ULTRASONIC TRANSDUCER OPERABLE IN A SURFACE ACOUSTIC WAVE (SAW) MODE

• US 20170326590A1
• Filed: 02/03/2017
• Published: 11/16/2017
• Est. Priority Date: 05/10/2016
• Status: Active Grant

• Current Assignee: Invensense Incorporated (TDK Corporation)
• Original Assignee: Invensense Incorporated (TDK Corporation)
• Inventors: DANEMAN, Michael
• Granted Patent: US 11,673,165 B2
• Time in Patent Office: Days
• CPC Class Codes: B06B 1/06 operating with piezoelectric effect or with electrostriction piezoelectric or electrostrictive devices per se H10N30/00
• CPC Class Codes: B06B 1/0603 using a piezoelectric bender, e.g. bimorph
• CPC Class Codes: B06B 1/0622 on one surface
• CPC Class Codes: B06B 1/0648 of rectangular shape
• CPC Class Codes: B06B 1/0651 of circular shape
• CPC Class Codes: H03K 2217/96003 using acoustic waves, e.g. ultrasound
• CPC Class Codes: H10N 30/1051 based on piezoelectric or electrostrictive films or coatings
• CPC Class Codes: H10N 30/85 Piezoelectric or electrostrictive active materials
• CPC Class Codes: H10N 30/875 Further connection or lead arrangements, e.g. flexible wiring boards, terminal pins

Abstract

A Piezoelectric Micromachined Ultrasonic Transducer (PMUT) device is provided. The PMUT includes a substrate and an edge support structure connected to the substrate. A membrane is connected to the edge support structure such that a cavity is defined between the membrane and the substrate, where the membrane is configured to allow movement at ultrasonic frequencies. The membrane includes a piezoelectric layer and first and second electrodes coupled to opposing sides of the piezoelectric layer. The PMUT is also configured to operate in a Surface Acoustic Wave (SAW) mode. Also provided are an integrated MEMS array, a method for operating an array of PMUT/SAW dual-mode devices, and a PMUT/SAW dual-mode device.

Claims

1. A Piezoelectric Micromachined Ultrasonic Transducer (PMUT) device comprising:

a substrate;

an edge support structure connected to the substrate;

a membrane connected to the edge support structure such that a cavity is defined between the membrane and the substrate, the membrane configured to allow movement at ultrasonic frequencies, the membrane comprising;

a piezoelectric layer, and

first and second electrodes coupled to opposing sides of the piezoelectric layer;

wherein the PMUT is also configured to operate in a Surface Acoustic Wave (SAW) mode.

2. The PMUT device of claim 1, further comprising an interior support structure disposed within the cavity and connected to the substrate and the membrane.

3. The PMUT device of claim 2, wherein the second electrode extends into the cavity and defines an area between the edge support structure and the interior support structure.

4. The PMUT device of claim 2, wherein at least one of the first electrode and the second electrode is electrically coupled through the interior support structure.

5. The PMUT device of claim 1, wherein the first electrode is a patterned layer.

6. The PMUT device of claim 1, the membrane further comprising:

a mechanical support layer connected to the first electrode.

7. The PMUT device of claim 1, wherein the membrane further comprises a mechanical support layer.

8. The PMUT device of claim 1, wherein the piezoelectric layer defines a continuous layer.

9. The PMUT device of claim 1, wherein the piezoelectric layer is a patterned layer.

10. The PMUT device of claim 1, wherein the PMUT device is substantially circular such that the edge support structure and the membrane are substantially circular.

11. The PMUT device of claim 1, wherein the PMUT device is substantially square-shaped such that the edge support structure and the membrane are substantially square-shaped.

12. The PMUT device of claim 1, wherein the edge support structure is connected to an electric potential.

13. The PMUT device of claim 1, wherein the substrate comprises a CMOS logic wafer.

14. The PMUT device of claim 1, which is selectively switchable between the Surface Acoustic Wave (SAW) mode and an ultrasonic mode.

