Bonded body and a method of producing the same

1 . A bonded body surface acoustic wave device comprising:

a supporting substrate comprising silicon and having a surface;

a piezoelectric material substrate having an opposing face opposing said surface of said supporting substrate, comprising a material selected from the group consisting of lithium niobate, lithium tantalate and lithium niobate-lithium tantalate and having a thickness of 0.2 to 60 μm; and

a bonding layer provided on said surface of said supporting substrate, said bonding layer having a thickness of 0.01 to 10 μm and comprising silicon oxide film, and said bonding layer being present between said surface of said supporting substrate and said opposing face of said piezoelectric material substrate;

wherein said bonding layer has a refractive index of 1.468 or higher and 1.474 or lower.

2 . The surface acoustic wave device of claim 1 , further comprising an input-side comb electrode of oscillating a surface acoustic wave and an output-side comb electrode receiving said surface acoustic wave, said input-side comb electrode and said output-side comb electrode being provided on said piezoelectric material substrate.

3 . A method of producing the surface acoustic wave device of claim 1 , said method comprising the steps of:

forming said bonding layer comprising silicon oxide film on said surface of said supporting substrate by reactive ion sputtering method, said reactive ion sputtering method being performed by providing a silicon target and flowing with at least an inert gas and oxygen gas in a ratio of a flow rate of said inert gas with respect to a flow rate of said oxygen gas adjusted at 1.5 to 2.0, wherein said silicon oxide film being formed in a film-forming rate of 0.17 to 0.4 nm/sec; and

bonding said bonding layer to said piezoelectric material substrate.

4 . The method of claim 3 , further comprising the step of providing an input-side comb electrode of oscillating a surface acoustic wave and an output-side comb electrode receiving said surface acoustic wave on said piezoelectric material substrate.

5 . The surface acoustic wave device of claim 1 , wherein said piezoelectric material substrate and said bonding layer include an activated bonding surface having an arithmetic average roughness Ra of 1 nm or less.

6 . The method of claim 3 , further including a step of flattening the bonding surface of the piezoelectric material substrate and the bonding surface of the bonding layer before said forming step to form flattened surfaces having an arithmetic average roughness Ra of 1 nm or less.

7 . The method of claim 6 , wherein the flattening step is by lapping or chemical mechanical polishing.