Composite piezoelectric substrate and preparation method thereof

The invention discloses a composite piezoelectric substrate and a preparation method thereof. The composite piezoelectric substrate comprises a supporting substrate, an auxiliary bonding layer and a piezoelectric material layer which are arranged in a stacked mode. The auxiliary bonding layer is in bonding connection with the piezoelectric material layer; the material of the piezoelectric material layer comprises lithium niobate or lithium tantalate; the material of the supporting substrate comprises polycrystalline silicon carbide prepared by adopting a chemical vapor deposition method, and polycrystalline silicon carbide grains in the supporting substrate have a preset length ratio, a preset oriented grain ratio difference and a preset size range; wherein the preset length ratio is the ratio of the length of the polycrystalline silicon carbide grains parallel to the thickness direction of the supporting substrate to the length of the polycrystalline silicon carbide grains parallel to the extension direction