Micro-Optical-Electro-Mechanical Systems (MOEMS) employ batch fabrication processes to construct miniature devices with macroscopic functionality. Surface micromachiend MOEMS structures are manufactured by the deposition and patterning of thin films. In marked contrast with conventional fabrication processes, the thin film materials used in surface micromachiend structures are formed as the device is processed. In general, the material properties of thin films are not controlled during deposition, and are only measured after processing is completed. Characterization techniques currently wafer curvature measurements and a variety of test structures. None of the thin film characterization techniques currently employed is entirely satisfactory and all methods rely on process repeatability to be useful. The ultimate optical performance of MOEMS depends directly on the materials properties of the thin films employed. Differing residual material stresses and residual stress gradients cause curvature which degrades the optical performance of nominally flat reflecting surfaces. For multilayer structures like most micromirrors curvature due to the bimetallic effect can not be ignored. Recent work in which foundry processes were used to fabricate low-0cost deformable mirrors for adaptive optics illustrates the impact of residual material stress on system level optical performance. In other MOEMS devices residual material stress can be exploited to produce unique structures. More precise monitoring and control of film stress during deposition remains as a challenge for MEMS and MOEMS. This paper will address the principal materials issues for MOEMS and suggest both design and process control solutions.
The presented latching-type 2 by 2 and 1 by 4 fiber-optic switches are based on full wafer micromachining of silicon wafers using anisotropic wet etching in KOH. Bulk micromachining allows the low-cost batch fabrication of structures with very high precision suitable for fiber alignment. The optical fiber switches consist of two thermally driven silicon actuators, a coupled U-shaped cantilever via thin flexible silicon beams and a stiff platform prevents angular displacement of the fibers. Switches have been fabricated with high yield, high mechanical stability, and good optical properties. Using standard single- mode fibers, the switches exhibit a crosstalk of < - 60 dB. Insertion losses below 1 dB and about 1 dB are achievable for 1 by 4 and 2 by 2 switches, respectively. A power below 0.6 W and 1.0 W for the 2 by 2 and 1 by 4 micromechanical fiber switch is needed during the switching time. Bistable 1 by 2 optical fiber switches have been tested for more than 1 X 106 switching cycles without any failure and after more than one year at room conditions they do not show any degeneration of optical properties and switching behavior.
We are developing a lithography process for a 2D array of microshutters which can be used as a high efficiency, high contrast field selection device for a multi-objects spectrometer for the Next Generation Space Telescope. The device is a close- packed array of shutters with an individual shutter size of 100 micrometers square and area filling factor of about 80 percent, produced in a 100 micrometers thick silicon wafer. Our current array size is 128 by 128. Ech shutter made of silicon nitride with an appropriate optical coating, pivots on a torsion flexure along one edge. A CMOS circuit embedded in the frame around the shutters allows individual selection. An original double-shutter mechanism is employed for actuation. Processing includes anisotropic back etching for wafer thinning, a DRIE back etch through the silicon to the mechanical active nitride membrane and a RIE to produce the shutters out of the nitride membrane. Our layout is based on a detailed mechanical analysis for which we determined crucial material parameters experimentally.
We have developed a novel concept for miniaturized fiber optic switches. It is base don microprisms moved into the path of one or several input beams which are de3flected hereby and directed to the output fibers. Coupling of the deflected light beams into the output fibers is achieved by microlens arrays. The overall optical system has been designed properly in order to minimize the switch dimensions and to obtain excellent optical parameters of the switches. Piezoelectric bending actuators with a characteristic translation range of > 0.5 mm have been sued for the microprism movement. First switch prototypes are characterized by excellent optical parameters and short switching time. Several methods for system integration have been developed and applied to prototype fabrication. The first important process is the integration of fiber arrays with microlens arrays. A special mounting procedure has been developed for this. The second critical integration process is the mounting procedure of the prisms to the bending actuators. For this purpose a special vacuum gripper has been built. With the help of this gripper all microprisms can be mounted in one step.
