We recently reported on the development of a 5-level polysilicon surface micromachine fabrication process consisting of four levels of mechanical poly plus an electrical interconnect layer and its application to complex mechanical systems. This paper describes the application of this technology to create micro-optical systems-on-a-chip. These are demonstration systems, which show that give levels of polysilicon provide greater performance, reliability, and significantly increased functionality. This new technology makes it possible to realize levels of system complexity that have so far only existed on paper, while simultaneously adding to the robustness of many of the individual subassemblies.

The assembly process for microelectromechanical systems often requires a wafer-joining process using low temperatures. In this work a bonding process investigated, which uses thin adhesive films to stack silicon wafers. The method can be extended to form patterned adhesive coatings using stamping technique. Characterization of the process has been carried out with respect to adhesion, hermeticity and chemical stability of the adhesive bond. In several applications this adhesive bonding process has been successfully applied to assemble sensors and actuators.

Wafer bonding is a key technology for the fabrication of micro mechanical systems which consist of two or more stacked silicon parts. Among the different bonding methods anodic bonding with an intermediate layer of Pyrex glass offers several advantages concerning the process flexibility and the stability of the bond. To use this technology the sputter deposition process of Pyrex glass was optimized and the anodic bonding process was characterized. A process for a capacitive pressure sensor was designed which included bond frames made out of sputtered glass. The electrical contact from both electrodes to contact pads was realized by lateral and vertical feedthroughs. The latter were obtained by an Au-Au thermocompression bond which was simultaneously fabricated with the anodic bond.

Sensor packaging has become a critical element of a competitive sensor industry, being determinant of sensor performance and cost. In the recent past we worked on a new packaging concept that enabled the development of a low-cost open window plastic package. A first product was developed for an optical sensor. This new development behaved very well on all reliability tests, except for the solder dip reflow test. During this test the package fails because of the stress induced inside the package by the high temperature and air pressure inside the package cavity. This paper presents some new possible developments we analyzed in order to find a new solution that will solve the failure problem arisen in the first development of the open quad flat pack (OQFP). In order to get to the appropriate solution we had to analyze the stress levels in critical points within the package. The finite element analysis was applied on the initial version of the OQFP, as well as on the new possible solutions. It enabled us to compare stress levels within each new possible development with those within the first OQFP and to choose the one that seemed to be the most appropriate. From stress analysis results we were able to decide on the optimal choice for a reliable, low-cost product. This newly found solution is being now tested.

Packages for many high sensitivity MEM devices (Micro- Electro-Mechanical devices) such as accelerometers need to operate in a vacuum in order to obtain their full performance. This vacuum is destroyed by the outgassing of species such as hydrogen and water vapor from the surfaces of the package exposed to this vacuum. To control this outgassing a getter is needed. MEM packages are too small to accommodate traditional sintered porous getters. A solution has been developed using a high porosity thick film getter material. The getter consists of a highly porous, mechanically stable, getter coating on a metal substrate. This getter reacts with active gases such as water vapor, hydrogen, oxygen, nitrogen, and carbon monoxide that outgas from the inner surfaces of the package. The physical characteristics and performance of this material will be demonstrated per ASTM sorption testing. The results of this testing will be used to demonstrate the potential for vacuum performance in a real world MEM package.

A novel chemical imaging sensor has been developed using a Si semiconductor. The sensor (Si₃N₄/SiO₂Si) is in contact with the electrolyte solution that serves as an objective sample. The backside of the Si substrate is illuminated by a modulated laser beam. The AC photocurrent flows through the electrolyte-insulator-semiconductor. The intensity of the photocurrent depends on the electrolyte solution pH value on only the illuminated region. A 2D pH distribution can be obtained by scanning the focused laser beam. The sensor visualizes the pH distribution in the gel solution induced by ion exchange resin and microorganisms. The spatial resolution of this sensor is restricted by the Si substrate thickness as well as the laser beam spot size. A practical sensor with a spatial resolution better than 5 micrometers was fabricated using a SOI wafer instead of Si wafer, and anisotropic chemical etching instead of mechanical polishing. Such a high spatial resolution makes it possible to detect the microscopic pH distribution in solution. A reduction of spatial resolution due to the lateral spread of the depletion layer was estimated at approximately 80 nm in the present sensor system. The pH resolution of this sensor was also estimated to be 0.01 pH.

