三田 信

A simple and new technique for interlayer electrical interconnection for silicon-on-insulator microelectromechanical systems (SOI-MEMS) micromachining was developed without using additional device layers or patterning processes. A part of the SOI microstructure was shaped into a slender cantilever and intentionally brought into contact onto the substrate surface by surface stiction force after sacrificial release. The contact resistance between the stiction bar and the substrate was studied with and without a subsequent metallization process. The stiction bar was found to improve the MEMS design flexibility in allocating electrical components (comb-drive electrodes and interconnection tethers) and mechanical components (suspensions and frame) to the SOI and the substrate layer and to make a high-density complex double-deck structure in a small footprint. As an example of the high-density design, we developed a micro-XYZ stage with the lateral and vertical comb-drive mechanisms and compared the design with the conventional bulk micromachined structures.

We report an equivalent circuit model for MEMS (microelectromechanical systems) electrostatic actuator using open-source circuit simulator Qucs (quite universal circuit simulator). Electrostatic force, equation of motion, and Kirchhoff's laws are implemented by using the EDD (equation defined device) function of Qucs. Mathematic integral operation in the equation of motion is interpreted into electrical circuits by using an ideal electrical capacitor that read input signal as current and returns accumulation result in terms of voltage. Seamless multi-physics mixed signal simulation between micro mechanics and electronics has become possible on the single platform of the circuit simulator.

We report a newly developed mixed-signal simulation tool for micro optoelectromechanical systems. Multi-physics signals in electrical, mechanical and optical domains are handed as electrical voltage or current in a circuit simulator Qucs, by implementing an equation-defined analytical model into the voltage-controlled current sources. This paper reports an equivalent circuit implementation of the electrostatic torsion mirror scanner. ©2009 IEEE.

This paper presents a new method of integrating multiple MEMS designs with 40 V class CMOS driver circuits in a multi-user-multi-chip manner. The multi-chip multi-user CMOS-MEMS process was done at 35 mm x 35 mm SOI chip. More than six different designs of SOI-bulk micromachined actuators including the pitch-tunable gratings were monolithically integrated onto the pre-fabricated high-voltage level-shifter circuits. We measured electro mechanical characteristics of the grating light valve integrated with high-voltage level-shifter and successfully demonstrated 1 MHz operation.

We have been developing ultra light-weight X-ray optics using MEMS (Micro Electro Mechanical Systems) technologies. We utilized crystal planes after anisotropic wet etching of silicon (110) wafers as X-ray mirrors and succeeded in X-ray reflection and imaging. Since we can etch tiny pores in thin wafers, this type of optics can be the lightest X-ray telescope. However, because the crystal planes are alinged in certain directions, we must approximate ideal optical surfaces with flat planes, which limits angular resolution of the optics on the order of arcmin. In order to overcome this issue, we propose novel X-ray optics based on a combination of five recently developed MEMS technologies, namely silicon dry etching, X-ray LIGA, silicon hydrogen anneal, magnetic fluid assisted polishing and hot plastic deformation of silicon. In this paper, we describe this new method and report on our development of X-ray mirrors fabricated by these technologies and X-ray reflection experiments of two types of MEMS X-ray mirrors made of silicon and nickel. For the first time, X-ray reflections on these mirrors were detected in the angular response measurements. Compared to model calculations, surface roughness of the silicon and nickel mirrors were estimated to be 5 nm and 3 nm, respectively.

A novel micromachined X-ray collector using anisotropically etched Si(111) side walls as X-ray mirrors for future astronomical missions is reported. The collector was designed to converge a phi 100 mm parallel X-ray beam into a phi 4 mm focus. In order to obtain smooth Si(111) side walls, dynashock-type ultrasonic waves were added during the anisotropic KOH etching. The surface roughness on the order of nm or less was achieved. The sidewalls or the X-ray mirrors were diced from the wafer as mirror chips and then adhered to a mount formed by deep reactive ion etching. The first light image was successfully obtained at Al K alpha 1.49 keV in a ISAS 30 m-long X-ray beam line. (C) 2007 Elsevier B.V. All rights reserved.

