Proceedings Volume 4561

MOEMS and Miniaturized Systems II

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Proceedings Volume 4561

MOEMS and Miniaturized Systems II

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Volume Details

Date Published: 2 October 2001
Contents: 9 Sessions, 37 Papers, 0 Presentations
Conference: Micromachining and Microfabrication 2001
Volume Number: 4561

Table of Contents

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Table of Contents

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  • Hot Topics
  • Shutter, Modulator, and Scanner I
  • Shutter, Modulator, and Scanner II
  • Fiber Optics and MOEMS Switches
  • Micro-optic Technologies
  • MOEM Integration
  • MOEMS for Monitoring and Control
  • Micromirrors
  • MOEMS-Related Sensors
  • Fiber Optics and MOEMS Switches
Hot Topics
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MEMS devices for all optical networks
Armand P. Neukermans
The coming of age of the internet and data networks has brought with it an enormous increase in broadband networking, which will be filled through optical networking. Optical networks in the past were confined to point to point static WDM links. These point to point links are rapidly migrating towards all-optical mesh networks where lightpaths can be quickly changed on demand. This migration is driven by the needs of the carriers for new services, and by considerations of cost, power, bit rate and protocol transparency. This in turn has created an enormous demand for inexpensive yet flexible components. In particular there is demand for small and very large switching fabrics for switching and protection, tunable lasers for wavelength conversion, variable optical attenuators for power leveling, and devices for dispersion compensation. For many of these applications, MEMS devices are good candidates as they offer cost effective solutions. The role of MEMS in these applications will be described, with particular emphasis on large size switching fabrics, for which MEMS appear to be the only viable solution.
MOEMS for optical communication: status of the European industrial activities and technical and economical trends for the next three years
Eric Mounier, Jean-Christophe Eloy
The fiber-optic telecommunication market has dramatically evolved. Over the 1999-2000 period, almost $110 billion have been exchanged for companies and new technology acquisitions by large groups. This market continues to stimulate the creation of new start-ups. 2 to 5 companies are created every month in Europe in this field and the same in the USA and numerous other ones are in launching phase. Moreover, there are still high investment efforts form Venture Capitalists in this field. Today, it is obvious that fiber-optics telecom is the new Killer Applications that microsystems technology was looking for. As the objective is to have all-optical routing systems, the routing function could be achieved using MEMS components, which is the only technology which could cope with the realization of large matrix size cross-connects. Moreover, as demand is not uniform in the network, there is also a growing need for reconfiguration of parts of the network (to create regions of higher capacity for example). MEMS are suitable components for reconfiguration: WDM add/drop, optical cross-connect or optical switches. The presentation will make the up-to-date analysis on who is doing what in this field in Europe and what are the products for which applications on MEMS for optical telecom.
Thermal management in optical MEMS
Joseph J. Talghader
Micromachined devices are often connected to their underlying substrate by only a few small beams and are susceptible to a host of unwanted thermal effects. For many non-optical structures, thermal degradation begins with buckling or catastrophic thermal breakdown. In optical devices, however, the wavelength of light places an upper limit on the acceptable mechanical deformation, and large aberrations can be induced by relatively small changes in shape. Calculating quantitative limits on the incident optical power, applied current, and operating temperature of a device will require a strong understanding of its heat transfer and elastic response. This paper discusses the heat transfer and thermal deformation of optical MEMS components. First, the thermal conductance of microfilaments and micromirrors is discussed followed by a treatment of the thermal expansion deformation of micromirrors with temperature. Finally, mirror shape stabilization using stress compensation and thermal conductance control using electrostatic actuation are summarized.
Shutter, Modulator, and Scanner I
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MEMS spatial light modulators with integrated electronics
The design and development of a microelectromechanical, micromachined spatial light modulator ((mu) SLM) with complementary metal-oxide semimconductor (CMOS) electronics, for control of optical phase in phase-only optical correlators is presented in this paper. A large array of piston-motion MEMS mirror segments make up the (mu) SLM. Each mirror segment will be capable of altering the phase of reflected light by up to one wavelength for infrared illumination ((lambda) =1.5micrometers ). The mirror segments, or pixels, are fabricated from metal in a low temperature process allowing for vertical integration of the (mu) SLM with CMOS based, 8-bit, control electronics. Proof-of- concept results, a proposed fabrication process and, preliminary process development results are also presented.
