Wideband filter with resonators and inductors
Aspects of the disclosure are directed to a bandpass filter including a first, second, third and fourth resonators, wherein the second and third resonators are in parallel, wherein the first resonator includes a first and second terminals, wherein the second resonator includes a second resonator top terminal and a second resonator bottom terminal, wherein the third resonator includes a third resonator top terminal and a third resonator bottom terminal, wherein the fourth resonator includes a third terminal and a fourth terminal; wherein the first terminal is coupled to the second resonator top terminal, wherein the second terminal is coupled to the third resonator top terminal, wherein the third terminal is coupled to the third resonator bottom terminal, wherein the fourth terminal is coupled to the second resonator bottom terminal; a first inductor coupled to the first and third terminals; and a second inductor coupled to the second and fourth terminals.
1. A method for forming one or more individual bandpass filters on an integrated circuit (IC), the method comprising:
forming a plurality of 3-dimensional (3D) inductors by performing the following:
(a) positioning a first redistribution layer (RDL) in a wafer layer on the integrated circuit (IC);
(b) placing one or more vertical conductive pillars above the wafer layer;
(c) coating a first passivation layer onto the wafer layer;
(d) plating a second redistribution layer (RDL) over the first passivation layer; and
(e) coating a second passivation layer above the second redistribution layer (RDL); and
assembling a plurality of planar resonator chips onto the wafer layer to electrically connect the plurality of planar resonator chips in parallel to the plurality of 3D inductors, wherein the plurality of planar resonator chips includes an intrinsic passband of a first filter transfer function of less than 5% of a center frequency, and wherein a combination of the plurality of planar resonator chips and the plurality of 3D inductors includes an extrinsic passband of a second filter transfer function of greater than 5% of the center frequency.
2. The method of claim 1 , wherein the wafer layer is a molded wafer layer.
3. The method of claim 1 , wherein the one or more vertical conductive pillars are either copper (Cu) pillars or aluminum (Al) pillars.
4. The method of claim 1 , wherein the wafer layer is a high-resistivity silicon (HRS) wafer, a gallium arsenide (GaAs) wafer or a glass wafer.
5. The method of claim 1 , wherein one of the plurality of resonator chips is a bulk acoustic wave (BAW) resonator.
6. The method of claim 1 , further comprising covering the wafer layer with a molding material to form a molded wafer layer.
7. The method of claim 6 , wherein the molding material is an epoxy.
8. The method of claim 6 , further comprising using a transfer-molding process or a compression molding process for covering the wafer layer with the molding material.
9. The method of claim 6 , further comprising back-grinding the molded wafer layer to expose the one or more vertical conductive pillars.
10. The method of claim 6 , further comprising forming an interconnection layer above the second passivation layer.
11. The method of claim 10 , wherein the interconnection layer includes one or more of a solder ball or a conductive pad.
12. The method of claim 10 , further comprising dicing the integrated circuit (IC) to obtain the one or more individual bandpass filters.