MEMS芯片正面结构释放时的保护

提出了一种MEMS后处理中正面结构释放的正面保护方法．尤其是针对在CMOS-MEMS工艺制造单片集成传感器时,MEMS后处理工艺中正面体硅湿法腐蚀时对已制作完成的CMOS电路部分的表面铝引线、铝焊盘和钝化层下多晶层的保护方法．将一种新型的复合膜结构和优化后的TMAH腐蚀液相结合,可以保证长时间高温腐蚀时腐蚀液不会渗透到钝化层下,同时完成正面MEMS结构释放．具有与CMOS工艺兼容、工艺实现简单等特点．     

Notching效应在MEMS单步干法制造工艺中的应用

研究了一种基于深反应离子刻蚀（DRIE）中notching效应的MEMS单步干法制造工艺.首先,基于DRIE刻蚀SOI硅片时notching现象产生的机理,设计了多种不同线宽的槽结构,验证notching效应的发生条件.实验结果表明,对于所采用的具有30μm器件层的SOI硅片,发生notching现象的临界槽宽为12μm,而notching释放的极限结构宽度同样为12μm.其次,为实现大面积结构的notching释放,研究了正方形、矩形、三角形及六边形等4种典型释放孔结构的干法释放效果.实验结果表明,六边形释放孔不但能够快速有效地释放结构,同时还能降低notch-ing效应的磨损,有利于惯性MEMS器件的加工.最后,设计了一种Z轴微机械陀螺结构以验证提出的设计及工艺.加工及测试结果表明,所提出的单步干法制造工艺完全满足微机械陀螺设计加工要求,工艺简单、成品率高,所测试的陀螺在常压下即可达到122的品质因数.     

用于MEMS结构的光刻胶牺牲层接触平坦化技术

实验研究一种新颖的光刻胶牺牲层的接触平坦化(contact planarization)技术,应用于MEMS结构制作.实验研究了温度与光刻胶流动性的关系,以及牺牲层厚度、施加压力和温度、MEMS结构密度等因素对平坦化效果的影响,在优化条件下,牺牲层的起伏台阶从2μm减小到20～40nm.与化学机械抛光技术相比,接触平坦化无明显凹陷(Dishing)效应,无衬底损伤,同时呈现出良好的局部和总体均匀性.     

基于电磁驱动及磁电／电容检测的硅谐振式双轴角速率传感器设计和测试

本文介绍了一种MEMS角速率传感器的设计、制作和测试．该传感器采用硅梁作为支撑和震动的结构．电磁力在驱动模式中被用来激励质量块做往复运动．驱动模式的频率被设计为5955．38Hz．针对另外两个轴向的角速率检测,设计检测模式的频率分别为6151．01Hz和6591Hz．质量块在驱动模式下的最大位移被设计为20μm．在器件的制作过程中使用了湿法刻蚀、电子柬蒸发、阳极键合、等离子体增强化学气相沉淀（PECVD）、lift—off、感应耦合等离子体活性离子蚀刻（ICP—RIE）等MEMS工艺．质量块的尺寸是1440μm×1400μm×33．6μm,硅梁的设计尺寸分别为10μm×562．5μm×33．6μm,10μm×532．5Ixm×33．6μm,芯片的外形尺寸是3127μm×3069μm．为了进行器件测试,搭建了真空测试平台．测试结果表明,驱动模式下器件的谐响应频率为9609Hz,使用磁电检测的模式其谐响应频率为9605Hz．器件中电容检测需要特殊的电路,该电路目前正在搭建中．分析发现实测结果与模拟仿真结果的差异在于加工过程中产生的误差．     

牺牲层刻蚀实验的在线观察与研究

设计了多种测试结构，采用在线实时观测的手段，深入研究了氢氟酸（HF）刻蚀二氧化硅牺牲层中，多种因素对刻蚀过程产生的影响，并对实验结果进行了详细分析．实验中可以明显观察到刻蚀过程中的反应限制阶段与扩散限制阶段，说明经过长时间的刻蚀，HF酸的扩散效应将成为影响刻蚀速率的主导因素．对于实验过程中观察到的“凹”状的刻蚀前端和“晕纹”现象，分析认为结构中的应力梯度以及材料间不同的亲水性质是产生这些现象的主要原因．实验方法与结论对MEMS牺牲层释放工艺的研究具有一定的参考意义．     

