Importance

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Abstract

A resonant strain gauge includes a silicon substrate, a polysilicon flexure beam fixed at both ends relative to the substrate, and a polysilicon rigid cover cooperating with the substrate to enclose the flexure beam within a sealed vacuum chamber. An upper bias electrode is formed on the cover, and a lower bias electrode is formed at the bottom of a trough in the substrate directly beneath the flexure beam. A drive electrode and a piezoresistive element are supported by the beam, formed over a silicon nitride thin film layer deposited onto the top surface of the flexure beam. A second silicon nitride layer covers the drive electrode and piezoresistor, cooperating with the first silicon nitride layer to dielectrically encapsulate the drive electrode and piezoresistor. The silicon nitride further extends outwardly of the beam to a location between the polysilicon layer that contains the beam, and the cover, to isolate the cover from the flexure beam. A polysilicon film is applied over the upper silicon nitride layer as a passivation layer to protect the silicon nitride during gauge fabrication. The process for fabricating the gauge includes a sequence of applying the various polysilicon and silicon nitride layers by low pressure chemical vapor deposition, in combination with selective etching to define the flexure beam, electric circuit components and vacuum chamber.

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First Claim