# US 8,148,878 B2 · Piezoelectric element and gyroscope

> Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt

- Number: US 8,148,878 B2
- Document ID: US8148878B2
- Status: Granted
- Kind: B2
- Application number: 12/659,997
- Filed: 2010-03-26
- Published: 2010-09-30
- Granted: 2012-04-03
- Earliest claimed: 2009-03-31
- Assignees: TDK Corporation
- Inventors: Kazuya Maekawa; Takao Noguchi; Kenichi Tochi; Ken Unno
- Web page: https://patentgrep.com/patent/US8148878B2

## CPC

- G01C 19/5607: using vibrating tuning forks (double-ended tuning forks using planar vibrating masses suspended at opposite ends G01C19/5719)
- H10N 30/708: {Intermediate layers, e.g. barrier, adhesion or growth control buffer layers}
- H10N 30/076: by vapour phase deposition
- H10N 30/8554: {Lead-zirconium titanate [PZT] based}
- G01C: MEASURING DISTANCES, LEVELS OR BEARINGS; SURVEYING; NAVIGATION; GYROSCOPIC INSTRUMENTS; PHOTOGRAMMETRY OR VIDEOGRAMMETRY (measuring liquid level G01F; radio navigation, determining distance or velocity by use of propagation effects, e.g. Doppler effects, propagation time, of radio waves, analogous arrangements using other waves G01S)
- H10N: ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR

## Abstract

A piezoelectric element having a crystal structure that enables a piezoelectric film to be formed in an unstressed state is provided. The piezoelectric film contains an a-axis oriented crystal and a c-axis oriented crystal, where a difference in lattice constant between the a-axis oriented crystal and the c-axis oriented crystal is not more than 0.06 Å. The present inventors have newly found that a stress accumulated in the piezoelectric film can be reduced while maintaining favorable piezoelectric properties when a condition that the difference in lattice constant between the a-axis oriented crystal and the c-axis oriented crystal is not more than 0.06 Å is satisfied. When the condition is satisfied, the c-axis oriented crystal and the a-axis oriented crystal are properly balanced and as a result crystal particles of the piezoelectric film are closest-packed on its base in an ideal state, which contributes to a reduced stress.

## Claims

### Claim 1

A piezoelectric element comprising:
a lower electrode;
an upper electrode; and
a piezoelectric film disposed between the lower electrode and the upper electrode,
wherein the piezoelectric film contains an a-axis oriented crystal and a c-axis oriented crystal, and
a difference between a lattice constant of the a-axis oriented crystal and a lattice constant of the c-axis oriented crystal is between 0.056 Å and 0.06 Å.

### Claim 2 (depends on 1)

The piezoelectric element according to claim 1, wherein the piezoelectric film contains columnar crystal particles that are grown in a c-axis direction, and
a particle diameter of the columnar crystal particles is not more than 49.8 nm.

### Claim 3 (depends on 1)

The piezoelectric element according to claim 1, wherein the piezoelectric film is a perovskite type composite oxide expressed by a chemical formula ABO3, and
an atomic ratio A/B is in a range of 1.1 to 1.2.

### Claim 4 (depends on 1)

The piezoelectric element according to claim 1, wherein arithmetic mean roughness Ra of the piezoelectric film is not more than 0.28 nm.

### Claim 5 (depends on 1)

The piezoelectric element according to claim 1, further comprising
a layer made of strontium ruthenate between the piezoelectric film and at least one of the lower electrode and the upper electrode.

### Claim 6 (depends on 2)

The piezoelectric element according to claim 2, wherein the columnar crystal particles are epitaxially grown in the c-axis direction.

### Claim 7 (depends on 1)

A gyroscope of a tuning fork vibrator type, comprising:
a base; and
a plurality of arms connected to the base,
wherein the base and the plurality of arms are integrally formed by the piezoelectric element according to claim 1.