High sensitivity acoustic wave chemical microsensors are being developed on GaAs substrates. These devices take advantage of the piezoelectric properties of GaAs as well as its mature microelectronics fabrication technology and nascent micromachining technology. The design, fabrication, and response of GaAs SAW chemical microsensors are reported. Functional integrated GaAs SAW oscillators, suitable for chemical sensing, have been produced. The integrated oscillator requires 20 mA at 3 V_DC, operates at frequencies up to 500 MHz, and occupies approximately 2 mm². Discrete GaAs sensor components, including IC amplifiers, SAW delay lines, and IC phase comparators have been fabricated and tested. A temperature compensation scheme has been developed that overcomes the large temperature dependence of GaAs acoustic wave devices. Packaging issues related to bonding miniature flow channels directly to the GaAs substrates have been resolved. Micromachining techniques for fabricating FPW and TSM microsensors on thin GaAs membranes are presented and GaAs FPW delay line performance is described. These devices have potentially higher sensitivity than existing GaAs and quartz SAW sensors.

Technological modules that are needed to fabricate sensors on CMOS wafers are discussed. None of the process steps of the CMOS technology are modified in order to guarantee that the electronics are not affected by the additional sensor process steps. The definition of standardized `add-on' sensor modules to the CMOS process of a foundry is intended to limit the development cost of smart sensors. The application of these modules to the fabrication of a CMOS multisensor chip is described.

KOH based silicon bulk micromachining of fully processed CMOS wafers is still a challenge since KOH heavily attacks the aluminum metallizations. At present, the protection of the front of such wafers is still accomplished using mechanical fixtures. These fixtures prevent batch processing. This paper reports a novel protection scheme for the front side of fully processed CMOS wafers against KOH solutions. Since no mechanical fixture is required the new scheme allows batch micromachining. The protection method uses standard CMOS equipment and materials only and is therefore fully CMOS compatible. Different protection schemes based on silicon nitride and oxynitride PECVD thin films are investigated. With a 4 hour etch in a 27 weight-% (wt%) KOH solution at 95 degree(s)C, membranes consisting of the CMOS dielectrics were successfully produced. After KOH etching the protection layers are removed in an reactive ion etcher (RIE). Two aspects of the protection schemes were investigated in detail. First, we analyzed the influence of the stress in the nitride layer on the fabrication yield. With an optimized recipe with a compressive stress of -150 MPa, more than 99% of all contact pads remain intact after the KOH etching. Secondly, potassium contamination of the RIE etcher is negligible if the wafers undergo an RCA cleaning procedure. Secondary ion mass spectroscopy showed that the total alkaline contaminations in thermal oxide, silicon, silicon nitride and silicon oxynitride after the RCA cleaning are not higher than those in reference samples not exposed to the KOH solution.

For the development of microsystems, actuators are required which can be triggered in various different ways, can be scaled down to the micro-range, and allow a cost-effective manufacturing process. Of special interest are materials which transform electrical into mechanical energy as they can directly be used as actuators. The corresponding energy conversion mechanisms are magnetostriction, piezoeffect, and shape memory effect. Especially thin film deposition of these materials present interesting opportunities to realize micro-actuators or sensors as they offer features like simple actuator design and mass-production compatible to microsystem manufacturing processes. This paper contains a description and discussion of various transducer materials like magnetostrictive films (amorphous, nanocrystalline and multilayered rare earth-Fe alloys), piezoelectric films (wurtzite- and perovskite-type materials), and shape memory films (TiNi-based alloys) which--as compounds with suitable micromachined substrates--can be used as bending transducers. Based on these materials' development, typical applications of these smart film compounds as actuators in MEMS (e.g. microfluidic devices, ultrasonic micromotors, and switches) are discussed.

