Abstract: The present disclosure relates to a wafer-level packaged (WLP) bulk acoustic wave (BAW) device, which includes a BAW resonator, a WLP enclosure, and an interconnect. The BAW resonator includes a piezoelectric layer with an opening, a bottom electrode lead underneath the opening, and an interface structure extending over the opening and in contact with the bottom electrode lead through the opening. The WLP enclosure includes a cap, an outer wall that extends from the cap toward the piezoelectric layer to form a cavity, and a through-WLP via that extends through the cap and the outer wall and is vertically aligned with the opening of the piezoelectric layer. A portion of the interface structure is exposed to the through-WLP via. The interconnect is formed in the through-WLP via and electrically connected to the interface structure.

Abstract: Acoustic filtering circuitry includes an input node, an output node, a signal transmission path, a series acoustic resonator, and a shunt acoustic resonator. The signal transmission path is between the input node and the output node. The series acoustic resonator is coupled between the input node and the output node in the signal transmission path. Further, a temperature coefficient of frequency (TCF) of a parallel resonance frequency of the series acoustic resonator is positive. The shunt acoustic resonator is coupled between the signal transmission path and ground. Further, a TCF of a series resonance frequency of the shunt acoustic resonator is negative. By providing the TCF of the series acoustic resonator and the shunt acoustic resonator in this manner, self-heating of the acoustic filtering circuitry may be significantly reduced, thereby improving the performance of the acoustic filtering circuitry.

Abstract: Acoustic filtering circuitry includes an input node, an output node, a signal transmission path, a series acoustic resonator, and a shunt acoustic resonator. The signal transmission path is between the input node and the output node. The series acoustic resonator is coupled between the input node and the output node in the signal transmission path. Further, a temperature coefficient of frequency (TCF) of a parallel resonance frequency of the series acoustic resonator is positive. The shunt acoustic resonator is coupled between the signal transmission path and ground. Further, a TCF of a series resonance frequency of the shunt acoustic resonator is negative. By providing the TCF of the series acoustic resonator and the shunt acoustic resonator in this manner, self-heating of the acoustic filtering circuitry may be significantly reduced, thereby improving the performance of the acoustic filtering circuitry.

Abstract: The present disclosure relates to a wafer-level packaged (WLP) bulk acoustic wave (BAW) device, which includes a BAW resonator, a WLP enclosure, and an interconnect. The BAW resonator includes a piezoelectric layer with an opening, a bottom electrode lead underneath the opening, and an interface structure extending over the opening and in contact with the bottom electrode lead through the opening. The WLP enclosure includes a cap, an outer wall that extends from the cap toward the piezoelectric layer to form a cavity, and a through-WLP via that extends through the cap and the outer wall and is vertically aligned with the opening of the piezoelectric layer. A portion of the interface structure is exposed to the through-WLP via. The interconnect is formed in the through-WLP via and electrically connected to the interface structure.

Abstract: Embodiments of a Bulk Acoustic Wave (BAW) resonator having a high quality factor (Q) and methods of fabrication thereof are disclosed. In some embodiments, a BAW resonator includes a piezoelectric layer, a first electrode on a first surface of the piezoelectric layer, and a second multi-layer electrode on a second surface of the piezoelectric layer opposite the first electrode on the first surface of the piezoelectric layer. In addition, the BAW resonator includes a Border (BO) ring positioned within the second multi-layer electrode around a periphery of an active region of the BAW resonator. The BO ring is either at a position within the second multi-layer electrode between two adjacent layers of the second multi-layer electrode or at a position within the second multi-layer electrode that is adjacent to the piezoelectric layer. In this manner, the quality factor (Q) of the BAW resonator is improved.