Bulk acoustic wave resonator device and method of manufacturing thereof
A bulk acoustic wave resonator device comprises bottom and top electrodes ( 120, 360 ). A piezoelectric layer ( 355 ) sandwiched therebetween has a thickness in the active resonator area different from the thickness in the surrounding area. A method of manufacturing the device comprises a bonding of a piezoelectric wafer to a carrier wafer and splitting a portion of the piezoelectric wafer by an ion-cut technique. Different thicknesses of the piezoelectric layer in the active area and the surrounding area are achieved by implanting ions at different depths.
1. A bulk acoustic wave resonator device, comprising:
a bottom electrode and a top electrode; and
a piezoelectric layer having a first portion disposed between the bottom electrode and the top electrode, the first portion having a thickness, the piezoelectric layer having a second portion on at least two sides of the first portion, the second portion having a thickness different from the thickness of the first portion, wherein the piezoelectric layer has a first surface facing the bottom electrode and a second surface opposite the first surface, the second surface including: a first surface portion facing the top electrode; a second surface portion associated with at least a portion of the second portion of the piezoelectric layer; and a transitional surface portion disposed between the first and second surface portions of the second surface, wherein the transitional surface portion has an oblique orientation with regard to the first surface portion and the second surface portion of the second surface.
2. The bulk acoustic wave resonator device according to claim 1 , wherein the thickness of the second portion of the piezoelectric layer is larger than the thickness of the first portion of the piezoelectric layer.
3. The bulk acoustic wave resonator device according to claim 1 , wherein the first portion of the piezoelectric layer is recessed with respect to the second portion.
4. The bulk acoustic wave resonator device according to claim 1 , wherein the piezoelectric layer comprises a monocrystalline piezoelectric material.
5. The bulk acoustic wave resonator device according to claim 1 , further comprising a Bragg mirror arrangement disposed on a carrier substrate, wherein the Bragg mirror arrangement is disposed opposite the bottom electrode from the piezoelectric layer.
6. The bulk acoustic wave resonator device according to claim 5 , wherein the Bragg mirror arrangement comprises a stack of alternate layers of materials having high and low acoustic impedance, respectively.
7. The bulk acoustic wave resonator device according to claim 1 , wherein the piezoelectric layer has a first surface facing the bottom electrode and a second surface opposite the first surface and wherein a layer of an insulating material is disposed over the first surface of the piezoelectric layer surrounding a cavity at the bottom electrode, wherein the bottom electrode faces the cavity.