VHF single-crystal silicon elliptic bulk-mode capacitive disk resonators-part I: design and modeling

This work, the first of two parts, presents the design and modeling of VHF single-crystal silicon (SCS) capacitive disk resonators operating in their elliptical bulk resonant mode. The disk resonators are modeled as circular thin-plates with free edge. A comprehensive derivation of the mode shapes and resonant frequencies of the in-plane vibrations of the disk structures is described using the two-dimensional (2-D) elastic theory. An equivalent mechanical model is extracted from the elliptic bulk-mode shape to predict the dynamic behavior of the disk resonators. Based on the mechanical model, the electromechanical coupling and equivalent electrical circuit parameters of the disk resonators are derived. Several considerations regarding the operation, performance, and temperature coefficient of frequency of these devices are further discussed. This model is verified in part II of this paper, which describes the implementation and characterization of the SCS capacitive disk resonators.     

High-Q single crystal silicon HARPSS capacitive beam resonators with self-aligned sub-100-nm transduction gaps

This paper reports on the fabrication and characterization of high-quality factor (Q) single crystal silicon (SCS) in-plane capacitive beam resonators with sub-100 nm to submicron transduction gaps using the HARPSS process. The resonating element is made of single crystal silicon while the drive and sense electrodes are made of trench-refilled polysilicon, yielding an all-silicon capacitive microresonator. The fabricated SCS resonators are 20-40 /spl mu/m thick and have self-aligned capacitive gaps. Vertical gaps as small as 80 nm in between 20 /spl mu/m thick silicon structures have been demonstrated in this work. A large number of clamped-free and clamped-clamped beam resonators were fabricated. Quality factors as high as 177000 for a 19 kHz clamped-free beam and 74000 for an 80 kHz clamped-clamped beam were measured under 1 mtorr vacuum. Clamped-clamped beam resonators were operated at their higher resonance modes (up to the fifth mode); a resonance frequency of 12 MHz was observed for the fifth mode of a clamped-clamped beam with the fundamental mode frequency of 0.91 MHz. Electrostatic tuning characteristics of the resonators have been measured and compared to the theoretical values. The measured Q values of the clamped-clamped beam resonators are within 20% of the fundamental thermoelastic damping limits (Q/sub TED/) obtained from finite element analysis.     

单硬盘网络终端信息物理隔离的设计与实现

阻止黑客攻击,预防上网终端机密信息泄漏已成为信息安全领域研究的重要课题.基于双硬盘实现网络信息物理隔离是目前采用较多的技术方案,但该方案实现成本较高.讨论了在单硬盘双网环境下,如何实现基于单硬盘的内外网信息的物理隔离.对硬盘的分区表结构及分区表链进行了深入分析,给出了一种单硬盘网络终端信息物理隔离的硬件设计实现方案,重点讨论了双网信息物理隔离的机制和实现方法,详细介绍了控制程序的设计方法和流程.根据设计方案研发的安全产品经国内多家单位安装使用反应较好,达到了低成本高安全性地实现上网终端双网信息物理隔离的设计目标.     

直拉硅单晶生长过程建模与控制研究综述

硅单晶是最重要的半导体材料,90%的半导体器件和集成电路芯片都制作在硅单晶上.随着集成电路技术的快速发展,对硅单晶的品质要求也不断提高.直拉法是生产硅单晶的主要方法,其科学原理与方法、生长技术与工艺、控制策略与手段一直是理论界和产业界高度关注和不断研究的热点.本文针对直拉法电子级硅单晶生长过程,以晶体生长基本原理为基础,从生长建模、变量检测、控制方法等方面进行了全面的阐述,特别针对当今大尺寸、高品质硅单晶生长的要求,总结了目前所取得的主要研究成果与面临的问题,并提出了相应的研究思路和方法.     

