BACKING MATERIAL FOR MICROMACHINED ULTRASONIC TRANSDUCER DEVICES

• US 20040113524A1
• Filed: 12/11/2002
• Published: 06/17/2004
• Est. Priority Date: 12/11/2002
• Status: Active Grant

• Current Assignee: General Electric Company
• Original Assignee: General Electric Company
• Inventors: Wildes, Douglas G., Smith, Lowell Scott, Mills, David M., Lewandowski, Robert S., Baumgartner, Charles E.
• Granted Patent: US 6,831,394 B2
• Time in Patent Office: Days
• US Class Current: 310/328
• CPC Class Codes: B06B 1/0292 Electrostatic transducers, e.g. electret-type
• CPC Class Codes: B06B 1/0685 on the back only of piezoelectric elements
• CPC Class Codes: B06B 1/0688 with foil-type piezoelectric elements, e.g. PVDF
• CPC Class Codes: G01H 11/06 by electric means
• CPC Class Codes: Y10T 29/49004 including measuring or testing of device or component part
• CPC Class Codes: Y10T 29/49005 Acoustic transducer
• CPC Class Codes: Y10T 29/4908 Acoustic transducer

Abstract

RD-28,709 22An ultrasonic transducer device comprising: an ultrasonic transducer array micromachined on a substrate; flexible electrical connections connected to the transducer array; and a body of acoustically attenuative material that supports the substrate and the flexible electrical connections. The acoustic backing material may contain additional features, such as tabs or notches, for use in positioning the transducer on fixtures during manufacturing or positioning the transducer within a housing during final assembly. Tabs or other features that are used only during manufacturing may be subsequently removed from the device. The MUT device itself may also be thinned so as to provide flexibility as desired. The backing material is preferably matched in acoustic impedance to the silicon wafer so as to prevent reflection at the interface of any acoustic energy propagating rearward, i.e., in the direction away from the device front surface. The backing material may also possess a high thermal conductivity to assist in removal of heat from the device.

Claims

1. A micromachined ultrasonic transducer device comprising:

an ultrasonic transducer array micromachined on a substrate;

flexible electrical connections connected to said ultrasonic transducer array; and

a body of acoustically attenuative material that supports said substrate and said flexible electrical connections.

2. The device as recited in claim 1, wherein said ultrasonic transducer array comprises a multiplicity of cMUT cells.

3. The device as recited in claim 1, wherein said ultrasonic transducer array comprises a multiplicity of pMUT cells.

4. The device as recited in claim 1, wherein said substrate has a first area and said body of acoustically attenuative material has a second area greater than said first area.

5. The device as recited in claim 1, wherein said substrate is made of a material having a first acoustic impedance and said acoustically attenuative material has a second acoustic impedance substantially matching said first acoustic impedance.

6. The device as recited in claim 1, wherein said body of acoustically attenuative material is joined to said substrate and to said flexible electrical connections.

7. The device as recited in claim 1, further comprising a layer of acoustic impedance matching material disposed between said substrate and said body of acoustically attenuative material, the acoustic impedance of said acoustic impedance matching material has a value that lies between the acoustic impedances of the material of said substrate and said acoustically attenuative material.

8. The device as recited in claim 1, wherein said substrate is made of silicon.

9. The device as recited in claim 1, wherein said body of acoustically attenuative material possesses a pair of tabs that extend beyond opposing side edges of said substrate, said tabs not supporting said flexible electrical connections.

10. The device as recited in claim 1, wherein said flexible electrical connections comprise conductive traces printed on a flexible substrate made of dielectric material.

11. The device as recited in claim 1, wherein said body of acoustically attenuative material adjoins said ultrasonic transducer array along its entire perimeter, and said flexible electrical connections adjoin respective front faces of respective portions of said body of acoustically attenuative material and said ultrasonic transducer array.

12. The device as recited in claim 1, wherein said acoustically attenuative material comprises tungsten particles dispersed in a matrix of polyvinyl chloride.

13. An ultrasound transducer comprising:

a silicon substrate;

an array of ultrasonic transducer cells supported by said silicon substrate; and

a body of acoustically attenuative material disposed on a side of said substrate opposite to said array, said acoustically attenuative material comprising tungsten particles dispersed in a matrix material, wherein the mass percent of tungsten lies in the range of 96.0% to 96.65%, with the remainder being said matrix material, and wherein a first fraction of said tungsten particles have a particle size on the order of 1 micron and a second fraction of said tungsten particles have a particle size on the order of 10 microns.

