In an elastic wave filter device, a first filter including a first pass band and a second filter including a second pass band are common-connected at a common connection point. The first filter includes, on the common connection point side, a serial arm resonator, a parallel arm resonator, or a longitudinally coupled resonator-type elastic wave filter, and generates a fundamental wave and a high-order mode. A resonant frequency of the high-order mode on a higher frequency side relative to the first pass band of the first filter is smaller than the second pass band. On the common connection point side, a serial arm resonator in which the resonant frequency is not the highest, a parallel arm resonator, or a longitudinally coupled resonator-type elastic wave filter, is disposed.

A surface acoustic wave filter is disclosed. The surface acoustic wave filter includes a substrate, and first and second surface acoustic wave filter structures disposed on first and second main surfaces of the substrate, respectively. The first surface acoustic wave filter structure includes a first piezoelectric layer a plurality of first surface acoustic wave resonators formed on a top surface of the first piezoelectric layer, and a first wiring layer connecting the first surface acoustic wave resonators to each other. The second surface acoustic wave filter structure includes a second piezoelectric layer, a plurality of second surface acoustic wave resonators formed on a bottom surface of the second piezoelectric layer, and a second wiring layer connecting the second surface acoustic wave resonators to each other. A plurality of through electrodes extends through the substrate, the first piezoelectric layer, and the second piezoelectric layer. A circuit including the first surface acoustic wave resonators and the first wiring layer on the top surface of the first piezoelectric layer forms at least one first radio frequency filter, and a circuit including the plurality of second surface acoustic wave resonators and the second wiring layer on the bottom surface of the second piezoelectric layer forms at least one second radio frequency filter. The at least one first radio frequency filter and the at least one second radio frequency filter belong to different frequency bands.

Communications devices, triplexers, high-pass filters, and low-pass filters are disclosed. A communications device includes a triplexer having a common port and first, second, and third branch ports. A hybrid LC/SAW high-pass filter is connected between the common port and the third branch port, a hybrid LC/SAW low-pass filter is connected between the common port and an internal node, an LC high-pass filter is connected between the internal node and the second branch port, and an LC low-pass filter is connected between the internal node and the first branch port.

In order to pass a signal having a wide pass bandwidth with respect to a center frequency of a pass band, a surface acoustic wave device includes a first surface acoustic wave element provided with a first pass band; and a second surface acoustic wave element having a second pass band in a high frequency band compared with the first pass band of the first surface acoustic wave element, in which the first surface acoustic wave element and the second surface acoustic wave element have a common input terminal and a common output terminal, and a frequency of a high frequency side of the first pass band of the first surface acoustic wave element is partially overlapped with a frequency of a low frequency side of the second pass band of the second surface acoustic wave element.

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.

A surface acoustic wave filter device includes surface acoustic wave filters, one of which includes a longitudinally coupled resonator-type first filter section and a longitudinally coupled resonator-type second filter section. The second filter section is electrically connected in parallel or series with the first filter section on at least one of an input signal side and an output signal side. The first filter section includes a first IDT group including three IDTs. The second filter section includes a second IDT group including three IDTs. Another surface acoustic wave filter includes a third IDT group that is cascade connected to the first filter section and the second filter section and includes IDTs arranged in order in a line in a surface acoustic wave propagation direction.

A duplexer includes a transmission filter with a ladder circuit configuration and a reception filter. The reception filter includes a series trap element connected to an antenna terminal and a longitudinally coupled resonator-type surface acoustic wave filter. In the transmission filter, a coupling capacitance is connected between an end portion at parallel arm resonators side of an inductance and a line connecting the series trap element to the longitudinally coupled resonator-type surface acoustic wave filter in the reception filter.

An acoustic wave filter includes a surface acoustic wave resonator and a bulk acoustic wave resonator. The SAW resonator includes a piezoelectric substrate and an interdigital transducer electrode on the substrate. The IDT electrode includes a pair of comb-shaped electrodes interdigitated with each other. Each comb-shaped electrode includes electrode fingers extending in parallel or substantially in parallel in a direction crossing the SAW propagation direction and a busbar electrode connecting the electrode fingers to each other at one end of each of the electrode fingers. The BAW resonator includes a lower electrode defined by a portion of a busbar electrode, a piezoelectric film on the busbar electrode, and an upper electrode on the piezoelectric film.

A multiplexer includes a common terminal, reception output terminals (120 and 130), a filter (20) that is connected between the common terminal and the reception output terminal (120), a filter (30) that is connected between the common terminal and the reception output terminal (130) and has a pass band different from a pass band of the filter (20), and an impedance matching circuit that is arranged between the common terminal and the filter (30). The impedance matching circuit includes a parallel-arm resonator that is connected between a node (N1) on a path connecting the common terminal to the filter (30) and a ground.