方形重掺杂硅薄膜的极限载荷分析*

考虑残余应力的情况下,薄膜在大挠度时总应力的解析表达式.通过实验观察,深腐蚀得到的浓硼重掺杂硅薄膜表面存在微蚀坑.考虑微蚀坑和残余应力的影响,运用总应力表达式和Griffith裂口强度理论,定量的得到方形浓硼重掺杂硅薄膜的最大挠度和极限载荷Pmax,与已报道的实验值相符.从而解释了浓硼重掺杂硅薄膜的实际断裂强度值远小于晶体理论断裂强度值的矛盾.可以得出,极限载荷Pmax不仅与薄膜的尺寸与形状有关,而且也与材料特性,特别是与制备工艺有关.     

多孔硅残余应力的研究

利用电化学腐蚀的方法在p型单晶硅(100)衬底上制备了多孔硅薄膜。利用微拉曼光谱法分别测量了处于湿化—干燥—再湿化3个阶段的多孔硅薄膜的拉曼频移,对多孔硅内应变引起的频移改变量和纳米硅晶粒因声子限制效应引起的频移改变量进行分离,找到多孔硅薄膜残余应力与拉曼频移之间的关系式。利用这一关系式,对不同孔隙率的多孔硅薄膜的残余应力进行了计算,获得了和声子模型拟合方法相一致的结果。研究中发现,多孔硅表面残余应力随孔隙率的增加而线性增大,其原因为随着孔隙率的增加,多孔硅晶格常数增大,且干燥过程中残液的蒸发产生的毛细应力使多孔硅薄膜与基体硅间晶格错配程度增大造成的。     

Ti 和 TiN 薄膜的制备以及残余应力的测试方法研究

基底曲率半径法是一种测量薄膜残余应力的常用方法,其中的光杠杆法应用最为广泛.文章在SUS304基底上使用电弧离子镀法制备了不同厚度的钛(Ti)和氮化钛(TiN)薄膜,研究了薄膜的形貌、密度以及物相,基于光杠杆原理分别从正面(正测法)和反面(背测法)对两种薄膜样品镀膜前后基底的曲率半径进行了测量,采用Stoney公式计算薄膜残余应力.通过对比正测法和反测法的测试结果,结合薄膜形貌、密度以及晶体结构表征分析,对背测法的测试误差和适用范围进行了分析.研究结果表明,背测法测得的应力值低于正测法的测量结果,薄膜残余应力水平越高,背测法的测量结果与正测法越接近:当薄膜残余应力水平较高(>1 GPa)时,背测法结果可以如实反映薄膜的应力水平;但当薄膜应力水平较低(<1 GPa)时,背测法结果存在较大误差.     

薄膜热膨胀系数测试技术研究

热膨胀系数是薄膜的重要热学性能参数,也是薄膜热应力和残余应力计算分析过程中的关键数据.文章基于热诱导弯曲原理,分别采用单基片法和双基片法对氮化钛(TiN)和铝(Al)薄膜的热膨胀系数进行测试,并着重对双基片法的测试误差和适用性进行了分析.研究结果表明,薄膜在不同材质基底上弹性模量的差异是影响双基片法薄膜热膨胀系数测试精度的重要因素.当不同材质基片上薄膜弹性模量差异较小时,双基片法测得的热膨胀系数与单基片法所获结果基本一致;而当不同材质基片上薄膜弹性模量相差较大时,双基片法将不再适用.此外,文章结合薄膜的形貌、结构和残余应力表征测试,对TiN和Al薄膜热膨胀系数与其块体材料的差异进行了分析,结果显示残余压应力会导致薄膜热膨胀系数增大,而残余拉应力则具有相反的效果.     

