Composite substrate, elastic wave device, and method for producing elastic wave device
A composite substrate 10 is formed by bonding together a piezoelectric substrate 12 and a support substrate 14 that has a lower thermal expansion coefficient than the piezoelectric substrate. The support substrate 14 is formed by directly bonding together a first substrate 14 a and a second substrate 14 b at a strength that allows separation with a blade, the first and second substrates being formed of the same material, and a surface of the first substrate 14 a is bonded to the piezoelectric substrate 12 , the surface being opposite to another surface of the first substrate 14 a bonded to the second substrate 14 b.
1. A composite substrate formed by bonding together a piezoelectric substrate and a support substrate that has a lower thermal expansion coefficient than the piezoelectric substrate,
wherein the support substrate is formed by directly bonding together a first substrate and a second substrate at a strength that allows separation with a blade, the first and second substrates being formed of the same material; and a surface of the first substrate is bonded to the piezoelectric substrate, the surface being opposite to another surface of the first substrate bonded to the second substrate.
2. The composite substrate according to claim 1 ,
wherein the first and second substrates are both silicon substrates.
3. The composite substrate according to claim 1 ,
wherein the strength that allows separation with a blade corresponds to a bonding energy per unit area of the first and second substrates in a range of 0.05 to 0.6 J/m 2 .
4. The composite substrate according to claim 1 ,
wherein the first and second substrates have a thickness of 100 to 600 μm.
5. The composite substrate according to claim 1 ,
wherein iron element and chromium element are contained between the first substrate and the second substrate.