Integrated force sensing element

• US 10,353,503 B2
• Filed: 10/29/2015
• Issued: 07/16/2019
• Est. Priority Date: 10/29/2015
• Status: Active Grant

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Shih, Wei-Yan, Kummerl, Steve, Toth, Mark Stephen, Lohia, Alok, Sculley, Terry Lee, Lee, Seung Bae, Summerfelt, Scott Robert
• Primary Examiner(s): Patel, Harshad R
• Assistant Examiner(s): Tran, Tran M.
• Application Number:
  US14/926,265
• Publication Number:
  US 20170123548A1
• Time in Patent Office: 1,356 Days
• CPC Class Codes: G01L 1/16 using properties of piezoelectric devices
• CPC Class Codes: G01L 1/22 using resistance strain gauges
• CPC Class Codes: G06F 3/0414 using force sensing means to determine a position
• CPC Class Codes: G06F 3/0416 Control or interface arrangements specially adapted for digitisers

Abstract

An integrated force sensing element includes a piezoelectric sensor formed in an integrated circuit (IC) chip and a strain gauge at least partially overlying the piezoelectric sensor, where the piezoelectric sensor is able to flex. A human-machine interface using the integrated force sensing element may include a conditioning circuit, temperature gauge, FRAM and a processor core.

Claims

1. An integrated force sensing element comprising:

a silicon layer having opposite first and second surfaces;

a first dielectric layer on the second surface;

a piezoelectric sensor including;

a first electrode on the first dielectric layer, a piezoelectric material on the first electrode, and a second electrode on the piezoelectric material;

a second dielectric layer on the second electrode;

a strain gauge on the second dielectric layer, the strain gauge at least partially overlying the piezoelectric sensor, the strain gauge including four thin film resistors forming a Wheatstone bridge;

a printed circuit board; and

a lead frame mounted to the printed circuit board, the first surface of the silicon layer being attached to the lead frame, with a cavity interposed between the printed circuit board and the piezoelectric sensor.

2. The integrated force sensing element of claim 1, wherein the silicon layer having a thickness of 75 microns or less.

3. The integrated force sensing element of claim 2, wherein the silicon layer having a thickness of 50 microns or less.

4. The integrated force sensing element of claim 1, wherein at least part of the cavity extends through the lead frame to the first surface.

5. The integrated force sensing element of claim 1, wherein the cavity is interposed between the printed circuit board and the lead frame.

6. The integrated force sensing element of claim 1, wherein at least part of the cavity is formed by etching the lead frame.

7. The integrated force sensing element of claim 1, further comprising a mold compound encapsulating at least the second dielectric layer and the strain gauge.

8. The integrated force sensing element of claim 1, wherein the piezoelectric sensor includes a ferroelectric material selected from a group consisting of:

lead zirconate titanate (PZT), aluminum nitride (AlN), and zinc oxide (ZnO).

9. The integrated force sensing element of claim 1, wherein the strain gauge includes silicon chromium (SiCr).

10. The integrated force sensing element of claim 1, wherein the silicon layer includes a signal conditioning circuit, the signal conditioning circuit including:

a first input coupled to the piezoelectric sensor;

a second input coupled to the strain gauge; and

a conditioned signal output.

11. A human machine interface (HMI) comprising:

an integrated force sensor including;

a silicon layer having opposite first and second surfaces;

a first dielectric layer on the second surface;

a piezoelectric sensor including a first electrode on the first dielectric layer, a piezoelectric material on the first electrode, and a second electrode on the piezoelectric material;

a second dielectric layer on the second electrode; and

a strain gauge on the second dielectric layer, the strain gauge at least partially overlying the piezoelectric sensor, the strain gauge including four thin film resistors forming a Wheatstone bridge;

a printed circuit board; and

a lead frame mounted to the printed circuit board, the first surface of the silicon layer being attached to the lead frame, with a cavity interposed between the printed circuit board and the piezoelectric sensor;

a processor core; and

a conditioning circuit including;

a first input coupled to the piezoelectric sensor;

a second input coupled to the strain gauge and a conditioned signal output counted to the processor core.

12. The HMI of claim 11, wherein the silicon layer having a thickness of 75 microns or less.

13. The HMI of claim 11, wherein at least part of the cavity extends through the lead frame to the first surface.

14. The HMI of claim 11, wherein the cavity is interposed between the printed circuit board and the lead frame.

15. The HMI of claim 11, wherein at least part of the cavity is formed by etching the lead frame.

16. The HMI of claim 11, further comprising a mold compound encapsulating at least the second dielectric layer and the strain gauge.

17. The HMI of claim 11, wherein the piezoelectric sensor includes a ferroelectric material selected from a group consisting of:

lead zirconate titanate (PZT), aluminum nitride (AlN), and zinc oxide.

18. The HMI of claim 11, wherein the strain gauge includes silicon chromium (SiCr).

19. The HMI of claim 11, wherein at least one of the processor core, the conditioning circuit, a random access memory (RAM), a temperature sensor or a communications interface is formed in the silicon layer.