Ruggedized MEMS force die

• US 9,487,388 B2
• Filed: 06/21/2013
• Issued: 11/08/2016
• Est. Priority Date: 06/21/2012
• Status: Active Grant

• Current Assignee: NextInput Inc. (Qorvo, Inc.)
• Original Assignee: NextInput Inc. (Qorvo, Inc.)
• Inventors: Brosh, Amnon
• Primary Examiner(s): Parker, Kenneth
• Assistant Examiner(s): CULBERT, CHRISTOPHER A
• Application Number:
  US13/923,998
• Publication Number:
  US 20130341741A1
• Time in Patent Office: 1,236 Days
• Field of Search: 257/415
• US Class Current: 1/1
• CPC Class Codes: B81B 3/0021 Transducers for transforming electrical into mechanical energy or vice versa dynamo-electric machines H02K99/00; electrostatic machines H02N1/00; piezoelectric devices H10N30/00
• CPC Class Codes: B81B 3/0072 For controlling internal stress or strain in moving or flexible elements, e.g. stress compensating layers
• CPC Class Codes: B81C 1/00158 Diaphragms, membranes manufacture process for semi-permeable inorganic membranes B01D67/0039
• CPC Class Codes: B81C 1/00666 Treatments for controlling internal stress or strain in MEMS structures
• CPC Class Codes: G01L 1/044 of leaf springs
• 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 5/0028 Force sensors associated with force applying means G01L5/0052, G01L5/0057, G01L5/0061 take precedence
• CPC Class Codes: G01L 5/0057 measuring forces due to spring-shaped elements
• CPC Class Codes: G01L 5/162 of piezoresistors

Abstract

Described herein are ruggedized wafer level MEMS force dies composed of a platform and a silicon sensor. The silicon sensor employs multiple flexible sensing elements containing Piezoresistive strain gages and wire bonds.

Claims

1. A MEMS force die, comprising:

a protective platform for receiving an applied force; and

a force sensor having a center and an outer edge, wherein the force sensor is bonded to the protective platform at a plurality of peripheral points along at least a portion of the outer edge, the force sensor comprising a plurality of flexible sensing elements having one or more piezoresistive strain gauges formed on an upper surface of the flexible sensing elements, each of the flexible sensing elements having a thickness less than a thickness at the center of the force sensor, the flexible sensing elements being configured to deflect in response to the applied force received by the protective platform and transferred to the force sensor, and the one or more piezoresistive strain gauges providing an output signal proportional to the applied force,

wherein the force sensor defines a gap at the center thereof, the gap being arranged between the protective platform and the force sensor, and a depth of the gap being configured to limit an amount of deflection of the flexible sensing elements,

wherein the protective platform is above the flexible sensing elements in a thickness direction, and

wherein the plurality of peripheral points are arranged over the flexible sensing elements.

2. The MEMS force die of claim 1, wherein the force sensor defines an upper side and a bottom side, the upper side of the force sensor being etched to form the gap.

3. The MEMS force die of claim 2, wherein the force sensor further defines a linking area on the upper side of the force sensor, the applied force being transferred to the flexible sensing elements via the linking area.

4. The MEMS force die of claim 1, wherein the force sensor further comprises a cross-shaped structure supporting the flexible sensing elements, and at least one of the flexible sensing elements has the one or more piezoresistive strain gauges formed thereon.

5. The MEMS force die of claim 4, wherein the force sensor defines an upper side and a bottom side, the bottom side of the force sensor being etched to form the cross-shaped structure and the flexible sensing elements.

6. The MEMS force die of claim 4, wherein the force sensor further comprises at least one wire bonding pad, the at least one wire bonding pad being arranged on the cross-shaped structure.

7. The MEMS force die of claim 6, wherein the protective platform has one or more apertures for providing access to the at least one wire bonding pad.

8. The MEMS force die of claim6, wherein the protective platform is configured to prevent damage to the flexible sensing elements and shield the at least one wire bonding pad from the applied force.

9. The MEMS force die of claim 1, wherein the force sensor is bonded to the protective platform through an anodic bond.

10. The MEMS force die of claim 1, wherein the one or more piezoresistive strain gauges are diffused or deposited on the plurality of flexible sensing elements.

11. The MEMS force die of claim 1, wherein the force sensor is a silicon sensor.

12. A method for manufacturing a MEMS force die, comprising:

etching an upper side of a sensor wafer to form a gap and at least one linking area;

etching a bottom side of the sensor wafer to form at least one diaphragm;

forming one or more piezoresistive strain gauges on the diaphragm;

bonding the at least one linking area of the sensor wafer to a protective platform wafer to form bonded areas at a plurality of peripheral points, wherein the gap is arranged between the bonded sensor wafer and protective platform wafer; and

dicing the bonded sensor wafer and protective platform wafer along one or more lines intersecting the bonded areas to form a plurality of flexible sensing elements from the diaphragm, the flexible sensing elements being configured to deflect in response to an applied force received by the diced protective platform wafer and transferred to the diced sensor wafer, and the one or more piezoresistive strain gauges providing an output signal proportional to the applied force,

wherein a depth of the gap is configured to limit an amount of deflection of the flexible sensing elements,

wherein the gap is at a center of the diced sensor wafer and the plurality of peripheral points are along at least a portion of an outer edge of the diced sensor wafer,

wherein each of the flexible sensing elements has a thickness less than a thickness at the center of the diced sensor wafer,

wherein the diced protective platform wafer is above the flexible sensing elements in a thickness direction,

wherein the one or more piezoresistive strain gauges are arranged on an upper surface of the flexible sensing elements, and

wherein the plurality of peripheral points are arranged over the flexible sensing elements.

13. The method of claim 12, further comprising forming at least one wire bonding pad on the sensor wafer.

14. The method of claim 13, wherein the protective platform wafer has one or more apertures for providing access to the at least one wire bonding pad.

15. The method of claim 14, wherein the diced protective platform wafer is configured to prevent damage to the flexible sensing elements and shield the at least one wire bonding pad from the applied force.

16. The method of claim 12, wherein the at least one linking area of the sensor wafer is bonded to the protective platform wafer through an anodic bond.

17. The method of claim 12, wherein the one or more piezoresistive strain gauges are formed on the diaphragm by diffusion or deposition.

18. The method of claim 12, wherein the sensor wafer is a silicon wafer.