining technologies (i.e, rectangular, hammer-head, triangular, and U-shaped cantilevers). For a complete wearable CANTOR-2, all components of the proposed detector can be grouped into two main units depending on their packaging placements (i.e., the NP sampler head and the electronics mounted in a handy-format housing). In the NP sampler head, a miniaturized electrophoretic aerosol sampler and a resonant silicon cantilever mass sensor are employed to collect the ENPs from the air stream to the cantilever surfaces and measuring their mass concentration, respectively. After calibration, the detected ENP mass concentrations of CANTOR-2 show a standard deviation from fast mobility particle sizer (FMPS, TSI 3091) of 8–14%.
Out-of-plane piezoelectric microresonator and oscillator circuit for monitoring engine oil contamination with diesel
J. Toledo, T. Manzaneque, V. Ruiz-Díez, et al.
Real-time monitoring of the physical properties of liquids is an important subject in the automotive industry. Contamination of lubricating oil by diesel soot has a significant impact on engine wear. Resonant microstructures are regarded to be a precise and compact solution for tracking the viscosity and density of lubricant oils. Since the measurement of pure shear forces do not allow an independent determination of the density and viscosity, two out-of-plane modes for the monitoring of oil dilution with diesel have been selected. The first one (12-mode) is working at 51 kHz and the second mode (14-mode) at 340 kHz. Two parameters were measured: the quality factor and the resonance frequency from which the viscosity and density of the fluids under test can be determined, requiring only a small amount of test liquid. A PLL-based oscillator circuit was implemented based on each resonator. Our results demonstrate the performance of the resonator in oils with viscosity up to 90 mPa·s. The quality factor measured at 25°C was 7 for the 12-mode and 19 for the 14-mode. A better resolution in density and viscosity was obtained for the 14-mode, showing a resolution of 3.92·10-5 g/ml for the density and 1.27·10-1 mPa·s for the viscosity, in pure lubricant oil SAE 0W30. An alternative tracking system, based on a discrete oscillator circuit, was tested with the same resonator, showing a comparable stability and supporting our approach.
Technology towards a SAW based phononic crystal sensor
Marc-Peter Schmidt, Aleksandr Oseev, Ralf Lucklum, et al.
Phononic crystals (PnC) with a specifically designed defect have been recently introduced as novel sensor platform. Those sensors feature a band gap covering the typical input span of the measurand as well as a narrow transmission peak within the band gap where the frequency of maximum transmission is governed by the measurand. This innovative approach has been applied for determination of compounds in liquids [1]. Improvement of sensitivity requires higher probing frequencies around 100 MHz and above. In this range surface acoustic wave devices (SAW) provide a promising basis for PnC based microsensors [2]. The respective feature size of the PnC SAW sensor has dimensions in the range of 100 μm and below. Whereas those dimensions are state of the art for common MEMS materials, etching of holes and cavities in piezoelectric materials having an aspect ratio diameter/depth is challenging. In this contribution we describe an improved technological process to manufacture considerably deep and uniform phononic crystal structures inside of SAW substrates.
Experimental investigations of creep in gold RF-MEMS microstructures
Aurelio Somà, Giorgio De Pasquale, Muhammad Mubasher Saleem
Lifetime prediction and reliability evaluation of micro-electro-mechanical systems (MEMS) are influenced by permanent deformations caused by plastic strain induced by creep. Creep in microstructures becomes critical in those applications where permanent loads persist for long times and thermal heating induces temperature increasing respect to the ambient. Main goal of this paper is to investigate the creep mechanism in RF-MEMS microstructures by means of experiments. This is done firstly through the detection of permanent deformation of specimens and, then, by measuring the variation of electro-mechanical parameters (resonance frequency, pull-in voltage) that provide indirect evaluation of mechanical stiffness alteration from creep. To prevent the errors caused be cumulative heating of samples and dimensional tolerances, three specimens with the same nominal geometry have been tested per each combination of actuation voltage and temperature. Results demonstrated the presence of plastic deformation due to creep, combined with a component of reversible strain linked to the viscoelastic behavior of the material.
Optical Devices
The next generation of MEMS-based optical microspectrometers
Reinoud F. Wolffenbuttel
MEMS-based optical microspectrometers are typically composed of MEMS devices for operation as dispersive element or as tunable resonator within an optical system. CMOS-compatible MEMS technologies enable on-chip integration of the MEMS optical components, detector and readout circuits. The actual realization and exploitation of this on-chip functional integration of the entire microspectrometer imposes several challenges. The state-of-the-art and some of the technology and design challenges will be outlined, followed by an introduction to some of the trends and upcoming application of high potential.
Input-shaped actuation of electromagnetic MEMS mirrors
Jörg Reitterer, Franz Fidler, Gerhard Schmid, et al.
For many applications of MEMS actuators a well-defined trajectory of the movable device component is crucial when using a simple and inexpensive open-loop controller. We have applied to quasi-statically actuated electromagnetic MEMS mirrors the control technique called "input shaping", which is widely used for systems at the macro-scale and to a lesser extent also to systems at the micro-scale. We derive the impulse response of a filter which suppresses the excitation of undesired resonant modes and present simulation and measurement results of the oscillation-free linear MEMS mirror movement. The robustness of different input shaping filter types with respect to errors in the estimation of the system parameters, i.e., resonance frequency and damping ratio, is analyzed.
2D stepping microdrive for hyperspectral imaging
Csaba Endrödy, Hannes Mehner, Adrian Grewe, et al.
In a novel hyperspectral imaging concept based on confocal chromatic microscopy, a pinhole array (matrix of pinholes) has to be scanned across an intermediate image plane to capture the full object plane. In this paper a two-axis stepping microdrive is presented for the pinhole array (6×7.5×0.2 mm3 of glass, weight 20 mg), featuring a 10 μm step size and a 200 μm displacement range in each direction. With the two-axis stepwise actuation of the pinhole array, the imaged area of the object plane is increased from 7% (fixed pinhole array) up to 89% with actuated array. The two-axis positioning is implemented with a three-axis inchworm motion driven by electrostatic forces. A combination of horizontal and vertical electrostatic actuators are arranged to achieve a precise in-plane actuation of the pinhole array. The microdrive is fabricated with established MEMS technologies and features a size about 1 cm2 with 1 mm thickness. The microdrive is capable to position the pinhole array over the displacement range. The array size enables a 1:1 optical imaging on an 8 mm diagonal size CCD. The presented stepping microdrive outperforms existing microsystem solutions with a combination of high payload, large step size, displacement range, and the large optical aperture. Furthermore, the device concept enables the positioning of milligram weights with a highly integrated microsystem.
Design and fabrication of an endomicroscopic imaging module for minimally invasive medical devices
C. G. Costa, J. S. Gomes, R. F. Wolffenbuttel, et al.
Medical imaging is an important part of diagnosis. The procedure should provide valuable information for diagnosis and, at the same time, should be minimally invasive for the patient. Therefore, when performing endoscopic imaging a system with reduced dimensions is crucial. The performance of imaging systems, used in several diagnosis endoscopic procedures, would highly benefit from the integration of an endomicroscopic imaging module (ENIM) able to perform in-vivo and real-time tissue microscopy. This paper proposes a miniaturized ENIM: its total length is 12.164 mm and has a lateral lens assembly of 3.894 mm. A microfabricated PDMS lens was included in the system, obtained by a hanging droplet approach, a very-low cost and effective method. A paraxial magnification of 14 times was achieved with a Modulation Transfer Function (MTF) around 38% at 50 lp/mm and maximum distortion about 1.8%.
Acoustic high-frequency effects inside the package of capacitive silicon microphones and their impact on the device performance
G. Schrag, T. Kuenzig, D. Pham, et al.
We present investigations on acoustic effects occurring inside the sound port of capacitive silicon microphones, which exert additional frequency-dependent damping forces on the sensing membrane and, thus, affect the overall performance of the microphone. Extensive FE simulations have been carried out in order to study the airflow inside the package, to identify relevant impact factors, and to optimize an existing acoustic network model intended for implementation in a fully coupled, multi-energy domain system-level model of the device.
Assessment of MEMS energy harvester for medical applications
Jan Smilek, Zdenek Hadas
This paper assesses the feasibility of the energy harvesting principle for the development of an autonomous power supply unit for a new generation of biomedical devices, e.g. artificial cochlear implants. Requirements for the harvester are set based on a research of power demands of state-of-the-art medical devices. Feasible methods of the energy conversion are then reviewed, and a simulation model of the generic energy harvester is developed. Acceleration in the head area of the user is measured and used as an input excitation for the model. Possible course of the follow-up research is outlined based on simulation and measurement results.
Optimization method for designing multimodal piezoelectric MEMS energy harvesters

Energy Harvesters (EH) are devices that convert environmental energy (i.e. thermal, vibrational, solar or electromagnetic) into electrical energy. One of the most promising solutions consists in transforming energy from vibrations using a piezoelectric material placed onto a mechanical resonator. The intrinsic drawback of this solution is the typically high quality factor of the device and so the device works effectively only within a narrow bandwidth. To overcome this limitation it is possible to tune the mechanical resonance of the device, to introduce non-linear elements (e.g. magnets) or to design the mechanical resonator with a multimodal behavior. In Ultra Low Power (ULP) applications the aspect of integration is of utmost importance and so MEMS-based (micro electro-mechanical systems) EHs are preferable. Within this scenario the multimodal solution is the more suitable considering the technological constraints imposed by the micro machining manufacturing process.

