Multi-band filter with suppressed shear horizontal mode

A radio frequency module comprising:

• a packaging board configured to receive a plurality of components;
• a multi-band filter implemented on the packaging board, the multi-band filter including:
• a piezoelectric substrate;
• a plurality of groups of electrodes disposed on the piezoelectric substrate, each group of the plurality of groups of electrodes forming a respective filter to allow signals to pass at a corresponding frequency band of multiple frequency bands, a first group of the plurality of groups of electrodes forming a first filter having a first frequency band and a second group of the plurality of groups of electrodes forming a second filter having a second frequency band, the first frequency band lower than the second frequency band;
• a dielectric film formed to cover at least a part of the piezoelectric substrate and the plurality of groups of electrodes;
• and a passivation film disposed on the dielectric film, the passivation film having a smaller thickness for the first group than for the second group, so as to suppress a spurious response generated in the piezoelectric substrate.

A mobile device comprising:

• an antenna configured to receive a radio frequency signal;
• and
• a front end system configured to communicate with the antenna, the front end system including a multi-band filter including:
• a piezoelectric substrate;
• a plurality of groups of electrodes disposed on the piezoelectric substrate, each group of the plurality of groups of electrodes forming a respective filter to allow signals to pass at a corresponding frequency band of multiple frequency bands, a first group of the plurality of groups of electrodes forming a first filter having a first frequency band and a second group of the plurality of groups of electrodes forming a second filter having a second frequency band, the first frequency band lower than the second frequency band;
• a dielectric film formed to cover at least a part of the piezoelectric substrate and the plurality of groups of electrodes;
• and a passivation film disposed on the dielectric film, the passivation film having a smaller thickness for the first group than for the second group, so as to suppress a spurious response generated in the piezoelectric substrate.