Abstract: A package that includes a first filter device and a second filter device coupled to the first filter device. The first filter device includes a first substrate comprising a first piezoelectric material, and a first metal layer coupled to a first surface of the first substrate. The second filter device includes a second substrate comprising a second piezoelectric material, and a second metal layer coupled to a first surface of the first substrate. The package includes a first pillar interconnect configured to be electrically coupled to the first metal layer of the first filter device, where the first pillar interconnect extends through the second filter device. The package further includes a second pillar interconnect configured to be electrically coupled to the second metal layer of the second filter device.

Abstract: Certain aspects of the present disclosure can be implemented in an electroacoustic device. The electroacoustic device generally includes a substrate and one or more resonator structures disposed above the substrate. In some cases, each resonator structure of the one or more resonator structures includes a bulk acoustic resonator, an acoustic mirror disposed below the bulk acoustic resonator, and one or more porous material layers disposed below the acoustic mirror and above the substrate.

Abstract: Electroacoustic devices with a capacitive element and methods for fabricating such electroacoustic devices. An example method includes forming an acoustic device above a first region of a substrate, and forming a capacitive element above a second region of the substrate and adjacent to the acoustic device. The forming of the capacitive element may include forming a protective layer above the substrate where a first portion of the protective layer is above the second region of the substrate and a second portion of the protective layer is above the first region of the substrate, forming a dielectric region above the protective layer, and forming an electrode above the dielectric region. The dielectric region may include a different material than the protective layer.

Abstract: In certain aspects, a chip includes an acoustic resonator, and a mirror under the acoustic resonator. The mirror includes a first plurality of porous silicon layers, and a second plurality of porous silicon layers, wherein the mirror alternates between the first plurality of porous silicon layers and the second plurality of porous silicon layers, and each of the first plurality of porous silicon layers has a higher porosity than each of the second plurality of porous silicon layers.

Abstract: A package that includes a first filter device and a second filter device coupled to the first filter device. The first filter device includes a first substrate comprising a first piezoelectric material, and a first metal layer coupled to a first surface of the first substrate. The second filter device includes a second substrate comprising a second piezoelectric material, and a second metal layer coupled to a first surface of the first substrate. The package includes a first pillar interconnect configured to be electrically coupled to the first metal layer of the first filter device, where the first pillar interconnect extends through the second filter device. The package further includes a second pillar interconnect configured to be electrically coupled to the second metal layer of the second filter device.