This paper investigates 3D active microcatheters having millimeter size outer diameters. The proposed architectures combine mechanical cells which involve new direct-drive tubular electrostatic micromotors and conventional shape memory alloy actuators. The tubular electrostatic motors are actuated by silicon surface micromachined flexible stators. The polysilicon stators integrate up to several thousands of direct-drive electrostatic microactuators. However, they have been designed in order to provide a gap compensation at the rotor/motor frame interface. Multiple stator/rotor contact interactions involve a significant speed reduction that allow a large torque amplification, as a consequence of the torque/speed duality. These mechanical interactions allow the rotor to be moved with respect to the motor frame through direct-drive contact mechanisms, therefore allowing high torque/low speed characteristics to be performed. In such a way to get a 3D behavior, the microcatheter combines tubular electrostatic motors having flexible rotors. The rotors integrate Ti-Ni shape memory alloy wires which actuate a 2D bending motion on each mechanical cell. The 3D global behavior of the catheter is provided by the relative rotation of each cell, with respect to the other ones. The proposed architecture is particularly convenient with respect to the electric power supply which is, usually, the major problem in designing active microcatheters. A (Phi) 1 mm 3D active catheter is given as an example, but external diameters less than one millimeter can be easily expected, opening therefore numerous applications in the near future.

The advent of microelectromechanical systems has enabled dramatic changes in diverse technological areas. In terms of control and distribution of liquids and gases (microfluidics), MEMS-based devices offer opportunities to achieve increased performance, and higher levels of functional integration, at lower cost, with decreased size and increased reliability. This work focuses on recent research and development of high-purity gags distribution and control systems for semiconductor processing. These systems include the following components, based upon both normally-open and normally-closed microvalves: pressure- based mass flow controllers; vacuum leak-rate shut-off valves; and pressure regulators. Advanced packaging techniques enable these components to be integrated into gas sticks and panels which have small size, corrosion-resistant wetted materials, small dead volumes, and minimal particle generation. Principles of operation of components and panels, and performance data at both the component and system level, will be presented. The potential for 10X size reduction (linear dimension), 2X product yield improvement (through increased reliability, improved flow accuracy and repeatability, and contamination reduction), and 5X reduction in process gas consumption, will also be addressed. Particular emphasis on characterization and verification of flow measurements in mass flow controllers (versus NIST standards), and the flow models used in designing and characterizing these systems, will be made.

Using a microengine as the primary test vehicle, we have examined several aspects of characterization. Parametric measurements provide fabrication process information. Drive signal optimization is necessary for increased microengine performance. Finally, electrical characterization of resonant frequency and quality factor can be more accurate than visual techniques.

In this talk, a micromachined scanning Fabry-Perot interferometer (FPI) employing electrostatic actuators and tuned to the visible spectrum is described. Previous authors have demonstrated micromachined Fabry-Perot devices. The FPI described here offers a simpler process flow and a broader tuning range. The FPI is constructed by separately fabricating a MEMS actuator and semi-transparent optical mirrors. These are then assembled to complete the device. The completed device consists of two plane parallel mirrors separated by a small gap (< 1 micrometers ). The gap is formed by a sacrificial layer which is etched away to free the gold beams. Devices have been fabricated using single layer aluminum mirrors. Modeling results of devices incorporating dielectric multi-layer stacks will be discussed. Present devices are suitable for scanning the entire visible region of the spectrum 450 - 750 nm. Actuating voltages of approximately 60 V are required. Devices fabricated with aluminum mirrors have resolving powers of up to 50. Proposed applications include in situ measurements of plasma composition, colorimetric, and chemical analysis.

HSG-IMIT is developing a silicon rate gyroscope of small size, low cost, and high performance. The device is called MARS-RR, which means Micromachined Angular Rate Sensor with two Rotary oscillation modes. Latest measurements with first prototypes yielded random walk and bias stability as low as 0.14 deg/(root)h (1 (sigma) ) and 65 deg/h, respectively. The rate equivalent rms noise corresponds to a resolution of 0.05 deg/s in a bandwidth from 0 to 50 Hz. This performance is achieved by a new sensor design featuring decoupling of the driving and the detection mechanisms. Because of this decoupling mechanical and electromechanical crosstalk, the main sources of errors of micromachined gyros, can be reduced and therefore the zero rate output almost disappears. Despite the small sensor area of 6 mm² the detection capacitance amounts to about 3 pF. Thus subatomic deflections are detectable and a high sensitivity is achieved. MARS-RR was manufactured within the Bosch Foundry process and therefore it was possible for us to reduce the development time considerably.

