A multiplexer includes elastic wave filters with different pass bands, a common terminal to which an inductance element is serially connected in a connection path between an antenna element and the common terminal; and an inductance element. Among the elastic wave filters, a reception input terminal of a first reception filter is connected to the common terminal via the inductance element and is connected to a parallel resonator. Transmission output terminals of transmission filters and a reception input terminal of a second reception filter are connected to the common terminal, are connected to series resonators, and are not connected to parallel resonators.

An apparatus includes: a substrate; a lid disposed over the substrate, and comprising posts disposed around a perimeter of the substrate, the posts enclosing a cavity between the lid and the substrate; an electronic device disposed over an upper surface of the substrate, and in the cavity; an electrical contact pad; and an electrically insulating layer disposed between the electrical contact pad and an upper surface of the lid.

At least one of a transmission filter and a reception filter of a duplexer includes a piezoelectric substrate, an elastic wave filter electrode portion on the piezoelectric substrate and including ground terminals to be connected to a ground potential, a support layer provided on the piezoelectric substrate, a cover provided on the support layer to seal a cavity in the support layer, and via hole electrodes penetrating the support layer and the cover and including first and second ends. The ground terminals are commonly connected on the piezoelectric substrate, and the ground terminals are electrically connected to the respective first ends of the plurality of via hole electrodes. The second ends of the via hole electrodes are connected to the ground potential outside of the at least one of the transmission filter and the reception filter.

An acoustic wave device includes: a support substrate; a first piezoelectric substrate bonded to a first principal surface of the support substrate, the first piezoelectric substrate being a single crystal substrate, a first acoustic wave resonator located on an opposite surface of the first piezoelectric substrate from a surface to which the support substrate is bonded, the first acoustic wave resonator including an IDT; a second piezoelectric substrate bonded to a second principal surface of the support substrate opposite from the first principal surface, the second piezoelectric substrate being a single crystal substrate; and a second acoustic wave resonator located on an opposite surface of the second piezoelectric substrate from a surface to which the support substrate is bonded, the second acoustic wave resonator including an IDT.

A filter component with a passive element includes a filter substrate, an elastic wave filter including an elastic wave resonator in a predetermined region of one main surface of the filter substrate, and a support substrate on another main surface of the filter substrate, wherein a passive element is provided in or on a support substrate, the passive element includes a wiring electrode and is electrically connected to the elastic wave filter.

A multiplexer includes elastic wave filters with different pass bands, a common terminal to which an inductance element is serially connected in a connection path between an antenna element and the common terminal; and an inductance element. Among the elastic wave filters, a reception input terminal of a first reception filter is connected to the common terminal via the inductance element and is connected to a parallel resonator. Transmission output terminals of transmission filters and a reception input terminal of a second reception filter are connected to the common terminal, are connected to series resonators, and are not connected to parallel resonators.

An acoustic wave device includes: a piezoelectric substrate that is made of a single crystal piezoelectric material, and includes a first region including an upper surface, and a second region that is located under the first region and has a density less than a density of the first region; and an IDT located on the upper surface of the piezoelectric substrate.

A composite filter device for use in carrier aggregation includes a first bandpass filter connected to an antenna common terminal and including a first pass band, and a second bandpass filter including a second pass band of a higher frequency than the first pass band. The first bandpass filter includes an LiNbO.sub.3 substrate, an IDT electrode which is provided on the LiNbO.sub.3 substrate and defines the first bandpass filter, and a dielectric film which covers the IDT electrode and includes silicon oxide as a main component. The first bandpass filter is defined by at least one elastic wave resonator, and a Rayleigh wave propagating in the LiNbO.sub.3 substrate is used and an acoustic velocity of a Sezawa wave in the elastic wave resonator is equal to or higher than about 4643.2 m/sec.

A high-frequency module that performs filtering of signals transmitted and received through an antenna includes an antenna terminal, a transmission terminal, a reception terminal, a reception filter connected between the antenna terminal and the reception terminal, a transmission filter connected between the antenna terminal and the transmission terminal, a first element connected between the antenna terminal and the transmission filter, and a second element connected in series between the transmission terminal and the transmission filter. The first element and the second element are capacitively coupled to each other.

An acoustic wave device includes a piezoelectric substrate, a pair of interleaved interdigital transducer electrodes disposed on the piezoelectric substrate, and a dielectric film including silicon oxynitride covering the pair of interleaved interdigital transducer electrodes. The dielectric film exhibits a temperature coefficient of velocity of substantially zero throughout an operating temperature range of the acoustic wave device of between 55 C. and 125 C.