Silicon diaphragm with integral bridge transducer

Claim 1

A pressure transducer comprising in combination a pressure-responsive diaphragm formed as a single crystal of silicon of negative conductivity type with the plane of the diaphragm parallel to a selected crystal plane that contains two crystal axes at right angles to each other, structure fixedly mounting the diaphragm periphery to permit pressure application to a diaphragm face, and a unitary bridge structure of positive conductivity type formed in the active peripheral zone of one diaphragm face and including one pair of opposite bridge arms extending radially of the diaphragm and parallel to one of said crystal axes, another pair of opposite bridge arms extending tangentially of the diaphragm and parallel to the other of said crystal axes, and terminal areas communicating with the arms for making electrical connections to energize the bridge and to tap an output signal therefrom, said crystal plane and axes being so selected that the transverse piezoresistive coefficients for both said pairs of bridge arms have absolute values at least about one-third of the corresponding longitudinal piezoresistive coefficients, and the resistance change due to radial stress in response to applied pressure predominates over that due to tangential stress in the radially extending bridge arms, and at least balances that due to tangential stress in the tangentially extending bridge arms.