Composite substrate, piezoelectric device, and method for manufacturing composite substrate

Patent metadata

Field	Value
Publication number	US-12095442-B2
Application number	US-201917278612-A
Country	US
Kind code	B2
Filing date	Sep 24, 2019
Priority date	Sep 25, 2018
Publication date	Sep 17, 2024
Grant date	Sep 17, 2024

Abstract

A composite substrate of the present disclosure includes a piezoelectric substrate having a first surface which is an element formation surface and a second surface which is a back surface of the first surface, a sapphire substrate having a third surface which is disposed opposing a second surface and a fourth surface which is a back surface of the third surface, a fifth surface opposing the second surface, and a sixth surface opposing the third surface. It includes an alumina layer bonding the second surface and the third surface, and an arithmetic mean roughness Ra of the third surface is 0.1 μm or more and 0.5 μm or less. The arithmetic mean roughness Ra of the fifth surface is 0.1 μm or less and is smaller than the arithmetic mean roughness Ra of the third surface.

First claim

The invention claimed is:

1. A composite substrate comprising a piezoelectric substrate having a first surface which is an element formation surface and a second surface which is a back surface of the first surface,
a sapphire substrate having a third surface disposed opposing the second surface and a fourth surface which is a back surface of the third surface, and
a bonding layer having a fifth surface opposing the second surface and a sixth surface opposing the third surface and bonding the second surface to the third surface,
wherein the bonding layer is composed of a material selected from the group consisting of the same material as the piezoelectric substrate, alumina, and an oxide having a thermal expansion coefficient intermediate between the piezoelectric substrate and alumina,
an arithmetic mean roughness Ra of the third surface is 0.1 μm or more and 0.5 μm or less, and an arithmetic mean roughness Ra of the fifth surface is 0.1 μm or less and is smaller than an arithmetic mean roughness Ra of the third surface.

2. A composite substrate according to claim 1 , wherein the bonding layer is polycrystal or amorphous.

3. A composite substrate according to claim 1 , wherein the thickness of the bonding layer is 0.5 μm or more and 5.0 μm or less.

4. A piezoelectric device which comprises the composite substrate according to claim 1 .

5. A piezoelectric device according to claim 4 , which is a surface acoustic wave device.

6. A method for manufacturing a composite substrate comprising:
preparing a piezoelectric substrate having a first surface which is an element forming surface and a second surface which is a back surface of the first surface and a sapphire substrate having a third surface and a fourth surface which is a back surface of the third surface;
roughening the third surface so as to have an arithmetic mean roughness Ra of 0.1 μm or more and 0.5 μm or less;
forming a bonding layer on the roughened third surface;
processing a fifth surface which is an exposed surface located on an opposite side of the sapphire substrate of the bonding layer so as to have an arithmetic mean roughness Ra of 0.1 μm or less and to be smaller than an arithmetic mean roughness Ra of the third surface; and
bonding the fifth surface of the bonding layer directly bonded to the second surface of the piezoelectric substrate;
wherein the bonding layer is composed of a material selected from the group consisting of the same material as the piezoelectric substrate, alumina, and an oxide having a thermal expansion coefficient intermediate between the piezoelectric substrate and alumina.

7. A composite substrate comprising:
a piezoelectric substrate having a first surface which is an element forming surface and a second surface which is a back surface of the first surface;
a sapphire substrate having a third surface which is disposed opposing the second surface and a fourth surface which is a back surface of the third surface; and
a bonding layer which is composed of a material selected from the group consisting of the same material as the piezoelectric substrate, alumina, and an oxide having a thermal expansion coefficient intermediate between the piezoelectric substrate and alumina, has a fifth surface opposing the second surface, a sixth surface opposing the third surface, and bonds the second surface to the third surface, wherein an arithmetic mean roughness Ra of the second surface is 0.1 μm or more and 0.5 μm or less, and an arithmetic mean roughness Ra of the sixth surface is 0.1 μm or less and is smaller than an arithmetic mean roughness Ra of the second surface.

8. A composite substrate according to claim 7 , wherein the bonding layer is polycrystal or amorphous.

9. A composite substrate according to claim 7 , wherein the thickness of the bonding layer is 0.5 μm or more and 5.0 μm or less.

10. A piezoelectric device which comprises the composite substrate according to claim 7 .

11. A piezoelectric device according to claim 10 , which is a surface acoustic wave device.

12. A method for manufacturing a composite substrate comprising:
preparing a piezoelectric substrate having a first surface which is an element forming surface and a second surface which is a back surface of the first surface and a sapphire substrate having a third surface and a fourth surface which is a back surface of the third surface;
roughening the second surface so as to have an arithmetic mean roughness Ra of 0.1 μm or more and 0.5 μm or less;
forming a bonding layer composed of a material selected from the group consisting of the same material as the piezoelectric substrate, alumina, and an oxide having a thermal expansion coefficient intermediate between the piezoelectric substrate and alumina on the roughened second surface;
processing the sixth surface which is an exposed surface located on the opposite side of the piezoelectric substrate of the bonding layer so as to have an arithmetic mean roughness Ra of 0.1 μm or less and to be smaller than an arithmetic mean roughness Ra of the second surface; and
pbonding the sixth surface of the bonding layer directly bonded to the third surface of the sapphire substrate.

Assignees

• Kyocera Corp

Inventors

• Umehara Motohiro
• Mitsuda Kuniaki
• Fujimoto Kazuyoshi

Classifications

• H03H9/02559

  of lithium niobate or lithium-tantalate substrates · CPC title

• H03H3/08

  for the manufacture of resonators or networks using surface acoustic waves · CPC title

• H10N30/086

  by polishing or grinding · CPC title

• H10N30/073

  by fusion of metals or by adhesives · CPC title

• H03H9/02574 Primary

  of combined substrates, multilayered substrates, piezoelectrical layers on not-piezoelectrical substrate · CPC title