BIOMETRIC SENSOR WITH FORCE DETECTION AND ULTRASONIC IMAGING CAPABILITY

• US 20180369866A1
• Filed: 06/26/2017
• Published: 12/27/2018
• Est. Priority Date: 06/26/2017
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Sammoura, Firas, Burns, David William, Shenoy, Ravindra Vaman
• Granted Patent: US 10,569,302 B2
• Time in Patent Office: Days
• CPC Class Codes: B06B 1/0622 on one surface
• CPC Class Codes: G06F 1/3262 Power saving in digitizer or tablet
• CPC Class Codes: G06F 2203/04105 Pressure sensors for measuring the pressure or force exerted on the touch surface without providing the touch position
• CPC Class Codes: G06F 3/0416 Control or interface arrangements specially adapted for digitisers
• CPC Class Codes: G06F 3/043 using propagating acoustic waves
• CPC Class Codes: G06V 40/1306 non-optical, e.g. ultrasonic or capacitive sensing
• CPC Class Codes: H10N 30/1071 with electrical and mechanical input and output, e.g. having combined actuator and sensor parts

Abstract

Implementations of the subject matter described herein relate to sensors including piezoelectric micromechanical ultrasonic transducer (PMUT) sensor elements and arrays thereof. The PMUT sensor elements may be switchable between a non- ultrasonic force detection mode and an ultrasonic imaging mode. A PMUT sensor element may include a diaphragm that is capable of a static displacement on application of a force and is capable of a dynamic displacement when the PMUT sensor element transmits or receives ultrasonic signals. In some implementations, a PMUT sensor element includes a two dimensional-electron gas structure on the diaphragm. The sensors may further include a sensor controller configured to switch between a non-ultrasonic force detection mode and an ultrasonic imaging mode for one or more of the PMUT sensor elements, wherein an applied force is measured in the non-ultrasonic force detection mode and wherein an object is imaged ultrasonically during the ultrasonic imaging mode.

Claims

1. An apparatus comprising:

a substrate;

a sensor including an array of piezoelectric micromechanical ultrasonic transducer (PMUT) sensor elements on the substrate, wherein each PMUT sensor element includes a diaphragm having a piezoelectric layer and a mechanical layer, wherein the diaphragm is capable of a static displacement upon application of an applied force and is capable of a dynamic displacement when the PMUT sensor element receives or transmits ultrasonic signals; and

a sensor controller configured to switch the sensor between a non-ultrasonic force detection mode and an ultrasonic imaging mode for one or more of the PMUT sensor elements, wherein the applied force is measured in the non-ultrasonic force detection mode and wherein an object is imaged ultrasonically during the ultrasonic imaging mode.

2. The apparatus of claim 1, wherein the apparatus is configured to detect a finger touch based on an on-threshold force being measured by the apparatus in the non-ultrasonic force detection mode.

3. The apparatus of claim 2, wherein the sensor controller is configured to provide, to an applications processor, a wake-up signal to activate one or more wake-up operations after the finger touch is detected.

4. The apparatus of claim 2, wherein the apparatus is configured to detect a finger lift after a detecting the finger touch based on an off-threshold force being measured by the apparatus in the non-ultrasonic force detection mode.

5. The apparatus of claim 4, wherein the off-threshold force is less than the on-threshold force.

6. The apparatus of claim 3, wherein the sensor controller is configured to initialize the ultrasonic imaging mode after the finger touch is detected.

7. The apparatus of claim 1, wherein the sensor controller is configured to initialize the ultrasonic imaging mode based on a minimum imaging threshold force being measured by the apparatus in the non-ultrasonic force detection mode.

8. The apparatus of claim 1, wherein one or more of the PMUT sensor elements includes a 2-D electron gas structure disposed on the diaphragm.

9. The apparatus of claim 1, wherein the sensor controller is configured to switch between the non-ultrasonic force detection mode and an ultrasonic imaging mode for each of the PMUT sensor elements in the array of PMUT sensor elements.

10. The apparatus of claim 1, wherein the sensor controller is configured to switch between the non-ultrasonic force detection mode and an ultrasonic imaging mode for a subset of the PMUT sensor elements in the array of PMUT sensor elements.

