A substrate for a surface acoustic wave device or bulk acoustic wave device, comprising a support substrate and an piezoelectric layer on the support substrate, wherein the support substrate comprises a semiconductor layer on a stiffening substrate having a coefficient of thermal expansion that is closer to the coefficient of thermal expansion of the material of the piezoelectric layer than that of silicon, the semiconductor layer being arranged between the piezoelectric layer and the stiffening substrate.

A hybrid structure for a surface acoustic wave device comprises a working layer of piezoelectric material assembled with a support substrate having a lower coefficient of thermal expansion than that of the working layer, and an intermediate layer located between the working layer and the support substrate. The intermediate layer is a sintered composite layer formed from powders of at least a first material and a second material different from the first.

A hybrid structure for a surface acoustic wave device comprises a working layer of piezoelectric material assembled with a support substrate having a lower coefficient of thermal expansion than that of the working layer, and an intermediate layer located between the working layer and the support substrate. The intermediate layer is a sintered composite layer formed from powders of at least a first material and a second material different from the first.

A process for fabricating a substrate for a radiofrequency device by joining a piezoelectric layer to a carrier substrate by way of an electrically insulating layer, the piezoelectric layer having a rough surface at its interface with the electrically insulating layer, the process being characterized in that it comprises the following steps: providing a piezoelectric substrate having a rough surface for reflecting a radiofrequency wave, depositing a dielectric layer on the rough surface of the piezoelectric substrate, providing a carrier substrate, depositing a photo-polymerizable adhesive layer on the carrier substrate, bonding the piezoelectric substrate to the carrier substrate by way of the dielectric layer and of the adhesive layer, in order to form an assembled substrate, irradiating the assembled substrate with a light flux in order to polymerize the adhesive layer, the adhesive layer and the dielectric layer together forming the electrically insulating layer.

A process for fabricating a substrate for a radiofrequency device by joining a piezoelectric layer to a carrier substrate by way of an electrically insulating layer, the piezoelectric layer having a rough surface at its interface with the electrically insulating layer, the process being characterized in that it comprises the following steps: providing a piezoelectric substrate having a rough surface for reflecting a radiofrequency wave, depositing a dielectric layer on the rough surface of the piezoelectric substrate, providing a carrier substrate, depositing a photo-polymerizable adhesive layer on the carrier substrate, bonding the piezoelectric substrate to the carrier substrate by way of the dielectric layer and of the adhesive layer, in order to form an assembled substrate, irradiating the assembled substrate with a light flux in order to polymerize the adhesive layer, the adhesive layer and the dielectric layer together forming the electrically insulating layer.

A bonding layer 3 is formed over a piezoelectric material substrate, and the bonding layer is made of one or more materials selected from the group consisting of silicon nitride, aluminum nitride, alumina, tantalum pentoxide, mullite, niobium pentoxide and titanium oxide. A neutralized beam is irradiated onto a surface of the bonding layer and a surface of a supporting body to activate the surface of the bonding layer and the surface of the supporting body. The surface of the bonding layer and the surface of the supporting body are bonded by direct bonding.

An acoustic wave resonator includes: a piezoelectric substrate; a pair of comb-shaped electrodes that is located on the piezoelectric substrate and excites an acoustic wave, each of the pair of comb-shaped electrodes including a plurality of electrode fingers; and a polycrystalline substrate that is located at an opposite side of the piezoelectric substrate from a surface on which the pair of comb-shaped electrodes is located, an average particle size of the polycrystalline substrate being equal to or less than 66 times an average pitch of the plurality of electrode fingers.

An acoustic wave resonator includes: a piezoelectric substrate; a pair of comb-shaped electrodes that is located on the piezoelectric substrate and excites an acoustic wave, each of the pair of comb-shaped electrodes including a plurality of electrode fingers; and a polycrystalline substrate that is located at an opposite side of the piezoelectric substrate from a surface on which the pair of comb-shaped electrodes is located, an average particle size of the polycrystalline substrate being equal to or less than 66 times an average pitch of the plurality of electrode fingers.

An acoustic wave device includes series resonators and parallel resonators formed on a main surface of a piezoelectric layer. The series resonators includes a first series resonator including first, second and third series-divided resonators and a second series resonator including fourth, fifth and sixth series-divided resonators. One of the first, second and third series-divided resonators which is disposed at a position where an electric signal is input first, has a first anti-resonance frequency. The others of the first, second and third series-divided resonators have a second anti-resonance frequency. One of the fourth, fifth and sixth series-divided resonators which is centrally disposed has the second anti-resonance frequency, the others of the fourth, fifth, and sixth series-divided resonators have the first anti-resonance frequency.

An acoustic wave device includes series resonators and parallel resonators formed on a main surface of a piezoelectric layer. The series resonators includes a first series resonator including first, second and third series-divided resonators and a second series resonator including fourth, fifth and sixth series-divided resonators. One of the first, second and third series-divided resonators which is disposed at a position where an electric signal is input first, has a first anti-resonance frequency. The others of the first, second and third series-divided resonators have a second anti-resonance frequency. One of the fourth, fifth and sixth series-divided resonators which is centrally disposed has the second anti-resonance frequency, the others of the fourth, fifth, and sixth series-divided resonators have the first anti-resonance frequency.