Recently, we demonstrated the feasibility of a novel 3D silicon bulk-micromachined accelerometer with an optical or a capacitive read-out. In this paper we will compare both detection techniques, and also show their potentials and limitations. The mechanical elements of the accelerometers are fabricated by an unconventional wet etching process of (100) silicon, resulting in symmetrically suspended seismic masses with a high lateral sensitivity and very low transverse sensitivities. For the detection of the seismic mass displacement under the effect of an acceleration, two possibilities are investigated. Firstly, by forming a Fabry- Perot cavity between the seismic mass and the output of an optical fiber, the acceleration can be sensed by measuring the optical path change. Secondly, comb shaped electrodes have been implemented to form a capacitive transducer. Both techniques can be used to build a 3D accelerometer system. Finally, we show that the noise floors of both devices are on the same order of magnitude, leading to a potentially high sensitivity (down to 1 (mu) g/(root)Hz). The optical device shows the advantage of multiplexing capability, passive fiber alignment, distant read-out, and immunity to electromagnetic interference. The capacitive transducer has beside the general advantages of an electrostatic transducer (such as possible closed loop-operation, wide temperature range, low power operation) a linear capacitive change versus displacements.

We propose a design of a 2-axis resonant accelerometer with high-quality and low-cost based on a new detection principle, which can be realized by a surface micromachining technology. The detection principle is based on frequency change that is induced by rigidity changes in the resonator. The sensor consists of four parallel-beam resonators, four folded-beam springs, and a square mass. Each resonator is driven by a first bending mode in the X-Y plane. The feasibility of this sensing principle was confirmed by a macro model of a parallel-beam resonator. The FEM analysis revealed that a frequency change rate of 1.55% (X-direction) and 0.74% (Y-direction) were realized when 5G acceleration was applied, and the optimum beam gap was determined.

To meet requirements in mobile communication and microwave integrated circuits, miniaturization of the inductive components that many of these systems require is of key importance. At present, active circuitry is used which simulates inductor performance and which has high Q-factor and inductance; however, such circuitry has higher power consumption and higher potential for noise injection than passive inductive components. An alternate approach is to fabricate integrated inductors, in which lithographic techniques are used to pattern an inductor directly on a substrate or a chip. However, integrated inductors can suffer from low Q-factor and high parasitic effects due to substrate proximity. To expand the applications of integrated inductors, these characteristics must be improved. High Q integrated spiral inductors are investigated using olymer/metal multilayer processing techniques and surface micromachining techniques. These inductors have spiral geometry with an air core and a large air gap (4Oim height) between the coils and the substrate (to reduce substrate capacitance), and thick, highly conductive electroplated copper conductor lines (to increase the quality factor). Various inductor geometries are investigated by designing and fabricating several inductors with differing core areas and numbers of turns. The fabricated inductors have a Q-factor of 40-75 at 300-700 MHz and an inductance at these frequencies between 30-7OnH.

A micromachined microwave switch has been made on a semi- insulating GaAs substrate using a suspended membrane, gold coplanar waveguide (CPW), and electrostatic actuation as the switching mechanism. The electrostatic traction comes from the dc voltage applied between the ground of the CPW and the suspended membrane.

This paper focuses on CMOS resonant sensors, i.e., resonant sensors fabricated with CMOS technology in combination with compatible micromachining steps. After reviewing resonant sensor principles, micromachining techniques applicable to CMOS resonant sensors are discussed. Subsequently, different excitation and detection mechanisms for silicon-based resonant sensors are compared. Finally, three examples of CMOS resonant microsensors, namely, an ultrasound proximity sensor, a chemical sensor and a vacuum sensor are discussed.

We report on the long-term stability of micromachined silicon membrane resonators for ultrasound based object detection and proximity sensing. The proximity sensor system measures distances up to 10 cm using either a phase or an acoustic Fabry-Perot measurement method. In these applications the transducer elements are continuously excited at their fundamental resonance using the thermomechanical excitation principle. The success of the sensor system depends on the reliability and stability of the micromachined devices, which are fabricated using an industrial pressure sensor process.

We present the concept of utilizing micro-electromechanical (MEM) energy storage for power conversion. A capacitor and inductor-free step-up converter based on mechanical resonance and silicon strain energy is introduced. In this circuit, a single MEM device is used to generate and supply high voltages, suitable for driving other MEM devices. A test converter using vertical polysilicon based resonators as energy storage elements is fabricated and tested, demonstrating the basic step-up function.

