Influence of polycrystalline silicon as electrical shield on reliability and stability of piezoresistive sensors

In this paper, the influence of polycrystalline silicon as a protective field shield on the reliability and stability of piezoresistive silicon sensors is investigated. For this purpose, the behaviour of piezoresistive sensors with and without polycrystalline silicon shield is observed under changes of environmental condition, such as relative humidity and temperature. The obtained sensor-offset change under humidity stimulation is smaller than that observed by temperature excitation. The samples with polycrystalline silicon shield exhibit a lower humidity and temperature coefficients as compared to the samples without this shield. The values of uncertainties in measurement are evaluated according to the ISO “Guide to the Expression of Uncertainties in Measurement” (GUM). The uncertainty contribution caused by internal disturbing of the sensors can be neglected. Comparing two types of piezoresistive sensors investigated, the samples with polycrystalline silicon shield produce a considerably reduction of all measurement uncertainty contributions. The results show that an additional polycrystalline silicon shield between two insulating layers connected to the supply voltage, which provides a determined potential distribution inside the passivation layer stack, improves the device reliability and the accuracy of measurement.     

Reliability of wireless sensors with code attestation for intrusion detection

Wireless sensor nodes are widely used in many areas, including military operation surveillance, natural phenomenon monitoring, and medical diagnosis data collection. These applications need to store and transmit sensitive or secret data, which requires intrusion detection mechanisms be deployed to ensure sensor node health, as well as to maintain sensor quality of service and survivability. Because wireless sensors have inherent resource constraints, it is crucial to reduce energy consumption due to intrusion detection activities. In this paper by means of a probability model, we analyze the best frequency at which intrusion detection based on code attestation on the sensor node should be performed so that the sensor reliability is maximized by exploiting the trade-off between the energy consumption and intrusion detection effectiveness. When given a set of parameter values characterizing the operational and networking conditions, the system verifier can dynamically set the intrusion detection rate identified by the mathematical model to maximize the sensor reliability and the expected sensor lifetime.     

大规模发布／订阅系统中的可靠性模型

大多数Internet上的大规模发布/订阅系统,其覆盖网络是不可靠的,系统的可靠性和处理故障的能力是一个挑战性的问题.基于轨迹序列和线性时态逻辑定义系统的可靠性条件,是路由算法可靠性分析的基础.设计了崩溃/恢复模式的路由协议,维持一致的、共享的系统状态,有效地处理具有局部性、临时性的路由器故障和链路故障.     

Development of high sensitivity tin oxide based sensors for gas/odour detection at room temperature

An effort has been made to develop thick film tin oxide gas sensors which could detect various gases/odours at room temperature. To achieve this, the fabricated sensors were annealed in oxygen plasma for various durations. It was then found that, the room temperature sensitivity of such sensors was increased to about ten times as compared to the sensitivity of the non-annealed sensors. Further, plasma annealed sensors are found to be practically independent of temperature and the room temperature sensitivity of these sensors are found to be about 1.5 times the sensitivity of the conventional sensors at its operating temperature of 300°C. Studies on the variation of d.c. resistance, sensitivity, temporal response, current–temperature characteristics and impedance spectroscopy with the annealing time have also been made. These studies reveal that, with the increase in annealing time, there is a permanent gradual reduction in the d.c. resistance of annealed sensors. Further, it is also observed that with the increase in annealing time, the response time improves, barrier height reduces, barrier capacitance increases and the dependence of the sensitivity with temperature reduces while the sensitivity itself improves many-fold.     

Pulsed laser deposited Y-doped BaZrO3 thin films for high temperature humidity sensors

Pulsed laser deposited (PLD) Y-doped BaZrO₃ thin films (BaZr_1-xY_xO_3-y/2, x = 0.2, y > 0), were investigated as to their viability for reliable humidity microsensors with long-term stability at high operating temperatures (T > 500 °C) as required for in situ point of source emissions control as used in power plant combustion processes. Defect chemistry based models and initial experimental results in recent humidity sensor literature [1] and [2]. indicate that bulk Y-doped BaZrO₃ could be suitable for use in highly selective, high temperature compatible humidity sensors. In order to accomplish faster response and leverage low cost batch microfabrication technologies we have developed thin film deposition processes, characterized layer properties, fabricated and tested high temperature humidity micro sensors using these thin films. Previously published results on sputtering Y-doped BaZrO₃ thin films have confirmed the principle validity of our approach [3]. However, the difficulty in controlling the stoichiometry of the films and their electrical properties as well as mud flat cracking of the films occurring either at films thicker than 400 nm or at annealing temperature above 800 °C have rendered sputtering a difficult process for the fabrication of reproducible and reliable thin film high temperature humidity microsensors, leading to the evaluation of PLD as alternative deposition method for these films.X-ray Photoelectron Spectroscopy (XPS) data was collected from as deposited samples at the sample surface as well as after 4 min of Ar⁺ etching. PLD samples were close to the desired stoichiometry. X-ray diffraction (XRD) spectra from all as deposited BaZrO₃:Y films show that the material is polycrystalline when deposited at substrate temperatures of 800 °C. AFM results revealed that PLD samples have a particle size between 32 nm and 72 nm and root mean square (RMS) roughness between 0.2 nm and 1.2 nm. The film conductivity increases as a function of temperature (from 200 °C to 650 °C) and upon exposure to a humid atmosphere, supporting our hypothesis of a proton conduction based conduction and sensing mechanism. Humidity measurements are presented for 200–500 nm thick films from 500 °C to 650 °C at vapor pressures of between 0.05 and 0.5 atm, with 0.03–2% error in repeatability and 1.2–15.7% error in hysteresis during cycling for over 2 h. Sensitivities of up to 7.5 atm⁻¹ for 200 nm thick PLD samples at 0.058 atm partial pressure of water were measured.     