In this paper we optimize a given multimodal mechanical geometry in order to maximize the number of resonances within a certain frequency band. In the particular case of piezoelectric energy harvesting, the strain distribution of each modes is critical and has to be taken into consideration for the designing of efficient device. The proposed optimization is FEM-based and it uses modal and harmonic simulations for both select the useful modes and then to design the device in a way that presents those modes within a predefined frequency range. This mechanical optimization could be considered the first step for maximizing the output power of a multimodal piezoelectric energy harvester. The second step focuses on the geometry optimization of the piezoelectric transducer element, starting from the desired resonant mode configuration defined in the first stage. The number of modes stimulated applying a vertical acceleration increases in number in the desired frequency range (i.e. around 1 kHz). As the output power is proportional to the stress of the flexible device, these promising results show clearly how an optimization of the geometry could significantly boost the performance of such devices.

Scaling effects for piezoelectric energy harvesters
D. Zhu, S. P. Beeby
This paper presents a fundamental investigation into scaling effects for the mechanical properties and electrical output power of piezoelectric vibration energy harvesters. The mechanical properties investigated in this paper include resonant frequency of the harvester and its frequency tunability, which is essential for the harvester to operate efficiently under broadband excitations. Electrical output power studied includes cases when the harvester is excited under both constant vibration acceleration and constant vibration amplitude. The energy harvester analysed in this paper is based on a cantilever structure, which is typical of most vibration energy harvesters. Both detailed mathematical derivation and simulation are presented. Furthermore, various piezoelectric materials used in MEMS and non-MEMS harvesters are also considered in the scaling analysis.
Thermal cycling reliability of RF-MEMS switches
V. Mulloni, G. Sordo, B. Margesin
Thermal cycling test are part of the standard space qualification procedure for RF-MEMS devices. Standardized tests are rather demanding in terms of equipment and experimental time. In this paper we present a fast thermal cycling test aimed at obtaining a rapid selection among different switch geometries in terms of thermal cycling resistance. Seven different switch typologies are examined and tested, evidencing that the most important source of deterioration is the mechanical deformation of the movable membrane. The principal characteristic found in the most resistant typologies is a more uniform distribution of the thermal strain over the whole membrane. To this respect, a careful design of the membrane anchors is extremely important for achieving a good thermal cycling resistance.
Microsystem integration from RF to millimeter wave applications
Radio frequency systems have been applied successfully to consumer products. Typically these radios operate up to 6 GHz. During recent years, interest towards microwave (up to 30 GHz) and millimeter wave frequencies (30 ... 300 GHz) has increased significantly. Technologies have been developed to have high performance microwave and millimeter wave components. On the other hand, integration and packaging technologies have not developed as fast while their importance is crucial especially in consumer applications. This presentation focuses to latest trends in wireless microsystem component integration and packaging trends backed up with demonstrators and measured results based on VTT’s demonstrations.
Tailoring design and fabrication of capacitive RF MEMS switches for K-band applications
Fabio Quaranta, Anna Persano, Giovanni Capoccia, et al.
Shunt capacitive radio-frequency microelectromechanical (RF MEMS) switches were modelled, fabricated and characterized in the K-band domain. Design allowed to predict the RF behaviour of the switches as a function of the bridge geometric parameters. The modelled switches were fabricated on silicon substrate, using a surface micromachining approach. In addition to the geometric parameters, the material structure in the bridge-actuator area was modified for switches fabricated on the same wafer, thanks to the removal/addition of two technological steps of crucial importance for RF MEMS switches performance, which are the use of the sacrificial layer and the deposition of a floating metal layer on the actuator. Surface profilometry analysis was used to check the material layer structure in the different regions of the bridge area as well as to investigate the mechanical behaviour of the moveable bridge under the application of a loaded force. The RF behaviour of all the fabricated switches was measured, observing the impact on the isolation of the manipulation of the bridge size and of the variations in the fabrication process.
Investigation of diaphragm deflection of an absolute MEMS capacitive polysilicon pressure sensor
C. Walk, A. Goehlich, A. Giese, et al.
This paper deals with the characteristics of circular shaped polysilicon pressure sensor diaphragms operating in the non-tactile mode. Using a phase shifting interferometer the main characteristics of diaphragms were investigated under applied pressure with respect to sensitivity, initial deflection and cavity height. Diaphragms with a thickness of 1 μm and a diameter of 96 μm were investigated in an intended pressure range of applied pressure of about 700 – 2000 hPa. Process parameters with major impact on performance and yield limitations were identified. These include the variance in diaphragm sensitivity and the impact of the variance of the sacrificial oxide layer defining the diaphragm cavity height on the contact pressure point. The sensitivity of these diaphragms including the variance was found to be - 19.8 ± 1.3 nm per 100 hPa. The impact of variance in the cavity height on the contact pressure point was found to be about 3.7 ± 0.5 hPa per nm. Summarizing both impacts a maximum variation of the contact pressure point of more than 450 hPa is possible to occur considering a nominal deflection of 300 nm. By optimizing the process of diaphragm deposition the variance in the sensitivity of the diaphragm was decreased by a factor of 2. A semi – empirical formula was evaluated that describes the deflection including initial deflection due to intrinsic stress and the process variations. A validation to the experimental obtained deflection lines showed a good agreement with deviations of less than 2 % for radial ranges of maximum deflection.
Smart sensors and calibration standards for high precision metrology
Uwe Brand, Sai Gao, Lutz Doering, et al.
The paper summarize the PTB activities in the field of silicon sensors for dimensional metrology especially roughness measurements and silicon calibration standards developed during the past ten years. A focus lies in the development of 2D silicon microprobes which enable roughness measurements in nozzles as small as 100 μm in diameter. Moreover these microprobes offer the potential for very fast tactile measurements up to 15 mm/s due to their tiny mass and therefore small dynamic forces. When developing high precision tactile sensors care has to be taken, not to scratch the often soft surfaces. Small probing forces and well defined tip radii have to be used to avoid surface destruction. Thus probing force metrology and methods to determine the radius and form of probing tips have been developed. Silicon is the preferred material for the calibration of topography measuring instruments due to its excellent mechanical and thermal stability and due to the fabrication and structuring possibilities of silicon microtechnology. Depth setting standards, probing force setting standards, tip radius and tip form standards, reference springs and soft material testing artefacts will be presented.
Characterization of a dispersion-controlled approach to surface profilometry on wafers using a white-light interferometer
Ch. Taudt, A. Augenstein, T. Baselt, et al.
In this paper an alternative approach to surface profilometry based on a combined time-spectral domain white-light interferometer is shown. Within the setup a reference interferometer arm contains of a fixed mirror and a material with known dispersion while the object arm is aligned to a sample e.g. a wafer surface. Under the usage of a translation stage different height profiles in the nm - regime are emulated and measured accordingly with the interferometer. The signal analysis and calculation of interesting parameters is performed by a fitting algorithm. This algorithm is based on theoretical considerations on a dispersion affected interferometer which are also shown in the work. The experimental configuration allows a measurement range of 12 μm while a theoretical average resolution of 28 nm is possible. In the results it is observable that the measurement of height changes on a surface with an RMS error of 18 nm at the maximum is possible. In conclusion sources of error and further improvement possibilities are discussed.
Piezoresistive position microsensors with ppm-accuracy
Vladimir Stavrov, Assen Shulev, Galina Stavreva, et al.
In this article, the relation between position accuracy and the number of simultaneously measured values, such as coordinates, has been analyzed. Based on this, a conceptual layout of MEMS devices (microsensors) for multidimensional position monitoring comprising a single anchored and a single actuated part has been developed. Both parts are connected with a plurality of micromechanical flexures, and each flexure includes position detecting cantilevers. Microsensors having detecting cantilevers oriented in X and Y direction have been designed and prototyped. Experimentally measured results at characterization of 1D, 2D and 3D position microsensors are reported as well. Exploiting different flexure layouts, a travel range between 50μm and 1.8mm and sensors’ sensitivity in the range between 30μV/μm and 5mV/μm@ 1V DC supply voltage have been demonstrated. A method for accurate calculation of all three Cartesian coordinates, based on measurement of at least three microsensors’ signals has also been described. The analyses of experimental results prove the capability of position monitoring with ppm-(part per million) accuracy. The technology for fabrication of MEMS devices with sidewall embedded piezoresistors removes restrictions in strong improvement of their usability for position sensing with a high accuracy. The present study is, also a part of a common strategy for developing a novel MEMS-based platform for simultaneous accurate measurement of various physical values when they are transduced to a change of position.
Multifunctional thin film sensor system as monitoring system in production
Saskia Biehl, Christian Rumposch, Nancy Paetsch
The two most important measurement categories in production are temperature and load. Therefore commercial sensors are applied in machinery as near as possible to the working parts. For a cost efficient production the integration of sensor elements directly on top of the surface in the heavily loaded regions is essential to get the real temperature and load distributions during the production process. Therefore a new multifunctional thin film sensor system is in development. This multilayer system combines thermoresistive sensor structures with piezoresistive ones and exists out of wear resistant carbon based layers [1, 2, 3, 4, 5]. The sensor data will lead to a deeper process understanding, to optimization of simulation tools, to reduction of rejects and to an improvement of flexibility in production.
Passive microsensor for binary counting of numerous threshold events
Hannes Mehner, Silvan Schwebke, Steffen Leopold, et al.
