A computational design and analysis of a microtab based aerodynamic loads control system is presented. The microtab consists of a small tab that emerges from a wing approximately perpendicular to its surface in the vicinity of its trailing edge. Tab deployment on the upper side of the wing causes a decrease in the lift generation whereas deployment on the pressure side causes an increase. The computational methods applied in the development of this concept solve the governing Reynolds-averaged Navier-Stokes equations on structured, overset grids. The application of these methods to simulate the flows over lifting surfaces including the tabs has been paramount in the development of these devices. The numerical results demonstrate the effectiveness of the microtab and that it is possible to carry out a sensitivity analysis on the positioning and sizing of the tabs before they are implemented in successfully controlling the aerodynamic loads.

This paper describes results from using a microcombustor to create two hydrocarbon gas sensors: one utilizing calorimetry and the other a flame ionization detector (FID) mechanism. The microcombustor consists of a catalytic film deposited on the surface of a microhotplate. This micromachined design has low heat capacity and thermal conductivity, making it ideal for heating catalysts placed on its surface. The catalytic materials provide a natural surface-based method for flame ignition and stabilization and are deposited using a micropen system, which allows precise and repeatable placement of the materials. The catalytic nature of the microcombustor design expands the limits of flammability (LoF) as compared with conventional diffusion flames; an unoptimized LoF of 1-32% for natural gas in air was demonstrated with the microcombustor, whereas conventionally 4-16% is observed. The LoF for hydrogen, methane, propane and ethane are likewise expanded. Expanded LoF permit the use of this technology in applications needing reduced temperatures, lean fuel/air mixes, or low gas flows. By coupling electrodes and an electrometer circuit with the microcombustor, the first ever demonstration of a microFID utilizing premixed fuel and a catalytically-stabilized flame has been performed; the detection of 1.2-2.9 % of ethane in a hydrogen/air mix is shown.

A photomask is a high precision plate used in the lithographic process for the fabrication of microcomponents and it is an important prerequisite for microfabrication. A binary photomask is composed of tranasparent and opaque elements wich from one layer of a pattern. Photomasks are currently fabricated using lithographic process, which is complex and time consuming because of several steps involved in the fabrication process. In order to address this issue, a simple technique is reported in this paper which is a single-step process. The required pattern is transferred to mask blank by direct writing with femtosecond laser pulses without the aid of photoresist. The opaque layer of the mask blank is removed by femtosecond laser ablation. An acousto-optic device based non-mechanical scanning system immune to effects of vibration has been developed to scan the laser beam with high positional accuracy and scan speed. The applicability of this technique for microfabrication has been proved conclusively by fabricating microfeatures with the photomask fabricated by this technique.

Sensors are an essential component of most electronic systems in the car. They deliver input parameters for comfort features, engine and emission control as well as for the active and passive safety systems. New technologies such as silicon micromachining play an important role for the introduction of these sensors in all vehicle classes. The importance and use of these sensor technologies in today’s automotive applications will be shown in this article. Finally an outlook on important current developments and new functions in the car will be given.

We developed a novel surface micromachining process to fabricate monocrystalline silicon membranes covering a vacuum cavity without any additional sealing steps. Heart of the process is anodic etching of porous silicon, annealing and epitaxial growth. The porous silicon layer consists of two parts, a starting mesoporous silicon layer with low surface porosity and a nanoporous silicon layer with a high porosity. The following annealing step removes native oxide within the later cavity, and the surface is sealed for the subsequent epitaxial layer deposition. The observed stacking fault density in the epitaxial layer about 1E5 cm-2. The temperature budget of the following ASIC-process leads to a complete transformation of the nanoporous silicon layer into a large cavity. The whole structure can be used as a pressure sensor. The estimated pressure in the cavity is smaller than 1 mbar. First integrated pressure sensors have been fabricated using this process. The sensors show a good linearity over the whole pressure range of 200 mbar to 1000 mbar. This novel process has several advantages compared to already published processes. It is a “MEMS first” process, which means that after the epitaxial growth the surface of the wafer is close to a standard wafer surface. Due to full IC compatibility, standard ASIC processes are possible after the fabrication of the membrane. The use of porous silicon enables a high degree of geometrical freedom in the design of membranes compared to standard bulk micromachining (KOH, TMAH). The monocrystalline membranes can be fabricated with surface micromachining without any additional sealing or backside processing steps.

