Showing papers in "IEEE\/ASME Journal of Microelectromechanical Systems in 1997"

M-TEST: A test chip for MEMS material property measurement using electrostatically actuated test structures

Abstract: A set of electrostatically actuated microelectromechanical test structures is presented that meets the emerging need for microelectromechanical systems (MEMS) process monitoring and material property measurement at the wafer level during both process development and manufacturing. When implemented as a test chip or drop-in pattern for MEMS processes, M-Test becomes analogous to the electrical MOSFET test structures (often called E-Test) used for extraction of MOS device parameters. The principle of M-Test is the electrostatic pull-in of three sets of test structures [cantilever beams (CB's), fixed-fixed beams (FB's), and clamped circular diaphragms (CD's)] followed by the extraction of two intermediate quantities (the S and B parameters) that depend on the product of material properties and test structure geometry. The S and B parameters give a direct measure of the process uniformity across an individual wafer and process repeatability between wafers and lots. The extraction of material properties (e.g., Young's modulus, plate modulus, and residual stress) from these S and B parameters is then accomplished using geometric metrology data. Experimental demonstration of M-Test is presented using results from MIT's dielectrically isolated wafer-bonded silicon process. This yielded silicon plate modulus results which agreed with literature values to within /spl plusmn/4%. Guidelines for adapting the method to other MEMS process technologies are presented.

Gaseous slip flow in long microchannels

Abstract: An analytic and experimental investigation into gaseous flow with slight rarefaction through long microchannels is undertaken. A two-dimensional (2-D) analysis of the Navier-Stokes equations with a first-order slip-velocity boundary condition demonstrates that both compressibility and rarefied effects are present in long microchannels. By undertaking a perturbation expansion in /spl epsiv/, the height-to-length ratio of the channel, and using the ideal gas equation of state, it is shown that the zeroth-order analytic solution for the streamwise mass flow corresponds well with the experimental results. Also, the effect of slip upon the pressure distribution is derived, and it is obtained that this slip velocity leads directly to a wall-normal migration of mass. The fabrication of wafer-bonded microchannels that possess well-controlled surface structure is described, and a means for accurately measuring the mass how through the channels is presented. Experimental results obtained with this mass-flow measurement technique for streamwise helium mass flow through microchannels 52.25-/spl mu/m wide, 1.33-/spl mu/m deep, and 7500-/spl mu/m long for a pressure range of 1.6-4.2 atmospheres (outlet pressures at atmospheric) are presented and shown to compare favorably with the analysis.

Design and fabrication of compliant micromechanisms and structures with negative Poisson's ratio

Abstract: This paper describes a new way to design and fabricate compliant micromechanisms and material structures with negative Poisson's ratio (NPR). The design of compliant mechanisms and material structures is accomplished in an automated way using a numerical topology optimization method, The procedure allows the user to specify the elastic properties of materials or the mechanical advantages (MA's) or geometrical advantages (GA's) of compliant mechanisms and returns the optimal structures. The topologies obtained by the numerical procedure require practically no interaction by the engineer before they can be transferred to the fabrication unit. Fabrication is carried out by patterning a sputtered silicon on a plasma-enhanced chemical vapor deposition (PECVD) glass with a laser micromachining setup. Subsequently, the structures are etched into the underlying PECVD glass, and the glass is underetched, all in one two-step reactive ion etching (RIE) process. The components are tested using a probe placed on an x-y stage. This fast prototyping allows newly developed topologies to be fabricated and tested within the same day.

A new technique for measuring the mechanical properties of thin films

Abstract: Accurate measurement of mechanical properties is very difficult for films that are only a few microns thick. Previously, these properties have been determined by indirect methods such as cantilever beam and diaphragm bulge tests. This paper presents a new technique to measure the Young's modulus of thin films in a direct manner consistent with its definition. Strain is measured by a laser-based technique that enables direct and accurate recording of strain on a thin-film specimen. Load is recorded with a 1-lb load cell, and an air bearing is used to eliminate friction in the loading system. The specimen is phosphorus-doped polysilicon that has a gage cross section of 3.5 /spl mu/m thick by 600 /spl mu/m wide. All 29 uniaxial tensile tests show brittle behavior, and the average values of Young's modulus and fracture strength are measured to be 170/spl plusmn/6.7 GPa and 1.21/spl plusmn/0.16 GPa, respectively. One fatigue test is also reported in this paper.

