# US 8,569,092 B2 · Method for fabricating a microelectromechanical sensor with a piezoresistive type readout

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- Number: US 8,569,092 B2
- Document ID: US8569092B2
- Status: Granted
- Kind: B2
- Application number: 12/647,660
- Filed: 2009-12-28
- Published: 2011-06-30
- Granted: 2013-10-29
- Earliest claimed: 2009-12-28
- Assignees: General Electric Company
- Applicants: Naresh Venkata Mantravadi; Sisira Kankanam Gamage
- Inventors: Naresh Venkata Mantravadi; Sisira Kankanam Gamage
- Web page: https://patentgrep.com/patent/US8569092B2

## CPC

- G01P 15/0802: {Details}
- B81C 1/00182: {Arrangements of deformable or non-deformable structures, e.g. membrane and cavity for use in a transducer}
- G01L 9/0042: {Constructional details associated with semiconductive diaphragm sensors, e.g. etching, or constructional details of non-semiconductive diaphragms (details about the integration or bonding of piezoresistor in or on the diaphragm G01L9/0052 and G01L9/0057 respectively)}
- G01L 19/0092: {Pressure sensor associated with other sensors, e.g. for measuring acceleration or temperature (G01L9/025, G01L9/045, G01L9/065, G01L9/085, G01L9/105, G01L9/125, G01L19/02, G01L19/04 take precedence; measuring two or more variable G01D21/02; temperature sensors with pressure compensation G01K1/26)}
- G01P 15/123: {by piezo-resistive elements, e.g. semiconductor strain gauges}
- B81B 2201/0235: Accelerometers
- B81B 2201/0264: Pressure sensors
- B81B 2203/0118: Cantilevers
- G01P: MEASURING LINEAR OR ANGULAR SPEED, ACCELERATION, DECELERATION, OR SHOCK; INDICATING PRESENCE, ABSENCE, OR DIRECTION, OF MOVEMENT (measuring or recording blood flow A61B5/02, A61B8/06; monitoring speed or deceleration of electrically-propelled vehicles B60L3/00; vehicle lighting systems adapted to indicate speed B60Q1/54; determining position or course in navigation, measuring ground distance in geodesy or surveying G01C; combined measuring devices for measuring two or more variables of movement G01C23/00; measuring velocity of sound G01H; measuring velocity of light G01J7/00; measuring direction or velocity of solid objects by reception or emission of radiowaves or other waves and based on propagation effects, e.g. Doppler effect, propagation time, direction of propagation, G01S; measuring speed of nuclear radiation G01T; measuring acceleration of gravity G01V; {measuring or recording the speed of trains B61L23/00; speed indicators incorporated in motor vehicles B60K35/00; measuring frequency or phase G01R; traffic control G08G})
- B81C: PROCESSES OR APPARATUS SPECIALLY ADAPTED FOR THE MANUFACTURE OR TREATMENT OF MICROSTRUCTURAL DEVICES OR SYSTEMS (making microcapsules or microballoons B01J13/02; processes or apparatus specially adapted for the manufacture or treatment of piezoelectric, electrostrictive or magnetostrictive elements per se H10N30/01)
- G01L: MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE (weighing G01G)
- B81B: MICROSTRUCTURAL DEVICES OR SYSTEMS, e.g. MICROMECHANICAL DEVICES (piezoelectric, electrostrictive or magnetostrictive elements per se H10N30/00, H10N35/00)

## Abstract

A method for fabricating a sensor is disclosed that in one embodiment bonds an etched semiconductor substrate wafer to an etched device wafer comprising a double silicon on insulator wafer to create a suspended structure, the flexure of which is sensed by an embedded piezoresistive sensor element. In one embodiment the sensor measures acceleration. In other embodiments the sensor measures pressure.

## Claims

### Claim 1

A method for fabricating a sensor, comprising the steps of:
forming a substrate recess in a semiconductor substrate wafer;
forming a device recess in a semiconductor device wafer, wherein said device wafer comprises a first device layer, a second device layer, a first oxide layer, and a second oxide layer, wherein said first oxide layer is located under said first device layer, said second device layer is located under said first oxide layer, and said second oxide layer is located under said second device layer, and wherein said device recess extends through said first device layer to expose said first oxide layer;
securing said first device layer to said substrate wafer, wherein said device recess is aligned over said substrate recess;
implanting a piezoresistive acceleration sensor at a first location in said second device layer and a piezoresistive pressure sensor in said second device layer at a second location, each of the sensors configured to sense flexure in said second device layer; and
selecting a thickness of each of the first device layer, the second device layer, the first oxide layer, and the second oxide layer that corresponds to a predetermined sensitivity factor of each of the acceleration sensor and the pressure sensor.

