Micro-electro-mechanical transducer having an optimized non-flat surface

• US 9,327,967 B2
• Filed: 03/09/2015
• Issued: 05/03/2016
• Est. Priority Date: 08/03/2005
• Status: Active Grant

• Current Assignee: Kolo Medical, Ltd.
• Original Assignee: Kolo Technologies, Inc.
• Inventors: Huang, Yongli
• Primary Examiner(s): TRAN, ANH Q
• Application Number:
  US14/642,306
• Publication Number:
  US 20150181348A1
• Time in Patent Office: 421 Days
• Field of Search: None
• US Class Current: 1/1
• CPC Class Codes: B06B 1/0292 Electrostatic transducers, e.g. electret-type
• CPC Class Codes: B81B 3/0027 Structures for transforming mechanical energy, e.g. potential energy of a spring into translation, sound into translation
• CPC Class Codes: B81C 1/00158 Diaphragms, membranes manufacture process for semi-permeable inorganic membranes B01D67/0039
• CPC Class Codes: B81C 1/00182 Arrangements of deformable or non-deformable structures, e.g. membrane and cavity for use in a transducer
• CPC Class Codes: B81C 1/00357 involving bonding one or several substrates on a non-temporary support, e.g. another substrate
• CPC Class Codes: B81C 1/00373 Selective deposition, e.g. printing or microcontact printing
• CPC Class Codes: B81C 1/00523 Etching material
• CPC Class Codes: B81C 1/00626 Processes for achieving a desired geometry not provided for in groups B81C1/00563 - B81C1/00619
• CPC Class Codes: H01L 2924/00 Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
• CPC Class Codes: H01L 2924/0002 Not covered by any one of groups H01L24/00, H01L24/00 and H01L2224/00
• CPC Class Codes: H02N 1/006 of the gap-closing type H02N1/004 takes precedence
• CPC Class Codes: H03H 3/0072 of microelectro-mechanical resonators or networks micromembranes or microbeams B81B2203/01; manufacture of microstructural devices in general B81C
• CPC Class Codes: H03H 9/02259 Driving or detection means
• CPC Class Codes: H03H 9/2405 of microelectro-mechanical resonators
• CPC Class Codes: H03H 9/462 Microelectro-mechanical filters
• CPC Class Codes: H04R 19/005 using semiconductor materials
• CPC Class Codes: H04R 2201/003 Mems transducers or their use of the electrostatic type H04R19/005
• CPC Class Codes: Y10T 29/42 Piezoelectric device making
• CPC Class Codes: Y10T 29/49005 Acoustic transducer

Abstract

A capacitive micromachined ultrasound transducer (cMUT) and fabrication method of the same are provided. The cMUT has a substrate, a curved membrane disposed on top of the substrate, and a flexible membrane disposed on top of the curved membrane. The curved membrane has a raised portion which is higher than a recessed portion relative to the substrate, and is supported by a support standing on a major surface of the substrate. The flexible membrane includes a first region mounted to the raised portion of the curved membrane, and a second region extending over the recessed portion of the curved member. Methods for fabricating the cMUT are also disclosed.

Claims

1. A capacitive micromachined ultrasound transducer (cMUT), comprising:

a substrate;

a curved membrane disposed on top of the substrate, the curved membrane having a raised portion higher than a recessed portion relative to the substrate, the raised portion being supported by a support standing on a major surface of the substrate, wherein at least one of the curved membrane and the substrate has a first electrode; and

a flexible membrane disposed on top of the curved membrane, either directly or indirectly supported by the curved membrane, wherein the flexible membrane has a second electrode opposing the first electrode to define a gap width therebetween.

2. The capacitive micromachined ultrasonic transducer as recited in claim 1, wherein the flexible membrane is directly supported by the raised portion of the curved membrane.

3. The capacitive micromachined ultrasonic transducer as recited in claim 1, wherein the flexible membrane is indirectly supported by the recessed portion of the curved membrane through a second support placed on the recessed portion, the second support being higher than the raised portion of the curved membrane.

4. The capacitive micromachined ultrasonic transducer as recited in claim 1, wherein the support is formed out of the substrate.

