A micromachined flow shear-stress sensor based on thermal transferprinciples

Microhot-film shear-stress sensors have been developed by using surface micromachining techniques. The sensor consists of a suspended silicon-nitride diaphragm located on top of a vacuum-sealed cavity. A heating and heat-sensing element, made of polycrystalline silicon material, resides on top of the diaphragm. The underlying vacuum cavity greatly reduces conductive heat loss to the substrate and therefore increases the sensitivity of the sensor. Testing of the sensor has been conducted in a wind tunnel under three operation modes-constant current, constant voltage, and constant temperature. Under the constant-temperature mode, a typical shear-stress sensor exhibits a time constant of 72 μs     

A microfabricated wall shear-stress sensor with capacitative sensing

A silicon-based micromachined, floating-element sensor for low-magnitude wall shear-stress measurement has been developed. Sensors over a range of element sizes and sensitivities have been fabricated by thin-wafer bonding and deep-reactive ion-etching techniques. Detailed design, fabrication, and testing issues are described in this paper. Detection of the floating-element motion is accomplished using either direct or differential capacitance measurement. The design objective is to measure the shear-stress distribution at levels of O(0.10 Pa) with a spatial resolution of approximately O(100 /spl mu/m). It is assumed that the flow direction is known, permitting one to align the sensor appropriately so that a single component shear measurement is a good estimate of the prevalent shear. Using a differential capacitance detection scheme these goals have been achieved. We tested the sensor at shear levels ranging from 0 to 0.20 Pa and found that the lowest detectable shear-stress level that the sensor can measure is 0.04 Pa with an 8% uncertainty on a 200 /spl mu/m/spl times/500 /spl mu/m floating element plate.     

A new micromachined sensor system for tactile measurements of high aspect ratio microstructures

A new tactile sensor with piezoresistive read-out is presented. The sensor is designed for measurements of high aspect ratio structures with a resolution of some 10 nm and a measuring range of hundreds of micrometer. Possible applications of the sensor are suggested. The silicon micromachining fabrication process is shown in detail next to the finite element simulations we performed. First measurements and a calibration process are described and the results are shown. The implementation into a measuring system is indicated.     

Micromachined thermal shear-stress sensor for underwater applications

This paper reports the development of micromachined thermal shear-stress sensors for underwater applications. The thermal shear-stress sensor is a polysilicon resistor sitting atop a vacuum-insulated nitride diaphragm. Special challenges for underwater measurements, such as the waterproof coating and minimization of pressure crosstalk, have been addressed. More rigid diaphragms than the aerial sensors are implemented to increase the operating range and reduce pressure crosstalk, with the cost of larger power consumption and lower sensitivity. Sensors with different diaphragm dimensions and resistor lengths have been fabricated and tested. Nearly zero pressure sensitivity has been achieved by either reducing the diaphragm width or adjusting the sensing element length. The effects of overheat ratio and operating mode on the sensor's pressure crosstalk have been discussed. Parylene C is chosen as the waterproof material for the underwater shear-stress sensors. The primary failure mode is identified as the corrosion of the soldering pads.     

IC-integrated flexible shear-stress sensor skin

This paper reports the successful development of the first IC-integrated flexible MEMS shear-stress sensor skin. The sensor skin is 1 cm wide, 2 cm long, and 70 /spl mu/m thick. It contains 16 shear-stress sensors, which are arranged in a 1-D array, with on-skin sensor bias, signal-conditioning, and multiplexing circuitry. We further demonstrated the application of the sensor skin by packaging it on a semicylindrical aluminum block and testing it in a subsonic wind tunnel. In our experiment, the sensor skin has successfully identified both the leading-edge flow separation and stagnation points with the on-skin circuitry. The integration of IC with MEMS sensor skin has significantly simplified implementation procedures and improved system reliability.     

Research on a micromachined flexible hot-wire sensor array for underwater wall shear stress measurement

Microsystem Technologies - This paper reports an innovative flexible hot-wire senor microarray and its experimental studies for underwater wall shear stress measurement. 20 parallel channels of the...     