Microsystems for autonomous limit monitoring can be used for triggering maintenance and thus help to reduce costs. We present a fully integrated passive microsystem for binary counting of off-limit conditions. The mechanical design and a mechanical characterization of the system fabricated using SOI (silicon-on-insulator) technology are shown. The binary counting mechanism is realized by utilizing mechanical coupling elements between bit elements. The mechanical energy needed for switching the first bit to the state "high" was found to be 0.1 μJ by moving the entrance 37 μm and applying a force of up to 8.2 mN. 0.36 μJ was determined for switching the bit back to the state "low" by applying a 69 μm distance and a force of up to 10.2 mN. The system needs input energy for counting only, not for storing the counter value.

Expanding the design to up to ten bit elements would offer a passive microsensor able to detect 1023 off-limit conditions. A mechanical binary microcounter is presented that does not require electrical energy supply. It is suitable for counting any physical event that can be converted into an adequate force-travel-characteristic.
Car glass microphones using piezoelectric transducers for external alarm detection and localization
Christian Bolzmacher, Valentin Le Guelvouit
This work describes the potential use of car windows as a long range acoustic sensing device for external alarm signals. The goal is to detect and localize siren signals (e.g. ambulances and police cars) and to alert presbycusic drivers of its presence by visual and acoustic feedback in order to improve individual mobility and increase the sense of security. The glass panes of a Renault Zoé operating as an acoustic antenna have been equipped with large 50 mm outer diameter piezoceramic rings, hidden in the lower part of the door structure and the lower part of the windshield and the rear window. The response of the glass to quasi-static signals and sweep excitation has been recorded. In general, the glass pane is acting as a high pass filter due to its inherent stiffness and provides only little damping. This effect is compensated by using a charge amplifier electronic circuit. The detection capability up to 120 m as well as a dynamic test where the car is moving towards the sound source is reported.
Autonomous solutions for powering wireless sensor nodes in rivers
E. Kamenar, S. Maćešić, G. Gregov, et al.
There is an evident need for monitoring pollutants and/or other conditions in river flows via wireless sensor networks. In a typical wireless sensor network topography, a series of sensor nodes is to be deployed in the environment, all wirelessly connected to each other and/or their gateways. Each sensor node is composed of active electronic devices that have to be constantly powered. In general, batteries can be used for this purpose, but problems may occur when they have to be replaced. In the case of large networks, when sensor nodes can be placed in hardly accessible locations, energy harvesting can thus be a viable powering solution. The possibility to use three different small-scale river flow energy harvesting principles is hence thoroughly studied in this work: a miniaturized underwater turbine, a so-called ‘piezoelectric eel’ and a hybrid turbine solution coupled with a rigid piezoelectric beam. The first two concepts are then validated experimentally in laboratory as well as in real river conditions. The concept of the miniaturised hydro-generator is finally embedded into the actual wireless sensor node system and its functionality is confirmed.
Chemical Sensors
The effect of sensor temperature and MOx layer thickness on the sensitivity of SnO2- and WO3-based chemiresistive sensors to ethylene gas
Matic Krivec, Raimund Leitner, Roland Waldner, et al.
Two types of MOx sensor structures, SnO2 and WO3, of different thicknesses were synthesized on top of the interdigitated Au electrodes and used for the measurements of the ethylene gas. The SEM micrographs revealed inhomogeneities of the WO3 layer and the presence of cracks on the edges of Au electrodes which correlates with the lack of reproducibility of the WO3 sensors. Both sensor structures showed a significant sensitivity to ethylene gas: the sensitivities of both MOx-types were higher at higher temperatures which was more evident in the case of SnO2 structure. The SnO2 layer had approximately 5-times higher sensitivity than the WO3 sensor of the same thickness. The saturation (T10) and desaturation (T90) times were shorter for WO3 sensors at lower temperatures while SnO2 was saturated and desaturated faster at higher temperatures. Sensors with thinner active layer possessed higher sensitivities and shorter T10 and T90 times.
MEMS-based platform optimized for inkjet printing of nano-sized, gas sensitive functional metal oxides to enable the measurement of gas induced changes of the heating power
B. Bierer, J. Kneer, J. Wöllenstein, et al.
Metal oxide based gas sensors are usually read-out by measuring the overall resistivity of the gas sensitive layer. However, the reaction of the gas species with the metal oxide surface does not only change the electrical conductivity but also effects the required heating power to maintain the layer’s temperature. This change in power consumption may be disregarded when using standard bulk sensor chips due to their overall high thermal mass. Nevertheless, micromachined Si based hotplate devices offer the possibility to measure these effects. Here we present results that have been obtained by using a novel hotplate platform optimized for low power consumption and inkjet printing of nano sized gas sensitive metal oxide particles. The temperature of the gas sensitive layer is controlled via the heater resistance and the power consumption is recorded with a fully automated gas measurement system. To separate changes in the heat conductivity of the gas matrix from the heat of the surface reaction, the measurements have been performed in parallel using hotplates with and without a metal oxide layer deposited onto them. Here layers composed of copper (II) oxide (CuO) have been used to highlight the possibilities of the novel approach. Determining both, the gas dependent resistivity as well as heating power yields two independent sensing quantities from one single device and might be an important cornerstone on the way towards selective metal oxide based gas sensors.
Photoacoustic CO2 sensor system: design and potential for miniaturization and integration in silicon
The detection of CO2 indoors has a large impact on today’s sensor market. The ambient room climate is important for human health and wellbeing. The CO2 concentration is a main indicator for indoor climate and correlates with the number of persons inside a room. People in Europe spend more than 90% of their time indoors. This leads to a high demand for miniaturized and energy efficient CO2 sensors. To realize small and energy-efficient mass-market sensors, we develop novel miniaturized photoacoustic sensor systems with optimized design for real-time and selective CO2 detection. The sensor system consists of two chambers, a measurement and a detection chamber. The detection chamber consists of an integrated pressure sensor under special gas atmosphere. As pressure sensor we use a commercially available cell phone microphone. We describe a possible miniaturization process of the developed system by regarding the possibility of integration of all sensor parts. The system is manufactured in precision mechanics with IR-optical sapphire windows as optical connections. During the miniaturization process the sapphire windows are replaced by Si chips with a special IR anti-reflection coating. The developed system is characterized in detail with gas measurements and optical transmission investigations. The results of the characterization process offer a high potential for further miniaturization with high capability for mass market applications.
Novel SH-SAW gas sensor based on graphene
I. Nikolaou, H. Hallil, G. Deligeorgis, et al.
In this article, a novel gas sensor platform has been studied. Several layers of graphene have been deposited on a SH-SAW, as a sensitive layer. Innovative methods of graphene solutions have been prepared in order to explore gas sensing applications. The real time detection measurement of the coated sensor under ethanol and humidity is presented. The adsorption of vapors leads to a frequency shift of 10.5 kHz and 22.7 kHz, at exposure of 100 ppm of ethanol and 6.22% of Relative Humidity, respectively. The experiments have been realized at room temperature; rapid response and recovery time were observed.
Poster Session
Real-time synchronization of wireless sensor network by 1-PPS signal
Marco Giammarini, Marco Pieralisi, Daniela Isidori, et al.
The use of wireless sensor networks with different nodes is desirable in a smart environment, because the network setting up and installation on preexisting structures can be done without a fixed cabled infrastructure. The flexibility of the monitoring system is fundamental where the use of a considerable quantity of cables could compromise the normal exercise, could affect the quality of acquired signal and finally increase the cost of the materials and installation. The network is composed of several intelligent "nodes", which acquires data from different kind of sensors, and then store or transmit them to a central elaboration unit. The synchronization of data acquisition is the core of the real-time wireless sensor network (WSN). In this paper, we present a comparison between different methods proposed by literature for the real-time acquisition in a WSN and finally we present our solution based on 1-Pulse-Per-Second (1-PPS) signal generated by GPS systems. The sensor node developed is a small-embedded system based on ARM microcontroller that manages the acquisition, the timing and the post-processing of the data. The communications between the sensors and the master based on IEEE 802.15.4 protocol and managed by dedicated software. Finally, we present the preliminary results obtained on a 3 floor building simulator with the wireless sensors system developed.
An active reference spring array for in-situ calibration of the normal spring constant of AFM cantilevers
S. Gao, U. Brand, S. Hahn, et al.
In this paper the concept of an "active reference spring array (ARSA)" for the AFM cantilever normal spring constant calibration is proposed. The ARSA with nominal stiffness varying from 0.4 N/m to 150 N/m will be available on these arrays with the aim to calibrate the normal stiffness of cantilevers ranging from 0.04 N/m to 1500 N/m. The fabrication process of the MEMS ARSA on basis of the Bonding Deep RIE technology developed at Chemnitz University of Technology is reported. A first characterization of the MEMS and the traceable determination of the stiffness of the MEMS suspending system have been realized. First experimental results compare very well with the Finite Element (FE) simulation of the numerical design, and prove the feasibility of the proposed concept.
Noise spectroscopy of nano- and microscopic periodic material structures
A. Nasswettrova, P. Drexler, J. Seginak, et al.
The authors discuss the application of a broadband noise signal in the research of periodic structures and present the basic testing related to the described problem. Generally, noise spectroscopy tests are carried out to verify the behaviour of the response of periodic structures, and the related objective consists in recording the properties of microscopic structures in natural and artificial materials. The aim is to find a metrological method to investigate structures and materials in the frequency range between 100 MHz and 10 GHz; this paper therefore characterizes the design of a suitable measuring technique based on noise spectroscopy and introduces the first tests conducted on a periodic structure. In this context, the applied instrumentation is also shown to complement the underlying theoretical analysis.
