Pressure-sensing capacitor and method of trimming same

Abstract

A pressure-sensing capacitor and a method for trimming the capacitor is disclosed. The capacitor includes a pair of spaced flexible quartz plates. A thin circular layer of conductive metal is formed on the opposing inner surfaces of the plates to define the electrodes of the capacitor. A glass frit sealing compound, forming a concentric ring about the conductive layers, is disposed between the plates to seal the evacuated space between the plates. The thickness of the ring is small enough so that the capacitance between the electrodes is higher by an unknown amount than the desired value of capacitance at every point in the range of variation of the value of pressure. The capacitor is trimmed by first measuring the capacitance value at zero pressure. In two of the embodiments disclosed the capacitance value at a maximum pressure is also measured. The dimensions and location of a path on one of the electrodes is computed from a measured capacitance value(s) and the deflection characteristics of the plates. Radiant energy in the form of a laser beam is applied to the electrode to cut through the electrode along the computed path to electrically insulate a first part of the layer from a second part of the layer so that the value of capacitance at zero pressure is substantially equal to the desired value.