A parametrized three-dimensional model for MEMS thermal shear-stress sensors

This paper presents an accurate and efficient model of MEMS thermal shear-stress sensors featuring a thin-film hotwire on a vacuum-isolated dielectric diaphragm. We consider three-dimensional (3-D) heat transfer in sensors operating in constant-temperature mode, and describe sensor response with a functional relationship between dimensionless forms of hotwire power and shear stress. This relationship is parametrized by the diaphragm aspect ratio and two additional dimensionless parameters that represent heat conduction in the hotwire and diaphragm. Closed-form correlations are obtained to represent this relationship, yielding a MEMS sensor model that is highly efficient while retaining the accuracy of three-dimensional heat transfer analysis. The model is compared with experimental data, and the agreement in the total and net hotwire power, the latter being a small second-order quantity induced by the applied shear stress, is respectively within 0.5% and 11% when uncertainties in sensor geometry and material properties are taken into account. The model is then used to elucidate thermal boundary layer characteristics for MEMS sensors, and in particular, quantitatively show that the relatively thick thermal boundary layer renders classical shear-stress sensor theory invalid for MEMS sensors operating in air. The model is also used to systematically study the effects of geometry and material properties on MEMS sensor behavior, yielding insights useful as practical design guidelines.     

Design and fabrication of a micromachined planar patch-clamp substrate with integrated microfluidics for single-cell measurements

We have designed, fabricated, tested, and integrated microfabricated planar patch-clamp substrates and poly(dimethylsiloxane) (PDMS) microfluidic components. Substrates with cell-patch-site aperture diameters ranging from 300nm to 12 /spl mu/m were produced using standard MEMS-fabrication techniques. The resistance of the cell-patch sites and substrate capacitance were measured using impedance spectroscopy. The resistance of the microfabricated apertures ranged from 200 k/spl Omega/ to 47 M/spl Omega/ for apertures ranging from 12 /spl mu/m to 750 nm, respectively. The substrate capacitance was 17.2 pF per mm/sup 2/ of fluid contact area for substrates with a 2-/spl mu/m-thick layer of silicon dioxide. In addition, the ability of the planar patch-clamp substrates to form high-resistance seals in excess of 1 G/spl Omega/ has been confirmed using Chinese hamster ovary cells (CHO-K1). Testing shows that the microfluidic components are appropriate for driving human embryonic kidney cells (HEK 293) to patch apertures, for trapping cells on patch apertures, and for exchanging the extracellular fluid environment.     

Asymmetric surface roughness measurements and meniscus modeling of polysilicon surface micromachined flaps

Polycrystalline silicon (polysilicon) films are primary structural materials for microelectromechanical systems (MEMS). Due to relatively high compliance, large surface-to-volume ratio, and small separation distances, micromachined polysilicon structures are susceptible to surface forces which can result in adhesive failures. Since these forces depend on surface properties especially surface roughness, three types of microhinged flaps were fabricated to characterize their roughness and adhesive meniscus properties. The flaps enabled access to both the top and bottom surfaces of the structural polysilicon layers. Roughness measurements using an atomic force microscope revealed that MEMS surfaces primarily exhibit non-Gaussian surface height distributions, and for the release procedures studied, the bottom surface of the structural layers was significantly smoother and prone to higher adhesion compared to the top surface. A non-symmetric surface roughness model using the Pearson system of frequency curves was coupled with a capillary meniscus adhesion model to analyze the effects of surface roughness parameters (root-mean-square, skewness, and kurtosis), relative humidity, and surface contact angle on the interfacial adhesion energy. Using the measured roughness properties of the flaps, four different surface pairs were simulated and compared to investigate their effects on capillary adhesion. It was found that since the base polysilicon layer (poly0) was rougher than the base silicon nitride and the structural layer on poly0 was also rougher than that on silicon nitride, depositing MEMS devices on poly0 layer rather than directly on silicon nitride will reduce the adhesion energy.     