High temperature stability of ScxAl1-xN (x=0.27) thin films
The stability of piezoelectric scandium aluminium nitride (ScxAl1-xN) thin films with x= 27% was investigated after post deposition annealings up to 1000°C. The ScxAl1-xN thin films targeted for applications in micro-electromechanical systems (MEMS) were deposited close to room-temperature applying DC magnetron sputtering. Varying deposition parameters yielded films with different microstructural properties and piezoelectric constants. Upon annealing, the crystalline quality of thin films with c-axis orientation increased, as found via characterization techniques such as X-ray diffractometry and fourier transform infrared absorbance measurements. Additionally, piezoelectric constants after annealing steps up to 1000°C are reported as obtained via a Berlincourt measurement principle. Furthermore, modifications in chemical composition during temperature loads up to 1000°C were recorded by thermal effusion measurements.
Impact of titanium layer and silicon substrate properties on the microstructure of c-axis oriented AlN thin films
E. Wistrela, A. Bittner, U. Schmid
Highly c-axis orientated sputter deposited aluminium nitride (AlN) thin films are widely used as piezoelectric layers in micro-electro-mechanical systems (MEMS). Therefore, stable and reliable deposition and patterning of the AlN thin films in the fabrication process of such devices is of utmost importance. In this work, we study the wet chemical etching behavior of highly c-axis oriented AlN layers as well as the film-related residuals after the etching procedure. To investigate the impact of the underlying material on the quality of the AlN films they are either deposited on pure silicon (Si) substrates or on Si substrates covered with a sputter-deposited thin titanium (Ti) film. The 620 nm thin AlN layers are synthesized simultaneously onto both substrate types and subsequently wet-chemical etched in a phosphorous acid based etching solution at a temperature of 80°C. We demonstrate a significant difference in surface roughness of the untreated AlN films when sputter-deposited on Ti or pure Si. Furthermore, we analyze the piezoelectric properties of the deposited films. Although the XRD analyses indicate a high c-axis orientated wurtzite structure for all deposited films, the absolute value of the piezoelectric coefficients |d33| of AlN thin films synthesized on Ti are 0.4-4.3 pC/N, whereas corresponding values of 5.2-6 pC/N are determined at those deposited on pure Si substrates,. Finally, after wet chemically etching a porous, but homogeneous AlN microstructure is observed for samples synthesized onto Ti layers, whereas AlN layers deposited directly on Si substrate are either etched very inhomogenously or almost completely with some etch resistant pyramidal-shaped residues. This might be due to a local change in polarity within the AlN layer.
Nonlinear numerical modelling and experimental validation of multilayer piezoelectric vibration energy scavengers
Scavenging of low-level ambient vibrations i.e. the conversion of kinetic into electric energy, is proven as effective means of powering low consumption electronic devices such as wireless sensor nodes. Cantilever based scavengers are characterised by several advantages and thus thoroughly investigated; analytical models based on a distributed parameter approach, Euler-Bernoulli beam theory and eigenvalue analysis have thus been developed and experimentally verified. Finite element models (FEM) have also been proposed employing different modelling approaches and commercial software packages with coupled analysis capabilities. An approach of using a FEM analysis of a piezoelectric cantilever bimorph under harmonic excitation is used in this work. Modal, harmonic and linear and nonlinear transient analyses are performed. Different complex dynamic effects are observed and compared to the results obtained by using a distributed parameter model. The influence of two types of finite elements and three mesh densities is also investigated. A complex bimorph cantilever, based on commercially available Midé Technology® Volture energy scavengers, is then considered. These scavengers are characterised by an intricate multilayer structure not investigated so far in literature. An experimental set-up is developed to evaluate the behaviour of the considered class of devices. The results of the modal and the harmonic FEM analyses of the behaviour of the multilayer scavengers are verified experimentally for three different tip masses and 12 different electrical load values. A satisfying agreement between numerical and experimental results is achieved.
Relaxation phenomena in nematic liquid crystals with multiwall carbon nanotubes adding
Cristina Cîrtoaje, Victor Stoian, Emil Petrescu, et al.
Theoretical and experimental studies about the influence of an external magnetic field on a nematic liquid crystal with carbon nanotubes adding are presented. Planar oriented cells filled with a mixture of MCL-6601 (Merck) nematic and multi-walled carbon nanotubes were subjected to a magnetic field higher than the critical one for the magnetic Freedericksz transition. A laser beam was used to observe the molecular director distortion. Dynamical measurements of the transmitted light intensity were performed when the magnetic field was switched on and off. The results were used to evaluate the relaxation times of the mixture and to show the influence of the carbon nanotubes on these parameters. We also present a theoretical model to explain the experimental results.
Efficiency of electromagnetic vibration energy harvesting system
Z. Hadas, V. Vetiska, J. Smilek, et al.
The paper deals with an efficiency calculation of an electromagnetic vibration energy harvesting system. The efficiency of this system is defined, measured, calculated and the energy harvesting model is verified. The effect of individual harvester’s parameters is observed with aim to improving design with the same volume and weight of the energy harvester. The impact of vibration energy harvesting systems has limitations in a resonance operation and a level of used mechanical vibrations. However the efficiency improvement could be useful for the wider using vibration energy harvesting systems in applications with lower level of mechanical vibrations.
Finite element analysis of AlGaN/GaN micro-diaphragms with diamond coating
J. Dzuba, G. Vanko, M. Vojs, et al.
In this work, we present a pressure sensor based on diamond coated AlGaN/GaN diaphragm with integrated high electron mobility transistor (HEMT). The influence of the diamond film thickness (in the range of 1 μm to 50 μm) on the properties of the AlGaN/GaN diaphragm is studied by finite element simulation method (FEM). The effect of thermal buckling as well as the induced piezoelectric charge of HEMTs as a function of pressure and temperature is investigated. It was found out that diamond coated sensor better prevents the effect known as thermal buckling of the diaphragm at elevated temperature. Thermal buckling of diaphragms with 1, 5, 10 μm diamond coating occurs at temperature 40, 73 and 142 °C, respectively. Compared with original GaN diaphragm, diamond expanded the operational temperature range of the pressure sensor. Moreover, compared with the operational range of pressure sensor based on pure GaN diaphragm (up to 30 kPa), diamond coated modified MEMS sensors withstand relatively higher pressures (2.2 MPa). The maximum load on the diaphragm increased two times by adding only 1 μm of diamond coating.
In-liquid characterization of high order out-of-plane modes in piezoelectric square plates
V. Ruiz-Díez, J. Toledo, T. Manzaneque , et al.
In this work, we study the modes of vibration for various aluminium nitride-actuated square microplates. We combine electrical and optical techniques to fully characterize the modes of vibration in different media, with special attention to the modes with the highest quality factor. An electronic speckle pattern interferometry technique is used for a full 3D detection of the movement of the microplates, allowing a precise identification of the modal shape, even under liquid immersion. The electrical characterization was carried out with an impedance analyser. Quality factors as high as 6700 were obtained in vacuum, and as high as 155 in isopropanol, for a high order out-of-plane mode. The effective excitation of these modes is made possible by a proper design of the electrode layout.
Numerical model a graphene component for the sensing of weak electromagnetic signals
A. Nasswettrova, P. Fiala, D. Nešpor, et al.
The paper discusses a numerical model and provides an analysis of a graphene coaxial line suitable for sub-micron sensors of magnetic fields. In relation to the presented concept, the target areas and disciplines include biology, medicine, prosthetics, and microscopic solutions for modern actuators or SMART elements. The proposed numerical model is based on an analysis of a periodic structure with high repeatability, and it exploits a graphene polymer having a basic dimension in nanometers. The model simulates the actual random motion in the structure as the source of spurious signals and considers the pulse propagation along the structure; furthermore, the model also examines whether and how the pulse will be distorted at the beginning of the line, given the various ending versions. The results of the analysis are necessary for further use of the designed sensing devices based on graphene structures.
Modeling distributed electrostatic effects in silicon microphones and their impact on the performance
Thomas Kuenzig, Gabriele Schrag, Alfons Dehé, et al.
We present a system-level model for fast and efficient investigations of distributed electrostatic effects in state-of-the-art silicon microphones. Combining lumped and distributed submodels it accounts for electrostatic forces and capacitive read-out, including non-linearities, fringing fields and parasitics. The derived model is calibrated using electrostatic finite element (FE) simulations and validated by measurements. The non-linearities caused by electrostatic effects have a decisive impact on the sensitivity of the microphone and the distortion of the transduced acoustical signal. Hence, the proposed model provides important insights into the operation of the device, which can be employed to optimize the microphone characteristics.
Optical characterization of MEMS-based multiple air-dielectric blue-spectrum distributed Bragg reflectors
The optical performance of a distributed Bragg reflector (DBR) is typically the determining factor in many optical MEMS devices and is mainly limited by the number of the periods (number of layers) and the refractive index contrast (RIC) of the materials used. The number of suitable available materials is limited and implementing a large number of periods increases the process complexity. Using air as a low-index material improves the RIC by almost 50% as compared with most conventional layer combinations and hence provides a higher optical performance at a given number of layers. This paper presents the design, fabrication, and optical characterization of multiple air-SiO2 Bragg reflectors with two airgap layers designed for the visible spectrum. Alternate polysilicon deposition and silicon-dioxide growth on the wafers followed by the selective etching of polysilicon layers in a TMAH-based solution results in a layer stack according to the optical design. However, unlike the conventional MEMS processes, fabrication of a blue-band airdielectric DBR demands several sacrificial layers in the range of 100 nm. Therefore, a successful release of the membrane after wet-etching is critical to the successful performance of the device. In this study, several DBRs with two periods have been fabricated using a CO2 supercritical drying process. The wide-area reflection measurements showed a peak reflectance of 65% and an FWHM of about 100 nm for a DBR centered at 500 nm. DBRs centered on 400 nm gave a much wider spectral response. This paper presents preliminary optical characterization results and discusses the challenges for a reflector design in the blue-visible range.
