Acoustic filters are disclosed. A bandpass filter has a passband between a lower band edge and an upper band edge. The bandpass filter includes a plurality of transversely-excited film bulk acoustic resonators (XBARs) connected in a ladder filter circuit. The plurality of XBARs includes at least one lithium tantalate (LT) XBAR and at least one lithium niobate XBAR. Each of the at least one LT XBAR includes an LT piezoelectric plate with Euler angles (0°, β, 0°), where β is greater than zero and less than or equal to 40 degrees.

Acoustic filters are disclosed. A bandpass filter has a passband between a lower band edge and an upper band edge. The bandpass filter includes a plurality of transversely-excited film bulk acoustic resonators (XBARs) connected in a ladder filter circuit. The plurality of XBARs includes at least one lithium tantalate XBAR and at least one lithium niobate XBAR.

There is disclosed acoustic resonators and filter devices. An acoustic resonator includes a substrate having a surface and a single-crystal piezoelectric plate having front and back surfaces, the back surface attached to the surface of the substrate except for a portion of the piezoelectric plate forming a diaphragm that spans a cavity in the substrate. An interdigital transducer (IDT) is formed on the front surface of the single-crystal piezoelectric plate such that interleaved fingers of the IDT are disposed on the diaphragm. The piezoelectric plate and the IDT are configured such that a radio frequency signal applied to the IDT excites a primary shear acoustic mode in the diaphragm. The interleaved fingers comprise a first layer proximate the diaphragm, a second layer over the first layer, and a third layer over the second layer, wherein adjacent layers are different materials.

An acoustic resonator device includes a conductor pattern formed on a surface of a piezoelectric plate. The conductor pattern includes a first busbar, a second busbar, and n interleaved parallel fingers of an interdigital transducer (IDT), where n is a positive integer. The fingers extend alternately from the first and second busbars. A first finger and an n′th finger are at opposing ends of the IDT. The conductor pattern also includes a first reflector element proximate and parallel to the first finger and a second reflector element proximate and parallel to the n′th finger. A distance pr between the first reflector element and the first finger and between the second reflector element and the n′th finger is not equal to a pitch p of the IDT.

Acoustic resonator devices and filters, and methods of making the same. An acoustic resonator includes a piezoelectric plate and an interdigital transducer (IDT) including interleaved fingers on the piezoelectric plate. The 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 piezoelectric plate. The acoustic resonator further includes a front-side dielectric layer on the piezoelectric plate between the fingers of the IDT, wherein a resonance frequency of the acoustic resonator device has an inverse dependence on a thickness of the front-side dielectric layer.

Acoustic resonator devices, filters, and methods are disclosed. An acoustic resonator includes a substrate and a lithium niobate (LN) plate having front and back surfaces and a thickness ts. The back surface faces the substrate. A portion of the LN plate forms a diaphragm spanning a cavity in the substrate. An interdigital transducer (IDT) is on the front surface of the LN plate with interleaved fingers of the IDT on the diaphragm. The LN plate and the IDT are configured such that a radio frequency signal applied to the IDT excites a shear primary acoustic wave in the diaphragm. Euler angles of the LN plate are [0°, β, 0°], where 0≤β≤60°. A thickness of the interleaved fingers of the IDT is greater than or equal to 0.8 ts and less than or equal to 2.0 ts.

Filter devices and methods are disclosed. A filter device includes a substrate having a surface. A back surface of a single-crystal piezoelectric plate is attached to the surface of the substrate, portions of the single-crystal piezoelectric plate forming a plurality of diaphragms spanning respective cavities in the substrate. A conductor pattern is formed on a front surface of the piezoelectric plate, the conductor pattern including a plurality of interdigital transducers (IDTs) of a plurality of resonators. Interleaved fingers of at least a first IDT of the plurality of IDTs are disposed on a diaphragm having a first thickness, and interleaved fingers of at least a second IDT of the plurality of IDTs are disposed on a diaphragm having a second thickness less than the first thickness.

An acoustic filter includes a piezoelectric plate on a substrate. Portions of the piezoelectric plate form one or more diaphragms, each diaphragm spanning a respective cavity in the substrate. A conductor pattern on a front surface of the piezoelectric plate includes interdigital transducers (IDTs) of acoustic resonators including a shunt resonator and a series resonator. Interleaved fingers of each IDT are on a diaphragm of the one or more diaphragms. A first dielectric layer with a first thickness is between the fingers of the IDT of the shunt resonator, and a second dielectric layer with a second thickness less than the first thickness is between the fingers of the IDT of the series resonator. The piezoelectric plate and the IDTs are configured such that radio frequency signals applied to the IDTs excite respective primary shear acoustic modes within the diaphragms.

Acoustic resonators and filter devices, and methods of making acoustic resonators and filter devices. An acoustic resonator includes a substrate having a surface and a single-crystal piezoelectric plate having front and back surfaces, the back surface attached to the surface of the substrate except for a portion of the plate forming a diaphragm that spans a cavity in the substrate. An interdigital transducer (IDT) is formed on the front surface with interleaved fingers of the IDT on the diaphragm. The plate and the IDT are configured such that a radio frequency signal applied to the IDT excites a primary shear acoustic mode in the diaphragm. The fingers include a first layer proximate the diaphragm, and a second layer over the first layer. The first and second layers are different metals. A transverse acoustic impedance of the second layer is higher than a transverse acoustic impedance of the first layer.

A bulk acoustic wave resonator and a formation method thereof are provided. The method for forming the bulk acoustic wave resonator includes forming a sacrificial structure on a substrate. A seed layer is formed on the sacrificial structure. A bottom electrode is formed on the seed layer. A piezoelectric layer is formed on the bottom electrode. A top electrode is formed on the piezoelectric layer. The sacrificial structure is removed to form a cavity. The seed layer is etched through the cavity.