Dielectric thin films for MEMS-based optical sensors

Abstract Nanoindentation and optical measurements have been employed in order to investigate the mechanical properties of low-temperature (50–330 °C) plasma-enhanced chemical vapour deposited (PECVD) SiN x , as well as thermally evaporated SiO x and Ge thin films for applications in micro-electro-mechanical systems (MEMS) fabricated on temperature sensitive, non-standard substrates. The temperature of the SiN x deposition process is found to strongly influence Young’s modulus, hardness, and stress, with a critical deposition temperature in the 100 °C to 150 °C range which depends on the details of other deposition conditions such as chamber pressure and RF-power. The properties of PECVD SiN x films deposited above this critical temperature are found to be suitable for MEMS applications, whereas films deposited at lower temperatures exhibit low Young’s modulus and hardness, as well as environment-induced stress instabilities. The investigated thin films have been incorporated into a monolithic integrated technology comprising low-temperature (∼125 °C) MEMS and HgCdTe IR detectors, in order to realize successful prototypes of tuneable IR microspectrometers.

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