As displacement and electrode gap coincide in parallel plate electrode configurations, electrostatic actuators struggle with elevated actuation voltages for reasonable displacements or restoring forces in MEMS. A curved-cantilever-beam-type actuator overcoming this dependence was presented by several workgroups for microvalves, microrelays or micro-mirrors. Stress gradients achieved during fabrication result in out-of-plane curvature of the beam electrode. The tip deflection can be scaled by the beam length, while the minimum electrode gap is kept small aiming at actuation voltages common to microelectronics. This actuator appeals to switching applications requiring low-power drive, high deflections and short cycle times. Our approach employs microelectroplating of nickel and thermal postprocessing instead of multi-layer stacks achieved from semiconductor-based fabrication technologies. As stress gradients needed for the beam curvature distribute on wafer level and may alter during packaging or even in operation, advanced methods for controlling the actuator’s bending geometry are needed. A bending predefinition can be obtained during electroplating. The final beam curvature is achieved by tempering on wafer level for stabilisation and succeeding fine-tuning with local LASER-treatment near the suspension. Advanced actuator prototypes for microvalves or microrelays will be presented. Also, the suitability of the actuator for rf-switches will be indicated.

The objective of this work was to develop a thermally-driven bimetallic actuator for application in high temperature environments. The actuator was designed to drive distributed air flow control valves in a gas turbine combustor. The valves control localized cooling air flows in response to rises in temperature, leading to more uniform and complete combustion. The actuator is a passive thermo-mechanical device formed from bimorph elements concatenated in a recurve architecture to obtain the required forces and deflections. An electroplating process for depositing an Invar-like alloy in deep recess was developed and used in the fabrication of prototypes. Fabrication of additional protypes and testing are continuing.

The evolution of ever-smaller microfabrication techniques, driven by market demand, has lead to multi-million transistor devices as a single piece part. Complimentary metal oxide semiconductor (CMOS) nanoelectronics will be mass-produced by the year 2004 when lateral structures smaller than 100-nm will become common. Beyond the next ten years the future is less certain, but other technologies such as nanometer-scale single electron transistors provide an idea of what may be possible in 20-to-25 years. Microelectromechanical systems (MEMS), which bring "eyes, ears, noses, and muscles" (sensing and actuation) to electronic systems, are fabricated using similar processes and will benefit from decreasing minimum feature size over time. Nanoelectronics and nanoelectromechanical systems will evolve over the next decade to provide ever-higher levels of functional density per unit area. The continuing increase in functional density will enable decreased spacecraft system size, and ultra-small spacecraft. Examples of prototype microengineered attitude determination and propulsion systems are given.

Future concepts for ultra-large lightweight space telescopes include the telescopes with segmented silicon mirrors. This paper describes a proof-of-concept inchworm actuator designed to provide nanometer resolution, high stiffness, large output force, long travel range, and compactness for ultraprecision positioning applications in space. A vertically actuating inchworm microactuator is proposed to achieve large actuation travel by incorporating compliant beam structures within a silicon wafer. An inchworm actuator unit consists of a piezoelectric stack actuator, a driver, a pair of holders, a slider, and a pair of polymer beams connected to a centrally clamped flexure beam. Deep reactive ion etch experiments have been performed for constructing the actuator.