基于干法刻蚀技术的氮化镓MEMS加工工艺(英文)

氮化镓(GaN)材料已成功应用于光电子器件、高频功率器件等领域.近年来,由于GaN优异的材料特性,例如机械、热、化学稳定性以及生物兼容性等,使基于GaN的微机电系统(MEMS)得到了学术界的广泛关注.针对氮化镓MEMS结构的有效的图形化及释放技术是工艺研究的重点.设计、采用了一种全干法刻蚀技术,实现了(111)晶向硅衬底上的氮化镓基MEMS微结构的加工制造.利用提出的工艺方案,实现了多种悬浮GaN微结构的加工与测试表征实验.通过电子扫描显微镜(SEM)和光学轮廓仪进行了基本形貌表征;利用微拉曼光谱实验进行了加工结构的残余应力表征.     

接触式串联射频MEMS开关的工艺研究

本文采用MEMS工艺制作接触式串联射频开关,射频开关采用双端固定的悬臂梁结构,悬梁为PECVD制作的SiN薄膜,溅射Au制作共平面波导,聚酰亚胺作为牺牲层,运用等离子体刻蚀法释放牺牲层.研究了悬梁、共平面波导以及电极的制作工艺,并分析了牺牲层的制作和刻蚀工艺对开关结构的影响.     

硅基热电堆真空传感器的耦合场分析

利用商业化的1．2μm标准CMOS生产流水线,配合无掩模体硅各向异性腐蚀工艺,制造了一种热电堆型真空传感器,器件敏感部分尺寸为124um×100μm,由5层薄膜组成,最大厚度为3．2μm．采用一种简化方式对传感器建立有限元模型．新模型一方面忽略了气体对流和热辐射的传热作用,另一方面将各层介质和热电堆结构层分别进行了合并．模型具有简单的断面结构,网格划分容易,收敛速度快．运用ANSYS软件对模型进行了电一热、热一电耦合场分析,直接得到了1．5v加热电压驱动时不同压强下的热电堆输出电压,并与0．1～200Pa之间的测试结果进行比较,结果表明,采用简化建模方式的计算结果与测试结果之间的偏差小于6％．     

ZnO压电薄膜的生长与应用

本文实验研究了ZnO压电薄膜的生长与表征,运用XRD和SEM测试了磁控溅射生长的ZnO压电薄膜的C轴择优取向生长情况和晶粒质量,比较了Si、覆盖在si基底上的Al薄膜和SixNy薄膜三种材料衬底以及退火处理对ZnO薄膜的结晶质量的影响.还开发了仍然采用Al作为底电极但用一层SixNy薄膜与ZnO层隔离的MEMS压电器件的微制造工艺,以满足生长高质量的ZnO压电薄膜并与CMOS工艺兼容的要求.     

基于中间硅片厚度可控的三层阳极键合技术

三层键合Glass-Silicon-Glass(GSG)结构在光MEMS、微惯性器件、微流体芯片、射频MEMS以及低成本圆片级封装技术领域里是一项重要技术.基于MEMS精密研磨抛光工艺和阳极键合,结合新型玻璃通孔的腐蚀工艺,开展了中间硅片厚度可控的三层阳极键合工艺研究,成功制备了带有通孔的GSG微流体器件.总厚度1360μm,中间硅片厚度60μm,通孔直径100μm,孔间距(圆孔的中心距离)200μm,孔内边缘圆滑无侧蚀.三层结构的键合几率为90%,为探索多层键合技术打下坚实基础.     

An Integrated Surface Micromachined Convex Microhotplate Structure for Tin Oxide Gas Sensor Array

This paper describes the fabrication process for a novel convex microhotplate (MHP) structure using surface micromachining technology. The process is used to fabricate an integrated 4times4 tin oxide gas sensor array. Surface micro-machining is selected for its simplified process and CMOS compatibility. However, limited sacrificial layer thickness usually leads to higher power consumption. In this work, a convex MHP structure is developed to increase the thermal efficiency, which is critical for large dimension and low-power gas sensor array integration. Before the structure release process, 700degC-950degC annealing process was carried out on the 190 times190 mum² MHP with 2.8 mum polysilicon sacrificial layer. It is shown that higher annealing temperature leads to lower tensional stress of the MHP membrane and larger curvature of the released structure, which enables higher thermal efficiency. Among the four annealing temperatures, the 950degC annealed MHP has the largest curvature of 2.438 cm^-1 and the highest thermal efficiency of 13degC/mW. Experimental results showing the responses of the sensor array to different combustible gases are also illustrated in this paper. Comparison of power consumption with other designs reported in the literature illustrates the effectiveness of the proposed process.     