基于Copula的ERCS系统软硬件综合可靠性建模与分析

在现代的电子业、制造业和工业控制等系统中,系统的可靠性越来越重要,而嵌入式实时控制系统(Embedded Real-time Control System,ERCS)大部分是控制系统的核心部分,其系统可靠性尤为重要。首先对嵌入式实时控制系统软硬件进行形式化抽象定义;然后对不可再分的软件模块和IP硬核进行可靠性建模,应用Copula函数对软件子系统和硬件子系统分别进行建模,并建立了ERCS系统的软硬件综合可靠性Copula模型;最后应用建立的模型,对具体的系统进行了软硬件综合可靠性计算。通过实例计算可知,用Copula建立的ERCS软硬件综合可靠性模型考虑了软件各个模块间、硬件各个IP硬核间和软硬件间的相依性,使得ERCS软硬件综合可靠性比独立时有所提高。     

激光装置可靠性仿真环境研究

针对某大型激光装置可靠性研究工作的需要，基于面向对象的设计、分析与多模型建模方法，提出了激光装置可靠性仿真环境(SERLF)的结构和功能，研究了实现该仿真环境的关键技术，给出了建立大型激光装置可靠性仿真环境的思路。在实际应用中，利用已建成的SERLF对某大型激光装置能源模块的性能可靠性进行了研究，研究成果表明该仿真环境的体系结构是合理的，能够满足用户对某大型激光装置进行灵活地可靠性建模、仿真以及仿真结果分析的需求。     

机电产品可靠性预计方法与程序研究

分析了开展可靠性预计的目的和作用,阐述了电子产品可靠性预计的基本方法：相似设备预计法、设备复杂性预计法、功能预计法、元器件计数预计法及应力分析法,探讨了电子产品可靠性预计的基本程序,同时还分析了机械零部件可靠性预计方法──静强度可靠性预计法的基本程序。     

交织码在无线通信可靠性中的应用研究

在对无线通信可靠性要求较高的系统中，如何保证信息的无误接收是关键。本文讨论了交织码的纠错原理，给出了具体的编码设计，对可靠性的提高进行了定性和定量的分析，并在工程中得到了验证。     

火力发电机组计算机监控系统高可靠性的设计

介绍了火力发电机组计算机监控系统的网络结构、软硬件设计思想及其具体实现方法。     

基于差分传输的多机通信可靠性

借助于差分传输的RS－485总线，以微控制器为核心的数据采集系统可方便地构成多机系统，可同时并行进行数据采集，然而，随着多机系统的应用，数据通信可靠性成为整个应用系统的关键。全面提出了提高多机系统通信可靠性的若干硬件和软件措施，这些措施在实际应用中表明，效果良好。     

微机电系统内温度传感器的负荷效应及其补偿

传感器对被测对象的负荷效应是微机电系统中不可忽视的一个问题.阐述了负荷效应的基本概念,提出了一种通过实验获取传感器负荷效应的方法,称之为"二减一法",并以聚合酶链式反应芯片内的温度传感器为例详细论述了该方法的具体应用.     

地铁直流牵引供电继电保护系统的可靠性评估

随着城市轨道交通的迅速发展,对地铁可靠性、安全性的关注也越来越强,地铁继电保护系统已成为牵引供电系统安全运行的保证。过去,人们总是把可靠性分析的重点放在一次系统上,这就导致了二次系统可靠性理论研究的延缓。本文从可靠性建模的角度,找出影响继电保护可靠性的各种因素,引入可靠性评估方法,建立继电保护装置及其系统的可靠性模型。克服了过去只关注保护装置本身可靠性的局限,并着重研究了二次回路中其它设备、保护动作逻辑和保护配置方案对继电保护可靠性的影响。     

HREELS study of Au/Fe2O3 thick film gas sensors

CO gas sensors based on Au-doped/Fe₂O₃ thick films were studied in ultra-high-vacuum (UHV) by high resolution electron energy loss spectroscopy (HREELS). Several adsorbed species were identified on HREEL spectra collected at room temperature on thick films annealed at different temperatures. Among these, carboxylate and formate species were postulated as intermediates of the complex reactions occurring on the surface between carbon monoxide and oxygen.