This paper describes a micro mechanical acoustic sensor modeling the basilar membrane of the human cochlea. The skeleton of the acoustic sensor is an array of resonators each of specific frequency selectivity. The mechanical structure of the sensor is designed using FEM analysis to have a particular geometrical structure looking like a fish bone that consists of cantilever ribs extending out from a backbone. Acoustic wave is supposed to be introduced to the diaphragm placed at one end of the backbone to travel in one way along the backbone. During traveling each frequency component of the wave is delivered to the corresponding cantilever according to its resonant frequency. The mechanical vibrations of each cantilever are detected in parallel by use of piezoresistors. The fish-bone structure is fabricated to be suspended in the air on a silicon substrate using silicon micromachining technology. We observe the frequency response of each cantilever to verify fairly sharp frequency selectivity associated with the one- way flow of the vibration energy. The present results encourage us to implement the human auditory system on a silicon chip toward the goal of silicon cochlea.

A major hurdle to the development of Micro Electro Mechanical Systems (MEMS) resides on the lack of communication link between the mechanical (or physical) world and the electronic world. Within a development phase, each team handles the tools traditionally used in its disciplines without any common interface. When using field solvers, e.g. finite element methods, MEMS engineers identify material properties and boundary conditions, and built a mesh, so the tool can run a 3D finite elements solution. The tool can predict the amount of stress and strain in the structures, the movement or any other interesting characteristics, but none of this information can be automatically transferred to an IC design tool. In addition, the straightforward advances within the latest developments of the mainstream semiconductor industry is the use of already available intellectual property (IP) in the development of systems optically matched to the end product specifications. These prospects call for a new generation of design tools that combines aspects of EDA and mechanical/thermal/fluidic CAD. The new product suite presented in this paper offers an integrated solution allowing a continuous design flow from front-end to back- end. The end objective is to bring to the system level designer, a complete design flow, down to the chip level, anchored on design re-use and reliable system-level simulation, thus leveraging standard IP products for the realization of sophisticated miniature systems, at low cost.

This paper describes cellular automata simulation techniques used to predict the anisotropic etching of single-crystal silicon. In particular, this paper will focus on the application of wet etching of silicon wafers using typical anisotropic etchants such as KOH, TMAH, and EDP. Achieving a desired final 3D geometry of etch silicon wafers often is difficult without requiring a number of fabrication design iterations. The result is wasted time and resources. AnisE, a tool to simulate anisotropic etching of silicon wafers using cellular automata simulation, was developed in order to efficiently prototype and manufacture MEMS devices. AnisE has been shown to effectively decrease device development time and costs by up to 50% and 60%, respectively.

We review some of the attractive attributes of microengineering and relate them to features of the highly successful silicon microelectronics industry. We highlight the need for cost effective functionality rather than ultimate performance as a driver for success and review key examples of polysilicon devices from this point of view. The effective exploitation of the data generated by the cost effective polysilicon sensors is also considered and we conclude that `non traditional' data analysis will need to be exploited if full use is to be made of polysilicon devices.

We report the first solder-bonding of low-cost silicon absolute pressure sensors. The goal of the work is to solder a pressure sensor wafer and a CMOS wafer containing the signal conditioning circuitry together face to face under vacuum. The result is a very flat capacitive absolute pressure sensor which can be used in harsh environments for automotive, medical, barometric, and other applications. We successfully demonstrated this approach using sensor wafers with micromachined silicon membranes and CMOS wafers without signal conditioning circuitry. Solder frames surrounding the membrane are electroplated on the sensor wafer. Different solder materials such as Au/Sn and SnPb were examined. Characterization of the hermetic prototypes in a pressure chamber showed a sensitivity of 0.8 fF/mbar, in good agreement with finite (FE) element simulations. With special regard to the sensitivity of the sensor a quadratic membrane, a rectangular membrane and a square membrane with a boss, all with an area of 2.25 mm², were compared using FE analysis. The rectangular membrane has the largest sensitivity.

A self-aligned reduced mask count micromachined polysilicon on nitride (SAMPSON) surface micromachining process is introduced. The self-alignment fabrication concept enables rapid fabrication, improves yields, and reduces parasitic capacitance of MEM devices. For many MEM devices the SAMPSON process results in a one mask savings over more conventional approaches. As a demonstration of the fabrication technique a burst-proof surface micromachined polysilicon resonant pressure sensor is fabricated using the SAMPSON process. This pressure sensor does not require a sealed cavity. It is also insensitive to mechanical property variations of the structural material, rendering its response essentially temperature independent.

