Stainless steel capacitive pressure sensor for high pressure and corrosive media applications

This paper reports an assembly-type, stainless steel (SS) capacitive gage pressure sensor comprising three key elements: two SS dies and a commercial SS Swagelok fitting that also serves as the package. The sensor is realized by placing a patterned silicon dioxide film deposited on the thinner of the two SS dies (diaphragm die) against a silicon nitride film deposited on the other SS die (backing plate) and housing the combination in a Swagelok fitting. Pressure measurements up to 1500 psi have been demonstrated using corrosive and benign media. Tested media include 45% wt. potassium hydroxide (KOH), 25% wt. tetramethylammonium hydroxide (TMAH), deionized (DI) water, and nitrogen gas. Extended-duration tests with a sensor subjected to KOH solution for 30 days demonstrate excellent repeatability. Random pressure fluctuation tests over a 15-day period also demonstrate good repeatability.