Three axes accelerometer

• US 5,487,305 A
• Filed: 07/12/1994
• Issued: 01/30/1996
• Est. Priority Date: 12/19/1991
• Status: Expired due to Term

• Current Assignee: Apple Inc.
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Ristic, Ljubisa, Dunn, William C., Koucheng, Wu, Calaway, Michael F., Gutteridge, Ronald J.
• Primary Examiner(s): Chapman, John E.
• Application Number:
  US08/274,128
• Time in Patent Office: 567 Days
• Field of Search: 73/517 R, 73/517 B, 73/510, 361/280
• US Class Current: 73/514.32
• CPC Class Codes: G01P 15/125 by capacitive pick-up
• CPC Class Codes: G01P 15/18 in two or more dimensions
• CPC Class Codes: G01P 2015/082 for two degrees of freedom of movement of a single mass

Abstract

A three axis accelerometer includes a semiconductor substrate with a plurality of layers of conductive material formed thereon by semiconductor manufacturing techniques, with each layer defining a plane and mounted in parallel spaced relation to each other. A first of the layers is fixedly mounted and a second layer is mounted for limited movement relative to the first layer with the first and second layers forming a first capacitance varying in accordance with acceleration of the accelerometer along a first axis defined by the first and second layers. A plurality of first surfaces and a plurality of electrically isolated plates are formed as a portion of the first and the second layers, respectively, and positioned in parallel juxtaposition, with the plates being moveable relative to the first layer. The first surfaces and the plates defining mutually orthogonal second and third axes with each other and the first axis and forming capacitances which vary in accordance with acceleration in the second and third axes.

Claims

1. A three axis accelerometer comprising:

a semiconductor substrate;

a plurality of layers of conductive material formed on the substrate, each layer of conductive material generally defining a plane and each mounted so the defined planes are parallel with and in spaced relation to each other, a first of the layers being fixedly mounted and with a second layer being mounted by a plurality of flexible arms each having a first end attached to a center post supported on the substrate and a second end attached to support the second layer for limited movement of the second layer relative to the first layer;

the first and second layers forming a first capacitance varying in accordance with acceleration of the accelerometer along a first axis perpendicular to the first and second layers;

a plurality of first surfaces and a plurality of electrically isolated plates formed as a portion of the second and the first layers, respectively, and positioned in parallel juxtaposition, the plurality of first surfaces being moveable with the second layer and relative to the first layer, the plurality of first surfaces and the plurality of electrically isolated plates being further formed to define second and third axes mutually orthogonal with each other and the first axis; and

variable capacitances being formed between the plurality of first surfaces and the plurality of electrically isolated plates, which capacitances vary in accordance with acceleration in the second and third axes, respectively.

2. A three axes accelerometer as claimed in claim 1 wherein the plurality of conducting layers includes a third layer fixedly positioned relative to the first layer and with the second layer positioned between the first and third layers, the second and third layers forming a second capacitance that varies in accordance with acceleration of the accelerometer along the first axis, which variations are opposite to the variations in the first capacitance.

3. A three axes accelerometer as claimed in claim 2 including in addition a plurality of second plates, similar to the first plates, formed as a portion of the third layer.

4. A three axes accelerometer as claimed in claim 3 wherein the pluralities of first and second surfaces are defined on conductive plates positioned in parallel spaced apart relationship.

5. A three axes accelerometer as claimed in claim 1 wherein the plurality of layers are supported by a semiconductor substrate and the substrate further supports circuitry connected to the first capacitance and the variable capacitances to provide signals indicative of acceleration in the first, second and third axes.

6. A three axes accelerometer as claimed in claim 5 wherein the accelerometer and the circuitry are formed in a single integrated circuit.

7. A three axes accelerometer as claimed in claim 1 wherein the single post is a generally centrally positioned post perpendicular to the plane of the first and the plane of the second layers.

8. A three axis accelerometer comprising:

a semiconductor substrate;

a first layer of conductive material formed on the substrate and generally defining a plane;

a second layer of conductive material mounted by a plurality of flexible arms each having a first end attached to a center post supported on the substrate and a second end attached to support the second layer and with a major surface of the second layer in spaced relation from the first layer and parallel to the plane for limited movement relative to the first layer;

a third layer of conductive material supported on the substrate and fixedly mounted relative to the first layer and parallel to the plane, the third layer being mounted adjacent and in spaced relation from a second major surface of the second layer;

the first and second layers forming a first capacitance and the second and third layers forming a second capacitance, each formed capacitance varying in accordance with acceleration of the accelerometer along a first axis defined by the first, second and third layers;

conductive plates formed as a portion of the first layer and a portion of the third layer and electrically isolated conductive surfaces formed as a portion of the second layer, the various conductive plates being positioned in juxtaposition with the conductive surfaces formed as a portion of the second layer moveable with the second layer, relative to the first and third layers, the surfaces and plates being further formed to define second and third axes mutually orthogonal with each other and the first axis; and

variable capacitances being formed between the various conductive surfaces and conductive plates which variable capacitances vary in accordance with acceleration in the second and third axes.

9. A three axes accelerometer as claimed in claim 8 wherein the surfaces are defined on conductive plates positioned in parallel spaced apart relationship.

10. A three axes accelerometer as claimed in claim 8 wherein the first, second and third layers of conductive material are formed of doped semiconductor material.

11. A three axes accelerometer as claimed in claim 10 wherein the semiconductor material is polysilicon.

12. A three axes accelerometer as claimed in claim 8 wherein the substrate further has formed thereon circuitry connected to the first and second capacitances and the variable capacitances to provide signals indicative of acceleration in the first, second and third axes.

13. A three axes accelerometer as claimed in claim 12 wherein the accelerometer and the circuitry are formed in a single integrated circuit.

14. A three axes accelerometer as claimed in claim 8 wherein the center post is a generally centrally positioned post perpendicular to the plane of the first and the plane of the second layers.