Piezoresistive MEMS pressure sensor and packaging for harsh oceanic environment

We report a fabrication and packaging approach for a piezoresistive micro electro mechanical (MEMS) pressure sensor designed to operate up to a depth of hundreds of meters under harsh seawater conditions. The pressure values at such depths would typically be in the range of 3000 psi and the temperature conditions would vary from as low as -5/spl deg/C to 60/spl deg/C. The sensor essentially consists of an array of silicon diaphragms 20-60 /spl mu/m in thickness with selective regions diffused with boron (p-type) that act as piezoresistors. The packaging solution involves a wafer-level and chip scale interconnection, approach taking into consideration appropriate material selection for harsh oceanic environments. The packaged pressure sensor is tested in a simulated harsh oceanic environment. Functional tests are performed in a custom-built pressure chamber, where the deep-sea water conditions were simulated (approximately depth of 1000 m). The tests demonstrated excellent mechanical integrity of the packaged device.