Damping in a vibratory mechanical device plays an important role in modulating the response of the system. It is of critical importance to understand the nature of damping and to be able to effectively control it for micro-machined devices such as sensors or actuators. For example, if damping is too low in a micro-machined lateral accelerometer, the severe degree of resonance of the accelerometer upon an impact of external force may produce such a large signal that cripples its control circuitry resulting in total system failure. High damping (near critical) is generally desired for accelerometers. As for yaw rate gyroscopic sensors, on the other hand, low damping is required in order to achieve sufficient sensitivity of the system under a given driving force and for certain types of applications. Therefore, in designing a MEMS device, the consideration of damping must be taken into account at the earliest stage. Micro-Electro-Mechanical-System (MEMS) devices are often operated in an isolated environment filled with nitrogen or other types of gas such that the gas functions as a working fluid and dissipates energy. A gas film between two closely spaced parallel plates oscillating in normal relative motion generates a force, due to compression and internal friction, which opposes the motion of the plates. The damping, related to energy loss of the system, due to such a force is referred to as squeeze film damping. In other cases, two closely spaced parallel plates oscillate in a direction parallel to each other, and the damping generated by a gas film in this situation is referred to as shear damping. Under the small motion assumption, both flow induced force is linearly proportional to the displacement and velocity of the moving plates. The coefficient of the velocity is the damping coefficient. The review will start with a discussion on effective viscosity coefficients that were used in some of the early work by T. Veijola et al., M. Andrews et al. and others. In general, the capping pressure for a micro-machined system is below or much below the atmospheric pressure. As pressure decreases, the mean free path of the gas molecules ( nitrogen for example) increases. When the mean free path is comparable to the air gap between two plates, one may no longer be able to treat the gas as continuum. Therefore, an effective viscosity coefficient is introduced such that governing equations of motion for fluid at relatively high pressures can still be used to treat fluid motion at low pressures where the mean free path is comparable or even larger than the air gap of the plates
A 10kN silicon force sensor is realized in which the force is measured by compressing a meander shaped polysilicon strain gage. A second gage which is not loaded, is used for temperature compensation, for compensation of bending and stretching stresses in the chip and for common changes in zero load resistor values. It is shown that the output of the bridge is a linear function of the force and is independent of the force distribution on the chip. By measuring the resistance change along both gages, the force distribution on the chip can be determined so that it can be detected whether the sensor has an oblique load or not. The production process of the chip is simple and robust. A package is designed to apply the load. Hysteresis experiments are performed at four temperatures between 25 $DEGC and 49 $DEGC. Hysteresis measurements at room temperature are in close agreement with finite element calculations. The maximum hysteresis error is within +/- 0.14% of the fill-scale output (fso). Creep was tested by loading it five times. It follows that creep is smaller than 0.01% of the fso. The total error including interpolation error is within +/- 0.23%.
Presented in this paper is the investigation on sensitivity of micromachined condenser microphone. The sound-sensitive diaphragm of the microphone is formed by surface micromachined thin-film that is normally initially stressed due to the deposition process of the thin-film. Three varieties of diaphragm constructions, conventional flat diaphragm (FD), corrugated diaphragm (CD) and deep cavity-shaped diaphragm (DCD), are involved into the study. Both analysis and finite element model (FEM) are used for comparison of the mechanical sensitivity of the different kinds of diaphragm. Reasonable initial stress range of poly crystalline silicon thin films is assumed for the microphones. The DCD shows a much higher mechanical sensitivity compared to the other two kinds of diaphragm for the assumed film-stress range. A fabrication technology of low tensile-stress poly-silicon film is also provided and proposed for the high sensitivity microphone with the DCD.
