Micromachined threshold pressure switch and method of manufacture

Abstract

A pressure activated threshold switch has two electrodes separated by a small distance across a cavity. One of the electrodes is made of a mechanically compliant material. As a uniform pressure is applied to the mechanically compliant electrode, a threshold is reached at which the electrode buckles under the applied load and makes contact with the second electrode thereby closing the switch. The switch exhibits mechanical hysteresis by subsequently opening under a lower applied load. The pressure threshold switch is fabricated using wafer to wafer silicon bonding along with conventional integrated fabrication steps. The techniques of integrated circuit technologies enable dimensional control to be very good and hence activation pressures are tightly controlled. The fabrication method exploits properties of wafer to wafer silicon bonding, such as residual pressure inside sealed cavities and plastic deformation of silicon. The buckling load or threshold pressure at which the switch closes is easily tailored to specific applications. Potential applications include threshold pressure sensors for indicating when automotive tires need inflation, tank pressure monitors in air and gas compressors, switches for keyboard pads, weight detectors and robotic tactile sensor arrays.