Optical deflection measurement for characterization of microelectromechanical systems (MEMS)

Nonintrusive measurement of small out-of-plane motions of microscale structures is critical to the development of microelectromechanical systems (MEMS). This paper presents a low-cost deflection measurement system for MEMS structures based on a fiber optic displacement sensor. The system is demonstrated in the characterization of a microwave switch. The deflection system had a demonstrated sensitivity of 290/spl plusmn/32 /spl mu/V/nm over a deflection range of 100 /spl mu/m. The calibration and linearity of the system are described, and the static and dynamic performance is compared to more elaborate systems.     

Design, fabrication and characterization of a capacitive micromachined ultrasonic probe for medical imaging

In this paper we report the design, fabrication process, and characterization of a 64-elements capacitive micromachined ultrasonic transducer (cMUT), 3 MHz center frequency, 100% fractional bandwidth. Using this transducer, we developed a linear probe for application in medical echographic imaging. The probe was fully characterized and tested with a commercial echographic scanner to obtain first images from phantoms and in vivo human body. The results, which quickly follow similar results obtained by other researchers, clearly show the great potentiality of this new emerging technology. The cMUT probe works better than the standard piezoelectric probe as far as the axial resolution is concerned, but it suffers from low sensitivity. At present this can be a limit, especially for in depth operation. But we are strongly confident that significant improvements can be obtained in the very near future to overcome this limitation, with a better transducer design, the use of an acoustic lens, and using well matched, front-end electronics between the transducer and the echographic system.     

用于微机电系统的类金刚石膜制备及表征

采用等离子体源离子注入和电子回旋共振-微波等离子体辅助化学气相沉积技术相结合的方法在Si衬底上制备出了性能良好的类金刚石膜.通过共聚焦Raman光谱验证了薄膜的类金刚石特性,用原子力显微镜、微摩擦计和扫描电镜等对薄膜的表面形貌、摩擦系数和耐磨损性能进行了表征和测量.结果表明,用离子注入法制备过渡层大大提高了DLC膜与衬底的结合强度,薄膜的表面比较光滑,粗糙度大约为0.198 nm,具有较低的摩擦系数(0.1～0.15),具有较好的耐磨损性能.     

Fabrication of diamond microstructures for microelectromechanical systems (MEMS) by a surface micromachining process

Selective polycrystalline diamond thin film has been grown on a silicon dioxide/silicon substrate using high pressure microwave plasma-assisted chemical vapor deposition from a gas mixture of methane and hydrogen at a substrate temperature of 950°C. A simple process flow has been developed to fabricate diamond microstructures such as diamond beams and cantilever beams using surface micromachining and photolithography for the first time. Scanning electron and optical microscopy has been used to characterize the surface micromachined diamond microstructures.     

Low temperature fabrication of immersion capacitive micromachined ultrasonic transducers on silicon and dielectric substrates

A maximum processing temperature of 250/spl deg/C is used to fabricate capacitive micromachined ultrasonic transducers (CMUTs) on silicon and quartz substrates for immersion applications. Fabrication on silicon provides a means for electronics integration via post-complementary metal oxide semiconductor (CMOS) processing without sacrificing device performance. Fabrication on quartz reduces parasitic capacitance and allows the use of optical displacement detection methods for CMUTs. The simple, low-temperature process uses metals both as the sacrificial layer for improved dimensional control, and as the bottom electrode for good electrical conductivity and optical reflectivity. This, combined with local sealing of the vacuum cavity by plasma-enhanced chemical-vapor deposition of silicon nitride, provides excellent control of lateral and vertical dimensions of the CMUTs for optimal device performance. In this paper, the fabrication process is described in detail, including process recipes and material characterization results. The CMUTs fabricated for intravascular ultrasound (IVUS) imaging in the 10-20 MHz range and interdigital CMUTs for microfluidic applications in the 5-20 MHz range are presented as device examples. Intra-array and wafer-to-wafer process uniformity is evaluated via electrical impedance measurements on 64-element ring annular IVUS imaging arrays fabricated on silicon and quartz wafers. The resonance frequency in air and collapse voltage variations are measured to be within 1% and 5%, respectively, for both cases. Acoustic pressure and pulse echo measurements also have been performed on 128 /spl mu/m/spl times/32 /spl mu/m IVUS array elements in water, which reveal a performance suitable for forward-looking IVUS imaging at about 16 MHz.     

