In the first part of this paper, we review the integration of MEMS and CMOS microtransducer technology and out-line the related IC MEMS CAD tools SOLIDIS and ICMAT. The IC microtransducer approach is illustrated by deflectable micromirrors, infrared sensors, and a thermally isolated n- well CMOS device. In the second part, we report two novel chemical microsensors based on CMOS MEMS technology: (i) a piezoresistive resonating beam with hydrocarbon-sensitive polymer layer and (ii) a microsystem chip including a piezoresistive and capacitive chemical sensors with co- integrated heating deice and circuitry.

The first-ever reliability stress test on surface micromachined microengines developed at Sandia National Laboratories has been completed. We stressed 41 microengines at 36,000 RPM and inspected the functionality at 60 RPM. We have observed an infant mortality region, a region of low failure rate, and no signs of wearout in the data. The reliability data are presented and interpreted using standard reliability methods. Failure analysis results on the stressed microengines are presented. In our effort to study the reliability of MEMS, we need to observe the failures of large numbers of parts to determine the failure modes. To facilitate testing of large numbers of micromachines, we designed and built an automated system that has the capability to simultaneously test 256 packaged micromachines. The Sandia high volume measurement of micromachine reliability system has computer controlled positioning and the capability to inspect moving parts. The development of this parallel testing system is discussed in detail.

Gear systems rotating on hubs have been operated to failure using Sandia's microengine as the actuation device. Conventional failure modes such as fatigue induced fracture did not occur, indicating that the devices are mechanically extremely robust. The generic route to failure observed for all rotating devices involves sticking of structures that are in sliding contact. This sticking evidently results from microscopic changes in the sliding surfaces during operation. The rate at which these changes occur is accelerated by excessive applied forces, which originate from non-optimized designs or inappropriate drive voltages. Precursors to failure are observed, enabling further understanding of the microscopic changes that occur in the sliding surfaces that ultimately led to failure.

We report on the design, construction, and initial testing of surface micromachined devices for the measurement of friction and wear. The devices measure friction coefficients on both horizontal deposited polysilicon surfaces and vertical etched polysilicon surfaces. The contact geometry of the rubbing surfaces is well-defined, and a method is presented for the determination of the normal and frictional forces. Initial observations on test devices which have been dried with supercritical CO₂ and devices coated with octadecyltrichlorosilane suggest that the coatings increase the lifetime of the devices and the repeatability of the results.

A process for fabricating a monolithic 256 X 256 bolometer-type uncooled IR detector array is presented that utilizes surface micromachining technology. Each pixel of the device is composed of two parts, a silicon readout integrated circuit in the lower part and suspended microbridge structures in the upper part. The device is based on vanadium oxide bolometer films, which typically exhibit a temperature coefficient of resistance of -2 percent K. The vanadium oxide film is subject to damage, especially during wet etching of the sacrificial layer. Hence, the material and deposition process of the passivation layer for vanadium oxide film were investigated toward attaining a damage-free and flat microbridge structure. This was achieved by adjusting both the thickness of the passivation layer and the stresses in the electrode and passivation layers. The stiction problem of the microbridge structure was solved, by investigating drying conditions after etching of the sacrificial layer. Since each pixel has a cavity structure of (lambda) /4 to absorb IR radiation of the wavelength (lambda) , the spectral response of the pixel was measured in the wavelength range of 2 to 12 micrometers . The interference characteristics can clearly be seen. From responsivity measurements both in vacuum and at one atmosphere, the thermal time constant, thermal mass, and thermal conductance were estimated.

In order to simplify an opto-electronic hybrid system for texture segmentation based on the multi-channel filtering framework in the human visual theory, a micro-binary optical element (BOE) is designed and fabricated. The BOE has the functions of splitting, filtering and imaging simultaneously. The focal length of the BOE is 150mm and the diameter is 4mm. It contains sixteen Gabor wavelet filters with scales decreased by 2 orders and with our orientations separated every 45 degree, which can be used to perform a nearly complete decomposition with wavelet transform. The relief surface structure with minimum feature scale of 1.5micrometers is fabricated by using the photolithography and ion etching technique. In this paper, the functions of the BOE and the simulation of the filtering are described in detail, the experimental results and improvement of the element are given.

