The multiplexer includes a plurality of IDT electrodes on a substrate, an insulating cover located on the substrate so as to configure one or more spaces above the plurality of IDT electrodes, an antenna terminal, transmission terminal, and reception terminal which are all located on the substrate and pass through the cover, and a reinforcing layer which is located on the cover and is made of metal. By the plurality of IDT electrodes, a transmission filter located in a signal path connecting the antenna terminal and the transmission terminal and a receiving filter located in a signal path connecting the antenna terminal and the reception terminal. The reinforcing layer includes a first area part facing the transmission filter and a second area part which faces the receiving filter and is separated from the first area part.

An elastic wave device includes a piezoelectric substrate made of LiNbO.sub.3, interdigital transducer electrodes on the piezoelectric substrate, and a first dielectric film provided on the piezoelectric substrate and the first dielectric film to cover the IDT electrodes and made of a silicon oxide. The IDT electrodes include a first metal film made of one metal selected from Pt, Cu, Mo, Au, W, and Ta. The Euler angles (ϕ, θ, ψ) of the piezoelectric substrate are (0±5°, −90°≤θ≤−70°, 0°±5°). The metal for the first metal film and the thickness hm/λ (%) match any of the combinations as follows: TABLE-US-00001 Metal for the first metal film Thickness hm/λ (%) of the first metal film Pt 6.5 ≤ hm/λ ≤ 25 Cu  13 ≤ hm/λ ≤ 25 Mo 15.5 ≤ hm/λ ≤ 25  Au 6.5 ≤ hm/λ ≤ 25 W 7.5 ≤ hm/λ ≤ 25 Ta .sup.  7 ≤ hm/λ ≤ 25.

An elastic wave device manufacturing method includes a preparing a piezoelectric wafer on which IDT electrodes are provided in elastic wave device forming portions, providing on a first main surface of the piezoelectric wafer support layers in the elastic wave device forming portions, bonding a cover member to cover the support layers to obtain a multilayer body, cutting the multilayer body in a first direction multiple times, cutting the multilayer body in a second direction orthogonal to the first direction to obtain elastic wave devices, in which a resin layer extends across a boundary between the elastic wave device forming portions adjacent to each other on the first main surface of the piezoelectric wafer, and the second cutting step is performed in a state in which the resin layer is present.

An elastic wave device includes a piezoelectric thin film, IDT electrodes on the piezoelectric thin film, an insulating layer surrounding the piezoelectric thin film on a primary surface of a support substrate, a spacer layer surrounding the piezoelectric thin film in plan view, and a cover on the spacer layer. The spacer layer includes an outer edge and an inner edge closer than the outer edge to the piezoelectric thin film in plan view. The primary surface of the insulating layer closer to the spacer layer includes a sloping region that extends where the insulating layer overlaps the spacer layer in plan view and in which the distance from the first primary surface of the support substrate along the direction perpendicular or substantially perpendicular to the support substrate increases from the outer edge toward the inner edge.

In an elastic wave device, an IDT electrode is disposed on a piezoelectric substrate and includes a close contact layer, which includes first and second main surfaces and side surfaces. The first main surface is in contact with the piezoelectric substrate, and at least two electrode layers are disposed on the close contact layer. The at least two electrode layers include a first electrode layer and a second electrode layer. The first electrode layer is made of a material that has a higher density than that of Al. The second electrode layer has a lower density than the first electrode layer. One of the at least two electrode layers has higher weather resistance than the close contact layer and covers the side surfaces of the close contact layer.

A surface acoustic wave (SAW) device including a substrate is provided. Multiple surface acoustic wave elements are disposed on the substrate. A conductive surrounding structure includes: a wall part, disposed on the substrate and surrounding the surface acoustic wave elements; and a lateral layer part, disposed on the wall part. The lateral layer part has an opening above the surface acoustic wave elements. A cap layer covers the lateral layer part and closes the opening.

An electronic device includes an insulation material layer provided on a first main surface of a piezoelectric substrate and surrounding a functional element, and a protective layer provided on the insulation material layer. The piezoelectric substrate and the insulation material layer define a hollow portion accommodating the functional element. The protective layer includes a first portion above the hollow portion, a second portion adjacent to the first portion at one end of the second portion, and a third portion adjacent to the second portion at another end of the second portion. A distance between the first main surface and a surface of the protective layer in the thickness direction is greatest at a location where the second portion is adjacent to or in a vicinity of the first portion, and the distance is shortest at a location where the second portion is adjacent to or in a vicinity of the third portion.

A electronic component includes a connection electrode on a wiring layer. An electrically conductive layer is connected to the wiring layer via the connection electrode. A protective film covers a cover portion and the electrically conductive layer. A solder bump is electrically connected to the electrically conductive layer via an opening. An alloy layer is between the solder bump and the electrically conductive layer in a thickness direction to join the solder bump to the electrically conductive layer and differs in composition and/or elements from the solder bump. The connection electrode does not overlap the solder bump. The surface of the electrically conductive layer that is located on a protective film side is in contact with the protective film between the alloy layer and an edge of the electrically conductive layer that is located on a connection electrode side.

An electronic device includes an insulation material layer provided on a first main surface of a piezoelectric substrate and surrounding a functional element, and a protective layer provided on the insulation material layer. The piezoelectric substrate and the insulation material layer define a hollow portion accommodating the functional element. The protective layer includes a first portion above the hollow portion, a second portion adjacent to the first portion at one end of the second portion, and a third portion adjacent to the second portion at another end of the second portion. A distance between the first main surface and a surface of the protective layer in the thickness direction is greatest at a location where the second portion is adjacent to or in a vicinity of the first portion, and the distance is shortest at a location where the second portion is adjacent to or in a vicinity of the third portion.

An acoustic wave device comprises a substrate including a piezoelectric material, interdigital transducer (IDT) electrodes including interdigitated electrode fingers disposed on a surface of the substrate, and a passivation layer formed on tops of the IDT electrodes and on the piezoelectric material in gaps between adjacent IDT electrodes, the passivation film being thicker on the tops of the IDT electrodes than on the piezoelectric material in the gaps between adjacent IDT electrodes to improve an electromechanical coupling factor of the acoustic wave device.