Microelectromechanical Systems (MEMS) is one of the three core enabling technologies within the Microsystems Technology Office (MTO) of the Defense Advanced Research Projects Agency (DARPA). Together with Photonics and Electronics, MEMS forms the foundation for a broad variety of advanced research projects sponsored by MTO as well as other offices within DARPA. MEMS technology merges the functions of compute, communicate and power together with sense, actuate and control to change completely the way people and machines interact with the physical world. Using an ever-expanding set of fabrication processes and materials, MEMS will provide the advantages of small size, low-power, low-mass, low-cost and high-functionality to integrated electromechanical systems both on the micro as well as on the macro scales. Further, demands for increased performance; reliability, robustness, lifetime, maintainability and capability of military equipment of all kinds can be met by the integration of MEMS into macro devices and systems. In the post-cold-war era, U.S. forces must be able to conduct prompt, sustained, and synchronized operations with our allies in specific situations and with the freedom to operate in all four domains of military engagementsea, land, air, and space. MEMS technology has now been demonstrated in all four domains. The long-term goal of the DARPA MEMS program is to merge information processing with sensing and actuation to realize new systems and strategies to bring co-located perception and control to systems, processes and the environment.
The Army Aviation and Missile Command (AMCOM), Morgan Research Corporation, and Aegis Research Corporation are developing an SOI-based vibratory-rate z-axis MEMS gyroscope utilizing force-feedback control, and intended for wide dynamic range and harsh environment applications. Rate sensing in small diameter ballistic missile guidance units requires a rate resolution of less than 1 degree(s)/hr over a range of -3000 to +3000 degree(s)/sec, resulting in a dynamic range of 107. In addition, the devices must operate through military specifications on temperature (-55 degree(s)C to +125 degree(s)C) and vibration (1000 g at 5 - 15 kHz). This paper presents modeling, simulation, and fabrication efforts, as well as initial test data, for an SOI-based rate sensor intended for this application. The prototyped gyroscope is a single layer structure consisting of a proof mass placed in a three-fold mode-decoupled symmetric suspension. The device is fabricated in a cost-effective and highly-controllable Silicon-on-Insulator (SOI) process for in-plane inertial devices. The mechanical structure is integrated in a vacuum-sealed hermetic package with a separate CMOS readout ASIC. At the present time, the device has undergone two design iterations, with the most recent just completed.
This work is intended to help improve the safety of software-controlled safety-critical systems, while also helping to improve the mathematical characterization of such systems. Software processing is an essential part of many safety-critical operations. However, safety and reliability vulnerabilities are inherent in typical software logic and in hardware implementations representing the software logic, because it is impossible to assure perfect software, and it is difficult to make microelectronics invulnerable to many environments. Also, the safety of systems depending on software control is very difficult to assure probabilistically.
Single-crystal silicon triple-torsional micro-oscillators have been fabricated, characterized, and modeled primarily for use in a magnetic resonance force microscope. These structures exploit a high-Q triple-torsional mode of oscillation while providing added stability. Fabrication involves lithography, reactive ion etch, and a final KOH wet-etch, with the final oscillator material being single-crystal boron-doped silicon. Typical oscillators were 250 nm thick and 10 - 200 microns in lateral dimensions. Finite element modeling provided the sequence and structure of the ten lowest-frequency modes and indicated that the upper torsional mode best isolates the motion from losses to the base. The oscillators were excited piezoelectrically and the resulting frequency-dependent motion was detected with fiber-optic interferometry, with a 0.002 nm/Hz1/2 resolution. Phase-sensitive motion detection at various points on the oscillator facilitated the assignment of the principle modes. Magnetic excitation was also investigated in order to best excite the torsional resonances. Cobalt micromagnets with moments below 10-12 J/T were electron-beam deposited onto oscillators, and the magnetic forces were measured. MRFM, the primary intended application of these novel structures, is discussed; in particular, an overview is given of an experiment which uses a double-torsional micro-oscillator for the force detection of nuclear magnetic resonance. All topics discussed in this work are being combined in order to achieve a NMRFM single-sweep sensitivity as low as 10-16 N/Hz1/2 at room temperature.
This paper presents an optimized method for microgyroscope design. A lumped dynamic model is presented to optimize the microgyroscope performances. The parameters are categorized into function variables and style variables to reduce optimization cost. The maximum sensitivity and minimum area of the device are selected and weighted as the combined multiple objective functions. The optimization is conducted with a solver in Excel 9.5TM Finite element simulation is used to verify these optimized results. Simulation results show good agreement with the calculation. The optimized microgyroscope was fabricated. The resonant characteristic from experiment is compared with the optimized results and simulation results.