Design optimization of an electrostatically driven micro scanning mirror
A design optimization of the electrostatically driven 1D Micro Scanning Mirror developed at the Fraunhofer Institute of Microelectronical Circuits and Systems has been carried out. The improvements are based on the use of non-Manhattan shaped structures for the mirror plate and the driving electrode combs. Several new design variants have been fabricated, characterized and are compared with devices of the previous design comprising quadratic mirror plates. The advantage of lower inertial moment favors the circular and elliptic design of the mirror plate. The capacity variation has been increased significantly by a special arrangement of the driving electrode fingers. Especially, a comb with star shaped fingers allows us to enhance the capacity variation remarkably. The experimental characterization of the devices shows that the elliptic plate with star shaped electrode combs is the variant to favor when the application requires large deflection angles for a given driving voltage and characteristic frequency. This meets the theoretical based expectation although the experimentally determined damping factor of devices with this design is significantly larger than for design variants with elliptic mirror plate and parallel electrode fingers. Devices of the novel design achieve mechanical deflection angles of up to +/- 14.0 degree(s) at a driving voltage of 11 V at low oscillation frequency. In comparison to the previous design this is an increase of 35 %.
High-frequency raster pinch correction scanner for retinal scanning displays
High-resolution (i.e., large pixel-count) and high frame rate dynamic microdisplays can be implemented by scanning a photon beam in a raster format across the viewer's retina. A resonant horizontal scanner and a linearly driven vertical scanner can create a 2-D raster for video display. The combined motion of the two scanners form a sinusoidal raster in the vertical direction and cause non-uniform line spacing for the case of bidirectional scanning as if the forward and return half-period raster lines are pinched near the edge of the display screen. Raster pinch effect degrades the image quality, especially for multi-beam scanning systems. What is needed is a vertical scanner that creates a stairstep motion instead of linear motion. A third scanner can be added to the system to create an approximation to a staircase motion in the vertical axis and correct for the non-uniform raster spacing. The raster pinch scanner requirements, mechanical and magnetic designs with FEA analysis, and preliminary test results are discussed in this paper.
Shutter, Modulator, and Scanner II
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Membrane mirrors for vision science adaptive optics
Peter Kurczynski, J. Anthony Tyson, Bernard Sadoulet, et al.
Adaptive optics provides a means to measure and correct aberrations in human vision. This technology is being used to diagnose vision problems, study the mechanism of human vision, and extend the capabilities of nature's optics. The ideal wavefront corrector for vision science adaptive optics would have greater stroke, and more degrees of freedom than is currently available. Micromachined deformable mirrors may soon meet these demands. Membrane mirrors in particular offer a promising alternative to other MEMS deformable mirror designs. A new type of mirror, employing a bound charge layer on the membrane, may overcome some of the limitations of previous membrane mirrors.
Magnetically actuated microshutter arrays
David Brent Mott, Shahid Aslam, Kenneth A. Blumenstock, et al.
Two-dimensional microshutter arrays are being developed at NASA Goddard Space Flight Center (GSFC) for the Next Generation Space Telescope (NGST) for use in the near-infrared region. Functioning as focal plane object selection devices, the microshutter arrays are 2-D programmable masks with high efficiency and high contrast. The NGST environment requires cryogenic operation at 45 K. Arrays are close-packed silicon nitride membranes with a unit cell size of 100x100 micrometer. Individual shutters are patterned with a torsion flexure permitting shutters to open 90 degrees with minimized mechanical stress concentration. The mechanical shutter arrays are fabricated with MEMS technologies. The processing includes a RIE front-etch to form shutters out of the nitride membrane, an anisotropic back-etch for wafer thinning, and a deep RIE (DRIE) back-etch down to the nitride shutter membrane to form frames and to relieve the shutters from the silicon substrate. A layer of magnetic material is deposited onto each shutter. Onto the side-wall of the support structure a metal layer is deposited that acts as a vertical hold electrode. Shutters are rotated into the support structure by means of an external magnet that is swept across the shutter array for opening. Addressing is performed through a scheme using row and column address lines on each chip and external addressing electronics.
