Capacitive accelerometer with mid-plane proof mass

• US 5,008,774 A
• Filed: 02/28/1989
• Issued: 04/16/1991
• Est. Priority Date: 02/28/1989
• Status: Expired due to Fees

• Current Assignee: Breed Automotive Technology, Inc. (Ningbo Junsheng Investment Group Co., Ltd.)
• Original Assignee: United Technologies Corporation (Raytheon Technologies Corporation d/b/a RTX)
• Inventors: Bullis, Robert H., Swindal, James L.
• Primary Examiner(s): GRIFFIN, DONALD
• Application Number:
  US07/317,258
• Time in Patent Office: 777 Days
• Field of Search: 361/283, 73/517
• US Class Current: 73/514.13
• CPC Class Codes: G01P 15/0802 Details
• CPC Class Codes: G01P 15/125 by capacitive pick-up

Abstract

A micromachined three-plate capacitive accelerometer incorporates a "sandwich" proof mass formed from two layers that are boron-doped to define hinges attached essentially to the midplane of the proof mass by being placed abutting a bonding interface region at the midplane.

Claims

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.

2. An accelerometer according to claim 1, further characterized in that said interface region is formed from a layer of metal bonded to said top and bottom silicon slabs.

3. An accelerometer according to claim 1, further characterized in that said interface region is formed from a layer of dielectric material.

4. An accelerometer according to claim 3, further characterized in that said interface region is formed from a layer of dielectric material and in which said top and bottom silicon slabs are electrically isolated from one another.

5. An accelerometer according to claim 1, further characterized in that said movable silicon sensing plate has a rectangular shape and opposite corners in said reference midplane and said at least one pair of flexures comprises a plurality of pairs of flexures disposed symmetrically about said acceleration axis with respect to a pair of diagonal axes extending in said reference midplane through said acceleration axis.

6. An accelerometer according to claim 5, further characterized in that said flexures of said plurality of pairs of flexures are disposed azimuthally about said acceleration axis and sequentially above and below said reference midplane.

7. An accelerometer according to claim 6, further characterized in that said silicon sensing plate has a square cross section in said reference midplane.