Optimization of PGS pattern of transformers/inductors in standard RF BiCMOS technology for RFIC applications

In this paper, a polysilicon PGS (pattern ground shield) pattern, which located exactly inside and outside the spiral metal wires of the RF transformers/ inductors in standard RF BiCMOS technology, was demonstrated. The proposed PGS pattern can effectively improve the drawback, i.e. large parasitics between the transformers/inductors and the PGS pattern, due to no direct overlap between them. The results show a 56.5% (from 6.12 to 9.58) and a 55.7% (from 5.55 to 8.64) increase in Q factor, a 18.2 % (from 0.67 to 0.79) and a 21.4% (from 0.66 to 0.8) increase in G_Amax, a 0.73 dB (from 1.74 dB to 1.01 dB) and a 0.85 dB (from 1.82 dB to 0.97 dB) decrease in NF_min, and a 18.4% (from 0.69 to 0.82) and a 21.2% (from 0.69 to 0.83) increase in magnetic-coupling factor k_im were achieved at 4.2 and 5.2 GHz, respectively, for a bifilar transformer with an overall dimension 230 times 215 mum² in standard BiCMOS process with substrate thickness of 318 mum, and substrate resistance of 10 Omega-cm. Furthermore, compared with the traditional PGS pattern, a 9.9% (from 10.1 GHz to 11.1 GHz) increase in resonant frequency f_SR was achieved. These results means the proposed PGS pattern is very help for RF engineers to design high-performance RF transformers for ultra-low-voltage high-performance transformer-feedback LNAs and VCOs, and other RF-ICs which include transformers for SOC applications