Integrated microanalytical system based on electrochemical detection and cell positioning

The development and preliminary evaluation of an integrated microanalytical system based on electrochemical detection and cell positioning is reported here. The chip includes ion-sensitive field effect transistors (ISFET), a single pair of castellated microelectrodes and a reference Ag/AgCl microelectrode. The ISFETs have shown good operating characteristics, with a 52 mV/pH response. Yeast cells and bacteria have been positioned on the gate region of the ISFET sensor using single pair of castellated microelectrodes.     

Ion-sensitive field-effect transistors in standard CMOS fabricated by post processing

Highly integrated ion-sensitive field-effect transistor (ISFET) microsystems require the monolithic implementation of ISFETs, CMOS electronics, and additional sensors on the same chip. This paper presents new ISFETs in standard CMOS, fabricated by post-processing of a standard CMOS VLSI chip. Unlike CMOS compatible ISFETs fabricated in a dedicated process, the new sensors are directly combined with state-of-the-art CMOS electronics and are subject to continuous technology upgrading. The ISFETs presented include an intermediate gate formed by one or more conducting layers placed between the gate oxide and the sensing layer. The combination of the highly isolating gate oxide of the MOS with a leaky or conducting sensing layer allows the use of low temperature materials that do not damage the CMOS chip. The operation of ISFETs with an intermediate gate and sensing layers fabricated at low temperature is modeled. ISFETs with a linear pH response and drift as low as 0.3 mV/h are reported.     

Continuous-Flow System for On-Line Water Monitoring Using Back-Side Contact ISFET-Based Sensors

A multiparametric continuous-flow system for on-line monitoring of water based on ISFET sensors is described. The ISFETs used have silicon nitride as gate material, and the electrical contacts are placed on the back side of the chip. This is a technological improvement that allows for a more compact ISFET packaging and greatly increases the lifetime of the sensor compared with planar type ISFETs, since the electrical parts are separated from the chemical environment. A special probe has been designed in order to encapsulate and apply these ISFETs into the flow system. Further, a reference electrode based on standard Ag/AgCl technology has been constructed according to the ISFET probe design in order to integrate both sensors in the same flow-through cell. These probes can be easily replaced in the flow system and are made of cheap and easily mechanized materials. Using these flow-through sensors, a continuous-flow system for the determination of pH, NH(4)(+), Ca(2+), and NO(3)(-) in waters has been designed. The system configuration is based on a modular design (one setup for each parameter and a common sampling channel), which allows simple manipulation and maintenance as well as a good flexibility for different analytical requirements. A study of the system characteristics was performed by following the specifications for water monitoring. Under the conditions established for the flow system, a sampling rate of 20 h(-)(1) was obtained for each parameter, and long-term stabilities of at least 3 weeks of daily work for ISFET sensors and 5 months for the reference electrode have been achieved. The response performances obtained show the feasibility of the BSC ISFET probe use in continuous-flow monitoring.     

A time-based VLSI potentiostat for ion current measurements

A time-based CMOS integrated potentiostatic control circuit has been designed and fabricated. The design maintains a constant bias potential between the reference and working electrodes for an amperometric chemical sensor. A technique of converting input currents into time for amperometric measurements is proposed. This technique eliminates current amplifying circuitry, reduces matching problems, and increases dynamic range while saving on area and power consumption. Redox currents ranging from 1 pA to 200 nA can be measured with a maximum nonlinearity of /spl plusmn/0.1% over this range. The design can be used to generate cyclic voltammograms for an electrochemical reaction by sweeping the voltages across a range specified by the user. Analog inputs are processed and digital outputs are generated without requiring a power-hungry A/D converter. A prototype chip has been fabricated in the 0.5-/spl mu/m AMI CMOS process. Experimental results are reported showing the performance of the circuit as a chemical sensor.     

