A threshold pressure switch utilizing plastic deformation of silicon

The authors report on the design, fabrication, and testing of a threshold pressure switch with mechanical hysteresis. The expansion of trapped gas in a sealed cavity formed by wafer bonding is used to plastically deform a thin silicon membrane bonded over the cavity, creating a spherically shaped cap. This deformed cap exhibits mechanical hysteresis in its deflection versus pressure characteristics at the point of buckling. It is this buckling phenomenon which is used to produce the hysteresis in the pressure switch. The authors describe the fabrication and testing of devices as well as a model to predict the onset of plastic deformation in these structures. They have tested the threshold pressure switch and found that it exhibits approximately 2 psi of hysteresis. Possible applications for this threshold pressure switch are tire pressure monitoring, tactile sensor arrays, keyboards, and scales.<>