Composite substrate
A composite substrate according to the present invention includes a piezoelectric substrate that is a single-crystal lithium tantalate or lithium niobate substrate, a support substrate that is a single-crystal silicon substrate, and an amorphous layer joining together the piezoelectric substrate and the support substrate. The amorphous layer contains 3 to 14 atomic percent of argon. The amorphous layer includes, in order from the piezoelectric substrate toward the composite substrate, a first layer, a second layer, and a third layer. The first layer contains a larger amount of a constituent element (such as tantalum) of the piezoelectric substrate than the second and third layers. The third layer contains a larger amount of a constituent element (silicon) of the support substrate than the first and second layers. The second layer contains a larger amount of argon than the first and third layers.
1. A composite substrate comprising a piezoelectric substrate that is a single-crystal substrate composed of lithium tantalate or lithium niobate, a support substrate that is a single-crystal silicon substrate, and an amorphous layer joining together the piezoelectric substrate and the support substrate, wherein
the amorphous layer contains 3 to 14 atomic percent of Ar.
2. The composite substrate according to claim 1 , wherein the amorphous layer has a thickness of 4 to 12 nm.
3. The composite substrate according to claim 1 , wherein
the amorphous layer includes, in order from the piezoelectric substrate toward the support substrate, a first layer, a second layer, and a third layer, the first layer containing a larger amount of a constituent element of the piezoelectric substrate than the second and third layers, the third layer containing a larger amount of a constituent element of the support substrate than the first and second layers, the second layer containing a larger amount of Ar than the first and third layers.
4. The composite substrate according to claim 3 , wherein the third layer is thicker than the first and second layers.
5. The composite substrate according to claim 1 , wherein an Fe content is less than 0.1 atomic percent.