In the rapidly developing optical telecommunication domain optical switch arrays lend themselves to the complex switching tasks. Therefore a prototype of an all-optical switch matrix with 2 in- and output channels has been developed in LIGA-technique. However, with the presented concept also switch arrays with more channels can be realized. The switch array has been designed for the telecommunication wavelength 1.55 micrometers and for single mode application. The optical signals are detoured inside a microoptical bench by means of moveable micromirrors. For the collimation of the light beams spherical glass lense are used. Fibers and lenses are passively aligned with mounts and stops in the LIGA-structured microoptical bench. The mirrors are placed by electrostatic wobble motors. Defined end positions for the micromirrors are realized by use of electromechanical dead stops. In order to avoid angular displacements of the deflected light beams double mirrors are used. The presented prototype features two 2 by 2 switch matrices on a 10 by 10 mm2 ceramic substrate with six micromotors with 1.7 mm diameter. Switching times down to 30 ms have been achieved. The crosstalk between different channels is 90 dB and first measurements of the insertion loss with passive alignment of the optical elements yielded 7 dB. Further work to reduce the insertion loss by optimization of the alignment features are under way.
A novel design for a polymer-based singlemode beam splitter with a refractive index difference of (Delta) n equals 0.01 has been developed to grant the functionality at higher tolerances of (Delta) n(+/- 0.002). This was done by interpreting simulations carried out using the beam propagation method. For efficiently increasing the fiber to waveguide coupling a double-sinus s-bend taper could be identified for adapting the beam shapes of the standard singlemode fiber to the waveguide. Before splitting the beam is led through a 'rib mode stripper' which allows the suppression of higher modes and causes only a negligible disturbance of the fundamental model. For realizing this component, a number of commercially available polymers for optical waveguide components has been analyzed under the aspect of temperature stability of refractive indices. For that purpose a heatable Abbe refractometer has been used. Core and substrate materials are showing different thermal behaviors. Therefore, we could prove that for waveguide designs requiring the standard singlemode fiber refractive index difference of (Delta) n equals 0.004, the necessary stability of (Delta) n may only be achieved within a typical temperature interval of about 10K. Only one optical core material enabled a temperature range of about 95K, still somewhat below the requirements of the Bellcore- specifications.
A compact confocal imaging instrument is described that makes use of a high-performance bi-axial Silicon torsion mirror, in concert with a reflective dynamic parabolic membrane mirror to provide 3D beam scanning. This beam scan engine is incorporated into a confocal imaging Raman spectrometer under development for exploration of Martian rocks and soil, designed to achieve optical resolution of 1 micrometers at (lambda) equals 850 nm, with a field of view of 300 micrometers and focus control of more than 200 micrometers . Fast x-y beam scanning is achieved with the bi-axial scanner, while the parabolic membrane provides both static and dynamic focus control for gross instrument focus as well as on-the fly field curvature correction or substrate contour tracing. In this paper we describe the MOEM elements as well as on-the-fly curvature correction or substrate contour tracing. In this paper we describe the MOEM elements as well as the overall instrument architecture. We also present initial imaging results using the torsion mirror scanner, and we describe the dynamic focus element fabrication, modeling and preliminary experimental characterization.
In the present study, a novel micro torsional mirror used as a high frequency optical scanner is proposed. The proposed micromachiend torsional mirror exploits the electrostatic torque generators and a reinforced mirror plate to improve the performance of the device. Although the torque generator is driven by gap closing electrodes, its traveling distance is remarkably magnified by a novel lever mechanism. Moreover, the torque generators could drive of the mirror plate without wobble motion. A reinforced frame is used to stiffen the mirror plate to improve the optical performance of the scanner. In order to demonstrate the concept proposed in this study, micromachined torsional mirrors were fabricated through the integration of the DRIE, the surface and the bulk micromachining processes. According to the measurement, the proposed micro torsional mirror could operation in relativity low voltage, the scanning frequency of the mirror can reach 17.7 kHz, and the optical scan angle is 5 degrees.
In this work, a scanning silicon micromirror using a bi- directionally movable magnetic microactuator is designed, fabricated and characterized. Although there have been technical difficulties in realizing bi-directional motion in magnetic MOEMS devices for the lack of a suitable structuring technique for permanent magnet components, we overcome those by using UV-LIGA process of thick CONiMnP alloy films and arrays. Based on this new fabrication technique, hard magnetic films or arrays are directly electroplated on silicon cantilever beams in order to compose moving mirror parts. A micromirror is constructed by combining the beam with an electromagnet. According to the change of current in electromagnets, the micromirrors are deflected either upward or downward depending on the direction of magnetic field generated by the electromagnets. Optical properties of the scanning mirrors are measured by a He-Ne laser beam source with the wavelength of 632.8 nm and an optical power detector. A prototype scanning micromirror shows +/- 60 micrometers deflections at the current of +/- 100 mA. The Gaussian profile of the laser beam is well preserved. The reflectance is above 98 percent for the mirrors coated with aluminum films.