Described in this paper is a micromachined vibratory gyroscope fabricated by combining anisotropic etching and DRIE process. The gyro consists of two chips, the sensor chip and the bottom chip. Two identical cantilever beam-mass structures are fabricated in the sensor chip and driving electrodes are made on the bottom chip. The beam-mass structure has two vibration modes: the vertical vibration mode for driving and the lateral vibration mode for sensing. Piezoresistive sensing elements are made on the surface of the beams to monitor the vertical and the lateral vibration. Gyroscopes can be formed using a single beam-mass structure or using two beam-mass structures (the dual beam-mass gyroscope). The effect of acceleration can be rejected if a differential operation mode is used for a dual beam-mass gyroscope. The gyroscope can operate in an atmospheric pressure due to the high Q value in lateral vibration mode dominated by slide-film air damping. Piezoresistive sensing avoids the difficulties caused by small capacitance detection. The packaging and testing costs can be reduced significantly. Preliminary results for a working device with a single beam-mass structure show that the sensitivity for angular rate signal is found to be about 15.6(mu) V/$DEG/sec/5V in an atmospheric pressure environment.
We have developed high dynamic range (105-106 g's) tunneling accelerometers1,2 that may be ideal for smart munitions applications by employing both surface and bulk micromachining processing techniques. The highly miniaturized surface-micromachined devices can be manufactured at very low cost and integrated on chip with the control electronics. Bulk-micromachined devices with Si as the cantilever material should have reduced long-term bias drift as well as better stability at higher temperatures. Fully integrated sensors may provide advantages in minimizing microphonics for high-g applications. Previously, we described initial test results using electrostatic forces generated by a self-test electrode located under a Au cantilever3. In this paper, we describe more recent testing of Ni and Au cantilever devices on a shaker table using a novel, low input voltage (5 V) servo controller on both printed wiring board and surface-mount control circuitry. In addition, we report our initial test results for devices packaged using a low-temperature wafer-level vacuum packaging technique for low-cost manufacturing.
We demonstrate micromechanical detection of ferromagnetic resonance (FMR) in thin magnetic films. FMR spectroscopy is performed on nanometer scale samples integrated with a micromachined silicon cantilever. We present several techniques by which the FMR signal is coupled to a mechanical response of the cantilever. Cantilevers with low spring constants and high mechanical Q are essential for these measurements. Sub-nanometer displacements of the cantilever are detected using a laser beam-bounce system typical of many atomic force microscopes (AFM). The high sensitivities achieved by integrating the sample with the detector allow magnetic measurements on samples with total magnetic moments smaller than detectable with conventional magnetometers. Metrology applications for micromachined magnetometers include ultra-thin film material characterization, magnetic field microscopy, microwave field imaging, and deposition process monitors.
Balanced doubly suspended structure has been used earlier for very precise high Q resonators. But here we have used the unbalanced half section which is sputter deposited with a magnetic film. The central axis acts like a torsion wire of about a micron width and thickness. The outer arm deflects downwards about the torsion axis when subjected to a magnetic field from beneath the sample. The deflection is measured by the reflected light presently under an optical microscope but can also be done by reflecting a laser beam as done in AFMs. The bending angle - versus - magnetic field is quite linear.
This paper focuses on the development of highly sensitive calorimetric flow sensors. Both the hydrodynamics of the flow channel, as well as the heat transfer are analyzed in detail. With the expressions for the hydraulic resistance of the flow channel and the hydraulic system requirements for the flow sensor, it is possible to optimize the design of the flow channel. It is theoretically shown why for small v the calorimetric flow sensor output is linear in v. Also it follows from theory that for a symmetrical configuration, in this linear regime the heater temperature is independent of v for constant heating power. This suggests that for low Reynolds Number King's Law has t obe modified. Different configurations and methods are analyzed: absolute, differential, two beam, three beam, CPA, CTA and TBA. The latter is a real thermal balance measurement and allows the use of non-linear sensing elements. From our experience with acoustical measurements it is possible to estimate practical attainable sensitivity. In combination with proper flow channel design, and a fabrication technology for narrow channels, it is shown that pL/s sensitivity is in reach.
