An integrated sensor for pressure, temperature, and relative humidity based on MEMS technology

This paper presents an integrated multifunctional sensor based on MEMS technology, which can be used or embedded in mobile devices for environmental monitoring. An absolute pressure sensor, a temperature sensor and a humidity sensor are integrated in one silicon chip of which the size is 5 mmX 5 mm. The pressure sensor uses a bulk-micromachined diaphragm structure with the piezoresistors. For temperature sensing, a silicon temperature sensor based on the spreading-resistance principle is designed and fabricated. The humidity sensor is a capacitive humidity sensor which has the polyimide film and interdigitated capacitance electrodes. The different piezoresistive orientation is used for the pressure and temperature sensor to avoid the interference between sensors. Each sensor shows good sensor characteristics except for the humidity sensor. However, the linearity and hysteresis of the humidity sensor can be improved by selecting the proper polymer materials and structures.     

A compact and fast nano-stylus profiling head for optical instruments

The current study developed a compact and high-speed stylus-profiling head with overall dimensions of 34.3 × 32.5 × 33.7 mm³. A simple linear flexure leaf spring was used as a precision guide method for the profiling head along a vertical axis and for the assembly of an infrared light-emitting diode. A position-sensitive photo-diode was used for as a simple sensing method. The static and dynamic forces, which can be controlled electronically using a vertical solenoid, were in the range of 10^?2 N to 10^?5 N. Displacement was in the range of 80 nm to 87.2 ??m, making it adequate for the precise surface measurements of hard materials. The sensor resolution was less than 10 nm. The designed profiling head had a moving mass of 1 mg and speed within 100 Hz.     

Study of unidirectional conductivity on the electrical discharge machining of semiconductor crystals

This paper investigates the unidirectional conductivity of semiconductor crystals machined by electrical discharge machining (EDM) by analyzing the properties of current–voltage (I–V) curves of the equivalent circuit. The simplified equivalent circuit of a semiconductor EDM consists of reverse-biased diodes and linear resistance. The I–V curve has three typical parameters, namely, conduction angle, breakdown angle, and breakdown point. The values of the conduction angle and the breakdown point are determined by the contact area of the reverse-biased diode, and the breakdown angle is determined by the value of linear resistance. Two diodes exist in the model with two metal electric feeders. To increase the current in this model, the diode with larger contact area should be reverse-biased. If the work piece is connected to anode in semiconductor EDM, the diode in the conduction side is reverse-biased and the avalanche voltage is only 42 V. If the work piece is connected to the cathode in semiconductor EDM, then the arc plasma, which is a termination with a small area, becomes reverse-biased. The temperature in the arc plasma side is high, causing the breakdown voltage to be much higher than the theoretical calculation value 88.5 V. As a result, when the work piece is connected to the cathode, spark production is difficult. Holes are bored on the P-type semiconductor crystals by positive and negative polarity, which could prove that machining with positive polarity is suitable for P-type semiconductor crystals during EDM. When the no-load voltage is set to 150 V, the penetration speed by positive polarity can reach 533 μm/min.     

Frictional Properties of a Mesoscopic Contact with Engineered Surface Roughness

Friction between titanium spheres and an artificially structured silicon surface was measured with a friction force microscope. Two spheres with radii of 2.3 μm and 7.9 μm were firmly glued to the tip of the microscope cantilever. A periodic stripe pattern with a groove depth of 26 nm and systematically increasing groove width from 500 nm to 3500 nm was fabricated from a silicon wafer with a focused ion beam. The sphere substrate friction coefficient shows a strong enhancement at a certain groove periodicity, which is related to geometrical interlocking of the two surfaces. This shows that careful modification of the surface roughness can help to control the tribological behavior of mesoscale contacts.     

耐高温压阻式压力传感器研究与进展

传统的硅扩散压阻式压力传感器用重掺杂4个P型硅应变电阻构成惠斯顿电桥的力敏检测模式，采用PN结隔离，高温压阻式压力传感器取消了PlN结隔离，与半导体集成电路平面工艺兼容，符合传感器的发展方向。根据力敏材料的分类，分别介绍了多晶硅中高温压力传感器、SiC高温压力传感器和单晶硅SOI（silicon on insulator）高温压力传感器的基本工作原理和国内外的发展现状，重点论述了BESOI（bonding and etch-backSOI）、SMARTCUT和SIMOX（separation by implanted oxygen）技术的SOI晶片加工工艺。以及由此晶片微机械加工成的芯片封装的高温微型压力传感器部分特性，对此领域的发展作了展望。     