带有力反馈控制的三明治式微机械干涉加速度计

设计了一种静电力反馈控制的三明治式微机械干涉加速度计,加速度计由敏感芯片、半导体激光器、光电二极管以及相应的驱动电路和反馈控制电路组成.敏感芯片为玻璃-硅-玻璃3层结构,通过硅-玻璃键合体硅工艺制成.硅质量块由铝梁支撑,底部玻璃基片上有金属光栅和电极,通过在质量块和底部玻璃基片上的电极之间施加电压可以调节质量块与玻璃基片间的间隙.入射激光照射到敏感芯片上的光栅上,产生衍射光束,其光强随质量块与下玻璃的间距而变化.反馈控制电路通过测量衍射光强的变化来改变质量块与底电极之间的电压,使得质量块与底部玻璃基片的距离保持为入射光波长1/8的奇数倍,从而提高输出线性度,改善灵敏度,增大量程.     

Analysis and design of a CMOS angular velocity- and direction-selective rotation sensor with a retinal Processing circuit

This paper implements and analyzes a CMOS angular velocity- and direction-selective rotation sensor with a retinal processing circuit. The proposed rotation sensor has a polar structure and is selective of the angular velocity and direction (clockwise and counterclockwise) of the rotation of images. The correlation-based algorithm is adopted and each pixel in the rotation sensor is correlated with the pixel that is 45/spl deg/ apart. The angular velocity selectivity is enhanced by placing more than one pixel between two correlated pixels. The angular velocity selectivity is related to both the number and the positions of the edges in an image. Detailed analysis characterizes angular velocity selectivity for different edges. An experimental chip consisting 104 pixels, which form five concentric circles, is fabricated. The single pixel has an area of 91/spl times/84/spl mu/m/sup 2/ and a fill factor of 20%, whereas the area of the chip is 1812/spl times/1825/spl mu/m/sup 2/. The experimental results concerning the fabricated chip successfully verified the analyzed characteristics of angular velocity and direction selectivity. They showed that the detectable angular velocity and range of illumination of this rotation sensor are from 2.5/spl times/10/sup -3/ /spl pi//s to 40 /spl pi//s and from 0.91 lux to 366 lux, respectively.     

A High-Resolution MEMS Piezoelectric Strain Sensor for Structural Vibration Detection

This paper presents the modeling, fabrication, and testing of a high-performance dynamic strain sensor. Using microelectromechanical systems (MEMS) technology, ZnO piezoelectric microsensors are directly fabricated on silicon and steel substrates. The sensors are intended to be used as point sensors for vibration sensing without putting an extra burden on the host structures. A model that incorporates piezoelectric effects into an RC circuit, representing the sensor architecture, is developed to describe the voltage output characteristics of the piezoelectric microsensors. It is shown that the sensitivity of microplanar piezoelectric sensors that utilize the $e_{31}$ effect is linearly proportional to sensor thickness but unrelated to sensor area. Sensor characterization was performed on a cantilever beam cut from a fabricated silicon wafer. The experimental data indicate that the overall sensor and circuit system is capable of resolving better than 40.3 nanostrain time domain signal at frequencies above 2 kHz. The corresponding noise floor is lower than 200 femto-strain per root hertz and the sensitivity, defined as the sensor voltage output over strain input, is calculated to be 340 V/$varepsilon$ . Micro ZnO piezoelectric sensors fabricated on steel hard disk drive suspensions also show excellent results. The sensor not only has a better signal-to-noise ratio but also detects more vibration information than the combination of two laser-doppler-vibrometer measurements in different directions.      

离体电生理检测微电极阵列传感器的设计与制备(英文)

针对动物离体组织电生理检测的实际需求,设计并制备了一种以载玻片为基底,以微电极阵列为敏感元件,并将灌流装置集成一体的传感器芯片.采用微电子机械系统(MEMS)技术中的薄膜工艺完成了微电极阵列的制备,其导电层和绝缘层分别是铂和氮化硅.采用聚二甲基硅烷(PDMS)浇铸制成埋有管道的方形灌流槽.该传感器可保持离体组织的生理活性,同时实现电生理信号的64通道同步记录.整个芯片结构紧凑,接口简单,使用方便.对芯片的电学性能进行了研究,结果表明,通过在微电极表面电镀修饰铂黑,可有效降低其交流阻抗,提高信噪比.     