Optical design and characterization of a gas filled MEMS Fabry-Perot filter
A concept for a highly integrated and miniaturized gas sensor based on infrared absorption, a Fabry-Perot type linear variable optical filter with integrated gas cell, is presented. The sample chamber takes up most of the space in a conventional spectrometer and is the only component that has so far not been miniaturized. In this concept the gas cell is combined with the resonator cavity of the filter. The optical design, fabrication, and characterization results on a MEMSbased realization are reported for a 24-25.5 μm long tapered resonator cavity. Multiple reflections from highly reflective mirrors enable this optical cavity to also act as a gas cell with an equivalent optical absorption path length of 8 mm. Wideband operation of the filter is ensured by fabrication of a tapered mirror. In addition to the functional integration and significant size reduction, the filter contains no moving parts, thus enables the fabrication of a robust microspectrometer
Low loss optomechanical cavities based on silicon oscillator
A. Borrielli, A. Pontin, F. S. Cataliotti, et al.
In an optomechanical cavity the optical and mechanical degree of freedom are strongly coupled by the radiation pressure of the light. This field of research has been gathering a lot of momentum during the last couple of years, driven by the technological advances in microfabrication and the first observation of quantum phenomena. These results open new perspectives in a wide range of applications, including high sensitivity measurements of position, acceleration, force, mass, and for fundamental research. We are working on low frequency pondero-motive light squeezing as a tool for improving the sensitivity of audio frequency measuring devices such as magnetic resonance force microscopes and gravitational-wave detectors. It is well known that experiments aiming to produce and manipulate non-classical (squeezed) light by effect of optomechanical interaction need a mechanical oscillator with low optical and mechanical losses. These technological requirements permit to maximize the force per incoming photon exerted by the cavity field on the mechanical element and to improve the element’s response to the radiation pressure force and, at the same time, to decrease the influence of the thermal bath. In this contribution we describe a class of mechanical devices for which we measured a mechanical quality factor up to 1.2 × 106 and with which it was possible to build a Fabry-Perot cavity with optical finesse up to 9 × 104. From our estimations, these characteristics meet the requirements for the generation of radiation squeezing and quantum correlations in the 100kHz region. Moreover our devices are characterized by high reproducibility to allow inclusion in integrated systems. We show the results of the characterization realized with a Michelson interferometer down to 4.2K and measurements in optical cavities performed at cryogenic temperature with input optical powers up to a few mW. We also report on the dynamical stability and the thermal response of the system.
Optoelectronic sensor device for monitoring ethanol concentration in winemaking applications
F. Jiménez-Márquez, J. Vázquez, J. Úbeda, et al.
The supervision of key variables such as sugar, alcohol, released CO2 and microbiological evolution in fermenting grape must is of great importance in the winemaking industry. However, the fermentation kinetics is assessed by monitoring the evolution of the density as it varies during a fermentation, since density is an indicator of the total amount of sugars, ethanol and glycerol. Even so, supervising the fermentation process is an awkward and non-comprehensive task, especially in wine cellars where production rates are massive, and enologists usually measure the density of the extracted samples from each fermentation tank manually twice a day. This work aims at the design of a fast, low-cost, portable and reliable optoelectronic sensor for measuring ethanol concentration in fermenting grape must samples. Different sets of model solutions, which contain ethanol, fructose, glucose, glycerol dissolved in water and emulate the grape must composition at different stages of the fermentation, were prepared both for calibration and validation. The absorption characteristics of these model solutions were analyzed by a commercial spectrophotometer in the NIR region, in order to identify key wavelengths from which valuable information regarding the sample composition can be extracted. Finally, a customized optoelectronic prototype based on absorbance measurements at two wavelengths belonging to the NIR region was designed, fabricated and successfully tested. The system, whose optoelectronics is reduced after a thorough analysis to only two LED lamps and their corresponding paired photodiodes operating at 1.2 and 1.3 μm respectively, calculates the ethanol content by a multiple linear regression.
Force monitoring transducers with more than 100,000 scale intervals
Vladimir Stavrov, Assen Shulev, Dimiter Chakarov, et al.
This paper presents the results obtained at characterization of novel, high performing force transducers to be employed into monitoring systems with very high accuracy. Each force transducer comprises of a coherently designed mechanical transducer and a position microsensor with very high accuracy. The range of operation for the mechanical transducer has been optimized to fit the 500μm travel range of the position microsensor. Respectively, the flexures’ stiffness corresponds to achieve the maximum displacement at 70N load force. The position microsensor is a MEMS device, comprising of two rigid elements: an anchored and an actuated ones connected via one monolithic micro-flexure. Additionally, the micro-flexure comprises of two strain detecting cantilevers having four sidewall embedded piezoresistors connected in a Wheatstone bridge. The particular sensor provides a voltage signal having sensitivity in the range of 240μV/μm at 1V DC voltage supply. The experimental set-up for measurement of the load curve of the force transducer has demonstrated an overall force resolution of about 0.6mN. As a result, more than 100,000 scale intervals have been experimentally assessed. The present work forms development of a common approach for accurate measurement of various physical values, when they are transduced in a multi-D displacement. Due to the demonstrated high accuracy, the force transducers with piezoresistive MEMS sensors remove most of the constraints in force monitoring with ppm-accuracy.
Impact of different polyimide-based substrates on the soft magnetic properties of NiFe thin films
Johannes Rittinger, Piriya Taptimthong, Lisa Jogschies, et al.
We investigated the impact of polymer substrates on the magnetic properties of soft magnetic thin films. Experiments were carried out to evaluate the performance of AMR (anisotropic magnetoresistive) sensors deposited on polymeric substrates and to give indications for the design of future sensors on flexible substrates. Sputtered permalloy (NiFe 81/19) was used as a soft magnetic thin film layer. As substrate materials, liquid polyimide precursors and DuPont Kapton® HN foil were examined. Surface roughness was determined for each substrate material. The dynamic of soft magnetic behavior of the permalloy thin films was observed in a homogenous alternating magnetic field. Resulting R-Hcurves were evaluated in regard to the magnitude of the magnetoresistive effect (ΔR / R0-ratio), as well as the resulting magnetic anisotropy of the tested samples. B-H-curves were obtained by means of a vibrating sample magnetometer (VSM).
Parameters influencing focalization spot in time reversal of acoustic waves
Harald Zophoniasson, Christian Bolzmacher, Moustafa Hafez
Time reversal is an approach that can be used to focus acoustic waves in a particular location on a surface, allowing a multitouch tactile feedback interaction. The spatial resolution in this case depends on several parameters, such as geometrical parameters, frequency used and material properties, described by the Lamb wave theory. This paper highlights the impact of frequency, geometrical parameters such as plate thickness and transducer’s surface on the focused spot dimensions. In this paper a study of the influence of the plate’s thickness and the frequency bandwidth used in the focusing process is presented. It is also shown that the dimension of the piezoelectric diaphragms used has little influence on the spatial resolution. Resonant behavior of the plate and its implication on focus point dimension and focalization contrast were investigated.
Experimental verification of a novel MEMS multi-modal vibration energy harvester for ultra-low power remote sensing nodes
J. Iannacci, G. Sordo, E. Serra, et al.
In this work, we discuss the verification and preliminary experimental characterization of a MEMS-based vibration Energy Harvester (EH) design. The device, named Four-Leaf Clover (FLC), is based on a circular-shaped mechanical resonator with four petal-like mass-spring cascaded systems. This solution introduces several mechanical Degrees of Freedom (DOFs), and therefore enables multiple resonant modes and deformation shapes in the vibrations frequency range of interest. The target is to realize a wideband multi-modal EH-MEMS device, that overcomes the typical narrowband working characteristics of standard cantilevered EHs, by ensuring flexible and adaptable power source to ultra-low power electronics for integrated remote sensing nodes (e.g. Wireless Sensor Networks – WSNs) in the Internet of Things (IoT) scenario, aiming to self-powered and energy autonomous smart systems. Finite Element Method simulations of the FLC EH-MEMS show the presence of several resonant modes for vibrations up to 4-5 kHz, and level of converted power up to a few μW at resonance and in closed-loop conditions (i.e. with resistive load). On the other hand, the first experimental tests of FLC fabricated samples, conducted with a Laser Doppler Vibrometer (LDV), proved the presence of several resonant modes, and allowed to validate the accuracy of the FEM modeling method. Such a good accordance holds validity for what concerns the coupled field behavior of the FLC EH-MEMS, as well. Both measurements and simulations performed at 190 Hz (i.e. out of resonance) showed the generation of power in the range of nW (Root Mean Square – RMS values). Further steps of this work will include the experimental characterization in a full range of vibrations, aiming to prove the whole functionality of the FLC EH-MEMS proposed design concept.