5. The capacitive micromachined ultrasonic transducer as recited in claim 1, wherein the substrate is conductive.

6. The capacitive micromachined ultrasonic transducer as recited in claim 1, wherein the curved membrane is conductive.

7. The capacitive micromachined ultrasonic transducer as recited in claim 1, further comprising:

an insulation layer disposed on a top surface the curved membrane facing the flexible membrane.

8. The capacitive micromachined ultrasonic transducer as recited in claim 1, wherein the curved membrane is a separate wafer material bonded to the substrate.

9. The capacitive micromachined ultrasonic transducer as recited in claim 1, wherein the support is aligned closely at a highest point of the raised portion of the curved membrane.

10. An array of capacitive micromachined ultrasound transducers (cMUT), each cMUT comprising:

a substrate;

a curved membrane disposed on top of the substrate, the curved membrane having a raised portion higher than a recessed portion relative to the substrate, the raised portion being supported by a support standing on a major surface of the substrate, wherein at least one of the curved membrane and the substrate has a first electrode; and

a flexible membrane disposed on top of the curved membrane, either directly or indirectly supported by the curved membrane, wherein the flexible membrane has a second electrode opposing the first electrode to define a gap width therebetween.

11. The array of capacitive micromachined ultrasonic transducers as recited in claim 10, wherein the flexible membrane is directly supported by the raised portion of the curved membrane.

12. The array of capacitive micromachined ultrasonic transducers as recited in claim 10, wherein the flexible membrane is indirectly supported by the recessed portion of the curved membrane through a second support placed on the recessed portion, the second support being higher than the raised portion of the curved membrane.

13. The array of capacitive micromachined ultrasound transducers as recited in claim 10, wherein the substrate is conductive.

14. The array of capacitive micromachined ultrasound transducers as recited in claim 10, wherein the curved membrane is a separate wafer material bonded to the substrate.

15. A method for fabricating a capacitive micromachined ultrasound transducer (cMUT), the method comprising:

providing a substrate;

forming a support on the substrate;

forming a curved membrane on the substrate, the curved membrane including a raised area higher than a recessed area relative to the substrate, wherein at least one of the curved membrane and the substrate has a first electrode; and

forming a flexible membrane layer over the first wafer, the flexible membrane being either directly or indirectly supported by the curved membrane, wherein the flexible membrane has a second electrode opposing the first electrode to define a gap width therebetween.

16. The method as recited in claim 15, wherein the forming the curved membrane comprises:

forming a bendable layer having a desired thickness profile;

placing the bendable layer over the substrate such that the bendable layer is supported by the support, and the bendable layer and the substrate define a cavity therebetween; and

bending the bendable layer to form the curved membrane.

17. The method of claim 15, wherein the recessed area of the curved membrane touches the substrate.

18. The method of claim 15 wherein the forming the curved membrane comprises annealing the curved membrane at a desired temperature and pressure.

19. The method of claim 15 wherein the curved membrane comprises a semiconductor material.

20. The method of claim 15, wherein the forming the curved membrane comprises:

selectively doping a membrane layer using a doping material with doping profile to introduce a desired stress profile in the first layer; and

annealing the membrane layer at a desired temperature and pressure to form the curved membrane.

21. A method for fabricating a capacitive micromachined ultrasound transducer (cMUT), the method comprising:

forming a support on a wafer;

joining the wafer to a substrate such that the support touches the substrate;

forming a curved membrane by bending the wafer, the curved membrane including a raised area higher than a recessed area relative to the substrate, and the raised area being aligned with the support; and

forming a flexible membrane layer over the curved membrane, the flexible membrane being either directly or indirectly supported by the curved membrane.

22. The method of claim 21, wherein forming the curved membrane comprises:

thinning the wafer to a membrane thickness; and

bending the thinned wafer.

23. The method of claim 21, wherein the recessed area of the curved membrane touches the substrate.

24. The method of claim 21, wherein the forming the curved membrane comprises:

selectively doping the wafer using a doping material with doping profile to introduce a desired stress profile in the wafer; and

annealing the wafer at a desired temperature and pressure to form the curved membrane.