一种基于微型压力传感器的气压高度计设计

基于微型绝压传感器和高度气压关系式,研制了一种气压高度计.高度计的电路由恒流源、专用处理电路、低通滤波器和模/数转换芯片组成.对高度计的性能参数进行了测试.全系统重量小于7 g,工作电压为5V,工作电流小于10 mA.高度计可以在-50 m～600 m的高度范围内工作,且分辨力可以达到0.5 m.温度漂移和气压变化会导致高度测量误差,为此设计了一种GPS辅助算法.相应的飞行试验也已完成,结果表明高度计可满足微型飞行器的要求.     

Study on pH at the point of zero charge of TiO2 pH ion-sensitive field effect transistor made by the sputtering method

In this article, the current-voltage curve of an ion-sensitive field effect transistor (ISFET) is used to find the pH_pzc (pH at the point of zero charge) of a pH-ISFET device. The pH_pzc is an important parameter of a pH-ISFET device that is used directly to obtain the relationship between the equilibrium constants, K_a and K_b, and pH sensitivity. In this study, titanium dioxide (TiO₂) acted as the sensitive membrane of a pH-ISFET, and was deposited by the sputtering method with a thickness of about 250 Å. A Keithley 236 Semiconductor Parameter Analyzer was used to measure the drain-source current (I_DS) versus the gate voltage (V_G) curve at room temperature. Furthermore, this was used to determine the sensitivity of the TiO₂ pH-ISFET, and then this information has substituted into the theoretical metal oxide semiconductor field effect transistor (MOSFET) model to determine the ISFET threshold voltage. Thus, the surface potentials of the TiO₂ pH-ISFET for different pH values were obtained. Furthermore, it is well known that when the pH is equal to the pH_pzc the surface potential must be zero and accordingly, we attained a pH_pzc of 6.2 for the TiO₂ pH-ISFET.     

Bias stress effects on different dielectric surfaces of pentacene thin-film transistors

In this paper, it was demonstrated that pentacene thin-film transistors (TFTs) were fabricated with an organic adhesion layer between an organic semiconductor and a gate insulator. In order to form polymeric film as an adhesion layer, a vapor deposition polymerization (VDP) process was introduced to substitute for the usual spin-coating process. Field effect mobility, threshold voltage, and on/off current ratio in pentacene TFTs with a 15 nm thick organic adhesion layer were about 0.4 cm2/Vs, -1 V, and 10(6), respectively. We also demonstrated that threshold voltage strongly depends on the stress time when a gate voltage has been applied for bias stress test. We suggest that a polyimide adhesion layer fabricated by the VDP method can be applied to realize organic TFTs with long-term stability because of lower threshold voltage shifts due to reduced charge trapping at the interface between the pentacene semiconductor and the polyimide layer.     

A Time-Domain Sub-Micro Watt Temperature Sensor With Digital Set-Point Programming

To realize the on-chip temperature monitoring of VLSI circuits, an accurate time-domain low-power CMOS thermostat based on delay lines is proposed. Contrary to the voltage-domain predecessors, the proposed circuit can benefit from the performance enhancement due to the scaling down of fabrication processes. By replacing R-string voltage division and voltage comparator with delay line time division and time comparator, only little static power is consumed. The power consumption and chip size can be reduced substantially. Without any bipolar transistor, the temperature sensor composed of a delay line is utilized to generate the delay time proportional to the measured temperature. Instead of a conventional voltage/current DAC or an external resistor, a succeeding multiplexer (MUX) along with a reference delay line is used to program the set-point. The test chips with mixed-mode design were fabricated in a TSMC CMOS 0.35-mum 2P4M digital process. The chip area is merely 0.4 mm². The effective resolution is around 0.5degC with a 256-to-1 multiplexer and -40degC ~ 80degC nominal temperature range. The achieved measurement error is within plusmn0.8degC for a total of 20 packaged chips over the temperature operation range of commercial ICs. The power consumption is 0.45 muW per conversion and a measurement rate as high as 1 MHz is feasible when necessary.     

