Capacitive accelerometer or acceleration switch

Abstract

An accelerometer or accelerator switch and its method of manufacture are disclosed. The device is fabricated from two substrates: a top substrate having a moveable mass, and a bottom substrate having at least one conductive plate. The top substrate is preferably a SOI substrate, and the mass and its suspending beams are formed in the silicon layer under which the insulator layer has been removed. The bottom substrate is preferably oxide. In one embodiment, the capacitance is formed using the mass as the first capacitor plate the conductive plate as the second plate. As the mass moves, the capacitance is detected to indicate the magnitude of the acceleration, or whether acceleration is above or below a threshold indicting an open or closed switch. The beams which suspend the mass can be serpentines, which make the device compact and render the mass more flexible. Alternatively, the bottom conductive plate can be split into two plates each coupling to the mass. Depending on the capacitance between the two split plates, this configuration allows for the formation of either a normally-open or normally-close acceleration switch.