Flicker noise in transistors

Measurements of the noise voltage appearing at the ac open-circuited emitter of a transistor with its collector ac grounded and with both an external base resistance and the operating point as parameters can be used to study the location of flicker-noise sources in transistors. A general flicker-noise model is assumed. It is shown by this method of measurement that for many modern transistors the flicker-noise sources are adequately represented by a single noise current generator connected in parallel with the emitter-base junction. The method permits evaluation of the magnitude of both the correlated and uncorrelated parts of a possible collector-base flicker-noise current generator as well as measurement of the emitter-base generator.     

A 2-GHz low-phase-noise integrated LC-VCO set with flicker-noiseupconversion minimization

A fully integrated 2-GHz very low-phase-noise LC-tank voltage-controlled oscillator (VCO) set with flicker noise upconversion minimization is presented. Using only integrated planar inductors, the measured phase noise is as low as -125.1 dBc/Hz at 600-kHz offset and -138 dBc/Hz at 3 MHz. The excellent phase-noise performance is achieved by means of an in-house-developed integrated inductor simulator optimizer. To minimize the upconversion of flicker noise to 1/f³ phase noise, a flicker-noise upconversion factor is defined, which can easily be extracted from circuit simulation. The technique is applied to demonstrate the relationship between the flicker-noise upconversion and the overdrive level of the oscillators' MOS cross-coupled pair and to develop circuit balancing techniques to even further reduce the flicker-noise upconversion. The 1/f³ phase-noise corner is minimized to be less than 15 kHz. The VCO's are implemented in a three-metal layer, 0.65-μm BiCMOS process, using only MOS active devices     

悬梁式陶瓷微热板的设计及热性能研究

结合传统陶瓷厚膜气体传感器和硅微加工气体传感器的特点,设计了基于陶瓷基底的悬梁式微热板结构,并提出一种无内引线的封装方式。对微热板的传热过程进行分析,并通过有限元工具对具有不同结构参数器件的热特性进行模拟,得到结构参数与器件热特性间的关系。通过控制工艺参数,在Al2O3陶瓷基底上制作出性能良好的Pt加热电阻及电极,并采用激光微加工技术实际制作了梁宽为0.2 mm和0.4 mm的两种结构器件。对器件的加热功率-温度关系进行测试,0.2 mm梁结构器件在400 mW加热功率下板上平均温度约为250℃,同模拟结果一致。     

微气体流量计的模拟与优化

温差法测流量是一种新型气体流量计的基本原理 ,温度传感器的布置对流量计的性能影响很大。本文使用基于分子运动理论的直接模拟MonteCarlo法对这种微气体流量计通道内的气体流动进行了数值模拟 ,对比了有无传感器时速度场和温度场的分布 ,指出传感器的布置对温度场的影响很小 ,并根据温差分布规律提出了传感器布置的优化方案。     

热电薄膜型气体流量传感器的热模拟分析

本文利用有限元分析工具ANSYS/FLOTRAN,模拟并分析了一个基于薄膜结构的热电型气体流量传感器的温度场.并具体地分析了在气体流量通道入口处气体的流向角度对传感器输出信号以及气体流动状态的影响.将最终的模拟计算结果与实验数据进行比较,发现二者基本吻合.利用此热学模型来模拟和分析此类传感器,不但可以减少大量的模拟分析过程而且可以降低计算的复杂度,同时也为该类传感器的进一步优化设计提供了一个非常简单而有效的方法.     

Multiplexing of optical fiber sensors using a frequency-modulated source and gated output

A novel method is proposed and demonstrated for multiplexing fiber-optic interferometric sensors using the FMCW technique. The method uses a gas laser whose optical frequency is modulated sinusoidally by an external modulator. The use of gating and appropriate signal processing can achieve low crosstalk between sensors. Experiments on two and three sensor systems are reported. The minimum detectable signal measured is 1 mrad/sqrt{Hz}and the crosstalk factor achieved is -35 dB. The major causes of crosstalk are also analyzed.     