基于ABAQUS的复合薄膜热结构有限元分析

半导体硅基复合薄膜悬臂梁在温度场、加速度以及二者耦合场作用下,挠度和应力会发生变化.通过加热可使得驱动元件本身的温度升高,结构内部将会产生热应力,会导致两种薄膜各自产生线应变,线膨胀系数小的薄膜受到拉力作用,线膨胀系数大的薄膜受到压力作用,自由端会受到力矩作用而向线膨胀系数小的薄膜方向弯曲,从而导致悬臂梁的挠度发生变化.当弯曲悬臂梁有加速度作用时,会产生一个与加速度方向相同的力作用在悬臂梁上,同样会导致悬臂梁的挠度发生变化[1].通过ABAQUS软件仿真[2],分别给出不同物理场中弯曲悬臂梁相对位移的大小,所得的结论为半导体硅基复合薄膜弯曲悬臂梁的应用装置提供了理论依据.     

微力微位移天平测试方法

介绍了一种简单有效的微力、微位移天平测试方法,通过对薄型硅悬臂梁进行力—挠度特性测试进而提取材料杨氏模量的方法是简便、可行的。还介绍了用于测量薄膜应力的悬臂梁挠曲法,对于硅上热生长1.1μm SiO_2的结构,测得SiO_2膜内的压应力为200～230MPa.微力微位移天平测试方法操作方便,仪器成本低,具有较高精度。     

高性能SOI基纳米硅薄膜微压阻式压力传感器的研究

针对高端领域对高性能微小量程压力传感器的迫切需求，设计并实现了一种应用于电子血压计的高性能SOI基纳米硅薄膜微压阻式压力传感器，并提出了相应的检测电路。根据小挠度弯曲理论设计了传感器方形敏感薄膜结构，确定了纳米硅薄膜压敏电阻的阻值大小和尺寸。采用ANSYS有限元分析（FEA）对所设计的传感器结构进行仿真，根据仿真结果确定了压敏电阻在膜片上的最佳放置位置。基于标准MEMS制造技术，在SOI基纳米硅薄膜上设计并实现了该压力传感器。实测结果表明，室温下，在0～40 kPa微压测量范围内所设计的传感器检测灵敏度可达0.45 mV/（kPa·V），非线性度达到0.108%F.S。在-40℃～125℃的工作温度范围内，温度稳定性好，零点温度漂移系数与灵敏度温度漂移系数分别为0.004 7%F.S与0.089%F.S。所设计的压力传感器及其检测电路，在现代医疗、工业控制等领域具有较大的应用潜力。     

微机械薄膜应力的在线测试结构

微机械薄膜应力对MEMS器件有较大的影响，因此应力测量对于工艺监控和MEMS器件设计是必须的。介绍了微机械薄膜应力的在线测试结构与方法，详细分析了各种方法的特点。对于MEMS薄膜应力测试结构设计有一定的参考价值。     

电化学腐蚀中多孔硅边缘效应的研究

多孔硅在微电子机械系统(MEMS)、生物等领域得到了广泛的研究,边缘效应是其进入应用的难题之一,边缘效应的存在会导致多孔硅薄膜机械强度的降低,进而影响整个多孔硅薄膜的一致性.在n型和P型2种硅晶片上,研究了电化学腐蚀中常见的多孔硅边缘效应,分析了边缘效应的产生机制,分别使用SU8光刻胶掩模法和边缘区域施加压力法对边缘效应进行了有效的抑制.并在不同类型的硅晶片上,使用压力法制备出了无边缘效应的宏孔多孔硅膜,P型多孔硅膜厚达到250μm.     

MEMS器件用Cavity-SOI制备中的晶圆键合工艺研究

微机电系统(MEMS)器件用预埋腔体绝缘体上硅(Cavity-SOI)直接键合制备过程中,预埋腔体刻蚀后残余应力导致的衬底层变形会影响绝缘体上硅(SOI)晶圆的面形参数和键合质量.对衬底层残余应力变形与Cavity-SOI键合质量的关系进行了实验研究,分析了衬底片残余应力变形与SOI面形之间的对应关系,用破坏性剪切试验...     