Quantum size aspects of the piezoresistive effect in ultra thin piezoresistors

Proximal probe sensors with an ability to detect extremely small forces (10(-15)-10(-18)N) play significant role in scanning probe microscopy applications. The detection of extremely low forces, require producing micromachined cantilevers with as small as possible spring constants, which is considered by the optimization of the sensor design. In the last year many papers describing the fabrication process of producing ultrathin cantilevers (below 100nm) with integrated piezoresistors for deflection read-out have been published. In the case of such cantilevers the required thickness of piezoresistors is in the range of 50nm. From a quantum mechanical point of view, an electrical carrier transport confinement in direction perpendicular to the cantilever surface can be expected and in this manner we have to consider the quantum size effect.The goal of the project described in this paper is to calculate and determine the piezoresistive coefficients in p type Si thin (under 50nm) piezoresistors taking into account the quantum size effect and to compare them with the corresponding coefficients for bulk material. The calculation of the band structure will use the mathematical apparatus of an exact analytical diagonalization six-band k.p model, modified with the envelope function approximation.The behaviour of the thin piezoresistors employed as integrated deflection read-out will be also discussed. Moreover, critical issues in the realization of piezoresistors formed by MOS transistor channel will be presented.     

Fabrication and characterization of a new MEMS fluxgate sensor with nanocrystalline magnetic core

This paper presents a new MEMS fluxgate sensor with a Fe-based nanocrystalline ribbon magnetic core and 3D micro-solenoid coils. The excitation coils were placed vertically to the sensing coil on the chip plane. Second harmonic operation principle was adopted in this fluxgate sensor. The total size of the fluxgate sensor was 6.25 mm × 4.85 mm × 120 μm. A simple testing system was established to characterize the fabricated devices. A band pass filter was used to pick up the second harmonic signals in the sensing coils. When excitation rms current of 120 mA and the operational frequency of 200 kHz were selected for the testing of the fabricated devices, the sensitivity of the developed fluxgate sensor was 1005 V/T in the linear range of −500 μT to +500 μT. Due to the combination of the 3D structure coils with the nanocrystalline core, relatively low sensor noise was achieved. The noise power density was 544 pT/Hz^0.5@1 Hz and the noise rms level was 9.68 nT in the frequency range of 25 mHz-10 Hz.     

宽禁带电力电子器件研发新进展

碳化硅和氮化镓是最有发展前途的半导体材料，可用于电力半导体器件的制造。与硅半导体电力电子器件相比，其优点是：标定阻断电压较高，功率损耗较低，工作温度较高，因此给这种器件增加了与硅器件竞争的活力。至于其发展水平，SiC肖特基二极管的标定阻断电压达1．2kV、电流20A，并已投入生产；SiC大功率二极管的研制水平，标定阻断电压达12．3kV，正向电流密度达100A／km^2。预期在数年内，SiC与GaN器件将在因节能而著称的电力电子设备中得到广泛采用。     

Measurement of fluid flow rate using nanocomposite silicone rubber sensor

This paper describes the use of an elastic nanocomposite sensor to measure the water flow rate in open and closed hydraulic circuits. A sensor was constructed of multiwalled carbon nanotubes (MWCNTs) dispersed in silicone rubber (SR) and subsequently tested to verify its ability to measure water flow rate. The results reveal that the correlation between the fluid flow rate and the pressure variation across the sensor entails that its electrical resistance can be correlated to the flow rate. The sensor constructed of 2 and 3 wt,% of MWCNTs in SR-based nanocomposite sensors exhibited a low percolation threshold. An electron microscope (HRSEM) was used to characterize the manufactured nanocomposite sensors and confirm the conductive networks. The variation in the electrical resistance of the sensor in terms of both water pressure and flow rate is described. The elastic sensor was calibrated to measure the water flow rate in the range of 0–35 l/min. The results show that an elastic sensor fabricated from MWCNTs dispersed in silicone rubber does exhibit sensitivity to the slight strain levels produced by dynamic water pressure and, as such, can be used to measure flow rate. In addition, the sensor's response to water flow in the presence of bubbles enables pump cavitation monitoring. This paper also investigates the reduction of sensor electrical conductivity in response to water immersion. The findings reveal that the elastic nanocomposite sensor could potentially be used as a liquid sensor to detect water leakage in hydraulic circuits.     

