Media compatible stainless steel capacitive pressure sensors

Self-packaged stainless steel (SS) capacitive pressure sensors are developed and studied for their harsh environment performance, i.e., measurements of high-pressures and in corrosive media. The transducer elements of the sensors are fabricated from SS and tungsten carbide (WC) commercial off-the-shelf parts with conventional- and micromachining techniques. A SS vacuum coupling radiation (VCR) tube fitting provides the housing to realize a self-packaged pressure sensor. Capacitive transduction is used to simplify the implementation. High-pressure capability up to 1500 psi and corrosive-media capability in 45% (wt./wt.) potassium hydroxide (KOH) solution, 25% (wt./wt.) tetramethylammonium hydroxide (TMAH) solution and 10% (wt./wt.) sodium chloride (NaCl) solution has been demonstrated. Long-term media compatibility is demonstrated by soaking the pressure sensors in NaCl solutions for over 1 month while subjecting them to repeated pressure cycles of up to 1000 psi daily. Long-term reliability to at least 1 million pressure cycles (by ramping the pressure up to 700 psi and then down to 0 psi) is also demonstrated. Finally, elevated temperature capability of the sensor up to temperatures of 320 °C has been explored.