MEMS technology, derived from the microelectronics industry, has enabled the manufacture of high volume sensors and actuators. However, the technology path for standard CMOS technology is smaller geometries, planar topology, and lower thermal budgets, while MEMS process technology have been moving towards high aspect features, high thermal budgets and non-aggressive lithography requirements. This has important implications for the viability of MEMS to be a mainstream technology that can support the products of a new generation of products and applications. This paper will review some of the emerging trends in MEMS technology and discuss some of the applications. The challenges in ensuring the manufacturing viability of MEMS technology will also be briefly discussed.

Electroactive polymer (EAP) transducers are an emerging technology with many features that are desirable for MEMS devices. These advantages include simple fabrication in a variety of size scales, and ruggedness due to their inherent flexibility. Dielectric elastomer, a type of EAP transducer that couples the deformation of a rubbery polymer film to an applied electric field, shows particular promise because it can produce high strain and energy density, high efficiency and fast speed of response, and inherent environmental tolerance. A variety of proof-of-principle dielectric elastomer actuator configurations have been demonstrated at the small size scales needed for MEMS devices, including rolled "artificial muscle" actuators for insect-inspired microrobots, framed and bending beam actuators for efficient opto-mechanical switches, diaphragm and enhanced-thickness-mode actuators for microfluidic pumps, and valves and arrays of diaphragms for haptic displays. Several challenges remain for EAPs, including integration with driving electronics, and operational lifetime.

This paper is motivated by the challenge to develop mechanical resonators with fundamental resonant frequencies in the infrasonic range 1-20 Hz that fit onto a single-chip module. In this paper, we present preliminary findings based on finite element modeling (FEM) analysis of designs prepared for fabrication based on SUMMiT V^TM surface micromachining technology using curve-shaped beams clamped at both ends. Circular shapes considered are a flat-horseshoe shape (thickness is transverse to plane of substrate) and a split-ring shape (width is transverse to plane of substrate). For the FEM simulation study, we considered a single-chip module space size of 6mm diameter and resonators with 1 μm beam thickness. Designs are considered with and without added mass. We find that an order of magnitude reduction in the 1st mode resonant frequency is achievable by curving beams into a space of fixed size. The simulation results show that infrasonic resonant frequencies 2-20 Hz are achievable by curve-shaped resonators with “added mass” with 1 μm beam thickness for single-chip 6mm-diameter size.

A readout mechanism has been developed for measuring the response of mechanical microresonators to be used in an array for a microfabricated acoustic spectrum analyzer. It is based on the piezo-resistive property of polysilicon. The piezo-resistive readout mechanism is constructed in a quarter Wheatstone bridge fashion in which four equal serpentine polysilicon patterns are fabricated on top of a dielectric layer of silicon nitride. Microresonator devices using cantilever and clamped-clamped beam types with piezo-resistive readout mechanisms are fabricated using the surface micromachining technology of SUMMiT^TM. The sensitivity of the piezo-resistive mechanism is characterized using 10 volts as supply on the Wheatstone bridge and no amplification of signal. The testing is conducted with electrostatic drive potentials 0-75 volts. Sensitivity of 1-5 millivolts per micron of beam deflection was observed by the characterization.

This paper compares the simulation results with the experimental results of impedance analysis and longitudinal vibration measurement of micro-fabricated 0.5 MHz silicon-based ultrasonic nozzles. Impedance analysis serves as a good diagnostic tool for evaluation of longitudinal vibration of the nozzles. Each nozzle is made of a piezoelectric drive section and a silicon-resonator consisting of multiple Fourier horns each with half wavelength design and twice amplitude magnification. The experimental results verified the simulation prediction of one pure longitudinal vibration mode at the resonant frequency in excellent agreement with the design value. Furthermore, at the resonant frequency, the measured longitudinal vibration amplitude gain at the nozzle tip increases as the number of Fourier horns (n) increases in good agreement with the theoretical value of 2ⁿ. Using this design, very high vibration amplitude at the nozzle tip can be achieved with no reduction in the tip cross sectional area. Therefore, the required electric drive power should be drastically reduced, decreasing the likelihood of transducer failure in ultrasonic atomization.

