Effect of thermal annealing and exposure to oxygen plasma on the properties of TiO2-Si structures

The effect of thermal annealing and exposure to oxygen plasma on the phase composition, structure, and microprofile of titanium-dioxide films deposited by high-frequency magnetron sputtering on silicon substrates is studied. The influence exerted by processing modes on the capacitance-voltage and conductance-voltage characteristics of Me-TiO₂-Si-Me structures and on the density of surface states at the semiconductor-insulator interface is examined. It is shown that TiO₂ films are amorphous upon their fabrication. Upon the annealing of films at 500°C in an argon atmosphere, crystallites of anatase and rutile appear in the amorphous matrix. The treatment of a titanium-dioxide film in oxygen plasma gives rise to rutile crystallites with new crystallographic planes. As a result of annealing at 750°C, the anatase phase disappears and the film becomes polycrystalline, containing only rutile crystallites. The capacitance of Me-TiO₂-Si-Me structures in the accumulation mode reaches the maximum value upon annealing at 750°C, which is due to the transformation of titanium dioxide to the rutile phase. The specific capacitance is 5.9 × 10^?2 F/cm³. The decrease in the capacitance of the structures and in the amount of fixed charge in the insulator upon exposure to oxygen plasma is due to the diffusion of oxygen atoms across the titanium-dioxide layer to give a SiO₂ film at the TiO₂-Si interface. As a result of the annealing and treatment of a titanium-dioxide film in oxygen plasma, the energy density of surface states decreases by more than an order of magnitude as compared with the unannealed samples.     

Wide Dynamic Range CMOS Amplifier Design for RF Signal Power Detection via Electro-Thermal Coupling

A differential temperature sensor for on-chip signal and DC power monitoring is presented for built-in testing and calibration applications. The amplifiers in the sensor are designed with class AB output stages to extend the dynamic range of the temperature/power measurements. Two high-gain amplification stages are used to achieve high sensitivity to temperature differences at points close to devices under test. Designed in 0.18 μm CMOS technology, the sensor has a simulated sensitivity that is tunable up to 210 mV/°C with a corresponding dynamic range of 13 °C. The sensor consumes 2.23 mW from a 1.8 V supply. A low-power version of the sensor was designed that consumes 1.125 mW from a 1.8 V supply, which has a peak sensitivity of 185.7 mV/°C over a 8 °C dynamic range.     

Coulomb blockade of the conductivity of SiO<Subscript>x</Subscript> films due to one-electron charging of a silicon quantum dot in a chain of electronic states

The electrical characteristics of metal-oxide-semiconductor (MOS) structures with silicon nanoparticles embedded in silicon oxide have been studied. The nanocrystals are formed by decomposition of an oversaturated solid solution of implanted silicon during thermal annealing at a temperature of ～1000°C. At liquid-nitrogen temperature, a stepped current-voltage characteristic is observed in a MOS structure consisting of Si nanocrystals in a SiO₂ film. The stepped current-voltage characteristic is, for the first time, quantitatively described using a model in which charge transport occurs via a chain of local states containing a silicon nanocrystal. The presence of steps is found to be associated with one-electron charging of the silicon nanocrystal and Coulomb blockade of the probability of a hop from the nearest local state to the conducting chain. The local states in silicon dioxide are assumed to be related to an excess of silicon atoms. The presence of such states is confirmed by measurements of the differential conductance and capacitance. For MOS structures implanted with silicon, the differential capacitance and conductance are found to be higher, compared to the reference structures, in the range of biases exceeding 0.2 V. In the same bias range, the conductance is observed to decrease under ultraviolet irradiation due to a change in the population of the states in the conductivity chains.     

Strain-insensitive and high temperature fiber sensor based on a Mach–Zehnder modal interferometer

In this paper, a strain insensitive high temperature fiber sensor based on the modal interferometer is proposed. It is composed of a piece of small-core photosensitive fiber (SCPSF) which is spliced between two pieces of single mode fiber (SMF). Compared to other high temperature fiber sensor based on the modal interferometer, the sensor owns the highest temperature sensitivity of 106.64 pm/°C from 200 °C to 1000 °C. The temperature to strain cross sensitivity of the sensor is low and only 0.00675 °C/με. The reasons for realizing the high temperature sensitivity is also discussed.     