Design and modeling aspects of torsional 1D and 2D Micro Scanning Mirrors are presented. During the oscillation of the mirror plate the inertial moment gives rise to a deformation of the plate. This dynamic deformation results in a defocusing of the reflected laser beam. Therefore, the scan frequency of a device with a given size of the mirror plate and deflection angle is limited. Further restrictions arise from the demanded mechanical robustness like resistivity against shock and torsional stress. This leads to a minimum eignefrequency of the device which in the case of a rectangular shaped is proportional to the width of the spring. To enable a single mode operation it is advantageous that the torsion around the springs is the lowest mode sufficiently separated from all others. A FEM-analysis has been carried out to determine the mode sequence of a 1D and a 2D Micro Scanner respectively. The analytical calculated eigenfrequencies agree well with the numerical determined. Taken into account the result of the analytical and numerical investigations 1D and 2D Micro Scanning Mirrors have been designed and fabricated. The mirror and the springs are defined in a 20 to 30 micrometers thick single crystal silicon layer. The results of the experimental investigations with respect to the shock resistivity and the long run behavior probe the suitability of the modeling.
This paper describes mechanical designed concepts for a class of pivoting micromirrors that permit relatively large angles of orientation to be obtained when configured in large arrays. Micromirror arrays can be utilized in a variety of applications ranging from optical switching to beam-front correction in a variety of technologies. This particular work is concerned with silicon surface micromachining. The multi-layer polysilicon surface micromachined process developed at Sandia National Laboratories is used to fabricate micromirror arrays that consists of capacitive electrode pairs which are used to electrostatically actuator mirrors to their desired positions and suitable elastic suspensions which support the 2 micrometers thick mirror structures. The designs described have been fabricated and successfully operated.
For the transfer of micro optical and mechanical components to an application, packaging currently represents a major problem. The electrical, optical and mechanical components are typically fabricated with lithographic techniques. Thus the relative distances are accurate, but the absolute position on the substrate is defined by the quality of the separation tool. Thus active alignment is usually necessary for the assembly. For the development of standardized MOEM - modules, designed to eliminate the problems of alignment, technological, optical and function considerations have to be addressed.
The evolution of computer chip technology has been marked by a steady progression toward higher performance which will soon be limited by the time delay associated with interconnects. This has led to consideration of alternate interconnect methods to complement or replace conventional metal/dielectric architectures for both intra-chip and chip to chip and detectors. The interconnect medium for this approach, however, is still under conceptual design and has spawned many candidates. Various configurations of static micro-optic arrays however, recent consideration has been given to active, reconfigurable optics based on micro-electro-mechanical systems (MEMS) technologies. These Optical MEMS or MOEMS have enabled innovative devices which can control phase, amplitude and direction of input light beams. One area which has recently received much attention is the creation and use of both reflective and diffractive arrays. This paper will present the development and use of active, reconfigurable MOEMS prototypes applied to proof of principle optical interconnect systems. We have been studying several array architectures consisting of gratings, columnar reflectors and micromirrors. For example, the patented MEMS-based compound grating (MCG) is currently being developed to enable a new class of diffractive arrays which can be used as a massively parallel switch. The MCG is a device which is a superposition of two or more diffraction gratings whose surface topology can be controlled. Various prototype arrays of these MCG devices have been designed, modeled, fabricated and tested. Initial result of these studies will be presented. In addition, application of the digital micromirror device to this problem will also be discussed. Using a custom control software and optical setup, preliminary results from the integration of a DMD into an optical interconnect test stand will be presented.
High power diode lasers have become very attractive as an intelligent tool for direct material processing as well as pump sources for miniaturized solid state lasers and fiber lasers since optical beam transformation systems generate the required beam circularization from the originally highly asymmetric brightness of the output beam. This presentation focuses on reliable microassembling processes to realize micro-optical beam transformation systems for high power diode laser bars and stacks for the efficient coupling of the beam into optical fibers at reasonable costs. The modular semi automatic micro assembly set up realized consists of a six axes alignment system with an accuracy in the submicron range for the three spatial areas as well as microrad for the three rotational axes, a semi-automatic glue dispenser as well as respective grippers and magazines which are necessary for the handling of the micro optical components. The established automatic processes for the mounting of the fast axis collimation lenses are of particular interest for the assembly of e.g. fiber coupled modules of diode laser stacks whereas more than 20 fast-axis collimations are necessary.