Modelling of silicon condenser microphones

Several models concerning the sensitivity of capacitive pressure sensors have been presented in the past. Modelling of condenser microphones, which can be considered to be a special type of capacitive pressure sensor, usually requires a more complicated analysis of the sensitivity, because they have a strong electric field in the air gap. It is found that the mechanical sensitivity of condenser microphones with a circular diaphragm, either with a large initial tension or without any initial tension, increases with increasing bias voltage (and the corresponding static deflection), whereas the mechanical sensitivity of other capacitive pressure sensors does not depend on the static deflection. It is also found that the mechanical sensitivity increases with increasing input capacitance of a preamplifier. In addition, the open-circuit electrical sensitivity and, consequently, the total sensitivity too, also increases with increasing bias voltage (or static deflection). However, the maximum allowable sound pressure at which the diaphragm collapses, an effect that has to be taken into account, decreases with increasing static deflection in most cases, ulthnately resulting in an optimum value for the bias voltage. The model for microphones with a circular highly tensioned diaphragm has been verified successfully for two microphone types.     

Verifying finite element simulation in miniature silicon based stacked diaphragm pressure sensors

Micro electro mechanical system are usually defined as highly miniaturized devices combining both electrical and mechanical components that are fabricated using integrated circuit batch processing techniques. Silicon based stacked diaphragm structure is a combination of silicon-di-oxide and the silicon layer. This work brings out a new approach of finding the sensitivity of stacked diaphragm with respect one of the important parameters like deflection. The sensitivity is also evaluated under thermal effect and, the analytical model developed for the same closely matches with the finite element model. The doping concentration of 10¹⁷cm^-3, in which single silicon shows maximum sensitivity has been selected and an increase in the sensitivity is observed on using a stacked diaphragm structure. The stacked diaphragm structure is designed, simulated and compared with existing single diaphragm design with respect to diaphragm deflection and sensor output voltage for linearity over a wider range. The effect of the buried oxide in the stacked diaphragm structure is also considered in this work. The work in this paper provides a mathematical expression for realizing the effect of boron implanted resistors on the stacked diaphragm structure. The simulation result reported in the literature evaluates the deflection at a particular temperature but the new analytical model developed in this paper evaluates the sensitivity of the diaphragm over a temperature range.     

A novel high sensitive MEMS intraocular capacitive pressure sensor

This paper presents a novel high sensitive MEMS capacitive pressure sensor that can be used as a part of LC tank implant circuit for biomedical applications. The pressure sensor has been designed to measure pressures in the range of 0–60 mmHg that is in the range of intraocular pressure sensors. Intraocular pressure sensors are important in detection and treatment of an incurable disease called glaucoma. In this paper two methods are presented to improve the sensitivity of the capacitive pressure sensor. First low stress doped polysilicon material is used as a biocompatible material instead of p++silicon in previous work (Gu in Microfabrication of an intraocular pressure sensor, M.Sc Thesis, Michigan State University, Department of Electrical and Computer Engineering, 2005) and then some slots are added to the poly Si diaphragm. The novelty of this research relies on adding some slots on the sensor diaphragm to reduce the effect of residual stress and stiffness of diaphragm. The slotted diaphragm makes capacitive pressure sensor more sensitive that is more suitable for measuring intraocular pressure. The results yield a sensor sensitivity of 1.811 × 10^?5 for p++silicon clamped, 2.464 × 10^?5 1/Pa for polysilicon clamped and 1.13 × 10^?4 1/Pa for polysilicon slotted diaphragm. It can be seen that the sensitivity of the sensor with slotted poly Si diaphragm increased 6.2 times compared with previous work (clamped p++silicon diaphragm).     