PLZT-based electro-optic modules for micromachined biophotonics systems
Yasser A. Abdelaziez, Chong Hyuk Ahn
In this paper we present the development and characterization of Lanthanum modified Lead Zirconate Titanate (PLZT)-based Electro-optic (EO) devices for micromacined bio-photonics systems. Spatial light modulator and Dynamic programmable microlens array have been designed, fabricated and initial results have been obtained for such applications. Fully integrating light sources, detectors and dynamic filtering in recently emerging bio-photonics and Capillary Electrophoresis (CE) systems is of immediate need. An optical module that contains such devices was made using microfabrication technologies on the optically active PLZT ceramic wafer. A PLZT wafer was polished and sandwiched and bonded between 2 plastic wafers to form such optical module. Laser micromachining was implemented to etch precise, and well aligned via holes in the plastic wafers to provide windows for light sources and electrical connections to our devices. The electro-optic coefficient for the PLZT was measured in the longitudinal configuration, where light propagates in the direction of the applied field. A mathematical expression was derived for the lens effect on the far field diffraction pattern of the dynamic microlens. Such diffraction pattern can be used to measure the focal length variation with the applied voltage. Preliminary results show the variation of focal lens with the applied voltage that ranges from 50 to 300 volts.
Fiber Optics and MOEMS Switches
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MOEMS: enabling technologies for large optical cross-connects
Patrick B. Chu, Shi-sheng Lee, Sangtae Park, et al.
Rapid growth in demand for optical network capacity and the sudden maturation of wavelength-division-multiplexing (WDM) technologies have led to development of long-haul optical network systems that transport tens to hundreds of wavelengths per fiber, with each wavelength modulated at 10Gb/s or more. Micro-optical-electromechanical systems (MOEMS) devices, such as mirrors and lenses, are found to be the enabling technologies to build the next-generation cost-effective and reliable large port-count optical cross-connects (OXCs). While the basic roles of these MOEMS devices in an optical cross-connect are easily understood, the detailed mechanical design, electronics integration, packaging, control, and usage of these devices must reflect the stringent system requirements of the optical design and the electronic hardware of the network switch element. Due to the inter-dependence of many design parameters, manufacturing tolerances, and performance requirements, careful tradeoffs must be made to create reliable and manufacturable MOEMS devices. We describe various design tradeoffs and multi-disciplinary system considerations for building MOEMS-based large OXCs.
Self-assembly of surface-micromachined structures using electrostatic attraction
The paper extends the work done using micro-fabricated hinges in surface micromachining to create fully 3D devices. These devices include free-space micro-optic systems and various sensors. While these applications are interesting, the assembly process is difficult. We present the basic theory and process necessary to perform the assembly using electrostatic interactions. The process is easy and reliable. We were able to lift early prototype mirrors with voltages as low as 35 volts.
Fast 1x2 and 2x2 fiber optic switches with piezoelectric actuation
Rolf Goering, Kay Kubitz
A novel design of a microoptical fiberoptic 2 x 2 and 1 x 2 switch is presented. The fiber input and output ports are realized with the use of silicon V-grove fiber arrays. The input beams are collimated by a microlens array consisting of two lenslets, separated by the same pitch as the fibers. These two collimated beams which are extremely parallel to each other, are focused into one spot by a simple plano-convex lens. The focal length of the microlenses and this plano-convex lens determine the magnification of the mode field diameter of the fiber. Switching is performed by using a special two-sided high reflectivity mirror placed in the focal plane of the plano-convex lens, with the use of a high speed piezoelectric actuator. For the microlens array - fiber array mounting process a special setup has been built up, allowing for semi-automatic alignment. The assembly technology for all the single components and modules is described, gluing is used as the main fixing techniques. First prototypes show excellent optical parameters (1.5 dB insertion loss, -70 dB crosstalk) and very short switching time of 0.3 ms.
Silicon-on-insulator micromechanical optical switch with postprocessed polymeric waveguides
Thor Bakke, Chris P. Tigges, Charles T. Sullivan
A micro-mechanical optical switch based on lateral deflection of a waveguide is described. The switching element is a suspended silicon beam formed by deep reactive ion etching and release of silicon-on-insulator (SOI). Actuation is implemented using integrated electrostatic comb drives. Dry etched polymeric optical waveguides are post processed onto the mechanical structure. We present design, simulations, and preliminary experimental results.
Low-cost fiber collimation for MOEMS switches by ink-jet printing
Weldon Royall Cox, Ting Chen, Donald J. Hayes, et al.
Micro-optoelectronic mechanical systems (MOEMS) typically rely on free-space optical interconnects for fiber array in/out connections. The fiber output collimating and input focusing functions may be performed by using either individual gradient-index-of-refraction (GRIN) microlens rods or, more typically, arrays of microlenses formed on a glass substrate, to which the fibers are butte-coupled. We present methods for fabricating, with micron precision, various configurations of micro-optics for fiber collimation using low-cost, ink-jet printing technology. These configurations range from micro-deposition of droplets of optical epoxy into the tips of fibers, positioned in either individual collets or fiber ribbon connector ferrules, to the printing of arrays of collimating/focusing microlenses onto glass substrates. In the latter case the flexibility of the data-driven printing process enables unique capabilities, such as the variation of microlens geometries within an array, in order, for example, to compensate for the varying distances between the input fibers and the individual micro-mirrors within an array of a MOEMS device. The processes and optical modeling approaches used for fabricating such fiber collimation structures utilizing ink- jet printing technology will be discussed in detail, along with process control issues and optical performance data.
