THREE-AXIS ACCELEROMETERS AND FABRICATION METHODS

• US 20090280594A1
• Filed: 07/15/2009
• Published: 11/12/2009
• Est. Priority Date: 05/10/2006
• Status: Active Grant

• Current Assignee: Panasonic Corporation (Panasonic Holdings Corporation)
• Original Assignee: Qualtre Incorporated (Panasonic Holdings Corporation)
• Inventors: Mehregany, Mehran
• Granted Patent: US 7,892,876 B2
• Time in Patent Office: Days
• US Class Current: 438/50
• CPC Class Codes: B81B 2201/0235 Accelerometers
• CPC Class Codes: B81C 1/00182 Arrangements of deformable or non-deformable structures, e.g. membrane and cavity for use in a transducer
• CPC Class Codes: B81C 2201/0111 Bulk micromachining
• 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: G01P 15/18 in two or more dimensions
• CPC Class Codes: G01P 2015/084 the mass being suspended at more than one of its sides, e.g. membrane-type suspension, so as to permit multi-axis movement of the mass
• CPC Class Codes: Y10T 29/49156 with selective destruction of conductive paths

Abstract

Disclosed are MEMS accelerometers and methods for fabricating same. An exemplary accelerometer comprises a substrate, and a proof mass that is a portion of the substrate and which is separated from the substrate surrounding it by a gap. An electrically-conductive anchor is coupled to the proof mass, and a plurality of electrically-conductive suspension anus that are separated from the proof mass extend from the anchor and are coupled to the substrate surrounding the proof mass. A plurality of sense and actuation electrodes are separated from the proof mass by gaps and are coupled to processing electronics. Capacitive sensing is used to derive electrical signals caused by forces exerted on the proof mass, and the electrical signals are processed by the processing electronics to produce x-, y- and z-direction acceleration data. Electrostatic actuation is used to induce movements of the mass for force balance operation, or self-test and self-calibration. The fabrication methods use deep reactive ion etch bulk micromachining and surface micromachining to form the proof mass, suspension arms and electrodes. The anchor, suspension arms and electrodes are made in the same process steps from the same electrically conductive material, which is different from the substrate material.

Claims

1. A method of fabricating an accelerometer, comprising;

providing a substrate;

forming an isolation layer on the substrate;

patterning the isolation layer disposed on the front side of the substrate;

etching cavities into the substrate where the isolation layer is patterned;

removing the back side isolation layer when necessary;

forming a sacrificial layer on the substrate that fills the cavities on the front side of the substrate;

removing the sacrificial layer on the isolation layer;

etching anchor holes and bond pad contact windows through the isolation layer to expose the underlying substrate;

forming a low-resistivity structural layer on the substrate;

patterning the low-resistivity structural layer on the front side of the structure to define suspension arms, sense and actuation electrodes, and bond pads;

removing the back side low-resistivity layer when necessary;

patterning the sacrificial layer on the back side of the substrate if such is formed;

etching the back side of the substrate to expose the sacrificial layer disposed beneath the low-resistivity structural layer on the front side of the substrate and to define outer edge of a proof mass; and

releasing the proof mass by dissolving the sacrificial layer.

2. The method recited in claim 1 wherein the sacrificial layer comprises oxide, and etching the back side of the substrate comprises dry reactive ion etching.

3. The method recited in claim 1 wherein the substrate comprises a semiconductor substrate.

4. The method recited in claim 1 wherein the substrate comprises a silicon substrate.

5. The method recited in claim 1 wherein the substrate comprises a semiconductor-on-insulator substrate.

6. The method recited in claim 1 wherein the substrate comprises a metal in which deep trenches may be fabricated by reactive ion etching.

7. The method recited in claim 1 wherein the structural layer comprises a semiconductor layer.

8. The method recited in claim 1 wherein the structural layer comprises doped polysilicon.

9. The method recited in claim 1 wherein the structural layer comprises metal.

10. A method of fabricating an accelerometer, comprising:

providing a substrate;

forming an isolation layer on the substrate;

patterning the isolation layer disposed on the front side of the substrate;

removing the back side isolation layer when necessary;

forming a sacrificial layer on the substrate;

removing the sacrificial layer on the isolation layer;

etching anchor holes and bond pad contact windows through the isolation layer to expose the underlying substrate;

forming a low-resistivity structural layer on the substrate;

patterning the low-resistivity structural layer on the front side of the structure to define suspension arms, sense and actuation electrodes, and bond pads;

removing the back side low-resistivity layer when necessary;

patterning the sacrificial layer on the back side of the substrate if such is formed;

etching the back side of the substrate to expose the sacrificial layer disposed beneath the low-resistivity structural layer on the front side of the substrate and to define outer edge of a proof mass; and

releasing the proof mass by dissolving the sacrificial layer.