This work gives an overview of silicon micromachined vibrating gyroscopes. Market perspectives and fields of application are pointed out. The advantage of using silicon micromachining is discussed and estimations of the desired performance, especially for automobiles are given. The general principle of vibrating gyroscopes is explained. Vibrating silicon gyroscopes can be divided into seven classes. for each class the characteristic principle is presented and examples are given. Finally a specific sensor, based on a tuning fork for automotive applications with a sensitivity of 250(mu) V/degrees is described in detail.

A bulk micromachined capacitive accelerometer for airbag applications based on (110) silicon anisotropic KOH etching is presented. The sensor is a two-chip accelerometer that consists of a glass-silicon-glass stacked sense element and an interface ASIC containing an impedance converter for capacitance detection, an EPROM and DACs for digital trimming, and a self-test feature for diagnosis. A simple switched-capacitor readout circuit with DC offset error cancellation scheme is proposed as the impedance converter. The dependence of narrow gap etching, surface roughness, and uniformity of the groove depth on the KOH concentration are also investigated for the fabrication of the device, and it is shown that the etch rate of the plane intrinsically controls the depth of the narrow gap with a KOH concentration of over 30 wt. percent, and smooth surface and uniformity of groove depth are obtained at 40 wt. percent KOH. The nonlinearity of the output is about 1.5 percent FS. The temperature coefficient of sensitivity and the off-axis sensitivity are 150 ppm/degree C and 2 percent respectively. The dimensions of the sensor are 10.3 X 10.3 X 3 mm.

The design of a second order (Sigma) - (Delta) converter based microaccelerometer is presented in this paper. This converter has a large dynamic range, i.e., can measure acceleration from 0.5 g to 500 g, and provides directly digital output. The force-rebalance circuitry constraints the sensor mass to move within 10 percent of the distance between the polysilicon layers. The system is inherently linear and has a simple electronic interface.

This paper deals with the technology of acoustic-wave sensor devices. The use of planar technologies for their fabrication gives them advantageous properties such as high reproducibility, small size and low production costs. Most acoustic-wave sensors are made of piezoelectric-crystal wafers. They are highly stable and reproducible and low-cost device fabrication is possible because the wafers are suited to be used in standard integrated circuit (IC) equipment such as metal-evaporation depositors and photo-lithographic machinery. The silicon-implementation of acoustic devices gives the possibility of making use of the best-developed technology every: the silicon IC-technology. Additional features are the possibility of integration of electronic circuitry on the acoustic device and the development of new types of devices. However, the silicon implementation is hampered by difficulties in the development of reproducible piezoelectric quartz and silicon wafers are combined could increase the performance of silicon integrated acoustic-wave devices.

Giant magnetostriction appears to be very promising for contactless actuation. However, very few attempts have been made to actually exploit that advantage in sensors and actuators. The 2D scanning actuator that is being developed is a cantilever based structure that benefits from another unique features of the magnetostrictive materials: the ability to produce both bending and torsion at the same time with two AC magnetic fields. The ability to drive bending and torsion modes has been proven but never on a micro- structure. The actuators are processed and released from SOI wafers and all the micromachining process is done before the deposition of the active layer. A two-cantilever-based actuator has been designed i) to decrease the resonant frequency of the first rank of the torsion mode ii) to achieve a good decoupling between the bending and the torsion motion iii) to enhance the displacement. The actuation is performed using one DC 60mT and two AC 3-12 mT magnetic fields. Depending on the size of the actuator, resonant frequencies from 1 kHz to 30 kHz have been investigated for both the bending and the torsion motion.

