PIEZOELECTRIC MEMS MICROPHONE

• US 20100254547A1
• Filed: 06/30/2009
• Published: 10/07/2010
• Est. Priority Date: 06/30/2008
• Status: Active Grant

• Current Assignee: Board of Regents of the University of Michigan (University of Michigan)
• Original Assignee: Board of Regents of the University of Michigan (University of Michigan)
• Inventors: Grosh, Karl, Littrell, Robert J.
• Granted Patent: US 8,531,088 B2
• Time in Patent Office: Days
• US Class Current: 381/114
• CPC Class Codes: B81B 2201/0257 Microphones or microspeakers
• CPC Class Codes: B81B 3/0021 Transducers for transforming electrical into mechanical energy or vice versa dynamo-electric machines H02K99/00; electrostatic machines H02N1/00; piezoelectric devices H10N30/00
• CPC Class Codes: B81C 1/0015 Cantilevers switches using MEMS H01H1/0036; electrostatic relays using micromechanics H01H59/0009; microelectro-mechanical resonators H03H9/02244
• CPC Class Codes: B81C 1/00158 Diaphragms, membranes manufacture process for semi-permeable inorganic membranes B01D67/0039
• CPC Class Codes: H04R 17/00 Piezoelectric transducers; Electrostrictive transducers piezoelectric or electrostrictive elements in general H10N30/00; details of piezoelectric or electrostrictive motors, generators or positioners H10N30/00
• CPC Class Codes: H04R 17/02 Microphones
• CPC Class Codes: H04R 17/10 Resonant transducers, i.e. adapted to produce maximum output at a predetermined frequency
• CPC Class Codes: H04R 2201/003 Mems transducers or their use of the electrostatic type H04R19/005
• CPC Class Codes: H10N 30/05 Manufacture of multilayered piezoelectric or electrostrictive devices, or parts thereof, e.g. by stacking piezoelectric bodies and electrodes
• CPC Class Codes: H10N 30/302 Sensors
• CPC Class Codes: H10N 30/306 Cantilevers
• CPC Class Codes: H10N 30/50 having a stacked or multilayer structure

Abstract

A piezoelectric MEMS microphone comprising a multi-layer sensor that includes at least one piezoelectric layer between two electrode layers, with the sensor being dimensioned such that it provides a near maximized ratio of output energy to sensor area, as determined by an optimization parameter that accounts for input pressure, bandwidth, and characteristics of the piezoelectric and electrode materials. The sensor can be formed from single or stacked cantilevered beams separated from each other by a small gap, or can be a stress-relieved diaphragm that is formed by deposition onto a silicon substrate, with the diaphragm then being stress relieved by substantial detachment of the diaphragm from the substrate, and then followed by reattachment of the now stress relieved diaphragm.

Claims

1. A piezoelectric MEMS microphone, comprising:

a substrate; and

a multi-layer acoustic sensor comprising at least three layers including a first electrode layer, an intermediate layer of piezoelectric material deposited over said first electrode layer, and a second electrode layer deposited over said piezoelectric material;

wherein said sensor is dimensioned such that the ratio of output energy to sensor area for the multi-layer sensor is at least 10% of the maximum ratio obtainable for a given input pressure, bandwidth, and piezoelectric material.

2. A piezoelectric MEMS microphone, comprising:

a substrate; and

a multi-layer acoustic sensor comprising at least three layers including a first electrode layer, an intermediate layer of piezoelectric material deposited over said first electrode layer, and a second electrode layer deposited over said piezoelectric material;

wherein said sensor is dimensioned such that an optimization parameter calculated according to the equation

3. A piezoelectric MEMS microphone as defined in claim 2, wherein said first and second electrode layers and said intermediate layer together have a thickness no greater than 8 μ

m.

4. A piezoelectric MEMS microphone as defined in claim 2, wherein said first and second electrode layers and said intermediate layer together have a thickness no greater than 2 μ

m.

5. A piezoelectric MEMS microphone as defined in claim 2, wherein said intermediate layer comprises a layer of piezoelectric material deposited directly onto a surface of said first electrode layer and said second electrode layer comprises a layer of electrode material deposited directly onto a surface of said piezoelectric material.