陶瓷微板热隔离半导体气体传感器阵列设计与实现

具有高浓度、挥发性、强氧化性的液氯、氮氧化物等危化品泄露、爆炸的安全检测一直是一个难点问题,要求检测传感器具有较宽量程和抗腐蚀设计。基于Al N陶瓷的微热板半导体气体传感器阵列设计,采用耐腐蚀的Al N陶瓷为衬底,物理化学性能稳定的Pt膜作为信号和加热器电极,经杂化修饰的In-Nb复合半导体氧化物为敏感材料,结合柔性光刻剥离工艺和激光微加工工艺,制备了陶瓷微板热隔离气体传感器阵列。为验证传感器阵列热结构设计的合理性,进行了有限元热仿真分析,优化了设计结构。经静态气敏测试分析,传感器阵列对浓度体积比500×10~(-6)的Cl_2和100×10~(-6)的NO_2两种气体的气敏响应时间分别为30 s和60 s左右,灵敏度最高分别为275倍和4倍,且在0~500×10~(-6)和0~100×10~(-6)检测范围均具有良好的气敏特性,对Cl_2等高浓度宽量程危化品气体检测具有良好的应用前景。     

Development and evaluation of a compact 6-axis force/moment sensor with a serial structure for the humanoid robot foot

In order to walk safely, forces and moments exerted on humanoid robot foot should be measured and used for controlling the robot. This paper describes the development and evaluation of a six-axis force/moment sensor used under humanoid robot foot. The developed sensor is capable of measuring 400 N horizontal force, 1000 N vertical force, 20 N·m moment about the horizontal axis and 10 N·m moment about the vertical axis using rectangular cross-sectional beams. The structure of the sensor is newly modeled, and the sensing elements are simulated by using finite element method (FEM). Then the sensor is fabricated by attaching strain gages onto the beams. Finally, a characteristic test of the developed sensor is carried out, and the output from FEM analysis agrees with those from the characteristic test.     

Design and precision construction of novel magnetic-levitation-based multi-axis nanoscale positioning systems

This paper presents two novel six-axis magnetic-levitation (maglev) stages capable of nanoscale positioning. These stages have very simple and compact structures, which is advantageous to meet the demanding positioning requirements of next-generation nanomanipulation and nanomanufacturing. Six-axis motion generation is accomplished by the minimum number of actuators and sensors. The first-generation maglev stage, namely the Δ-stage, is capable of generating translation of 300 μm and demonstrates position resolution better than 2 nm root-mean-square (rms). The second-generation maglev stage, namely the Y-stage, is capable of positioning at a resolution better than 3 nm rms over a planar travel range of 5 mm × 5 mm. A novel actuation scheme was developed for the compact structure of this stage that enables six-axis force generation with just three permanent-magnet pieces. This paper focuses on the design and precision construction of the actuator units, the moving platens, and the stationary base plates. The performance of the two precision positioners is compared in terms of their positioning and load-carrying capabilities and ease of manufacture. Control system design for the two positioners is discussed and an experimental plant transfer function model is presented for the Y-stage. The superiority of the developed instruments is also demonstrated over other prevailing precision positioning systems in terms of the travel range, resolution, and dynamic range. The potential applications of the maglev positioners include semiconductor manufacturing, microfabrication and assembly, nanoscale profiling, and nanoindentation.     

Piezoresistive sensors for scanning probe microscopy

In this article we summarize the efforts devoted to the realization of our ideas of the development of piezoresistive sensor family used in scanning probe microscopy. All the sensors described here are fabricated based on advanced silicon micromachining and standard CMOS processing. The fabrication scenario presented in this article allows for the production of different sensors with the same tip deflection piezoresistive detection scheme. In this way we designed and fabricated, as a basic sensor, piezoresistive cantilever for atomic force microscopy, which enables surface topography measurements with a resolution of 0.1 nm. Next, by introducing a conductive tip isolated from the beam we obtained a microprobe for scanning capacitance microscopy and scanning tunneling microscopy. With this microprobe we measured capacitance between the microtip and the surface in the range of 10(-22) F. Furthermore, a modification of the piezoresistors placement, based on the finite element method (FEM) simulation permits fabrication of the multipurpose sensor for lateral force microscopy, which enables measurements of friction forces with a resolution of 1 nN. Finally, using the same basic device idea and only slightly modified process sequence we manufactured femtocalorimeter for the detection of heat energy in the range of 50 pJ.     

