Supplemental sensor modes and systems for ultrasonic transducers

• US 10,441,975 B2
• Filed: 01/30/2017
• Issued: 10/15/2019
• Est. Priority Date: 05/10/2016
• Status: Active Grant

• Current Assignee: Invensense Incorporated (TDK Corporation)
• Original Assignee: Invensense Incorporated (TDK Corporation)
• Inventors: Apte, Nikhil, Berger, Renata Melamud, Daneman, Michael
• Primary Examiner(s): Pihulic, Daniel
• Application Number:
  US15/419,835
• Publication Number:
  US 20170326591A1
• Time in Patent Office: 988 Days
• CPC Class Codes: B06B 1/0292 Electrostatic transducers, e.g. electret-type
• 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 1/064 with multiple active layers
• CPC Class Codes: B06B 2201/51 Electrostatic transducer
• CPC Class Codes: B06B 2201/55 Piezoelectric transducer

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 configured to allow movement at ultrasonic frequencies. The membrane comprises a piezoelectric layer and first and second electrodes coupled to opposing sides of the piezoelectric layer. For operation in a Capacitive Micromachined Ultrasonic Transducer (CMUT) mode, a third electrode is disposed on the substrate and separated by an air gap in the cavity from the second electrode. Also provided are an integrated MEMS array, a method for operating an array of PMUT/CMUT dual-mode devices, and a PMUT/CMUT 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;

a first electrode coupled to one side of the piezoelectric layer; and

a second electrode coupled to an opposing side of the piezoelectric layer; and

a third electrode disposed on the substrate and separated by an air gap in the cavity from the second electrode;

wherein the PMUT is configured to operate in a Capacitive Micromachined Ultrasonic Transducer (CMUT) mode, wherein the PMUT is selectively switchable between the CMUT mode and an ultrasonic mode;

wherein in the CMUT mode, an AC voltage is placed between the first and third electrodes, where the second electrode is either the same potential as the first electrode or floating; and

wherein in the ultrasonic mode, an AC voltage is placed between the first and second electrodes, where the third electrode is either the same potential as the second electrode or floating, causing the device to produce a flexural mode of motion in the membrane.

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, the membrane further comprising:

a mechanical support layer connected to the first electrode.

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

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

8. 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.

9. 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.

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

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

19. The PMUT device of claim 1, wherein the piezoelectric layer comprises aluminum nitride.

20. The PMUT device of claim 1, wherein the piezoelectric layer comprises lead zirconate titanate.

12. 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 Capacitive Micromachined Ultrasonic Transducer (CMUT) mode and an ultrasonic mode, wherein the plurality of MEMS PMUTs comprise a piezoelectric layer of a same material, wherein the piezoelectric layer comprises aluminum nitride, and wherein each of the plurality of MEMS PMUTs 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.

13. The integrated MEMS array of claim 12, wherein the first shape is selected from a circle, an oval, a square, a rectangle, a hexagon, an octagon, or a chevron.

14. The integrated MEMS array of claim 12 wherein each PMUT includes a first electrode disposed on one side of the piezoelectric layer, a second electrode disposed on an opposing side of the piezoelectric layer, and a third electrode disposed on a substrate opposite the second electrode and separated by an air space therefrom;

wherein in the CMUT mode, an AC voltage is placed between the first and third electrodes, where the second electrode is either the same potential as the first electrode or floating; and

wherein in the ultrasonic mode, an AC voltage is placed between the first and second electrodes, where the third electrode is either the same potential as the second electrode or floating, causing the PMUT to produce a flexural mode of motion in the membrane.

15. A method for operating an array of Piezoelectric Micromachined Ultrasonic Transducer (PMUT)/Capacitive Micromachined Ultrasonic Transducer (CMUT) dual-mode devices, each dual-mode device including a piezoelectric layer, a first electrode disposed on one side of the piezoelectric layer, a second electrode disposed on an opposing side of the piezoelectric layer, and a third electrode disposed on a substrate opposite the second electrode and separated by an air space therefrom, the method comprising:

selecting a CMUT mode by placing an AC voltage between the first and third electrodes, where the second electrode is either the same potential as the first electrode or floating;

or

selecting a PMUT mode by placing an AC voltage between the first and second electrodes, where the third electrode is either the same potential as the second electrode or floating, causing the device to produce a flexural mode of motion in the membrane; and

selectively switching between the PMUT mode and the CMUT mode, wherein sensing can occur in either of the two modes.

16. The method of claim 15, 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 CMUT mode.

21. The method of claim 15, wherein the piezoelectric layer comprises aluminum nitride.

22. The method of claim 15, wherein the piezoelectric layer comprises lead zirconate titanate.

17. A Piezoelectric Micromachined Ultrasonic Transducer (PMUT)/Capacitive Micromachined Ultrasonic Transducer (CMUT) 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,

a first electrode coupled to one side of the piezoelectric layer, and

a second electrode coupled to an opposing side of the piezoelectric layer; and

a third electrode disposed on the substrate opposite the second electrode in the cavity;

wherein in the CMUT mode, an AC voltage is placed between the first and third electrodes, where the second electrode is either the same potential as the first electrode or floating; and

wherein in the PMUT mode, an AC voltage is placed between the first and second electrodes, where the third electrode is either the same potential as the second electrode or floating, causing the device to produce a flexural mode of motion in the membrane.

18. An array of Piezoelectric Micromachined Ultrasonic Transducer (PMUT)/Capacitive Micromachined Ultrasonic Transducer (CMUT) dual-mode devices, the array comprising a plurality of the PMUT/CMUT dual-mode devices of claim 17.

23. The PMUT/CMUT dual-mode device of claim 17, wherein the piezoelectric layer comprises aluminum nitride.

24. The PMUT/CMUT dual-mode device of claim 17, wherein the piezoelectric layer comprises lead zirconate titanate.