H2S气体传感器的进展

综述了Ｈ２Ｓ半导体气体传感器的制备及敏感机理，添加剂ＣｕＯ化合物可以明显提高对Ｈ２Ｓ气体的灵敏度与选择性，最后，介绍了一种似乎合理的敏感机制。     

一种提高气敏元件热稳定性的优化设计

本文提出一种新的具有较好热稳定性的气敏元件结构。在这种结构里,气敏元件的输出无需外接取样电阻即可获得。文中对现有气敏元件和新型结构气敏元件的热稳定性作了理论分析和实验对比。本设计也适用于其它类型半导体气敏元件。     

The fifth sense-on the scent of the electronic nose

The author describes how electronic sensors for scent and odours work. Gases produce changes in the properties of an array of sensors, resulting in electrical signals, which are then amplified, linearised for gas concentration and digitised before being fed into a pattern-recognition system. The gas sensitive layer is tin oxide with catalytic additives for detection of particular gases. The author discusses how different sensors combined with pattern recognition techniques, can discriminate between different odours. The different types of sensor and their application to gas testing systems are also discussed     

基于MATLAB的SiC肖特基二极管气体传感器模拟

提出了SiC-SBD气体传感器器件分析模型,利用当前流行的MATLAB强大的计算编程功能,模拟了SiC-SBD气体传感器的电流-电压特性,结果与实验数据吻合很好,较好地解释了Pd-SiC肖特基二极管比较灵敏的原因,并根据模拟结果提出了提高传感器灵敏度的方法。     

Humidity-Initiated Gas Sensors for Volatile Organic Compounds Sensing

A new volatile organic compounds (VOCs) sensing concept called humidity-initiated gas (HIG) sensors is described and demonstrated. HIG sensors employ the impedance of water assembled at sensor interfaces when exposed to humidity to sense VOCs at low concentrations. Here, two HIG sensor variants are studied—Type I and Type II. Type I sensors benefit from simplicity, but are less attractive in terms of key performance metrics, including response time and detection limits. Type II sensors are more complex, but are more attractive in terms of key performance metrics. Notably, it is observed that the best-in-class Type II HIG sensors achieve <2 min response times and <10 ppb detection limit for geranyl acetone, a VOC linked to the asymptomatic form of Huanglongbing (HLB) citrus disease. Both Type I and Type II sensors are assembled from off-the-shelf materials and demonstrate remarkable stability at high humidity. HIG sensors are proposed as an attractive alternative to existing VOCs sensors for remote field detection tasks, including VOCs detection to diagnose HLB citrus disease.     

Simulation and Fabrication of SAW-Based Gas Sensor with Modified Surface State of Active Layer and Electrode Orientation for Enhanced H<Subscript>2</Subscript> Gas Sensing

The design, analysis, optimization, and fabrication of layered and nanostructure-based surface acoustic wave (SAW) gas sensors are presented. A lithium niobate and zinc oxide (ZnO) nano multilayer structure is proposed to enhance the sensitivity of the SAW-based gas sensor. Different materials are considered for the intermediate layer in the design for optimization purposes. The sensitivity of the sensor could be improved due to increased active surface area obtained by varying the aspect ratio of the nanorods, the thickness of the intermediate layer, and the gap between the electrodes. The total displacement and frequency shift of the device were significantly improved. Overall, the mechanically engineered surface-based (nanorod) SAW gas sensor offered better sensing response than the layered SAW gas sensor in terms of sensitivity performance.     

Flicker (1/f) noise generated by a random walk of electrons in interfaces

Flicker noise can be generated by a random walk of mobile electrons in interfaces via interface states. It is proposed that these electrons interact with surface phonons to form polarons, which have very low mobilities. The flicker-noise model is a general one and may be used to explain flicker noise on MOSFET's, clean Si surfaces, metallic resistors, grain boundaries, amorphous layers, electron tubes, metal-insulator-metal junctions, diodes, and transistors. The dependence of the noise intensity is calculated as a function of device parameters such as interface state density, source-drain current, source-drain voltage, gate voltage, oxide layer thickness, grain size, temperature, size of the cathode, diode current, base current, and the surface recombination in the emitter-base area. Hooge's parameter is calculated quantitatively for several devices.     