A hybrid voltage-variable capacitor

A new voltage-variable tuning capacitor is described. Using conventional fabrication techniques, metal-insulator-semiconductor and p-n junction structures are combined to obtain the high voltage sensitivity and low capacitance tolerances required to tune the AM broadcast band. Other potential applications are cited. A simple theory of operation based on nonequilibrium conditions is given together with experimental verification. Devices fabricated with a 530-Å-thick SiO2insulator on n/n⁺epitaxial silicon exhibit capacitance ratios of 15:1 in 14 V with a minimum Q of 170. The reverse current is two orders of magnitude higher than expected. This is attributed to growth defects in the epitaxial layer which give rise to a low minority carrier lifetime τ0∼0.1 µs and a high surface recombination velocity S0∼500 cm/s.     

Analog ASIC for improved temperature drift compensation of a high sensitive porous silicon pressure sensor

The paper focuses on the design of a CMOS analog ASIC for temperature-drift compensation of a high sensitivity piezoresistive micro-machined porous silicon pressure sensor to avoid analog-to-digital conversion, limit chip area and reduce power consumption. For implementing the compensation circuitry, multilayered perceptron (MLP) based artificial neural network (ANN) with inverse delayed function model of neuron has been optimized. The temperature drift compensation CMOS ASIC has been implemented to make porous silicon pressure sensor an excellent SMART porous silicon pressure sensor. Using the compensation circuit, the error in temperature-drift has been minimized from 93% to about 0.5% as compared to 3% using conventional neuron model in the temperature range of 25–80°C. The entire circuit has been designed using 0.35 μm AMS technology model and simulated using mentor graphics ELDO Simulator.     

新型磁驱动增大检测电容的高精度MEMS惯性传感器研究

增大传感器振子的质量和静态测试电容可以减小电容式MEMS惯性传感系统的噪声,而深度粒子反应刻蚀工艺由于复杂的工艺原因,当深宽比较大时,不能刻蚀出大质量和大初始电容的传感器.据此,本文研究了一种磁驱动增大检测电容的MEMS惯性传感器,通过电磁驱动器,传感器的静态测试电容可以大幅增加,在梳齿电容上刻蚀阻尼槽后,其机械噪声达到0.61μg每根号赫兹,仿真其共振频率为598Hz,静态位移灵敏度为0.7μm每重力加速度,基于硅 玻璃键合工艺,制作了栅形条电容式惯性传感器,并用电磁驱动的方式测试其品质因子达到715,从而验证了制作工艺的可行性和电磁驱动器改变传感器初始静态测试电容的可行性.     

A 1/2-in. CCD image sensor overlaid with a hydrogenated amorphous silicon

A half-inch size CCD image sensor overlaid with a hydrogen-erated amorphous silicon (α-Si:H) as a photodetector has been developed. The array consists of 506V × 404H picture elements. The glow-discharged α-Si:H film has high quantum efficiency of 0.75-0.8 in the visible wavelength range and low dark current of 0.2 nA/cm²and is formed on the CCD scanner with vertical overflow drain. This CCD image sensor has a sensitivity of 0.014 µA/lx (3200 K)and a S/N ratio of 73 and 68 dB for fixed-pattern noise and random noise, respectively. Smearing signal is suppressed to below 5 percent at incident light intensity of 1000 times saturation exposure. The blooming and highlight lag are completely suppressed by the vertical overflow drain structure.     

SENSIM: A simulation program for solid-state pressure sensors

A simulation program is described which is capable of calculating the output response of silicon piezoresistive or capacitive pressure sensors as a function of both pressure and temperature. A thermoelastic plane-stress formulation is used in calculating the stress and deflection of the transducer diaphragm. Both analytical and finite-difference solution methods are available, depending on the sensor structure. Diaphragm thickness taper, oxide and package stress, and rim effects are simulated. For capacitive structures, the program accurately predicts the diaphragm deflection and pressure sensitivity as a function of pressure and temperature. Stepped diaphragm structures are shown to be capable of improving pressure sensitivity by as much as 50 percent. The package-induced thermal drift for electrostatically sealed glass-silicon devices is typically less than 0.05 mmHg/°C.     

双极化无芯片RFID金属裂纹传感器

为检测金属结构中裂纹的宽度及方向,提高检测的灵敏度和可靠性,设计了一种基于频率信号的双极化无芯片RFID传感器。在2.2~6.2 GHz频率范围内进行四频带分段设计,传感器为圆盘及双模圆盘多微带谐振器结构,利用HFSS软件对传感器进行结构优化与性能仿真。结果表明,传感器在x极化和y极化方向激励下,分别产生两组四位谐振。金属裂纹的方向根据谐振频率偏移方向判断,两种极化方式共产生八位谐振偏移信息供判定,可实现对0°、45°、90°、135°方向裂纹的准确识别;对各方向上裂纹宽度与传感器谐振频率偏移量进行拟合,两者间呈现良好的线性关系,且通过极化复用大幅提高了传感器的灵敏度,分辨率可达亚毫米级,在各个方向上灵敏度分别为40.71 MHz/0.1 mm、11.28 MHz/0.1 mm、26.04 MHz/0.1 mm、15.19 MHz/0.1 mm。制作了传感器实物并进行实验测试。设计的RFID传感器具有无源、低成本、灵敏度高的特点,在结构健康监测中具有应用潜力。     