Fracture and fatigue behavior of single crystal silicon microelements and nanoscopic AFM damage evaluation

Quasi-static bending and fatigue tests of single-crystal silicon microelements fabricated by photoetching were performed. The microelements were subjected to simple bending and three-point bending with two-support roll length of 1.5 mm. The tests were conducted by using a specially designed electromagnetic actuator based testing machine (load range: 0.1 mN–5 N, accuracy: 0.02 mN), which enables mechanical testing including fatigue of microelements. Mechanical testing including fatigue of microelements could be performed with sufficient precision. Single-crystal silicon microelements deformed elastically until final catastrophic failure, showing a brittle nature. The influence of specimen size on quasi-static fracture behavior was investigated: fracture strength increased with a decrease in sample width, and the maximum fracture strength reached 7.7 GPa. The influence of water on fatigue strength was discussed. The fracture surface and sample surface were examined using an atomic force microscope. Nanoscopic damage during testing was evaluated, and the fracture mechanisms were discussed. Received 20 October 1997/Accepted 5 January 1998     

单晶硅等效机械特性的实验研究

单晶硅广泛应用于MEMS器件中.根据等效刚度原理,单晶硅可以简化为各向同性材料.介绍了一种采用湿法腐蚀工艺加工的倾斜硅梁,并利用频率响应特性测试了其等效杨氏模量和等效泊松比.采用(100)硅片制作了八组不同尺寸参数的倾斜硅梁.梁的宽度尺寸间隔为30 μm,尺寸范围为30 μm～ 240 μm,对应宽高比为1/8～1.实验结果证明了等效杨氏模量与倾斜梁尺寸无关,而等效泊松比不仅和单晶硅的特性相关,而且受倾斜梁尺寸的影响.实验得到的等效杨氏模量为170.51 GPa±2.08 GPa.对等效泊松比的测量结果在Matlab中进行了多项式拟合,7次拟合多项式已经与测试结果具有很好的一致性.     

A high Q micromachined single crystal silicon bulk mode resonator with pre-etched cavity

In this paper, a novel method of fabricating micromachined single crystal silicon bulk mode resonators is demonstrated. The most distinguishing feature of this method is that the resonator structure is fabricated and released simultaneously in the end of the process, as a cavity for structure release is pre-etched in the substrate layer. The advantages of this process include: simplifying the fabrication process by fabricating and releasing the device structure simultaneously; enhancing fabrication yield through eliminating the sacrificial release step needed for existing process. The complete process has been validated and prototypes have been fabricated. The transmission performance of a 4.13 MHz Lamé mode square resonator fabricated using this method is presented, with a quality factor of 8,400 in air and exceeding one million at pressure of 0.11 mbar, respectively.     

微小型一体化电容式测压器的设计与实现

设计了一种高精度、低成本的微小型电容式测压器.该测压器利用壳体本身作为压力敏感元件,将压力信号的改变通过瞬变小电容转换电路转换为电容值的变化,利用差动式直流充电法将电容信号转换为单片机可以采样存储的电压信号.该电容式测压器具有功耗低、体积小、分辨率高、成本低的特点.详细阐述了微小型电容式测压器的基本原理和具体实现,并通过比较ANSYS软件仿真结果和实测数据证明其可行性.     

Plastic deformation of nanometric single crystal silicon wire inAFM bending test at intermediate temperatures

This paper focuses on revealing specimen size and temperature effects on mechanical properties of nanometric single crystal silicon (SCS) wires at intermediate temperatures. Mechanical properties of the nanometric SCS wires were characterized by bending tests with an atomic force microscope (AFM). The fixed-fixed SCS wires with widths from 200 nm to 800 nm and a thickness of 255 nm were fabricated on a silicon diaphragm by means of field-enhanced anodization with AFM and anisotropic wet etching. The AFM bending tests of the SCS wires were carried out at temperatures ranging from 295 K to 573 K in high vacuum. Elastic moduli of the SCS wires showed temperature dependence, but had no size effect. However, plastic properties such as critical resolved shear stress and plastic deformation range showed a clear dependence on both of specimen size and temperature. The critical resolved shear stress ranged from 4.2 GPa to 7.2 GPa, which was 10 times higher than that in a millimeter scale specimen. Force-displacement curves and AFM observations of the slip line also showed that plastic flow in the nanometric SCS wires was induced at 373 K, which was very close to room temperature. A dislocation model is proposed on the basis of the AFM observation, which was able to rationalize that the nanometric specimen had a large influence on the activation Gibbs free energy in the thermal activated process     

