Pressure transducer and mounting

Abstract

A capacitive pressure transducer whose diaphragm is formed of single crystal, highly doped silicon by etching in opposite sides the recesses which define the deflecting region of the diaphragm. This deflecting region serves as one electrode of the transducer. Two support plates of silicon are anodically bonded to opposite sides of the diaphragm along its periphery using thin layers of borosilicate glass to form with the etched recesses pressure receiving cavities. These thin layers of borosilicate glass are interposed between the diaphragm and a support plate, and extend over the entire surface of the support plate facing the diaphragm to provide for electrical isolation as well as the bonding between the diaphragm and the support plates. These layers of glass are made as thin as possible consistent with the need to maintain the stray capacitance below a certain value. The transducer is mounted to a pressure receiving assembly by using a silicon stub having a passage for communicating one pressure to be measured to the transducer. The stub is joined at one end to the transducer by anodic bonding using a thin layer of borosilicate glass. A weldable tube is attached to the stub. This tube is long with respect to the stub and has a reduced diameter at one end which fits into the passage of the stub. The reduced diameter is kept at a minimum. The tube is welded to the pressure receiving body at its end to provide mechanical isolation for the transducer.