Multiple element electrode cMUT devices and fabrication methods

• US 8,008,835 B2
• Filed: 02/28/2005
• Issued: 08/30/2011
• Est. Priority Date: 02/27/2004
• Status: Active Grant

• Current Assignee: Georgia Tech Research Corporation (University System of Georgia)
• Original Assignee: Georgia Tech Research Corporation (University System of Georgia)
• Inventors: Degertekin, F. Levent
• Primary Examiner(s): ROSENAU, DEREK JOHN
• Application Number:
  US11/068,005
• Publication Number:
  US 20050200241A1
• Time in Patent Office: 2,374 Days
• Field of Search: 310/309, 310/322, 310/324, 310/330, 310/332, 310/334, 310/365, 310/366, 600/459, 381/174, 361/174
• US Class Current: 310/309
• CPC Class Codes: B06B 1/0292 Electrostatic transducers, e.g. electret-type
• CPC Class Codes: G01N 29/2406 Electrostatic or capacitive probes, e.g. electret or cMUT-probes

Abstract

Multiple electrode element capacitive micromachined ultrasonic transducer (“cMUT”) devices and fabrication methods are provided. A cMUT device generally comprises a top electrode disposed within a membrane, a bottom electrode disposed on a substrate, and a cavity between the membrane and the bottom electrode. In a preferred embodiment of the present invention, at least one of the first electrode and the second electrode comprises a plurality of electrode elements. The electrode elements can be positioned and energized to shape the membrane and efficiently transmit and receive ultrasonic energy, such as ultrasonic waves. Other embodiments are also claimed and described.

Claims

1. A cMUT comprising:

a multi-element electrode having at least a first electrode element and a second electrode element, the first and second electrode elements being spaced apart from each, forming part of different circuits, and operatively configured to transmit or receive an ultrasonic wave separately from each other such that the first electrode element can transmit or receive an ultrasonic wave separately from the second electrode element receiving or transmitting an ultrasonic wave; and

a membrane, the second electrode element being disposed proximate a central region of the membrane such that the second electrode element is positioned to actuate the central region of the membrane, the first electrode element being disposed generally between an edge region of the membrane and the central region to actuate a region intermediate the edge region and the central region, and the first electrode element and the second electrode element having cross-sectional widths less than the cross-sectional width of the membrane.

2. The cMUT of claim 1, wherein at least one of the first electrode element and the second electrode element is a hot electrode of the cMUT.

3. The cMUT of claim 1, wherein the first and second electrode elements are disposed within the membrane in at least one of a substantially co-planar arrangement or non-planar arrangement.

4. The cMUT of claim 1, wherein the first and second electrode elements are proximate a substrate.

5. The cMUT of claim 1 further comprising a third electrode element coupled to the first electrode element to form an electrode element pair, the electrode element pair being spaced apart from sides of the second electrode element such that the electrode element pair and the second electrode element can separately receive or transmit an ultrasonic wave and is electrically isolated from the second electrode element.

6. The cMUT of claim 1 further comprising a membrane shaping means to shape the membrane for reception or transmission of an ultrasonic wave, the membrane shaping means including at least one of the first electrode element and the second electrode element.

7. The cMUT of claim 1, the multi-element electrode further comprising a third electrode element, the third electrode element being disposed in an opposing position from the first electrode element such that the third electrode element is located generally between the central region of the membrane and a second edge region of the membrane to actuate a region of the membrane intermediate the second edge region and the central region.

8. The cMUT of claim 1, wherein the first electrode element and the second electrode element are a side electrode element pair adapted to cooperatively shape the membrane during transmission or receipt of an ultrasonic signal.

9. The cMUT of claim 1, the cMUT further comprising a bottom electrode and an electrode element pair, the electrode element pair comprising the first electrode element and a third electrode element,

the membrane and the bottom electrode being separated by a gap distance in an electrically neutral state, and the electrode element pair being operatively configured to flex at least a portion of the membrane by more than one third of the gap distance during transmission of an ultrasonic wave.

10. The cMUT of claim 1, further comprising a third electrode element and a side electrode element pair that comprises the first electrode element and the third electrode element,

the side electrode element pair being transmit elements, the second electrode element being a receive element, and the first and third electrode elements of the side electrode element pair each being so located at respective, opposing sides of the cMUT to make use of leveraged bending by flexing one or more regions of the membrane.

11. The cMUT of claim 6, the membrane shaping means being operatively configured to shape the membrane and not receive or transmit ultrasonic waves when shaping the membrane.

