Force transducer etched from silicon

Claim 1

A method for fabricating an accelerometer from silicon, comprising the steps of: etching a pair of cavities through a silicon substrate from an exposed surface of said silicon substrate to define a first suspended beam therebetween, said first suspended beam being deflectable in response to acceleration; forming a first conductive portion on said first suspended beam; bonding a silicon based material to an opposite surface of said silicon substrate; etching a pair of cavities through said silicon based material bonded to said substrate to define a second suspended beam suspended opposite said first suspended beam; forming second and third conductive portions on said second suspended beam opposite said first conductive portion; coupling an electrical oscillator circuit between said first and second conductive portions for oscillating said second suspended beam; and coupling an electrical detector circuit between said first and third conductive portions for sampling electrical power between said first and third conductive portions at sample times provided by said oscillation of said second beam.

Claim 2

A method for fabricating an accelerometer from silicon, comprising the steps of: etching a pair of cavities through a silicon substrate from an exposed surface of said silicon substrate to define a first suspended beam therebetween, said first suspended beam being deflectable in response to acceleration; forming a first conductive portion on said first suspended beam; bonding a silicon based material to an opposite surface of said silicon substrate; etching a pair of cavities through said silicon based material bonded to said substrate to define a second suspended beam suspended opposite said first suspended beam; forming second and third conductive portions on said second suspended beam opposite said first conductive portion; coupling an electrical oscillator circuit between said first and second conductive portions for oscillating said second suspended beam; and coupling an electrical detector circuit between said first and third conductive portions for sampling electrical power between said first and third conductive portions at sample times provided by said oscillation of said second beam.

Claim 5

A method for fabricating an accelerometer from silicon, comprising the steps of: forming a sacrificial layer of a silicon based material reactive to an etchant over one planar surface of a silicon substrate; forming a layer of polysilicon over said sacrificial layer; etching a pair of cavities from a surface opposite to said planar surface through said silicon substrate to define a first suspended beam therebetween, said first suspended beam being suspended opposite said first suspended beam and deflectable in response to acceleration; forming a second beam by selectively etching parallel cavities through said polysilicon layer to define said second beam between said cavities; etching away said sacrificial layer to suspend said second beam over said first suspended beam; forming a first conductive portion on said first beam; forming second and third conductive portions on said second beam; coupling an electrical oscillator between said first and second conductive portions for oscillating said second beam; and coupling sensing circuitry between said second and third conductive portions for sensing the applied force by sensing capacitive changes between said conductive portions at sample times determined by said oscillation of said second beam.

Claim 6

A method for fabricating an accelerometer from silicon, comprising the steps of: forming a sacrificial layer of a silicon based material reactive to an etchant over one planar surface of a silicon substrate; forming a layer of polysilicon over said sacrificial layer; etching a pair of cavities from a surface opposite to said planar surface through said silicon substrate to define a first suspended beam therebetween, said first suspended beam being suspended opposite said first suspended beam and deflectable in response to acceleration; forming a second beam by selectively etching parallel cavities through said polysilicon layer to define said second beam between said cavities; etching away said sacrificial layer to suspend said second beam over said first suspended beam; forming a first conductive portion on said first beam; forming second and third conductive portions on said second beam; coupling an electrical oscillator between said first and second conductive portions for oscillating said second beam; and coupling sensing circuitry between said second and third conductive portions for sensing the applied force by sensing capacitive changes between said conductive portions at sample times determined by said oscillation of said second beam.