Acoustic filter devices and methods of making filter devices. An acoustic filter device includes a transversely-excited film bulk acoustic resonator (XBAR) including a plurality of sub-resonators and conductors to connect the plurality of sub-resonators in parallel between a first node and a second node. The conductors are configured such that a path length from the first node to the second node is effectively the same through each of the plurality of sub-resonators.

An elastic wave device includes a piezoelectric layer including a first main surface and a second main surface facing the first main surface, an acoustically reflective layer stacked on the first main surface of the piezoelectric layer, an excitation electrode disposed on the piezoelectric layer, and a support layer. The acoustically reflective layer overlaps at least the excitation electrode in a plan view of the piezoelectric layer from the side of the second main surface. The support layer surrounds the acoustically reflective layer in a plan view of the piezoelectric layer from the side of the second main surface.

An elastic wave device includes a supporting substrate, an acoustic multilayer film on the supporting substrate, a piezoelectric substrate on the acoustic multilayer film, and an IDT electrode on the piezoelectric substrate. The acoustic multilayer film includes at least four acoustic impedance layers. The at least four acoustic impedance layers include at least one low acoustic impedance layer and at least one high acoustic impedance layer having an acoustic impedance higher than the low acoustic impedance layer. The elastic wave device further includes a bonding layer provided at any position in a range of from inside the acoustic impedance layer, which is the fourth acoustic impedance layer from the piezoelectric substrate side towards the supporting substrate side, to an interface between the acoustic multilayer film and the supporting substrate.

A BAW device including a substrate, and a piezoelectric element formed on a front surface of the substrate is provided. The substrate is provided on a back surface side thereof with an acoustic wave diffusion region including a recess formed by partially melting a back surface of the substrate.

An RF diplexer circuit device using modified lattice, lattice, and ladder circuit topologies. The diplexer can include a pair of filter circuits, each with a plurality of series resonator devices and shunt resonator devices. In the ladder topology, the series resonator devices are connected in series while shunt resonator devices are coupled in parallel to the nodes between the resonator devices. In the lattice topology, a top and a bottom serial configurations each includes a plurality of series resonator devices, and a pair of shunt resonators is cross-coupled between each pair of a top serial configuration resonator and a bottom serial configuration resonator. The modified lattice topology adds baluns or inductor devices between top and bottom nodes of the top and bottom serial configurations of the lattice configuration. A multiplexing device or inductor device can be configured to select between the signals coming through the first and second filter circuits.

An RF diplexer circuit device using modified lattice, lattice, and ladder circuit topologies. The diplexer can include a pair of filter circuits, each with a plurality of series resonator devices and shunt resonator devices. In the ladder topology, the series resonator devices are connected in series while shunt resonator devices are coupled in parallel to the nodes between the resonator devices. In the lattice topology, a top and a bottom serial configurations each includes a plurality of series resonator devices, and a pair of shunt resonators is cross-coupled between each pair of a top serial configuration resonator and a bottom serial configuration resonator. The modified lattice topology adds baluns or inductor devices between top and bottom nodes of the top and bottom serial configurations of the lattice configuration. A multiplexing device or inductor device can be configured to select between the signals coming through the first and second filter circuits.

A back side of a diamond or other substrate is thinned using plasma etches and a mask situated away from the back side by a spacer having a thickness between 50 μm and 250 μm. Typically, a combined RIE/ICP etch is used to thin the substrate from 20-40 μm to less than 1 μm. For applications in which color centers are implanted or otherwise situated on a front side of the diamond substrate, after thinning, a soft graded etch is applied to reduce color center linewidth, particularly for nitrogen vacancy (NV) color centers.

A bulk-acoustic wave resonator includes: a substrate; and a resonator including a first electrode, a piezoelectric layer, and a second electrode sequentially stacked on the substrate. The piezoelectric layer is formed of aluminum nitride (AlN) containing scandium (Sc), the content of scandium in the piezoelectric layer is 10 wt % to 25 wt %, and the piezoelectric layer has a leakage current density of 1 μA/cm2 or less.

A bulk acoustic wave (BAW) structure includes a single crystal piezoelectric material layer, a first electrode, a second electrode and an acoustic reflector. The first and second electrodes are respectively located on a first surface and a second surface of the single crystal piezoelectric material layer. The area of the second electrode is greater than or equal to that of the second surface of the single crystal piezoelectric material layer, and the contact area of the single crystal piezoelectric material layer with the second electrode is equal to the area of the second surface of the single crystal piezoelectric material layer. The acoustic reflector is disposed on a surface of the first electrode.

A piezoelectric resonator can include a substrate and a piezoelectric aluminum nitride layer on the substrate, where the piezoelectric aluminum nitride layer is doped with a dopant selected from the group consisting of Si, Mg, Ge, C, Sc and/or Fe at a respective level sufficient to induce a stress in the piezoelectric aluminum nitride layer in a range between about 150 MPa compressive stress and about 300 MPa tensile stress.