Modeling and optimal design of piezoelectric cantilever microactuators

Abstract: A novel model is described for predicting the static behavior of a piezoelectric cantilever actuator with an arbitrary configuration of elastic and piezoelectric layers. The model is compared to deflection measurements obtained from 500-/spl mu/m-long ZnO cantilever actuators fabricated by surface micromachining. Modeled and experimental results demonstrate the utility of the model for optimizing device design. A discussion of design considerations and optimization of device performance is presented.

Magnetically actuated, addressable microstructures

Abstract: Surface-micromachined, batch-fabricated structures that combine plated-nickel films with polysilicon mechanical flexures to produce individually addressable, magnetically activated devices have been fabricated and tested. Individual microactuator control has been achieved in two ways: (1) by actuating devices using the magnetic field generated by coils integrated around each device and (2) by using electrostatic forces to clamp selected devices to an insulated ground plane while unclamped devices are freely moved through large out-of-plane excursions by an off-chip magnetic field. The present application for these structures is as micromirrors for microphotonic systems where they can be used either for selection from an array of mirrors or else individually for switching among fiber paths.

Micromechanical switches fabricated using nickel surface micromachining

Abstract: Micromechanical switches have been fabricated in electroplated nickel using a four-level surface micromachining process. The simplest devices are configured with three terminals, a source, a drain, and a gate and are 30 /spl mu/m wide, 1 /spl mu/m thick, and 65 /spl mu/m long. A voltage applied between the gate and source closes the switch, connecting the source to the drain. Devices switch more than 10/sup 9/ cycles before failure and exhibit long-lifetime hot switching currents up to 5 mA. The initial contact resistance is less than 50 m/spl Omega/. The breakdown (stand-off) voltage between the source and the drain is greater than 100 V and the off-current is less than 20 fA at 100 V.

Scratch drive actuator with mechanical links for self-assembly of three-dimensional MEMS

Abstract: The self-assembling of three-dimensional (3-D) MEMS from polysilicon surface micromachined part is very attractive. To avoid risky external manipulation, the practical use of integrated actuator to perform the assembling task is required. To that goal, this paper presents detailed characteristics of the electrostatic surface micromachined scratch drive actuator (SDA). First, from numerous SDA tests, it is shown that this actuator is able to produce a threshold force of 30 /spl mu/N, with a yield above 60%. With polysilicon devices consisting of SDA mechanically linked to buckling beam, a horizontal force of 63 mN has been demonstrated with /spl plusmn/112 V pulse, and up to 100 /spl mu/N can be obtained with higher voltage. With buckling beams, displacements up to 150 /spl mu/m have been obtained in the vertical direction. The generation of vertical force of 10 /spl mu/N was confirmed with a 100 /spl mu/m displacement producing 1 nJ work in the vertical direction. Finally, SDA overcomes the usual sticking of surface machined polysilicon by producing enough vertical force to completely release wide polysilicon plate (500 /spl mu/m/spl times/50 /spl mu/m) without external manipulation. The above characteristic, both in terms of structure releasing and vertical/horizontal forces and displacements provides the SDA with the capability of self-assembling complex 3-D polysilicon part, opening new integration capabilities and new application field of MEMS.

Micromachined flat-walled valveless diffuser pumps

Abstract: The first valveless diffuser pump fabricated using the latest technology in deep reactive ion etching (DRIE) is presented. The pump was fabricated in a two-mask micromachining process in a silicon wafer polished on both sides, anodically bonded to a glass wafer. Pump chambers and diffuser elements were etched in the silicon wafer using DRIE, while inlet and outlet holes are etched using an anisotropic etch. The DRIE etch resulted in rectangular diffuser cross sections. Results are presented on pumps with different diffuser dimensions in terms of diffuser neck width, length, and angle. The maximum pump pressure is 7.6 m H/sub 2/O (74 kPa), and the maximum pump flow is 2.3 ml/min for water.