Robust miniaturized amplification unit for piezoelectric actuators: comparison of single crystal silicon and superelastic nickel titanium as membrane materials

In this work, amplification units made of robust metallic nickel titanium (NiTi) and single crystal silicon are compared and evaluated for the application in miniaturized piezoelectric actuators for flow control purposes. The amplification mechanism with a sliced membrane structure is based on a mechanical lever in order to amplify the low piezoelectrically induced deformation. Therefore, an enhanced output stroke can be provided up to high frequencies. The different membrane fabrication processes using laser ablation for the NiTi alloy and deep reactive ion etching for the silicon substrate, as well as the results of finite element simulations and experimental measurements are reported. An amplification factor of 9 has been achieved for an optimized load transmission point position. The dynamic response shows a quality factor of 25 and 494 at the first fundamental mode for NiTi and silicon membranes, respectively. Compared to silicon, NiTi shows enhanced properties against failure and facilitates the integration process.     

A single crystal silicon 3 dimensional processing technique with applications in large displacement electrostatic actuation

 A new process has been developed to produce mechanical structures of multiple levels on a silicon substrate. The process lends itself to high aspect ratio bulk micromachining of single crystal silicon. Structures can be fabricated at multiple levels with a single lithography step and without alignment requirements. Any required difference in height between levels is defined precisely at intermediate etch steps. One application of this process utilizes the out of plane asymmetries produced by the multiple levels to create a large displacement, large force and highly linear out of plane actuator stage. This technique is easily combined with single level high aspect ratio MEMS processing methods. Received: 10 August 2001/Accepted: 24 September 2001     

移动硬盘硬件加密的设计与实现

安全存储是继通信保密问题之后信息安全领域的一个研究热点。设计并实现了一种基于FPGA的USB移动硬盘硬件加密方案,提出了一种采用具有安全计算功能智能卡的双向认证和密钥获取技术及一种簇级别的数据完整性验证方法。实验结果表明,系统在安全性和读写速率方面均具有较大提升,可用于防止因移动硬盘丢失、被盗、废弃引起的泄密问题及对数据的非法篡改。     

Quality based design approach for a single crystal silicon microactuator using DOE technique and response surface model

 This paper discusses the use of DOE technique and response surface model as an efficient quality based design approach to optimize coupled electromechanical behavior of a single crystal silicon micro-actuator for hard disk drives (HDD). A number of experiments for different settings of the microactuator parameters are planned and analyzed. The fitted response surface models are built using the regression technique. Finite element method (FEM), boundary element method (BEM) and optimization techniques are utilized to predict and verify the microactuator performance. Example results show that the proposed approach is effective to guide microactuator design to achieve a robust and reliable design in a most efficient way. Received: 5 July 2001/Accepted: 17 October 2001     

Novel capacitive sensor: Fabrication from carbon nanotube arrays and sensing property characterization

A sandwich-structured gas sensor based on vertically aligned carbon nanotube (CNT) arrays was fabricated and investigated for ammonia and formic acid sensing. Vertically aligned CNT arrays were synthesized by acetone pyrolysis in anodized aluminum oxide (AAO) templates without the use of catalysts. The capacitance change of the sensor with target gas exposure was used as the sensing parameter. The sensor had relatively short response and recovery time. It was completely recovered within 6 min, without requiring any external stimuli. The possible mechanism of the responses was also discussed.     

