PIEZOELECTRIC ULTRASONIC TRANSDUCER AND PROCESS

• US 20150165479A1
• Filed: 12/12/2014
• Published: 06/18/2015
• Est. Priority Date: 12/12/2013
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Lasiter, Jon Bradley, Shenoy, Ravindra Vaman, Gousev, Evgeni Petrovich, Burns, David William, Griffiths, Jonathan Charles, Ganti, Suryaprakash, Panchawagh, Hrishikesh, Kuo, Nai-Kuei
• Granted Patent: US 10,478,858 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: B06B 1/0666 used as a diaphragm
• CPC Class Codes: G06F 3/017 Gesture based interaction, e.g. based on a set of recognized hand gestures interaction based on gestures traced on a digitiser G06F3/04883
• CPC Class Codes: G06F 3/0412 Digitisers structurally integrated in a display
• CPC Class Codes: G06F 3/043 using propagating acoustic waves
• CPC Class Codes: G06F 3/0436 in which generating transducers and detecting transducers are attached to a single acoustic waves transmission substrate
• CPC Class Codes: G06V 40/1306 non-optical, e.g. ultrasonic or capacitive sensing
• CPC Class Codes: G06V 40/20 Movements or behaviour, e.g. gesture recognition recognition of facial expressions G06V40/16
• CPC Class Codes: G10K 9/125 with a plurality of active elements
• CPC Class Codes: H10N 30/01 Manufacture or treatment
• CPC Class Codes: H10N 30/07 Forming of piezoelectric or electrostrictive parts or bodies on an electrical element or another base
• CPC Class Codes: H10N 30/2047 Membrane type
• CPC Class Codes: Y10T 29/42 Piezoelectric device making

Abstract

A piezoelectric micromechanical ultrasonic transducer (PMUT) includes a multilayer stack disposed on a substrate. The multilayer stack may include an anchor structure disposed over the substrate, a piezoelectric layer stack disposed over the anchor structure, and a mechanical layer disposed proximate to the piezoelectric layer stack. The piezoelectric layer stack may be disposed over a cavity. The mechanical layer may seal the cavity and, together with the piezoelectric layer stack, is supported by the anchor structure and forms a membrane over the cavity, the membrane being configured to undergo one or both of flexural motion and vibration when the PMUT receives or transmits ultrasonic signals.

Claims

1. A piezoelectric micromechanical ultrasonic transducer (PMUT) comprising:

a multilayer stack disposed on a substrate and including;

an anchor structure disposed over the substrate;

a piezoelectric layer stack disposed over the anchor structure; and

a mechanical layer disposed proximate to the piezoelectric layer stack;

wherein;

the piezoelectric layer stack is disposed over a cavity; and

the mechanical layer seals the cavity and, together with the piezoelectric layer stack, is supported by the anchor structure and forms a membrane over the cavity, the membrane being configured to undergo one or both of flexural motion and vibration when the PMUT receives or transmits ultrasonic signals.

2. The PMUT of claim 1, wherein the mechanical layer has a thickness such that a neutral axis of the multilayer stack is displaced, relative to a neutral axis of the piezoelectric layer stack, towards the mechanical layer to allow an out-of-plane bending mode.

3. The PMUT of claim 2, wherein the mechanical layer is substantially thicker than the piezoelectric layer stack.

4. The PMUT of claim 2, wherein the neutral axis passes through the mechanical layer.

5. The PMUT of claim 1, wherein:

the cavity is formed by removing a sacrificial material through at least one release hole;

the mechanical layer is formed after removing the sacrificial material; and

forming the mechanical layer seals the cavity by sealing the at least one release hole.

6. The PMUT of claim 1, wherein the piezoelectric layer stack includes a piezoelectric layer, a lower electrode disposed below the piezoelectric layer, and an upper electrode disposed above the piezoelectric layer.

7. The PMUT of claim 1, wherein the mechanical layer includes a recess where the mechanical layer is locally thinned.

8. The PMUT of claim 1, wherein the mechanical layer is disposed over a side of the piezoelectric stack opposite to the substrate.

9. The PMUT of claim 1, wherein the mechanical layer is disposed below a side of the piezoelectric stack facing the substrate.

10. The PMUT of claim 1, further comprising an acoustic coupling medium disposed above the piezoelectric layer stack, wherein the PMUT is configured to receive or transmit ultrasonic signals through the coupling medium.

