Wafer level MEMS force dies

• US 9,493,342 B2
• Filed: 06/21/2013
• Issued: 11/15/2016
• 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:
  US13/924,047
• Publication Number:
  US 20130341742A1
• Time in Patent Office: 1,243 Days
• Field of Search: 257/417
• 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

A composite wafer level MEMS force dies including a spacer coupled to a sensor is described herein. The sensor includes at least one flexible sensing element, such as a beam or diaphragm, which have one or more sensor elements formed thereon. Bonding pads connected to the sensor elements are placed on the outer periphery of the sensor. The spacer, which protects the flexible sensing element and the wire bonding pads, is bonded to the sensor. For the beam version, the bond is implemented at the outer edges of the die. For the diaphragm version, the bond is implemented in the center of the die. An interior gap between the spacer and the sensor allows the flexible sensing element to deflect. The gap can also be used to limit the amount of deflection of the flexible sensing element in order to provide overload protection.

Claims

1. A MEMS force die, comprising:

a spacer for receiving an applied force; and

a sensor having a center and an outer edge, wherein the sensor is bonded to the spacer at a plurality of linking areas along at least a portion of the outer edge, the sensor comprising at least one flexible sensing element having one or more sensor elements formed on an upper surface of the at least one flexible sensing element, the at least one flexible sensing element having a thickness less than a thickness at the center of the sensor, the at least one flexible sensing element being configured to deflect in response to the applied force received by the spacer and transferred to the sensor, and the one or more sensor elements changing at least one electrical characteristic based on an amount of the applied force,

wherein at least one of the spacer or the sensor defines a gap, the gap being arranged between the spacer and the sensor, the gap extending over the center of the sensor, the plurality of linking areas being arranged to at least partially surround the gap, and a depth of the gap being configured to limit an amount of deflection of the at least one flexible sensing element,

wherein the spacer is above the at least one flexible sensing element in a thickness direction, and

wherein the plurality of linking areas are arranged over the at least one flexible sensing element.

2. The MEMS force die of claim 1, wherein the sensor further comprises a plurality of flexible sensing elements, each of the flexible sensing elements being supported by a support structure.

3. The MEMS force die of claim 2, wherein the sensor defines an upper side and a bottom side, the bottom side of the sensor being etched to form the flexible sensing elements and the support structure, and at least one of the flexible sensing elements having the one or more sensor elements formed thereon.

4. The MEMS force die of claim 3, wherein the upper side of the sensor is etched to form the gap.

5. The MEMS force die of claim 3, wherein the spacer is etched to form the gap.

6. The MEMS force die of claim 1, wherein the at least one flexible sensing element comprises a diaphragm.

7. The MEMS force die of claim 6, wherein the sensor defines an upper side and a bottom side, the bottom side of the sensor being etched to form the diaphragm.

8. The MEMS force die of claim 7, wherein the upper side of the sensor is etched to form the gap.

9. The MEMS force die of claim 7, wherein the spacer is etched to form the gap.

10. The MEMS force die of claim 3, wherein the linking areas are arranged on the upper side of the sensor, the applied force being transferred to the at least one of the flexible sensing elements via at least one of the linking areas.

11. The MEMS force die of claim 1, wherein the sensor further comprises at least one wire bonding pad provided on the upper side of the sensor.

12. The MEMS force die of claim 11, wherein the spacer has one or more apertures for providing access to the at least one wire bonding pad.

13. The MEMS force die of claim 11, wherein the spacer is configured to prevent damage to the at least one flexible sensing element and shield the at least one wire bonding pad from the applied force.

14. The MEMS force die of claim 1, wherein the sensor is bonded to the spacer using at least one of an anodic bonding, glass fit, thermo-compression and eutectic bonding techniques.

15. The MEMS force die of claim 1, wherein the one or more sensor elements are piezoresistive strain gauges.

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

etching a sensor wafer to form at least one flexible sensing element;

etching at least one of the sensor wafer or a spacer wafer to form a gap;

forming one or more sensor elements on the at least one flexible sensing element;

bonding at least a portion of the sensor wafer and at least a portion of the spacer wafer to form a plurality of bonded areas, wherein the gap is arranged between the bonded sensor and spacer wafers; and

dicing the bonded sensor and spacer wafers along one or more lines intersecting the bonded area, wherein the at least one flexible sensing element is configured to deflect in response to an applied force received by the diced spacer wafer and transferred to the diced sensor wafer, the diced sensor wafer having a center and an outer edge, the gap extending over the center of the diced sensor wafer, the plurality of bonded areas being arranged to at least partially surround the gap along at least a portion of the outer edge of the diced sensor wafer, the one or more sensor elements changing at least one electrical characteristic based on an amount of the applied force, a depth of the gap being configured to limit an amount of deflection of the at least one flexible sensing element, and the at least one flexible sensing element having a thickness less than a thickness at the center of the diced sensor wafer, wherein the diced spacer wafer is above the at least one flexible sensing element in a thickness direction, wherein the one or more sensor elements are arranged on an upper surface of the at least one flexible sensing element, and wherein the plurality of bonded areas are arranged over the at least one flexible sensing element.

17. The method of claim 16, wherein the sensor wafer defines an upper side and a bottom side, the upper side of the sensor wafer being etched to form the gap and the bottom side of the sensor wafer being etched to form the at least one flexible sensing element.

18. The method of claim 16, wherein the sensor wafer defines an upper side and a bottom side, the bottom side of the sensor wafer being etched to form the at least one flexible sensing element, and the spacer wafer being etched to form the gap.

19. The method of claim 16, further comprising forming at least one wire bonding pad on the sensor wafer.

20. The method of claim 19, wherein the spacer wafer has one or more apertures for providing access to the at least one wire bonding pad.