Microelectromechanical lateral accelerometer

A microelectromechanical accelerometer, comprising:

• a support beam having an elongated axis and being axially movable in response to applied forces to be measured;
• a plurality of laterally extending, spaced parallel fingers extending from and carried by said support beam and movable with said beam, said support beam and said fingers each having a double-beam structure with interconnecting bridges to provide a high degree of stiffness;
• and
• a flexible restoring spring connected to and carrying said elongated support beam, said spring allowing axial motion of said axially movable support beam and urging said support beam toward a rest position, said movable beam, said movable fingers, and said spring having high aspect ratios with minimum dimensions in the range of 1-3 .mu.m.

A microelectromechanical accelerometer, comprising:

• a single crystal silicon substrate;
• a support beam having an axis, said beam being fabricated from said substrate and being released from said substrate so as to be axially movable with respect to said substrate in response to applied forces to be measured;
• and
• a cantilevered restoring spring fabricated from said substrate and connected between said support beam and said substrate, said spring allowing axial motion of said support beam and urging said beam toward a rest position, said support beam and said restoring spring having respective cross-sectional heights greater than their respective cross-sectional widths to provide a high aspect ratio beam and a high aspect ratio spring having flexibility in a first direction and stiffness in a second direction.

A highly sensitive, microelectromechanical force detector having extremely small dimensions fabricated on an integrated circuit wafer containing electrical circuitry connectable to the detector, comprising:

• a single crystal silicon wafer carrying a pre-existing circuit element;
• a movable beam fabricated from said single crystal silicon wafer and released from said wafer for motion with respect to said wafer, said beam incorporating an elongated backbone and integral laterally extending first sensor fingers having a high aspect ratio;
• a cantilevered spring integral with said wafer and supporting said beam for motion, said spring urging said beam toward a rest position;
• second high aspect ratio sensor fingers integral with said wafer, corresponding first and second fingers having opposed side walls;
• a conformed electrically conductive layer on said opposed finger side walls to provide capacitive plates;
• and
• electrically conductive connectors between said plates and said circuit elements for connecting said plates to circuitry for detecting relative motion between said beam and said wafer.

An accelerometer formed by low temperature reactive ion etching comprising:

• a base comprising single crystal silicon;
• a proof mass responsive to an applied acceleration vector along an axis of sensitivity, said proof mass formed by defining one or more integral beams from said base by a vertical reactive ion etch followed by an isotropic etch for removing the silicon out from under said one or more beams, thereby releasing them for movement;
• a mount connecting said one or more integral beams with said base for constraining said proof mass to move along the axis of sensitivity in response to the applied acceleration vector and for restoring said proof mass to an equilibrium position;
• a transducer for converting the movement of said proof mass to a signal representative of said applied acceleration vector, said transducer formed by providing a layer of conductive material over one or more of said integral beams and over an adjacent corresponding vertical wall of said base so that a parallel plate capacitor is formed between said one or more of said beams and the corresponding adjacent wall of said base, whereby movement of said proof mass relative to said base provides a change in capacitance;
• and
• signal conditioning circuitry responsive to said change in capacitance for converting said change in capacitance to a signal representative of said applied acceleration.

An accelerometer comprising:

• a wafer of single crystal silicon having a major face;
• a proof mass formed by defining a selected region in said major face and etching vertically downwardly using a low temperature reactive ion etch, and undercutting a portion of the wafer underlying the proof mass with an isotropic release etch for releasing said proof mass to move in response to an applied acceleration vector along an axis of sensitivity, said proof mass characterized by a major surface having a high aspect ratio formed by said vertical reactive ion etch;
• and
• a transducer for converting movement of the proof mass in response to an applied acceleration vector and for producing an output signal representative of the magnitude of said acceleration vector.

An accelerometer comprising:

• a wafer comprising single crystal silicon;
• a proof mass for moving along an axis of sensitivity in response to an applied input acceleration vector, said proof mass formed by a vertical reactive ion etch of said wafer to form one or more beams with vertical side walls, each beam side wall disposed adjacent to a corresponding vertical wall of the wafer, said beams being undercut with an isotropic etch to release a sufficient portion of the beam from the wafer for movement in the axis of sensitivity in response to said applied input acceleration vector;
• a transducer formed by coating the vertical side wall of said one or more beams and the adjacent corresponding vertical wall of said wafer with a conductive material to provide adjacent capacitor plates for producing a differential capacitance upon relative motion of the proof mass in response to an applied acceleration vector;
• and
• wherein the one or more beams of the proof mass are characterized by high aspect ratio surfaces exhibiting stiffness and insensitivity to acceleration vectors which are not parallel to the axis of sensitivity.