Capacitive accelerometer with mid-plane proof mass

Claim 1

A solid-state silicon accelerometer comprising: a three-plate capacitor including fixed top and bottom plates and a silicon movable sensing plate having a top surface separated from said top plate by a top gap and a bottom surface separated from said bottom plate by a bottom gap, defining a reference midplane and being connected to support members by flexible connections extending across a support gap between said silicon sensing plate and said support members to move between said top and bottom plates in response to acceleration along an acceleration axis perpendicular to said reference midplane, whereby acceleration along said acceleration axis displaces said silicon sensing plate from said reference midplane and alters the capacitance between said silicon sensing plate and said top and bottom plates, in which; said top and bottom plates and said support members are bonded together to form a rigid structure; said silicon sensing plate is connected to said support members by at least one pair of flexures extending a predetermined hinge width along opposite sides of said sensing plate and having a predetermined hinge length less than the length of said sensing plate, so that a communication path is established between a top chamber between said top and said silicon sensing plates and a bottom chamber between said bottom and said silicon sensing plates; at least one chamber has motion stops disposed therein and grooves to facilitate squeeze-film damping in one of said silicon sensing plate and said fixed plate; and electronic means for measuring the capacitance of at least one of said chambers, characterized in that: said silicon sensing plate is formed from top and bottom silicon slabs bonded together at an interface region, each of said silicon slabs being boron doped on a flexure surface abutting said interface region, and is connected to said support members by flexures lying substantially in said flexure surfaces and being disposed about said support gap in a predetermined pattern, whereby said top and bottom silicon slabs combine to form a composite sensing plate connected to said support members by said at least one pair of flexures disposed symmetrically in said top and bottom plates and substantially in said sensing plate midplane, said top silicon slab, a corresponding top slab portion of said support members and a corresponding top slab flexure and said bottom silicon slab, a corresponding bottom slab portion of said support member and a corresponding bottom slab flexure being micromachined from a block of silicon.