BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an acoustic wave filter device having a structure in which a substrate made of a semiconductor and a piezoelectric layer are stacked with a layer of another material located therebetween, and a composite filter device.

2. Description of the Related Art

In an RF stage of a smartphone, a composite filter device, such as a multiplexer, is used to support multiple bands. For example, in a multiplexer disclosed in WO 2016/117676 A1 described below, first to third acoustic wave filters are connected to an antenna terminal. The first acoustic wave filter has a pass band of a low-band cellular band. Furthermore, the second acoustic wave filter has a pass band including GPS and GLONASS bands. The third acoustic wave filter has a pass band of a middle-band cellular band.

Meanwhile, WO 2012/086639 A1 described below discloses an elastic wave device including a supporting substrate made of Si. On the supporting substrate made of Si, a low-acoustic-velocity film, a piezoelectric layer, and an IDT (interdigital transducer) electrode are stacked in this order from the bottom. A material of the supporting substrate made of Si is a high-acoustic-velocity material, and thus an elastic wave is effectively confined within the piezoelectric layer by a laminated structure including the supporting substrate made of Si and the low-acoustic-velocity film.

As disclosed in WO 2016/117676 A1, in the case of the multiplexer including a plurality of filters sharing a common connection, distortion caused by simultaneously transmitting a plurality of signals often becomes an issue. For example, when a Band 7 Tx signal is transmitted from the third acoustic wave filter, second-order intermodulation distortion in a frequency band coincident with a frequency band of a Band 7 Rx occurs from the antenna terminal due to a signal in a 5 GHz WiFi band leaking from another circuit in the same smartphone and the Band 7 Tx signal. For this reason, there is a possibility that reception sensitivity in the Band 7 Rx may decrease. Thus, a composite filter device, such as a multiplexer, is demanded that is superior to an existing band pass filter in linearity.

Meanwhile, the inventor of preferred embodiments of the present application has discovered that the structure disclosed in WO 2012/086639 A1 in which the low-acoustic-velocity film is disposed on the supporting substrate made of Si does not provide sufficient linearity. For this reason, when an acoustic wave filter having such a structure is used for a composite filter device, such as a multiplexer, the occurrence of distortion in a reception signal or the like, in particular, becomes an issue.

SUMMARY OF THE INVENTION

Preferred embodiments of the present invention provide acoustic wave filter devices that each have a structure in which a substrate including a semiconductor and a piezoelectric layer are stacked with a layer of another material located therebetween and that each have excellent linearity.

Preferred embodiments of present invention also provide composite filter devices that each include an acoustic wave filter device according to a preferred embodiment of the present invention and in each of which there is little distortion in a signal.

A preferred embodiment of the present invention provides an acoustic wave filter device including an antenna terminal electrically connected to an antenna; an input or output terminal; and an acoustic wave filter electrically connected between the antenna terminal and the input or output terminal and including a plurality of acoustic wave resonators. The plurality of acoustic wave resonators include a piezoelectric layer, an IDT (interdigital transducer) electrode provided on the piezoelectric layer, a low-acoustic-velocity film in which an acoustic velocity of a bulk wave propagating through the low-acoustic-velocity film is lower than an acoustic velocity of an acoustic wave propagating through the piezoelectric layer, and a substrate in which an acoustic velocity of a bulk wave propagating through the substrate is higher than an acoustic velocity of an acoustic wave propagating through the piezoelectric layer and that includes a semiconductor. The piezoelectric layer is provided on the substrate with the low-acoustic-velocity film located between the piezoelectric layer and the substrate, and, above the piezoelectric layer, a routing line electrically connected to the antenna terminal is provided on an insulating film provided on the piezoelectric layer.

Another preferred embodiment of the present invention provides an acoustic wave filter device including an antenna terminal electrically connected to an antenna; an input or output terminal; and an acoustic wave filter electrically connected between the antenna terminal and the input or output terminal and including a plurality of acoustic wave resonators. The plurality of acoustic wave resonators include a substrate including a semiconductor, a piezoelectric layer provided on the substrate including the semiconductor and including first and second major surfaces facing each other, a first electrode provided on the first major surface of the piezoelectric layer, and a second electrode provided on the second major surface of the piezoelectric layer and facing the first electrode with the piezoelectric layer interposed between the second electrode and the first electrode. The acoustic wave filter device further includes an insulating film provided on the piezoelectric layer, and a routing line provided on the insulating film and electrically connected to the antenna terminal.

In an acoustic wave filter device according to a preferred embodiment of present invention, the substrate is a silicon substrate.

In an acoustic wave filter device according to a preferred embodiment of present invention, the insulating film includes a synthetic resin.

In an acoustic wave filter device according to a preferred embodiment of present invention, the insulating film includes an inorganic insulating material.

A composite filter device according to a preferred embodiment of present invention includes an acoustic wave filter device according to a preferred embodiment of present invention, and at least one other acoustic wave filter device sharing a common electrical connection to the antenna terminal.

A composite filter device according to a preferred embodiment of present invention may be a multiplexer.

Furthermore, a composite filter device according to a preferred embodiment of present invention may include a plurality of acoustic wave filter devices that share a common electrical connection to the antenna terminal through a switch and in which at least one acoustic wave filter device of the plurality of acoustic wave filter devices is an acoustic wave filter device according to a preferred embodiment of present invention.

In the acoustic wave filter devices according to the preferred embodiments of present invention, linearity is improved. Thus, in the composite filter devices according to the preferred embodiments of present invention, distortion in a signal is reduced.

The above and other elements, features, steps, characteristics and advantages of the preferred embodiments of present invention will become more apparent from the following detailed description of the preferred embodiments with reference to the attached drawings.