We demonstrate dome-shaped, radio frequency, micromechanical resonators with integrated thermo-elastic actuators. Such resonators can be used as the frequency-determining element of a local oscillator or as a combination of a mixer and IF filter in a superheterodyne transceiver. The dome resonators (shallow shell segments clamped on the periphery) are fabricated utilizing pre-stressed thin polysilicon film over sacrificial silicon dioxide. The shell geometry enhances the rigidity of the structure, providing a resonant frequency several times higher than a flat membrane of the same dimensions. The finite curvature of the shell also couples out-of-plane deflection with in-plane stress, providing an actuation mechanism. Out-of-plane motion is induced by employing non-homogeneous, thermomechanical stress, generated in plane by local heating. A metal resistor, lithographically defined on the surface of the dome, provides thermal stress by dissipating 4 μW of Joule heat. The diminished heat capacity of the MEMS device enables a heating/cooling rate comparable to the frequency of mechanical resonance and allows operation of the resonator by applying AC current through the microheater. Resistive actuation can be readily incorporated into integrated circuit processing and provides significant advantages over traditional electrostatic actuation, such as low driving voltages, matched 50-ohm impedance, and reduced cross talk between drive and detection. We show that when a superposition of two AC signals is applied to the resistive heater, the driving force can be detected at combinatory frequencies, due to the fact that the driving thermomechanical stress is determined by the square of the heating current. Thus the thermoelastic actuator provides frequency mixing while the resonator itself performs as a high quality (Q~10,000) intermediate frequency filter for the combinatory frequencies. A frequency generator is built by closing a positive feedback loop between the optical detection of the mechanical motion of the dome and the resistive drive. We demonstrate self-sustained oscillation of the dome resonator with frequency stability of 1.5 ppm and discuss the phase noise of the oscillator.

In recent years, much efforts have been dedicated to the development of variable RF capacitors, a device which can take a clear benefit of MEMS technology. The most widely designed variable MEMS capacitors have an electrostatic force as actuation principle. This implies a limitation in the controlled tuning range due to the pull-in effect. In this paper we study and design three solutions in order to improve the controlled tuning range of RF MEMS variable capacitors, based both on electrostatic and electrothermal actuation principles and manufactured with the PolyMUMPS^TM process. Measurements of a conventional electrostatically-actuated variable capacitor are compared to measurements of three variable capacitors with extended tuning range, based on the two above mentioned actuation principles, with the main purpose of improving the pull-in limitation and assessing and comparing their behaviour and, especially, their tuning ranges. The most important advantages and disadvantages of extendended tuning range capacitors are identified and are here reported and empirically characterized, focusing in device repeatability, understood as capacity deviation due to large capacity sensitivity to tuning voltage, for small gaps between electrodes, which arises from the strongly non-linear behaviour of the capacity vs the gap between electrodes.

We have developed radio frequency microelectromechanical systems (RF MEMS) capacitive switches using amorphous diamond (a-D) as a novel tunable dielectric with controlled leakage. The switch is fabricated from sputtered and electroplated metals using surface micromachining techniques. The mechanical stress and resistivity of the a-D dielectric are controlled by the parameters of a high-temperature annealing process. These initial devices exhibit a down-state capacitance of 2.6 pF, giving an isolation of better than 18 dB at 18 GHz, and a predicted static power dissipation of 10 nW. This technology is promising for the development of reliable, low power RF MEMS switches.

We have fabricated and characterized radio frequency microelectromechanical systems (RF MEMS) ohmic switches for applications in discrete tunable filters and phase shifters over a frequency range of 0 to 20 GHz. Our previously reported cantilever switches have been redesigned for higher isolation and are now achieving 22 dB of isolation at 10 GHz. The measured insertion loss is 0.15 dB at 10 GHz. We have also fabricated and characterized new devices, designated “crab” switches, to increase isolation and contact forces relative to the cantilever design. The measured insertion loss and isolation are 0.1 dB per switch at 20 GHz and 22 dB at 10 GHz, respectively. A simple and accurate equivalent model has been developed, consisting of a transmission line segment and either a series capacitor to represent the blocking state or a series resistor to represent the passing state. Experimental analysis of the switch shows that high contact and substrate capacitive coupling degrades the isolation performance. Simulations indicate that the isolation improves to 30 dB at 10 GHz by reducing these capacitances. The crab switch design has a measured contact force of 120 μN, which represents a factor of four increase over the cantilever switch contact force and results in consistent, low-loss performance.