The technical and economic rationale for the selection and use of MEMS optical scanning devices for Retinal Scanning Display systems is discussed. While several new technologies and manufacturing approaches to microdisplays have been proposed and demonstrated in the display industry, a number of significant challenges related to cost and complexity of fabricating very dense integrated matrix displays are observed. Factors relating to the choice of a MEMS-based scanned beam approach are presented with special emphasis on the economics of silicon processing and light valve manufacturing. Related imaging applications for the high-precision scanning capabilities of the MEMS scanner are described.
A dual-axis, raster-scanning laser display based on a monolithic micromachined scanning mirror is presented. The scanner consists of a micromirror located at the end of a thermally actuated bimorph beam. The novelty of the device is that an 'L'-shape cantilever, which is simultaneously excited at non-resonance and at resonance, gives the two orthogonal angular motions. The high sensitivity of the thermal bimorph actuator allows a low frequency movement of the scanner in one direction. The second orthogonal scanning direction is a resonance torsion motion. The micro-device has a raster scanning frequency varying from 1000 Hz to 5000 Hz depending on the geometry, and if combined with a 50 Hz frame signal, has a definition of up to 100 lines. Mechanical scan amplitudes over 15 degrees in two orthogonal directions have been achieved. The typical power consumption is 5 mW. In this paper, the resolution of the scanner is discussed which is limited by the diffraction from the 500 micrometers to 300 micrometers mirror and its flatness. The performance of the new device is demonstrated by projecting a 2D image using a modulated laser diode and the two orthogonal mirror deflections.
High-resolution and high frame rate dynamic microdisplays can be implemented by scanning a photon beam in a raster format across the viewer's retina. Microvision is developing biaxial MEMS scanners for such video display applications. This paper discusses the optical performance requirements for scanning display systems. The display resolution directly translates into a scan-angle-mirror-size product and the frame rate translates into vertical and horizontal scanner frequencies. (theta) -product and fh are both very important figures of merit for scanner performance comparison. In addition, the static and dynamic flatness of the scanners, off-axis motion and scan repeatability, scanner position sensor accuracy all have a direct impact on display image quality.
Scanned displays have potential for achieving high brightness and see-through configurations in many display applications. A MEMS- based solution based on these tradeoffs for SVGA level performance is presented, with test data illustrating optical, mechanical, and electrical performance. Comparison of this scanner against video requirements and other scanners previously reported are illustrated. The feasibility of MEMS-based scanners for Retinal Scanning Displays and other applications is discussed, with extension to higher video performance standards.
Recent developments in the are of micromachining and microfabrication are accelerating commercial awareness of microstructures. Product applications ranging form automotive and medical devices to industrial, chemical and consumer products show the necessity of adequate fabrication methods for microstructures. These fabrication methods include high resolution measurement technologies. Images of the machined area, recorded via videography by a CCD-camera based computer vision system are evaluated to obtain the two dimensions of the microstructured devices. Height measurement is performed by automatically focusing on two different levels of the workpiece. The achieved accuracy of the measurement data is evaluated. During structuring of microdevices an autofocus system is used to control the removal process by laser radiation to obtain the desired geometry. The mathematical algorithms used by the vision system to guide the focus of the CCD-camera are discussed. The designed measurement system is tested by microstructuring of hard metals and ceramics with short pulse laser radiation.