掺杂改善SnO_2甲醛气敏元件灵敏度特性的研究

用纳米SnO2制作了旁热式气敏元件。用掺杂方法提高SnO2甲醛气敏元件的灵敏度,掺杂剂包括Pd,Sb,Ti,Zr,Cu,Ag,Mn等。在SnO2气敏元件中分别掺杂质量分数2%Pd和2%Zr对提高元件灵敏度有显著效果。未掺杂SnO2、掺杂质量分数2%Pd和2%Zr的气敏元件对体积分数为5×10-5甲醛的灵敏度分别为1.33,2.38,2.08,但是掺杂在改善元件对乙醇的选择性方面作用不大。分析了掺杂改善SnO2气敏元件灵敏度的原理,当SnO2表面吸附还原性气体时,吸附气体提供电子,使半导体表层的导电电子数增加,引起电导率增加、电阻下降。吸附气体浓度越高,电阻率变化越大,元件灵敏度越大。     

MQS1型一氧化碳气敏元件

氧空位与材料的气敏特性有着密切的关系，气敏材料的电导率由氧空位的形成和氧化过程共同决定，氧空位浓度越大，气敏效应越明显。根据氧化锡的这一气敏机理，以９９．９９％的锡为原料，掺入合适的添加剂，制成了ＭＱＳ１型一氧化碳气敏元件。它的灵敏度高、选择性好、响应恢复快、受温度和湿度的影响小。     

气体声表面波传感器的研究进展

主要从声表面波(SAW)结构和敏感膜的角度综述了SAW气体传感器的研究现状。重点分析了国外出现的换能器新型结构,对其优点进行了初步分析,并和传统的SAW气体传感器结构做了比较,指出这些新结构尽管存在一些缺点,目前还不能取代传统的通用式结构,但是在某些特殊场合具有传统结构所不具备的优点。在敏感膜方面,主要从新材料方面入手,分析了目前主要使用的敏感膜材料,并结合SAW气体传感器的发展趋势,总结出敏感膜的发展方向。同时,对SAW气体传感器的其他组成部分如衬底材料和信号处理电路也作了简单的回顾,最后结合国内外研究成果对SAW气体传感器的发展做了展望。     

基于最小二乘法的气体传感器精度的研究

文中介绍了气体传感器特性曲线拟合的最新研究。由于传统的模型及方法已不能满足现代科学对数据精度与曲线匹配性高的要求,需要采取一种有效的、低误差的改进校准方案。文中采用虚拟仪器技术与最小二乘法大幅度提高了气体传感器的测量精度。     

微波辅助合成纳米WO_3/TiO_2复合材料及其气敏性能

为改善WO3基敏感材料的气敏性能,采用微波回流法一次性合成了纳米WO3/TiO2复合材料,并研究TiO2掺杂量对用其制备的气敏元件气敏性能的影响。结果表明:此气敏元件对体积分数为100×10-6的NOx、二甲苯、H2S和丙酮气体具有较强的敏感性,掺杂w(TiO2)为20%的元件,对H2S和NOx的灵敏度分别为31.18和695.84;掺杂w(TiO2)为30%的元件,对二甲苯和丙酮的灵敏度分别为39.19和35.69。     

Optical fiber gas sensor based on self-assembled gratings

The electrostatic self-assembled monolayer synthesis process is used to fabricate gas sensors by building up grating sensor elements on the ends of multimode optical fibers. These novel sensors can be designed to operate in the transmission windows of standard optical fibers and implemented using specific reference wavelengths to normalize the output signals. Experimental results for such sensors designed to detect dichloromethane gas are presented     

三电极碳纳米管传感器的极间距优化

三电极碳纳米管传感器各电极之间的间距大小是影响检测精度的关键因素之一。在用传感器阵列检测多组分气体混合物时,各传感器的极间距很难确定。为三电极碳纳米管气体传感器提出一种基于粒子群算法(PSO)的极间距优化方法。该方法包括设计极间距、组建由不同极间距的多个传感器组成的传感器阵列、建立包括极间距及检测离子电流的数据库、建立混合气体定量分析模型及极间距优化等步骤。采用多组由不同极间距的三个碳纳米管传感器构成的传感器阵列对NO和SO2 混合气体进行测量,其中各传感器的极间距均采用上述方法优化。实验结果显示,上述极间距优化方法能够有效地选择电极之间的最佳间距,优化极间距后的传感器也获得了更高的检测灵敏度。