An ultra light-weight X-ray optic using MEMS technologies was designed for X-ray astronomy. Numerical simulation was utilized to estimate allowable fabrication accuracies. Obtained X-ray images with a fabricated optic were consistent with the design.

A technique is described for measuring the far-field radiation pattern, gain, and the transmissivity of each portion of an aperture of lightwave (optical) antennas. First, the compatibility of lightwave antennas to a system is mentioned. Then, the principles and setup for each measurement term are presented. A comparison with radio-wave antennas is also given.

High-performance antennas at lightwave frequency require optimal curved surfaces and high mechanical precision in order to realize high aperture efficiencies. We have developed a novel micro lightwave antenna by employing the micro electromechanical system processing technology. We describe a transparent antenna that has a multilevel step structure with a diameter of 4 millimeters. The ideal curve of the antenna surface is discretized by steps of constant height. The characteristics of the fabricated antenna have been measured; its gain is 84.1 dBi, which is 0.83 dB less than that of a reference antenna with a uniform field distribution. The aperture efficiency is 82.6%. The power radiation pattern is measured through the Fourier transform lens method and is in good agreement with the simulation result.

In this paper, we report an array of f-theta microlens optical scanners developed for 3-D optical cross connect (OXC) system using the bulk-silicon micromachining technique. An electrostatic XY-stage mechanism for the 2-D lens scanner was designed to have a small footprint (2 mm x 2 mm), compared with an integrated silicon lens (diameter 1 mm) due to the newly developed double-deck actuator design; all the mechanical parts (suspensions and frames) were made in the substrate layer of a silicon-on-insulator (SOI) wafer, and the electrostatic actuation mechanism (electrodes and electrical interconnection) was made in the SOI layer. A silicon lens was integrated on top of the XY-stage by transferring the spherical profile of a thermal-reflow photoresist pattern into the SOI layer by reactive-ion etching. The XY lens scanner was found to operate at lateral displacement of 19 mu m in the X-directions and 23 mu m in the Y-directions at drive voltages of 110 and 60 V, respectively. For an optical assembly of the OXC, we used additional lenses in a telescope formation to double the beam angle that was steered by the f-theta microlens scanner by which the lens displacement could be designed to be smaller by a factor of 1/2.

In this paper, we demonstrate the multi-object conveyance by a micro system of actuator / sensor array, which is a stack- integrated transparent actuator array chip on a photo sensor array chip of 16 x 16 cells. The system can convey not only an object to a desired point by the feedback control but also two objects to different directions independently; nevertheless each cell of the system is not controlled independently but by only 16 x 4 pads, which are situated peripherally on 4 edges of the system.

A novel micromachined X-ray collector using anisotropically etched Si (111) planes as X-ray mirrors for future astronomical missions is reported. Mirrors, fabricated using dynashock-type ultrasonic waves, have very smooth surfaces with ail rms roughness of nm or less. After the etching, mirror chips were cut front the wafer with a dicing machine and adhered to a mount formed by deep reactive ion etching, in order to collect parallel X-ray beam (phi 100 mm) on a tiny focus (phi 4 mm). The first light image was successfully obtained at Al K-alpha 1.49 keV in a ISAS 30m-long beam line.

This paper describes the on-orbit results and lessons-learned of the small scientific satellite "INDEX" (REIMEI) for aurora observation and demonstration of advanced satellite technologies. INDEX is a small satellite with 72kg mass, and is provided with three-axis attitude controll capabilities for aurora observation. INDEX was launched into a nearly sun synchronous polar orbit on Aug. 23rd, 2005 (UT) from Baikonur, Kazakhstan by Dnepr rocket. INDEX satellite has been satisfactorily working on the orbit for 24 months at present of August,2007. Three axis control is achieved with accuracy of 0.1 deg(3 σ). Multi-spectrum images of aurora are taken with 8Hz rate and 2 km spatial resolution to investigate the aurora physics. INDEX is performing the simultaneous observation of aurora images and particle measurements. INDEX indicates that even a small satellite launched as a piggy-back can successfully perform unique scientific mission purposes. Copyright IAF/IAA. All rights reserved.

