MINIATURIZED AND RUGGEDIZED WAFER LEVEL MEMS FORCE SENSORS

• US 20160332866A1
• Filed: 01/13/2015
• Published: 11/17/2016
• Est. Priority Date: 01/13/2014
• Status: Active Grant

• Current Assignee: NextInput Inc. (Qorvo, Inc.)
• Original Assignee: NextInput Inc. (Qorvo, Inc.)
• Inventors: Diestelhorst, Ryan, Nasiri, Steven, Brosh, Amnon
• Granted Patent: US 9,902,611 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: B81B 2201/0264 Pressure sensors
• CPC Class Codes: B81B 2201/0292 Sensors not provided for in B81B2201/0207 - B81B2201/0285
• CPC Class Codes: B81B 3/0056 Adjusting the distance between two elements, at least one of them being movable, e.g. air-gap tuning
• CPC Class Codes: B81C 1/00626 Processes for achieving a desired geometry not provided for in groups B81C1/00563 - B81C1/00619
• CPC Class Codes: G01L 1/18 using properties of piezo-resistive materials, i.e. materials of which the ohmic resistance varies according to changes in magnitude or direction of force applied to the material
• CPC Class Codes: G01L 1/205 using distributed sensing elements
• CPC Class Codes: G01L 9/0047 Diaphragm with non uniform thickness, e.g. with grooves, bosses or continuously varying thickness
• CPC Class Codes: G01L 9/0048 Details about the mounting of the diaphragm to its support or about the diaphragm edges, e.g. notches, round shapes for stress relief

Abstract

Described herein is a miniaturized and ruggedized wafer level MEMS force sensor composed of a base and a cap. The sensor employs multiple flexible membranes, a mechanical overload stop, a retaining wall, and piezoresistive strain gauges.

Claims

1. A force sensor, comprising:

a base comprising at least one rigid boss, and

a cap, wherein the cap is attached to the base at a surface defined by the at least one rigid boss,

wherein at least one flexure is formed in the base and around the at least one rigid boss by etching,

wherein a portion of the base is etched to produce an overload stop between the base and the cap such that the at least one flexure will not deform beyond its breaking point,

wherein a plurality of piezoresistors are deposited or implanted on a bottom surface of the base beneath the at least one flexure to create a Wheatstone bridge, and

wherein the piezoresistors are arranged such that the Wheatstone bridge is configured to output a voltage signal proportional to the strain induced in the piezoresistors.

2. The force sensor of claim 1, further comprising:

an etched shelf around a perimeter of the base to serve as a channel for extraction of debris during wafer dicing.

3. The force sensor of claim 1, further comprising:

machined holes in the cap to serve as a channel for extraction of debris during wafer dicing.

4. The force sensor of claim 1, further comprising:

a retaining wall around a periphery of the base released by slots etched into the base.

5. The force sensor of claim 1,

wherein the at least one flexure is formed in a corner of the base.

6. A wafer section of force sensors of claim 1, comprising:

bridges to secure the bosses during attachment of the cap to the base and positioned to be removed during dicing.

7. A wafer section of force sensors of claim 1, comprising:

etched holes at the edges of the flexures, such that a dicing blade will not come into contact with the flexures.

8. A force sensor, comprising:

a base comprising at least one rigid boss and an outer wall,

a cap attached to the base at a surface defined by the at least one rigid boss and the outer wall, wherein the cap and the base form a sealed cavity,

at least one flexure formed in the base and around the at least one rigid boss to convert force applied to the cap into strain,

a gap between the base and the cap that narrows with the application of the force to the cap such that the at least one flexure will not deform beyond its breaking point, and

a sensor configured to sense strain on a bottom surface of the base.

9. The force sensor of claim 8, wherein the at least one flexure is formed in the base and around the at least one rigid boss by etching.

10. The force sensor of claim 8, wherein the sensor comprises at least one of a piezoresistive, piezoelectric, or capacitive transducer.

11. The force sensor of claim 8, wherein the sensor is configured to produce an electrical voltage, current, or charge signal proportional to the strain.

12. The force sensor of claim 8, further comprising a plurality of electrical terminals formed on the bottom surface of the base, wherein the electrical signal produced by the sensor is routed to the electrical terminals.

13. The force sensor of claim 12, wherein the electrical terminals comprise solder bumps.

14. The force sensor of claim 8, wherein the base further comprises grooves to focus mechanical strain on the at least one flexure.

15. The force sensor of claim 8, wherein the sealed cavity is formed by at least one surface adhered between the cap and the base.

16. The force sensor of claim 15, wherein the base further comprises a cavity formed by etching the at least one flexure, wherein the cavity is bounded by a surface of at least one of the at least one flexure, the at least one rigid boss, or the outer wall.

17. The force sensor of claim 16, wherein the cavity is bounded by a respective surface of each of the at least one flexure, the at least one rigid boss, and the outer wall.

18. The force sensor of claim 16, wherein the cavity is sealed between the base and the cap.

19. The force sensor of claim 18, wherein the cap comprises a contact surface and a surface opposite to the contact surface, and wherein the sealed cavity is further bounded by the surface opposite to the contact surface.

20. The force sensor of claim 15, wherein the sealed cavity is sealed from an environment external to the force sensor.