### Claim 2 (depends on 1)

The method for fabricating a sensor of claim 1, wherein said step of forming said device recess in said semiconductor device wafer further comprises the step of etching said first oxide layer using dry oxide etching techniques.

### Claim 3 (depends on 1)

The method for fabricating a sensor of claim 1, wherein said step of forming said device recess in said semiconductor device wafer further comprises the step of etching said first oxide layer using wet oxide etching techniques.

### Claim 4 (depends on 1)

The method for fabricating a sensor of claim 1, wherein said first oxide layer improves the high temperature performance of said sensor.

### Claim 5 (depends on 1)

The method for fabricating a sensor of claim 1, wherein said first oxide layer balances internal stresses within said sensor and improves the sensitivity of said sensor.

### Claim 6 (depends on 1)

The method for fabricating a sensor of claim 1, wherein the thickness of said first device layer, said first oxide layer and said second oxide layer determine the sensitivity of said sensor.

### Claim 7 (depends on 1)

The method for fabricating a sensor of claim 1, further comprising the step of:
forming a suspended structure in said device wafer disposed over said substrate recess, wherein said suspended structure includes a boundary region that is released from other portions of said device wafer except in a flexure region of the boundary region, wherein said suspended structure includes a proof mass comprised of portions of said first device layer, said first oxide layer and said second device layer, wherein said flexure region of said boundary region and released portion of said boundary region are disposed to permit movement of said proof mass in response to a force, wherein said movement of said proof mass causes flexure in said flexure region, and wherein at least one of said piezoresistive acceleration sensor and said piezoresistive pressure sensor senses said flexure in said flexure region.

### Claim 8 (depends on 7)

The method for fabricating a sensor of claim 7, wherein in said step of forming said suspended structure in said device wafer disposed over said substrate recess said boundary region is released from said other portions of said device wafer using dry semiconductor and oxide etching techniques.

### Claim 9 (depends on 7)

The method for fabricating a sensor of claim 7, wherein said step of forming said device recess in said semiconductor-device wafer further comprises the step of forming a proof mass recess in said device wafer, wherein said proof mass recess extends through said first device layer to expose said first oxide layer, wherein in said step of forming said suspended structure in said device wafer disposed over said substrate recess said boundary region is released from said other portions of said device water using dry semiconductor and oxide etching techniques, and wherein a portion of said proof mass recess forms a portion of said proof mass.

### Claim 10 (depends on 9)

The method for fabricating a sensor of claim 9, wherein said step of forming said proof mass recess in said device wafer uses dry semiconductor etching techniques.

### Claim 11 (depends on 9)

The method for fabricating a sensor of claim 9, wherein said step of forming said proof mass recess in said device wafer uses wet semiconductor etching techniques.

### Claim 12 (depends on 7)

The method for fabricating a sensor of claim 7, wherein in said step of securing said first device layer of said device wafer to said surface of said substrate wafer said device recess is aligned entirely over said substrate recess.

### Claim 13 (depends on 1)

The method for fabricating a sensor of claim 1, wherein said second device layer forms a diaphragm over said device recess and said substrate recess that allows flexure in said second device layer, and wherein at least one of said piezoresistive acceleration sensor and said piezoresistive pressure sensor senses said flexure in said diaphragm.

### Claim 14 (depends on 13)

The method for fabricating a sensor of claim 13, wherein in said step of securing said first device layer of said device wafer to said surface of said substrate wafer said device recess is centered over said substrate recess.

### Claim 15 (depends on 13)

The method for fabricating a sensor of claim 13, wherein said piezoresistive pressure sensor measures pressure.

### Claim 16 (depends on 1)

The method for fabricating a sensor of claim 1, wherein said step of forming a substrate recess in said semiconductor substrate wafer is performed using dry semiconductor etching techniques.

### Claim 17 (depends on 1)

The method for fabricating a sensor of claim 1, wherein said step of forming a substrate recess in said semiconductor substrate wafer is performed using wet semiconductor etching techniques.

### Claim 18 (depends on 1)

The method for fabricating a sensor of claim 1, wherein said step of forming said device recess in said semiconductor device wafer is performed using dry semiconductor etching techniques.

### Claim 19 (depends on 1)

The method for fabricating a sensor of claim 1, wherein said step of forming said device recess in said semiconductor device wafer is performed using wet semiconductor etching techniques.