A comparative study between SMS interferometers and lossy mode resonace optical fiber devices for sensing applications
A. B. Socorro, M. Hernaez, I. Del Villar, et al.
Optical fiber sensors are of great interest due to their intrinsic advantages over electronic sensors. In this work, the sensing characteristics of two different and novel optical fiber devices are compared, after simultaneously depositing a thin-film using the layer-by-layer assembly deposition process. The first one is an SMS structure, formed by splicing two single-mode fiber pigtails on both sides of a coreless multimode fiber segment. This structure induces an interferometric phenomenon that generates several attenuation and transmission bands along the spectrum. These bands are sensitive to variations in the surrounding refractive index, although this sensitivity has been enhanced by a TiO2/PSS thin-film. The other device is a 40 mm uncladded segment of a 200 μm-core multimode optical fiber. When coated by a TiO2/PSS thinfilm, part of the light transmitted into the uncladded core is coupled into the thin-film, generating a lossy mode resonance (LMR). The absorption peaks due to these phenomena red-shift as long as the thin-film thickness increases or the external RI becomes higher. The performance of these devices as refractometers and relative humidity sensors are tested. Results show that the LMR-based sensor is more sensitive in both situations, in spite of its lower sensitivity. Particularly, it presents a 7-fold sensitivity enhancement when measuring surrounding medium refractive index changes and a 10-fold sensitivity enhancement when measuring environmental relative humidity. To our knowledge, this is the first time that a comparative study between SMS and LMR sensors is performed.
High-sensitive lossy mode resonance-based optical fiber refractometers by means of sputtered indium oxide thin-films
P. Sanchez, K. Gonzalez, C. R. Zamarreño, et al.
Three different optical fiber refractometers based on lossy mode resonances (LMRs) have been fabricated by means of the deposition of indium oxide thin-films. The sensitivity of the devices as well as the full-width at half maximum (FWHM) has been characterized as a function of the surrounding medium refractive index (from 1.332 to 1.471. Obtained results revealed that thinner coating possess higher sensitivities. However, the FWHM is better for thicker coatings. As a general rule, the thicker the In2O3 coating the lower the sensitivity, but the better the FWHM. Thus, a compromise is required depending on the necessities of the application.
Optical fiber pH sensor based on gold nanoparticles into polymeric coatings
A pH optical fiber sensor based on electromagnetic resonances generated in a waveguide-nanocoating interface is presented here. The incorporation of gold nanoparticles (AuNPs) into polymeric thin films has been deeply studied and the deposition of these thin-films onto an optical fiber core has been performed in order to obtain a resonance-based optical fiber device. The presence of both the metal nanoparticles and the polymers in the coating allows the generation of two different electromagnetic resonances: localized surface plasmon resonance (LSPR) and lossy mode resonance (LMR). These phenomena can be simultaneously observed in the transmitted spectrum. The resultant device has shown a high sensitivity to pH changes from pH 4.0 to pH 6.0, with a large dynamical range and a very fast response.
Development of silicon microforce sensors integrated with double meander springs for standard hardness test instruments
Hutomo Suryo Wasisto, Lutz Doering, Alwin Daus, et al.
Silicon microforce sensors, to be used as a transferable standard for micro force and depth scale calibrations of hardness testing instruments, are developed using silicon bulk micromachining technologies. Instead of wet chemical etching, inductively coupled plasma (ICP) cryogenic deep reactive ion etching (DRIE) is employed in the sensor fabrication process leading to more precise control of 300 μm deep structures with smooth sidewall profiles. Double meander springs are designed flanking to the boss replacing the conventional rectangular springs and thereby improving the system linearity. Two full p-SOI piezoresistive Wheatstone bridges are added on both clamped ends of the active sensors. To realize passive force sensors two spring-mass elements are stacked using glue and photoresist as joining materials. Correspondingly, although plastic deformation seems to occur when the second spring is contacted, the kink effect (i.e., abrupt increase of stiffness) is obviously observed from the first test of the passive stack sensor.
Optimal design of piezoelectric microtransducers for static response
D. Ruiz, A. Donoso, J. C. Bellido, et al.
In this work, we present a systematic procedure to design piezoelectric transducers by simultaneously optimizing the host structure and the electrode layout. The technique allows maximizing any electromechanical coupling of output efficiency of the transducer. Either the output current collected at the electrodes when a mechanical force is applied (sensors), or the in-plane displacement when a given voltage is applied to the electrodes (actuators) can be optimized. We introduce a new idea to avoid the typical problem in topology optimization of the appearance of gray areas, getting finally 0-1 designs, some of which have been manufactured. Also, mathematical demonstration of reciprocity of the piezoelectric effect is shown. Many MEMS-based actuators like microgrippers, surface probes, or micro-optical devices can be optimized following this procedure. A similar approach has been demonstrated previously in modal sensors/actuators, although restricted to the design of the electrode layout for a given structure. The novel method shown here allows the simultaneous optimization of both shapes, for electrode and structure in the static case.
Features design and manufacturing technology in microelectromechanical encapsulated devices
O. Britkov, S. Timoshenkov, N. Korobova, et al.
Research methodology for measuring the natural frequency of the inner and outer frames of micromechanical oscillating system with an electrostatic actuator in filling spaces inside corps with nitrogen, and verification methodology of a micromechanical sensor element (SE) on the basis of rotation angle measurement has been developed. Developed new technical solution was consisted in that for correcting errors in the form of etched shapes compensator topology with special configuration has been used. It was possible to obtain the moving parts of MEMS with etched rectangular shape figures and with a large etching depth about 400 microns. Hydrogenated silicon surface layers were investigated by IR - spectroscopy. It was shown that substrate temperature plays a primary role in the formation of hydrogen-defect layer in silicon. The behavior of the low-frequency band in the region of stretching vibrations of Si-H during annealing has been analyzed. The dependence character of the resonance frequency of the movable (SE) part of MEMS torsion type vs temperature has been investigated. It was found that when the temperature changes from 25 to 80 °C, so natural SE frequency does not change more than 1%. The dependence of the quality factor and the natural frequency of the moving SE part from the inside corps pressure on the various modes of oscillation was investigated.
Fabrication of microfluidic chips using lithographic patterning and adhesive bonding of the thick negative photoresist AZ 125 nXT
Thorsten Knoll, Andreas Bergmann, Dominic Nußbaum
In this work, for the first time the negative photoresist AZ 125 nXT was used for the fabrication of a microfluidic chip. Usually, fabrication of microfluidic devices on the basis of silicon or glass substrates is done by using the epoxy-based negative photoresist SU-8 or other thick film polymer materials. The suitability of SU-8 for various microfluidic applications has been shown in the fields of bioanalytic devices, lab-on-chip systems or microreaction technology. However, processing is always a very challenging task with regard to the adaptation of process parameters to the individual design and required functionality. Now, the AZ 125 nXT allows for the fabrication of structures in a wide thickness range with only one type of viscosity. In contrast to SU-8, the AZ 125 nXT is fully cross-linked during UV exposure and does not require a time-consuming post-exposure bake. 90 μm deep microfluidic channels were defined by lithographic patterning of AZ 125 nXT. Sealing of the open microfluidic channels was performed by a manual adhesive bonding process at a temperature of 100 °C. The fluidic function was successfully tested with flow rates up to 20 ml/min by means of a microfluidic edge connector. Long term stability and chemical resistance of the fabricated microfluidic channels will be investigated in the near future. The presented work shows the potential of AZ 125 nXT as a possible alternative to SU-8 for the fabrication of microfluidic chips.
Laser ablation for membrane processing of AlGaN/GaN- and micro structured ferroelectric thin film MEMS and SiC pressure sensors for extreme conditions
J. Zehetner, G. Vanko, J. Dzuba, et al.
AlGaN/GaN based high electron mobility transistors (HEMTs), Schottky diodes and/or resistors have been presented as sensing devices for mechanical or chemical sensors operating in extreme conditions. In addition we investigate ferroelectric thin films for integration into micro-electro-mechanical-systems (MEMS). Creation of appropriate diaphragms and/or cantilevers out of SiC is necessary for further improvement of sensing properties of such MEMS sensors. For example sensitivity of the AlGaN/GaN based MEMS pressure sensor can be modified by membrane thickness. We demonstrated that a 4H-SiC 80μm thick diaphragms can be fabricated much faster with laser ablation than by electrochemical, photochemical or reactive ion etching (RIE). We were able to verify the feasibility of this process by fabrication of micromechanical membrane structures also in bulk 3C-SiC, borosilicate glass, sapphire and Al2O3 ceramic substrates by femtosecond laser (520nm) ablation. On a 350μm thick 4H-SiC substrate we produced an array of 275μm deep and 1000μm to 3000μm of diameter blind holes without damaging the 2μm AlN layer at the back side. In addition we investigated ferroelectric thin films as they can be deposited and micro-patterned by a direct UV-lithography method after the ablation process for a specific membrane design. The risk to harm or damage the function of thin films was eliminated by that means. Some defects in the ablated membranes are also affected by the polarisation of the laser light. Ripple structures oriented perpendicular to the laser polarisation promote creation of pin holes which would perforate a thin membrane. We developed an ablation technique strongly inhibiting formation of ripples and pin poles.
Microstructures replication using high frequency excitation
Arvydas Palevicius, Giedrius Janusas, Elingas Cekas, et al.
Diffraction efficiency of grating, created by hot imprint process on the surface of polycarbonate is one of the parameters, which determines the quality of microstructure. Microstructures are replicated by using hot imprint process with and without high frequency excitation and during the quality investigation, diffraction efficiencies were measured on purpose to find microstructure of best possible optical quality, as well determine whether high frequency excitation and other process parameters during the process affect this parameter. Process parameters include: temperature, excitation frequency, force of mechanical load and duration of hot imprint process, the purpose is to determine the collection of parameters, which influences the diffraction efficiency most positively. The novel vibro active pad is proposed for microstructures replication. The main dynamical characteristics of the vibropad are presented in the paper.
