Electromechanical pressure transducer

Abstract

An improved ceramic capacitive pressure sensor adaptable for use in automobiles is disclosed. The pressure sensor comprises a thin flexible diaphragm disc having a capacitor electrode deposited on it. A thick cylindrical base substrate has a top surface with a second capacitor electrode deposited thereon and the diaphragm is bonded to the top surface of the base substrate by an annular glass ring such that the first and second electrodes are separated from each other and face each other directly across an air gap. The diaphragm, the top surface of the base substrate and the annular glass ring form an internal cavity in which a reference vacuum is stored. In response to pressure changes outside of this cavity, the diaphragm will flex and thereby change the capacitance created by the first and second electrodes. At least one channel portion is provided in the base substrate top surface which opens into the cavity storing the reference vacuum. This improves the electrical and mechanical characteristics of the pressure sensor. The diaphragm electrode is substantially larger than the base electrode and extends substantially over all of the central portion of the diaphragm within the glass annular ring and in this manner the electrode acts as a shield against conductive elements which are exterior to the internal cavity and are adjacent to the thin diaphragm.