Harmonic cMUT devices and fabrication methods

• US 20050200242A1
• Filed: 02/28/2005
• Published: 09/15/2005
• 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
• Granted Patent: US 7,612,483 B2
• Time in Patent Office: Days
• US Class Current: 310/334
• CPC Class Codes: B06B 1/0292 Electrostatic transducers, e.g. electret-type

Abstract

Harmonic capacitive micromachined ultrasonic transducer (“cMUT”) devices and fabrication methods are provided. In a preferred embodiment, a harmonic cMUT device generally comprises a membrane having a non-uniform mass distribution. A mass load positioned along the membrane can be utilized to alter the mass distribution of the membrane. The mass load can be a part of the membrane and formed of the same material or a different material as the membrane. The mass load can be positioned to correspond with a vibration mode of the membrane, and also to adjust or shift a vibration mode of the membrane. The mass load can also be positioned at predetermined locations along the membrane to control the harmonic vibrations of the membrane. A cMUT can also comprise a cavity defined by the membrane, a first electrode proximate the membrane, and a second electrode proximate a substrate. Other embodiments are also claimed and described.

Claims

1. A cMUT comprising:

a membrane; and

a membrane frequency adjustor for adjusting a vibration mode of the membrane to a predetermined frequency.

2. The cMUT of claim 1, wherein the membrane frequency adjustor comprises the membrane having a non-uniform mass distribution along at least a portion of it length.

3. The cMUT of claim 2, wherein the membrane frequency adjustor comprises a mass load proximate the membrane.

4. The cMUT of claim 3, wherein the mass load comprises a plurality of separate mass load elements.

5. The cMUT of claim 3, wherein the mass load is an electrode element of the cMUT.

6. The cMUT of claim 3, wherein the mass load is Gold.

7. The cMUT of claim 4, wherein the plurality of mass load elements modify the frequency response of the membrane.

8. The cMUT of claim 1, the membrane having a plurality of vibration modes, and the membrane frequency adjustor adapted to harmonically relate at least two of the plurality of vibration modes.

9. The cMUT of claim 1, wherein the membrane is adapted to vibrate at a fundamental frequency and the membrane frequency adjustor adjusts the membrane to vibrate at a frequency substantially equal to twice the fundamental frequency.

10. The cMUT of claim 1, further comprising an electrode element proximate the membrane in a location associated with a vibration mode of the membrane.

11. A method of controlling vibration modes of a cMUT comprising the steps of:

providing a membrane;

determining a target vibration frequency of the membrane; and

altering the mass distribution of the membrane along at least a portion of the length of the membrane to induce the target vibration frequency of the membrane.

12. The method of claim 11, wherein the target vibration frequency of the membrane is substantially twice a fundamental frequency of the membrane.

13. The method of claim 11, wherein the step of altering the mass distribution of the membrane along at least a portion of the length of the membrane comprises providing a membrane having a varying thickness along at least a portion of the length of the membrane.

14. The method of claim 11, wherein the step of altering the mass distribution of the membrane along at least a portion of the length of the membrane comprises providing a membrane having a varying density along at least a portion of the length of the membrane.

15. The method of claim 11, wherein the membrane has a first vibration mode and a second vibration mode that is approximately twice the frequency of the first vibration mode, the membrane being adapted to transmit ultrasonic energy at the first vibration mode and receive ultrasonic energy at the second vibration mode.

16. A method of fabricating a cMUT comprising the steps of:

providing a membrane; and

configuring the membrane to have a non-uniform mass distribution to receive energy at a predetermined frequency.

17. The method of claim 16, wherein the step of configuring the membrane to have a non-uniform mass distribution comprises providing a plurality of mass loads proximate the membrane.

18. The method of claim 16, further comprising the step of adapting the membrane to transmit ultrasonic energy at a first vibration mode and receive ultrasonic energy at a second vibration mode, wherein the second vibration mode is approximately twice the frequency of the first vibration mode.

19. The method of claim 16, further comprising the step of adapting the membrane so that the vibration modes of the membrane are harmonically related.

20. The method of claim 19, further comprising the step of positioning an electrode element proximate a vibration mode of the membrane.