We have developed several types of mechanical and electro- mechanical acoustic sensors using SOI (silicon on insulator) micromachining technique. This paper describes the design, the fabrication and the characterization of three such acoustic sensors. The goal of our research is to integrate a preprocessor for a voice/speech recognition system on a silicon chip, and to create an implantable hearing aid device.

In this paper a new concept for a micro coil for the realization of a displacement sensor or angular sensor is presented. The sensor consists of a 3D coil, consisting of two half coils and a movable iron core. Though the coil is fabricated by means of silicon bulk micromachining, it is possible to move an iron core through the coil without destroying the windings. The inductance of the coil is 0.25 (mu) H without core and 7.2 (mu) H with core. The ohmic resistance has a value of 60 (Omega) . The sensors developed are used in gesture recognition. For this application several micro coils are mounted on a data glove. The sensors have the task to measure the flexion of fingers.

This paper reports a microfabricated array of probes suitable for highly localized temperature manipulation (cooling or heating) or temperature manipulation of micro- sized subject. These microprobes were fabricated with `LIGA' (German acronym for Lithographie, Galvanoformung, Abformung) process--one of the MEMS (microelectromechanical systems) technologies. The LIGA technology is based on X-ray lithography and electroplating and suitable for making high- aspect-ratio metal or alloy structures with aspect-ratio up to 100 times. The array of microprobes with a height of 1000 m was fabricated on the top surface of a conventional electronic cooling device based on Peltier effect. Electrical current supplied to the cooling chip causes a cooling effect and thermal conduct effect of the microprobes carries the heat from the sample subject to be cooled to the cooling chip surface. A one-stage semiconductor-cooling device with a maximum temperature difference of 20 degree(s)C was used. It was found that the maximum temperature difference that could be achieved was very close to the temperature at the surface of the electronic device and the difference is small.

A novel magnetometer which utilizes the Lorentz force to measure vector magnetic fields has recently been described. The device, based on a classical resonating xylophone bar, has an extremely wide dynamic range and is ideally suited to miniaturization using a variety of technologies. The overall dimensions of the xylophone bar are limited by the width of the nodal supports which act as current electrodes and ultimately govern the resonance qualities. Minimum xylophone lengths of 10 and 5 mm mare attainable by electrostatic discharge machining and chemical milling of metal foils, respectively. Significantly smaller devices are achievable using polycrystalline silicon-based MEMS processing. However, the sheet resistivity of the silicon restricts the drive current through the xylophone bar and thus limits the sensitivity. This sensitivity can potentially by regained by replacing the silicon xylophone bar with a metal/piezoelectric/metal sandwich structure.

Shear sensing ability it important in many fields such as robotics, rehabilitation, teleoperation and human computer interfaces. A shear sensitive tactile sensor prototype is developed based on the principles of the piezoresistive effect in silicon, and using microfabrication technology. Analogous to the conventional silicon piezoresistive pressure sensor, piezoresistive resistors embedded in a silicon diaphragm are used to sense stress change. An additional mesa is fabricated on the top of the diaphragm and serves to transform an applied force to a stress. Both the shear and normal components of the force are resolved by measuring the resistance changes of the four resistors placed at the corners of a prism mesa. The prototype is tested both statically and dynamically when a spatial force of 0 - 300 gram is applied. Good linearity (R > 0.98) and high repeatability are observed. In this paper, the force sensing mechanism and force determination approach are described. The fabrication process is presented. The preliminary testing results are presented and discussed.

Presently, the torsional actuator has gained a lot of attentions among the area of micro actuators. Because the torsional actuator can not carry a substantial mechanical loading in the out-of-plane direction, it is frequently used in some optical or electrical applications such as light modulators and spatial scanner devices. However, the performance of torsional actuator is limited to the fabrication process and operating conditions. For instance, it is difficult to fabricate a torsional actuator with both large rotating angle and big size moving plate. A novel electrostatically driven torsional actuator is proposed in this paper. The torsional actuator is fabricated through the integration of surface and bulk micromachining processes. Thus the goal of fabricating a torsional actuator with a cavity right beneath the edge of the moving plate is reached. In addition, special design of the driving electrode is also available in this research. The advantage of the proposed design is to increase the traveling distance of the actuator as well as to increase the area of the moving plate. In short, the proposed design provides the possibility of increasing the size of moving plates without reducing its rotating angle. Therefore, the applications of the torsional actuator, such as image scanner and positioner, are widened.

