THIN FILM ORGANIC PASSIVATION COATINGS FOR MEDIA COMPATIBLE PRESSURE SENSORS
Original Publication Date: 1995-Jul-01
Included in the Prior Art Database: 2002-Mar-25
Silicon piezoresistive pressure sensors have been successfidly assembled with Parylene C" in place of fluorosilicone gels. Parylene" is a conformal coating (Figure 1) that is chemically resistant to most known solvents below 175°C. Therefore, it is being used to provide media compatibility for conventional pres- sure sensors. The Parylene" coating places an addi- tional, controllable stress on the transducers. More- over, heating of this room-temperature, vacuum- deposited film, above its glass transition tempera- ture initially causes a change in the stress that is applied to the transducer. This "annealing" effect occurs only during the first heating cycle and is prob- ably the result of a reduction in residual stress and/or crystallinity formation. Parylene" thin films cause sensitivity changes in the transducer that are a func- tion of thickness. Finite element modeling has con- firmed this and is accurate to within 10% presently. Offset and linearity are not significantly affected by the addition ofthe thin film.