Micro-optic Technologies
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Transfer of micro-optical structures into GaAs and diamond
Mikael Karlsson, Fredrik K. Nikolajeff
Transfer of continuous-relief micro-optical structures from resist into GaAs, by use of direct-write electron-beam lithography followed by dry etching in an inductively coupled plasma, is demonstrated. A BCl3/Ar chemistry has been found to give satisfactory results, N2 and Cl2 have been added to change the selectivity between GaAs and e-beam resist. The transfer process generates smooth etched structures. Distortion of the diffractive structures in the transfer process has been examined. Blazed gratings with a period of 10 micrometers have been optically evaluated using a 940 nm VCSEL. The diffraction efficiency was 67% in the first order with a theoretical value of 87%. Also, simulations of the optical performance for the transfered diffractive elements have been made using Fourier transform of the grating profile. For integrating the optical element with VCSELs there are several possible alternatives. We have fabricated the optical structure on the same substrate that is used for the VCSEL and characterization is presently under way. We also show our initial results on transfer of micro-optical structures from resist into diamond using dry etching.
Microlens fabrication using glass transition temperature modification by the LIGA process
Sung-Keun Lee, Kwang-Cheol Lee, Seung-Seob Lee
A microlens is one of the most important components in optical microsystems. In the last decade, a lot of attempts have been done to fabricate a microlens or microlenses array, however, most of them are relatively complicated in the fabrication process and have difficulties in getting good surface roughness and realizing microlenses array. In this paper, we represent a very simple fabrication technology of the microlens or microlenses array which is based upon a deep X-ray exposure and a thermal treatment of a resist, usually PMMA. The molecular weight and Tg of PMMA is reduced when it is exposed to the deep X-ray. The microlens is produced through the effect of surface tension and reflow by adding a thermal treatment on the irradiated PMMA. A configuration of the microlens is determined by parameters such as absorbed X-ray dose on PMMA, heating temperature, and heating time in the thermal treatment. Diameters of the produced microlens range from 100 micrometers to 1500 micrometers and their changed heights are between 10 micrometers and 20 micrometers .
Improvement on the surface roughness of microlens array in the excimer laser machining process
Shuh-Yi Wang, Chi-Sheng Huang, Hsau-Yu Chou, et al.
A new process that improves the surface roughness of microlens array after the excimer laser machining is studied. The results show that the smoother surface has been fabricated by this innovatory method. The excimer laser with mask projection machining has been successfully applied for the fabrication of 2.5D micro parts. Furthermore, the workpiece dragging machining is capable of manufacturing microstructure array with curved surface by using various shape of mask. But during the machining process, the laser is cutting shoot by shoot and the material is gradually removed layer by layer. The laser marks on the curved surface of micro lens array is obvious and inevitable. This defect limits the product of dragging in real optical application. To overcome this drawback, an improved process is studied. When the desired shape of lens array was machined by the excimer laser machining, the attaching photo resist with the thickness of several micro meter is coated on the rough surface by spin coating or spraying. Then the lens array is baked to get the mirror surface. This original method combines the advantage of the higher fill factor and the smoother surface for the fabrication of micro lens array.
Integration nanometer indicating system for reducing temperature drift of interferometer
Jian Wu, Chunyong Yin
The positioning system based on surface plasmon resonance (SPR) can achieve nanometer resolution and repeatility. A special retroreflector is designed that incidence angle of its first reflection surface is equal to resonance angle of SPR to implement the integrate SPR positioning system into the interferometer. At the beginning of a measurement, a zero position is determined by SPR positioning system. If there is drift during measurement, reset interferometer data to diminish drift as soon as the special retroreflector reaches the zero position. The integration interferometer is set up. Experiments show that long time uncertainty of interferometer is reduced from 60nm to 10nm. The measurement precision and stability of interferometer is increased.
