A composite filter device includes a first filter and a plurality of second filters with different passbands. End portions of the first filter and the plurality of second filters are connected to a common connection. The first filter includes a piezoelectric substrate made of LiNbO.sub.3, an IDT electrode provided on the piezoelectric substrate, and a dielectric layer provided on the piezoelectric substrate so as to cover the IDT electrode. The first filter utilizes a fundamental wave of Rayleigh waves. The passband of the first filter is arranged in a frequency band that is lower than any of the passbands of the plurality of second filters.

A method for manufacturing an elastic wave device includes successively stacking conductive films on a piezoelectric substrate on which a pattern of a first resist has been formed, removing the first resist from the piezoelectric substrate on which the conductive films have been stacked; applying a second resist to the piezoelectric substrate from which the first resist has been removed and subjecting the second resist to exposure and development, thus forming a protective layer that protects a first region with the second resist, and etching the second conductive material in a state in which the first region is protected by the protective layer.

In an elastic wave device, a piezoelectric substrate is laminated on a support substrate including a recess. On one of a first principal surface and a second principal surface of the piezoelectric substrate, a functional electrode including an IDT electrode is provided. Passing-through sections are provided in the piezoelectric substrate and connected to a hollow section enclosed by the recess and the piezoelectric substrate. In a plan view of the piezoelectric substrate seen from the first principal surface, at least a portion of the passing-through sections is inside a minimum rectangular or substantially rectangular region encompassing an outer circumference of a region including the functional electrode.

A surface acoustic wave device includes a piezoelectric substrate and an IDT electrode on the piezoelectric substrate. The IDT electrode includes a main electrode layer and a barrier layer between the piezoelectric substrate and the main electrode layer. The main electrode layer is inside a region in which the barrier layer is provided in plan view to suppress diffusion between the piezoelectric substrate and the main electrode layer when a voltage is applied to the IDT electrode.

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 first filter of a multiplexer includes a ladder filter structure with a plurality of series resonators and a plurality of parallel resonators. Each resonator is an acoustic wave resonator that includes an InterDigital Transducer (IDT) electrode including a pair of comb-shaped electrodes. A total number of reflection electrode fingers of the reflectors of at least one of the series resonator that is closest to the common terminal among the series resonators and the parallel resonator that is closest to the common terminal is smaller than a total number of reflection electrode fingers of the reflectors of each of a remainder of the resonators.

An elastic wave resonator includes an interdigital transducer electrode provided on a piezoelectric substrate and including a first electrode layer made of Al or an alloy with Al as its primary component and including a first main surface on a side where the piezoelectric substrate is located and a second main surface on the opposite side from the first main surface. An SH wave is used as a propagated elastic wave. When a resonant frequency of the elastic wave resonator is fr and an anti-resonant frequency of the elastic wave resonator is fa, a minimum value of an absolute value of a distortion component in the first main surface calculated through a two-dimensional finite element method is about 1.4×10.sup.−3 or less at a frequency f expressed as:

f=fr+0.06×bw, where bw is fa−fr.

An acoustic wave element (100) according to certain examples includes a piezoelectric body (130), an interdigital transducer (IDT) electrode (140, 150) disposed above the piezoelectric body (130), and a connection electrode (160) disposed above the piezoelectric body (130) and connected to the IDT electrode (140, 150). A first insulation layer (172) covers the connection electrode (160), and a second insulation layer (174a, 174b) covers the IDT electrode (140, 150). The first insulation layer (172) disposed above the connection electrode (160) has a first thickness T in a direction perpendicular to an upper surface of the piezoelectric body (130) and the second insulation layer (174b) disposed above the IDT electrode (150) has a second thickness K in the direction perpendicular to the upper surface of the piezoelectric body (130). The first thickness T is less than the second thickness K based on FIG. 2C and the relevant description.

An elastic wave device includes a first piezoelectric substrate including a first principal surface and a second principal surface, a second piezoelectric substrate including a first principal surface and a second principal surface and with a greater thickness than that of the first piezoelectric substrate, and ground terminals located on the second principal surface of the first piezoelectric substrate. The first principal surface of the first piezoelectric substrate and the first principal surface of the second piezoelectric substrate are joined to face each other. On the first principal surface of the first piezoelectric substrate, a first elastic wave filter is located. On the first principal surface of the second piezoelectric substrate, a second elastic wave filter is located. The out-of-band attenuation of the first elastic wave filter is greater than the out-of-band attenuation of the second elastic wave filter.

An elastic wave device includes a low acoustic velocity film, a piezoelectric film, and an IDT electrode, which are laminated on a high acoustic velocity material. In the IDT electrode, first electrode fingers, or second electrode fingers, or each of the first electrode fingers and the second electrode fingers, includes a wide width portion with a dimension in a width direction larger than a dimension at a center in a length direction and being provided closer to at least one of a side of a proximal end and a side of a distal end than a central region, at least one of a first busbar and a second busbar includes cavities arranged in a busbar length direction, and at least one of the first busbar and the second busbar includes an inner busbar portion which is positioned closer to a side of the first electrode fingers or a side of the second electrode fingers than the cavities are and which extends in the length direction of the first busbar and the second busbar, a central busbar portion that includes the cavities, and an outer busbar portion.