A circuit module includes a mounting substrate including a conductor wiring, an elastic wave element provided in or on a main surface of the mounting substrate, an electric element provided in or on the main surface, the electric element being different from the elastic wave element, and an insulating resin portion provided in or on the main surface to cover the elastic wave element and the electric element. The elastic wave element and the electric element are connected to each other by the conductor wiring. A height of the elastic wave element is about 0.28 mm or less, which is less than that of the electric element. The thickness of the resin portion in a region in which the resin portion covers the elastic wave element is greater than the thickness of the resin portion in a region in which the resin portion covers the electric element.

A ceramic substrate is formed of polycrystalline ceramic and has a supporting main surface. At the supporting main surface of the ceramic substrate, the mean of grain sizes of the polycrystalline ceramic is 15 μm or more and less than 40 μm and the standard deviation of the grain sizes is less than 1.5 times the mean.

A ceramic substrate is formed of polycrystalline ceramic and has a supporting main surface. At the supporting main surface of the ceramic substrate, the mean of grain sizes of the polycrystalline ceramic is 15 μm or more and less than 40 μm and the standard deviation of the grain sizes is less than 1.5 times the mean.

A multiplexer includes a transmission-side filter electrically connected to a common terminal and a transmission input terminal, and a transmission-side filter electrically connected to the common terminal and a transmission input terminal. The transmission-side filter includes a plurality of series arm resonators and a plurality of parallel arm resonators. Capacitance elements are respectively electrically connected in parallel to the series arm resonator and the parallel arm resonator, which are connected most proximately to the common terminal. IDT electrodes of a series arm resonator and a parallel arm resonator connected most proximately to the common terminal do not include a thinning electrode, and others of the series arm resonators and the parallel arm resonators include thinning electrodes.

A multimode longitudinally coupled surface acoustic wave resonator is disclosed. The multimode longitudinally coupled surface acoustic wave resonator can include a first interdigital transducer electrode that is positioned over a piezoelectric layer. The first interdigital transducer electrode includes fingers having a first pitch. The multimode longitudinally coupled surface acoustic wave resonator can also include first and second sets of reflectors that are positioned over the piezoelectric layer. The first and second sets of reflectors include a first number of reflectors having a second pitch and a second number of reflectors having a third pitch, respectively. The first pitch is greater than the second pitch. The multimode longitudinally coupled surface acoustic wave resonator can further include a second interdigital transducer electrode that is positioned over the piezoelectric layer and between the first interdigital transducer electrode and the first set of reflectors. The second interdigital transducer electrode includes fingers having a fourth pitch.

A multimode longitudinally coupled surface acoustic wave resonator is disclosed. The multimode longitudinally coupled surface acoustic wave resonator can include a first interdigital transducer electrode that is positioned over a piezoelectric layer. The first interdigital transducer electrode includes fingers having a first pitch. The multimode longitudinally coupled surface acoustic wave resonator can also include first and second sets of reflectors that are positioned over the piezoelectric layer. The first and second sets of reflectors include a first number of reflectors having a second pitch and a second number of reflectors having a third pitch, respectively. The first pitch is greater than the second pitch. The multimode longitudinally coupled surface acoustic wave resonator can further include a second interdigital transducer electrode that is positioned over the piezoelectric layer and between the first interdigital transducer electrode and the first set of reflectors. The second interdigital transducer electrode includes fingers having a fourth pitch.

A surface acoustic wave (SAW) filter includes a bottom substrate, a piezoelectric layer disposed above the bottom substrate, the piezoelectric layer having a bottom surface facing the bottom substrate and a top surface opposite to the bottom surface, a cavity disposed below the piezoelectric layer, an interdigital transducer (IDT) disposed on the top surface of the piezoelectric layer, and a back electrode disposed on the bottom surface of the piezoelectric layer. At least a portion of the back electrode is exposed in the cavity.

A surface acoustic wave (SAW) filter includes a bottom substrate, a piezoelectric layer disposed above the bottom substrate, the piezoelectric layer having a bottom surface facing the bottom substrate and a top surface opposite to the bottom surface, a cavity disposed below the piezoelectric layer, an interdigital transducer (IDT) disposed on the top surface of the piezoelectric layer, and a back electrode disposed on the bottom surface of the piezoelectric layer. At least a portion of the back electrode is exposed in the cavity.

A fabrication method of a surface acoustic wave (SAW) filter, includes: obtaining a piezoelectric substrate; forming a back electrode on a first portion of the piezoelectric substrate; forming a sacrificial layer on the first portion of the piezoelectric substrate, covering the back electrode; forming a first dielectric layer on the first portion of the piezoelectric substrate, covering the sacrificial layer; bonding a bottom substrate to the first dielectric layer; removing a second portion of the piezoelectric substrate to expose the first portion of the piezoelectric substrate, the first portion of the piezoelectric substrate constituting a piezoelectric layer; forming one or more release holes through the piezoelectric layer; forming an interdigital transducer (IDT) on the piezoelectric layer; and etching and releasing the sacrificial layer via the one or more release holes to form a lower cavity exposing the back electrode.

A fabrication method of a surface acoustic wave (SAW) filter, includes: obtaining a piezoelectric substrate; forming a back electrode on a first portion of the piezoelectric substrate; forming a sacrificial layer on the first portion of the piezoelectric substrate, covering the back electrode; forming a first dielectric layer on the first portion of the piezoelectric substrate, covering the sacrificial layer; bonding a bottom substrate to the first dielectric layer; removing a second portion of the piezoelectric substrate to expose the first portion of the piezoelectric substrate, the first portion of the piezoelectric substrate constituting a piezoelectric layer; forming one or more release holes through the piezoelectric layer; forming an interdigital transducer (IDT) on the piezoelectric layer; and etching and releasing the sacrificial layer via the one or more release holes to form a lower cavity exposing the back electrode.