Fabrication of resistance type humidity sensor based on CaCu3Ti4O12 thick film

A resistance type humidity sensor has been fabricated from an assembly of CaCu₃Ti₄O₁₂ thick film, Ag interdigitated electrodes, and an Al₂O₃ ceramic substrate. The humidity sensing properties were measured using the direct current (DC) analysis method. The results show that the electrical properties of the CaCu₃Ti₄O₁₂ thick film are dependent on humidity and applied voltage. At low humidity, the film exhibited low conductivity and behaved as an insulator. However, at high humidity, the conductivity of the film increased due to the enhancement of ion conduction. These outcomes indicate that the measured resistance is highly dependent on the applied bias voltage within the whole humidity range i.e. 20–90% relative humidity (RH) at ambient temperature. The response and recovery times as well as sensitivity were determined to be around 2.8 min, 25 min, and 98.2%, respectively. Therefore, it is concluded that CaCu₃Ti₄O₁₂ thick film has good humidity sensing properties and has high potential in the application for fabrication of high-performance humidity sensors.     

Study of multi-electrode excitation mode for 3D electrical resistance tomography

Multi-electrode excitation is an effective way to improve the performance of 3D electrical tomography (ET) system compared with single electrode excitation. This paper systematically discusses various sensing strategies for multi-electrode excitation with different combinations in radial and axial directions. A typical 3 × 8 3D ERT sensor is adopted to analyze the influence of different excitation modes on performance indexes, such as number of independent measurements, dynamic range of measurements, sensitivity distribution and correlation coefficient of image reconstruction. On the basis of radial rotation angle between the excitation electrodes mapped to the same plane and whether the excitation electrodes are located in the same axial layer, five typical electrode combination modes are designed under dual-electrode excitation and single-electrode measurement protocol. The results show that the variation trend of different indexes influenced by excitation mode is inconsistent. The entropy-based method is applied to comprehensively evaluate the different excitation modes with the selected multiple performance indexes. Among all above modes, the mode in which excitation electrodes are vertically aligned is better universal one. The experimental results show that the position characteristics of the preferable mode can obtain better image reconstruction quality in different distribution models. Furthermore, the better excitation mode will provide guidance for design of other multi-electrode excitation in 3D ET systems with different structures.     

Research and design of a novel,low-cost and flexible tactile sensor array

At present, the flexible tactile sensor array has become a hot research topic in the field of robotics. This paper introduces the design, fabrication and measurement of a novel tactile sensor array based on soft materials and sensor’s piezoresistivity. This sensor array is capable of detecting the contact force and contact location via a triangular location algorithm. This triangular algorithm, which uses response of different sensing elements to a contact force, can reduce the amount of processing data and the density of the sensor array can get lower. The flexible pressure sensing elements are integrated in a flexible PDMS (polydimethylsiloxane) film, which can avoid the limitation that traditional rigid sensing elements have during their bending deformation. The sensor array’s performance has been experimentally evaluated. The results show that the proposed sensor array has an accuracy of 88.23% for the force and spatial resolution of the sensor array can reach 2.5 mm.     

Hand-held unit for liquid-type recognition,based on interdigital capacitor

The implementation of a unit capable to recognize liquids based on an interdigital capacitive sensor (IDC) is presented. The sensor’s structure was fabricated on standard FR-4 PCB board. Its capacitance change relies upon permittivity change of the medium above IDC electrodes, representing dielectric properties of the liquid used. Along with the microcontroller and simple interface circuit, information about the type of the liquid is presented on a 2 × 16 character display and through RS232 connection on PC. Implemented unit was tested against seven liquids (benzene, phenol, acetone, ethanol, methanol, formaldehyde and distillated water) and a steady state when unit only detected air. Results imply usage of this approach for the fabrication of cost effective, portable devices for on-field sensing applications.     

与气相色谱仪联用的声表面波传感器

文中介绍了一种与气相色谱仪联用的声表面波气体传感器.传感器由声表面波谐振器作反馈单元的振荡器和半导体制冷器组成.谐振器采用ST-X石英压电基片上双端对谐振式结构,Q值高(1 896)、插入损耗低(4.7 dB).采用在最低损耗点进行相位匹配以改善振荡器短期频率稳定度的方法,其短期频率稳定度达到了11 Hz/s(10-8量级).与气相色谱联用的气体检测试验给出对苯蒸气的检测下限约为150 ppb.     

A new application of functionalized platinum nanoparticles as chemiresistor coating

Chemiresistor sensor based on Pt nanoparticles stabilized with 11-mercaptoundecanoic acid was developed for detection of some volatile organic compounds (VOCs). This sensor was prepared by drop coating technique onto interdigitated microelectrode. This film displayed linear current–voltage (I–V) characteristics and decrease the resistance at room temperature. The chemiresistive sensing properties were measured over a concentration range of 1.4–400 mg L⁻¹ for methanol, ethanol, ethyl acetate and acetone vapors. The results showed good sensitivity to methanol vapors and low detection limits for all examined vapors.