Fabrication of wear-resistant silicon microprobe tips for high-speed surface roughness scanning devices
Hutomo Suryo Wasisto, Feng Yu, Lutz Doering, et al.
Silicon microprobe tips are fabricated and integrated with piezoresistive cantilever sensors for high-speed surface roughness scanning systems. The fabrication steps of the high-aspect-ratio silicon microprobe tips were started with photolithography and wet etching of potassium hydroxide (KOH) resulting in crystal-dependent micropyramids. Subsequently, thin conformal wear-resistant layer coating of aluminum oxide (Al2O3) was demonstrated on the backside of the piezoresistive cantilever free end using atomic layer deposition (ALD) method in a binary reaction sequence with a low thermal process and precursors of trimethyl aluminum and water. The deposited Al2O3 layer had a thickness of 14 nm. The captured atomic force microscopy (AFM) image exhibits a root mean square deviation of 0.65 nm confirming the deposited Al2O3 surface quality. Furthermore, vacuum-evaporated 30-nm/200-nm-thick Au/Cr layers were patterned by lift-off and served as an etch mask for Al2O3 wet etching and in ICP cryogenic dry etching. By using SF6/O2 plasma during inductively coupled plasma (ICP) cryogenic dry etching, micropillar tips were obtained. From the preliminary friction and wear data, the developed silicon cantilever sensor has been successfully used in 100 fast measurements of 5- mm-long standard artifact surface with a speed of 15 mm/s and forces of 60–100 μN. Moreover, the results yielded by the fabricated silicon cantilever sensor are in very good agreement with those of calibrated profilometer. These tactile sensors are targeted for use in high-aspect-ratio microform metrology.
Wafer edge protection kit for MEMS and TSV Si-etching
Robert Wieland, K. Nguyen, U. Seidelmann, et al.
A new process kit for a SPTS Pegasus DRIE Si-Etch tool has been developed and tested for several different process regimes, e.g. bulk-Si cavity etching and TSV (through-Silicon-Via) etching with high aspect ratios <10:1, using the socalled Bosch process. Additionally, Si-etch back (recess etching) with a single step process has been tested as well. The especially developed "edge protection kit", consisting of Al2O3 material and optionally of PEEK material, covers the edge of a wafer, preventing it from being etched or even being etched away. However, placing such a part on top of the cathode, results in changes of the electric field distribution and the gas flow behavior compared to the standard process kit supplied by SPTS. The consequences may be altered Si-etch rates combined with changes of the tilt and side wall taper of the etched structures, mainly near the outside regions of the wafer. To this end, extensive investigations on the mask and bulk-Si etch rates, the tilt and taper angle of various MEMS test structures and their respective uniformity over the wafer surface have been performed. Additionally, simulations applying Comsol Multiphysics have been carried out to visualize the potential impact of the new process kit on the electrical field distribution. A simplex-optimization was carried out, varying the platen power and source power, in order to improve the tilt and to maintain the proper taper angle. One major advantage of the new process kit design compared to the original one is the reduction of movable parts to a minimum.
Research and development of capacitive transducer with linear acceleration
Natalia Korobova, Elena Kochurina, Sergey Timoshenkov, et al.
Paper presents the study results and modeling of functional characteristics of the linear acceleration transducers, enabling sensors creation with the specified parameters. Sensing element made for linear acceleration transducer with torsion cruciform section has been proposed on the based design and technological principles. It allows minimizing the impact of cross-acceleration and gives the maximum of center mass displacement for high sensors sensitivity in the given dimensions. The range of measured acceleration from ± 0.2g to ± 50g was provided by changing the torsion bar thickness n = 34 ÷ 56 microns. The transducers frequency range of linear acceleration 100-150 Hz depends on the gas pressure P = 700-800Pa in which the sensor element was located. Methods converting displacement of sensing element in the sensor output have been provided. On their basis the linear acceleration transducers with analog output signal having a predetermined frequency range and high linearity of the transformation (nonlinearity 0.2-1.5%) was developed. Also the linear acceleration transducers with digital signal consuming little (no more than 850 μA), low noisy (standard deviation to 0.1mg/rt-Hz) and high sensitivity (up to 0.1mg) to the accelerations was made. Errors in manufacturing process of sensitive elements and operating environment temperature affect the changes in the characteristics of the linear acceleration transducers. It has been established that different plate thickness up to 3.6% leads to the scale factor error to 4.7%. Irreproducibility of depth anisotropic etching of silicon up to 6.6% introduces an error in the output signal of 2.9 ... 13.8mg.
Characterization of cross-spring pivots for micropositioning applications
Compliant mechanisms gain at least part of their mobility from the deflection of flexible member. They are characterised by high precision, as well as no backlash and wear. Several analytical and numerical methods are used in this work to characterise the behaviour of compliant rotational mechanisms, known as cross-spring pivots, aimed at micropositioning applications. When ultra-high precision is required, the limits of applicability of approximated calculation algorithms have to be determined. The results obtained by employing these methods are thus compared with results obtained by using nonlinear finite element calculations tuned with experimental data reported in literature. The finite element model allows also considering the influence of lateral loads and of non-symmetrical pivot configurations where the angle or point of intersection of the leaf springs, or even the initial curvature of the springs, can be varied. The aim of this part of the work is to determine the influence of the cited design parameters on the minimisation of the parasitic shifts of the geometric centre of the pivot as well as on the minimisation of the variability of the rotational stiffness of the pivot so as to ensure its stability. The obtained results allow therefore determining design solutions applicable in ultra-high precision micropositioning applications, e.g. in the field of production or of handling and assembly of MEMS.
Modeling and simulation of the multiphase flow involving magnetophoresis-based microfluidic systems
Saud A. Khashan, Anas Alazzam, Bobby Mathew
In this study, we use the Lagrangian-Eulerian model, usually termed as Discrete Particle Model(DPM), and the Eulerian mixture model to numerically simulate the magnetophoresis-based separation of magnetic beads in a microfluidic system. The separation is based on High Gradient Magnetic Separation (HGMS) principle. A comparative assessment of both computational models was conducted. Mixture model provides a solution similar to that obtained using the DPM but with reduced computational time. However, the fidelity of mixture model can be attained only by the proper modeling of the slip velocity between the particle and the carrier fluid. For both of DPM and mixture approaches, the appropriate constitutive physics models for drag, lift, slip were resolved.
Electrospray ionization deposition of BSA under vacuum conditions
Dominic Hecker, Daniel Gloess, Peter Frach, et al.
Vacuum deposition techniques like thermal evaporation and CVD with their precise layer control and high layer purity often cannot be applied for the deposition of chemical or biological molecules. The molecules are usually decomposed by heat. To overcome this problem, the Electrospray ionization (ESI) process known from mass spectroscopy is employed to transfer molecules into vacuum and to deposit them on a substrate. In this work, a homemade ESI tool was used to deposit BSA (Bovine serum albumin) layers with high deposition rates. Solutions with different concentrations of BSA were prepared using a methanol:water (MeOH:H2O) mixture (1:1) as solvent. The influence of the substrate distance on the deposition rate and on the transmission current was analyzed. Furthermore, the layer thickness distribution and layer adhesion were investigated.
Numerical analysis of a smart composite material mechanical component using an embedded long period grating fiber sensor
Dan Savastru, Sorin Miclos, Roxana Savastru, et al.
Results obtained by FEM analysis of a smart mechanical part manufactured of reinforced composite materials with embedded long period grating fiber sensors (LPGFS) used for operation monitoring are presented. Fiber smart reinforced composite materials because of their fundamental importance across a broad range of industrial applications, as aerospace industry. The main purpose of the performed numerical analysis consists in final improved design of composite mechanical components providing a feedback useful for further automation of the whole system. The performed numerical analysis is pointing to a correlation of composite material internal mechanical loads applied to LPGFS with the NIR absorption bands peak wavelength shifts. One main idea of the performed numerical analysis relies on the observed fact that a LPGFS embedded inside a composite material undergoes mechanical loads created by the micro scale roughness of the composite fiber network. The effect of this mechanical load consists in bending of the LPGFS. The shifting towards IR and broadening of absorption bands appeared in the LPGFS transmission spectra is modeled according to this observation using the coupled mode approach.
Design of a smart superstructure FBG torsion sensor
Sorin Miclos, Dan Savastru, Roxana Savastru, et al.
The paper presents the results obtained in simulation of a Superstructure Fiber Bragg Grating (SFBG) torsion sensor. The SFBG sensor simulation points to an improved smart composite or metallic parts design to be operated under torsion loads in various applications. SFBG sensor simulation consists of correlating the fiber deformation under applied mechanical loads with the modified FBG characteristic reflection spectrum considering the polarization mode variations. The analyzed SFBG is developed by the selective deposition of on-fiber periodic metal thin films on regular FBGs. The torsion mechanical loads induced shifts in the characteristic reflection spectrum of Bragg wavelength and side bands are analyzed. For obtaining information about an optimal structure of SFBG sensor, simulation is performed for four commercially available photosensitive single mode silica optical fibers having different geometric and optical characteristics, mainly core and clad refractive index values. It is considered that, by using an UV writing technique, Brag gratings are induced into the simulated SFBG. Simulations are performed considering different geometric characteristics of the shaft used as mechanical mount of SFBG. The simulation results are in fairly good agreement with the experimental ones reported in literature.