MOEM Integration
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High-efficiency optical MEMS by the integration of photonic lattices with surface MEMS
James G. Fleming, Seethambal S. Mani, Shawn-Yu Lin
An overview is given of the integration of 1,2 and 3D photonic lattice structures with surface MEMS (MicroElectroMechanical Systems). The properties of the photonic lattice arise as a result of a high index contrast between two or more media arranged in an appropriate fashion. Increased photonic lattice functionality is obtained as the arrangement of high and low index materials is extended into other dimensions. Potential photonic lattice functions which can be integrated with surface MEMS include mirrors, cavities and wavelength dependent switches in 1D, waveguides and prisms in 2D and 3D waveguides, prisms, polarization, dispersion, thermal and spontaneous emission control in 3D.
Light-activated self-generation and parametric amplification for MEMS oscillators
Maxim Zalalutdinov, Alan T. Zehnder, Anatoli Olkhovets, et al.
High-frequency microoptoelectromechanical systems (MOEMS) are proposed as active devices for radio frequency signal processing. Parametric amplification (PA), generation, frequency modulation and frequency conversion on the micromechanical level were demonstrated at MHz range by microfabricated single-crystal silicon mechanical resonators. A focused laser beam was used to pump energy into the motion of the oscillator, to control the frequency response and to provide a carrier signal for the frequency up-conversion. Laser light interaction with the microelectromechanical system (MEMS) was realized through the stress pattern induced within the microfabricated structure by the focused laser beam. Stress-induced stiffening of the oscillator provides control over the effective spring constant and leads to a parametric mechanism for amplification of mechanical vibrations. Periodic modulation of the laser intensity synchronized with the driving force allowed us to demonstrate a degenerate (phase-sensitive) PA scheme with gain in access of 30dB. Design of the oscillator as a part of the built-in Fabry-Perot cavity provides auto-modulation of the effective spring constant as a result of the position-dependent absorption of the light by the oscillator. The auto-modulation mechanism allows a parametric self-excitation induced by continuous wave (CW) laser beam. Self-sustained generation was observed when laser power exceeded a threshold of few hundred microWatts. Nonlinear effects cause frequency dependence vs. laser power, providing a mechanism for frequency modulation of the self-generated vibrations. The same type of optical scheme can also work as an ideal frequency mixer, which combines the self-generated response with an external high-frequency modulation of the laser intensity.
Component development and integration issues for MOEMS
James Castracane, Bai Xu, Yahong Yao, et al.
Following over a decade of MOEMS component development, attention in the research, development and commercial arenas has begun a significant shift to system-level integration of these structures. Applications abound in fields including optical communications, integrated sensors and bio/chemo diagnostics. Furthermore, the impending need for wafer- level integration of MOEMS with logic and actuation is driving R&D into developing a compatible process flow for ultimate, low-cost technology deployment. This paper will describe recent advances in MOEMS development and integration projects at the UAlbany Institute for Materials (UAIM). This discussion will focus on operational details of selected MOEMS projects including diffractive/reflective arrays, VCSEL arrays, and integrated sensor systems. These research and development details will be presented against a backdrop of the NanoFab 200 at UAIM, a unique 200 mm wafer prototyping and integration facility. In particular, reconfigurable diffractive and reflective arrays are currently under development in several complementary programs at UAIM. These programs encompass optical interconnect studies, active spectroscopy and metrology development. This paper will present the current status of these programs that are focused on optical performance improvements, process flow integration, packaging and lifetime tests. To complement these activities, selected MOEMS components are being integrated with VCSEL arrays for application to a variety of sensor systems. Development details of the VCSEL arrays and compatibility issues with custom MOEMS systems will be described. Finally, selected details of 200mm wafer-level integration studies will be presented to illustrate challenges and opportunities.
Flip-chip fabrication of integrated micromirror arrays using a novel latching off-chip hinge mechanism
M. Adrian Michalicek, Victor M. Bright
This paper presents the design, fabrication, modeling, and testing of various arrays of cantilever micromirror devices integrated atop CMOS control electronics. The upper layers of the arrays are prefabricated in the MUMPs process and then flip-chip transferred to CMOS receiving modules using a novel latching off-chip hinge mechanism. This mechanism allows the micromirror arrays to be released, rotated off the edge of the host module and then bonded to the receiving module using a standard probe station. The hinge mechanism supports the arrays by tethers that are severed to free the arrays once bonded. The resulting devices are inherently planarized since the bottom of the first releasable MUMPs layer becomes the surface of the integrated mirror. The working devices are formed by mirror surfaces bonded to address electrodes fabricated above static memory cells on the CMOS module. These arrays demonstrate highly desirable features such as compatible address potentials, less than 2 nm of RMS roughness, approximately 1 micrometers of lateral position accuracy and the unique ability to metallize reflective surfaces without masking. Ultimately, the off-chip hinge mechanism enables very low-cost, simple, reliable, repeatable and accurate assembly of advanced MEMS and integrated microsystems without specialized equipment or complex procedures.