To date, the usefulness of piezoresistive pressure sensors is still limited by their instability and inaccuracy. Therefore, the physical protection of the sensor elements and the robustness of the output signals with respect to environmental disturbances are important issues in the design and manufacturing of piezoresistive sensors. One approach to the encapsulation of small piezoresistive sensors is to adapt the passivation techniques commonly used in microelectronic manufacturing. An ideal passivation system is one that eliminates cross- sensitivities while not affecting the transfer behavior of the sensor. In reality, however, the same physical mechanisms that prevent cross-sensitivities will generally also modify the sensor's transfer function. The paper describes how accuracy and stability of non-encapsulated silicon pressure sensors can be optimized under consideration of mechanisms connected to environmental conditions like temperature and humidity. The performance of pressure sensors as a function of passivation layer properties and climatic conditions was experimentally studied. Valuation criteria were stochastic shares of the output voltage (noise). It was found that fast changes in the ambient climate induce significant measurement errors. Experimental results will be given that suggest new conclusions regarding the physics behind instabilities in piezoresistive sensors and yield approaches for improved sensor design.

Microscale chemical devices have potential application as fuel processors to produce high purity hydrogen for PEM fuel cells from hydrocarbon fuels such as methane, methanol, ethanol, or gasoline. The fabrication of a novel stainless steel catalytic microcombustor/reactor suitable for use to high temperatures is described. The device consisted of three parts to accommodate catalyst loading: a laminated reactor body, a laminated combustor, and a solid cover plate. The laminated components were produced using stacks of photochemically machined stainless steel shims. When formed into solid leak-tight components using a diffusion bonding process, the laminated parts were designed to contain a complex series of internal gas-flow microchannels that could not be produced in a solid metal block by other fabrication methods. Included within the reactor body was an array of heat exchanger microchannels 250 microns wide and 5000 microns deep that were designed to extract heat from the catalytic reaction region and pre-heat the reactant gases. Catalytic combustion of hydrogen or hydrocarbon fuel occurred in a separate laminated combustor plate. The laminated combustor/reactor design has potential for use in a variety of chemical processing and heat exchanger applications.

Since the 0.6 micrometers SPTM (Single Polysilicon and Three Metals) process provided by TSMC (Taiwan Semiconductor Manufacturer Company) has three metal layers available, miscellaneous microwave passive components are feasible and easily fabricated. The aim of our study is to minimize the conventional microwave couplers by commercial CMOS process. Combining communication application and semiconductor technology, this study takes advantages as following: (1) Miniaturization of the microwave passive components is feasible by CMOS process. (2) Only small area is required. (3) Microwave characteristics can be tested on-wafer. (4) Almost following the commercial CMOS process provided by TSMC, there is no post-process.

In this article, a micromachining technique is described which is an improvement to our previous technique. It allows metallic sharp and self-aligned tips to be fabricated for use as a gas detector. The fabrication technique has important advantages which makes it applicable to a wide variety application, in particular gas detection. These include simplicity and a low manufacturing cost. These tips were designed and fabricated with standard IC microfabrication technologies. However, the major highlight and achievement is the use of a low-resolution mask to position sharp tips very close to a second electrode in a simple self-aligned process. The detector exhibits a linear sensitivity response. The minimum-measured sensitivity of the detector, for the selected sample gas (CH₃COOH), is 14 ppm and this was accomplished at a modest operating voltage of only 5 V. The voltage versus measured current of the detector, reveals a exponential behavior which indicates the field ionization to be responsible for detection process.

In this article, we present micromachined 2D array flextensional transducers that can be used to generate sound in air or water. Individual array elements consist of a thin piezoelectric ring and a thin, fully supported, circular membrane. We manufacture the transducer in 2D arrays using planar silicon micromachining combined with reactive ion etching of bulk silicon to provide back access holes. Such an array could be combined with an on-board driving and an addressing circuitry.

