Multiplexer, radio-frequency module, and communication apparatus

A multiplexer comprising:

• a first filter connected to a common terminal and having a first pass band including a first band to send a signal, the first filter being a bulk acoustic wave filter;
• a second filter connected to the common terminal and having a second pass band including a second band, the second band being positioned at a lower frequency than the first band to send a signal, the second filter being a surface acoustic wave filter;
• and
• a third filter connected to the common terminal and having a third pass band including a third band,
• wherein a frequency of an unwanted wave of a second-order or fourth-order distortion mode, which is generated when a first transmitted signal of the first band and a second transmitted signal of the second band are simultaneously transmitted, is included in at least one of the first pass band, the second pass band, and the third pass band, and a frequency of an unwanted wave of a third-order distortion mode, which is generated when the first transmitted signal and the second transmitted signal are simultaneously transmitted, is included in at least one of the first pass band, the second pass band, and the third pass band,
• the first filter includes
• at least one bulk acoustic wave resonator,
• at least one series arm resonator disposed on a series arm path, the series arm path connecting the common terminal and a radio-frequency input terminal configured to receive the first transmitted signal,
• at least one parallel arm resonator disposed on a parallel arm path, the parallel arm path connecting the series arm path and a ground, and
• a capacitor element connected between the common terminal and a resonator which is connected to a closest position to the common terminal among the at least one series arm resonator and the at least one parallel arm resonator.

A multiplexer comprising:

• a first filter connected to a common terminal and having a first pass band including a first band to send a signal, the first filter being a bulk acoustic wave filter;
• a second filter connected to the common terminal and having a second pass band including a second band, the second band being positioned at a lower frequency than the first band to send a signal, the second filter being a surface acoustic wave filter;
• and
• a third filter connected to the common terminal and having a third pass band including a third band,
• wherein a frequency of an unwanted wave of a second-order or fourth-order distortion mode, which is generated when a first transmitted signal of the first band and a second transmitted signal of the second band are simultaneously transmitted, is included in at least one of the first pass band, the second pass band, and the third pass band, and a frequency of an unwanted wave of a third-order distortion mode, which is generated when the first transmitted signal and the second transmitted signal are simultaneously transmitted, is included in at least one of the first pass band, the second pass band, and the third pass band,
• the first filter includes at least one bulk acoustic wave resonator,
• the at least one bulk acoustic wave resonator is a solidly mounted resonator (SMR), and
• each of the at least one bulk acoustic wave resonator includes
• a support substrate,
• a bottom electrode disposed above the support substrate,
• a top electrode disposed above the bottom electrode, and
• a first piezoelectric layer disposed between the bottom electrode and the top electrode;
• and
• a relative dielectric constant of the first piezoelectric layer of a resonator which is connected to a closest position to the common terminal among the at least one bulk acoustic wave resonator is lower than a relative dielectric constant of the first piezoelectric layer of a rest of the at least one bulk acoustic wave resonator.