Single-side microelectromechanical capacitive accelerometer and method of making same

• US 6,718,605 B2
• Filed: 06/21/2001
• Issued: 04/13/2004
• Est. Priority Date: 09/08/1997
• Status: Expired due to Term

• Current Assignee: Board of Regents of the University of Michigan (University of Michigan)
• Original Assignee: Board of Regents of the University of Michigan (University of Michigan)
• Inventors: Yazdi, Navid, Najafi, Khalil, Salian, Arvind
• Primary Examiner(s): Arbes, Carl J.
• Assistant Examiner(s): Nguyen, Tai V
• Application Number:
  US09/885,953
• Publication Number:
  US 20010042404A1
• Time in Patent Office: 1,027 Days
• Field of Search: 29/254.1, 29/254.2, 298/31, 298/46, 735/143.2, 735/141.8, 735/141.6, 735/141.7
• US Class Current: 29/25.42
• CPC Class Codes: G01P 15/0802 Details
• CPC Class Codes: G01P 15/125 by capacitive pick-up
• CPC Class Codes: G01P 15/131 with electrostatic counterbalancing means
• CPC Class Codes: Y10T 29/43 Electric condenser making
• CPC Class Codes: Y10T 29/435 Solid dielectric type
• CPC Class Codes: Y10T 29/49128 Assembling formed circuit to base
• CPC Class Codes: Y10T 29/4913 Assembling to base an electrical component, e.g., capacitor, etc.

Abstract

A high sensitivity, Z-axis, capacitive microaccelerometer having stiff sense/feedback electrodes and a method of its manufacture on a single-side of a semiconductor wafer are provided. The microaccelerometer is manufactured out of a single silicon wafer and has a silicon-wafer-thick proof mass, small and controllable damping, large capacitance variation and can be operated in a force-rebalanced control loop. One of the electrodes moves with the proof mass relative to the other electrode which is fixed. The multiple, stiffened electrodes have embedded therein damping holes to facilitate force-rebalanced operation of the device and to control the damping factor. Using the whole silicon wafer to form the thick large proof mass and using thin sacrificial layers to form narrow uniform capacitor air gaps over large areas provide large-capacitance sensitivity. The manufacturing process is simple and thus results in low cost and high yield manufacturing.

Claims

1. In a method for making a high-sensitivity, microelectromechanical capacitive accelerometer including a proof mass having a thickness along an input axis of the accelerometer and first and second conductive electrodes from a single semiconductor wafer having a predetermined thickness, the improvement comprising:

depositing first and second planar layers on a single-side of the wafer, the planar layers being relatively thin along the input axis;

stiffening the first and second planar layers to form the first and second conductive electrodes, respectively, which are stiff so as to resist bending movement along the input axis; and

forming substantially uniform, first and second narrow gaps between the first conductive electrode and the proof mass and between the second conductive electrode and the first conductive electrode, respectively, wherein the first electrode is suspended above the proof mass and wherein the second electrode is supported on the proof mass to move therewith relative to the first electrode and wherein the thickness of the proof mass is at least one order of magnitude greater than either the thickness of the first planar layer or the thickness of the second planar layer.

2. The method as claimed in claim 1, wherein the thickness of the proof mass is substantially equal to the predetermined thickness of the wafer.

3. The method as claimed in claim 1, wherein the semiconductor wafer is a silicon wafer.

4. The method as claimed in claim 1 wherein the step of stiffening includes the step of forming a stiffening metallic layer on at least one of the planar layers.

5. The method as claimed in claim 1 wherein the step of stiffening includes the step of forming stiffening ribs on at least one of the planar layers.

6. The method as claimed in claim 5 wherein the step of forming the stiffening ribs includes the steps of forming trenches in the proof mass and refilling the trenches with a sacrificial layer having a substantially uniform thickness and an electrode material and wherein the step of forming the substantially uniform, first narrow air gap includes the step of removing the sacrificial layer.

7. The method as claimed in claim 1 wherein the step of stiffening includes the step of electroplating the first and second planar layers.

8. The method as claimed in claim 1 further comprising forming a plurality of beams for suspending the proof mass at upper and lower portions thereof.

9. In a method for making a high-sensitivity, microelectromechanical capacitive accelerometer including a proof mass having a thickness along an input axis of the accelerometer and first and second conductive electrodes from a single semiconductor wafer having a predetermined thickness, the improvement comprising:

depositing first and second planar layers on a single-side of the wafer, the planar layers being relatively thin along the input axis;

stiffening the first and second planar layers to form the first and second conductive electrodes, respectively, which are stiff so as to resist bending movement along the input axis; and

forming substantially uniform, first and second narrow gaps between the first conductive electrode and the proof mass and between the second conductive electrode and the first conductive electrode, respectively, wherein the thickness of the proof mass is at least one order of magnitude greater than either the thickness of the first planar layer or the thickness of the second planar layer wherein the step of stiffening includes the step of forming stiffening ribs on at least one of the planar layers and wherein the step of forming the stiffening ribs includes the steps of forming trenches in the proof mass and refilling the trenches with a sacrificial layer having a substantially uniform thickness and an electrode material and wherein the step of forming the substantially uniform, first narrow air gap includes the step of removing the sacrificial layer.