The motion of human scale objects requires MEMS-like device arrays capable of providing reasonable forces ($GTR mN) over human scale distances (10-100 cm). In principle batch fabricated values controlling air jets can satisfy these actuation requirements. By extending printed circuit board technology to include electromechanical actuation, analogous to the extension of VLSI to MEMS, the requirement of low system cost can be achieved through batch fabrication and integration of the transduction elements with computational and communication elements. In this paper we show that modulated air jets arrayed with position sensors can support and accelerate flexible media without physical contact. Precise motion control with three degrees of freedom parallel to the array, using high flow, low pressure air jet arrays is enabled using electrostatic valves having opening and closing times of approximately equals 1 ms. We present results of an exemplary platform based on printed circuit board technologies, having an array of 576 electrostatic flap valvves (1152 for double-sided actuation) and associated oriented jets, and an integrated array of 32,000 optical sensors for high resolution detection of paper edge positions. Under closed loop control edge positioning has a standard deviation of approximately equals 25 microns. Fabrication and control of the system is described.
The Spiral Wound Transducer (SWT) is a muscle-like actuator comprising an array of deformable capacitors. The SWT is fabricated as a flat multilayer metallized plastic structure on a silicon wafer. Conventional microelectronic manufacturing techniques are used and will be described. The novel aspect of fabrication occurs after the flat SWT structures (tapes) are lifted off the wafer. In order to form a volumetric three- dimensional actuator the tapes are wound up upon themselves and bounded using a laminating process. This work as well as a characterization of the performance of the SWTs will be presented.
A magnetic actuator with torsional-polysilicon flexures, capable of very large out-of-plane displacement (the order of 1mm), and individually controlled with integrated coils that will be discussed in this paper. Magnetic actuator uses coils to produce the magnetic field required for individual microactuator motion, while the off-chip magnetic actuates unclamped devices. The advantages of the actuators are exploited: large deflections are achieved using magnetic forces to actuate compliant microflexure structures; Actuation is achieved using magnetic fields generated by off-chip sources; The actuating force is applied in a conducting environment such as a saline fluid. Individually prototype- torsional actuators are deflected over 70$DEG out of the plane of the wafer, when a current of 100 mA flows through a twenty-turn coil integrated into each actuator. The magnetic actuator provides an interaction force of several tens (mu) N between the coil-driven and the off-chip magnetic field. The micro actuators are capable of achieving large deflections (100s of micrometers ) in stationary air and fluid dynamic flow. A completed model of static mechanical and magnetic is built up to characterize mechanical properties including angular deflection, vertical deflection, bending stresses of thin plate. Both the coil- driven and the actuator structure are constructed in polysilicon surface micromachinging process.
Proc. SPIE 4176, Theoretical and experimental characterization of the in-plane tip force and deflection achieved with asymmetrical polysilicon electrothermal microactuators, 0000 (15 August 2000); doi: 10.1117/12.395623
Several microactuator technologies have recently been investigated for positioning individual elements in large-scale microelectromechanical systems (MEMS). Electrostatic, magnetostatic, piezoelectric and thermal expansion are the most common modes of microactuator operation. This research focuses on the design and experimental characterization of two types of asymmetrical MEMS electrothermal microactuators. The motivation is to present a unified description of the behavior of the electrothermal microactuator so that it can be adapted to a variety of MEMS applications. Both MEMS polysilicon electrothermal microactuator design variants use resistive (Joule) heating to generate thermal expansion and movement. In a conventional electrothermal microactuator, the hot arm is positioned parallel to a cold arm, but because the hot arm is narrower than the cold arm, the electrical resistance of the hot arm is higher. When an electric curren passes through the microactuator (through the series connected electrical resistance of 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 along its length, thus forcing the tip of the device to rotate about a mechanical flexure element. The new thermal actuator design eliminates the parasitic electrical resistance of the cold arm by incorporating an additional hot arm. The second hot arm results in an improvement in electrical efficiency by providing an active return current path. Additionally, the rotating cold arm can have a narrower flexure than the flexure in a conventional single-hot arm device because it does not have to pass an electric current. The narrower flexure element results in an improvement in mechanical efficiency. Deflection and force measurements of both actuators as a function of applied electrical power are presented.
Three promising methods of technology transfer from university to industry are illustrated by examples from the area of MEMS and microsensors. These methods are, in order of priority, the foundation of spin-off companies, the infiltration of companies by know-how carriers moving from university to industry, and joint research projects. Examples include micromachined CMOS infrared and chemical sensors and their packaging, the spin-off company SENSIRION and the Venture programs of ETH Zurich. Also mentioned are notorious transfer obstacles and how they may be overcome.