14. The transducer as recited in claim 13, said first and second fractions being approximately 15% and 85% respectively by mass of the total tungsten in said body of acoustically attenuative material.

15. The transducer as recited in claim 13, wherein said matrix material is polyvinyl chloride.

16. An ultrasound transducer comprising:

a silicon substrate;

an array of ultrasonic transducer cells supported by said silicon substrate;

a body of acoustically attenuative material disposed on a side of said substrate opposite to said array; and

a layer of acoustic impedance matching material disposed between said substrate and said body of acoustically attenuative material, the acoustic impedance of said acoustic impedance matching material having a value that lies between the acoustic impedance of silicon and the acoustic impedance of said acoustically attenuative material.

17. The transducer as recited in claim 16, wherein said array of ultrasonic transducer cells comprises a multiplicity of cMUT cells.

18. The transducer as recited in claim 16, wherein said array of ultrasonic transducer cells comprises a multiplicity of pMUT cells.

19. The transducer as recited in claim 16, wherein said layer of acoustic impedance matching material has a thickness approximately equal to one-quarter of the wavelength of an acoustic wave propagating rearward from said array.

20. An ultrasound transducer comprising:

a silicon substrate;

an array of ultrasonic transducer cells supported by said silicon substrate; and

a body of acoustically attenuative material disposed on a side of said substrate opposite to said array, said acoustically attenuative material comprising tungsten particles and particles of highly thermally conductive filler material dispersed in a matrix material.

21. The transducer as recited in claim 20, wherein said array of ultrasonic transducer cells comprises a multiplicity of cMUT cells.

22. The transducer as recited in claim 20, wherein said array of ultrasonic transducer cells comprises a multiplicity of pMUT cells.

23. The device as recited in claim 20, wherein said highly thermally conductive filler material comprises W, BN, AlN, Al₂O₃ or diamond.

24. The device as recited in claim 20, wherein the mass percent of tungsten lies in the range of 96.0% to 96.65%, with the remainder being said matrix material.

25. A method of manufacturing an ultrasound transducer comprising the following steps:

attaching a substrate to a layer of acoustic backing material;

thinning said substrate while it is attached to said layer of acoustic backing material; and

micromachining an array of ultrasonic transducer cells on said substrate.

26. The method as recited in claim 25, wherein said thinning step comprises etching, polishing or grinding.

27. The method as recited in claim 25, wherein said backing material attenuates acoustic waves produced by said array of ultrasonic transducer cells that pass through said substrate and into said backing material.

28. The method as recited in claim 27, wherein said backing material is matched in acoustic impedance to the material of said substrate to prevent reflection at an interface of said substrate and said layer of backing material.

29. A method of manufacturing an ultrasound transducer comprising the following steps:

micromachining an array of ultrasonic transducer cells on a substrate;

attaching a front face of said array to a support membrane;

thinning said substrate while supported by said support membrane;

attaching a formed or conformal layer of backing material to said thinned substrate; and

removing said supporting membrane.

30. The method as recited in claim 29, wherein said thinning step comprises etching, polishing or grinding.

31. The method as recited in claim 29, wherein said backing material attenuates acoustic waves produced by said array of ultrasonic transducer cells that pass through said substrate and into said backing material.

32. The method as recited in claim 31, wherein said backing material is matched in acoustic impedance to the material of said substrate to prevent reflection at an interface of said substrate and said layer of backing material.

33. A micromachined ultrasonic transducer device comprising:

an ultrasonic transducer array micromachined on a generally rectangular substrate;

flexible electrical connections connected to said ultrasonic transducer array; and

a body of acoustically attenuative material that supports said substrate and extends beyond opposing sides of said substrate.

34. A method of manufacturing an ultrasound transducer comprising the following steps:

attaching a substrate having a first area to a layer of acoustic backing material having a second area greater than said first area, said substrate being placed so that respective portions of said layer of acoustic backing material extend beyond opposing side edges of said substrate;

thinning said substrate while it is attached to said layer of acoustic backing material;

micromachining an array of ultrasonic transducer cells on said substrate; and

trimming off said respective portions of said layer of acoustic backing material subsequent to said micromachining step.