Design and fabrication of a capacitance switch array usable on aDTCXO

This work is based on a premanufacturing evaluation of a capacitance switch array (CSA). The main idea of this study is the replacement in a digitally temperature-compensated crystal oscillator (DTCXO) of the usual compensation system composed of a digital analog converter coupled with a varactor, in order to decrease the total power consumption and the supply voltage     

Design, fabrication and testing of a composite bracket for aerospace applications

In this paper the results of a programme, in which a composite bracket as a replacement for a metal forging was developed, will be presented. The finite-element method (FEM) in combination with an optimization module was used to design the bracket. Compared to its metal counterpart, the composite bracket demonstrated a weight reduction of 43%. Two composite brackets were fabricated by resin transfer moulding (RTM). One bracket was loaded statically to 1.38 × Design Ultimate Load. The bracket did not fail at this load level.     

Direct synthesis of nano-sized glass powders with spherical shape by RF (radio frequency) thermal plasma

A new route for obtaining very small, spheroid glass powders is demonstrated using an RF (radio frequency) thermal plasma system. During the process, four kinds of chemicals, here SiO₂, B₂O₃, BaCO₃, and K₂CO₃, were mixed at pre-set weight ratios, spray-dried, calcined at 250 °C for 3 h, and crushed into fragments. Then, they were successfully reformed into nano-sized amorphous powders (< 200 nm) with spherical shape by injecting them along the centerline of an RF thermal plasma reactor at ~ 24 kW. The as-synthesized powders show negligible (< 1%) composition changes when compared with the injected precursors of raw material compounds.     

一种MEMS平板型同位素微电池的设计与制作

针对倒三角直槽型或倒金字塔型能量转换结构的同位素微电池难于加工以及放射性薄膜不均匀等缺陷,设计了一种较为简单的平板型能量转换结构.引入金属区这一结构,增强了放射源薄膜的接触稳定性.63Ni放射源电镀实验最终得到了一组理想的短路电流和开路电压数据.结果表明,该结构与传统的能量转换结构相比有更稳定的功率输出.     

陶瓷基复合材料涡轮叶盘设计、制备与考核验证

涡轮转子是燃气涡轮发动机的核心部件。针对SiC/SiC涡轮叶盘设计、制备与考核验证开展研究,采用蛛网仿形(SWS)SiC纤维预制体作为涡轮叶盘的增强体,预制体表面分别沉积BN界面相与SiC基体,通“在线加工”方式对SiC/SiC涡轮叶盘分别进行粗加工和精加工,采用大气等离子喷涂方法制备环境障碍涂层,形成满足设计要求的涡轮叶盘。采用CT对SiC/SiC涡轮叶盘进行无损检测,表征叶盘内部缺陷分布。针对制备的SiC/SiC涡轮叶盘开展性能评价、超转试验、台架试验等考核验证,研究表明：SiC/SiC涡轮叶盘最大破坏强度达到300 MPa;在室温超转试验中,当转速达到n=104 166 r/min时,叶片发生断裂,当转速达到n=108 072 r/min时,轮体发生破裂;在发动机台架试验中,累积完成了N=994次最高转速n_max=60 000 r/min的循环载荷及N=100次最高转速n_max=70 000 r/min的循环载荷试车考核。2022年1月1日,SiC/SiC涡轮叶盘在株洲成功完成了首次飞行试验验证,这也是国内陶瓷基复合材料转子首次配装平台...     

大位移MEMS静电梳齿驱动器的设计及制作

文章提出了一种大位移低驱动电压的MEMS静电梳齿驱动器,对器件进行了设计、模拟、制作以及测试.梳齿驱动器的侧向不稳定性即侧向吸合现象限制了梳齿驱动器的最大驱动位移,发现侧向稳定因子S,随支撑梁刚度比ky/kx以及梳齿间隙g的增加而增加,随梳齿交叠长度的增加而减小;而驱动器的驱动电压随梳齿间隙的增加而升高.在以上研究的基础上,提出了一种采用小间隙无初始交叠、长度线性递增梳齿结构和高纵/横向刚度比的预弯曲支撑梁结构的梳齿驱动器.器件测试结果表明,驱动电压71V时,可以达到100μm的驱动位移,进一步测试表明,驱动器的基模共振频率为573Hz,Q值为35.88.     