Microsystems involve several fabrication technologies, but share the common trait of dimensions and motions measured in microns. Small feature sizes and deflections make the detection of microdevice motion particularly difficult. The rapid operating frequencies of many microactuators compound the detection problem. Effective feedback, control, and performance measurement of microactuators thus become problematic. These measurements are particularly important, however, due to the developmental nature of many microsystem technologies. Wear, lifetime issues, and optimized drive signals, for example, are poorly understood for many actuation devices. As microactuators move out of the development stage and begin to perform work on external assemblies and environments, the various load conditions will also come into account. Since microactuators involve small masses and inertias, effective driving of external loads may require feedback-based control of the microdevice. Optical sensing technologies offer solutions to these problems of sensor motion, microactuator analysis during the development process, and integrated feedback for microactuators driving external loads. Optical methods also end themselves to the effectively 1D nature of many microsystem motions, limiting the required signal analysis to practical levels that support real-time measurement and control. This paper describes several optical techniques for sensing motion, performance, and feedback data, some of which can integrated with the microsystems themselves. For microactuators, experimental results indicate that real-time performance measurements are particularly revealing for understanding device motion and response. For microsensors, experimental result are also presented for interpreting motion using external and integrated optical techniques.
As microelectromechanical systems (MEMS) become widely implemented, the application of closed-loop control methods to MEMS will lead to higher degrees of certainty and reliability of microelectromechanical operation in physically demanding environments. By including planar diffractive optics in these systems, an optical method of determining MEMS microstructure position that is fully decoupled from the means of mechanical actuation can be realized. This paper presents the result of initial research evaluating both open and closed-loop nonlinear proportional-integral-differential (PID) control routines using a 1.3 micrometers wavelength through-wafer free-space optical probe to obtain a position signal from a lateral comb resonator fabricated using Chronos Integrated Microsystems' Multi-User MEMS Process service. The implementation of sliding control methods is illustrated through simulation results, and the design considerations for a proposed integrated optical monitoring architecture is presented.
MEMS/MOEMS devices are ubiquitous and span a diverse set of markets and technology circles. Typically these devices are inserted into the final product with only a minimal amount of precision inspection. It is imperative that micro inspection and other micro packaging techniques are implemented at the front end of the manufacturing process to avoid costly yield problems. Metrology and Machine Vision can increase yields, reduce throughputs, and reduce downtime by minimizing reliance on human vision and manual dexterity. In this work we begin to define a systems view of the different types of MEMS/MOEMS devices and associated micro packaging and inspection techniques and issues.
Spatial light modulators (SLM) with addressing through a silicon backplane are gaining importance as microdisplays, for pattern generation in direct-writing systems and for several other applications. The use of CMOS technology has lead to small devices with a high grade of inspection. With the focus on direct-writing systems for photolithographic patterning we have developed tow micromechanical actuator technologies for SLMs with silicon backplane. Here we report on a third technology that employs an oil film on a mirror as micromechanical actuator. The principle of operation is explained and fabrication is described in detail. Demonstrators with 256 by 256 pixels have been fabricated with 16 micrometers and 20 micrometers pixel size. Photographs of programmed images are presented. Measurements of passive devices demonstrated a contrast ratio of 43:1 and a switching time of below 5ms.
Micro actuators are critical elements in all micro-systems which require components that are not stationary. Numerous technologies have been developed in the field of MEMS to provide actuation. These devices are both surface and bulk micromachined and employ a variety of methods including electrostatics, thermal expansion and magnetism to generate forces and displacements. With the rapid growth of micro-optical system applications new actuators are required with unique characteristics. In this paper a review of common actuation technologies is presented. In addition two actuation methods, asymmetric combdrives and electrothermal vibromotors, which are well suited for optical systems are presented. Finally, the importance of control in micro-optical systems is discussed.
We present design, analysis and characterization of surface- micromachined mirrors developed for fiber-optical cross-connects (OXCs). These mirrors are controlled by electrostatic microactuators, and are optimized for our beam-steering OXC switch architecture. Their geometry leads to high-density switch matrices, and the absence of frictional hinges in their actuation mechanism allows highly repeatable operation. This mirror structure features an adjustable maximum deflection angle that can be set during initial assembly or dynamically varied by integration with a standard surface-micromachined linear actuator. A commercial three-layer polysilicon surface- micromachining process is used for fabrication of the micromirrors.
Two monolithically integrated frequency tuners have been analyzed, designed and fabricated. The potential applications for WDM have also been studied. The frequency tuners use 3D micromirrors integrated with single-mode Fabry-Perot laser diodes and anti-reflection coated optical fibers. The difference between the two frequency tuners is that one uses the movable 3D micromirror driven by comb-drive to change the external cavity length, and the other uses the rotatable 3D micromirror driven by thermal-actuator to change the external feedback strength. For the frequency tuner that uses movable 3D micromirror, a wavelength tunability of 16 nm is obtained using 3V driving voltage. As for the frequency tuner that uses rotatable 3D micromirror, a wavelength tunability of 7nm is obtained while using 10mA driving current.