We present a newly developed technology platform for monolithically integrating high voltage DMOS (Double-diffused Metal Oxide Semiconductor) circuits upwards of 40V with bulk-micromachined actuators (XY-stage) using both the top and the bottom surfaces of an SOI (Silicon-on-Insulator) wafer. Driver circuits were pre-fabricated on an 8-mu m-thick SOI wafer by the DMOS processes, after which MEMS electrostatic actuators were integrated into the identical SOI layer as well as the substrate by post-processing using DRIE (Deep Reactive Ion Etching). Thanks to this monolithic integration technique, multi-layered high-aspect-ratio structures were produced.

We have developed a two-dimensionally maneuverable micro impact-actuator for space applications with high mobility and robustness using impact motion of a suspended mass. Compared with our previous device using an electrostatic parallel plate mechanism, stepping efficiency has been greatly improved by the using comb-drive mechanism to drive inertia-mass two-dimensionally. Typical rover speed of 8 - 9 microns/sec was observed with pulse voltage of 100 V at 200 Hz. ©2007 IEEE.

We stack-integrated a transparent actuator array chip on a photo sensor array chip and demonstrated 2-D conveyance of an object on the array with closed loop feedback. The actuator array has 16 x 16 cells; each cell has four thermo-bimorph actuators. Matched array of photo-diodes detected the shadow of the object; this information is processed by FPGA that controls the actuator array to energize. We have demonstrated an automatic feedback conveyance to the target point by energizing the actuators just under the object.

We have newly observed the gold atom migration and rearrangement at the artificially made point contact in a well controlled manner using microactuated probes with nano positioning accuracy. In-situ TEM observation revealed that the initial gold facet before contact strongly influences the shape of a nanobridge during the tensile test. Crystallographic facets of (21 (11) over bar), (10 (1) over bar) and (1 (1) over bar0) at the nanocontact correspond to the formation of an inhomogeneous nanowire, a thinned nanocontact, and a homogeneous nano-contact, respectively.

The first light of a ultra-lightweight and low-cost micro-pore X-ray optic utilizing MEMS (Micro Electro Mechanical Systems) technologies is reported. Our idea is to use silicon (111) planes appeared after anisotropic wet etching of silicon wafers. As a first step to Wolter type-1 optics, a single-stage optic with a focal length of 750 mm and a diameter of 100 mm was designed for energies below 2 keV. The optic consists of 218 mirror chips for X-ray reflection and an optic mount for packing these chips. Design parameters and required fabrication accuracies were determined with numerical simulations. The fabricated optic satisfied these accuracies and its imaging quality was measured at the ISAS X-ray beam line at Al K-alpha 1.49 keV. A focused image was successfully obtained. The measured image size of similar to 4 mm was consistent with the chip sizes. The estimated X-ray reflectivity also could be explained by micro-roughness of less than 3 nm and geometrical occulting effect due to large obstacle structures on the reflection surface.

We have found an interesting phenomenon of self-excited oscillation of electrostatic micro-cantilever; the device was found to be self-oscillated under an applied dc voltage, by repeating charge and discharge between the fixed and the movable electrodes. Oscillation frequency is changed by changing apply de voltage. The phenomenon can be used to make a MEMS version of voltage-controlled oscillator (VCO) for constructing a simple voltage-controlled oscillator that is free from external inductors or capacitors.