15. The PMUT device of claim 14, wherein the first electrode includes two pairs of interdigitated electrodes coupled to one side of the piezoelectric layer and wherein the second electrode is coupled to an opposing side of the piezoelectric layer;

wherein in the SAW mode, a first pair of interdigitated electrodes is to inject an AC signal and generate a surface acoustic wave, which is to be received by a second pair of interdigitated electrodes, while the second electrode is either ground or floating; and

wherein in the ultrasonic mode, the two pairs of interdigitated electrodes are all to be driven at the same potential, while the second electrode is to be driven at another potential, causing the device to produce a flexural mode of motion in the membrane.

16. An integrated MEMS array comprising:

a plurality of MEMS Piezoelectric Micromachined Ultrasonic Transducers (PMUTs) for transmitting ultrasonic beams and receiving ultrasonic signals;

wherein at least a portion of the PMUTs are operable in two modes, a Surface Acoustic Wave (SAW) mode and an ultrasonic mode.

17. The integrated MEMS array of claim 16, wherein the plurality of MEMS PMUT elements and the MEMS SAW elements comprise a piezoelectric layer of a same material.

18. The integrated MEMS array of claim 17, wherein the piezoelectric layer comprises aluminum nitride.

19. The integrated MEMS array of claim 18, wherein each of the plurality of MEMS PMUT elements is defined by an active membrane having first shape and a first size, and at least one other element is defined by an active membrane having a second shape and a second size, the first shape and the second shape being different but related by proportionality of the first size and the second size so that the integrated MEMS array is contiguous.

20. The integrated MEMS array of claim 19, wherein the first shape is selected from a circle, an oval, a square, a rectangle, a hexagon, an octagon, or a chevron.

21. The integrated MEMS array of claim 16 wherein each PMUT includes two pairs of interdigitated electrodes coupled to one side of a membrane comprising a piezoelectric layer and a fifth electrode coupled to an opposing side of the piezoelectric layer;

wherein in the SAW mode, a first pair of interdigitated electrodes is to inject an AC signal and generate a surface acoustic wave, which is to be received by a second pair of interdigitated electrodes, while the second electrode is either ground or floating; and

wherein in the ultrasonic mode, the two pairs of interdigitated electrodes all to be driven at the same potential, while the second electrode is to be driven at another potential, causing the PMUT to produce a flexural mode of motion in the membrane.

22. A method for operating an array of Piezoelectric Micromachined Ultrasonic Transducer (PMUT)/Surface Acoustic Wave (SAW) dual-mode devices, comprising:

operating the PMUT/SAW array in an active operational mode, comprising;

transmitting ultrasonic beams during a first phase,

receiving ultrasonic signals during a second phase, the received ultrasonic signals characteristic of reflections or echoes of the transmitted ultrasonic beams, and

selectively switching between the PMUT mode and the SAW mode, wherein

sensing can occur in either of the two modes.

23. The method of claim 23, wherein the array includes heterogeneous elements, in which some elements are configured for performance in the PMUT mode and other elements are configured for performance in the SAW mode.

24. A Piezoelectric Micromachined Ultrasonic Transducer (PMUT)/Surface Acoustic Wave (SAW) dual-mode device, comprising:

a substrate;

an edge support structure connected to the substrate; and

a membrane connected to the edge support structure such that a cavity is defined between the membrane and the substrate, the membrane configured to allow movement at ultrasonic frequencies, the membrane comprising;

a piezoelectric layer, and

two pairs of interdigitated electrodes coupled to one side of the piezoelectric layer and a fifth electrode coupled to an opposing side of the piezoelectric layer;

wherein in a first mode, a first pair of interdigitated electrodes is to inject an AC signal and generate a surface acoustic wave, which is to be received by a second pair of interdigitated electrodes, while the second electrode is either ground or floating; and

wherein in a second mode, the fifth electrode is either ground or floating, with the two pairs of interdigitated electrodes all to be driven at the same potential, while the second electrode is to be driven at another potential, causing the device to produce a flexural mode of motion in the membrane.

25. An array of Piezoelectric Micromachined Ultrasonic Transducer (PMUT)/Surface Acoustic Wave (SAW) dual-mode devices, the array comprising a plurality of the PMUT/SAW dual-mode devices of claim 25.