The state of the art of III-V semiconductor based MOEMS is presented with a special emphasis on InP and related materials. It is shown that the MOEMS technology can enhance considerably the capabilities of optical micro-cavities, which are considered as a major component for optical signal processing and light generation. Illustrations of the potential of III-V MOEMS are given in the fields of optical telecommunications. Design and fabrication of highly selective and widely tunable optical filters for wavelength division multiplexing systems are presented. These devices are monolithic and are based on surface micro-machining technology. They combine a variety of very attractive properties such as low control power, low insertion loss, tunability, small bandwidth no polarization dependence, simple fiber coupling, no memory effects and reasonable tuning speed. Fiber to fiber transmission characterizations of packaged filters are presented, including bit error rate measurements. Future prospects implying the use of multi-air-gap MOEMS structures as a basic building-block for a wide variety of routing photonic devices are proposed.
We present a miniaturized Fourier transform (FT) spectrometer based on silicon micromachined. The FTS is a Michelson interferometer with one scanning mirror. The motion of the mirror is carried out by a n electrostatic comb drive actuator. The mirror displacement is 39 micrometers and its reproducibility is +/- 13 nm, which leads to a resolution better than 10 nm in the visible wavelength range. A new design of this chip has been realized in order to integrate an input fiber, a collimating lens system as well as a beam splitting plate. This new design allows to undertake spectroscopy with white light. The limitation of light collimation and the effect of the size of the source have been studied by numerical simulations.
Electrostatically actuated, 500micrometers diameter, Si surface micromachined 2-axis tilting micromirrors were designed and fabricated in a 2 structural + 1 interconnect layer polysilicon process. The mirrors are capable of large, continuous, controlled, DC tilt in any direction at moderate actuation voltages. The lowest-mode resonance frequency is sufficiently high to decouple from the ambient vibration noise and allow setting times of less than a few milliseconds. The Au- coated reflectors, suspended in gimbal mounts via torsional springs and bearings, are tilted by applying voltage to four electrically independent sets of fixed electrodes on the substrate. The electrodes and the springs are designed to optimize actuation voltages, resonance frequencies and the deflection range. To achieve the range, the mounts are lifted and fixed fifty microns above the substrate surface during the release process by a self-assembly mechanism powered by tailored residual stress in a separate metalization layer. Square arrays with 1 mm pitch containing independently addressable identical 16, 64 and 256 mirrors were fabricated and hermetically packaged. Based on these devices, fully functional, bitrate and wavelength independent, single stage, low insertion loss, single mode fiber optical crossconnect system are built.
We are developing as micro-machined electrostatically actuated Fabry-Perot tunable filter with a large clear aperture for application in high through-put wide-field imaging spectroscopy and lidar systems. In the first phase of this effort, we are developing key components based on coupled electro-mechanical simulations. In particular, the movable etalon plate design leverages high coating stress to yield a flat surface in drum- head tension over a large diameter. In this approach, the cylindrical silicon movable plate is back etched, resulting in an optically coated membrane that is suspended from a thick silicon support ring. Underestimating the interaction between the support ring, suspended membrane, and coating is critical to developing surfaces that are flat to within stringent etalon requirements. In this work, we present the simulations used to develop the movable plate, spring suspension system, and electrostatic actuation mechanism. We also present results form test of fabricated proof of concept components.
The main focus of this contribution will be the description of already realized applications of micromirrors and micromirror arrays and future opportunities. As an example image projection and environmental monitoring will be discussed. The micro scanning elements where fabricated by using monocrystalline silicon and are convenient for continuous scanning with working frequencies between several 100 Hz up to 100 kHz.
For wavefront correction in adaptive optics mirror devices are required, which provide a pure phase shift capability with a fine partition over the optical cross section. For this purpose we investigated arrays of piston-type micromirrors. In order to predetermine the basic deformation characteristics and to estimate appropriate design parameters a simple analytical model was derived. We then designed and fabricated arrays of different mirror elements on top of passive address devices by means of surface-micromachining realizing pixel side lengths of 75, 100, 120 and 150 micrometers . Experimental investigations of the electromechanical behavior were done by surface profile measurements using white light interferometry, which reveals a good overall functionality of the mirror arrays. Furthermore, an analog deflection range of up to 1.2 micrometers at address voltages below 32V were obtained together with a load dependent height level accuracy of 80 to 100 nm.