The electrostatic comb finger drive has become an integral design for microsensor and microactuator applications. This paper reports on utilizing the levitation effect of comb fingers to design vertical-to-the-substrate actuation for interferometric applications. For typical polysilicon comb drives with 2 micrometers gaps between the stationary and moving fingers, as well as between the microstructures and the substrate, the equilibrium position is nominally 1-2 micrometers above the stationary comb fingers. This distance is ideal for many phase shifting interferometric applications. Theoretical calculations of the vertical actuation characteristics are compared with the experimental result, and a general design guideline is derived from these result. The suspension flexure stiffness, gravity forces, squeeze film damping, and comb finger thicknesses are parameters investigated which affect the displacement curve of the vertical microactuator. By designing a parallel plate capacitor between the suspended mass and the substrate, in situ position sensing can be used to control the vertical movement, providing a total feedback-controlled system. Fundamentals of various capacitive position sensing techniques are discussed. Experimental verification is carried out by a Zygo distance measurement interferometer.

Quad-level polysilicon surface micromachining technology, comprising three mechanical levels plus an electrical interconnect layer, is giving rise to a new generation of micro-electromechanical devices and assemblies. Enhanced components can now be produced through greater flexibility in fabrication and design. New levels of design complexity that include multi-level gears, single-attempt locks, and optical elements have recently been realized. Extensive utilization of the fourth layer of polysilicon differentiates these latter generation devices from their predecessors. This level of poly enables the fabrication of pin joints, linkage arms, hinges on moveable plates, and multi-level gear assemblies. The mechanical design aspects of these latest micromachines will be discussed with particular emphasis on a number of design modifications that improve the power, reliability, and smoothness of operation of the microengine. The microengine is the primary actuation mechanism that is being used to drive mirrors out of plane and rotate 1600-micrometers diameter gears. Also discussed is our most advanced micromechanical system to date, a complex proof-of-concept batch-fabricated assembly that, upon transmitting the proper electrical code to a mechanical lock, permits the operation of a micro-optical shutter.

Understanding the mechanisms that impact the performance of microelectromechanical systems (MEMS) is essential to the development of optimized designs and drive signals, as well as the qualification of devices for commercial applications. Silicon micromachines include engines that consist of orthogonally oriented linear comb drive actuators mechanically connected to a rotating gear. These gears are as small as 50 micrometers in diameter and can be driven at rotation rates exceeding 300,000 rpm. Optical techniques offer the potential for measuring long term statistical performance data and transient responses needed to optimize designs and manufacturing techniques. We describe the development of micromachine optical probe (MOP) technology for the evaluation of micromachine performance. The MOP approach is based on the detection of optical signal scattered by the gear teeth or other physical structures. We present experimental results for a prototype system designed to measure engine parameters as well as long term performance data.

Packaging influences the reliability and performance of microsystems. A brief history of developments in packaging is presented along with an overview of 3D packaging philosophy. An example of the integration of a micromachined silicon membrane pump into a 3D vertical multichip module package is presented. Finite element techniques are used to analyze the encapsulation stress in the assembled structure to improve the integrity of the packaged microsystem.

This paper presents a low-cost transfer mould packaging concept for sensors, based on a direct-mold principle.The advantage of this method is that up to the molding step the whole process is compatible with standard lead-frame processing. The molding concept and package structures allow plastic sensor packaging with one or more environmental access paths to be created in a single molding step. As an application of the new packaging concept, a plastic sensor package with a single access path has been developed for commercial production. The performances of this new low cost package are satisfactory and reliability tests show good results. Furthermore, packaging of other types of sensors is in preparation.

Among the main benefits of microsystem technology are its contributions to cost reductio, reliability and improved performance. however, the packaging of microsystems, and particularly microsensor, has proven to be one of the biggest limitations to their commercialization and the packaging of silicon sensor devices can be the most costly part of their fabrication. This paper describes the integration of 3D packaging of a microsystem. Central to the operation of the 3D demonstrator is a micromachined silicon membrane pump to supply fluids to a sensing chamber constructed about the active area of a sensor chip. This chip carries ISFET based chemical sensors, pressure sensors and thermal sensors. The electronics required for controlling and regulating the activity of the various sensors ar also available on this chip and as other chips in the 3D assembly. The demonstrator also contains a power supply module with optical fiber interconnections. All of these modules are integrated into a single plastic- encapsulated 3D vertical multichip module. The reliability of such a structure, initially proposed by Val was demonstrated by Barrett et al. An additional module available for inclusion in some of our assemblies is a test chip capable of measuring the packaging-induced stress experienced during and after assembly. The packaging process described produces a module with very high density and utilizes standard off-the-shelf components to minimize costs. As the sensor chip and micropump include micromachined silicon membranes and microvalves, the packaging of such structures has to allow consideration for the minimization of the packaging-induced stresses. With this in mind, low stress techniques, including the use of soft glob-top materials, were employed.