With recent developments in micromachining technology, fabrication of discrete microdevices is maturing; consequently, system integration is becoming an ever more important issue. One obstacle to such systems is the diverse power requirements of microdevices, especially actuators. Since some types of actuators exhibit relatively high voltage or power requirements, it is not feasible to integrate power supplies on-chip, and it is often inconvenient for the MEMS system to be tethered to interconnects for purposes of supplying power. On-chip wireless power sources can be implemented to circumvent this problem.
Applications of laser micromachining to the manufacture and prototyping of MEMS and MOEMS devices are presented. Examples of microturbines, biofactory on a chip, microfluidic components and microoptical elements manufactured by laser micromachining are described.
This paper discusses recent developments in MEMS devices and Si-micromachined circuits. Specifically, the issue of poor isolation in individual MEMS switches is addressed in the context on creative designs that lead to the development of very-high isolation MEMS switch architectures operating in a very broad frequency range. Furthermore, Si-micromachined circuits appropriate for use in modern communications systems are described, and novel K- thru W-band 3D multi- layer architectures are presented.
This paper presents the design, fabrication and measurement of membrane supported double-folded slot coplanar waveguide (CPW) feed antenna structures. The central operating frequency for the two antennas are 77 GHz and 94 GHz. The antennas were fabricated on 1.5 micrometers thick SiO2/Si3N4 dielectric membranes micromachined from a 350 micrometers thick high resistivity silicon substrate. The design was based on electromagnetic simulations using Zeland IE3D software package and a circuital approach for modeling the CPW feed lines. The experimental results show a return loss of -24.35 dB at 74.5 GHz for the 77 GHz antenna structure and -27.5 dB at 92.85 GHz for the 94 GHz antenna structure. The agreement between the frequency dependence of the return loss of the experimental and simulated results is very good. These results will be used in the design and fabrication of micromachined microsystems front-ends as millimeter wave transmitters and receivers.
One of the well-known benefits of micro scale is enhanced heat transfer. This fact provides the motivation for fabricating a variety of micro heat exchangers using derivatives of the LIGA micromachining process. These heat exchangers can be made of polymers, nickel (electroplated or electroless), or ceramics (Si3N4 and alumina are presently being investigated). These heat exchangers are envisioned for applications such as gas turbine blades, mechanical seals and/or bearings, boilers, condensers, radiators, evaporators, electronic component cooling, and catalytic converters. In this paper, methods to fabricate an array of heat exchangers for different applications are described. In addition, simple analytic models that illustrate the motivation for fabricating micro cross flow heat exchanges are shown to compare favorably with experimental heat transfer results.
By using distributed arrays of micro-actuators as effectors, micro-sensors to detect the optimal actuation location, and microelectronics to provide close loop feedback decisions, a low power control system has been developed for controlling a UAV. Implementing the Microsensors, Microactuators, and Microelectronics leads to what is known as a M3 (M-cubic) system. This project involves demonstrating the concept of using small actuators (approximately micron-millimeter scale) to provide large control forces for a large-scale system (approximately meter scale) through natural flow amplification phenomenon. This is theorized by using fluid separation phenomenon, vortex evolution, and vortex symmetry on a delta wing aircraft. By using MEMS actuators to control leading edge vortex separation and growth, a desired aerodynamic force can be produced about the aircraft for flight control. Consequently, a MEMS shear stress sensor array was developed for detecting the leading edge separation line where leading edge vortex flow separation occurs. By knowing the leading edge separation line, a closely coupled micro actuation from the effectors can cause the required separation that leads to vortex control. A robust and flexible balloon type actuator was developed using pneumatic pressure as the actuation force. Recently, efforts have started to address the most elusive problem of amplified distributed control (ADC) through data mining algorithms. Preliminary data mining results are promising and this part of the research is ongoing. All wind tunnel data used the baseline 56.5 degree(s) sweepback delta wing with root chord of 31.75 cm.