Surface charge sensitivity of silicon nanowires: size dependence

Silicon nanowires of different widths were fabricated in silicon on insulator (SOI) material using conventional process technology combined with electron-beam lithography. The aim was to analyze the size dependence of the sensitivity of such nanowires for biomolecule detection and for other sensor applications. Results from electrical characterization of the nanowires show a threshold voltage increasing with decreasing width. When immersed in an acidic buffer solution, smaller nanowires exhibit large conductance changes while larger wires remain unaffected. This behavior is also reflected in detected threshold shifts between buffer solutions of different pH, and we find that nanowires of width >150 nm are virtually insensitive to the buffer pH. The increased sensitivity for smaller sizes is ascribed to the larger surface/volume ratio for smaller wires exposing the channel to a more effective control by the local environment, similar to a surrounded gate transistor structure. Computer simulations confirm this behavior and show that sensing can be extended even down to the single charge level.     

基于组织液超滤提取的MEMS血糖检测传感器

基于超滤原理提取组织液、并对其进行后续葡萄糖检测,是实现长期血糖持续监测的一种有效途径．本文提出一种可用于组织液超滤提取及葡萄糖持续检测的传感器微系统．该系统主要由微流控底座和葡萄糖传感器芯片组成．其中微流控底座由PDMS微通道、SU一8单向阀等微加工器件组成,在压力作用下可完成组织液提取及将检测过的组织液排出的功能．采用体硅加工方法制作葡萄糖传感器芯片微型腔体及腔体底部的微孔膜,研制出具有扩散控制功能的三电极检测芯片,并在其上通过琼脂糖包埋方法固定葡萄糖氧化酶、基于电化学原理实现葡萄糖浓度的检测．实验结果表明,该系统可以实现液体的灵活提取,并且葡萄糖检测响应时间小于5s,在0．4V工作电压下线性测量范围达0．2～20mmol／L,灵敏度为9．76nA／（mmol·L-1）,相关系数为0．9954．多次测量5mmoL／L样本,差异系数3．48％．可见该传感系统具有较好的稳定性,并且体积小、易于集成,有望用于组织液灵活提取及其葡萄糖持续监测．     

Direct, fast, and accurate measurement of VTand K of an MOS transistor using a VT-siftcircuit

Based on a V_T-sift circuit, a new characterization technique is presented with which the value of both K, the transconductance constant, and V_T, the device threshold voltage, of an MOS transistor can be measured directly, obtained from the drain current of the device to be tested and the voltage difference between the output and input nodes of the V _T-sift circuit, respectively. The proposed method has been verified experimentally and compared advantageously with the commonly used linear regression technique in transistor characterization and wafer manufacturing. An additional application field of the V _T-sift circuit is temperature compensation of analog circuits     

The microfluxgate magnetic sensor having closed magnetic path

This paper presents a microfluxgate magnetic sensor in printed circuit board (PCB). In order to observe the effect of the closed magnetic path, the magnetic cores of rectangular ring and two bars were each fabricated. Each fluxgate sensor consists of five PCB stack layers including one layer magnetic core and four layers of excitation and pickup coils. The center layer as a magnetic core is made of a Co-based amorphous magnetic ribbon with extremely high dc permeability of /spl sim/100,000. Four outer layers as excitation and pickup coils have a planar solenoid structure and are made of copper foil. In the case of the fluxgate sensor having the rectangular ring-shaped core, excellent linear response over the range of -100 to +100 /spl mu/T is obtained with 780-V/T sensitivity at an excitation sine wave of 3 V/sub P-P/ and 360 kHz. The chip size of the fabricated sensing element is 7.3/spl times/5.7 mm/sup 2/. The very low power consumption of /spl sim/8 mW was measured.     