In this paper, we describe research into extending the General Electric chip-on-flex (COF) process for packaging microelectromechanical systems (MEMS). COF is a derivative of the high density interconnect (HDI) used for multichip module packaging of microelectronics. COF is a high performance, low cost multichip packaging technology in which die are encased in a molded plastic substrate and interconnects are made via a thin-film structure formed over the components. For MEMS packaging, the standard COF process has been modified to include laser ablating windows in the interconnect overlay to allow access to MEMS. Special purpose surface and bulk micromachining test die were developed and packaged with CMOS electronics using the COF process. The COF/MEMS packaging technology is well-suited for applications in which monolithic integration of MEMS and electronics is not optimal.

This paper reviews recent trends and evolutions in the low- end color printing market which is currently dominated by thermal inkjet (TIJ) based products. Micro electromechanical systems technology has been an enabler for the unprecedented cost/performance ratio of these printing products. The generic TIJ operating principles are based on an intimate blend of thermodynamics, fluid dynamics and LSI electronics. The key principles and design issues are outlined and the fabrication of TIJ printheads illustrated with an implementation by the Xerox Corporation.

We have developed a method to pattern self assembled monolayer films of n-octadecyltrichlorosilane on silicon and glass substrates using a simple lift-off procedure. By defining hydrophobic regions at definite locations in microchannels and using an external pressure source, we can split off precise nanoliter volume liquid drops and control the motion of those drops through the microchannels. We have also constructed an on-chip pressure source for drop splitting and motion by heating air trapped in a micromachined chamber. Both techniques can produce and move drops on the order of 50 nl.

This paper describes the fabrication and testing of plastic fluidic connectors suitable for the assembly of multichip microfluidic systems. The connectors basically consist of a series of 50-200 X 20 micrometers ² capillaries embedded in a 70 micrometers -thick flexible polyimide substrate with large access holes ion both ends. The capillary walls and the connector exterior are coated with a thin layer of p- xylylene providing a high degree of chemical inertness and biocompatibility. These flexible connectors are inherently planar for ease of connection to flat substrates and are constructed using conventional batch lithographic techniques. The connector flow characteristics were tested in nitrogen gas and water. Multiple channel connectors with 3 and 5 capillaries 1.3-4.0 cm-long were constructed successfully.

Space exploration in the coming century will emphasize cost effectiveness and highly focused mission objectives, which will result in frequent multiple missions that broaden the scope of space science and to validate new technologies on a timely basis. MEMS is one of the key enabling technology to create cost-effective, ultra-miniaturized, robust, and functionally focused spacecraft for both robotic and human exploration programs. Examples of MEMS devices at various stages of development include microgyroscope, microseismometer, microhygrometer, quadrupole mass spectrometer, and micropropulsion engine. These devices, when proven successful, will serve as models for developing components and systems for new-millennium spacecraft.

This paper presents the development of a pressure sensor based on epi-poly processing technology. The use of epi-poly creates an SOI structure and thus facilitates the use of an oxide etch-stop for the bulk micromachining. This avoids the requirement for the complicated electrochemical techniques. This simplification of the process greatly enhances the batch fabrication capabilities. Furthermore, the epi-poly deposition can be performed at the same time as the standard epitaxy used for the electronics. By defining the oxide layer only where a membrane is required, all other areas of the chip can be used for the fabrication of the read-out electronics. Etching from the back of the wafer, to define the membrane, is performed after completion of the bipolar processing. This etching is performed in KOH or TMAH which has a high etch selectivity over the oxide layer. This paper presents the fabrication and initial measurement results of the epi-poly pressure sensor.