Integrated SWCNT sensors in micro-wind tunnel for air-flow shear-stress measurement

We have developed SWCNT sensors for air-flow shear-stress measurement inside a polymethylmethacrylate (PMMA) “micro-wind tunnel” chip. An array of sensors is fabricated by using dielectrophoretic (DEP) technique to manipulate bundled single-walled carbon nanotubes (SWCNTs) across the gold microelectrodes on a PMMA substrate. The sensors are then integrated in a PMMA micro-wind tunnel, which is fabricated by SU-8 molding/hot-embossing technique. Since the sensors detect air flow by thermal transfer principle, we have first examined the I–V characteristics of the sensors and confirmed that self-heating effect occurs when the input voltage is above ~1 V. We then performed the flow sensing experiment on the sensors using constant temperature (CT) configuration with input power of ~230 μW. The voltage output of the sensors increases with the increasing flow rate in the micro-wind tunnel and the detectable volumetric flow is in the order of 1 × 10⁻⁵m³/s. We also found that the activation power of the sensors has a linear relation with 1/3 exponential power of the shear stress which is similar to conventional hot-wire and polysilicon types of convection-based shear-stress sensors. Moreover, measurements of sensors with different overheat ratios were compared, and results showed that sensor is more sensitive to the flow with a higher overheat ratio.     

微机械陀螺的误差抑制电路研究

分析了微机械陀螺的正交误差和同相误差的来源及特点,提出了利用静电力反馈控制来抑制误差的技术方案.该方案利用反馈静电力在检测模态上产生等效电刚度和电阻尼,从而影响陀螺仪驱动和检测模态之间的刚度和阻尼耦合系数,进而抑制误差.为实现误差抑制设计了带有反馈校正环节的闭环检测电路并完成了仿真,仿真结果表明校正环节能够使系统的幅值和相位裕度达到25 dB和36.5°.对微机械陀螺进行频谱分析和性能测试比较,结果表明闭环检测情况下,误差量较开环测试减小了50%,标度因子的非线性度从2.89%减小到1.47%、带宽增加了15 Hz、零偏稳定性提高了1.3倍.     

Solid-based CAPP for surface micromachined MEMS devices

Process planning for a MEMS device is almost always conducted manually by the designer to date. As the structures of MEMS devices become more and more complicated, in order to release the designers from the hard and tedious work and speed up the development of MEMS products, such a situation should be changed. In this study, a solid based CAPP method for surface micromachined MEMS device is presented. With this method, a MEMS device is designed with a traditional CAD system, and its process planning is conducted automatically based on the solid model created. The process features with engineering semantics are extracted first. Then, the process layer model is constructed with each process layer of the model being coincident with the fabrication layer of surface micromachining. Finally, the masks are synthesized and the fabrication process is generated. Furthermore, to guarantee the manufacturability of the designed MEMS device, a systematic evaluation method is proposed. The proposed design and CAPP methods enable designers to concentrate on functional and shape design of MEMS devices.     

A design flow for micromachined electromechanical systems

I present a design flow for integrated microelectromechanical systems (MEMS), with particular focus on electromechanical devices. Several design examples of real-world devices are given     

超声波传感器在墙面平整度测量中的应用

简要介绍超声波传感器的工作原理及各组成部分。设计了合适的测量方案,对反射系数不同的被测墙面进行了位移特性测量,通过分析数据得到了相应的线性输出关系;并分析了发送与接收传感器轴间距对输出的影响。在实际测量中,可参照分析结果,根据被测物的情况选取合适的测量点。     

Surface micromachined paraffin-actuated microvalve

Normally-open microvalves have been fabricated and tested which use a paraffin microactuator as the active element. The entire structure with nominal dimension of /spl phi/600 /spl mu/m /spl times/ 30 /spl mu/m is batch-fabricated by surface micromachining the actuator and channel materials on top of a single substrate. Gas flow rates in the 0.01-0.1 sccm range have been measured for several devices with actuation powers ranging from 50 to 150 mW on glass substrates. Leak rates as low as 500 /spl mu/sccm have been measured. The normally-open blocking microvalve structure has been used to fabricate a precision flow control system of microvalves consisting of four blocking valve structures. The control valve is designed to operate over a 0.01-5.0 sccm flow range at a differential pressure of 800 torr. Flow rates ranging from 0.02 to 4.996 sccm have been measured. Leak rates as low as 3.2 msccm for the four valve system have been measured.     