Feasibility of micro power supplies for MEMS

Abstract: Most microelectromechanical systems (MEMS) designed today use macroscopic power supplies, thereby placing limits on the functionality of MEMS in many applications. An alternative to this approach is to design MEMS with integral microscopic distributed power supplies. This paper examines the feasibility of creating micro power supplies by considering three functions common to MEMS power systems: (1) capture energy; (2) store energy; and (3) drive actuation, of these, only the capture energy function is highly dependent on the specific application. For each of the three functions, a table is presented which compares various means of performing the function. This information makes it possible to determine what design alternatives are feasible for the creation of a micro power supply for any specific application of MEMS. We use smart bearings with active surface features as an example application and develop a design for a micro power supply suitable for this work.

Vertical mirrors fabricated by deep reactive ion etching for fiber-optic switching applications

Abstract: We report on vertical mirrors fabricated by deep reactive ion etching of silicon. The mirror height is 75 /spl mu/m, covering the fiber core of a single-mode fiber when the latter is placed into a groove of equal depth and etched simultaneously with the mirror. To obtain a uniform etch depth, etching is stopped on a buried oxide layer. Using the buried oxide as a sacrificial layer allows to fabricate mirrors with suspension and actuation structures as well as fiber-alignment grooves in one and the same processing step. A minimal mirror thickness of 2.3 /spl mu/m was achieved, resulting in an aspect ratio higher than 30. The verticality was better than 89.3/spl deg/. In the upper part of the mirror a surface roughness below 40 nm rms was obtained. At a wavelength of 1300 nm the reflectivity of the aluminum-coated mirrors was measured to be higher than 76%. Using a reactive ion etched mirror we have fabricated an optical fiber switch with electrostatic actuation. The coupling loss in the bar state of two packaged prototypes was between 0.6 and 1.7 dB and between 1.4 and 3.4 dB in the cross state. The switching time is below 0.2 ms.

Thermal characterization of surface-micromachined silicon nitride membranes for thermal infrared detectors

Abstract: The aim of this work is to provide a thorough thermal characterization of membrane structures intended for thermal infrared detector arrays. The fabrication has been conducted at temperatures below 400/spl deg/C to allow future post processing onto existing CMOS readout circuitry. Our choices of membrane material and processing technique were plasma enhanced chemical vapor deposited silicon nitride (SiN) and surface micromachining, respectively. The characterization gave for the thermal conductance (G) and thermal mass between the membrane and its surroundings 1.8/spl middot/10/sup -7/ W/K and 1.7/spl middot/10/sup -9/ J/K, respectively, which are close to the best reported values elsewhere. From these results the thermal conductivity and specific heat of SiN were extracted as 4.5/spl plusmn/0.7 W/m.K and 1500/spl plusmn/230 J/kg.K. The contribution to G from different heat transfer mechanisms are estimated. A model describing the pressure dependence of G was developed and verified experimentally in the pressure interval [5/spl middot/10/sup -3/, 1000] mbar. Finally, the influence of the thermal properties of the membrane on infrared detector performance is discussed.

A liquid-filled microrelay with a moving mercury microdrop

Abstract: A micromechanical relay that switches by moving a mercury microdrop is introduced. While microrelays have been introduced to MEMS on several occasions, all are based on solid-solid contacts, making them subject to contact wear, signal bounce, and general loss of performance with use. The goal of our device is to use mercury to eliminate the common problems of solid-contact switches. Descriptions of the design and fabrication of a micromechanical mercury-contact relay, including the technique for formation of microscale mercury droplets, are presented. The deionized (DI) water-filled microrelay has a mercury droplet, 5-25 /spl mu/m in diameter, placed near a disconnected set of electrodes in a V-groove throat. The throat connects two reservoirs containing suspended heaters. By turning on one heater, we grow a vapor bubble in one reservoir and induce a momentary water flow along the throat, forcing the mercury droplet to move and create the signal conduction path. Heating of the second reservoir can drive the mercury drop back to its original position. A microgasketing technique along with UV-curing epoxy sealing method is introduced to seal a chip containing many microdevices, each filled with liquid, at room temperature. Initial test results of the relay are also provided.

