# US 2018/0124521 A1 · Piezoelectric mems sensor, such as force, pressure, deformation sensor or microphone, with improved sensitivity

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- Number: US 2018/0124521 A1
- Document ID: US20180124521A1
- Status: Published application
- Kind: A1
- Application number: 15/629,518
- Filed: 2017-06-21
- Published: 2018-05-03
- Earliest claimed: 2016-10-31
- Assignees: STMicroelectronics S.r.l.
- Applicants: Stmicroelectronics S.R.L.
- Inventors: Domenico GIUSTI; Sebastiano CONTI
- Web page: https://patentgrep.com/patent/US20180124521A1

## CPC

- H04R 17/02: Microphones
- B81B 3/0037: {For increasing stroke, i.e. achieve large displacement of actuated parts}
- B81C 1/00158: {Diaphragms, membranes (manufacture process for semi-permeable inorganic membranes B01D67/0039)}
- G01L 9/0042: {Constructional details associated with semiconductive diaphragm sensors, e.g. etching, or constructional details of non-semiconductive diaphragms (details about the integration or bonding of piezoresistor in or on the diaphragm G01L9/0052 and G01L9/0057 respectively)}
- G01L 9/0073: {using a semiconductive diaphragm}
- H04R 19/005: {using semiconductor materials}
- H04R 19/04: Microphones (H04R19/01 takes precedence)
- H04R 31/003: {for diaphragms or their outer suspension}
- H10N 30/072: by laminating or bonding of piezoelectric or electrostrictive bodies
- H10N 30/302: {Sensors}
- H10N 30/308: {Membrane type}
- H10N 30/802: {Circuitry or processes for operating piezoelectric or electrostrictive devices not otherwise provided for, e.g. drive circuits}
- B81B 2201/0235: Accelerometers
- B81B 2201/0257: Microphones or microspeakers
- B81B 2201/0264: Pressure sensors
- B81B 2203/0127: Diaphragms, i.e. structures separating two media that can control the passage from one medium to another; Membranes, i.e. diaphragms with filtering function
- B81B 2203/0315: Cavities
- B81B 2203/04: Electrodes
- B81B 2207/012: the micromechanical device and the control or processing electronics being separate parts in the same package
- H04R 2201/003: Mems transducers or their use
- H04R: LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; ELECTRIC HEARING AIDS; PUBLIC ADDRESS SYSTEMS (producing sounds with frequency not determined by supply frequency G10K)
- B81B: MICROSTRUCTURAL DEVICES OR SYSTEMS, e.g. MICROMECHANICAL DEVICES (piezoelectric, electrostrictive or magnetostrictive elements per se H10N30/00, H10N35/00)
- B81C: PROCESSES OR APPARATUS SPECIALLY ADAPTED FOR THE MANUFACTURE OR TREATMENT OF MICROSTRUCTURAL DEVICES OR SYSTEMS (making microcapsules or microballoons B01J13/02; processes or apparatus specially adapted for the manufacture or treatment of piezoelectric, electrostrictive or magnetostrictive elements per se H10N30/01)
- G01L: MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE (weighing G01G)
- H10N: ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR

## Abstract

A MEMS sensor, in particular a microphone, of a piezoelectric type, formed in a membrane of semiconductor material accommodating a compliant portion, which extends from a first surface to a second surface of the membrane. The compliant portion has a Young's modulus lower than the rest of the membrane. A sensitive region having piezoelectric material extends on the first surface, over the compliant portion and is fixed at its ends to the membrane on opposite sides of the compliant portion. A third area of the membrane, arranged between the compliant portion and the second surface, forms a hinge element.

## Claims

### Claim 1

A piezoelectric MEMS sensor, comprising:
a membrane of semiconductor material having a first surface and a second surface;
a compliant portion within the membrane, the compliant portion extending from the first surface toward the second surface of the membrane and separating a first area of the membrane from a second area of the membrane and forming a third area that is between the compliant portion and the second surface, the third area forming a hinge element, the first and second areas arranged on different sides of the compliant portion, the compliant portion having a Young's modulus of elasticity that is lower than a Young's modulus of elasticity of the semiconductor material; and
a sensitive region comprising piezoelectric material on the first surface of the compliant portion and covering the compliant portion, the sensitive region having a first portion fixed to the first area of the membrane and a second portion fixed to the second area of the membrane.

### Claim 2 (depends on 1)

The MEMS sensor according to claim 1, wherein the compliant portion comprises a cavity in the membrane.

### Claim 3 (depends on 2)

The MEMS sensor according to claim 2, wherein the cavity is filled with a material having a Young's modulus of elasticity that is lower than the Young's modulus of elasticity of semiconductor material.

### Claim 4 (depends on 3)

The MEMS sensor according to claim 3, wherein the material that fills the cavity is chosen from a dielectric material, a semiconductor material different from the semiconductor material of the membrane, and porous semiconductor material.

### Claim 5 (depends on 1)

The MEMS sensor according to claim 1, wherein the compliant portion is one of a plurality of compliant portions arranged adjacent to each other in the membrane, wherein the sensitive region is one of a plurality of sensitive regions extending on the first surface over a respective compliant portion, the plurality of sensitive regions being fixed to the membrane on opposite sides of the respective compliant portions.

