Miniaturized millimeter-wave narrow bandpass filter in 0.18 μm CMOS technology using spiral inductors and inter digital capacitors

In this paper, first, we demonstrate that millimeter wave bandpass filters at 60 GHz can be realized using miniaturized lumped capacitors and spiral inductors instead of traditional microstrip transmission line structures. Second, at these frequencies, inter digital capacitors are shown to have a much higher quality factor (Q) than high density metal- insulator-metal (MIM) capacitors. All the circuit elements are layout optimized using electro-magnetic tools which resulted in Qs ≥ 15 over the frequency band of operation. The filter is fabricated in 0.18 μm high resistivity RF silicon on insulator CMOS technology with a top thick metal built especially for the design of low loss inductors. The filter has a center frequency of 51 GHz and 3dB bandwidth of 9 GHz, with a fractional bandwidth of 17.6% and a loaded Q of 5.6. The chip area of the filter is 160 μm × 135 μm excluding the pads. Since the proposed filter implementation does not require MIM processing, significant process cost savings can be achieved when compared to existing lumped filter implementations.