Through the application of a new approach to energy analysis to microelectromechanical systems (MEMS), the Flat Plasma Spectrometer (FlaPS) presented here provides a solution to the investigation of plasma distributions in space. It is capable of measuring the kinetic energy and angular distributions of ions/electrons in the space environment for energies ranging from a few eV to 50keV. A single pixel of a FlaPS instrument has been designed, built and tested to occupy a volume of approximately one cubic centimeter, and is characterized by a high throughput-to-volume ratio, making it an ideal component for small-scale satellites. The focus of this paper is on the design, fabrication, simulation, and testing of the instrument front end that consists of a collimator, parallel plate energy analyzer, and energy selector mask. Advanced micro-fabrication techniques enable fabrication of the miniature plasma spectrometer with geometric factor 4.9x10^-5 cm²-sr per pixel and an entrance aperture area of 0.01cm². Arrays of narrow collimator channels with 4° angular divergence and high transmission allow energy analysis of ions/electrons without the need for focusing, the key feature that enables large mass reduction. It is also shown that the large plate factors achievable with this approach to energy analysis offers definite advantages in reducing the need for excessively high voltages.

Small satellites with their low thermal capacitance are vulnerable to rapid temperature fluctuations. Therefore, thermal control becomes important, but the limitations on mass and electrical power require new approaches. Possible solutions to actively vary the heat rejection of the satellite in response to variations in the thermal load and environmental condition are the use of a variable emissivity coating (VEC), micro-machined shutters and louvers, or thermal switches. An elegant way the radiate heat is to switch the thermal contact between the emitting surface and the radiator electrostatically. This paper describes the design and fabrication of an active radiator for satellite thermal control based on such a micro electromechanical (MEMS) thermal switch. The switch operates by electrostatically moving a high emissivity surface layer in and out of contact with the radiator. The electromechanical model and material considerations for the thermal design of the MEMS device are discussed. The design utilizes a highly thermal conductive gold membrane supported by low-conductance SU-8 posts. The fabrication process is described. Measured actuation voltages were consistent with the electrostatic model, ranging from 8 to 25 volts.

This paper presents a novel micro flextensional actuator design consisting of bulk PZT bonded to a silicon microbeam. The fabrication process includes boron doping, EDP etching, dicing, and bonding to produce actuators with large displacements (8.7 μm) and gain factors (32) at 100V. The theoretical model predicts that a thin beam with properly designed initial imperfection maximizes the actuator displacement and gain factor. For large PZT displacement, small imperfection maximizes gain factor but may not gaurantee, the desired (up or down) displacement direction. For small PZT displacement, large initial imperfection improves performance and guarantees displacement in the (desired) direction of the initial imperfection. The theoretical model, based on the measured initial beam shape, predicts the experimentally measured direction and magnitude of beam displacement for two devices.

In this paper, we report a research effort to design, analyze, and fabricate a novel type of microaccelerometer using UV lithography of SU-8 and UV-LIGA process. Instead of using SU-8 only as photo resist as in silicon-based MEMS fabrication processes, cured SU-8 was used as the primary structural material in fabricating the micro sensors. A commercial software, ANSYS, was used to design the suitable size for the spring-mass and capacitors to achieve the desired bandwidth and the maximum sensitivity. The preliminary results obtained so far have proved the feasibility of fabrication of micro accelerometer using cured SU-8 polymer as the primary structural material and using UV-LIGA as the major fabrication tool.

A monolithic resonant micro actuator was developed, fabricated by CMOS-compatible micro machining technology, tested and evaluated. The component is able to measure acceleration in at least two directions. The device made of single-crystal silicon oscillates perpendicularly to the surface plane at a constant frequency in the 8 kHz range. A square-pulse shaped voltage of double the oscillation frequency drives it. It comprises an oscillating plate with a capacitance formed by interdigitating comb fingers. The acceleration in the direction orthogonal to the surface plane is detected by comparing the position of the plate to a reference plane. Without acceleration applied the position is centred in average. Upon acceleration the crossover point of the oscillation is shifted and the magnitude of acceleration can be related to the difference. The acceleration in a second direction can be measured by the common way of comparing e.g. the change of capacitance of two electrodes to each other. The component’s stability in frequency and amplitude during testing is shown. Simulation and measurement data is presented and compared.

A novel microassembly system has been developed to assemble surface micromachined micro-parts, into 3D microstructures. This work describes the tether and joint design of micro-parts used in the microassembly process. The process consists of (a) grasping a micro-part which is tethered to the substrate of a chip, (b) removing the micro-part from the substrate by breaking the tethers, (c) manipulating the micro-part from its original location of fabrication to the target assembly location, and (d) joining the micro-part to another micro-part. In this way, out-of-plane or in-plane microstructures can be assembled from a set of initially planar micro-parts. The tether design is an integral part of the grasping and removal process. The tethers provide restraint on the micro-parts while they are grasped by a passive, compliant microgripper, and are designed to break-away at pre-defined locations, after the grasping process. In addition, the tethers ensure that the micro-parts do not translate or rotate from their fabricated and released positions, during transportation of the carrier chip. The joint system used to join micro-parts together is called "snap-lock’ microassembly. It is based on the elastic deflection of a plug feature that forms an interference fit with a mating slot feature.

