A method of forming a piezoelectric thin film can include depositing a material on a first surface of a Si substrate to provide a stress neutral template layer. A piezoelectric thin film including a Group III element and nitrogen can be sputtered onto the stress neutral template layer and a second surface of the Si substrate that is opposite the first surface can be processed to remove that Si substrate and the stress neutral template layer to provide a remaining portion of the piezoelectric thin film. A piezoelectric resonator can be formed on the remaining portion of the piezoelectric thin film.

An acoustic resonator device, filter devices, and methods of making the same. An acoustic resonator device includes a substrate having a surface and a single-crystal piezoelectric plate having front and back surfaces, where the back surface is 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. The device further includes an interdigital transducer formed on the front surface of the piezoelectric plate, where interleaved fingers of the IDT disposed on the diaphragm are configured such that a radio frequency signal applied to the IDT excites a primary shear acoustic mode in the diaphragm. The interleaved fingers include a first layer adjacent the diaphragm and a second layer over the first layer, the second layer having a narrower width than the first layer.

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 adjacent the diaphragm and a second layer over the first layer opposite the diaphragm, the second layer having a greater width than the first layer.

A filter comprises a series unit, and a shunt unit disposed between the series unit and a ground. The shunt unit includes resonators that are selectively operated, and each of the shunt resonators includes a film bulk acoustic resonator.

A notch filter includes a substrate having piezoelectricity, the substrate including a high-acoustic-velocity member, a low-acoustic-velocity film provided on the high-acoustic-velocity member, and a piezoelectric thin film provided on the low-acoustic-velocity film; an interdigital transducer electrode provided on the piezoelectric thin film; and reflectors provided on both sides of the interdigital transducer electrode in an acoustic wave propagation direction. An IR gap is within one of two ranges: 0.1G.sub.IR<0.5 or 0.5<G.sub.IR0.9, where is a wavelength determined by an electrode finger pitch of the interdigital transducer electrode, and the IR gap is a distance between electrode finger centers of an electrode finger of the interdigital transducer electrode closest to the reflector out of the electrode fingers of the interdigital transducer electrode, and an electrode finger of the reflector closest to the interdigital transducer electrode, out of the electrode fingers of the reflector.

Aspects and examples provide improvement in the attenuation level near the passband within the stopband of the bandpass-type filter using a ladder-type circuit formed by a BAW resonator. In one example the filter includes a ladder-type circuit formed by a bulk acoustic wave (BAW) resonator, and a loop circuit connected between two distinct points on a signal path extending from an input to an output of the ladder-type circuit for phase-cancellation of signals at the two distinct points. The two distinct points may be the input and the output of the ladder-type circuit. The loop circuit may include a SAW resonator or a BAW resonator. The BAW resonator may be a film bulk acoustic resonator (FBAR) or solidly mounted resonator (SMR).

Radio frequency (RF) acoustic wave resonator (AWR) filter circuits and methods. Embodiments essentially de-couple the stopband or notch characteristics of an RF filter from the passband characteristics. Accordingly, the de-coupled parameters can be individually designed to meet the specifications of a particular application. Partially-hybridized or fully-hybridized series-arm and parallel-arm AWR filter building blocks enable de-coupled RF filters having (1) wideband and low insertion loss passbands and (2) wideband deep notches (stopbands) with a specifically placed notch center frequency, without compromising the passband characteristics. The AWR filter building blocks include an inductance L that matches (resonates with) the electrostatic capacitance CO of the corresponding AWR within a desired passband. The resonance and anti-resonance frequencies of the building block AWRs are selected to be spaced apart from the specified passband in order to provide independent stopband or notch characteristics without substantially affecting the passband characteristics.

An acoustic resonator is fabricated by forming a patterned first photoresist mask on a piezoelectric plate at locations of a desired interdigital transducer (IDT) pattern. An etch-stop layer is then deposited on the plate and first photoresist mask. The first photoresist mask is removed to remove parts of the etch-stop and expose the plate. An IDT conductor material is deposited on the etch stop and the exposed plate. A patterned second photoresist mask is then formed on the conductor material at locations of the IDT pattern. The conductor material is then etched over and to the etch-stop to form the IDT pattern which has interleaved fingers on a diaphragm to span a substrate cavity. A portion of the plate and the etch-stop form the diaphragm. The etch-stop and photoresist mask are impervious to this etch. The second photoresist mask is removed to leave the IDT pattern.

A method and structure for a transfer process for an acoustic resonator device. In an example, a bulk acoustic wave resonator (BAWR) with an air reflection cavity is formed. A piezoelectric thin film is grown on a crystalline substrate. A first patterned electrode is deposited on the surface of the piezoelectric film. An etched sacrificial layer is deposited over the first electrode and a planarized support layer is deposited over the sacrificial layer, which is then bonded to a substrate wafer. The crystalline substrate is removed and a second patterned electrode is deposited over a second surface of the film. The sacrificial layer is etched to release the air reflection cavity. Also, a cavity can instead be etched into the support layer prior to bonding with the substrate wafer. Alternatively, a reflector structure can be deposited on the first electrode, replacing the cavity.

A tunable notch filter is disclosed with a first acoustic resonator coupled in series with a first inductive element between a filter input node and a filter output node. A first capacitor is coupled in parallel with the first acoustic resonator and the first inductive element. In at least one embodiment, the first capacitor is configured to have variable capacitance that is electronically tunable by way of an electronic controller. A second acoustic resonator is coupled in series with a second inductive element between the filter output node and a signal ground node. A second capacitor is coupled in parallel with the second inductive element. In at least one embodiment, the second capacitor is electronically tunable. The tunable notch filter is configured to provide a highly selective notch filter response between the filter input node and the filter output node with high attenuation.