Fabrication and testing of bulk micromachined silicon carbide piezoresistive pressure sensors for high temperature applications

This paper explores the development of high-temperature pressure sensors based on polycrystalline and single-crystalline 3C-SiC piezoresistors and fabricated by bulk micromachining the underlying 100-mm diameter (100) silicon substrate. In one embodiment, phosphorus-doped APCVD polycrystalline 3C-SiC (poly-SiC) was used for the piezoresistors and sensor diaphragm, with LPCVD silicon nitride employed to electrically isolate the piezoresistor from the diaphragm. These piezoresistors fabricated from poly-SiC films deposited at different temperatures and doping levels were characterized, showing -2.1 as the best gauge factor and exhibited a sensitivities up to 20.9-mV/V*psi at room temperature. In a second embodiment, epitaxially-grown unintentionally nitrogen-doped single-crystalline 3C-SiC piezoresistors were fabricated on silicon diaphragms, with thermally grown silicon dioxide employed for the piezoresistor electrical isolation from the diaphragm. The associated 3C-SiC/SiO/sub 2//Si substrate was fabricated by bonding a (100) silicon wafer carrying the 3C-SiC onto a silicon wafer with thermal oxide covering its surface. The 3C-SiC handle wafer was then etched away in KOH. The diaphragm was fabricated by time etching the silicon substrate. The sensors were tested at temperatures up to 400/spl deg/C and exhibited a sensitivity of 177.6-mV/V*psi at room temperature and 63.1-mV/V*psi at 400/spl deg/C. The estimated longitudinal gauge factor of 3C-SiC piezoresistors along the [100] direction was estimated at about -18 at room temperature and -7 at 400/spl deg/C.     

一种高性能横向接触式微机械RF开关的分析与设计

设计了一种新型横向接触式微机械RF开关,描述了其结构和工作原理．采用以电镀为主的工艺流程,并利用SU8光刻胶实现特殊器件结构,可实现Post-CMOS集成．利用模拟软件CoventorWare 2004和MEMS Pro 5．0（包含ANSYS8．0）协同设计,对该器件进行了静态、模态和瞬态分析,得到吸合电压和吸合时间等重要性能参数．尤其在瞬态分析时运用了集总参数建模的方法,简化了计算．该器件的吸合电压低于30V,在驱动电压为50V的情况下,吸合时间达到16．1ms．     

Fabrication of fine-grained spherical tungsten powder by radio frequency (RF) inductively coupled plasma spheroidization combined with jet milling

Fine-grained spherical tungsten powder with particle size from 6 μm to 11 μm has been fabricated by a well-designed method with two simple steps. A pretreatment of tungsten powder was carried out in the first step. Complete dispersion, effective classification and favorable shape modification have been achieved by jet milling process. Accordingly, monodisperse tungsten powders with narrow particle size distribution were obtained. On the basis of the existing calculation and simulation results, plasma spheroidization parameters have been optimized. Thus, fine-grained spherical tungsten powder with narrow particle size distribution has been prepared by subsequent radio frequency (RF) inductively coupled plasma spheroidization. Furthermore, the presented method can be useful in fabricating spherical tungsten powder of different particle size with narrow particle size distribution as well as for process control in large-scale continuous production.     

Simulation, fabrication and characterization of ZnO based thin film transistors grown by radio frequency magnetron sputtering

We report the performance of the thin film transistors (TFTs) using ZnO as an active channel layer grown by radio frequency (RF) magnetron sputtering technique. The bottom gate type TFT, consists of a conventional thermally grown SiO2 as gate insulator onto p-type Si substrates. The X-ray diffraction patterns reveal that the ZnO films are preferentially orientated in the (002) plane, with the c-axis perpendicular to the substrate. A typical ZnO TFT fabricated by this method exhibits saturation field effect mobility of about 0.6134 cm2/V s, an on to off ratio of 102, an off current of 2.0 x 10(-7) A, and a threshold voltage of 3.1 V at room temperature. Simulation of this TFT is also carried out by using the commercial software modeling tool ATLAS from Silvaco-International. The simulated global characteristics of the device were compared and contrasted with those measured experimentally. The experimental results are in fairly good agreement with those obtained from simulation.     