This paper presents an extensive experiment results of measuring properties of thermopile detector produced by CMOS compatible process and front-side Si bulk etching. The thermoelectric materials used are n- polysilicon and aluminum. Several parameters of thermopile detectors, such as width of polysilicon, length of thermopile, number of thermocouple, overlap length of hot junction into absorber area, and area of absorption layer are investigated in this study. Any physical characteristics of thermopile detectors, such as responsivity and detectivity of each device are measured as well. The heat conductance, resistance of thermopile structure, and the thermal-electric coefficient of thermocouple are critical to the performance of thermopile. All of them will affect the characters of sensor. In general case, a trade-off relation is among these parameters. When we design thermopile devices, we must consider these issue and determine a set of optimized parameters. In our investigation, the relation of each parameter and the device characters are measured. And the effect and correlation of these parameters versus thermopile property are evaluated. Based on these experiment results we can know the operation mechanism and correlation effect of these parameters. Establishment of accurate model for thermopile helps us to design an optimized device for various applications.
Gas and chemical sensors are used in many applications. Industrial health and safety monitors allow companies to meet OSHA requirements by detecting harmful levels of toxic or combustible gases. Vehicle emissions are tested during annual inspections. Blood alcohol breathalizers are used by law enforcement. Refrigerant leak detection ensures that the Earth's ozone layer is not being compromised. Industrial combustion emissions are also monitored to minimize pollution. Heating and ventilation systems watch for high levels of carbon dioxide (CO2) to trigger an increase in fresh air exchange. Carbon monoxide detectors are used in homes to prevent poisoning from poor combustion ventilation. Anesthesia gases are monitored during a patients operation. The current economic reality is that two groups of gas sensor technologies are competing in two distinct existing market segments - affordable (less reliable) chemical reaction sensors for consumer markets and reliable (expensive) infrared (IR) spectroscopic sensors for industrial, laboratory, and medical instrumentation markets. Presently high volume mass-market applications are limited to CO detectros and on-board automotive emissions sensors. Due to reliability problems with electrochemical sensor-based CO detectors there is a hesitancy to apply these sensors in other high volume applications. Applications such as: natural gas leak detection, non-invasive blood glucose monitoring, home indoor air quality, personal/portable air quality monitors, home fire/burnt cooking detector, and home food spoilage detectors need a sensor that is a small, efficient, accurate, sensitive, reliable, and inexpensive. Connecting an array of these next generation gas sensors to wireless networks that are starting to proliferate today creates many other applications. Asthmatics could preview the air quality of their destinations as they venture out into the day. HVAC systems could determine if fresh air intake was actually better than the air in the house. Internet grocery delivery services could check for spoiled foods in their clients' refrigerators. City emissions regulators could monitor the various emissions sources throughout the area from their desk to predict how many pollution vouchers they will need to trade in the next week. We describe a new component architecture for mass-market sensors based on silicon microelectromechanical systems (MEMS) technology. MEMS are micrometer-scale devices that can be fabricated as discrete devices or large arrays, using the technology of integrated circuit manufacturing. These new photonic bandgap and MEMS fabricataion technologies will simplify the component technology to provide high-quality gas and chemical sensors at consumer prices.
A rapid micro-polymerase chain reaction ((mu) -PCR) system was integrated to amplify the complementary DNA (cDNA) molecules of hepatitis C virus (HCV). This system consists of a rapid thermal cycling system and a (mu) PCR chip fabricated by MEMS fabrication techniques. This rapid (mu) PCR system is verified by using serum samples from patients with chronic hepatitis C. The HCV amplicon of the rapid (mu) PCR system was analyzed by slab gel electrophoresis with separation of DNA marker in parallel. The (mu) PCR chip was fabricated on silicon wafer and Pyrex glass using photolithography, wet etching, and anodic bonding methods. Using silicon material to fabricate the raction well improves the temperature uniformity of sample and helps to reach the desired temperature faster. The rapid close loop thermal cycling system comprises power supplies, a thermal generator, a computer control PID controller, and a data acquisition subsystem. The thermoelectric (T.E.) cooler is used to work as the thermal generator and a heat sink by controlling the polarity of supplied power. The (mu) PCR system was verified with traditional PCR equipment by loading the same PCR mixture with HCV cDNA and running the same cycle numbers, then comparing both HCV amplicon slab gel electrophoresis. The HCV amplicon from the (mu) PCR system shows a DNA fragment with an expected size of 145 base pairs. The background is lower with the (mu) PCR system than that with the tradional PCR equipment. Comparing the traditional PCR equipment which spends 5.5 hours for 30 cycles to gain the detectable amount of HCV amplicon in slab gel separation, this (mu) PCR system takes 30 minutes to finish the 30 thermal cycles. This work has demonstrated that this rapid (mu) PCR system can provide rapid heat generation and dissipation, improved temperature uniformity in DNA amplification.