This paper describes frequency vibration sensors for signature analysis on (electro)mechanical components. The application is predictive diagnostics and condition based maintenance on Xerographic printer and copier products. The vibration signature analysis (VSA) sensing devices consist of micromachined arrays of closely spaced silicon mechanical resonators covering a frequency range of 120 Hz to 100 kHz. Resonance of a particular element is detected with a Wheatstone bridge of implanted piezoresistors and the bridge outputs are multiplexed onto a common output line using on- chip p-MOS transistor switches. The design and fabrication of the VSA devices is presented.

Besides foundry facilities, computer-aided design tools are also required to potentially move integrated MEMS from research prototypes to an industrial market. This paper presents the different available facilities for low cost collective manufacturing of MEMS and reports on the various significant developments of MEMS design environments. Making the inventory of these activities illustrates how the industry is answering the question of will MEMS technology delivers.

This paper presents a new local refining meshing algorithm which is referred to as the exposed face mesh (EFM) algorithm, for 3D coupled electromechanical analysis with multiple dielectrics. This algorithm allows for the independent refinement of the electrostatic mesh and mechanical mesh in a coupled system. This approach is compared to the commonly used volume refining mesh method in which both the electrostatic and mechanical mesh domains are refined concurrently. The new EFM method is shown to have substantial improvement in increasing accuracy of results and reducing computational expense especially for fringe electric field dominated structures. For a typical comb drive structure, the EFM algorithm generates much fewer volume mesh nodes for mechanical analysis and fewer surface mesh panels for electrostatic analysis than the standard volume refining mesh method. At the same time, the EFM method showed an improvement in accuracy from 15 percent to within 5 percent for this case. The IntelliCAD MEMS modeling software has incorporated this EFM algorithm and made it a unique software system to handle general device structures accurately.

In this paper, an analytical approach based on the energy relationship between microcomponents has been applied to derive the characteristics of a square diaphragm silicon micropump to consider its nonlinear effects. The methodology caters for all relevant energy terms corresponding to the stiffness of the diaphragm including bending, tensile, stretch forces, the mass of the diaphragm, and of the air in the vicinity of diaphragm. The stiffness of the pump chamber and the input/output tube, the fluidic mass and the frictional losses of the input/output tube are also incorporated in the model. Equivalent electrical circuit is derived to calculate the lumped parameters using the energy expressions. The approach is applied to the pneumatically driven micropump.

At the creation and application of biosensors appeared a number of problems which are: 1) optimization of process connected with stabilization of the structure of biomolecules at the integration with the transducers to preserve their maximum activity and 2) search of approaches to accomplish repeated analysis of substances which are irreversible inhibitors of activity of above mentioned molecules. In this article the results obtained in time of solving of these problems at the usage of enzymes as sensitive bilayer of biosensors are analyzed. For stabilization of the structure of such enzymes as:(beta) - glucose oxydase, urease, cholinesterases during their immobilization the following approaches were examined: 1) usage of one or combination of chemical substances: protein, saccharose, ethylendiamine tetraacetic acid (EDTA), glycerol, ditiotrie-tole (DTT) and specific substrates or their homologues; 2) variation of covalent crosslinking methods including usage of bifunctional reagents in aqueous and vaporous phases; 3) change of time of the influence of this reagent. Optimization of these parameters can allow to preserve about 70-80 percent of initial enzyme activity at the usage of such bifunctional reagent as glutaraldehyde. For repeated analysis of phosphoroganic pesticides and heavy metal ions which are irreversible inhibitors of enzymes the following approaches were applied: 1) treatment of enzyme membrane by special reactivating substances ; 2) usage of easily replaceable enzymatic membrane. It was shown that the last way is more preferable, particularly if alginate gel or nitrocellulose is used for direct enzyme immobilization or preparation of separated biomembrane respectively. Standard deviation of sensor responses for different membrane castings did not exceed 10 percent. At the same time this parameter changed more strongly after even one use of reactivating reagents.