Analysis of the interchannel response in a MEMS 1 x N(2) wavelength-selective switch

A theoretical model based on Fourier optics and the power-coupling overlap integral is built to investigate the interchannel response in a micro-electro-mechanical systems 1xN(2) wavelength-selective switch. The simulation results demonstrate that the interchannel response depends significantly on the output port location and the radius of curvature of the micromirrors. For the output originally aligned with the input along the dispersion direction, it is possible to achieve interchannel-response suppression by rotating the two-dimensional (2D) collimator array by a slight angle, e.g., 20 degrees. Experimental results under different conditions are also shown.     

Design, fabrication, and evaluation of high frequency, single-element transducers incorporating different materials

The performance of high frequency, single-element transducers depends greatly on the mechanical and electrical properties of the piezoelectric materials used. This study compares the design and performance of transducers incorporating different materials. The materials investigated include 1-3 lead zirconate titanate (PZT) fiber composite, lead titanate (PbTiO₃) ceramic, poly(vinylidene fluoride) (PVDF) film, and lithium niobate (LiNbO₃) single crystal. All transducers were constructed with a 3-mm aperture size and an f-number between 2 and 3. Backing and matching materials were selected based on design goals and fabrication limitations. A simplified coaxial cable tuning method was employed to match the transducer impedance to 50 Ω for the PZT fiber composite and PbTiO₃ ceramic transducers. Transducers were tested for two-way loss and -6 dB bandwidth using the pulse/echo response from a flat quartz target. Two-way loss varied from 21 to 46 dB, and bandwidths measured were in the range from 47 to 118%. In vitro ultrasonic backscatter microscope (UBM) images of an excised human eye were obtained for each device and used to compare imaging performance. Both press-focusing and application of a lens proved to be useful beam focusing methods for high frequency. Under equal gain schemes, the LiNbO ₃ and PbTiO₃ transducers provided better image contrast than the other materials     

Design of a double-layered spiral antenna for radio frequency identification applications

In this study, the authors describe a novel circularly polarised (CP) double-layered spiral antenna (DLSA) consisting of two main spiral radiators printed on a thin substrate, a feed line and a folded ground plane for a ultra-high-frequency (UHF) band radio frequency identification (RFID) reader. The proposed antenna exhibits broad impedance and CP bandwidth characteristics. The fabricated prototype has an axial ratio of less than 3 dB, a return loss of less than 10 dB over an 860 960 MHz range and a gain of 6.7 dB in the operating frequency range. This performance confirms that the proposed antenna is appropriate for commercial RFID use in the UHF band.     

Design,fabrication and cryogenic testing of 0.6 MJ SMES coil

Our centre has taken up a project of development of superconducting magnetic energy storage (SMES) technology to have better power quality for its accelerator program. In the first phase, a prototype cryostable coil has been designed, fabricated and commissioned in a standard bath cryostat. The various parameters of the magnet coil have been determined in order to maximize stored energy taking into consideration the constraints like geometry, maximum current limit etc. Winding tension (Pre-stress) of 13.6 MPa is maintained to keep radial stress compressive in all possible scenarios (i.e. during cool-down, excitation, etc.). Mylar is used for turn to turn insulation while 1 mm thick glass epoxy based picket fences (G-10) are placed symmetrically azimuthally for layer to layer insulation as well as to ensure passage of liquid helium inside the winding.Cryostability of the conductor implies more copper to superconductor ratio and is desired as far as stability of the coil is concerned. Cryostability, however may degrade when helium vapor is trapped in between two layers. Therefore, quench behavior of the magnet along with protection system has also been studied and implemented. This paper describes issues related to design study, fabrication and also cryogenic test results of the coil.