Thin film bulk acoustic wave resonator and filter, and radio frequency module using them
A thin film bulk acoustic wave (BAW) resonator structure and filter which can be fabricated by inexpensive manufacturing techniques and in smaller size than conventional such products are to be provided. The BAW resonator structure and filter have a substrate, a first BAW resonator placed over the substrate, an acoustic reflection layer placed over the first BAW resonator and a second BAW resonator placed over the acoustic reflection layer, and the acoustic reflection layer is electroconductive. Herein, the acoustic reflection layer constitutes a first electrode, and this first electrode electrically connects and acoustically separates the first BAW resonator and the second BAW resonator.
1. A thin film bulk acoustic wave resonator structure comprising:
a substrate;
at least one acoustic reflection layer;
a plurality of thin film bulk acoustic wave resonators stacked with the acoustic reflection layer in-between and disposed over the substrate;
an input terminal; and
an output terminal,
wherein each of the thin film bulk acoustic wave resonators has a piezoelectric layer and a pair of electrodes stacked with the piezoelectric layer in-between,
wherein the acoustic reflection layer is electroconductive, and two of the thin film bulk acoustic wave resonators stacked with the acoustic reflection layer in-between are electrically connected via the acoustic reflection layer,
wherein at least one of the thin film bulk acoustic wave resonators is electrically connected between the input terminal and the output terminal via the acoustic reflection layer, and
wherein the acoustic reflection layer is a Bragg reflection layer which includes a combination of a high-impedance metal layer and a low-impedance metal layer.
2. A thin film bulk acoustic wave resonator structure comprising:
a substrate;
at least one acoustic reflection layer;
a plurality of thin film bulk acoustic wave resonators stacked with the acoustic reflection layer in-between and disposed over the substrate;
an input terminal; and
an output terminal,
wherein each of the thin film bulk acoustic wave resonators has a piezoelectric layer and a pair of electrodes stacked with the piezoelectric layer in-between,
wherein the acoustic reflection layer is electroconductive, and two of the thin film bulk acoustic wave resonators stacked with the acoustic reflection layer in-between are electrically connected via the acoustic reflection layer,
wherein at least one of the thin film bulk acoustic wave resonators is electrically connected between the input terminal and the output terminal via the acoustic reflection layer,
wherein the plurality of thin film bulk acoustic wave resonators include
a first thin film bulk acoustic wave resonator stacked over the substrate, the acoustic reflection layer being stacked over the first thin film bulk acoustic wave resonator, and
a second thin film bulk acoustic wave resonator stacked over the acoustic reflection layer,
wherein the first thin film bulk acoustic wave resonator comprises
a first piezoelectric layer, and
a first metal layer and a second metal layer respectively stacked underneath the lower face and over the upper face of the first piezoelectric layer,
wherein the second thin film bulk acoustic wave resonator comprises
a second piezoelectric layer, and
a third metal layer and a fourth metal layer respectively stacked underneath the lower face and over the upper face of the second piezoelectric layer,
wherein a stacked conductor including the acoustic reflection layer, the second metal layer and the third metal layer functions as a first electrode, the first metal layer functions as a second electrode, and the fourth metal layer functions as a third electrode,
wherein the first thin film bulk acoustic wave resonator and the second thin film bulk acoustic wave resonator are electrically connected by the first electrode, and
wherein the substrate has a cavity which opens in the face over which the first thin film bulk acoustic wave resonator is stacked, and the second electrode has a part overlapping with the cavity.