12. A method of transceiving ultrasonic waves comprising:

providing a cMUT having a membrane and a multi-element first electrode comprising a first electrode element and a second electrode element, both having cross-sectional widths less than the cross-sectional width of the membrane;

providing the first electrode element proximate a first portion of the cMUT membrane such that the first electrode element can actuate the first portion of the cMUT membrane;

providing the second element electrode proximate a second portion of the cMUT membrane such that the second electrode element can actuate the second portion of the cMUT membrane; and

adapting the cMUT to receive applying a first voltage at the first electrode element and a second voltage at the second electrode element such that the first electrode element and the second electrode element transmit an ultrasonic wave separate from each other.

13. The method of claim 12, further comprising adapting the cMUT to receive a bias voltage at least one of the first electrode element and the second electrode element for shaping the membrane to receive or transmit an ultrasonic wave signal.

14. The method of claim 13, further comprising adapting the cMUT to optically sense the received ultrasonic wave signal.

15. The method of claim 13, further comprising adapting the cMUT to electrically sense the received ultrasonic wave signal.

16. A method of fabricating a cMUT array comprising one or more cMUTs, the method comprising:

providing a top conductor;

providing a bottom conductor separated by a gap distance from the top conductor;

configuring at least one of the top and bottom conductors into a plurality of electrode elements such that a number of the electrode elements can transmit and receive ultrasonic waves separate from another number of the electrode elements receiving or transmitting ultrasonic waves;

configuring at least one of the plurality of electrode elements into at least a set of three conductors for each cMUT, the set of three conductors comprising a first electrode element, a second electrode element, and a third electrode element each having a cross-sectional width less than the cross-sectional width of the cMUT;

providing the first and the third electrode elements proximate opposing cross-sectional width portions of the cMUT such that the first and third electrode elements can actuate opposing cross-sectional width portions of the cMUT; and

providing the second electrode element intermediate the first and second electrode elements such that ends of the second electrode element are spaced apart from opposing ends of the first and third electrode elements.

17. The method of claim 16, further comprising configuring the top and bottom conductors to be electrically coupled to a voltage source.

18. The method of claim 16, further comprising:

adapting the first and the third electrode elements to receive a first voltage to shape at least one of the opposing cross-sectional width ends of the cMUT for receiving or transmitting ultrasonic waves; and

adapting the second electrode element to receive a second voltage to shape a membrane region of the cMUT intermediate the opposing cross-sectional width ends of the cMUT.

19. The method of claim 16, further comprising:

providing a sacrificial layer proximate the bottom conductor;

providing a first membrane layer proximate the sacrificial layer;

providing a second membrane layer proximate the top conductor; and

removing the sacrificial layer.

20. The method of claim 19, further comprising disposing the top conductor between the first membrane layer and the second membrane layer.

21. The method of claim 16, further comprising electrically coupling at least two of the electrode elements of the plurality of electrode elements.

22. A cMUT for use with ultrasonic imaging, the cMUT comprising:

a multi-element electrode comprising a first electrode element, a second electrode element, and a third electrode element, the first electrode element being proximate a first side region of the cMUT, the second electrode element being proximate a second side region of the cMUT, and the third electrode element being proximate a middle region of the cMUT;

the first electrode element and the second electrode element forming a side electrode element pair and being electrically coupled to one another to cooperatively shape a membrane of the cMUT during transmission or reception of an ultrasonic signal; and

the side electrode element pair being transmit elements, the third electrode element being a receive element, and the first and second electrode elements of the electrode element pair each being so located at side regions of the cMUT to make use of leveraged bending.

23. The cMUT of claim 22, wherein at least one of the first electrode element, the second electrode element, and the third electrode element is a hot electrode of the cMUT.

24. The cMUT of claim 22, wherein at least one of the first electrode element, the second electrode element, and the third electrode element are disposed proximate at least one of a substrate or the membrane.

25. The cMUT of claim 22 further comprising a membrane shaping means, the membrane shaping means including at least one of the first electrode element, the second electrode element, and the third electrode element, the membrane shaping means operatively adapted to shape the membrane in a reception state to receive ultrasonic waves and a transmission state to transmit ultrasonic waves.

26. The cMUT of claim 22, the cMUT further comprising a bottom electrode, wherein the membrane and the bottom electrode are separated by a gap distance in an electrically neutral state, and wherein the side electrode element pair is adapted to flex the membrane by more than one third of the gap distance during transmission of an ultrasonic wave.

27. The cMUT of claim 22, wherein the first electrode element, the second electrode element, and the third electrode element each have a cross sectional width less than the cross sectional width of the membrane.

28. The cMUT of claim 22, wherein the first electrode element, the second electrode element, and the third electrode element are disposed at least partially within the membrane in at least one of a substantially co-planar arrangement or non-planar arrangement with each other.