可动RF MEMS器件失效机理研究

This project focuses on the failure mechanism of RF MEMS switches which are the typical example of movable RF MEMS devices. Firstly, using the mechanical analysis to extract the elastic coefficient, bias voltage and the stress distribution of the switch and building the dynamic model. To research the crack problem of MEMS switch, fatigue analysis are used by FEM to get the limit of yielding and fracture toughness of the switch; Comparing the phenomenon of the dielectric charging in the capacitive MEMS switch to the capacity charging so can simplify this problem, by testing the relationship between voltage of the dielectric layer and time to get the C-V curve so can establish the equivalent circuit model which can describe the dielectric charging of MEMS switch. Combining this equivalent circuit model and the dynamic model to analysis the failure caused by the dielectric charging. As to the metal-contact MEMS switch, scanning the surface of the contact area by the electron microscope to get the feature size of the micro bulge on the surface and analyse the contact status between the switch and the signal line. Utilizing the stress distribution of the contracting area and the material yield limit of the switch , analyzing the contact damage problem. Finally, this project will design a fabricating process of low stress switch which containing wafer level package used the sacrificial film technology based on the MEMS processing technic handed.

本项目以RF MEMS开关为例，开展对可动RF MEMS器件失效机理的研究。首先采用力学分析提取开关机械参数，建立动态特性模型，结合有限元分析获得开关梁屈服极限和断裂韧度与结构之间的关系，设计低应力薄膜开关梁结构，缓解疲劳断裂问题；针对电容式开关的介质层电荷注入现象，通过C-V特性测试，建立等效电路模型表征注入电荷与驱动电压之间的关系，设计加速电荷耗散的控制信号波形，提升开关寿命；对于DC接触式MEMS开关，通过电镜扫描获取开关接触区轮廓，采用微丘表征其粗糙度，将开关接触过程等效为微丘与信号线之间的点状接触，获得开关接触区的应力分布，结合材料屈服极限，分析开关触头损伤问题；最后，立足于MEMS开关微加工工艺，设计低应力开关梁加工方案并完成基于牺牲薄膜技术的圆片级封装研究。

针对可动RF MEMS器件可靠性问题，围绕开关残余应力、电荷注入、触点损伤及开关封装进行了研究。分析研究了MEMS开关残余应力问题，设计了低残余应力的以单层石墨烯为夹层的三明治结构MEMS开关梁结构，开发了相应的微加工工艺流程，并加工获取了加工样品；针对电容式开关电荷注入问题，研究注入电荷与开关失效机理，建立了开关寿命模型；针对接触式开关触点损伤机理，提出改变开关触点材料的解决方案；对MEMS开关圆片级封装技术，提出了基于阳极键合和玻璃浆料键合的两种封装方案；研究人员根据研究内容及成果撰写了研究报告《可动RF MEMS器件失效机理分析及优化方案》.国内外核心期刊上发表论文12篇； 申请发明专利12项，其中6项获授权；参加国内外学术交流4次，邀请国外专家讲学4次；培养博士研究生4名，硕士研究生8名。