We report a monolithic XYZ-stage with electrostatic comb-mechanisms integrated in only two silicon layers and by three photolithography steps that topologically switches the allocation of layer for electrical and elastic components. The XY-stage moved in the X- and the Y-direction by 19 mu m independently, and also in the diagonal direction. We have successfully demonstrated maximum 2.12 mu m in the Z-direction with applied voltage of 200 V.

In this paper, different types of vertical electrostatic comb-drive actuators are proposed. The aim of design is to minimize the cross talk between vertical and lateral motions with a relatively simple fabrication process, namely, with only two ICP-RIE steps from the front side with layered masks. Three designs are analyzed by MEMCAD, a finite-element modeling package, combined with a micromachining process simulator. After optimization based on the calculation, all types were fabricated and tested. The experimental results are qualitatively in good agreement with the calculations. Because of the excess undercutting in our ICP-RIE machine, the supports were softer than designed. The displacement was larger than expected. According to obtained results, we can expect to generate a vertical force of 0.5 μN per tooth at around 50 V. The measured cross talk between vertical motion and the horizontal motion was 20%. The resonant frequency of a typical device is 9 kHz and the displacement is 1.5 μm at 50 V. © 2007 Institute of Electrical Engineers of Japan.

To develop x-ray mirrors for micropore optics, smooth silicon (111) sidewalls obtained after anisotropic wet etching of a silicon (110) wafer were studied. A sample device with 19 mu m wide (111) sidewalls was fabricated using a 220 mu m thick silicon (110) wafer and potassium hydroxide solution. For what we believe to be the first time, x-ray reflection on the (111) sidewalls was detected in the angular response measurement. Compared to ray-tracing simulations, the surface roughness of the sidewalls was estimated to be 3-5 nm, which is consistent with the atomic force microscope and the surface profiler measurements. (c) 2006 Optical Society of America.

LIDAR(LIght Detection And Ranging) that measures distance by the laser pulse is a necessary sensor of navigation for a deep space explorer that doses a planetary exploration. Two dimension of LIDAR scanning is required from both sides of the navigation control and the science observation in order to make a 3D map of surface efficiently. This paper proposes a novel method on the beam scanning mechanism for a receiver telescope with big aperture by using MEMS technology. In addition, it reports on the result of executing the basic function experiment of the beam scanning mechanism. The scanning optics system is composed of a telecentric telescope, and a micro shutter array. This optical system has achieved a narrow viewing angle corresponding to aperture of the shutter by limiting the view of the telescope that has a wide viewing angle with the shutter. We experimented by using the shutter array of 6mm×6mm size. As a result, it succeeded that the scanning angle in the achievement of azimuth angle 8.8deg, elevation angle 8.1deg, and the field of view angle of azimuth angle 1.8deg and elevation angle 0.6deg.

We have developed novel device architecture of comb-driven double-gimbal XY-stage of high fill-factor (stage area / chip size), which has been realized for the first time by topologically separating the actuator elements in two layers: all the electrical parts (electrodes and interconnections) are in the Silicon-on-Insulator (SOI) layer, while the mechanical parts (suspensions, frame, and XY-stage) are in the substrate. Thanks to the new layered structures, the overall footprint of the actuator has been made small. The XY-stage moved 19µm in the X and the Y direction independently, and also in the diagonal direction.

Recent development of the extremely light-weight micro pore optics based on the semiconductor MEMS (Micro Electro Mechanical System) technologies is reported. Anisotropic chemical wet etching of silicon (110) wafers were utilized, in order to obtain a row of smooth (111) side walls vertical to the wafer face and to use them as X-ray mirrors. To obtain high performance mirrors with smooth surfaces and a high aspect ratio, several modifications were made to our previous manufacturing process shown in Ezoe et al. (2005). After these improvements, smooth surfaces with rms roughness of the order of angstroms and also a high aspect ratio of 20 were achieved. Furthermore, a single-stage optic was designed as a first step to multi-stage optics. A mounting device and a slit device for the sample optic were fabricated fully using the MEMS technologies and evaluated.

