Solidly-mounted transversely-excited film bulk acoustic resonator

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

• forming an acoustic Bragg reflector by depositing material layers on one or both of a surface of a device substrate and a first surface of a single-crystal piezoelectric plate having a second surface attached to a sacrificial substrate;
• bonding the single-crystal piezoelectric plate attached to the sacrificial substrate to the device substrate such that the layers of the acoustic Bragg reflector are sandwiched between the first surface of the single-crystal piezoelectric plate and the device substrate;
• removing the sacrificial substrate to expose the second surface of the single-crystal piezoelectric plate;
• and
• forming a conductor pattern on the second surface of the single-crystal piezoelectric plate, the conductor pattern including a plurality of interdigital transducers (IDTs) of a respective plurality of resonators including a shunt resonator and a series resonator;
• depositing a first dielectric layer having a first thickness over the IDT of the shunt resonator;
• and
• depositing a second dielectric layer having a second thickness less than the first thickness over the IDT of the series resonator,
• wherein the single-crystal piezoelectric plate and all of the plurality of IDTs are configured such that respective radio frequency signals applied to the IDTs excite respective shear primary acoustic modes within the single-crystal piezoelectric plate, and
• wherein the acoustic Bragg reflector is configured to reflect the respective shear primary acoustic modes excited by all of the plurality of IDTs.

A filter device comprising:

• a substrate having a surface;
• a single-crystal piezoelectric plate having parallel front and back surfaces;
• an acoustic Bragg reflector sandwiched between the surface of the substrate and the back surface of the single-crystal piezoelectric plate;
• and
• a conductor pattern formed on the front surface of the single-crystal piezoelectric plate, the conductor pattern including a plurality of interdigital transducers (IDTs) of a respective plurality of resonators including a shunt resonator and a series resonator;
• a first dielectric layer having a first thickness deposited over the IDT of the shunt resonator;
• and
• a second dielectric layer having a second thickness less than the first thickness deposited over the IDT of the series resonator, wherein
• all the plurality of IDTs are configured to excite respective shear primary acoustic modes in the single-crystal piezoelectric plate in response to respective radio frequency signals applied to the IDTs, and
• the acoustic Bragg reflector is configured to reflect the respective shear primary acoustic modes excited by all of the plurality of IDTs.

A method of fabricating an acoustic resonator device comprising:

• forming an acoustic Bragg reflector by depositing material layers on one or both of a surface of a device substrate and a first surface of a single-crystal piezoelectric plate having a second surface attached to a sacrificial substrate;
• bonding the single-crystal piezoelectric plate attached to the sacrificial substrate to the device substrate such that the layers of the acoustic Bragg reflector are sandwiched between the first surface of the single-crystal piezoelectric plate and the device substrate;
• removing the sacrificial substrate to expose the second surface of the single-crystal piezoelectric plate;
• and
• forming an interdigital transducer (IDT) on the second surface of the single-crystal piezoelectric plate,
• wherein the single-crystal piezoelectric plate and the IDT are configured such that a radio frequency signal applied to the IDT excites a shear primary acoustic mode within the single-crystal piezoelectric plate, and
• wherein the acoustic Bragg reflector is configured to reflect the primary shear acoustic mode.