11. A piezoelectric micromechanical ultrasonic transducer (PMUT) comprising:

a multilayer stack disposed on a substrate and including;

an anchor structure disposed over the substrate;

a piezoelectric layer stack disposed over the anchor structure; and

a mechanical layer disposed proximate to the piezoelectric layer stack, the mechanical layer including a recess where the mechanical layer is locally thinned;

wherein

the piezoelectric layer stack is disposed over a cavity; and

the mechanical layer, together with the piezoelectric layer stack, is supported by the anchor structure and forms a membrane over the cavity, the membrane being configured to undergo one or both of flexural motion and vibration when the PMUT receives or transmits ultrasonic signals.

12. The PMUT of claim 11, wherein:

the cavity is formed by removing a sacrificial material through at least one release hole;

the mechanical layer is formed after removing the sacrificial material; and

forming the mechanical layer seals the cavity by sealing the at least one release hole.

13. The PMUT of claim 11, wherein the mechanical layer is disposed over a side of the piezoelectric stack opposite to the substrate.

14. The PMUT of claim 11, wherein the mechanical layer is disposed below a side of the piezoelectric stack facing the substrate.

15. The PMUT of claim 11, further comprising an acoustic coupling medium disposed above the piezoelectric layer stack, wherein the PMUT is configured to receive or transmit ultrasonic signals through the coupling medium.

16. A method of making a piezoelectric micromechanical ultrasonic transducer (PMUT) comprising:

forming an anchor structure over a substrate, the anchor structure disposed proximate to regions of sacrificial material;

forming a piezoelectric layer stack over the anchor structure;

removing the sacrificial material so as to form a cavity under the piezoelectric layer stack; and

disposing a mechanical layer proximate to the piezoelectric layer stack, wherein the piezoelectric layer stack and the mechanical layer form part of a multilayer stack, the mechanical layer seals the cavity and, together with the piezoelectric layer stack, is supported by the anchor structure and forms a membrane over the cavity, the membrane being configured to undergo one or both of flexural motion and vibration when the PMUT receives or transmits ultrasonic signals.

17. The method of claim 16, wherein removing the sacrificial material includes removing the sacrificial material through at least one release hole and the mechanical layer seals the at least one release hole.

18. The method of claim 16, wherein the anchor structure is disposed in a lower layer, the lower layer being parallel to the piezoelectric layer stack and including the regions of sacrificial material.

19. The PMUT of claim 16, wherein the mechanical layer has a thickness such that a neutral axis of the multilayer stack is displaced, relative to a neutral axis of the piezoelectric layer stack, towards the mechanical layer to allow an out-of-plane bending mode.

20. The PMUT of claim 19, wherein the mechanical layer is substantially thicker than the piezoelectric layer stack.

21. The PMUT of claim 19, wherein the neutral axis passes through the mechanical layer.

22. An apparatus comprising:

an array of piezoelectric micromechanical ultrasonic transducer (PMUT) sensors; and

an acoustic coupling medium, wherein;

at least one PMUT includes a multilayer stack disposed on a substrate and including an anchor structure disposed over the substrate, a piezoelectric layer stack disposed over the anchor structure and a cavity, and a mechanical layer disposed proximate to the piezoelectric layer stack, the mechanical layer sealing the cavity;

the acoustic coupling medium is disposed above the piezoelectric layer stack; and

the PMUT is configured to receive or transmit ultrasonic signals through the coupling medium.

23. The apparatus of claim 22, wherein the mechanical layer, together with the piezoelectric layer stack, forms a membrane over the cavity, the membrane being configured to undergo one or both of flexural motion and vibration when the PMUT receives or transmits ultrasonic signals.

24. The apparatus of claim 22, wherein the mechanical layer has a thickness such that a neutral axis of the multilayer stack is displaced, relative to a neutral axis of the piezoelectric layer stack, towards the mechanical layer to allow an out-of-plane bending mode.

25. The apparatus of claim 24, wherein the mechanical layer is substantially thicker than the piezoelectric layer stack.

26. The apparatus of claim 24, wherein the neutral axis passes through the mechanical layer.

27. The apparatus of claim 22, wherein:

the cavity is formed by removing a sacrificial material through at least one release hole;

the mechanical layer is formed after removing the sacrificial material; and

the mechanical layer seals the cavity by sealing the at least one release hole.

28. The apparatus of claim 22, wherein the mechanical layer includes a recess where the mechanical layer is locally thinned.

29. The apparatus of claim 22, wherein the mechanical layer is disposed over a side of the piezoelectric stack opposite to the substrate or below a side of the piezoelectric stack facing the substrate.