A micro strain gauge with mechanical amplifier

Abstract: A passive micro strain gauge with a mechanical amplifier has been designed, analyzed, and tested. The mechanical amplifier provides a high gain such that residual strain in thin films can be directly measured under an optical microscope. This strain gauge can be in situ fabricated with active micro sensors or actuators for monitoring residual strain effects, and both tensile and compressive residual strains can be measured via the strain gauge. It is shown that a very fine resolution of 0.001% strain readouts can be achieved for a micro strain gauge with a 500 /spl mu/m-long indicator beam. Beam theories have been used to analyze the strain gauge with a mechanical amplifier, and the results were verified by a finite-element analysis. Experimental measurements of both polysilicon and silicon-riched silicon-nitride thin films fabricated by surface micromachining processes are presented.

Magnetic and mechanical properties of micromachined strontium ferrite/polyimide composites

Abstract: In this work, strontium ferrite/polyimide composite thin films are fabricated and characterized for micromachining applications. The application of these materials in microelectronics and micromachining dictates the use of different polymers than those previously used for conventional plastic magnets due to fabrication compatibility constraints. The material investigated here consists of magnetically anisotropic strontium ferrite particles suspended in a benzophenone tetracarboxylic dianhydride-oxydianiline/metaphenylene diamine polyimide matrix. Magnetic mechanical, and processability properties of these composites are investigated for a strontium ferrite loading range of 55%-80% by volume. Intrinsic coercivity H/sub ci/ residual magnetic flux density B/sub r/ and maximum energy product (BH)/sub max/ have been determined. For an 80% by-volume concentration loading of ferrite, H/sub ci/ of 318 kA/m B/sub r/, approaching 0.3 T, and (BH)/sub max/ of 11900 T/spl middot/A/m have been achieved. Biaxial Young's modulus and residual stress are determined using a slightly modified in situ load/deflection technique. The biaxial Young's modulus increases with increasing the magnetic powder loading. The materials have been deposited and patterned using two techniques: (1) screen-printing and (2) spin-casting, followed by photolithography. Finally, a simple magnetic microactuator made with those materials has been fabricated and tested, which demonstrates the usefulness of those materials to micromachining.

A silicon resonant sensor structure for Coriolis mass-flow measurements

Abstract: We present the first mass-flow sensor in silicon, based on the Coriolis-force principle. The sensor consists of a double-loop tube resonator structure with a size of only 9/spl times/18/spl times/1 mm. The tube structure is excited electrostatically into a resonance-bending or torsion vibration mode. A liquid mass flow passing through the tube induces a Coriolis force, resulting in a twisting angular motion phase shifted and perpendicular to the excitation. The excitation and Coriolis-induced angular motion are detected optically. The amplitude of the induced angular motion is linearly proportional to the mass flow and, thus, a measure thereof. The sensor can be used for measurement of fluid density since the resonance frequency of the sensor is a function of the fluid density. The measurements show the device to be a true mass-flow sensor with direction sensitivity and high linearity in the investigated flow range of as low as 0-0.5 g/s in either direction. A sensitivity of 2.95 (mV/V)/(g/s) and standard deviation for the measured values of 0.012 mV/V are demonstrated.

Deflection and maximum load of microfiltration membrane sieves made with silicon micromachining

Abstract: With the use of silicon micromachining, an inorganic membrane sieve for microfiltration has been constructed having a silicon nitride membrane layer with thickness typically 1 /spl mu/m and perforations typically between 0.5 /spl mu/m and 10 /spl mu/m in diameter. As a support a -silicon wafer with openings of 1000 /spl mu/m in diameter has been used. The thin silicon nitride layer is deposited on an initially dense support by means of a suitable chemical vapor deposition method (LPCVD). Perforations in the membrane layer are obtained with use of standard photo lithography and reactive ion etching (RIE). The deflection and maximum load of the membrane sieves are calculated in a first approximation. Experiments to measure the maximum load of silicon-rich silicon nitride membranes have confirmed this approximation.