Multi-level micro-electrode structures have been produced using excimer laser ablation techniques to obtain devices for the electro-manipulation of bioparticles using traveling electric field dielectrophoresis effects. The system sued to make these devices operates with a krypton fluoride excimer laser at a wavelength of 248 nm and with a repetition rate of 100Hz. The laser illuminates a chrome-on-quartz laser at a wavelength of 248nm and with a repetition rate of 100Hz. The laser illuminates a chrome-on-quartz mask which contains the patterns for the particular electrode structure being made. The masks then imaged by a high-resolution lens onto the sample. Large areas of the mask pattern are transferred to the sample by using synchronized scanning of the mask and workpiece with sub-micron precision. Electrode structures with typical sizes of approximately 10 micrometers are produced and a multi-level device is built up by ablation of electrode patterns and layering insulators. To produce a traveling electric field suitable for the manipulation of bioparticles, a linear array of 10 micrometers by 200 micrometers micro- electrodes, placed at 20 micrometers intervals, is used. The electric field is created by energizing each electrode with a sinusoidal voltage 90 degrees out of phase with that applied to the adjacent electrode. On exposure to the traveling electric field, bioparticles become electrically polarized and experience a linear force and so move along the length of the linear electrode array. The speed and direction of the particles is controlled by the magnitude and frequency of the energizing signals. Such electromanipulation devices have potential uses in a wide range of biotechnological diagnostic and processing applications.

This paper reports on modeling the behavior of micromachined polysilicon thermal actuators. The thermal actuators used in this research were fabricated using the DARPA-sponsored multi-user MEMS processes. Data collected in both air and vacuum demonstrates that thermal actuators can be controlled and positioned using a pulsed input with a period much less than the thermal time constant of the device. Both pulse width and pulse amplitude modulation have been successfully employed to position lateral actuators, lateral actuator arrays, and piston micro-mirrors. In order to better exploit the power averaging characteristics of thermal actuators, SPICE models for polysilicon thermal actuators were developed using relationships between resistance, deflection, and average power. These models incorporate the polysilicon thermal actuators electrical load and transient characteristics necessary for predicting actuator performance and developing CMOS drive circuits. The SPICE models exhibit good agreement with theory and measured performance of the polysilicon thermal actuators.

Results of investigations in the field of scientific problems are presented and prospects for creation of new pressure sensors, based on the pressure-sensitivity effect in metal-semiconductor mesa-structures, are analyzed in this paper. Principle characteristics of such devices - motion sensors, vibrometers, deflectometers, elastic wave meters are discussed.

This paper presents a new polysilicon actuator design. In a typical thermally-driven actuator, the hot arm is thinner than the cold arm, so the electrical resistance of the hot arm is higher. When electric current passes through the device (both the hot and cold arms), the hot arm is heated to a higher temperature than the cold arm. This temperature increase causes the hot arm to expand in length, thus forcing the tip of the device to rotate about a flexure. The new thermal actuator design eliminates the parasitic electrical resistance of the cold arm through the use of an additional hot arm. The second hot arm results in an improvement in electrical efficiency by providing an active return current pass. Also, the rotating cold arm can have a thinner flexure than the flexure in a traditional device because it does not have to pass an electric current. The thinner flexure results in an improvement in mechanical efficiency. This paper compares single and double hot arm thermallydriven actuator designs, and demonstrates various devices constructed with the new thermal actuator design. Deflection and force measurements of both actuators as a function of applied electrical current are presented. Keywords: MEMS, Polysilicon, Actuator, Motor, Mirror.

Refractive index of polymethyl methacrylate (PMMA) and polystyrene decreases with increase of temperature and due to variation of refractive index the propagation constant of PMMA and polystyrene thin films change. Using this property of those polymer thin films a simple thermal sensor is demonstrated where a channel waveguide to polymer thin-film coupler is used. A thin film of PMMA is deposited on the channel waveguide to polymer thin-film coupler is used. A thin film of PMMA is deposited on the channel waveguide by spin coating method. Optical power from an LED of wavelength (lambda) equals 1.3 micrometers is coupled to the channel waveguide and the throughput power of the channel waveguide is detected by a p-i-n diode at different temperatures. Variation of the throughput channel power is correlated with the change in temperature for potential use in thermal sensing and switching applications. A thin film of polystyrene is also deposited on another channel waveguide and same experiment is performed. It shows the increase in range of temperature for measurement.

