Abstract: A method for producing a piezoelectric composite substrate having a single-crystal thin film of a piezoelectric material includes an ion-implantation step and a separation step. In the ion-implantation step, He+ ions are implanted into the single-crystal base made of the piezoelectric material to form localized microcavities in a separation layer located inside the single-crystal base and apart from a surface of the single-crystal base. In the separation step, the microcavities formed in the ion-implantation step are subjected to thermal stress to divide the separation layer of the piezoelectric single-crystal base, thereby detaching the single-crystal thin film.

Abstract: A method for producing a piezoelectric composite substrate with satisfactory productivity controls the inclination of the crystal axis and the polar axis of a single-crystal thin film and prevents an adverse effect due to pyroelectricity in a production process. The method for producing a piezoelectric composite substrate provided with a plurality of piezoelectric materials includes an ion-implantation step, a bonding step, and a separation step. In the ion-implantation step, H+ ions are implanted into a piezoelectric single crystal material. In the bonding step, the piezoelectric single crystal material is bonded to a piezoelectric single crystal material. At this time, the polarity of the polar surface of the piezoelectric single crystal material is opposite to the polarity of the polar surface of the piezoelectric single crystal material, the polar surfaces being bonded to each other.

Abstract: An acoustic wave device includes an acoustic wave element including an IDT electrode provided on a substrate, and a protective film arranged to cover the acoustic wave element so as to stabilize characteristics. The protective film is a silicon nitride film composed of silicon and nitrogen as main components and when a composition ratio of the silicon to the nitrogen is represented by 1:X, X is about 1.15 or less.

Abstract: A method for producing a piezoelectric composite substrate with satisfactory productivity controls the inclination of the crystal axis and the polar axis of a single-crystal thin film and prevents an adverse effect due to pyroelectricity in a production process. The method for producing a piezoelectric composite substrate provided with a plurality of piezoelectric materials includes an ion-implantation step, a bonding step, and a separation step. In the ion-implantation step, H+ ions are implanted into a piezoelectric single crystal material. In the bonding step, the piezoelectric single crystal material is bonded to a piezoelectric single crystal material. At this time, the polarity of the polar surface of the piezoelectric single crystal material is opposite to the polarity of the polar surface of the piezoelectric single crystal material, the polar surfaces being bonded to each other.

Abstract: An acoustic wave device includes an acoustic wave element including an IDT electrode provided on a substrate, and a protective film arranged to cover the acoustic wave element so as to stabilize characteristics. The protective film is a silicon nitride film composed of silicon and nitrogen as main components and when a composition ratio of the silicon to the nitrogen is represented by 1:X, X is about 1.15 or less.

Abstract: A method for producing a piezoelectric composite substrate having a single-crystal thin film of a piezoelectric material includes an ion-implantation step and a separation step. In the ion-implantation step, He+ ions are implanted into the single-crystal base made of the piezoelectric material to form localized microcavities in a separation layer located inside the single-crystal base and apart from a surface of the single-crystal base. In the separation step, the microcavities formed in the ion-implantation step are subjected to thermal stress to divide the separation layer of the piezoelectric single-crystal base, thereby detaching the single-crystal thin film.