INTEGRATED FORCE SENSING ELEMENT

• US 20170123548A1
• Filed: 10/29/2015
• Published: 05/04/2017
• 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, Lohia, Alok, Sculley, Terry Lee, Lee, Seung Bae, Summerfelt, Scott Robert, Toth, Mark Stephen
• Granted Patent: US 10,353,503 B2
• Time in Patent Office: 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 is also disclosed and may include a conditioning circuit, temperature gauge, FRAM and a processor core.

Claims

1. An integrated force sensing element comprising:

a piezoelectric sensor formed in an integrated circuit (IC) chip; and

a strain gauge at least partially overlying the piezoelectric sensor, wherein the piezoelectric sensor is able to flex.

2. The integrated force sensing element as recited in claim 1 wherein the IC chip is thinned to 75 microns or less.

3. The integrated force sensing element as recited in claim 2 wherein the IC chip is thinned to 50 microns or less.

4. The integrated force sensing element as recited in claim 2 wherein the IC chip is packaged in a manner that creates a cavity adjacent the piezoelectric sensor.

5. The integrated force sensing element as recited in claim 4 wherein the IC chip is attached to a lead frame such that the piezoelectric sensor is adjacent a gap between the bottom of the lead frame and a printed circuit board.

6. The integrated force sensing element as recited in claim 4 wherein the IC chip is attached to a lead frame, the lead frame having been etched so as to create the cavity underlying the piezoelectric sensor.

7. The integrated force sensing element as recited in claim 1 wherein the piezoelectric sensor extends over a Micro-Electro-Mechanical System (MEMS) cavity filled with a compliant material, the piezoelectric sensor further comprising a compliant layer deposited over the piezoelectric sensor.

8. The integrated force sensing element as recited in claim 1 wherein the piezoelectric sensor comprises a ferroelectric material chosen from the group comprising lead zirconate titanate (PZT), aluminum nitride (AlN), and zinc oxide (ZnO).

9. The integrated force sensing element as recited in claim 1 wherein the strain gauge comprises silicon chromium (SiCr).

10. The integrated force sensing element as recited in claim 1 wherein the strain gauge comprises four thin film resistors forming a Wheatstone bridge.

11. The integrated force sensing element as recited in claim 1 further comprising a signal conditioning circuit integrated on the IC chip to condition a first signal from the piezoelectric sensor and a second signal from the strain gauge.

12. A Human Machine Interface (HMI) comprising:

an integrated circuit (IC) chip comprising an integrated force sensor that comprises a piezoelectric sensor and a strain gauge, the strain gauge at least partially overlying the piezoelectric sensor, wherein the piezoelectric sensor is able to flex;

a processor core; and

a conditioning circuit attached to receive the output from the piezoelectric sensor and the strain gauge and to provide a conditioned signal to the processor core, the processor core being operably connected to send a control signal to a device.

13. The HMI as recited in claim 12 wherein the IC chip thinned to 75 microns or less.

14. The HMI as recited in claim 13 wherein the piezoelectric sensor is adjacent a cavity that allows the piezoelectric sensor to flex.

15. The HMI as recited in claim 14 wherein the cavity is provided by one of an etched lead frame to which the IC chip is attached and a lead frame that provides an offset between the IC chip and a printed circuit board (PCB) to which the lead frame is attached.

16. The HMI as recited in claim 14 wherein the IC chip further comprises a ferroelectric random access memory (FRAM).

17. The HMI as recited in claim 16 wherein the piezoelectric sensor and the FRAM each comprise a layer of lead zirconate titanate (PZT) formed during an FRAM process.

18. The HMI as recited in claim 14 further comprising a temperature sensor.

19. The HMI as recited in claim 14 further comprising a communications interface.

20. The HMI as recited in claim 14 wherein at least one of a processor core, a conditioning circuit, a FRAM, a temperature sensor and a communications interface are integrated on the IC chip with the piezoelectric sensor and the strain gauge.