Research On Residual Stress Of Bistable Structure Based On SOI-MEMS Technology

The reliability of MEMS devices is an important issue in device design,fabrication and performance evaluation,and among all controllable factors,residual stress is the main factor that directly affects device performance.The residual stress in SOI-MEMS devices essentially changes the performance of the device and reduces the reliability and yield of the device.Therefore,for the residual stress in SOI-MEMS bistable structure,this thesis proposed a method to characterize the residual stress in SOI wafer,and analyzed the thermal stress caused by operating temperature.The main contributions of this thesis are as follows:Firstly,the background and significance of the research on residual stress in SOI-MEMS bistable structure are clarified.The sources of residual stress in SOI-MEMS devices and related research progress at home and abroad are summarized.At the same time,the MEMS bistable inertial switch structure and it's working principle are introduced,the mechanical properties of SOI-MEMS bistable structure are analyzed,and the core role of the bistable structure to the realization of the switch structure function is determined.Secondly,the mechanism of the residual stress in SOI wafer is analyzed and the mechanical theoretical model is established.Through studying the silicon direct bonding technique for the preparation of the SOI wafer,the generation mechanism and distribution of the residual stress in SOI wafer are determined.The mechanical deformation of cantilever beam structure and fixed beam structure are analyzed in detail,then,the mechanical theoretical model of the residual stress in SOI wafer is established.And by analyzing the various characterization methods of the residual stresses,a method more suitable for the characterization of the residual stresses in SOI wafer is designed.Thirdly,the experimental test of residual stress in SOI wafer are conducted.The tested samples are designed and prepared,and the laser scanning confocal microscope is used to measure the 3D topography,obtained the deflection of two sets of samples,combined with the mechanical theoretical model characterized the residual stress values in SOI wafer,and the accuracy and feasibility of the residual stress characterization method designed in this thesis are verified.Then,through numerical simulation analysis,it is found that under the action of residual stress,the inclination angle of the bistable beam structure decrease and the threshold force required for the steady state switching increase.Finally,the mechanical properties of SOI-MEMS bistable structure in the operating temperature range are studied.Using finite element to numerical simulation the thermal stress of bistable structure in-40?~80? temperature range.And the influence of the thermal stress on the mechanical characteristics of bistable beam structure is analyzed,the result show that the inclination of the bistable beam structure is sensitive to the operating temperature,and the threshold force required for the steady state switching of the beam structure will increase due to the existence of thermal stress.In this thesis,mechanical theory modeling and the experimental test verification methods are adopted to analyze the residual stress in SOI wafer,and the influence of residual stress and thermal stress on the mechanical properties of the SOI-MEMS bistable structure is explored,which provides theoretical reference and data support for the subsequent design and optimization of the SOI-MEMS bistable structure.