Piezoelectric aluminum nitride (AlN) thin films have been developed to realize ultrasonic transducers. AlN up to 1.5m is deposited at low temperature (140 degree(s)C) by reactive DC magnetron sputtering of an Al target in argon and nitrogen on Si, Si/SiO2/Al, and Si/Al substrates, and is wet etched (rates from 0.1 micrometers /min to 0.2 micrometers /min and selectivity of 1:10 with Al, and no etching with Si). SiO2/Al/AlN/Al, Al/AlN/Al and Si/AlN/Al square and circular membranes, from 10 micrometers to 1.5 mm size are fabricated using silicon deep reactive ion etching (DRIE), which gives etch profiles about 90, which allows larger integration density than wet anisotropic etching for ultrasonic transducers arrays. By varying size and thickness of membranes, resonance frequencies from 10 kHz to 20 MHz are expected, acoustic and electrical measurements are in progress. Ultrasonic transducers using this technology will be used to measure flows velocity by Doppler method. Other potential applications for ultrasonic transducers include medical ultrasounds and sonar. Other structures are also in progress such as Thin Film Bulk Acoustic Resonator (TFBAR), and Lamb wave devices using this technology.
Vacuum pressure measuring has been a field low permeated by micromachined devices until now. We designed a micromachined resonating system for friction vacuum gauge and tested it with the related electronics. The Silicon resonator is electrostically driven and capacitively sensed. Working at the fundamental resonant frequency (14 kHz), the damping of the oscillation is a measure for the pressure. We use bulk micromaching for the fabrication of the sensor cells. They consist of two fusion bonded silicon layers forming the resonator and two anodically bonded glass layers for caring sensing electrodes. A modified tuning fork design has been used for the resonator. It has a mechanical Q-factor of 33.000 at the low measurement range. The electronic circuit consists of a phase locked loop for driving at resonance and a PI controller to keep a constant vibration magnitude. The sensor has a nearly logarithmic transfer in a vacuum pressure range of 10-3 mbar ... 100 mbar.
The microelectromechanical system (MEMS) switch offers many benefits in radio frequency (RF) applications. These benefits include low insertion loss, high quality factor (Q), low power, RF isolation, and low cost. The ability to manufacture mechanical switches on a chip with electronics can lead to higher functionality, such as single-chip arrays, and smart switches. The MEMS switch is also used as a building block in devices such as phase shifters, filters, and switchable antenna elements. The MEMS designer needs models of these basic elements in order to incorporate them into their applications. The objective of this effort is to develop lumped element models for MEMS RF switches, which are incorporated into a CAD software. Tanner Research Inc.'s Electronic Design Automation (EDA) software is being used to develop a suite of mixed-signal RF switch models. The suite will include switches made from cantilever beams and fixed-fixed beams. The switches may be actuated by electrostatic, piezoelectric or electromagnetic forces. The effort presented in this paper concentrates on switches actuated by electrostatic forces. The lumped element models use a current-force electrical-mechanical analogy. Finite element modeling and device testing will be used to verify the Tanner models. The effects of materials, geometries, temperature, fringing fields, and mounting geometries are considered.
With recent developments in micromachining technology, fabrication of discrete microdevices is maturing; consequently, system integration is becoming an ever more important issue. One obstacle to such systems is the diverse power requirements of microdevices, especially actuators. Since some types of actuators exhibit relatively high voltage or power requirements, it is not feasible to integrate power supplies on-chip, and it is often inconvenient for the MEMS system to be tethered to interconnects for purposes of supplying power. On-chip wireless power sources can be implemented to circumvent this problem. Here, a simple wireless powering scheme, which utilizes a transformer with an air gap in its core, is demonstrated. The transformer secondary is fabricated on-chip and is detachable from the transformer. Experiments and simulations are performed to maximize the coupling between the primary and secondary. Coupling coefficient close to 0.8 was obtained. Frequency properties of the transformer were studied. In the case of the thin-film secondaries demonstrated here, the transformer operates at frequencies less than a few MHz. Usably high voltage (223.4 Vpp) and high power delivered to a load (4.5 Wrms) were obtained from the secondary to demonstrate the transformer capabilities.
Piezoelectric accelerometers fabricated from Lead-Zirconate-Titanate (PZT) thin films are expected to achieve higher sensitivities and better signal-to-noise ratios (SNR) in comparison with capacitive and piezoresistive accelerometers. This paper will present, for the first time, the fabrication and performance of piezoelectric, bulk-micromachined accelerometers using PZT thin films operating in the d33-mode. Using sol-gel techniques, 0.6 mm thick PZT films with high piezoelectric coefficients were deposited. Measurements on these PZT films show a remnant polarization Pr < 19 (mu) C/cm2, dielectric constants Er > 800, and d33 coefficient of 120 pC/N. The PZT accelerometers operating in the d33 mode were successfully fabricated. Interdigitated capacitors were used to achieve the d33 mode of operation and deep reactive ion etching was used to define the proof-mass of the accelerometers. Measurements on these accelerometers show sensitivities ranging from 0.85 - 1.67 mV/g with resonance frequencies ranging from 22.4 - 15.4 kHz respectively. In addition to the improved sensitivity, advantages of d33-mode accelerometers include use of thinner PZT films, and the ability to optimize the impedance of the device to achieve a higher SNR. The performance of MEMS d33-mode accelerometers will also be compare with the previously reported d31-mode accelerometers using PZT thin films.
