Abstract: A sensor element includes an element body and a porous protective layer arranged to cover a part of a surface of the element body. The protective layer includes an inlet protective layer arranged to cover a gas inlet formed in the surface of the element body, and at least a part of a face included in the surface of the element body, the face on which the gas inlet is opens, and an arithmetic average roughness Rap of an inner peripheral surface of an internal space of the inlet protective layer satisfies at least one of conditions below: the arithmetic average roughness Rap is 8 ?m or more, and the arithmetic average roughness Rap is higher than an arithmetic average roughness Rac of a bonding surface of the protective layer, the bonding surface at which the protective layer is bonded to the element body.

Abstract: A sensor element includes an element body and a porous protective layer arranged to cover a part of a surface of the element body. The protective layer includes an inlet protective layer arranged to cover a gas inlet formed in the surface of the element body, and at least a part of a face included in the surface of the element body, the face on which the gas inlet is opens, and an arithmetic average roughness Rap of an inner peripheral surface of an internal space of the inlet protective layer satisfies at least one of conditions below: the arithmetic average roughness Rap is 8 ?m or more, and the arithmetic average roughness Rap is higher than an arithmetic average roughness Rac of a bonding surface of the protective layer, the bonding surface at which the protective layer is bonded to the element body.

Abstract: A sensor element includes an element body having a measurement-object gas flow section formed therein, and a porous protective layer arranged to cover first to fifth surfaces of the element body. When an external wall that is the thinnest of parts of an external wall which constitute the element body and extend from the measurement-object gas flow section to the first to fifth surfaces is defined as a thinnest external wall and a surface corresponding to the thinnest external wall is defined as a closest surface, a part of the protective layer which covers the closest surface overlaps the entirety of the thinnest external wall when viewed in a direction perpendicular to the closest surface, and has one or more internal spaces formed therein which overlaps 80% or more of the thinnest external wall when viewed in the direction perpendicular to the closest surface.

Abstract: A composite substrate according to the present invention includes a support substrate having a diameter of 2 inches or more, and a piezoelectric substrate having a thickness of 20 ?m or less and bonded to the support substrate to transmit light. The piezoelectric substrate has a thickness distribution shaped like a fringe. A waveform having an amplitude within a range of 5 to 100 nm in a thickness direction and a pitch within a range of 0.5 to 20 mm in a width direction appears in the thickness distribution of the piezoelectric substrate in a cross section of the composite substrate taken along a line orthogonal to the fringe, and the pitch of the waveform correlates with a width of the fringe. In the piezoelectric substrate, the fringe may include either parallel fringes or spiral or concentric fringes.

Abstract: A composite substrate according to the present invention includes a support substrate having a diameter of 2 inches or more, and a piezoelectric substrate having a thickness of 20 ?m or less and bonded to the support substrate to transmit light. The piezoelectric substrate has a thickness distribution shaped like a fringe. A waveform having an amplitude within a range of 5 to 100 nm in a thickness direction and a pitch within a range of 0.5 to 20 mm in a width direction appears in the thickness distribution of the piezoelectric substrate in a cross section of the composite substrate taken along a line orthogonal to the fringe, and the pitch of the waveform correlates with a width of the fringe. In the piezoelectric substrate, the fringe may include either parallel fringes or spiral or concentric fringes.