Thermal Mechanical Stress Analysis Of Quatrz MEMS Sensors And Packages

The micro-electro-mechanical systems (MEMS) devices integrate more and morediverse materials in a complicated three-dimensional structure with small sizes. Theperformance leaps of these devices are so attractive; meanwhile the failure modesbecome more urgent in this area. Among all of the failure modes, thethermal-mechanical aspect is always one major concern. Due to the Coefficient ofThermal Expansion (CTE) mismatch between different bonding materials, thermalstress would form in the materials when the devices are in operation and finally damagethe devices. This thesis will cover the following issues.One is the stress concentration that leads to many failure modes. This research issupported by the The New Energy and Industrial Technology Development Organization (NEDO)in Japan and was finished in Ueda Lab., Waseda University. In MEMS devices, the integrateddiverse materials are of different thermal mechanical properties, and usually bondedtogether to form sharp features, such as trenches, wedges, corners or junctions. Thesesharp features can concentrate stresses, which in turn fail the devices in ways ofcracking, debonding, or injecting dislocations, etc. In this study, finite element method(FEM) is carried out to investigate the thermal residual stresses in a MEMS LTCCpackage and the chip of a MEMS gas sensor. Validated FEM models have beenestablished with the material properties and boundary conditions. Some experiments arealso designed to measure the boundary conditions. Coupled thermo-mechanical analysisis implemented by FEM software (ANSYS, Comsol) to find the maximum themal stressconcentration area on the corresponding components. Optimal designs are also carriedout to reduce the thermal residual stress and improve the reliability based on theestablished numerical model.