The catalytic and sensing properties of the Au/iron oxide samples towards CO have been also investigated showing the better performances of the co-precipitated samples in comparison to impregnated ones and the influence of annealing temperature. Data reported were correlated to the presence of oxygenate intermediates detected by HREELS.     

Potential of SAR sensors TerraSAR-X, ASAR/ENVISAT and PALSAR/ALOS for monitoring sugarcane crops on Reunion Island

Multi-temporal TerraSAR-X, ASAR/ENVISAT and PALSAR SAR data acquired at various incidence angles and polarizations were analyzed to study the potential of these new spaceborne SAR systems for monitoring sugarcane crops. The sensitivity of different radar parameters (wavelength, incidence angles, and polarization) to sugarcane growth stages was analyzed to determine the most suitable radar configuration for better characterisation of sugarcane fields and in particular the monitoring of sugarcane harvest.Correlation between backscattered signals and crop height was also carried out. Radar signal increased quickly with sugarcane height until a threshold height, which depended on radar wavelength and incidence angle. Beyond this threshold, the signal increased only slightly, remained constant, or even decreased. The threshold height is higher with longer wavelengths (L-band in comparison with C- and X-bands) and higher incidence angles (~ 40° in comparison with ~ 20°).The radar backscattering coefficients (σ°) were also compared to the Normalized Difference Vegetation Index (NDVI) calculated from SPOT-4/5 images. Results showed a high correlation between the behaviors of σ° and NDVI as a function of sugarcane crop parameters. A decrease in NDVI for fully mature sugarcane fields due to drying of the sugarcane (water stress) was also observed in the radar signal. This decrease in radar signal was of the same order as the decrease in radar signal after the sugarcane harvest. In general, it is more suitable to monitor the sugarcane harvest using high incidence angles regardless of the radar wavelength. SAR data in L- and C-bands showed an ambiguity between the signals of ploughed fields and those of fields in vegetation because of the high sensitivity of the radar signal at these wavelengths to surface roughness of bare soils. Indeed, sometimes the radar signal of ploughed fields was of the same order as that of harvested or mature sugarcane fields. Results showed better discrimination between ploughed fields and sugarcane fields in vegetation (sugarcane canopy) when using TerraSAR-X data (X-band).Concerning the influence of radar polarization, results showed that the co-polarizations channels (HH and VV) were well correlated, but had slightly less potential than cross-polarization channels (HV and VH) for the detection of the sugarcane harvest. Finally, SAR data at high spatial resolution were shown to be useful and necessary for better analysis of SAR images when the fields were of small size.     

火炮火控系统软件可靠性定量评估方法研究

火炮火控系统软件的可靠性直接决定着火炮战技性能的发挥．软件可靠性模型是定量评估软件可靠性的技术基础。通过对软件可靠性概念和软件可靠性模型的分析研究。提出了综合使用Nelson模型和硬一软件复合系统结构模型的可靠性定量评估方法．该方法可以综合两种模型的优点,实现对火炮火控系统软件可靠性的有效评估。     

可修K/N(G)系统可靠性指标的仿真算法研究

利用Monte Carlo随机抽样技术,采用而向事件和面向固定时间间隔的双推进机制,提出了基于事件模块的可修K/N(G)系统可靠性指标仿真算法,算法能有效解决非指数分布类情况下,考虑部件已工作时间和不同维修策略等因素影响时,解析方法难以处理的系统可靠性分析难题,并且算法能同时对系统可靠性的平均指标和瞬时指标进行分析,从而可为指导装备的使用与维修管理提供有力的依据.算法采取的双推进机制保证了算法的仿真效率,基于事件模块的设计思想保证了算法的可扩展性,而且,经与解析算法比较,验证了仿真算法的正确性.     

基于连通可靠度的交通网络重要路段评价算法

如何提高交通网络的连通可靠度,是交通领域的一个重要问题,通过提高重要路段的连通度来提高交通网络的连通可靠度是一个重要的方法。引入复杂网络理论中接近度、关键度等概念,结合交通网络中的流量分布,利用图的对偶理论识别出交通网络的重要路段,提出评价交通网络中路段重要度的算法,通过实例验证所提方法的有效性和应用价值。     

The low temperature polysilicon (LTPS) thin film MOS Schottky diode on glass substrate for low cost and high performance CO sensing applications

The Au/SnO₂/n-LTPS MOS Schottky diode prepared on a glass substrate for carbon monoxide (CO) sensing applications is studied. The n-LTPS (n-type low temperature polysilicon) is prepared by excimer laser annealing and PH₃ plasma treatment of an amorphous Si thin film on glass substrate. The developed Schottky diode exhibits a high relative response ratio of ∼546% to 100 ppm CO ambient under condition of 200 °C and −3 V bias. The response ratio is better than the reported SnO₂ based resistive type CO sensors of 100% and 37%, respectively on poly-alumina and glass substrates or comparable to 390% of Pt-AlGaN/GaN Schottky diode CO sensor. Thus, the Au/SnO₂/n-LTPS Schottky diode has the potential to develop a low cost high performance CO sensor.