Capacitor center of area sensitivity in angular motion micro-electromechanical systems

• US 6,000,287 A
• Filed: 08/28/1998
• Issued: 12/14/1999
• Est. Priority Date: 08/28/1998
• Status: Expired due to Fees

• Current Assignee: Visteon Global Technologies Incorporated (Visteon Corporation)
• Original Assignee: Ford Motor Company
• Inventors: Menzel, Christoph P.
• Primary Examiner(s): Williams, Hezron
• Assistant Examiner(s): Kwok, Helen C.
• Application Number:
  US09/143,255
• Time in Patent Office: 473 Days
• Field of Search: 73/514.32, 73/514.36, 73/514.16, 73/514.21, 73/1.37, 73/1.38, 361/280, 361/283.1, 361/292
• US Class Current: 73/514.32
• CPC Class Codes: G01P 15/0802 Details
• CPC Class Codes: G01P 15/125 by capacitive pick-up
• CPC Class Codes: G01P 2015/0828 the mass being of the paddle type being suspended at one of its longitudinal ends
• CPC Class Codes: G01P 2015/0831 the mass being of the paddle type having the pivot axis between the longitudinal ends of the mass, e.g. see-saw configuration
• CPC Class Codes: G01P 21/00 Testing or calibrating of apparatus or devices covered by the preceding groups

Abstract

A method is provided that may be used to design a family of capacitive microaccelerometers with different members of the family having different sensitivities to acceleration without having to make a radical design change to the basic construction. The microaccelerometer is a capacitively sensed angular motion micro-electromechanical system. The microaccelerometer includes a stationary plate electrode and a movable plate electrode substantially parallel with the stationary plate electrode. The movable plate electrode rotates through a dielectric fluid about an axis of rotation parallel to the stationary plate electrode in response to acceleration. The method includes determining the desired sensitivity and changing the stationary plate center of area relative to the movable plate so as to obtain the desired sensitivity.

Claims

1. A method for designing a capacitively sensed, angular motion micro-electromechanical sensor (MEMS) wherein the sensor comprises a stationary electrode and a movable electrode separated by a dielectric fluid, the stationary electrode and the movable electrode substantially parallel, the movable electrode operative to rotate through the dielectric fluid about an axis of rotation parallel to the stationary electrode in response to a sensed parameter, the stationary electrode having a center of area relative to the movable electrode, the method comprising:

determining a desired sensitivity; and

changing the stationary electrode center of area relative to the movable electrode so as to obtain the desired sensitivity.

2. A method as in claim 1 wherein the stationary electrode and the movable electrode are rectangular, each electrode with sides defining a width, the width extending parallel to the axis of rotation, the stationary electrode further having sides defining a length normal to the width, changing the stationary electrode center of area relative to the movable electrode comprising chancing the stationary electrode length.

3. A method as in claim 1 wherein changing the stationary electrode center of area relative to the movable electrode comprises moving the stationary electrode relative to the movable electrode.

4. A micro-electromechanical system (MEMS) comprising:

a substrate having a top surface;

a rigid support member attached to the substrate;

a deflection member attached to the support member so as to deflect relative to the support member, the deflection member having a bottom surface substantially parallel with the substrate top surface;

a first electrode on the bottom surface of the deflection member; and

a second electrode on the top surface of the substrate, the second electrode having an area with a center of area, the first electrode and the second electrode forming a capacitor with capacitance based on the deflection of the deflection member;

wherein the second electrode center of area is positioned relative to the first electrode to achieve a desired sensitivity of change in capacitance for a given deflection.

5. A micromachined accelerometer comprising:

a substrate;

a movable plate substantially parallel to and above the substrate comprising

an aperture,

a pedestal positioned within the aperture, the pedestal rigidly attached to the substrate, and

at least one torsional member connecting the pedestal to at least one edge of the aperture, the at least one torsional member allowing the movable plate to rotate relative to the substrate about a flexure axis in the presence of an acceleration normal to the substrate;

a first electrode on the movable plate;

a second electrode on the substrate located generally below the first electrode, the second electrode having an area with a second electrode center of area, the first electrode and the second electrode forming a first capacitor with capacitance varying with rotation of the movable plate, wherein the second electrode center of area is positioned relative to the first electrode to achieve a desired first capacitor sensitivity, the desired first capacitor sensitivity expressed as change in capacitance of the first capacitor for a given acceleration normal to the substrate;

a third electrode on the movable plate formed at a position opposite of the flexure axis from the first electrode; and

a fourth electrode on the substrate located generally below the third electrode and formed at a position opposite of the flexure axis from the second electrode, the fourth electrode having an area with a fourth electrode center of area, the third electrode and the fourth electrode forming a second capacitor with capacitance varying with rotation of the movable plate, wherein the fourth electrode center of area is positioned relative to the third electrode to achieve a desired second capacitor sensitivity, the desired second capacitor sensitivity expressed as change in capacitance of the second capacitor for a given acceleration normal to the substrate.

6. A micromachined accelerometer as in claim 5 wherein the desired first capacitor sensitivity is equal to the desired second capacitor sensitivity.

7. A micromachined accelerometer as in claim 5 wherein the desired first capacitor sensitivity is not equal to the desired second capacitor sensitivity.

8. A micromachined accelerometer as in claim 5 wherein the movable plate is shaped substantially in the form of a trident with the first electrode on a handle of the trident and the third electrode on a center prong of the trident.

9. A micromachined accelerometer as in claim 5 wherein the movable plate is operable to function as the first electrode and the third electrode.