On-chip mm-wave spherical dielectric resonator bandpass filter

On-chip mm-wave dielectric resonator filters are presented. Low-loss alumina ceramic spheres resonating in a non-radiative mode are used as dielectric resonators. Accurate placement of the resonator spheres is ensured by precise etching of shallow crates in the back-end-of-line low-permittivity dielectric layers atop the semiconductor chip. The spheres are placed in and aligned by these crates. The multi-sphere filter is fed by on-chip microstrip lines. Coupling between microstrip line and sphere can be enhanced by quarter-wave on-chip microstrip resonators. A metallic plate atop the spheres and parallel to the chip holds the spheres in position and prevents radiation. Filters are fabricated on a standard silicon wafer with two metal layers on top, separated by polymer dielectric. Measurements of 3-pole filters at 65 GHz and 95 GHz show an insertion loss of 1.4 dB and 1.0 dB, for a bandwidth at 3 dB insertion loss of 3.5% and 3.9%, respectively.