Micromechanical accelerometer with plate-like semiconductor wafers

• US 5,614,742 A
• Filed: 01/02/1996
• Issued: 03/25/1997
• Est. Priority Date: 05/05/1993
• Status: Expired due to Term

• Current Assignee: Northrop Grumman Systems Corporation (Northrop Grumman Corporation)
• Original Assignee: Litef GmbH (Northrop Grumman Corporation)
• Inventors: Vetter, Egbert, Gessner, Thomas, Wiemer, Maik, Leinfelder, Peter, Hafen, Martin, Handrich, Eberhard, Ryrko, Bruno
• Primary Examiner(s): MINTEL, WILLIAM A
• Application Number:
  US08/587,604
• Time in Patent Office: 448 Days
• Field of Search: 257/254, 257/417, 257/420, 257/418, 73/DIG. 1, 73/514.22, 73/514.21, 73/514.23, 73/514.32, 73/524.36
• US Class Current: 257/254
• 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: Y10S 148/012 Bonding, e.g. electrostatic for strain gauges
• CPC Class Codes: Y10S 73/01 Vibration

Abstract

A high precision micromechanical accelerometer comprises a layered structure of five (5) semiconductor wafers insulated from one another by thin oxide layers. The accelerometer is formed by first connecting a coverplate and a baseplate to associated insulating plates. Counter-electrodes, produced by anisotropic etching from the respective insulating plates, are fixed to the coverplate and the baseplate respectively. The counter-electrodes are contactable through the cover or baseplate via contact windows. A central wafer contains a unilaterally linked mass (pendulum) that is also produced by anisotropic etching and which serves as a movable central electrode of a differential capacitor. The layered structure is hermetically sealed by semiconductor fusion bonding. A stepped gradation from the top is formed at a wafer edge region for attaching contact pads to individual wafers to permit electrical contacting of individual wafers. The invention permits fabrication of a μB device characterized by extremely small leakage capacitances and high temperature stability.

Claims

1. A micromechanical accelerometer in which a movably suspended mass forms the central electrode of a differential capacitor comprising, in combination:

a) a coverplate including an upper, frame-like insulating plate disposed therebelow;

b) a baseplate having a lower frame-like insulating plate disposed thereabove;

c) each of said coverplate and said baseplate comprising a semiconductor wafer bonded to said associated insulating plate;

d) an interior counterelectrode associated with each of said coverplate and said baseplate, each counterelectrode having opposed surfaces and being surrounded on all sides at the margin by the frame of the associated insulating plate acting as screening and each counterelectrode being insulated from the associated coverplate and baseplate by an oxide layer lying therebetween;

e) a frame-like central plate disposed between said coverplate and said baseplate with said associated frame-like insulating plates;

f) said central plate including a plate-like mass for functioning as a pendulum, said plate-like mass being articulated to a frame spar on one side and integrally connected to said frame, said plate-like mass being deflectable perpendicular to the plane of said plate and at the same time forming the movable central electrode of said differential capacitor in opposition to and alignment with said counterelectrodes whereby said accelerometer is characterized by a multilayer, plate-like layered structure of differently etched semiconductors insulated from one another by oxide layers and externally hermetically sealed by wafer bonding.

2. A micromechanical accelerometer as defined in claim 1 wherein the surfaces of said counterelectrodes facing said deflectable plate-like mass are coated with silica.

3. A micromechanical accelerometer as defined in claim 2 wherein the surfaces of said counterelectrodes facing said deflectable plate-like mass are coated with silicon nitride.

4. A micromechanical accelerometer as defined in claim 1 further including semiconductor material oxide layers arranged to insulate said counterelectrode contact windows from said coverplate and from said baseplate.

5. A micromechanical accelerometer produced by the process of:

a) preparing an upper coverplate and a lower baseplate by bonding an inner wafer forming an insulating plate to each of two unstructured wafers;

then

b) generating contact windows, to counterelectrodes opposite a movable mass, that extend through said coverplate and said baseplate to said insulating plates by anisotropic etching after masking of said coverplate and said baseplate; and

c) defining said counterelectrodes by anisotropic etching of said insulating plates; and

d) forming a unilaterally linked plate-shaped mass which is perpendicularly movable with respect to a central semiconductor wafer plane by masking and anisotropic etching of said central semiconductor wafer disposed between said coverplate and said baseplate including said insulating plates; and

then

e) connecting said coverplate and said baseplate, with associated insulating plates, with said central semiconductor wafer, including said movable mass, disposed therebetween in hermetically sealed fashion by semiconductor fusion bonding under ambient temperature in air whereby said accelerometer is produced as a layered composite of a plurality of individual plate-like semiconductor wafers.

6. A micromechanical accelerometer as defined in claim 5 further characterized in that said plate-like semiconductor wafers are individually contactable from one side to said layered structure.

7. A micromechanical accelerometer as defined in claim 6 wherein said individual semiconductor wafers are exposed along one edge by stepwise offset etching-away and are electrically contactable on exposed step plateaus by a means of associated metal pads including a bonded-on connecting wire.

8. A micromechanical accelerometer as defined in claim 7 wherein the surfaces of said counterelectrodes facing said deflectable plate-like mass are coated with silica.

9. A micromechanical accelerometer as defined in claim 7 wherein the surfaces of said counterelectrodes facing said deflectable plate-like mass are coated with silicon nitride.