SU-8 is an ultra-thick negative photoresist with low optical absorption in the near UV range, which makes it an ideal material for generating thick molds for electroforming as well as a structural material for MEMS devices. However, the MEMS fabrication of using SU-8 is largely limited by its well-known poor adhesion to metallic layers as well as the high internal stress induced after baking. In this paper, an optimized process for fabricating ultra-thick low stressed SU-8 mold is developed and good adhesion between SU-8 and metals is obtained by applying a newly developed material, Omnicoat from Microchem Inc. A laminated (sandwiched) micro heat exchanger has been fabricated using the developed process in which sandwiched microchannels (one layer of Ni and one layer of SU-8) has been fabricated using the patterned SU-8 and nickel electroforming process. Test results show that the micro structure fabricated can stand at cryo temperature (77K) without damages such as cracks or delamination.

Previously, a compressible gas flow model was proposed, which couples microvalve structural parameters to gas parameters and flow boundary conditions, and which explained the behavior of compressible flow over a large range of conditions. However, only a limited set of data, from a single orifice for the valve seat, was used to substantiate the model. Multiple-hole or large-periphery valve seat structures were not measured. In this work, the proposed comprehensive compressible gas flow model for microvalves is confirmed using measurements of flow through multi-hole valve seat structures in microvalves.

The increasing interest for light and movable electronic systems, cell phones and small digital devices, drives the technological research toward integrated regenerating power sources with small dimensions and great autonomy. Conventional batteries are already unable to deliver power in more and more shrunk volumes maintaining the requirements of long duration and lightweight. A possible solution to overcome these limits is the use of miniaturized fuel cell. The fuel cell offers a greater gravimetric energy density compared to conventional batteries. The micromachining technology of silicon is an important tool to reduce the fuel cell structure to micrometer sizes. The use of silicon also gives the opportunity to integrate the power source and the electronic circuits controlling the fuel cell on the same structure. This paper reports preliminary results concerning the micromachining procedure to fabricate an arrays of microchannels for a Si-based electrocatalytic membrane for miniaturized Si-based proton exchange membrane fuel cells. Several techniques are routinely used to fabricate arrays of microchannels embedded in crystalline silicon. In this paper we present an innovative microchannel formation process, entirely based on surface silicon micromachining, which allows us to produce rhomboidal microchannels embedded on (100) silicon wafers. Compared to the traditional techniques, the proposed process is extremely compatible with the standard microelectronics silicon technology. The kinetics of rhomboidal microchannel formation is monitored by cyclic voltammetry measurements and the results are compared with a detailed structural characterisation performed by scanning electron microscopy. The effectiveness of this process is discussed in view of the possible applications in the fuel cell application.

The paper presents a application method of detecting moving ground target based on micro accelerometer. Because vehicles moving over ground generate a succession of impacts, the soil disturbances propagate away from the source as seismic waves. Thus, we can detect moving ground vehicles by means of detecting seismic signals using a seismic tranasducer, and automatically classify and recognize them by data fusion method. The detection system on the basis of MEMS technology is small volume, light weight, low poer, low cost and can work under poor circumstances. In order to recognize vehicle targets, seismic properties of typical vehicle targets are researched in the paper. A data fusion technique of artifical neural networks (NAA) is applied to recognition of seismic signals for vehicle targets. An improved back propagation (BP) algorithm and ANN architecture have been presented to improve learning speed. The improved BP algorithm had been used recognition of vehicle targets in the outdoor environment. Through experiments, it can be proven that target seismic properties acquired are correct. ANN data fusion is effective to solve the recognition problem of moving vehicle target, and the micro accelerometer can be used in target recognition.