MOEMS for Monitoring and Control
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MOEMS integrated optical monitoring
Lawrence Anthony Hornak, Parviz F. Famouri, Jeremy M. Dawson, et al.
For certain classes of MEMS, implementation of closed loop feedback control and system model-based fault detection offer significant performance advantages. Such systems include those in safety critical applications and systems in which dynamic loads are anticipated. Detailed continuous knowledge of the positional state of the microstructure is needed in order for accurate system models to be developed and experimentally verified, control techniques to be effectively applied, and model based fault detection evaluated. Moreover, this positional state information must be fully decoupled from the microstructure voltage drive signal. This paper reviews the group's current efforts exploring the use of integrated optics to provide this MEMS state feedback information and the merits and challenges of its application for microstructure control and fault detection. Modeling and experimental results using a 1.3 micron wavelength coherent optical probe for optical state monitoring will be presented including work integrating the probe optics within a folded diffractive optical element coplanar with MEMS die. Use of this signal in system model parameter estimation and real-time position control of a lateral comb resonator stage will be demonstrated and the potential for application to MEMS model-based fault detection discussed.
Vertical stiffening members for flatness control of surface-micromachined structures
B. Jeffrey Lutzenberger, David L. Dickensheets
Surface-micromachined devices with large length-to-thickness ratios can deform considerably once released from the substrate. This can be a serious problem for large aperture optical components where deformation due to internal stresses must be controlled. Adding stiffening fins with various geometric configurations to surface micromachined structures has been shown to significantly reduce stress-related deformations. The stiffening fins have also been shown to control deformations in uni-axial and bi-axial tilt mirrors. In this paper we investigate the use of stiffening members with various lattice configurations to reduce stress-induced deformation of silicon nitride cantilever beams. Stiffness and flatness of these structures are investigated both experimentally and analytically.
Control of image-shifting coils for vibration isolation of an electron microscope
Koichi Matsuda, Yoichi Kanemitsu, Shinya Kijimoto, et al.
This paper proposes a new approach to control of image-shifting coils for vibration isolation of a scanning electron microscope. Image-shifting coils move the electron probe of the microscope out of phase with undesirable motion of a specimen due to any disturbance source. Two acceleration sensors are located at the root of the specimen chamber of the microscope to detect the disturbance. The outputs of the acceleration sensors are fed forward into a controller to move the probe by the image-shifting coils. The feed-forward controller is based on a transfer function from the sensor outputs to the relative displacement of a specimen to the electron probe that is assumed to be at rest. The microscope is put on a table attached to a shaker. Sinusoidal excitation tests are made by the shaker to measure the transfer function data using a video signal and the sensor outputs. The relative displacement of the specimen is estimated by identifying the measured video signal with a simulated one in a least-squares sense. The controller is implemented as a digital filter running on a digital signal processor. The amplitude of the vibrating images is significantly reduced by the controller at the natural frequency of the system.
Optomechanical variations and control in a MOEMS switch model
Thomas E. Plowman, Robert A. Stoll, David A. Winick, et al.
This work demonstrates how optomechanical alignment inaccuracies affect the operation of a small port-count, fiber coupled, MOEMS switch using six degrees of freedom, parameterized behavioral models. Simulation results show that a control system is essential to stabilize the switch when it is subjected to the variations that would otherwise degrade its performance.
Micromirrors
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Design and fabrication of micromirror arrays for UV lithography
Modern UV-lithography is searching for new highly parallel writing concepts. Spatial light modulation (SLM) offers such possibilities but special emphasis must be put on the ability of SLM devices to handle ultraviolet light (UV). We designed and fabricated micromirror arrays which fulfill these requirements. Possible applications for such UV-SLMs are direct writing systems for semiconductor and printing, and UV-stimulated biochemistry. For deep UV laser pattern generation (248 nm) e.g. we designed and fabricated a 2048x512 pixel UV-SLM with individually addressable aluminum micromirrors. They are illuminated by an excimer laser pulse and imaged onto a photomask substrate. A complete pattern is stitched together at a rate of 1 kHz. The minimum feature size is 320 nm and analog modulation of the pixels allows to realize an address grid of only 1.6 nm. The design of the array is modular so that other array sizes can be tailor made to customers needs. Design and fabrication aspects for a CMOS compatible realization of these micromirror arrays are addressed as well as their performance in lithography applications.