Over the last few years, high resolution spatial light modulators (SLMs) have been developed at the IMS Dresden. These are fabricated using one of two different technological processes. In one version a flexible, highly reflecting aluminum coating of about 50nm is evaporated onto a elastic layer, while the other version has quite rigid aluminum mirrors that are suspended by flexible hinges above the substrate. Both versions are fabricated on top of a CMOS DRAM matrix, which allows the addressing of individual pixels. So far SLMs with over 2 million pixels have been produced. In order to ensure a high quality of these SLMs a map of the SLM under test is needed showing the exact position of defective pixels together with the type of defect e.g. not responding, always deflected, wrong spring constant, poorly reflecting surface. Additionally information on the local and global flatness is required. This task can only be handled by an automated test stitching together many single measurements. A test system has bene set up using a white light interferometer. This allows to measure the response of each and every SLM pixel to applied voltages.
A 2D array of individually addressable micro-mirrors with 100 micrometers by 100 micrometers pixel size, capable of tilting +/- 100 by electrostatic actuation is being developed and fabricated at the Detector Development Laboratory of NASA, GSFC. The development requires integration of CMOS and MEMS fabrication processes. We have competed extensive analytical studies and performed laboratory test to compare model predictions with actual performance of a 3 by 3 array. We are testing the address and driver circuit for a 32 by 32 array and also developing the process integration of the CMOS and MEMS fabrication of the larger arrays. The mirrors are capable of operating at cryogenic temperature for astronomical applications. Our goal is to extend the development to a 25 6by 256 array for a wide variety of space applications including the multi-object-spectrometer in the next generation space telescope.
Arrays of pressure sensors utilizing microelectromechanical systems (MEMS) technology for fabrication of the sensing element and interrogation by fiber optics are described. Optically interrogated MEMS devices are potentially more suitable for many propulsion applications involving harsh environments than electrically interrogated MEMS devices. Pressure sensor elements form a Fabry-Perot interferometer so that reflected light measures pressure. Rationale for the design of the geometry of sensor elements and array configurations will be presented. These devices are designed to provide sensitivity over a given pressure range, ease of fabrication, and array configurations useful for propulsion characterization. Sensor element and array fabrication will be discussed. These sensor elements are fabricated by etching shallow cavities in glass substrates followed by electrostatic bonding of silicon onto the glass over the cavity. The silicon is then etched to form the pressure sensitive diaphragm. Linear arrays having 6 elements will be described. Experimentally results for static pressure tests and dynamic pressure test carried out in a shock tube demonstrate reasonable linearity, sensitivity and time response.
Pressure sensors utilizing MEMS technology for fabrication of the sensing element, interrogation by fiber optics, and which are suitable for propulsion applications are described. Devices utilizing micro-opto-electro-mechanical systems (MOEMS) technology are often better suited for harsh environments than electrically interrogated MEMS devices, so with sturdy packaging these optical devices may be useful to many propulsion applications. MOEMS pressure sensors can also be incorporated into arrays for detailed spatial characterization along with inherent high speed temporal characterization. Such characterization is expected to be very useful for propulsion systems. This presentation will first review optical-MEMS pressure sensor configurations. We will then concentrate on configurations most suitable for high speed applications in harsh environments. Examples of experimental results for static pressure test as well as for dynamic pressure test carried out in a shock tube demonstrating good linearity, sensitivity and time response will then be presented. Hybrid and monolithic array configurations will be presented. A discussion of the use of wavelength division multiplexing for efficient accessing of array elements will also be included.
A novel shape design of the comb drive to achieve digital switches while avoiding the unstable pull-in is presented. The statics and dynamics of switching are discussed and the voltage- displacement-transfer characteristic is demonstrated. The degradation of the transfer characteristic can be caused by either the overshoot of actuators in the transient switching or the actuator geometry. An optimal design of the actuator geometry is proposed to improve the quality of the transfer characteristic. On the other hand, the settling time of the comb drive's transient response to a step excitation will be minimized for high-speed switches. To achieve this, two non-dimensional control parameters are identified and physically interpreted. Then a transient optimization is carried out by introducing an optimal electrical damping and choosing a zero static comb overlap. The optimal transient response is obtained by analytically solving the linearized force/moment and electric equations. Finally numerical simulation is performed to verify the analytic solution and extend the analysis to the nonlinear regime.