Dry release for surface micromachining with HF vapor-phase etching

Abstract: A new method for dry etching of silicon dioxide for surface micromachining is presented to obtain very compliant polysilicon microstructures with negligible stiction problem and to greatly simplify the overall releasing procedure as well. By etching the sacrificial silicon dioxide with hydrofluoric acid (HF) vapor instead of conventional aqueous HF solution, the need for subsequent rinsing and an elaborate drying procedure is eliminated. Condensation of water on the etch surface is first identified as the cause that prevented the success of HF vapor release in the past. Use of an anhydrous HF/CH/sub 3/OH mixture under low pressure solves the problem of water condensation and enables us to take advantage of vapor-phase etching (VPE) for surface micromachining. The mechanism of oxide etching with the HF/CH/sub 3/OH mixture is explained, and the developed VPE system is described and characterized. Polysilicon cantilevers up to 1200 /spl mu/m in length are successfully released with this HF VPE technique. The beams tested are 2 /spl mu/m thick with a 2-/spl mu/m gap from the substrate, and no antistiction dimples are used. The fabricated structures are observed using both scanning electron microscopy (SEM) and an optical profilometer. The reported VPE technique provides a robust releasing method for polysilicon microstructures and is compatible with integrated circuit (IC) fabrication, even including cluster processors.

A system for the dynamic characterization of microstructures

Abstract: This paper describes a fully automated measurement system designed to evaluate the dynamic characteristics of micromechanical structures (millimeter dimensions). To validate the system, vibration measurements have been carried on two structures-a micromachined silicon cantilever and bridge-and the results are presented. Out-of-plane measurements show that for the cantilever, both the mode shapes and resonant frequencies agree with beam theory predictions. However, for the bridge structure, tension due to boron doping causes a change from beam-like behavior and a more complex model is required. Mode-shapes natural frequencies and modal damping are determined from data obtained by vibrating the structures using a piezoelectric mounting system and deriving the transfer function between the piezodrive voltage and beam vibrational velocity.

Elimination of post-release adhesion in microstructures using conformal fluorocarbon coatings

Abstract: The adhesion of polysilicon microstructures to their substrates is eliminated using a relatively conformal hydrophobic fluorocarbon (FC) coating grown in a field-free zone of a plasma reactor. Experiments show that the FC film deposition on top of the microstructure and on the underside was approximately 2:1. The FC coating is able to cover the entire underside of a 200/spl times/200 /spl mu/m/sup 2/ plate, with a 20% deposition nonuniformity. The coating exhibits a contact angle of 110/spl deg/ and is able to prevent adhesion of cantilever beams and doubly supported beams to their substrates even after direct immersion in DI water. The durability of the coating was tested using an accelerated aging method, predicting a lifetime of greater than ten years at 150/spl deg/C. Periodic wear tests indicate that the coating remains hydrophobic even after 10/sup 7/ contact cycles.

Microfabricated Lamb wave device based on PZT sol-gel thin film for mechanical transport of solid particles and liquids

Abstract: The fabrication using silicon micromachining and characterization of an acoustic Lamb wave actuator is presented. The intended use of the device is for mass transport and sensor applications. The device consists of dual interdigitated transducers patterned on a thin-film composite membrane of silicon nitride, platinum, and a sol-gel-derived piezoelectric ceramic (PZT) thin film. The acoustic properties of the device are presented along with preliminary applications to mechanical transport and liquid delivery systems. Improved acoustic signals and improved mass transport are achieved with PZT over present Lamb wave devices utilizing ZnO or AlN as the piezoelectric transducer.

