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 method of manufacturing a bulk acoustic wave resonator, comprising the steps of:
providing a wafer comprising a piezoelectric layer;
depositing a metal material on the wafer and structuring the metal material to form a bottom electrode;
forming a dielectric layer of an insulating material on the wafer and on the bottom electrode;
implanting ions through the dielectric layer into the piezoelectric layer of the wafer;
providing a workpiece comprising at least one layer comprising silicon;
bonding the dielectric layer of the wafer to the at least one layer of the workpiece;
splitting the piezoelectric layer of the wafer and removing a split portion of the piezoelectric layer such that a first portion of the piezoelectric layer has a first thickness that is different from a second thickness of a second portion of the piezoelectric layer; and
forming a top electrode on the split surface of the piezoelectric layer of the wafer opposite the bottom electrode.
2 . The method according to claim 1 , wherein the step of implanting ions comprises implanting the ions into the piezoelectric layer of the wafer at a first depth in a region of the bottom electrode and at a second depth in the region surrounding the bottom electrode, wherein the second depth is greater than the first depth.
3 . The method according to claim 2 , wherein the step of splitting the piezoelectric layer comprises splitting the piezoelectric layer along the region of the implanted ions at the first and second depths.
4 . The method according to claim 1 , wherein the step of providing a workpiece comprises providing the workpiece with a Bragg mirror arrangement formed on a carrier substrate.
5 . The method according to claim 1 , further comprising removing the dielectric layer of an insulating material and the at least one layer of the workpiece in a region opposite the bottom electrode to obtain a cavity at the bottom electrode.
6 . The method according to claim 1 , wherein the piezoelectric layer of the wafer is a monocrystalline piezoelectric material, wherein the dielectric layer of an insulating material of the wafer and the at least one layer of the workpiece each comprise a layer of silicon dioxide and wherein the step of bonding comprises bonding the layers of silicon dioxide of the wafer and of the workpiece together.
7 . The method according to claim 1 , wherein the second portion of the piezoelectric layer is on at least two sides of the first portion of the piezoelectric layer.
8 . The method according to claim 1 , wherein the piezoelectric layer has a first surface facing the bottom electrode and a second surface opposite the first surface.
9 . The method according to claim 8 , wherein the second surface of the piezoelectric layer includes:
a first surface portion facing the top electrode; and
a second surface portion associated with at least a portion of the second portion of the piezoelectric layer.
10 . The method according to claim 9 , wherein the second surface of the piezoelectric layer includes a transitional surface portion disposed between the first and second surface portions of the second surface.
11 . The method according to claim 10 , 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.
12 . A method of manufacturing a bulk acoustic wave resonator, comprising the steps of:
providing a wafer comprising a piezoelectric layer;
depositing a mask material on the wafer;
implanting ions into the piezoelectric layer of the wafer;
removing the mask material;
depositing a metal material on the wafer and structuring the metal material to form a bottom electrode;
forming a dielectric layer of an insulating material on the wafer and on the bottom electrode;
providing a workpiece comprising at least one layer comprising silicon;
bonding the dielectric layer of the wafer to the at least one layer of the workpiece;
splitting the piezoelectric layer of the wafer and removing a split portion of the piezoelectric layer such that a first portion of the piezoelectric layer has a first thickness that is different from a second thickness of a second portion of the piezoelectric layer; and
forming a top electrode on the split surface of the piezoelectric layer of the wafer opposite the bottom electrode.
13 . The method according to claim 12 , wherein the second portion of the piezoelectric layer is on at least two sides of the first portion of the piezoelectric layer.
14 . The method according to claim 12 , wherein the piezoelectric layer has a first surface facing the bottom electrode and a second surface opposite the first surface.
15 . The method according to claim 14 , wherein the second surface of the piezoelectric layer includes:
a first surface portion facing the top electrode; and
a second surface portion associated with at least a portion of the second portion of the piezoelectric layer.
16 . The method according to claim 15 , wherein the second surface of the piezoelectric layer includes a transitional surface portion disposed between the first and second surface portions of the second surface.
17 . The method according to claim 16 , 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.