Assembly is a crucial process during the production of microsystems. Especially automated and economic assembly of flip- chip at small and medium batch sizes is not solved at the moment in industry. For flexible and economic assembly of standard and flip-chip elements a tool was developed, which makes it possible to assemble MOEMS with an accuracy of less than 8 micrometers by a standard industrial robot. This is done by integrating a fine positioning drive and sensors into the tool. Moreover, a special optics module for the assembly of flip-chip elements was developed, which can be used in different positioning devices in a manual and automatic modus.
This integrated optical motion detection microsystem combines an analog programmable interpolator, digital drivers, differential analog front-end, signal monitoring outputs and contains an array of light sensitive cells with microstripe raster. Interpolating values are generated from orthogonal sinusoidal signals coming from illuminated integrated photosensors. Optical microsystem composes autocalibration on analog front-end to get proper interpolating signals. It consists of three symmetrical analog channels: sin, cosine and reference signal channel. Each channel combines a current gain stage operating as a fully differential current to voltage converter and thus guarantees the best phase relating between ordinary and inverted analog signals. Integrated analog buffers are used for outputting processed analog signals for monitoring purpose. The signal bandwidth of analog channels is designed to be large enough not to limit the system response and therefore maximize the useful signal range.
We present a tunable interference filter for IR and visible light that scans the desired part of the optical spectrum within milliseconds. A single pixel detector measures serially the intensity at selected wavelengths. This concept avoids expensive linear detectors as used for grating spectrometers. The tunable optical interference filter is fabricated by a new porous silicon batch technology using only tow photolithography steps. The refractive index of this filter microplate is gradually modulated in depth to create a Bragg mirror or a Fabry-Perot bandpass filter for a transmission wavelength between 400 nm and 6 micrometers . Two thermal bimorph micro-actuators tilt the plate by up to 90 degrees, changing the incidence angle of the beam to be analyzed. This tunes the wavelength transmitted to be detected by a factor of 1.5, e.g. form 4 micrometers to 6 micrometers . The filter area can be chosen between 0.27 mm by 0.70 mm and 2.50 mm by 3.00 mm, its thickness is typically 30 micrometers . The spectral finesse of 25 is sufficient for most diagnosis applications, e.g. detection of CO2 and CO in combustion processes by their IR absorption bands. Online colorimetery and color correction of desktop printers can be envisaged.
Silicon micromechanics in an emerging field which is beginning to impact almost every area of science and technology. In areas as diverse as the chemical, automotive, aeronautical, cellular and optical communication industries, Silicon micromachines are becoming the solution of choice for many problems. In this paper we will describe what they are, how they are built, and show how they have the potential to revolutionize lightwave systems. Devices such as optical switches, variable attenuators, active equalizers, add/drop multiplexers, optical crossconnects, gain tilt equalizers, data transmitters and many others are beginning to find ubiquitous application in advanced lightwave systems. We will show examples of these devices and describe some of the challenges in attacking the billions of dollars in addressable markets for this technology.
Silicon bulk micromachining which is based on a silicon etching and a glass- silicon anodic bonding plays important roles to make micro sensors and micro actuators. Three dimensional microfabrication of other functional materials as piezoelectric materials are also important to develop high performance microactuators, micro energy source and so on. Vacuum sealing is required to prevent a viscous dumping for packages micromechanical sensors. Extremely small structures as microprobe are required for high resolution, high sensitivity and quick response. As sophisticated microsystems which are made of many sensors, circuits and actuators are required for example for maintenance tools used in a narrow space. Developments for those required will be described.
The continuous progress in micro- and nano-system technologies has allowed the successful development of many innovative products in process control, environmental monitoring, healthcare, automotive and aerospace as well as information processing systems. In this paper on overview will be given of current progress in micro- and nanofabrication process technologies, such as deep reactive ion etching, micro-electro discharge machining, thick photoresistant processing and plating. The availibility of these micro- and nanofabrication processes will be illustrated with examples of new generations of silicon-based sensors, actuators and Microsystems with a particular emphasis on real applications of these components and systems.