Digital pressure-switch array with aligned silicon fusion bonding

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Abstract
The design, fabrication and testing of a micromechanical pressure-switch array is described. This two-terminal device array is formed using aligned fusion bonding of two prefabricated silicon wafers. A pattern-etched thermally grown silicon dioxide is used to determine the size of pressure membranes with the desired switch gap set by the oxide thickness. The silicon membranes are formed by controlled thinning of one of the bonded silicon wafers. Pressure-switch points of 1/4, 1/2, 3/4, and 1 atm are designed as the threshold levels in this work. The switches operate on the principle of closing electrical contacts by deflecting diaphragms in the array to a point of contact with the bottom wafer. It is found that the switches close at the desired pressure threshold with negligible hysteresis for both directions of pressure change. The array produces a digital output describing the pressure level being monitored. Experimental accuracy to within 4% of calculated pressure-switch points have been achieved.

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