3-Axis Accelerometer With Gap-Closing Capacitive Electrodes

• US 20100212425A1
• Filed: 09/09/2009
• Published: 08/26/2010
• Est. Priority Date: 02/25/2009
• Status: Active Grant

• Current Assignee: National Tsing Hua University
• Original Assignee: National Tsing Hua University
• Inventors: Wu, Ming-Ching, Hsu, Chia-Pao, Fang, Weileun
• Granted Patent: US 8,443,670 B2
• Time in Patent Office: Days
• US Class Current: 73/514.320
• CPC Class Codes: G01P 15/0802 Details
• CPC Class Codes: G01P 15/125 by capacitive pick-up
• CPC Class Codes: G01P 15/18 in two or more dimensions

Abstract

Disclosed is a novel three-axis capacitive-type accelerometer implemented on SOI wafer. The accelerometer consists of four springs, one proof mass, four pairs of gap-closing sensing electrodes (each pair of gap-closing sensing electrode containing one movable electrode and one stationary electrode), and several metal-vias as the electrical interconnections. The movable electrodes are on the proof mass, whereas the stationary electrodes are fixed to the substrate. The three-axis accelerometer has five merits. (1) The sensitivity of the accelerometer is improved since the proof-mass is increased by containing both device and handling silicon layers; (2) The sensitivity is also improved by the gap-closing differential capacitive sensing electrodes design; (3) The parasitic capacitance at bond pad is reduced by the existing of metal-vias between the device Si layer and handling Si layer; (4) The sensing gap thickness is precisely defined by the buried oxide of SOI wafer; (5) The stationary sensing electrodes anchored to the substrate also act as the limit stops to protect the accelerometer.

Claims

1. A sensing accelerometer, comprising:

a substrate; and

a movable unit further comprising;

a movable element; and

plural components connected to the substrate and the movable element.

2. The accelerometer according to claim 1, wherein the substrate has plural inner edges each of which has an opposite one of the plural inner edges.

3. The accelerometer according to claim 1, wherein the movable element has plural edges, the plural components are the plural flexible components, and the substrate is a fixing substrate and comprises:

plural fixed anchors respectively connected to the plural flexible components; and

plural fixed electrode plates disposed respectively beside the plural edges of the movable element.

4. The accelerometer according to claim 3, wherein each of the plural fixed anchors has a corner, and the plural flexible components connect the respective corners of the plural fixed anchors.

5. The accelerometer according to claim 3, wherein each of the plural fixed anchors, each of the plural fixed electrode plates and the movable element have an intermediary disposed therein.

6. The accelerometer according to claim 5, wherein the substrate and the movable unit are made of a Silicon on Insulator (SOI) wafer, and the respective intermediaries conduct the substrate and the movable unit.

7. The accelerometer according to claim 5, wherein the respective intermediaries are filled by one selected from a group consisting of a silver paste, a polycrystalline silicon deposition and a metal sputtering.

8. The accelerometer according to claim 3, wherein the movable unit and each of the fixed electrode plates have a gap therebetween, and the fixed electrode plates are differential type capacitive sensing electrodes.

9. The accelerometer according to claim 3, wherein the plural fixed electrode plates comprises:

plural lower electrode plates respectively placed along a first group of the plural edges of the moveable element, and providing a lower limit of the movable unit in a Z-axis movement, wherein every two ones of the first group of the plural edges are opposite to each other, and the ones of the first group of the plural edges have an even total number; and

plural upper electrode plates respectively placed along a second group of the plural edges of the moveable element, and providing an upper limit in the Z-axis movement for the movable unit, wherein every two ones of the second group of the plural edges are opposite to each other, and the ones of the second group of the plural edges have an even total number,

wherein each of the plural fixed electrode plates has a portion being held over the movable element.

10. The accelerometer according to claim 9, wherein the movable unit is movable in X-axis and Y-axis.

11. The accelerometer according to claim 1, wherein each of the plural components is a spring.

12. The accelerometer according to claim 1 being a capacitive sensing accelerometer with a gap-closing differential electrode.

13. A multi-axes accelerometer, comprising:

plural fixing element; and

a movable element having plural components respectively connected to the plural fixing element;

wherein the multi-axes accelerometer is a capacitive sensing accelerometer with a gap-closing differential electrode.

14. The accelerometer according to claim 13 further comprising plural stationary electrode plates configured by the movable element, wherein the plural fixing elements are plural fixing anchors.

15. The accelerometer according to claim 14, wherein the movable element has plural edges having a first and a second groups, and the plural stationary electrode plates are classified as:

plural lower electrode plates respectively placed along the first group of the plural edges of the moveable element, and providing a lower restriction of the movable unit in a Z-axis movement; and

plural upper electrode plates respectively placed along the first group of the plural edges of the moveable element, and providing an upper limit of the restriction movable unit in the Z-axis movement,

wherein each of the plural stationary electrode plates has a portion being held over the movable element.

16. The accelerometer according to claim 14, wherein each of the plural fixing anchors, each of the plural stationary electrode plates and the movable element are made of a Silicon On Insulator (SOI) wafer and have an intermediary configured therein, and the respective intermediaries conduct the plural fixing anchors, the plural stationary electrode plates and the movable element.

17. A multi-axes accelerometer, comprising:

a movable element; and

plural stationary electrode plates respectively configured to provide a moving limit of a Z-axis movement of the movable unit.

18. The multi-axes accelerometer according to claim 17, wherein the movable element has plural edges having a first and a second groups, the plural stationary electrode plates are classified into plural lower stationary electrode plates and plural upper stationary electrode plates, the plural lower stationary electrode plates are respectively configured along the first group of the plural edges and provide a lower limit of the moving limit, the plural upper stationary electrode plates are respectively configured along the second group of the plural edges and provide an upper limit of the moving limit, the movable element and each of plural stationary electrode plates have a gap therebetween, and each of the plural stationary electrode plates has a portion being held over the movable element.

19. The accelerometer according to claim 17 further comprising a fixing substrate having plural anchors and the plural stationary electrode plates, wherein the movable element has plural flexible components respectively connected to the plural anchors.

20. The accelerometer according to claim 17, wherein the plural stationary electrode plates are differential type capacitive sensing electrodes.