We report the design, fabrication and electromechanical performance of a newly developed micro electromechanical XY-scanner for micro-optical spatial light modulation using the silicon micromachining technology. A two-dimensional stage is integrated with a silicon micro lens to scan a transmitting infrared light of 1.55-micron-wavelength by the mechanism of the f-theta lens scanner. Mechanical displacement of up to +/- 10 microns ( optical angle of +/- 0.57 degrees) was obtained with a drive voltage of 30 V; optical simulation has suggested that the scanner can be used to construct a free-space optical crossconnect of 9-input by 9-output port counts.

In this paper, we have successfully developed an integrated micromechanical system for controlling tunneling current. A pair of nanoscale tunneling tips have been integrated with a silicon micromachined electrostatic actuator of high-aspect ratio. The tip sharpness has been observed to be as sharp as commercial tips by scanning over surface of carbon graphite as an atom scale. We have also succeeded to observe the tunneling current in the air and in the vacuum condition (in TEM). © 2005 IEEE.

We present a novel design of comb-driven double-gimbal XY-stage actuators for a 2D optical micro lens scanner, which has been realized for the first time by topologically separating the actuator elements in two layers: all the electrical parts (electrodes and interconnections) are in the SOI (Silicon-on-Insulator) layer, while the mechanical parts (suspensions, frame, and XY-stage) are in the substrate. The XY-stage moved 19 mu m in the X and Y direction independently.

This paper proposes a new optical and mechanical design for an optical crossconnect using MEMS 2D lens scanner. Optical simulation justified the use of telescope optics for low loss and compact OXC design. The suspensions and the electrostatic mechanism were designed in separate SOI layers to compress the device footprint and to accommodate more optical channels.

We have successfully developed a novel electrostatic actuator by the silicon bulk micromachined MEMS device that looks like a "Foxtail." The hairs of the actuator push the driving electrode to generate driving force. The generated thrust force of foxtail like actuator has found to be larger than 60 micro Newton.

We have developed a two-dimensionally maneuvable micro rover driven by electrostatic impact motion of the suspended mass. Stepping efficiency has been greatly improved by optimizing the inertia-mass distribution for the impact drive over static friction between the bottom surface and the playground. The actuator has only one suspended silicon mass to maneuver two dimensionaly.

In this paper, we report monolithic integration of MEMS (Micro Electro Mechanical Systems) actuators and high-voltage driver circuits into a silicon chip. Driver circuits of up to 40 V were prepared on an 8- mu m-thick SOI (Silicon-on-Insulator) wafer by the. DMOS (Double- diffused Metal Oxide Semiconductor) processes, after which MEMS electrostatic actuators were integrated into an identical SOI layer by post-processing using DRIE (Deep Reactive Ion Etching). This technique opens up a new way of high-voltage ASIC (Application Specific Integrated Circuit) for MEMS designer. As a prototype application model, we have developed micro lens optical scanners and other elementary MEMS electrostatic actuators with multi-channel driver circuits.

True random number is strongly required for encrypted secure communication and high speed computer simulation. A new micromechanism "Micro Dice" for generating series of true random numbers has been developed by using highly unpredictable phenomenon of electrostatic pull-in effect.

We report an electrostatic micro shutter array for astronomical telescopes for parallel processing infrared spectroscopy of multiple celestial objects using bulk-micromachining of silicon-on-insulator wafers. Successful operation of micro torsion shutter to a 90-degree-deflection has been demonstrated with applied voltages of up to 95V DC.

