Long Term Stability of Polysilicon Microelectromechanical Structures

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9410989 Brown This effort will examine failure modes and long term structural stability of polysilicon microelectromechnical structures(MEMS). We find the current absence of research on MEMS reliability striking given that many MEMS are designed to last long periods of time under adverse conditions. Specifically, we intend to address the following goals. 1. Identify failure modes for polysilicon microelectromechanical structures. Long term performance of MEMS cannot be achieved until possible failure modes are understood. 2. Provide a protocol for accelerated testing of MEMS. Although MEMS are meant to operate for decades, they cannot be tested for that period before being put to use. Accelerated testing techniques must be developed to assess the long term performance of the devices. 3. Characterize the reliability of polysilicon structures as a function of processing and geometry. We have shown the possibility of crack growth in a single crystal silicon microelectromechanical structure due to environmental effects. In light of additional microstructural features s such as grain boundaries, we may expect additional failure modes in polysilicon. 4. Design test structures to indicate incipient or possible failure. These structures are meant to be placed with operating MEMS devices to detect crack initiation, permanent deformation, shock, or changes in structural response. This work is essential to ensure reliable MEMS applications. ***