Magnetically actuated MEMS microshutter arrays are being developed at the NASA Goddard Space Flight Center for use in a multi-object spectrometer on the James Webb Space Telescope (JWST), formerly Next Generation Space Telescope (NGST). The microshutter arrays are designed for the selective transmission of light with high efficiency and high contrast. The JWST environment requires cryogenic operation at 45K. Microshutter arrays are fabricated out of silicon-on-insulator (SOI) wafers. Arrays consist of close-packed shutters made on silicon nitride (nitride) membranes with a pixel size of 100 × 100 m. Individual shutters are patterned with a torsion flexure permitting shutters to open 90°, with a minimized mechanical stress concentration. Shutters operated this way have survived fatigue life test. The mechanical shutter arrays are fabricated using MEMS technologies. The processing includes a multi-layer metal deposition, patterning of shutter electrodes and magnetic pads, reactive ion etching (RIE) of the front side to form shutters in a nitride film, an anisotropic back-etch for wafer thinning, and a deep RIE (DRIE) back-etch, down to the nitride shutter layer, to form support frames and relieve shutters from the silicon substrate. An additional metal deposition and patterning has recently been developed to form electrodes on the vertical walls of the frame. Shutters are actuated using a magnetic force, and latched electrostatically. One-dimensional addressing has been demonstrated.

A novel type of micro power relay has been designed and fabricated using UV-LIGA technology. The relay is based on electrostatic actuation and SU-8 was used as a functional material. The unique character of this novel power relay is that other than a SU-8 structure used both as an electrical insulator and a mechanical connector, all other components are made of metal or alloys. Because UV-LIGA technology has the advantages of broad material selection and the capability of making high aspect ratio microstructures, the technology is best suited for fabricating microelectromechanical power relays. A multi-step, multi-layer UV-LIGA process has been successfully developed and a prototype relay has been successfully fabricated.

In this paper a process for complete monolithic integration of semiconductor devices and radio-frequency micro-electro-mechanical systems (RF-MEMS) on a single substrate is presented. Our attempt was to combine RF-Schottky-Diodes to form sub-harmonic mixer and RF-MEMS-phaseshifters on a single chip. The diodes were etched from a molecular beam epitaxy grown silicon stack using two mesa etching steps. Nickel forms a nickel-silicon alloy (nickel silicide) during a rapid thermal processing step acting as Schottky-metallisation. On this stack, the RF-MEMS-fabrication starts with its metallisation layers as a back-end process. To insulate the relatively high actuation voltage (20-40 V) from the RF circuitry, a new concept for bias decoupling is presented. To demonstrate the functionality of the semiconductor integration approach, a mixer for 24 GHz has been designed in coplanar waveguide technology, the local oscillator frequency is at 12 GHz. Fabricated within the same run, switched line phaseshifters are used to show the MEMS capabilities. First tests of diodes revealed good results in their DC- and RF characteristics, the conversion loss of the subharmonic zero biased mixer reached 20 dB for 6 dBm power of the local oscillator. Fabricated teststructures of the phaseshifters achieved good results showing that transmission losses lower than 3 dB at a phaseshift of 180° can be reached.

RF-MEMS Compiler uses a component synthesis approach instead of the more traditional analysis approach. It starts from system designer requirements and creates, in a one-click operation, a ready-to-fabricate layout and a passive equivalent SPICE circuit (when relevant). This methodology shortcuts the trial and error procedure which is long, difficult, and offers no guarantee of obtaining the targeted performances. Furthermore, no single designer typically has the skills needed to effectively carry out these tasks. As demonstrated in the case of inductors, the approach can be easily generalized to any RF-MEMS component fabricated through a predefined process. First results are very promising. The inductor compiler lost no more than 5% accuracy compared to the equivalent circuit and produced no more than 11% dispersion of the generated geometry.

We report on out-of-plane micro-machined inductors exhibiting record high quality factors (Q) on silicon integrated circuits. The coils are made by three-dimensional self-assembly of stress-engineered structures fabricated with standard semiconductor batch processing techniques. Coils fabricated on low resistance CMOS-compatible silicon exhibit quality factors of over 70 at 1 GHz. BiCMOS test oscillators utilizing these micro-machined coils show significant phase noise reduction over similar oscillators using conventional spiral coils.