Hybrid postprocessing etching for CMOS-compatible MEMS

Abstract: A major limitation in the fabrication of microstructures as a postCMOS (complimentary metal oxide semiconductor) process has been overcome by the development of a hybrid processing technique, which combines both an isotropic and anisotropic etch step. Using this hybrid technique, microelectromechanical structures with sizes ranging from 0.05 to /spl sim/1 mm in width and up to 6 mm in length were fabricated in CMOS technology. The mechanical robustness of the microstructures determines the limit on their dimensions. Examples of an application of this hybrid technique to produce microwave coplanar transmission lines are presented. The performance of the micromachined microwave coplanar waveguides meets the design specifications of low loss, high phase velocity, and 50 /spl Omega/ characteristic impedance. Various commonly used etchants were investigated for topside maskless postmicromachining of silicon wafers to obtain the microstructures. The isotropic etchant used is gas-phase xenon difluoride (XeF/sub 2/), while the wet anisotropic etchants are either ethylenediamine-pyrocatechol (EDP) or tetramethylammonium hydroxide (TMAH). The advantages and disadvantages of these etchants with respect to selectivity, reproducibility, handling, and process compatibility are also described.

6-MHz 2-N/m piezoresistive atomic-force microscope cantilevers with INCISIVE tips

Abstract: Piezoresistive atomic force-microscope (AFM) cantilevers with lengths of 10 /spl mu/m, displacement sensitivities of (/spl Delta/R/R)/A 1.1/spl times/10/sup -5/, displacement resolutions of 2/spl times/10/sup -3/ A//spl radic/Hz, mechanical response times of less than 90 ns, and stiffnesses of 2 N/m have been fabricated from a silicon-on-insulator (SOI) wafer using a novel frontside-only release process. To reduce mass, the cantilevers utilize novel inplane crystallographically defined silicon variable aspect-ratio (INCISIVE) tips with radius of curvature of 40 A. The cantilevers have been used in an experimental AFM data-storage system to read back data with an areal density of 10 Gb/cm/sup 2/. Four-legged cantilevers with both imaging and thermomechanical surface modification capabilities have been used to write 2-Gb/cm/sup 2/ data at 50 kb/s on a spinning polycarbonate sample and to subsequently read the data. AFM imaging has been successfully demonstrated with the cantilevers. Some cantilever designs have sufficient displacement resolution to detect their own mechanical-thermal noise in air. The INCISIVE tips also have applications to other types of sensors.

Fabrication of an S-shaped microactuator

Abstract: We have developed a new fabrication process for electrostatic actuators having an S-shaped film element, which we previously invented for such applications as gas valves. The developed process allows batch fabrication of the actuator whose S-shaped structure height, which is equal to the amount of vertical film displacement, is of the order of a few hundred micrometers. The microactuators are fabricated by stacking three wafers. The middle wafer contains the sputtered Ni film strip which is buckled into an S-shape during the stacking process. The length of film necessary for the S-bend profile has a folded structure which is stretched after stacking. The size of the fabricated chip was 5 mm/spl times/5 mm, and the vertical film displacement was 220 /spl mu/m. The actuator was operated by electrostatic force when the applied voltage was more than 70 V.

Fabrication of high-aspect-ratio microstructures on planar and nonplanar surfaces using a modified LIGA process

Abstract: Large surface areas (tens of square centimeters to square meters) covered with high-aspect-ratio microstructures (HARMs) have potential applications in a wide range of fields including heat transfer, adaptive aerodynamics, acoustics, catalysts, seal and bearing design, and composite materials. HARMs are typically hundreds of micrometers in height, with widths ranging from a few micrometers to tens of micrometers, and they can be manufactured from a variety of materials such as metals, polymers, and ceramics. Three of the barriers to extensive use of large HARM-covered surfaces are cost, nonplanarity of typical surfaces, and adhesion of the microstructures to the surface. A starting point for inexpensive reproduction of large arrays of HARMs is the plastic molding step of the LIGA micromanufacturing process. In order to address the latter two problems, the standard LIGA process was modified/extended. Free-standing polymer sheets, perforated with a pattern of high-aspect-ratio throughholes, were clamped to conductive substrates. The sheets provide a template for electrodeposition of nickel microstructures onto the target surface. This process makes it economically feasible to electroform metal microstructures directly onto large planar and nonplanar metal surfaces (cylinders).