Applications of MEMS to RF/microwaves wireless communications circuits and systems are presented. The ability of MEMS' fabrication techniques to enhacne the performance of passive components in particular, capacitors, inductors, transmission lines, and switches is addressed. A number of potential wireless system opportunities, in particular, wireless transceivers, routing networks, and tracking antennas for mobile multimedia communications, awaiting the maturation of MEMS are pointed out.
Although Microelectromechanical system (MEMS) technology has been used extensively in constructing microelectronic and micromechanical structures, there are very few reports on the research and development of MEMS antenna. This paper reports the investigation results of MEMS patch antennas in different shapes and structures. Like conventional patch antenna, MEMS patch antenna has narrow bandwidth, however, it is found among three basic shapes: circular, square and triangular.Square patch antenna has the best overall performance. Two simple methods to improve the performances of MEMS patch antenna are also proposed. When the feed inset position in polysilicon layer of a MEMS microstrip patch antenna is optimized, the impedance bandwidth of the antenna can be enhanced without deteriorating the radiation pattern of the antenna. Also, the resonance frequency of MEMS patch antenna is reduced by etching holes on the radiating patch.
In this paper, it presents an improvement over a simple free-free resonator via structural modification. Two modified designs have been considered and named as an Inverse-Pi and Inverse-T free-free beam micromechanical resonator, utilizing torsional-mode support springs. The operating range, according to the simulation is 90-130 MHz. This is a great improvement over its predecessor2 whose operating frequency is 30-90 MHz. Three main design aspect of this resonator are the modified structural design, the support beam structure and the operation parameter. In the former, the relationship between the natural frequency and resonator beam thickness, width and length are found to be interrelated. For the supporting structure design, the length of the supporting beam is determined by (lambda) /4 based on torsional vibration studies. Finally, in the operation parameter, the pull down electrostatic force voltage of the transducer is determined. The experimental testing was done on an inverse-T structure and found that it conforms with the simulation results.
A new type of compliant interconnect derived from a thin metal film fabricated with a controlled stress profile is being developed for flip- flop interconnects and probing devices. Interconnections have been demonstrated on lateral pitches as tight as 6 microns. The interconnect is highly elastic and can provide up to hundreds of microns of vertical compliance.
TRONIC'S Microsystems has developed in collaboration with LETI and ELA Recherche a Chip Size Packaging for MEMS and ICs using standard MST technologies and batch wafer processing. It allows to integrate on a single package the Electro-Mechanical Structure of the circuits, the connections and the encapsulation. After dicing, the device which is a package of its own can be easily handled and directly mounted on a circuit board. The connection pads allows the mounting on a board using standard Surface Mounting Technologies and the reworkability.
Ultrasonic transducers are generally based on the piezoelectric effect and they are used in a variety of applications (medical imaging, NDE, ranging). Some of the main reasons for choosing an alternative technology, based on electrostatic effect, are low impedance mismatch with air and in water, low energy density, high efficiency, low costs, good integration with control electronics. Capacitive ultrasonic transducer consists in a parallel plates capacitor (like a condensor microphone) with a fixed electrode and a free one (membrane). A cMUT (capacitive Micromachined Ultrasonic Transducer) consists of an array of capacitive ultrasonic transducer with a metallized membranes suspended on silicon bulk. The membrane thickness is 0.4 micrometers . Tests of these transducers ( 2.5 MHz) fabricated in our laboratories are in progress.