Energy Harvesting and Low Power Design
Interdigitated design of a thermoelectric microgenerator based on silicon nanowire arrays
I. Donmez, M. Salleras, C. Calaza , et al.
Silicon nanowires thermoelectric properties are much better than those of silicon bulk. Taking advantage of silicon microfabrication techniques and compatibilizing the device fabrication with the CVD-VLS silicon nanowire growth, we present a thermoelectric microgenerator based on silicon nanowire arrays with interdigitated structures which enhance the power density compared to previous designs presented by the authors. The proposed design features a thermally isolated silicon platform on the silicon device layer of an SOI silicon wafer. This silicon platform has vertical walls exposing <111< planes where gold nanoparticles are deposited by galvanic displacement. These gold nanoparticles act as seeds for the silicon nanowires. The growth takes place in a CVD with silane precursor, and uses the Vapor-Solid-Liquid synthesis. Once the silicon nanowires are grown, they connect the silicon platform with the silicon bulk. The proposed thermoelectric generator is unileg, which means that only one type of semiconductor is used, and the second connection is made through a metal. In addition, to improve the thermal isolation of the silicon platform, multiple trenches of silicon nanowire arrays are used, up to a maximum of nine. After packaging the device with nanowires, we are able to measure the Seebeck voltage and the power obtained with different operation modes: harvesting mode, where the bottom device is heated up, and the silicon platform is cooled down by natural or forced convection, and test mode, where a heater integrated on the silicon platform is used to produce a thermal gradient.
Fabrication and characterization of a fuel flexible micro-reformer fully integrated in silicon for micro-solid oxide fuel cell applications
D. Pla, M. Salleras, I. Garbayo, et al.
A novel design of a fuel-flexible micro-reactor for hydrogen generation from ethanol and methane is proposed in this work. The micro-reactor is fully fabricated with mainstream MEMS technology and consists of an array of more than 20000 through-silicon vertically aligned micro-channels per cm2 of 50 μm in diameter. Due to this unique configuration, the micro-reformer presents a total surface per projected area of 16 cm2/cm2 and per volume of 320 cm2/cm3. The active surface of the micro-reformer, i.e. the walls of the micro-channels, is homogenously coated with a thin film of Rh- Pd/CeO2 catalyst. Excellent steam reforming of ethanol and dry reforming of methane are presented with hydrogen production rates above 3 mL/min·cm2 and hydrogen selectivity of ca. 50% on a dry basis at operations conditions suitable for application in micro-solid oxide fuel cells (micro-SOFCs), i.e. 700-800ºC and fuel flows of 0.02 mLL/min for ethanol and 36 mLG/min for methane (corresponding to a system able to produce one electrical watt).
An efficient start-up circuitry for de-energized ultra-low power energy harvesting systems
Leander B. Hörmann, Achim Berger, Lukas Salzburger, et al.
Cyber-physical systems often include small wireless devices to measure physical quantities or control a technical process. These devices need a self-sufficient power supply because no wired infrastructure is available. Their operational time can be enhanced by energy harvesting systems. However, the convertible power is often limited and discontinuous which requires the need of an energy storage unit. If this unit (and thus the whole system) is de-energized, the start-up process may take a significant amount of time because of an inefficient energy harvesting process. Therefore, this paper presents a system which enables a safe and fast start-up from the de-energized state.
Scaling of dynamic thermoelectric harvesting devices in the 1-100 cm3 range
M. E. Kiziroglou, A. Elefsiniotis, N. Kokorakis, et al.
Aircraft sensors are typically cable powered, imposing a significant weight overhead. The exploitation of temperature variations during flight by a phase change material (PCM) based heat storage thermoelectric energy harvester, as an alternative power source in aeronautical applications, has recently been flight tested. In this work, a scaled-down and a scaled-up prototype are presented. Output energy of 4.1 J per gram of PCM from a typical flight cycle is demonstrated for the scaled-down device, and 3.2 J per gram of PCM for the scaled-up device. The observed performance improvement with scaling down is attributed to the reduction in temperature inhomogeneity inside the PCM. As an application demonstrator for dynamic thermoelectric harvesting devices, the output of a thermoelectric module is used to directly power a microcontroller for the generation of a pulse width modulation signal.
Embedded Systems Applications
Computationally efficient models enabling behaviour exploration of large scale cyber physical systems by simulations

Cyber physical systems (CPS) enable applications not previously possible by networking components incorporating tightly connected physical and computational (cyber) functions.

We propose a method for studying and optimizing such systems at an early development stage by using simulation. Models, which mimic the cyber physical components behaviour, combine analytical models for the physical part with neural network models for the cyber part. Such models are computationally efficient, can be easily upgraded and can be networked to simulate even large scale cyber physical systems.

Applications for studying architectural issues, overall reliability and commercial aspects of cyber physical energy systems will be discussed.

On improving low-cost IMU performance for online trajectory estimation
Risang Yudanto, Agusmian P. Ompusunggu, Abdellatif Bey-Temsamani
We have developed an automatic mitigation method for compensating drifts occurring in low-cost Inertial Measurement Units (IMU), using MEMS (Microelectromechanical systems) accelerometers and gyros, and applied the method for online trajectory estimation of a moving robot arm. The method is based on an automatic detection of system’s states which triggers an online (i.e. automatic) recalibration of the sensors parameters. Stationary tests have proven an absolute reduction of drift, mainly due to random walk noise at ambient conditions, up to ~50% by using the recalibrated sensor parameters instead of using the nominal parameters obtained from sensor’s datasheet. The proposed calibration methodology works online without needing manual interventions and adaptively compensates drifts under different working conditions. Notably, the proposed method requires neither any information from an aiding sensor nor a priori knowledge about system’s model and/or constraints. It is experimentally shown in this paper that the method improves online trajectory estimations of the robot using a low-cost IMU consisting of MEMS-based accelerometer and gyroscope. Applications of the proposed method cover automotive, machinery and robotics industries.
Ultra-low power sensor for autonomous non-invasive voltage measurement in IoT solutions for energy efficiency
Clemente Villani, Domenico Balsamo, Davide Brunelli, et al.
Monitoring current and voltage waveforms is fundamental to assess the power consumption of a system and to improve its energy efficiency. In this paper we present a smart meter for power consumption which does not need any electrical contact with the load or its conductors, and which can measure both current and voltage. Power metering becomes easier and safer and it is also self-sustainable because an energy harvesting module based on inductive coupling powers the entire device from the output of the current sensor. A low cost 32-bit wireless CPU architecture is used for data filtering and processing, while a wireless transceiver sends data via the IEEE 802.15.4 standard. We describe in detail the innovative contact-less voltage measurement system, which is based on capacitive coupling and on an algorithm that exploits two pre-processing channels. The system self-calibrates to perform precise measurements regardless the cable type. Experimental results demonstrate accuracy in comparison with commercial high-cost instruments, showing negligible deviations.
Use of a prototype pulse oximeter for time series analysis of heart rate variability
Erika González, Jehú López, Mathieu Hautefeuille, et al.
This work presents the development of a low cost pulse oximeter prototype consisting of pulsed red and infrared commercial LEDs and a broad spectral photodetector used to register time series of heart rate and oxygen saturation of blood. This platform, besides providing these values, like any other pulse oximeter, processes the signals to compute a power spectrum analysis of the patient heart rate variability in real time and, additionally, the device allows access to all raw and analyzed data if databases construction is required or another kind of further analysis is desired. Since the prototype is capable of acquiring data for long periods of time, it is suitable for collecting data in real life activities, enabling the development of future wearable applications.
Networking and Embedded Computing
Abstraction of communication resources in model-based design frameworks for CPS

This paper discusses the Model-Based design approach in the applicative design of Cyber Physical Systems and, in particular, focuses upon the abstraction of the Communications resources used in such systems. Two relevant cases are considered in the discussion, namely the HTTP protocol and the ModBUS-RTU protocol.

The discussed approach has been implemented in an existing Model-Based technology, TaskScript. The above mentioned protocols, among others, have been made available to the applicative designer at the Model Level, abstracted according to the presented approach. Results are reported, demonstrating the effectiveness of the approach: real case applications have been effectively developed in less than one day.

Gbps wireless transceivers for high bandwidth interconnections in distributed cyber physical systems
Sergio Saponara, Bruno Neri
In Cyber Physical Systems there is a growing use of high speed sensors like photo and video camera, radio and light detection and ranging (Radar/Lidar) sensors. Hence Cyber Physical Systems can benefit from the high communication data rate, several Gbps, that can be provided by mm-wave wireless transceivers. At such high frequency the wavelength is few mm and hence the whole transceiver including the antenna can be integrated in a single chip. To this aim this paper presents the design of 60 GHz transceiver architecture to ensure connection distances up to 10 m and data rate up to 4 Gbps. At 60 GHz there are more than 7 GHz of unlicensed bandwidth (available for free for development of new services). By using a CMOS SOI technology RF, analog and digital baseband circuitry can be integrated in the same chip minimizing noise coupling. Even the antenna is integrated on chip reducing cost and size vs. classic off-chip antenna solutions. Therefore the proposed transceiver can enable at physical layer the implementation of low cost nodes for a Cyber Physical System with data rates of several Gbps and with a communication distance suitable for home/office scenarios, or on-board vehicles such as cars, trains, ships, airplanes
Embedded system for supervision analysis and control of photovoltaic power plants
A. Cabitto, P. Lambruschini, M. Raggio
This paper describes a supervision system able to collect data from photovoltaic plants, and to analyse them providing prevision and control of energy production. The supervision system integrates different functionality usually demanded to single separated subsystems and advanced features devoted to the maintenance of the installations and security. The supervision system is able to interact with the photovoltaic plant varying its functionality.