6. A piezoelectric MEMS microphone as defined in claim 2, further comprising a transistor having a control input connected to said electrode layers such that signals received from said sensor on said control input are amplified by said transistor.

7. A piezoelectric MEMS microphone as defined in claim 2, wherein said multi-layer acoustic sensor comprises a stress-relieved diaphragm suspended above said substrate.

8. A piezoelectric MEMS microphone as defined in claim 7, wherein said diaphragm is attached to said substrate about a perimeter of said diaphragm and has a first portion of said perimeter attached to said substrate as a direct deposition of at least one of said layers onto said substrate, and has a second portion of said perimeter attached to said substrate by separate adhesion of said second portion onto said substrate.

9. A piezoelectric MEMS microphone as defined in claim 8, wherein said first and second electrode layers comprise respective first and second electrodes that are located centrally on said diaphragm and include lead traces that extend to said substrate at said first portion.

10. A piezoelectric MEMS microphone as defined in claim 9, wherein said sensor further comprises third and fourth electrodes, with said third electrode being disposed under said piezoelectric material and in a ring or band shape that surrounds said first electrode while being electrically isolated from said first electrode, and said fourth electrode being disposed over said piezoelectric material in a region that overlaps said third electrode with said fourth electrode surrounding said second electrode while being electrically isolated from said second electrode.

11. A piezoelectric MEMS microphone as defined in claim 10, wherein said first and fourth electrodes are electrically connected together and said second and third electrodes are electrically connected together.

12. A piezoelectric MEMS microphone as defined in claim 7, wherein said diaphragm is covered with an insulating layer and wherein said microphone includes a pressure equalization port, whereby said microphone comprises a hydrophone.

13. A piezoelectric MEMS microphone as defined in claim 2, wherein said sensor comprises a plurality of beams each supported at one end by said substrate such that each beam is cantilevered and extends between a fixed end and a free end, each beam comprising said electrode and intermediate layers.

14. A piezoelectric MEMS microphone as defined in claim 13, wherein at least two of said beams are positioned such that free ends of each beam face one another and are separated by a gap of no greater than 3 μ

m.

15. A piezoelectric MEMS microphone as defined in claim 13, wherein adjacent beams are separate by a gap that is no greater than 10 μ

m.

16. A piezoelectric MEMS microphone as defined in claim 13, wherein said plurality of beams include a plurality of stacked beam sets, each stacked beam set including at least five alternating layers of electrode material and piezoelectric material.

17. A piezoelectric MEMS microphone as defined in claim 13, wherein said beams are tapered to toward their free end such that the width of the beams are narrower at their free end than at their cantilevered end.

18. A piezoelectric MEMS microphone as defined in claim 13, wherein said beams are covered with an insulating layer, whereby said microphone comprises a hydrophone.

19. A piezoelectric MEMS microphone, comprising:

a silicon substrate;

a plurality of beams each supported at one end by said substrate such that each beam is cantilevered and extends between a fixed end and a free end, each beam comprising a deposited layer of electrode material and a deposited layer of piezoelectric material overlying said electrode material;

wherein at least some of said beams are stacked such that the stacked beams include alternative layers of deposited electrode material and deposited piezoelectric material with no additional layers therebetween.

20. A piezoelectric MEMS microphone as defined in claim 19, wherein each of said layers of piezoelectric material has a thickness of no greater than 2 μ

m.

21. A piezoelectric MEMS microphone as defined in claim 19, wherein said piezoelectric material comprises a material selected from the group consisting of PZT, ZnO, PVDF, PNMPC, and A1N.

22. A piezoelectric MEMS microphone, comprising:

a substrate; and

a stress-relieved diaphragm suspended above said substrate, said diaphragm comprising a multi-layer acoustic sensor having at least three layers including a first electrode layer, an intermediate layer of piezoelectric material deposited over said first electrode layer, and a second electrode layer deposited over said piezoelectric material.

23. A piezoelectric MEMS microphone as defined in claim 22, wherein said diaphragm is attached to said substrate about a perimeter of said diaphragm, with a first portion of said perimeter being attached to said substrate as a direct deposition of at least one of said layers onto said substrate, and a second portion of said perimeter being attached to said substrate by separate adhesion of said second portion onto said substrate.