Development of a new light-weight and low-cost micro pore optics is reported. Utilizing anisotropic chemical wet etching of MEMS (Micro Electro Mechanical System) technology, a number of smooth sidewalls are obtained at once. These sidewalls are potential X-ray mirrors. As a first step of R&D, basic characters of sidewalls such as surface roughness and X-ray reflectivity are experimentally studied. Rms-roughness of 10 similar to 20 angstrom is confirmed in a KOH-etched wafer. Furthermore, the X-ray reflection is for the first time detected at Mg K alpha 1.25 keV. Based on the obtained results, numerical simulations of four-stage MEMS X-ray optics are performed for future satellite mission.

We have successfully developed a novel micromechanism of random number generator (RNG) by using the silicon micromachining technique. The MEM(Micro Electro Mechanical)RNG produce a series of random numbers by using the pull-in instability of electrostatic actuation operated with a typical dc 150 volt. The MEM RNG is made by the deep reactive ion etching of a silicon-on-insulator(SOI) wafer, and is very small compared with the conventional RNG hardware based on the randomness of thermal noise or isotope radiation. Quality of randomness has been experimentally confirmed by the self-correlation study of the generated series of numbers. The MEM RNG proposed here would be a true random number generation, which is needed for the highly secured encryption system of today’s information technology.

We have newly developed a prototype model of silicon microfabricated piggyback actuator for positioning a read/write head of magnetic hard-disk drive, which is usually referred to as a dual servo system because the piggyback actuator for fine control is used in collaboration with the voice-coil motor for coarse control. The actuator is made of a 50-micron-thick SOI (silicon on insulator) wafer processed by deep RIE (reactive ion etching) of high-aspect ratio. Actuation mechanism is based upon electrostatic force generated by multiple parallel plates. Maximum displacement of 0.2μ with a dc driving voltage of 20V has been achieved with a 1mm × 0.3mm actuator of its resonance at 25kHz. An analytical model for predicting electromechanical performance has also been developed.

The micro-miniature JT cooler is a promising cooling device as an element of the micro-thermal system for semiconductor devices, which dissipate an incredible amount of heat. In particular, the thermal management of laser diodes is a serious problem because they require a large amount of power but must maintain a fixed temperature. Considering such a situation, the performance of a micro-miniature JT cooler was calculated under the assumption of a countercurrent heat exchanger operating with a laminar gas flow, and the guidelines of a micro-miniature JT cooler for optimizing pump power and size were designed from the viewpoint of minimizing the cost. The authors present the results in this paper. A micro-miniature JT cooler was fabricated from Si wafer using a photolithographic process, which is available for operation with C₂H₆ from 3 MPa to 0.1 MPa. It is shown that a cooling power of 2.1 W was obtained at 239 K with a mass flow of 51.7 mg/s.

This paper deals with the new method that makes micro-holes with electrodeposition photoresist (EDPR) as a sacrificial layer. The EDPR was deposited on a silicon-mold made by ICP-RIE. Ni film was plated on a silicon-mold covered with EDPR. Etched through a gap between a silicon-mold and the Ni film, the Ni film came off from the silicon-mold. As a result, we could make Ni films that have micro hole of 9.2µm in diameter, and 56µm in depth on an experimental basis, and verified the silicon-mold that lateral faces of columns did not bare scratch marks. Moreover, the circularity roundness was able to fill 1.5µm which was the specification of the printer nozzle.

This paper reports a new fabrication process and designing method to integrate MEMS piggyback actuators on a silicon-on-insulator (SOI) wafer with magnetic read/write heads of hard-disk drives. Large bandwidth of the tracking servo system is designed by reducing the load mass for the tracking microactuator to be around 40 mug. A prototype electrostatic MEMS actuator (2 mm x 3 mm x 0.6 mm) of multiple parallel plates has been successfully integrated by using high-aspect ratio microstructures (gap opening 2 mum into 50-mum-SOI wafer) patterned by deep reactive-ion-etching (DRIE). A dc displacement of 0.5 mum, which is almost the same size as data track width, has been obtained at a driving voltage of dc 60 V and the fundamental resonance is found at 16 kHz. An analytical model of the MEMS piggyback actuator has been proposed to predict electromechanical performance. The fabrication method proposed here is very simple and straightforward to put the head-element-drive mechanism into practice.