A comparison of three different large-displacement microactuator technologies fabricated by deep reactive ion etching (DRIE) in silicon-on insulator (SOI) substrates is presented. Electrothermal, curved electrode electrostatic, and combdrive electrostatic actuator designs are considered, with each actuator design capable of producing more than 100 mm of displacement. Analytic models for each actuator type are reviewed, and both theoretical and experimental data for fabricated devices are analyzed and compared with respect to displacement, force, and power consumption.
A microscale power device, composed of a fuel processor and a fuel cell, is described, and results of testing conducted with the fuel reformer are presented. The microscale fuel reformer strips hydrogen from a hydrocarbon fuel, such as methanol, and the hydrogen-rich stream can then be fed to a fuel cell to generate electrical power. In the tests discussed here, the fuel reformer, utilizing methanol, was able to provide up to 100 mWe of hydrogen at an efficiency of up to 4.8%. The device was able to operate independent of any additional external heating, even during start-up.
This paper presents the fabrication processes for micromachined millimeter wave devices on micromachined GaAs substrate. For the first time, a 2.2 micrometers thin GaAs/AlGaAs membrane, obtained by MBE growth and micromachining of semiinsulating <100> GaAs, is used as support for millimeter wave filter structures. Cascaded coplanar waveguide open-end series stubs filter type structures, with central frequency of 38 respectively 77 GHz were designed and manufactured on GaAs micromachined substrate. `On wafer' measurements for the filter structures were performed. Losses less than 1.5 dB at 38 GHz and less than 2 dB at 77 GHz have been obtained for both the silicon as well as for the GaAs based micromachined filters.
Miniaturization technologies such as Micro-Electro-Mechanical Systems (MEMS) have been used to fabricate a prototype 100-gm class cold gas propulsion system suitable for use on a Co-Orbiting Satellite Assistant (COSA). The propulsion system is fabricated from bonded layers of photostructurable glass (Foturan glass; the design is based on fabricating integrated modular parts. Thus, the propulsion system is mass producible, expandable, expendable (low unit cost), and highly integrated.
An approach to calculate flat-parallel-type electrostatic microrelay operation voltage taking into account inertia forces is proposed. The versions to determine parameters influencing inertia masses acceleration are considered. Analysis of interacting factors is performed. Experimental microrelay calculation data and recommendations on inertia forces lowering are presented.
A frequency tunable magnetostatic wave (MSW) straight edge resonator (SER) made by a YIG film has been used as a selective frequency component in a micromachined resonating filter. S-parameters have been measured at different DC magnetic bias fields, with a frequency tunability between 2 GHz and 6 GHz ca.. An improvement of the performances for the SERs excited by micromachined microstrip transducers has been clearly demonstrated. Moreover, the utilization of silicon membranes to support MSW-SERs offers important openings toward the integration of magnetostatic wave devices with micromachined structures.
The manuscript presents the results of research of different processes of micro brands (identification marks) manufacturing. Two methods are taken into consideration, namely, the projection method and the method based on making brand by deep laser marking. These manufacturing methods are compared in terms of their accuracy, manufacturing flexibility and efficiency. There are a lot of micro brand manufacturing processes and one of them is laser deep marking. In this paper we consider brand manufacturing by Copper vapor lasers and compare it with well-known Nd:YAG laser. A copper vapor laser has a diffraction-limited divergence, a short pulse, and a high repetition rate. These properties enable an efficient evaporation of any material with a very small heat affected zone and with a minimal amount of the melted material. In the projection method a copper vapor laser cuts a mask of 0.15 mm copper foil. The mask image being projected to a material surface is five times less than the original mask. A pulse solid-state laser illuminating the mask evaporates the exposed material. An impact tool for brand stamping is made of steel by precision deep (0.5 mm) marking using a copper vapor laser. A laser beam 10 mm in diameter is deflected by electromechanical scanners and evaporates material layer by layer at the raster movement. Copper vapor laser marking makes possible the direct manufacturing of brands on gold surfaces at 0.5 mm depth with 10 mm accuracy as well.