This paper describes a piezoresistive, absolute pressure transducer. It is designed to meet the stringent requirements of intake manifold pressure measurement on turbocharged engines. Pressure media containing gasoline, oil or water have virtually no effect on the transducer's performance.
In the past, the demand for a sealed, vacuum reference has required using the active (electrically connected) side of the silicon chip as the pressure interface. To allow other than clean, dry air as a pressure medium, protective coatings or liquid isolation have frequently been used. But their use often requires performance tradeoffs.
No isolation or coating is required with the design described in this paper. Instead, the active chip side is evacuated, exposing only the passive side to the pressure media. This effectively eliminates the need for tradeoffs in achieving media compatibility.