The development of a micromachined accelerometer with high frequency response in described. The accelerometer is based on a thin film layer of polysilicon suspended over a field- effect transistor (FET), forming a moveable-gate transistor. The field effect-transistor is designed for depletion-mode operation. Frequency response greater than 20,000 Hz is predicted with analytical models of the cantilever beam structure. Feedback control electrodes are included for closed-loop operation. The force-balance feedback control produces greater dynamic range and frequency response. The mechanical and electrical modeling of the micromachined structure with MEMCAD 3.0 are described. Results of the device modeling based on SUPREM-3 simulations are also included. This model includes the results of a short loop run carried out at MCNC to determine the interface charge in the transistor gate oxide. The anticipated effect of the oxide charge on the threshold voltage of the FET is included.

This paper describes a polysilicon pressure sensor fabricated by silicon micromachining technology. The starting materials of the sensor are (100) orientated monocrystal silicon wafers with double side polishing. The semiconductor integrated circuit process is also used in the testing. The polysilicon piezoresistors are deposited by LPCVD on the thermallygrown oxide film of the silicon wafer. In order to increase sensitivity, a so-called "twin isles" structure has been used. This type of structure consists of a square silicon diaphragm with twin square isles, which are formed by anisotropic etching into the back side of the monocrystal silicon substrate wafer. A main problem in preparation is the convex corner undercutting effect in the etching process. The relationships between the corner undercutting rate and the etching depth in TMAH solution have been obtained experimentally. Two masks of the special pattern are designed to compensate for corner undercutting. 1). A compensating angle bounded by <210< orientation is added to convex corner of twin square isles. The width of the compensation angles depends on the etching depth. 2). A narrow stripe is added to each convex corner along <110< orientation. The length of the narrow stripe depends on the etching depth. The optimized structures of the square diaphragm with twin square isles have been fabricated using the above two methods, respectively. Each method has its own advantages. The fabricated polysilicon pressure sensors have high sensitivity at elevated operation temperature and good accuracy. key words: silicon micromachining, comer undercutting, polysilicon pressure sensor, compensating method.

In this paper, a basic mechanism of 3D micromechanisms is proposed by making use of number synthesis of mechanisms. The output point of the proposed mechanism can move in the vertical direction when two linear input points move in the inverse horizontal direction, and can move horizontal direction when two linear input points move in the same horizontal direction. The validity and the characteristics of the proposed mechanism are investigated theoretically and experimentally by using a polyethylene macromodel manufactured by a small modeling injection machine. Finally, an example of a micromechanism manufactured by semiconductor fine-machining technique is shown.

The mechanical properties of thin film microstructures depend on size and shape and on the film manufacturing process. Hence, the test structures that are used to measure mechanical properties should have dimensions of the same order of magnitude as an application structure. The microstructures are easily monitored in a scanning electron microscope (SEM), but to be handled and tested in situ a micromanipulator was developed. The parts of the micromanipulator essential to the tests are two independently moveable tables driven by electric motors. The test structures and a testing unit are mounted on the tables. A testing unit was designed to measure force and displacement with high resolution. The testing unit consists of an arm actuated by a piezoelectric element and equipped with a probe. An optical encoder measures the movement of the arm, while strain gauges measure the force in the arm. Test structures consist typically of a released beam fixed at one end with a ring at the other. The micromanipulator is used to position the probe of the testing unit in the ring. The testing unit then executed a tensile test of the beam. Test structures of polysilicon films produced under various process conditions were used to verify the possibility of measuring Young's modulus with an accuracy of +/- 5 percent, as well as fracture strength.Young's modulus is calculated using the difference in elongation for different beam lengths. The fracture strength of the beams was evaluated with Weibull statistics.