基于椭圆曲线的CA系统的设计与实现

在网上交易中,作为交易双方相互信赖的第三方,CA系统的主要用途是发放和验证数字证书.因此,保证CA系统的安全性具有十分重要的意义.椭圆曲线密码体制不仅具有密钥短和计算效率高的优点,而且能够提供最高的位安全强度.从实践的角度,运用系统的方法,在研讨当前CA系统基础之上,将椭圆曲线密码体制应用于CA系统.在目前的电子商务交易中,基于椭圆曲线的CA系统的设计与实现,为认证系统的设计提供了一种新的参考.     

The surface/bulk micromachining (SBM) process: a new method forfabricating released MEMS in single crystal silicon

This paper presents the surface/bulk micromachining (SBM) process to allow fabricating released microelectromechanical systems using bulk silicon. The process starts with a (111)-oriented silicon wafer. The structural patterns are defined using the reactive ion etching technique used in surface micromachining. Then the patterns, as well as sidewalls, are passivated with an oxide film, and bare silicon is exposed at desired areas. The exposed bare silicon is further reactive ion etched, which defines sacrificial gap dimensions. The final release is accomplished by undercutting the exposed bulk silicon sidewalls in aqueous alkaline etchants. Because {111} planes are used as etch stops, very clean structural surfaces can be obtained. Using the SBM process, 5-, 10-, and 100-μm-thick arbitrarily-shaped single crystal silicon structures, including comb-drive resonators, at 5-, 30-, and 100-μm sacrificial gaps, respectively, are fabricated. An electrostatic actuation method using p-n junction isolation is also developed in this paper, and it is applied to actuate comb-drive resonators. The leakage current and junction capacitance of the reversed-biased p-n junction diodes are also found to be sufficiently small for sensor applications. The developed SBM process is a plausible alternative to the existing micromachining methods in fabricating microsensors and microactuators, with the advantage of using single crystal silicon     

Structural and capacitive humidity sensing properties of nanocrystal magnetite/silicon nanoporous pillar array

A composite thin film was fabricated by coating nanocrystal magnetite (nc-Fe₃O₄) on silicon nanoporous pillar array (Si-NPA), which shows a regular hierarchical structure composed by the pillar array in micron dimension and the nanoporous structure in the film of Fe₃O₄. Capacitive humidity sensors were made based on nc-Fe₃O₄/Si-NPA and the corresponding sensing properties were investigated. The experimental results disclosed that nc-Fe₃O₄/Si-NPA sensor exhibits high sensitivity, strong output signal intensity, and short response times. These high performances of nc-Fe₃O₄/Si-NPA sensor are explained on the basis of the structural and compositional factors of nc-Fe₃O₄/Si-NPA.     

基于椭圆曲线数字签名系统的设计与实现

通过网络传输获取信息,这在人们日常生活中日益普及.信息在网络传输过程中面临着被截获、被修改等安全性威胁.数字签名技术能够在数据传输过程中提供一系列的安全保障服务.基于C/C++和椭圆曲线数字签名算法,设计并实现了一个数字签名系统.测试表明,该系统具有良好性能并满足签名算法的安全性要求.     

RAID0.5: design and implementation of a low cost disk array data protection method

RAID has long been established as an effective way to provide highly reliable as well as high-performance disk subsystems. However, reliability in RAID systems comes at the cost of extra disks. In this paper, we describe a mechanism that we have termed RAID0.5 that enables striped disks with very high data reliability but low disk cost. We take advantage of the fact that most disk systems use offline backup systems for disaster recovery. With the use of these offline backup systems, the disk system needs to only replicate data since the last backup, thus drastically reducing the storage space requirement. Though RAID0.5 has the same data loss characteristics of traditional mirroring, the lower storage space comes at the cost of lower availability. Thus, RAID0.5 is a tradeoff between lower disk cost and lower availability while still preserving very high data reliability. We present analytical reliability models and experimental results that demonstrate the enhanced reliability and performance of the proposed RAID0.5 system.