Chip-based bioassay using bacterial sensor strains immobilized in three-dimensional microfluidic network

A whole-cell bioassay has been performed using Escherichia coli sensor strains immobilized in a chip assembly, in which a silicon substrate is placed between two poly(dimethylsiloxane) (PDMS) substrates. Microchannels fabricated on the two separate PDMS layers are connected via perforated microwells on the silicon chip, and thus, a three-dimensional microfluidic network is constructed in the assembly. Bioluminescent sensor strains mixed with agarose are injected into the channels on one of the two PDMS layers and are immobilized in the microwells by gelation. Induction of the firefly luciferase gene expression in the sensor strains can be easily carried out by filling the channels on the other layer with sample solutions containing mutagen. Bioluminescence emissions from each well are detected after injection of luciferin/ATP mixtures into the channels. In this assay format using two multichannel layers and one microwell array chip, the interactions between various types of samples and strains can be monitored at each well on one assembly in a combinatorial fashion. Using several genotypes of the sensor strains or concentrations of mitomycin C in this format, the dependence of bioluminescence on these factors was obtained simultaneously in the single screening procedure. The present method could be a promising on-chip format for high-throughput whole-cell bioassays.     

同步发电机无传感器转速测量方法及应用

介绍了一种无需转速传感器的单片机检测同步发电机转速的方法.利用PIC16C57单片机的I/O端口直接从发电机输出的相电压取样,测定正半波的时间宽度作为测量动力机转速的依据,从而省去了转速传感器,简化了安装和调试,降低了系统成本,也简化了PIC16C57外围电路的设计.同时给出了晶闸管自励恒压交流同步发电机在防止低速励磁发生中的应用方法.     

Amperometric uric acid biosensors fabricated of various types of uricase enzymes

Preparation process of an enzyme-based bipotentiostatic amperometric uric acid sensor has been investigated. The suitability of three different Uricase (EC 1.7.3.3) enzymes (from porcine liver, Candida Utilis, Bacillus Fastidiosus) is described in this paper. The sensor fabricated of Uricase from Candida Utilis showed a linear response to uric acid in the 0-0.9 mM concentration range and the response current range was 0-3.3 /spl mu/A. The sensor fabricated of Uricase from Bacillus Fastidiosus has been saturated at 0.72 mM and the response was not linear above 0.24 mM. The response current range was 0-0.9 /spl mu/A. The sensor fabricated of Uricase from porcine liver has not given detectable electrical signal due to its very low specific activity. The substrate was prepared by screen printing on sintered alumina ceramic sheets using pastes of Au or Pd-Pt as working (W) and counter (C) and Pt-Ag as a reference (R) electrode. Galvanostatic electrocopolymerization of dodecyl sulfate doped poly-N-methyl-pyrrole (pNMPy) layer was used for enzyme immobilization. The layout of the sensor consists of four electrode surfaces (W/sub 1/, W/sub 2/, R, and C). By the bipotentiostatic technique, the two working electrodes (with and without the enzyme) are identically prepared and polarized, while the currents in the two circuits are measured simultaneously; thus, the current of the W/sub 2/-C circuit (I/sub 2/) can be substracted as a nonspecific background noise. The nonspecific oxidation of uric acid on the poly-N-methyl-pyrrole layer at 0.2 V has been demonstrated in oxygen bubbled buffer solution.     

Microcantilever Array Pressure Measurement System for Biomedical Instrumentation

An analog signal processing integrated circuit for microcantilever array has been designed for pressure measurement in biomedical applications. The chip consists of analog multiplexer, instrumentation amplifier, sample-and-hold circuit, on-chip voltage and current references, successive approximation register analog-to-digital converter (ADC) and digital control unit. Root sum square (RSS) error from the overall pressure measurement system including microcantilever array and the application specific integrated circuit (ASIC) is only ±1.79 KPa within the measurement range of 0-300 KPa. The 8-bit ADC attains 45.4 dB signal-to-noise-and-distortion ratio (SNDR) and 56.4 dB spurious-free dynamic range (SFDR), while operating at 772 KHz. The integrated circuit has been fabricated using 0.35-?m 2-poly 4-metal CMOS process technology. The chip occupies an area of 1.54 mm² and consumes 17.8 mW of power with a single 3.3 V supply.