Microelectromechanical lateral accelerometer
First Claim
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1. A microelectromechanical accelerometer fabricated by single mask reactive ion etching comprising:
- a single crystal silicon substrate;
a single crystal silicon movable beam element fabricated from said single crystal silicon substrate by a deep vertical silicon reactive ion etch to produce a trench having vertical sidewalls surrounding the beam element and forming a cavity in said substrate, followed by an isotropic dry etch to thereafter release the beam element from the substrate;
a resilient spring integral with said substrate and said beam element and fabricated from said substrate by said reactive ion etch and isotropic dry etch simultaneously with the formation of said movable beam element to support said beam element for relative motion with respect to said substrate, said spring urging said beam element to a rest position with the beam element being movable from its rest position in response to a force to be measured;
a mass on said beam element for providing a selected inertia to said beam element; and
a sensor fabricated in part on said beam element and in part on said substrate for measuring relative motion between said beam element and said substrate in response to said force to be measured.
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Abstract
A microelectromechanical accelerometer having submicron features is fabricated from a single crystal silicon substrate. The accelerometer includes a movable portion incorporating an axial beam carrying laterally-extending high aspect ratio released fingers cantilevered above the floor of a cavity formed in the substrate during the fabrication process. The movable portion is supported by restoring springs having controllable flexibility to vary the resonant frequency of the structure. A multiple-beam structure provides stiffness in the movable portion for accuracy.
172 Citations
29 Claims
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1. A microelectromechanical accelerometer fabricated by single mask reactive ion etching comprising:
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a single crystal silicon substrate; a single crystal silicon movable beam element fabricated from said single crystal silicon substrate by a deep vertical silicon reactive ion etch to produce a trench having vertical sidewalls surrounding the beam element and forming a cavity in said substrate, followed by an isotropic dry etch to thereafter release the beam element from the substrate; a resilient spring integral with said substrate and said beam element and fabricated from said substrate by said reactive ion etch and isotropic dry etch simultaneously with the formation of said movable beam element to support said beam element for relative motion with respect to said substrate, said spring urging said beam element to a rest position with the beam element being movable from its rest position in response to a force to be measured; a mass on said beam element for providing a selected inertia to said beam element; and a sensor fabricated in part on said beam element and in part on said substrate for measuring relative motion between said beam element and said substrate in response to said force to be measured. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21)
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22. A microelectromechanical force detector, comprising:
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an integrated circuit wafer of single crystal silicon carrying circuit elements for connecting a detector to circuitry on said wafer; a cavity formed in a surface of said wafer; a horizontal, movable, single crystal silicon beam element fabricated from said wafer and located in said cavity; a vertical pedestal located in said cavity, fabricated from said wafer, and integral with said wafer and said beam element, said pedestal supporting said beam element for torsional motion about the pedestal in a horizontal plane in response to an applied force; an electrically conductive layer on said wafer and on said beam element a sensor having a first component comprising a first portion of said electrically conductive layer on said relative motion with respect to said first component, said first and second components including first and second capacitor plates, respectively, whereby an applied force causes relative motion of said capacitor plates to vary the capacitance therebetween for detecting said force; and an electrical connector between said first portion of said conductive layer and said circuit elements, whereby said sensor is connectable to circuitry on said wafer. - View Dependent Claims (23, 24, 25, 26, 27, 28)
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29. A method of detecting torsional acceleration, comprising:
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defining, on the surface of an integrated circuit wafer containing integrated circuit elements, a pattern for a movable accelerometer component and a stationary accelerometer component, the movable component including at least a horizontal portion and a vertical spring arm portion for mechanically supporting said horizontal portion; etching, by vertical reactive ion etching, a trench surrounding said pattern to produce in said wafer a cavity having a vertical side wall and containing mesas having vertical side walls in said pattern; coating said side walls with a protective layer; deepening said trenches by further reactive ion etching; undercutting said mesas in said pattern by an isotropic dry etch to release at least said horizontal movable component, from said wafer while retaining a mechanical connection between said spring arm portion and said wafer to support said movable component for rotational movement in a horizontal plane within said cavity; coating said released movable component and said stationary component with a conformed electrically conductive layer; and patterning said conductive layer to produce first and second opposed capacitor plates on said movable and stationary components, respectively, and to electrically connect said plates to said integrated circuit elements, whereby relative motion between said movable and stationary components due to acceleration of said wafer changes the capacitance between said opposed capacitor plates to produce a corresponding output signal representing said acceleration.
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Specification