Surface micromachined metallic microneedles

In this paper, a method for fabricating surface micromachined, hollow, metallic microneedles is described. Single microneedle and multiple microneedle arrays with process enabled features such as complex tip geometries, micro barbs, mechanical penetration stops and multiple fluid output ports were fabricated, packaged and characterized. The microneedles were fabricated using electroplated metals including palladium, palladium-cobalt alloys and nickel as structural materials. The microneedles were 200 mm-2.0 cm in length with a cross-section of 70-200 /spl mu/m in width and 75-120 /spl mu/m in height, with a wall thickness of 30-35 /spl mu/m. The microneedle arrays were typically 9.0 mm in width and 3.0 mm in height with between 3 and 17 needles per array. Using water as the fluid medium, the average inlet pressure was found to be 30.0 KPa for a flow rate of 1000 /spl mu/L/h and 106 KPa for a flow rate 4000 /spl mu/L/h.     

CMOS interface circuitry for a low-voltage micromachined tunnelingaccelerometer

This paper describes the design and development of three types of complementary metal-oxide-semiconductor (CMOS) interface circuitry for low-voltage micromachined tunneling accelerometers. Using a simple inductance-capacitance-resistance (LCR) circuit as well as two nonlinear current/voltage-controlled current sources, an electromechanical model enables simulating and predicting the performance of the accelerometer with CMOS interface circuitry. Of the three types of interface circuitry, the one utilizing a pn-junction diode as a logarithmic current-to-voltage converter has the best performance. The hybrid sensor-circuit module can be incorporated into a portable battery-operated multisensor instrumentation microsystem. Only one 12-V power supply is required for device operation with a power dissipation of 2.5 mW. The accelerometer has a sensitivity of 125 mV/g and bandwidth of 2.5 kHz with a measurement range of 30 g. The noise spectral density with a 1/f behavior drops from 4 mg/√(Hz) (at 0.5 Hz) to 0.1 mg/√(Hz) (at 2.5 kHz). The accelerometer in turn provides a dynamic range over 71 dB with a minimum detectable acceleration of 8 mg in a bandwidth of 2.5 kHz. In continuous operation over 720 h, the long-term variations of the output offset voltage and device sensitivity are ±10 mV (0.12%) and ±0.2 mV/g (0.15%), respectively     

Low-cost surface micromachined microhotplates for chemiresistive gas sensors

Microsystem Technologies - Microhotplate (MHP) based gas sensors have gained significant attention recently due to their small size, low power and feasibility for integration of electronics on the...     

Wireless micromachined ceramic pressure sensor for high-temperature applications

In high-temperature applications, such as pressure sensing in turbine engines and compressors, high-temperature materials and data retrieval methods are required. The microelectronics packaging infrastructure provides high-temperature ceramic materials, fabrication tools, and well-developed processing techniques that have the potential for applicability in high-temperature sensing. Based on this infrastructure, a completely passive ceramic pressure sensor that uses a wireless telemetry scheme has been developed. The passive nature of the telemetry removes the need for electronics, power supplies, or contacts to withstand the high-temperature environment. The sensor contains a passive LC resonator comprised of a movable diaphragm capacitor and a fixed inductor, thereby causing the sensor resonant frequency to be pressure-dependent. Data is retrieved with an external loop antenna. The sensor has been fabricated and characterized and was compared with an electromechanical model. It was operated up to 400/spl deg/C in a pressure range from 0 to 7 Bar. The average sensitivity and accuracy of three typical sensors are: -141 kHz Bar/sup -1/ and 24 mbar, respectively.