利用银锡共晶键合技术的MEMS压力传感器气密封装

为了提高MEMS压力传感器的气密封装效果,利用银锡(Ag-Sn)焊片共晶键合的方法实现封装.首先介绍了工艺流程,然后利用X射线能谱(EDX)和剪切强度分析对共晶键合的温度和时间参数进行了优化,接着对9组静载荷下的剪切强度、Ag-Sn合金分布和键合层断面做了对比分析,最后做了X光检测、氦泄漏率对比测试及MEMS压力传感器实际效果测试.实验结果表明,在温度为230℃、加热时间为15 min、静载荷范围为0.003 9 MPa～0.007 8 MPa时,MEMS压电传感器的平均剪切强度达到14.22 MPa～18.28 MPa,X光检测无明显空洞,氦泄漏率不超过5×10-4Pa.cm3/s,测试曲线表明线性度较好.     

MEMS-Capacitive Pressure Sensor Fabricated Using Printed-Circuit-Processing Techniques

Microelectromechanical systems (MEMS)-based capacitive pressure sensors are typically fabricated using silicon-micromachining techniques. In this paper, a novel liquid-crystal polymer (LCP)-based MEMS-capacitive pressure sensor, fabricated using printed-circuit-processing technique, is reported. The pressure sensor consists of a cylindrical cavity formed by a sandwich of an LCP substrate, an LCP spacer layer with circular holes, and an LCP top layer. The bottom electrode and the top electrode of the capacitive pressure sensor are defined on the top side of the LCP substrate and the bottom side of the top-LCP layer, respectively. An example pressure sensor with a diaphragm radius of 1.6 mm provides a total capacitance change of 0.277 pF for an applied pressure in the range of 0-100 kPa     

An integrated 16/spl times/16 PVDF pyroelectric sensor array

This paper presents a fully integrated PVDF-on-silicon pyroelectric sensor array. The pyroelectric sensor has two main features: a subpixel low noise charge amplifier and a self-absorbing layered structure. The integrated low noise charge amplifier is implemented in a standard CMOS process technology. It is located directly under the sensing structure, maximizing the pixel fill factor. The self-absorbing pyroelectric sensor is a three-layer stack, consisting of a conductive polymer as an absorber layer and front electrode, a thin PVDF film as the pyroelectric material, and a rear metal layer acting as a reflector layer and rear electrode. The manufacture of the pyroelectric sensor array requires five maskless post-CMOS processing steps and is compatible with any n-well, double metal, double polysilicon, CMOS process. The array has an average pixel voltage sensitivity of 2200 V/W at 100 Hz, an NEP of 2.4/spl times/10/sup -11/ W//spl radic/Hz at 100 Hz, and a specific detectivity of 4.4/spl times/10/sup 8/ cm /spl radic/Hz/W at 100 Hz.     

A CMOS Time-of-Flight Range Image Sensor With Gates-on-Field-Oxide Structure

This paper presents a new type of CMOS time-of-flight (TOF) range image sensor using single-layer gates on field oxide structure for photo conversion and charge transfer. This simple structure allows the realization of a dense TOF range imaging array with 1515 mum² pixels in a standard CMOS process. Only an additional process step to create an n-type buried layer which is necessary for high-speed charge transfer is added to the fabrication process. The sensor operates based on time-delay dependent modulation of photocharge induced by back reflected infrared light pulses from an active illumination light source. To reduce the influence of background light, a small duty cycle light pulse is used and charge draining structures are included in the pixel. The TOF sensor chip fabricated measures a range resolution of 2.35 cm at 30 frames per second and an improvement to 0.74 cm at three frames per second with a pulsewidth of 100 ns.     