### Claim 6 (depends on 5)

The MEMS sensor according to claim 5, wherein plurality of sensitive regions are coupled together in series.

### Claim 7 (depends on 5)

The MEMS sensor according to claim 5, wherein:
each sensitive region of the plurality of sensitive regions comprises a stack of layers including a first electrode, a piezoelectric material region, and a second electrode, and
the first electrodes of the plurality of sensitive regions is coupled to the second electrodes of an adjacent sensitive region of the plurality of sensitive regions.

### Claim 8 (depends on 5)

The MEMS sensor according to claim 5, wherein the plurality of compliant portions and the plurality of sensitive regions extend along closed lines.

### Claim 9 (depends on 8)

The MEMS sensor according to claim 8, wherein the plurality of compliant portions and the plurality of sensitive regions extend along concentric circles.

### Claim 10 (depends on 1)

The MEMS sensor according to claim 1, forming a sensor selected in the group comprising a pressure sensor, a force sensor, a microphone, a load sensor, and a deformation sensors.

### Claim 11 (depends on 1)

The MEMS sensor according to claim 1, wherein the hinge element is of a material different from the material of the first and second areas of the membrane and having a greater Young's modulus of elasticity than the Young's modulus of elasticity of the compliant region.

### Claim 12

An electronic device, comprising:
a microprocessor control unit; and
an acoustic transductor coupled to the microprocessor control unit, the acoustic transductor comprising:
a membrane of semiconductor material having a first surface and a second surface;
a cavity extending from the first surface of the membrane toward the second surface, wherein a portion of the membrane forms a hinge between a bottom surface of the cavity and the second surface of the membrane; and
a sensitive region on the first surface and covering the cavity, the sensitive region having a first portion fixed to the membrane at a first side of the cavity and a second portion fixed to the membrane at a second side of the cavity.

### Claim 13 (depends on 12)

The electronic device according to claim 12 wherein the acoustic transducer includes a material filling the cavity, wherein the material in the cavity has a Young's modulus of elasticity that is lower than a Young's modulus of elasticity of the semiconductor material.

### Claim 14 (depends on 13)

The electronic device according to claim 13 wherein the material filling the cavity is one of an oxide, an epoxy resin, a semiconductor material different from the semiconductor material of the membrane, and a porous semiconductor material.

### Claim 15 (depends on 12)

The electronic device according to claim 12 wherein the cavity of the acoustic transducer is one of a plurality of cavities, each of the plurality of cavities forming hinges between bottom surfaces of the cavities and the second surface of the membrane, wherein the sensitive region is one of a plurality of sensitive regions, each of the plurality of sensitive regions being on the first surface of the membrane and covering a respective cavity.

### Claim 16

A method comprising:
detecting forces or deformations according to a piezoelectric principle, wherein detecting comprises detecting forces acting transversely to a MEMS sensor including:
a membrane of semiconductor material having a first surface and a second surface;
a compliant portion within the membrane, the compliant portion extending from the first surface to the second surface of the membrane and separating a first area from a second area of the membrane, the first and second areas arranged on different sides of the compliant portion, the compliant portion having a Young's modulus of elasticity that is lower than a Young's modulus of elasticity of the first and second areas of the membrane; and
a sensitive region comprising piezoelectric material, the sensitive region extending on the first surface and over the compliant portion, the sensitive region having at least one first portion fixed to the first area of the membrane and one second portion fixed to the second area of the membrane, a third area of the membrane arranged between the compliant portion and the second surface and forming a hinge element, wherein the forces act in a direction transverse to the first surface, wherein detecting comprises:
converting the forces acting in the direction transverse to the first surface into tensile forces acting, respectively, on the first and second portions of the sensitive region in opposite directions; and
measuring, on the sensitive region, an electrical quantity variable with the transverse forces.

### Claim 17 (depends on 16)

The method according to claim 16 wherein the compliant portion is a cavity that is filled with a material having Young's modulus of elasticity that is lower than a Young's modulus of elasticity of the first and second areas of the membrane.

### Claim 18

A process for manufacturing a MEMS sensor comprising:
forming a cavity in membrane of semiconductor material at a first surface of the membrane toward a second surface of the membrane, wherein forming the cavity forms a hinge element in the membrane between the cavity and the second surface; and
coupling a sensitive region comprising piezoelectric material to the first surface over the cavity, wherein coupling includes coupling a first portion a first portion of the membrane to a first side of the cavity and a second portion to a second portion of the membrane that is on a second side of the cavity.

### Claim 19 (depends on 18)

The process according to claim 18, wherein prior to coupling the sensitive region to the first surface, the process comprises filling the cavity with a material, wherein the material has a Young's modulus of elasticity that is lower than a Young's modulus of elasticity of the semiconductor material.

### Claim 20 (depends on 15)

The process according to claim 15 comprising forming the membrane by removing semiconductor material from a first side of a wafer to expose the second surface and form the membrane.