Active-matrix-addressed micromirror array for wavefront correction in adaptive optics
Andreas Gehner, Wolfgang Doleschal, Andreas Elgner, et al.
For an enhanced wavefront correction in Adaptive Optics especially in the case of high-order aberrations we developed a new monolithic integrated micromirror device providing a dense array of 240 x 200 piston-type mirror elements on top of an active CMOS address matrix for a closer wavefront approximation. After an analytical and numerical modeling the micromirrors were designed and fabricated by means of aluminum surface-micromachining. Using a basic pixel size of 40 x 40 micrometers 2 a mechanical stroke of at least 450 nm could be achieved at address voltages below 30V, which is suitable for both active matrix addressing and a phase correction modulo 2p in the visible. This also includes the option of an incremental increase of the actual mirror size in units of the address grid in order to allow for an extended analog deflection range. Furthermore, we designed and fabricated an active address matrix using a special high voltage CMOS process providing a full analog capability for address voltages up to 35V. Thereby, also a special light shielding as well as chemical mechanical polishing (CMP) for a high surface planarization have been incorporated. The completed devices were experimentally characterized by surface profile measurements using white light interferometry. After determining the deflection characteristic we successfully demonstrated the analog operation capability by programming different height patterns into the matrix at an 8 bit resolution provided by the external driving board.
Silicon nitride biaxial pointing mirrors with stiffening ribs
Todd J. Kaiser, B. Jeffrey Lutzenberger, Robert A. Friholm, et al.
Gold-coated silicon nitride mirrors designed for two orthogonal rotations were fabricated. The devices were patterned out of nitride using surface micromachining techniques, and then released by a sacrificial oxide etch and bulk etching the silicon substrate. Vertical nitride ribs were used to stiffen the members and reduce the curvature of the mirrored surfaces due to internal stress in the nitride and the metal layer. This was accomplished by initially etching the silicon substrate to form a mold that was filled with nitride to create a stiffening lattice-work to support the mirrored section. Mirror diameters ranging from 100 mm to 500 mm have been fabricated, with electrostatic actuation used to achieve over four degrees of tilt for each axis.
Optical performance of pivoting micromirrors
Olga Blum Spahn, Ernest J. Garcia, Victor C. Esch, et al.
In this paper we describe optical and dynamic performance of tip/tilt micromachined mirrors fabricated using the SUMMIT V surface micromachining process. We find that the tilt angle for a given mirror design is determined by a combination of geometric factors and stiffness of the capacitive suspension. Switching speeds of ~40-50 microsecond(s) econds are measured for 50 micrometers -square mirrors. Finally surface roughness and curvature before and after metallization are obtained using white light interferometry.
Fabrication of five-level ultraplanar micromirror arrays by flip-chip assembly
M. Adrian Michalicek, Victor M. Bright
This paper reports a detailed study of the fabrication of various piston, torsion, and cantilever style micromirror arrays using a novel, simple, and inexpensive flip-chip assembly technique. Several rectangular and polar arrays were commercially prefabricated in the MUMPs process and then flip-chip bonded to form advanced micromirror arrays where adverse effects typically associated with surface micromachining were removed. These arrays were bonded by directly fusing the MUMPs gold layers with no complex preprocessing. The modules were assembled using a computer-controlled, custom-built flip-chip bonding machine. Topographically opposed bond pads were designed to correct for slight misalignment errors during bonding and typically result in less than 2 micrometers of lateral alignment error. Although flip-chip micromirror performance is briefly discussed, the means used to create these arrays is the focus of the paper. A detailed study of flip-chip process yield is presented which describes the primary failure mechanisms for flip-chip bonding. Studies of alignment tolerance, bonding force, stress concentration, module planarity, bonding machine calibration techniques, prefabrication errors, and release procedures are presented in relation to specific observations in process yield. Ultimately, the standard thermo-compression flip-chip assembly process remains a viable technique to develop highly complex prototypes of advanced micromirror arrays.
MOEMS-Related Sensors
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Development of optical MEMS carbon dioxide sensors
A NDIR-based sensor-chip using MEMS Si micro-bridge elements, with integrated PBG structure for wavelength tuning is discussed. The effects of processing on device performance, especially device release, were investigated. Thermal and electrical device characterization was used to quantify loss mechanisms. Thermally isolated, uniformly heated emitters were ultimately achieved using a backside release etch fabrication process. The fully released devices demonstrated superior electric to thermal (optical) conversion, with the requisite narrow band emission for CO2 detection. Using the MEMS sensor-chips, 20% CO2 detection was demonstrated, with projected sensitivities of ~3% CO2.