Constructing single- and multiple-helical microcoils and characterizing their performance as components of microinductors and microelectromagnets

Abstract: This paper describes a means for producing single- and multiple-helical microcoils by using microcontact printing to print lines on cylinders. This method was used to fabricate coils made of wires with widths and spaces between 150-25 /spl mu/m wrapped around cylinders with diameters between 100-400 /spl mu/m. Results show that microelectromagnets using these microcoils produce magnetic flux densities in excess of 0.4 T and can be switched on and off on a submillisecond time scale.

SOLIDIS: a tool for microactuator simulation in 3-D

Abstract: SOLIDIS is an engineering software tool tailored for the coupled three-dimensional (3-D) analysis of microactuators. Surface electrostatic forces, thermomechanics, and piezoelectric effects are correctly treated. The solution algorithms implemented enable efficient and accurate static analysis and optimization of MEMS actuators. Adaptive mesh refinement results in near-optimal meshes in the sense of achieving maximum accuracy for a given number of mesh nodes. A zone partitioning scheme permits efficient simulation of complex actuator structures. Additional key issues are mesh updating using a Monte Carlo algorithm to account for the actuator's movement and the application of smoothing algorithms for the extraction of accurate electrostatic forces.

Electrostatic aluminum micromirrors using double-pass metallization

Abstract: The fabrication of aluminum spatial light modulators has so far required costly process engineering efforts. In this paper, a low-cost process approach is presented, suitable for the manufacture of electrostatic micromirror arrays. The mirrors are made from the second metallization of complementary metal oxide semiconductor (CMOS) or bipolar processes deposited in two passes. This metal2 is protected by a photoresist layer that can be patterned using the top passivation mask of the process. No additional layer deposition and layer structuring is necessary during postprocessing. The actuators are released in a simple surface micromachining postprocessing sequence based on a sacrificial aluminum and silicon dioxide etch. Our approach allows one metallization to be used for both the circuitry and the electrooptomechanicaI devices. Deformable mirror arrays of up to 16/spl times/16 pixels were fabricated. Static self-consistent electromechanical simulations using the finite-element method (FEM) toolbox SOLIDIS were performed for a theoretical analysis and optimization of the actuator devices.

Correction To "M-test: A Test Chip For Mems Material Property Measurement Using Electrostatically Actuated Test Structures"

Abstract: A set of electrostatically actuated microelectromechanical test structures is presented that meets the emerging need for microelectromechanical systems (MEMS) process monitoring and material property measurement at the wafer level during both process development and manufacturing. When implemented as a test chip or drop-in pattern for MEMS processes, M-Test becomes analogous to the electrical MOSFET test structures (often called E-Test) used for extraction of MOS device parameters. The principle of M-Test is the electrostatic pull-in of three sets of test structures [cantilever beams (CB’s), fixed–fixed beams (FB’s), and clamped circular diaphragms (CD’s)] followed by the extraction of two intermediate quantities (the S and B parameters) that depend on the product of material properties and test structure geometry. TheS and B parameters give a direct measure of the process uniformity across an individual wafer and process repeatability between wafers and lots. The extraction of material properties (e.g., Young’s modulus, plate modulus, and residual stress) from theseS and B parameters is then accomplished using geometric metrology data. Experimental demonstration of M-Test is presented using results from MIT’s dielectrically isolated wafer-bonded silicon process. This yielded silicon plate modulus results which agreed with literature values to within 4%. Guidelines for adapting the method to other MEMS process technologies are presented. [204]

Fabrication and characterization of truly 3-D diffuser/nozzle microstructures in silicon

Abstract: We present microfabrication and characterization of truly three-dimensional (3-D) diffuser/nozzle structures in silicon. Chemical vapor deposition (CVD), reactive ion etching (RIE), and laser-assisted etching are used to etch flow chambers and diffuser/nozzle elements. The flow behavior of the fabricated elements and the dependence of diffuser/nozzle efficiency on structure geometry has been investigated. The large freedom of 3-D micromachining combined with rapid prototyping allows one to characterize and optimize diffuser/nozzle structures.