Theoretical and experimental studies on the parylene diaphragms for microdevices

In this paper, parylene diaphragms with planar and corrugated shapes are fabricated and tested. Although, recently in MEMS, parylene has been used for a diaphragm material due to its excellent property, no theoretical and analytical studies of the parylene diaphragm have been performed. Therefore, the characterization of the parylene diaphragms is studied through both experiments and simulations. Thermal and load-deflection analyses for diaphragms are carried out to find the effect of residual stress on the behavoir of the diaphragm. The measured deflections are compared with both analytical calculations and FEM simulations that considers the influence of the thermal stress. Those results show excellent agreement. In order to find an optimum shape of the corrugated diaphragm, the influence of the corrugation number and the corrugation depth on the mechanical sensitivity of the corrugated diaphragm is studied parametrically.The authors would like to thanks to Dr. Sang Sik Yang and coworkers in the Microsystems Lab., School of Electronics Engineering, Ajou University for the help with device processing. This research was sponsored by Institute for Applied Science and Technology of Sogang University.     

The design, fabrication, and testing of corrugated silicon nitridediaphragms

Silicon nitride corrugated diaphragms of 2 mm×2 mm×1 μm have been fabricated with 8 circular corrugations, having depths of 4, 10, or 14 μm. The diaphragms with 4-μm-deep corrugations show a measured mechanical sensitivity (increase in the deflection over the increase in the applied pressure) which is 25 times larger than the mechanical sensitivity of flat diaphragms of equal size and thickness. Since this gain in sensitivity is due to reduction of the initial stress, the sensitivity can only increase in the case of diaphragms with initial stress. A simple analytical model has been proposed that takes the influence of initial tensile stress into account. The model predicts that the presence of corrugations increases the sensitivity of the diaphragms, because the initial diaphragm stress is reduced. The model also predicts that for corrugations with a larger depth the sensitivity decreases, because the bending stiffness of the corrugations then becomes dominant. These predictions have been confirmed by experiments. The application of corrugated diaphragms offers the possibility to control the sensitivity of thin diaphragms by geometrical parameters, thus eliminating the effect of variations in the initial stress, due to variations in the diaphragm deposition process and/or the influence of temperature changes and packaging stress     

Modelling and analysis of diaphragm integrated SU8/CB nanocomposite piezoresistive polymer microcantilever biosensor

Microsystem Technologies - This study investigates the effect of cantilever size and diaphragm size on deflection, frequency, stress and sensitivity characteristics of a diaphragm integrated SU8/CB...     

Residual stress influences on the sensitivity of ultrasonic sensor having composite membrane structure

Stress and sensitivity of arrayed ultrasonic sensors utilizing piezoelectric thin film (lead–zirconate–titanate film: Pb(Zr_0.52Ti_0.48)O₃) having composite membrane structure are demonstrated. Due to different thermal and elastic characteristics of each constitutive layer, a subsequent residual stress and deflection is generated on the resultant composite membrane. We present the influence of residual stress on the mechanical behaviors and sensitivities of a Si-based integrated sensor device. The design of sensor structure and the fabrication process especially relating to thermal treatment have significant effects on the stress state of the composite membrane, and the relationships among the stress states, deflections of membrane and sensitivities of sensor devices are considered. Tensile stress induced on the membrane consequently leads to sensitivity deterioration, while compressive stress improves sensitivity. Sensitivities of each sensor structure are expressed as the ratio of output voltage (V) to the acoustic pressure (P), and the variations of those are discussed relating to the residual stress states, PZT film properties and mechanical behaviors of each composite membrane.     

基于GaAs MMIC技术的残余应力测试结构的模拟与设计

残余应力对开关梁的力学特性有着重要的影响。梁的弹性系数k由梁的形状和材料特性(杨氏模量和残余应力)来决定。应力梯度会使悬臂梁发生卷曲,对k也会产生影响。由残余应力引起的梁的长度变化量在微米级别,一般实验仪器难于测量。基于GaAs基和Si基的器件残余应力不同,相应的测试结构需重新设计。为了克服这些问题,本论文重新模拟并优化了微旋转式残余应变测试结构,尽量简化对测试仪器的要求。本文使用Intellisuite仿真软件以及Matlab软件优化,同时采用对称式的结构增加了测试精度。最后本文还给出了应力梯度的测试方法。