Based on an article in print this paper presents a hybrid assembled bi-directional micro dosing system for a water flow range of -40 (mu) l/min to 80 (mu) l/min. The system consists of a silicon micropump/valve chip (9 mm X 9 mm) and a silicon flow sensor (6 mm X 12 mm). The valve/pump can be driven by either a piezoelectric disk or an electrostatic actuator. Both, piezoelectric and electrostatic actuation for the pump/valve, the technology of each component and the hybrid assembling of the whole system are described. Results of transient numerical simulation of the pump and the mass flow sensor are presented and compared with experimental results. Descriptions of two different operational modes of the micro dosing system are given. The new pulse-width modulated control method for the actuator makes controlling the system easier. It allows an open-loop control of the pump rates without changing the driving frequency. All reported micropumps were driven by a square-wave signal which causes a relatively high noise level. In contrast to this, sawtooth and sinusoidal signals generate a smooth and quiet operation because of the small drag force on the fluid ports. Results of different driving methods are presented and compared.

In this paper, a bulk micromachined silicon load cell is presented, designed for loads up to 1000 kg. ANSYS simulations were used to determine the load cell dimensions and strain gauge positions. The load cell consists of two parts, which are bonded to each other using Low Temperature Silicon Direct Bonding processes. To isolate the membrane with the sensors from lateral displacements within the load cell (e.g. expansion due to compression) thin silicon springs are incorporated in the design. To make these springs, a cryogenic RIE process with a high selectivity for resist was developed. A special housing was developed to apply a homogeneous load to the load cell. The sensor was successfully tested with loads up to 1000 kg using poly- silicon strain gauges.

Using a microengine as the primary test vehicle, we have examined several aspects of characterization. Parametric measurements provide fabrication process information. Drive signal optimization is necessary for increased microengine performance. Finally, electrical characterization of resonant frequency and quality factor can be more accurate than visual techniques.

Microassembly promises to extend MEMS beyond the confines of silicon micromachining. This paper surveys research in both serial and parallel microassembly. The former extends conventional `pick and place' assembly into the micro- domain, where surface forces play a dominant role. Parallel assembly involves the simultaneous precise organization of an ensemble of micro components. This can be achieved by microstructure transfer between aligned wafers or arrays of binding sites that trap an initially random collection of parts. Binding sites can be micromachined cavities or electrostatic traps; short-range attractive forces and random agitation of the parts serve to fill the sites. Microassembly strategies should furnish reliable mechanical bonds and electrical interconnection between the micropart and the target substrate or subassembly.

Silicon became well known as the base material for high performance microstructures on the basis of cost, performance, durability, and excellent mechanical as well as electrical properties. Numerous market surveys and projections have identified a myriad of high volume opportunities over the past two decades. Yet true commercial success has remained in isolated pockets. The appeal of mechanical and electrical on the same miniature device combined with the photogenic resulting structures has resulted in a general hype of the technology. In concept, microstructures in silicon can fill just about any role as a small scale physical to electrical interface. However, the danger lies in assuming that these applications justify the cost. These costs of ownership include infrastructure cost, cost of compensating for performance limits, time to market, and hidden manufacturing costs. Many technically elegant microstructure solutions become solutions looking for problems. This presentation looks first at the opportunity and characteristics of silicon microstructures that make it an enabling technology, followed by examples where the technology has found markets. A summary of the industry characteristics and a comparison and contrast with the traditional electronics industry follows. A profile of successful microstructure applications and future trends leads to insight on how to structure a commercially viable approach. Finally, a summary of the market drivers and requirements and the true cost of ownership provides guidance on markets where a microstructure solution makes sense.

An overview of the key micromachining technologies that enable communications applications for MEMS is presented with a focus on frequency-selective devices. In particular, micromechanical filters are briefly reviewed and key technologies needed to extend their frequencies into the high VHF and UHF ranges are anticipated. Series resistance in interconnect or structural materials is shown to be a common concern for virtually all RF MEMS components, from mechanical vibrating beams, to high-Q inductors and tunable capacitors, to switches and antennas. Environmental parasites--such as feedthrough capacitance, eddy currents, and molecular contaminants--are identified as major performance limiters for RF MEMS. Strategies for eliminating them via combination of monolithic integration and encapsulation packaging are described.