Solidly-mounted transversely-excited film bulk acoustic device and method

A method of fabricating a filter device, the method comprising:

• fabricating a bulk acoustic resonator chip comprising:
• forming a first conductor pattern on a front surface of a piezoelectric layer, the first conductor pattern comprising a first plurality of contact pads and interdigital transducers (IDTs) of a plurality of acoustic resonators comprising a shunt resonator and a series resonator;
• forming an acoustic Bragg reflector between a surface of a substrate and a back surface of the piezoelectric layer;
• depositing a first dielectric layer on and between interleaved fingers of the IDT of the shunt resonator, the first dielectric layer having a first thickness between;
• and
• depositing a second dielectric layer on and between the interleaved fingers of the IDT of the series resonator, the second dielectric layer having a second thickness less than the first thickness;
• fabricating an interposer comprising:
• forming a second conductor pattern on a surface of the interposer that faces the bulk acoustic resonator chip, the second conductor pattern comprising a second plurality of contact pads;
• forming a polymer cover that is cast over the bulk acoustic resonator chip to seal a space between the bulk acoustic resonator chip and the interposer;
• and
• forming gold bumps by thermocompression or ultrasonic bonding to connect each contact pad of the first plurality of contact pads to a respective contact pad of the second plurality of contact pads.

A method of fabricating a filter device, the method comprising:

• fabricating an acoustic resonator chip comprising:
• forming a first conductor pattern on a front surface of a piezoelectric layer, the first conductor pattern comprising a first plurality of contact pads and interdigital transducers (IDTs) of a plurality of acoustic resonators comprising a shunt resonator and a series resonator;
• forming an acoustic Bragg reflector between a surface of a substrate and a back surface of the piezoelectric layer;
• forming a first dielectric layer on and between interleaved fingers of the IDT of the shunt resonator, the first dielectric layer having a first thickness;
• and
• forming a second dielectric layer on and between the interleaved fingers of the IDT of the series resonator, the second dielectric layer having a second thickness less than the first thickness;
• fabricating an interposer comprising:
• forming a second conductor pattern on a surface of the interposer that faces the acoustic resonator chip, the second conductor pattern comprising a second plurality of contact pads;
• forming a plurality of recesses in the surface of the interposer to face the IDTs of the plurality of acoustic resonators;
• sealing a perimeter of the piezoelectric layer to a perimeter of the interposer;
• and
• directly bonding each contact pad of the first plurality of contact pads to a respective contact pad of the second plurality of contact pads,
• wherein each of the plurality of recesses has a depth such that a distance from a bottom of each recess to the respective IDT is greater than or equal to 15 microns and less than or equal to 100 microns.