Abstract: A bonding structure and an acoustic wave device relate to the field of filters. The bonding structure includes a supporting substrate and a piezoelectric layer formed on the supporting substrate. The supporting substrate is made of a polycrystalline material, and a porosity of the supporting substrate is less than 0.0045% or greater than 0.6%. The bonding structure can effectively improve the generation of interference of spurious emission and improve the performance of the device.

Abstract: A method for making a composite substrate of a filter includes: processing a base substrate to form a centrally protruding structure having a height that decreases in a radially outward direction from a center of the base substrate to an outer periphery of the base substrate; connecting a first side of the base substrate having the centrally protruding structure to a piezoelectric layer so as to obtain a multilayer substrate; and thinning the piezoelectric layer of the multilayer substrate followed by polishing a surface of the piezoelectric layer.

Abstract: A method for blackening at least one wafer includes: (a) performing a reduction treatment on the at least one wafer; and (b) illuminating the at least one wafer with an ultraviolet light. The at least one wafer after the illumination of the UV light has a blackening uniformity value (DE value) smaller than 0.6, and a chromatic value (L value) smaller than 54. In addition, a blackened wafer made from the method is also provided.