Challenges in SiC power MOSFET design

The impact of fundamental and technological parameters is considered for SiC power MOSFETs. The wide bandgap nature of SiC increases the surface electric field by 2× at inversion compared to silicon, placing an important role on surface roughness in reducing the field-effect mobility. The presence of interface-trapped charges also acts to reduce the channel mobility and increases the sensitivity of the threshold voltage to temperature. The high critical electric field of SiC increases the stored energy in the switch output capacitance by 10× compared to silicon. For hard-switched converters, it is important to design SiC MOSFETs with a high saturation current to enable high-speed turn-on transients required to discharge the integral drain-source capacitance.     

Highly Miniaturized On‐Chip 180° Hybrid Employing Periodic Ground Strip Structure for Application to Silicon RFIC

A highly miniaturized on‐chip 180° hybrid employing periodic ground strip structure (PGSS) was realized on a silicon radio frequency integrated circuit. The PGSS was placed at the interface between SiO₂ film and silicon substrate, and it was electrically connected to top‐side ground planes through the contacts. Owing to the short wavelength characteristic of the transmission line employing the PGSS, the on‐chip 180° hybrid was highly miniaturized. Concretely, the on‐chip 180° hybrid exhibited good radio frequency performances from 37 GHz to 55 GHz, and it was 0.325 mm², which is 19.3% of a conventional 180° hybrid. The miniaturization technique proposed in this work can be also used in other fields including compound semiconducting devices, such as high electron mobility transistors, diamond field effect transistors, and light emitting diodes.     

一种新型高精度宽电压范围的CMOS温度传感器

介绍了一种用于环境温度监测的新型高精度宽电压范围的CMOS温度传感器,采用0.13μm标准CMOS工艺的厚氧器件实现,芯片面积为37μm×41μm。该温度传感器在-20～60°C的温度范围内,采用两点校正方法之后,温度误差为-0.2°C/0.5°C。该温度传感器可以在1.8～3.6V的电源电压范围内安全可靠地工作,并且具有较高的电源抑制比。测试结果表明,其输出电压斜率为3.9mV/°C,1.8V下功耗为1.3μW。     

十字差动式小视场超高精度太阳敏感器

设计了一种专门用于对日观测成 像稳像系统的超高精度太阳敏感器。针对传统的四象限 太阳敏感器的不足,设计了一种基于十字差动式太阳硅光电池片 的探测器,以提高灵敏度和抗干扰能力。该系统在有效视场 (1°)内具有10''的低误差。     

Monolithic pressure-flow sensor

A new silicon-based monolithic pressure-flow sensor has been developed. Its operation is based on the piezoresistive effect for pressure sensing and heat transfer for flow sensing. The sensor chip has a thermal isolation structure that is made of an oxidized porous silicon membrane. This structure thermally isolates the heating element located on the membrane from the rim of the chip. The sensor, in which the chip was mounted on a wall of an acrylate plastic pipe, was designed for biomedical applications. Measurements were made at pressures of 0-300 mmHg, water flow rates of 0-7 1/min, and fluid temperatures of 25-45°C. The temperature difference between the heating element and the fluid temperature sensing element was kept at 5°C. The sensor showed a pressure sensitivity of 1.32 µV/mmHg for 1-mA current supplied, a nonlinearity of 0.5 %F.S. for pressure sensing, an accuracy of ±10 %F.S. for flow sensing, and 90-percent response time of below 100 ms for flow sensing. The sensor was applied to the simultaneous measurements of pressure and flow rate in pulsedflow experimental systems.     

MOS Integrated silicon pressure sensor

An MOS integrated silicon-diaphragm pressure sensor has been developed. It contains two piezoresistors in a half-bridge circuit, and a new simple signal-conditioning circuit with a single NMOS operational amplifier. The negative temperature coefficient of the pressure sensitivity at the half-bridge is compensated for by a positive coefficient of the variable-gain amplifier with a temperature-sensitive integrated feedback resistor. The sensor was fabricated using the standard IC process, except for the thin diaphragm formation using the N2H4. H2O anisotropic etchant. Tile silicon wafer was electrostatically adhered to the glass plate to minimize induced stress. The -1750 ppm/°C temperature coefficient of sensitivity at the half-bridge was compensated for to less than +190 ppm/°C at the amplifier output in the 0- 70°C range. A less than 20-mV thermal-output offset shift was also Obtained after 26-dB amplification in the same temperature range.     

