Piezoelectric MEMS microphone

• US 8,531,088 B2
• Filed: 06/30/2009
• Issued: 09/10/2013
• 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.
• Primary Examiner(s): Dougherty, Thomas
• Assistant Examiner(s): GORDON, BRYAN P
• Application Number:
  US12/495,195
• Publication Number:
  US 20100254547A1
• Time in Patent Office: 1,533 Days
• Field of Search: 310/338, 310/367, 310/368, 310/332, 381/114
• US Class Current: 310/332
• 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
• 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 an optimization parameter calculated according to the equation

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, comprising:

a substrate; and

a multilayer acoustic sensor comprising a plurality of cantilevered beams, each beam comprising 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 each beam is supported at a fixed end by said substrate and extends between said fixed end and a free end, and at least two of said free ends are separated by a gap and face one another across said gap, wherein adjacent beams are separated by a gap that is no greater than 10 microns.

4. A piezoelectric MEMS microphone as defined in claim 3, 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.

5. A piezoelectric MEMS microphone as defined in claim 3, wherein said sensor is dimensioned such that an optimization parameter calculated according to the equation

6. A piezoelectric MEMS microphone as defined in claim 3, wherein said gap is no greater than 3 μ

m.