Two band-stop SERs (resonator A and resonator B) on silicon membrane were obtained and characterized. The frequency tunability domain of these resonators was between 3 GHz and 9.5 GHz ca. obtained by changing the dc magnetic bias field between H_appl = 0.02 T and H_appl = 0.34 T. The measurements of the S₂₁ parameter demonstrate a suppression of more than 20 dB of the high order modes, showing a good selectivity of this kind of resonator. The rejection ratio was better than -20 dB in the frequency domain from f = 3 GHz to f = 9.5 GHz for the resonator A and better than -20 dB between f = 4.2 GHz and f = 9.5 GHz for the resonator B. These results demonstrate the possibility to obtain microwave band-stop resonators supported on silicon membrane with high isolation and rejection ratios.

This paper explores the usefulness of RF MEMS and reconfigurable antennas in the context of modern communication systems and other applications. Simulation studies on a fractal antennas with switches and phase shifters provide beam steering and beam scanning characteristics. A brief description of the design aspects of two MEMS based coplanar waveguide (CPW) phase shifters for microwave and millimeter wave antenna applications are also provided here. One phase shifter design consists of a unique bilateral interdigital structure on a silicon substrate deposited with a thin film of electrically tunable barium strontium titanate. The dielectric constant of the thin film, and hence the effective permittivity of the transmission line changes by the application of a bias voltage. The second device is a distributed microelectromechanical system (MEMS) phase shifter fabricated on a high resistivity silicon substrate using microstereolithography technique is presented here. The distributed MEMS phase shifter consists of a high-impedance CPW transmission line and several MEMS bridges of uniform height. By applying a voltage the height of these bridges can be adjusted. This results in a variation in the distributed capacitance of the segment of the transmission line, which manifests in the phase shift at the output terminal. The fabrication procedure described here shows significant promise for the use of microstereolithography techniques for RF MEMS devices.

The integration of MEMS, IDTs (interdigital transducers) and required microelectronics and conformal antennas to realize programmable, robust and low cost passive microsensors suitable for many military structures and systems including aircraft, missiles and munitions is presented in this paper. The technology is currently being applied to the structural health monitoring of critical aircraft components. The approach integrates acoustic emission, strain gauges, MEMS accelerometers, gyroscopes and vibration monitoring devices with signal processing electronics to provide real-time indicators of incipient failure of aircraft components with a known history of catastrophic failure due to fracture. Recently a combination of the need for safety in the air and the desire to control costs is encouraging the use of in-flight monitoring of aircraft components and systems using light-weight, wireless and cost effective microsensors and MEMS. An in-situ Aircraft structural health monitoring (ASHM) system, with sensors embedded in the composite structure or surface-mounted on the structure, would permit the timely detection of damage in aircraft. Micromachining offers the potential for fabricating a range of microsensors and MEMS for structural applications including load, vibration and acoustics characterization and monitoring. Such microsensors are extremely small; they can be embedded into structural materials, can be mass-produced and are therefore potentially cheap. Additionally a range of sensor types can be integrated onto a single chip with built-in electronics and ASIC (Application Specific Integrated Circuit), providing a low power Microsystems. The smart sensors are being developed using the standard microelectronics and micromachining in conjunction with novel Penn State smart electronics or wireless communication systems suitable for condition monitoring of aircraft structures in-flight. A hybrid accelerometer and gyroscope in a single chip suitable for inertial navigation system and other microsensors for health monitoring and condition-based maintenance of structures, drag sensing and control of aircraft, strain and deflection of structures and systems, ice sensing on aircraft, remote temperature and humidity measurement of propellant in munitions, chemical sensing, etc. are discussed.

It is of great interest to develop an efficient and reliable manufacturing approach that allows for the integration of microdevices each of which is optimally fabricated using a different process. We present a new method to achieve electrical and mechanical interconnects for use in heterogeneous integration. This method combines metal reflow and a self-aligned, 3-D microassembly approach. The results obtained so far include a self-aligned, 3-D assembly of MEMS to MEMS, post-processing which selectively deposited indium on 50 μm-thick MEMS structures, and reflow tests of indium-on-gold samples demonstrating 15-45 mΩ resistances for contact areas ranging from 100 to 625 μm². 3-D microassembly coupled with metal reflow allows for the batch processing of a large number of heterogeneous devices into one system without sacrificing performance. In addition, its 3-D nature adds a new degree of freedom in system design space. Downward scalability of the method is also discussed.