Currently, nearly all microcomponents are fabricated by microelectronic production technologies like etching, deposition and other (photo)lithographic techniques. In this way, main emphasis has been put on surface micromechanics. The major challenges for the future will be the development of real 3D microstructures. Electro-discharge machining (EDM) is a so-called non-conventional machining technique, whereby material is removed through the erosive action of electrical discharges provided by a generator. As shown in this paper, electro-discharge machining proves to be a versatile technique which is very well suited for machining complex microstructures. First, an overview of the applicability of micro electro-discharge machining for manufacturing silicon micromechanical parts is given. Also the machine on which these structures were made is introduced. The main advantages of micro-EDM are its low installation cost, high accuracy and large design freedom. Micro-EDM can indeed easily machine complex 3D shapes that prove difficult for etching techniques. Next, the appropriate setting of the machining parameters in order to keep the material removal on the tool electrode at least an order of magnitude smaller than the material removal on the workpiece electrode are discussed. Micro-EDM requires electrodes as a tool A reliable method for producing these electrodes, with custom shape and small sizes is also presented. The primary applications of micro-EDM are in rapid prototyping and products with small batchsizes. However, the technique is versatile enough to be adapted to large series. Several examples are given of the possibilities of micro-EDM: an electric force motor, micromirrors at any angle with respect to the wafer plane, an acceleration sensor, and micro bevel and spur gears.

The fabrication of microchannel chemical sensors with seven laminated individual functional modules is described. The sensors, used to detect chromium in nuclear and chemical waste streams, were fabricated using laser micromachining, bulk silicon micromachining, photolithographic techniques, sputter coating deposition, and anodic and adhesive bonding processes. The size of the sensor was 2 cm by 2.2 cm, with a total thickness of 2.2 cm. It consisted of two or more reservoir modules to hold the liquids being evaluate, two or more micropump modules to pump the liquids through the sensor, a chemical mixing module, a reaction module, and a sensor module with electrical circuitry for connection to external measurement equipment. The fluids were directed through the layers by interconnecting flow channels. The reservoir modules were fabricated by machining Pyrex and anodic bonding to silicon. The chemical mixing module was fabricated by wet etching Pyrex and anodic bonding to silicon. The reaction module contained a serpentine 200- micrometers -wide channel, and was formed by laser micromachining polyimide. The first prototype of this sensor employed external micropumps, while the second prototype will use off-the-shelf piezoelectric micropumps. The detector layer consisted of iridium, silver, and platinum sensor pads connected to gold contact strips. The modules were joined using adhesive bonding, and an electrostatic technique was used for silicon-Pyrex bonding.

Fully CMOS-compatible, surface-micromachined polysilicon microbridges have ben designed, fabricated, and tested for use in catalytic, calorimetric gas sensing. To improve sensor behavior, extensive electro-thermal modeling efforts were undertaken using SPICE. The validity of the SPICE model was verified by comparing its simulated behavior with experimental results. The temperature distribution of an electrically-heated microbridge was measured using an IR microscope. Comparisons among the measured distribution, the SPICE simulation, and distributions obtained by analytical methods show that heating at the ends of a microbridge has important implications for device response. Additional comparisons between measured and simulated current-voltage characteristics, as well as transient response characteristics, further support the accuracy of the model. A major benefit of electro-thermal modeling with SPICE is the ability to simultaneously simulate the behavior of a device and its control/sensing electronics. Results for the combination of a unique constant-resistance control circuit and microbridge gas sensor ar given. Models of in situ techniques for monitoring catalyst deposition are shown to be in agreement with experiment. Finally, simulated chemical response of the detector is compared with the data, and methods of improving response through modifications in bridge geometry are predicted.

Thermal actuation using a bimorph structure has been combined with electrostatic actuation in cantilever devices. An analytical model was given for thermal actuation, where temperature dependent internal stress in both layers was included in 1D beam equations. The results were compared with the test results and numerical simulation results and showed good agrement. A novel micromotor was designed and fabricated to demonstrate one possible application. The force created by the bimorph actuator is in micro Newton range, and transient thermal power less than 50mW is enough to turn rotors with a diameter of 250 micrometers . Potential applications of the micromotor are accurate positioning of active and passive devices including lasers and micromirrors, and light modulation as an optical shutter.