Optical sensors with MEMS, slit masks, and micromechanical devices
Concepts to increase the performance of optical sensors by combination with optical MEMS are discussed. Architectures of subsystems are reviewed, which modulate or switch the amplitude of the light by scanning, multiplexing and selecting interesting signal components (multi-object-mode). Arrangements with MEMS for optical sensors and instruments can decrease the pixel size and increase their number by creating virtual pixels. A number of signal components can be detected with a smaller number of detectors (detector pixels) by scanning. If the scanning is substituted by multiplexing the best efficiency is achieved. The measurement time can be reduced by selecting interesting objects or signal components to be detected. Architectures which combine single sensors, linear sensor arrays or two dimensional detector arrays with MEMS, slit masks, and micro-mechanical devices are discussed. Such devices are micro-mirrors, micro-shutters, the slit positioning system, the fibre positioning system, and other optical switches.
Calculating the modulation transfer function of a pyroelectric infrared sensor array
Guenter Milde, Gerald Gerlach, Joerg Drescher, et al.
Pyroelectric infrared sensor arrays are imaging devices for infrared radiation that utilize the temperature dependence of the remanent polarization in pyroelectric materials. An analytic calculation of the modulation transfer function of a pyroelectric sensor array was carried out for a simplified model. More realistic models, however, require the use of numerical methods like the finite element method. We present a method to derive the modulation transfer function from simulation data of a finite-element model and compare the results of the analytic and numerical calculations for a test model.
Finite element modeling of the thermo-electro-mechanical coupling in pyroelectric infrared sensor arrays
Joerg Drescher, Herbert Balke, Hans-Achim Bahr, et al.
For the example of a Lithiumtantalate (LiTaO3) sensor array, the coupled thermo-electro-mechanical fields are examined using the finite element method. The temperature distribution is computed in a preliminary thermal analysis, and the numerical results are compared with an analytical model. The calculated temperature field is used as input for a subsequent electro-mechanical analysis, wehre the thermo-elastic and the pyroelectric source terms are simulated by body forces and body charges, respectively. The investigations of various FEM-models showed, that different mechanical boundary conditions and the piezoelectric coupling of LiTaO3 influence the electric system response by only about 6...7%.
Novel optical MEMS/micromechanical devices as field selectors for imaging spectrometry
Multi-object spectrometry is a special version of imaging spectrometry, where only a relatively small number of objects or interesting image points of a scene is spectrally resolved. This allows to measure nearly all interesting points of a typical astronomical scene within one or only a few measurement steps. The essential component of a multi-object spectrometer is the field selector device, which selects multiple image points for a simultaneous measurement. Reconfigurable field selectors or reconfigurable slit masks can be MEMS, such as micro mirror or micro shutter arrays. Alternative field selectors will be based on micro-mechanical devices and can mostly be referred to as slit positioning systems, since the elements which form the slits are mechanically positioned. Novel examples for such field selectors are an individual micro-mirror element positioner and bar arrays with slit structures. Two layer devices are presented, which form transmissive and reflective slits. The concepts are focused on the near infrared multi-object-spectrometer for the Next Generation Space Telescope.
Fiber Optics and MOEMS Switches
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Development of advanced micromirror arrays by flip-chip assembly
M. Adrian Michalicek, Victor M. Bright
This paper presents the design, commercial prefabrication, modeling and testing of advanced micromirror arrays fabricated using a novel, simple and inexpensive flip-chip assembly technique. Several polar piston arrays and rectangular cantilever arrays were fabricated using flip-chip assembly by which the upper layers of the array are fabricated on a separate chip and then transferred to a receiving module containing the lower layers. Typical polar piston arrays boast 98.3% active surface area, highly planarized surfaces, low address potentials compatible with CMOS electronics, highly standardized actuation between devices, and complex segmentation of mirror surfaces which allows for custom aberration configurations. Typical cantilever arrays boast large angles of rotation as well as an average surface planarity of only 1.779 nm of RMS roughness across 100 +m mirrors. Continuous torsion devices offer stable operation through as much as six degrees of rotation while binary operation devices offer stable activated positions with as much as 20 degrees of rotation. All arrays have desirable features of costly fabrication services like five structural layers and planarized mirror surfaces, but are prefabricated in the less costly MUMPs process. Models are developed for all devices and used to compare empirical data.