A stress gradient was induced in two directions (through the plane of the beam and along its length) to produce a beam deflection of specific curvature. The stress gradient was produced by altering the conditions during electroplating. The pull-down characteristics of four electrostatic actuators were measured. Stressed, hard gold was patterned in a triangular shape on top of stress-free soft gold. This stress gradient along the length of the beams significantly improved the tuning range compared with devices containing spatially uniform stress. The tuning range of the variably stressed gold devices improved by 30 percent for the double-hinged square devices, by 45 percent for the double-hinged elliptical devices, and by 35 percent for the double-hinged rectangular device. Voltage cycling and temperature variation has no significant impact on the pull-down characteristics of the actuator.

Inertia micro-switches have been designed and realized using a low-temperature metal-electroplating technology compatible with processed substrates containing micro-electronic circuits. A simple but accurate lumped spring-mass model is developed based on analytical and numerical analyses. Predictions of the behavior of switches with different geometric designs have been verified using both drop hammer and shaker tests. With the application of an anti-stiction hydrophobic coating, improved storage time and un-encapsulated switches making over 50 million contacts have been demonstrated in room ambient.

The developed and fabricated model of III-shaped non-assembled planar micro-relay is formed of aluminium anodic oxide, which possesses of high electromechanical properties. Film electrodes are formed using local plasma deposition for metallization of corresponding parts. Small-cells structure of the oxide together with photolithography and electrochemical treatment guarantees precision formation of slots and branches sizes, as well as perpendicularity of their walls relative to the substrate plane. The main sizes of the model are: width of the anchor is 60 μm, thickness of the anchor equal inter-electrodes gap is 14 μm, length of electrode is 1000 μm, inter-electrodes gap is 12 μm, active area of the micro-relay is 1,4 mm². Planar design along with the micro-relay parameters enhancement simplify and shorten technological process, eliminate assembling, lower laboriousness and spoilage.

Novel tapered-width micro-cantilevers are introduced to give more design parameters in design space for controlling and synthesizing their pull-in (actuation) voltages. For a given fabrication process, the pull-in voltage of a micro-cantilever is generally a function of the taper function of width along the length, its initial width, and its length. By controlling these design parameters, a specific pull-in voltage for a micro-cantilever can be obtained. Three types of taper functions, linear, parabolic, and exponential, were selected as the width taper functions of micro-cantilevers in this study. Pull-in voltage as low as 1V is achieved with a fast growing taper function for a micro-cantilever. From the simulation and measurement results it shows that a micro-cantilever with a fast growing width along the length has a smaller pull-in voltage but occupies more area and has a smaller bandwidth.

A surface-micro-machined tunneling-based accelerometer has been designed. A simpler fabrication process has been proposed and illustrated. Performance optimization has been tried by tuning the tunneling tip, beam and proof-mass design.

We have fabricated and tested a surface micromachined, metal-metal contacting radio frequency microelectromechanical systems (RF MEMS) switch. The switch was fabricated out of electroplated metals on semi-insulating GaAs at process temperatures below 300°C. It was anchored by folded springs to one end of a coplanar waveguide (CPW) gap, forming a cantilever. This configuration allowed us to simplify the fabrication process by eliminating mechanical dielectric films that are normally necessary to isolate the switch contact from the actuation metal. The measured insertion loss and isolation at S band were 0.21 dB and 28 dB isolation, respectively. An average switching speed of 83 μs at 55 volts was measured. This switch demonstrated >10⁵ cold switching cycles without sticking, however rapid increase of the contact resistance was observed. A new switch was designed to increase isolation and reduce insertion loss by decreasing the coupling capacitance and increasing the contact force.