Method for producing piezoelectric composite substrate

A method for producing a piezoelectric composite substrate including a single-crystal thin film made of a piezoelectric material, the method comprising:

• an ion-implantation step of implanting rare-gas ions into a single-crystal base made of the piezoelectric material to form localized microcavities in a separation layer located inside the single-crystal base and spaced apart from a surface of the single-crystal base;
• a separation step of subjecting the microcavities formed in the ion-implantation step due to thermal stress and dividing the separation layer of the single-crystal base to detach the single-crystal thin film;
• a polishing step of polishing a surface of the single-crystal thin film at which the single-crystal thin film is divided from the single-crystal base so as to have a roughness of less than about 1 nm;
• and
• a polarization step of polarizing the piezoelectric composite substrate by intermittently applying a pulse voltage to the single-crystal thin film at a temperature of above 200° C. to about 1200° C. and at a temperature that is at least about 100° C. lower than the Curie temperature of the piezoelectric material;
• wherein
• the polarization step is performed after the separation step.