Contrary to traditional analysis flows as expensive FEM simulation tools or inaccurate electrical models extractors, we developed MemsCompiler that implements a new real synthesis approach for RF MEMS. The new flow starts from system designer requirements and generates, in a one-click operation, a ready-to-fabricate layout (GDSII) and a passive fitted equivalent Spice circuit. Concerning the circuit, physical considerations give us an equivalent schematic in which circuit parameters values must be adjusted to fit the required performances. As to the GDSII, which constitutes the main contribution of this work, Design Of Experiment technique, used in the first version of the synthesizer, gave about 11% of dispersion and found to be unsatisfactory in some cases. A more accurate modeling was indispensable. Thus, we developed a neural networks-based modeling for circular inductors, which are considered by designers among the most stubborn components. This new modeling has shown to be very accurate: MemsCompiler produced about 3% of dispersion compared to the equivalent circuit and about 6% of dispersion for generated geometries. This modeling is flexible and could be rapidly generalized to other components.

The in-plane motion of microelectrothermal actuator ("heatuator") has been analysed for Si-based and metallic devices. It was found that the lateral deflection of a heatuator made of a Ni-metal is about ~60% larger than that of a Si-based actuator under the same power consumption. Metals are much better for thermal actuators as they provide a relatively large deflection and large force, for a low operating temperature, and power consumption. Electroplated Ni films were used to fabricate heatuators. The electrical and mechanical properties of electroplated Ni thin films have been investigated as a function of temperature and plating current density, and the process conditions have been optimised to obtain stress-free films suitable for MEMS applications. Lateral thermal actuators have been successfully fabricated, and electrically tested. Microswitches and microtweezers utilising the heatuator have also been fabricated and tested.

This paper proposes an insight view on the motion behavior of Micro-Array Thermal Actuator, MATA, applied in Micro-Electro-Mechanical Systems, MEMS. There are three basic kinds of {2 x 1}, MATA, opposite type, parallel type and orthogonal type. That will be analyzed in simulation and experiment. The effects of voltage, flexure length, connecting length and position on the variations of displacement and temperature distribution of devices will be investigated in this work. In this investigation, the longer the flexure length is, the greater the displacement is for the opposite type MATA. However, when the flexure length increases, the variation of displacement of the parallel type is against to that of opposite type. In addition, there is a little effect of connecting length on the variation of displacement for three kinds of MATA through the detailed analysis of simulation. Finally, there are many interesting phenomena which include suspension, sticking, side etching, undercut, and overly etching in surface micromachining engineering. These will be fully discussed through FE-SEM for MATAs. Mechanism of poly3 peeled off is systematically developed. First, poly3 can not be fully covered on poly2 due to side etching. Then, as releasing time increases, undercut is going in sequentially until poly3 is peeled off due to overly etching.

This research is about a thermal flow sensor, suggesting a new structure to improve the detection of airflow directions in any flow direction as well as to realize its interface circuit with simple OP amp circuits. A flow direction sensor was fabricated using MEMS technology. Pt was used as resistive material because of its very stable physical properties. The structure of the sensor, consisting of one heater at the center and four detectors surrounding the heater, is a symmetrical circular-type to generate uniform output regardless of various flow directions. The designed sensor operates based on the relative output difference of the four detectors in response to temperature variations induced by airflow. Therefore, flow directions can be easily detected by amplifying and calculating each output signal of the four detectors. As a result, the interface circuit could be realized with simple circuits. It was designed with popular instrumentation amplifiers and OP amps and integrated into ASIC chips using CMOS technology. The fabricated sensors were tested at 5 m/s and 10 m/s. The response time was some ten seconds and the maximum angle difference compared to flow angle was 5°. The results demonstrate that the suggested structure of sensors could be applied to the detection of flow directions and the test results could be obtained with a simple interface circuit.

Two design versions are proposed for optical microscanners: the first one - with two steps of the stationary electrode symmetrically arranged on the base relative to the symmetry axis, and the second one - with one step. Both schemes make use of a Push-Pull system, i.e. attraction and repulsion moments are taken into account, which make it possible to obtain basic curve on the relative scale. In the symmetrical scheme, compensation of electrostatic forces is achieved by increasing of the inter-electrode distance under the anchor ends. The optimal value of the working rotation angle of the mirror α_T=0.95α_max has been obtained for m₀=0.2; m₁=0.9; m₂=0.46. The one-sided scheme uses a repulsion moment value at small rotation angles. It also ensures a controlled rotation of the anchor in the range α_T/α_max=0.95 with the electrode gap-to-electrode distance ratios of t₁=0.2t; t₂=2t. It should be noted that zones of smooth transition on the curves are excluded, which results in considerably increased beam addressing accuracy. Also, a relatively small (1.5…2-fold) increase in the operating voltage is worth noting. Thus, changing of the geometry of the electrode gap can be one of the effective ways towards optimization of optical microscanner parameters.