11. The apparatus of claim 10, wherein the subset of the PMUT sensor elements are located at the periphery of the array of PMUT sensor elements.

12. The apparatus of claim 10, wherein the PMUT sensor elements of the subset of the PMUT sensor elements differ from a remainder of the PMUT sensor elements of the array of PMUT sensor elements in one or more of a shape or a size.

13. An apparatus comprising:

a substrate;

a diaphragm including a mechanical layer disposed over a cavity, the cavity being positioned between the diaphragm and the substrate; and

a 2-D electron gas structure disposed on the diaphragm.

14. The apparatus of claim 13, wherein the 2-D electron gas structure is an aluminum gallium nitride/gallium nitride (AlGaN/GaN) transistor.

15. The apparatus of claim 13, wherein the diaphragm and the 2-D electron gas structure are part of a sensor element, the diaphragm is capable of a static displacement upon application of an applied force, and the 2-D electron gas structure is a strain-sensitive structure configured to provide a static displacement signal that corresponds to the applied force.

16. The apparatus of claim 15, wherein the diaphragm is further capable of a dynamic displacement when the sensor element receives or transmits ultrasonic signals.

17. The apparatus of claim 16, further comprising a sensor controller configured to switch the sensor element between a non-ultrasonic force detection mode and an ultrasonic imaging mode, wherein the applied force is measured in the non-ultrasonic force detection mode and wherein an object is imaged ultrasonically during the ultrasonic imaging mode.

18. The apparatus of claim 15, wherein the sensor element is one of an array of sensor elements on the substrate, each sensor element including a diaphragm and a mechanical layer disposed over a cavity, the cavity being positioned between the diaphragm and the substrate, and each sensor element including a 2-D electron gas structure disposed on the diaphragm.

19. The apparatus of claim 15, further comprising an array of piezoelectric micromechanical ultrasonic transducer (PMUT) sensor elements on the substrate.

20. The apparatus of claim 13, further comprising a piezoelectric layer stack disposed on the diaphragm, wherein the piezoelectric layer stack is configured to excite the diaphragm and generate ultrasonic waves.

21. The apparatus of claim 13, wherein the 2-D electron gas structure is configured to detect static displacements or dynamic displacements of the diaphragm.

22. A non-transitory computer readable medium storing instructions executable by one or more processors coupled to a fingerprint sensor, the fingerprint sensor including an array of piezoelectric ultrasonic transducer (PMUT) sensor elements, the instructions comprising:

instructions for operating the PMUT sensor elements in a force detection mode;

instructions for measuring an applied force on the fingerprint sensor operating in the force detection mode;

instructions for determining that a finger of a user has touched the fingerprint sensor based on the measured applied force;

instructions for operating the PMUT sensor elements in an ultrasonic imaging mode to acquire fingerprint image information of the finger; and

instructions for authenticating the user based on the fingerprint image information.

23. The non-transitory computer readable medium of claim 22, wherein the instructions for determining that a finger has touched the fingerprint sensor based on the applied force include instructions for comparing the applied force to an on-threshold force.

24. The non-transitory computer readable medium of claim 23, further comprising instructions for determining, after detecting that the finger has touched the fingerprint sensor, that the finger has lifted off the fingerprint sensor based on an off-threshold force being measured by the apparatus in the force detection mode.

25. The non-transitory computer readable medium of claim 24, wherein the off-threshold force is less than the on-threshold force.

26. The apparatus of claim 23, further comprising instructions for determining that the applied force is greater than or equal to a minimum imaging threshold force.

27. The apparatus of claim 26, further comprising instructions for initializing the ultrasonic imaging mode after determining that the applied force is greater than or equal to a minimum imaging threshold force.

28. A method of operating a fingerprint sensor, the method comprising:

measuring a finger force of a finger positioned on the fingerprint sensor;

imaging the finger when the finger force exceeds a pressed-finger threshold level; and

authenticating the finger based on imaging the finger.

29. The method of claim 28, wherein imaging the finger includes acquiring ultrasonic image information of the finger and wherein authenticating the finger is based on the ultrasonic image information.

30. The method of claim 28, wherein imaging the finger includes acquiring ultrasonic image information of the finger when the finger force exceeds a minimum imageable-finger threshold level.