This paper deals with the new method that makes micro-holes with electrodeposition photoresist (EDPR) as a sacrificial layer. The EDPR was deposited on a silicon-mold made by ICP-RIE. Ni film was plated on a silicon-mold covered with EDPR. Etched through a gap between a silicon-mold and the Ni film, the Ni film came off from the silicon-mold. As a result, we could make Ni films that have micro hole of 20.9μm in diameter, and 56μm in depth on an experimental basis, and verified the silicon-mold that lateral faces of columns did not bare scratch marks.

We propose a new type of 3rd generation MEMS piggyback actuator mechanism, which is suitable for integration with a read/write head device. An SOI wafer is patterned into a multiple-plate electrostatic actuator (2 μm gap) by a deep RIE process. Prototype actuators (2 mm x 3 mm x 0.6 mm) without a head device have been developed to test the electromechanical characteristics. Typical mechanical stroke of 0.5 microns with a voltage of DC 60 V and resonant frequency of 16 kHz have been obtained. An analytical model has predicted that a 0.15 micron displacement would be possible for 200 Gbit/in2 model when the electrostatic gap is designed to be 0.5 micron.

We have successfully fabricated a tunneling tip integrated with a silicon micromachined electrostatic actuator of high aspect ratio. Tip sharpness has been investigated by scanning over carbon graphite as an atom scale.

This paper describes the fabrication and actuation of a novel device composed of twin nano probes. The size of the probes are 200nm-high, 280nm-wide and 5 mum-long, which are formed by silicon anisotropic etching. The initial gap of about 400nm between the probes become 84nm when 101mW input power was given to the thermal expansion micro actuators integrated with the probes. Precise motion down to 4nm/mW was confirmed by simultaneous TEM observation.

A silicon shadow mask for evaporation or sputtering of any shape of patterns was fabricated by Al-Delay Masking Process (DMP). Using DMP, a Si high aspect ratio structure having arbitrary number of multiple-depth can be fabricated. By applying two layers of DMP, Si shadow mask with a mechanical alignment structure was fabricated. A Si chip on which deposition should be performed was successfully inserted to the mechanical alignment structure by tweezer, ensuring the high alignment precision less than ±5μm of the shadow mask aperture to the chip. With three layers of DMP, a shadow mask for deposition of a doughnuts-like shape was fabricated. The successful deposition of the doughnuts-like shape showed the large freedom of deposition patterns.

This paper presents a novel micromechanism for precise positioning by using an N-bit digital code. The mechanism is an N-stage network of connected suspensions, in which an electrostatic actuator is attached to the longer suspensions of compliance 2C, and N of such unit structures are connected side by side with the shorter suspensions of compliance C. Each actuator is an electrostatic shuttle moving back and forth between the driving electrodes, and is operated by the corresponding digit of the input code. The N-bits of Local displacement accumulate in the suspension network to synthesize an analog output, which is proportional to the analog value coded with the N-bit input. The output displacement is independent of the fluctuation of the driving voltage since the traveling distance of the shuttle is clipped by mechanical stoppers. We call the mechanism a microelectromechanical digital-to-analog converter (MEMDAC) since the function is equivalent to the electrical digital-to-analog converter known as the R-2R resistor network. Three different types of MEMDAC's are compared, Preliminary results of a silicon micromachined 4-bit MEMDAC successfully showed a total stroke of 5.8 mu m with a step of 0.38 mu m. The positioning resolution can be made finer by simply increasing the number of chained units.

A new micromachining process is described that guarantees highly accurate optical alignment in the free-space optics of matrix switches. This process is demonstrated using a 2 x 2 elementary cell, which is easily scalable to a larger M x N matrix. Promising performances such as low insertion loss (0.30-0.70dB) and a fast switching time (300 mu s) are obtained.