The dissolution mechanism of oxide precipitates in czochralski silicon degenerately doped with boron during high temperature annealing

The morphology of oxide precipitation induced defects in Czochralski silicon degenerately doped with boron and annealed at 800° and 1050°C, respectively, was examined using a transmission electron microscope. After an extended annealing at 800°C, the predominantly observed defects were the oxide precipitate platelets having the {001}-type habit planes and sides parallel to <110> and <112> crystallographic directions. The morphology of the oxide precipitates as derived from the residual oxygen calculation is suggested to be that of a thin octahedral shape. During a subsequent high temperature annealing, the octahedral precipitate platelets became thermodynamically unstable and dissolved. Based upon the defect morphology observed after a 1050°C anneal, it is suggested that the dissolving precipitate introduces a tensile strain into the surrounding silicon lattice. Contrary to precipitate growth, the lattice strain introduced by precipitate dissolution is relieved primarily through mechanisms involving vacancy injection from the precipitate interface and a condensation of excess silicon interstitials via a formation of an interstitial-type dislocation loop.     

Piezoelectric Sensors Operating at Very High Temperatures and in Extreme Environments Made of Flexible Ultrawide-Bandgap Single-Crystalline AlN Thin Films

Extreme environments are often faced in energy, transportation, aerospace, and defense applications and pose a technical challenge in sensing. Piezoelectric sensor based on single-crystalline AlN transducers is developed to address this challenge. The pressure sensor shows high sensitivities of 0.4–0.5 mV per psi up to 900 °C and output voltages from 73.3 to 143.2 mV for input gas pressure range of 50 to 200 psi at 800 °C. The sensitivity and output voltage also exhibit the dependence on temperature due to two origins. A decrease in elastic modulus (Young's modulus) of the diaphragm slightly enhances the sensitivity and the generation of free carriers degrades the voltage output beyond 800 °C, which also matches with theoretical estimation. The performance characteristics of the sensor are also compared with polycrystalline AlN and single-crystalline GaN thin films to investigate the importance of single crystallinity on the piezoelectric effect and bandgap energy-related free carrier generation in piezoelectric devices for high-temperature operation. The operation of the sensor at 900 °C is amongst the highest for pressure sensors and the inherent properties of AlN including chemical and thermal stability and radiation resistance indicate this approach offers a new solution for sensing in extreme environments.     

MEMS based low cost piezoresistive microcantilever force sensor and sensor module

In the present work, we report fabrication and characterization of a low-cost MEMS based piezoresistive micro-force sensor with SU-8 tip using laboratory made silicon-on-insulator (SOI) substrate. To prepare SOI wafer, silicon film (0.8 µm thick) was deposited on an oxidized silicon wafer using RF magnetron sputtering technique. The films were deposited in argon (Ar) ambient without external substrate heating. The material characteristics of the sputtered deposited silicon film and silicon film annealed at different temperatures (400–1050 °C) were studied using atomic force microscopy (AFM) and X-ray diffraction (XRD) techniques. The residual stress of the films was measured as a function of annealing temperature. The stress of the as-deposited films was observed to be compressive and annealing the film above 1050 °C resulted in a tensile stress. The stress of the film decreased gradually with increase in annealing temperature. The fabricated cantilevers were 130 μm in length, 40 μm wide and 1.0 μm thick. A series of force–displacement curves were obtained using fabricated microcantilever with commercial AFM setup and the data were analyzed to get the spring constant and the sensitivity of the fabricated microcantilever. The measured spring constant and sensitivity of the sensor was 0.1488 N/m and 2.7 mV/N. The microcantilever force sensor was integrated with an electronic module that detects the change in resistance of the sensor with respect to the applied force and displays it on the computer screen.     

三维螺旋极板电容传感器的静态分析与设计

针对电容传感器检测场较为复杂的特点,借助ANSYS软件对其进行三维静态模拟,分析了传感器结构参数对三维检测场的均匀性与灵敏度等指标的影响。通过有限元计算和优化设计,得到了最优的传感器结构参数,如屏蔽罩半径R3=27.37mm,极板长度L=207.39mm,极板旋转角度θP=270°,极板张角θ=135°等。优化后的传感...