Acoustic resonators, such as bulk acoustic wave (BAW) resonators, are disclosed that include phase shift structures. Acoustic resonators, including stacked crystal filters (SCFs) and coupled resonator filters (CRFs), may include inverted piezoelectric layers that are configured to provide built-in phase shift capabilities. Circuit topologies that include such SCFs may be provided with simplified structures and reduced loss. Circuit topologies with such CRFs may be provided with more symmetrical electrical connections and improved phase balance over operating frequencies. SCFs with phase shift structures may additionally include spurious mode suppression by modifying piezoelectric coupling profiles within one or more layers. Mode suppression configurations may include structures with one or more inverted polarity piezoelectric layers, one or more non-piezoelectric layers, one or more thicker electrodes of the SCF, and combinations thereof.

Acoustic resonators, such as bulk acoustic wave (BAW) resonators, are disclosed that include mode suppression structures. Acoustic resonators, including stacked crystal filters (SCFs), are disclosed that include spurious mode suppression by modifying a piezoelectric coupling profile within one or more layers of an SCF. Mode suppression configurations may include structures with one or more inverted polarity piezoelectric layers, one or more non-piezoelectric layers, one or more thicker electrodes of the SCF, and combinations thereof. Symmetric input and output electrical response for SCFs with mode suppression configurations may be exhibited by including piezoelectric materials with different electromechanical coupling values and/or by dividing stress profiles differently by configuring different thicknesses for input and output sides of SCFs.

An acoustic filter circuit for noise suppression outside resonance frequency is provided. The acoustic filter circuit includes a first filter branch and a second filter branch. The first filter branch and the second filter branch are both configured to resonate at a resonance frequency to pass a radio frequency (RF) signal, but in opposite phases. The acoustic filter circuit also includes a shunt circuit coupled between the first filter branch and the second filter branch. As discussed in various embodiments in the detailed description, the shunt circuit can be configured to protect the RF signal located inside the resonance frequency and suppress noises located outside the resonance frequency. As such, the acoustic filter circuit can provide improved noise rejection and reduce insertion loss.

A notch filter includes a first inductor coupled between an input node and an output node, a dual-resonator structure coupled between the input node and the output node, and a second inductor coupled between the dual-resonator structure and ground, and a bandpass filter includes a capacitor coupled between an input node and an output node, and a dual-resonator structure coupled between the input node, the output node, and ground.

Acoustic resonators, such as bulk acoustic wave (BAW) resonators and, in particular, acoustic resonators including stacked crystal filters (SCFs) are disclosed. SCF structures are disclosed with increased spurious free ranges by providing various arrangements of acoustically soft materials in one or more locations that correspond with high stress regions of one or more modes. For SCFs operating in first order modes, relative amounts of acoustically soft materials within shared electrodes may be increased. One or more additional layers of acoustically soft materials may also be added to SCF structures near shared electrodes. Accordingly, SCFs may be provided with increased frequency spreads between first order modes and second order modes.

In accordance with an embodiment, a method of operating an RF system includes filtering a wideband RF signal using an adjustable center frequency bandpass filter to produce a filtered RF signal; amplifying the filtered RF signal to produce an amplified RF signal; and band stop filtering the amplified RF signal to produce a band stopped RF signal.

A method of fabricating an FBAR filter device including an array of resonators, each resonator comprising a single crystal piezoelectric film sandwiched between a first metal electrode and a second metal electrode, wherein the first electrode is supported by a support membrane over an air cavity, the air cavity embedded in a silicon dioxide layer over a silicon handle, with through-silicon via holes through the silicon handle and into the air cavity, the side walls of said air cavity in the silicon dioxide layer being defined by perimeter trenches that are resistant to a silicon oxide etchant.

An acoustic wave device includes: a piezoelectric film made of an aluminum nitride film containing a divalent element and a tetravalent element, or a divalent element and a pentavalent element; and an electrode that excites an acoustic wave propagating through the piezoelectric film.

A filter may include a plurality of bulk acoustic wave resonators including one or more series resonators and one or more shunt resonators formed by a first electrode, a piezoelectric layer, and a second electrode sequentially stacked on a substrate, a cap accommodating the plurality of bulk acoustic wave resonators therein, and one or more switches provided on the cap.

A filter includes: series resonators connected to each other in series; shunt resonators connected to first nodes between some of the series resonators; and a variable capacitor connected to a second node between some of the series resonators, and forming a pole configured to suppress harmonics.