System integration design in MEMS — A case study of micromachined load cell

One of the critical issues in large scale commercial exploitation of MEMS technology is its system integration. In MEMS, a system design approach requires integration of varied and disparate subsystems with one of a kind interface. The physical scales as well as the magnitude of signals of various subsystems vary widely. Known and proven integration techniques often lead to considerable loss in advantages the tiny MEMS sensors have to offer. Therefore, it becomes imperative to think of the entire system at the outset, at least in terms of the concept design. Such design entails various aspects of the system ranging from selection of material, transduction mechanism, structural configuration, interface electronics, and packaging. One way of handling this problem is the system-in-package approach that uses optimized technology for each function using the concurrent hybrid engineering approach. The main strength of this design approach is the fast time to prototype development. In the present work, we pursue this approach for a MEMS load cell to complete the process of system integration for high capacity load sensing. The system includes; a micromachined sensing gauge, interface electronics and a packaging module representing a system-in-package ready for end characterization. The various subsystems are presented in a modular stacked form using hybrid technologies. The micromachined sensing subsystem works on principles of piezo-resistive sensing and is fabricated using CMOS compatible processes. The structural configuration of the sensing layer is designed to reduce the offset, temperature drift, and residual stress effects of the piezo-resistive sensor. ANSYS simulations are carried out to study the effect of substrate coupling on sensor structure and its sensitivity. The load cell system has built-in electronics for signal conditioning, processing, and communication, taking into consideration the issues associated with resolution of minimum detectable signal. The packaged system represents a compact and low cost solution for high capacity load sensing in the category of compressive type load sensor.     

Smart MEMS Flow Sensor: Theoretical Analysis and Experimental Characterization

This paper presents analytical and experimental studies of a new microelectromechanical system (MEMS) smart flow sensor for the measurement of gas flow. The flow sensor has an array of curved-up cantilever beams that are surface-micromachined with two layers of deposition under two sets of different process parameters. The differential residual stress between the two layers of the polysilicon deposition causes the beams to curve upward from the substrate surface when the sacrificial layer is released. Each beam of the array of beams of different lengths vibrates successively as the flow rate increases, enabling more accurate sensing and identification of range of flow rates based on the vibration characteristics, thus making this a smart sensor design. Design and fabrication of these sensors are discussed. Experiments were conducted on this MEMS flow sensors to characterize the deflection of the curved cantilever beams with respect to flow rates. In addition, backflow tests were also conducted separately. Results of the analytical study are presented to investigate the cause of vibration of beams when subjected to flow. Finite-element analyses of vibration of the sensors comply with the experimental observation. Based on the analysis of fundamental natural frequencies, possible arrangement for the distribution of lengths of the beams is proposed to enhance its functionality as a sensor. Future work and plan of the on-board capacitive metrology and other practical issues are discussed     

A Novel MEMS Respiratory Flow Sensor

A novel CMOS-process-compatible MEMS sensor for monitoring respiration is presented. This resistive flow sensor was manufactured by the TSMC 0.35 $mu{hbox {m}}$ CMOS/MEMS mixed-signal 2P4M Polycide process. The sensor was demonstrated to be sensitive enough to detect the respiratory flow rate, and the relationship between flow rate and sensed voltage is quite linear. If one can integrate the sensor with its sensing circuit into a single chip, the cost of a pneumotach system can be greatly reduced. Moreover, the proposed sensor is useful in both invasive and noninvasive applications.      

Suspended aluminum nitride structures grown via metal organic vapor phase epitaxy

The development of III-Nitride suspended structures for Micro-Electro Mechanical Systems (MEMS) and Nano-Electro Mechanical Systems (NEMS) is challenging due to lack of selective etching techniques. Recent efforts have focused on the removal of sacrificial layers based on material properties, such as crystalline quality, bandgap, polarity, doping, etc. These techniques require several processing steps in addition to precise control over the sacrificial and functional layer properties. In this work, conditions have been identified for the growth of etch-resistant polycrystalline AlN films via Metal Organic Vapor Phase Epitaxy (MOVPE) on silicon oxide surfaces, thus allowing silicon oxide to be used as a sacrificial layer in a surface micro-machining process. The MOVPE growth conditions reported result in a well oriented crystal with superior mechanical strength demonstrated by the fabrication of unsupported AlN structures with widths from 5 μm to 110 μm and air gaps ranging from 200 nm to 800 nm. This technique simplifies the fabrication process of AlN suspended structures and is well suited for achieving group III-Nitride heteroepitaxial MEMS/NEMS systems.