Current research on microstructures for semiconductor gas sensors is on development on low power and robust substrates. In this paper a microstructure based on the combination of micromachined silicon substrates and glass wafers is presented. This device shows high robustness and can reach high temperatures up to 700$DEGC with good power consumption. The optimisation of the design and the process fabrication is described.
We designed and fabricated a planar-type thermoelastic microactuator with a latch-up operation for optical switching. Latch-up actuation is prerequisite to implement an optical switch with low power consumption and high reliability. The proposed microactuator consists of four cantilever-shaped thermal actuators, four displacement linkages, two shallow arch-shaped leaf springs, a mobile shuttle mass with a micromirror, and four elastic boundaries. The planar microactuator consists of phosphorous-doped 12 micrometers -thick polysilicon as a structural layer and LTO (Low Temperature Oxide) of 3 micrometers thickness as a sacrificial layer on polysilicon substrate. The experimental displacement of the microactuator was more than 21 micrometers at 10V input voltage for the prototype of a thermoelastic microactuator. The frequency response for square wave input was measured up to 50Hz, which was the highest frequency we can detect using optical microscope for now. The proposed microactuators have advantages of easy assembly with other optical component by way of fiber alignment in the substrate plane, and its fabrication process features simplicity while retaining batch-fabrication economy.
This paper demonstrates a novel technique of microfabrication for sub- millimeter waves circuits. The proposed technique enables E-plane high Q filters, low loss transitions and directional couplers to be formed for operating frequencies about W-band. The overall processing includes realization of ultra-thin E-plane components and rectangular waveguides with a think positive photoresist (known as SU8) onto a metal block that has been mechanically milled with standard flanges. The thickness of the E-plane substrate made with this methodology can be tailored down to a few microns. The measured insertion losses of an E-plane transmission line is typically below 0.1 dB per millimeter and the guide wavelength was found to be very close to the free-space wavelength. The methodology to achieve a thickness of dielectric substrate below ten microns also enables a transmission line of less than 30 ohm to realized with negligible losses. In addition, by glowing a conducting photoresist layer with precise thickness onto an oversize waveguide channel, it is possible to attain a re-scaled waveguide operating at submillimeter wave frequencies. In this paper, the this technique is first presented with particular reference given to the requirement of submillimeter wave applications. Our recent measurements is then given to substantiate the presentation.
Silicon micromechanics in an emerging field which is beginning to impact almost every area of science and technology. In areas as diverse as the chemical, automotive, aeronautical, cellular and optical communication industries, Silicon micromachines are becoming the solution of choice for many problems. In this paper we will describe what they are, how they are built, and show how they have the potential to revolutionize lightwave systems. Devices such as optical switches, variable attenuators, active equalizers, add/drop multiplexers, optical crossconnects, gain tilt equalizers, data transmitters and many others are beginning to find ubiquitous application in advanced lightwave systems. We will show examples of these devices and describe some of the challenges in attacking the billions of dollars in addressable markets for this technology.
Silicon bulk micromachining which is based on a silicon etching and a glass-silicon anodic bonding plays important roles to make micro sensors and micro actuators. Three dimensional microfabrication of other functional materials as piezoelectric materials are also important to develop high performance microactuators, micro energy source and so on. Vacuum sealing is required to prevent a viscous dumping for packages micromechanical sensors. Extremely small structures as microprobe are required for high resolution, high sensitivity and quick response. As sophisticated microsystems which are made of many sensors, circuits and actuators are required for example for maintenance tools used in a narrow space. Developments for those required will be described.
The continuous progress in micro- and nano-system technologies has allowed the successful development of many innovative products in process control, environmental monitoring, healthcare, automotive and aerospace as well as information processing systems. In this paper on overview will be given of current progress in micro- and nanofabrication process technologies, such as deep reactive ion etching, micro-electro discharge machining, thick photoresistant processing and plating. The availibility of these micro- and nanofabrication processes will be illustrated with examples of new generations of silicon-based sensors, actuators and Microsystems with a particular emphasis on real applications of these components and systems.