High-Performance On-Chip Transformers With Partial Polysilicon Patterned Ground Shields (PGS)

Abstract

In this brief, we propose the concept of patterned ground shields (PGSs) to improve the performances of RF passive devices, such as inductors and transformers. Partial PGS can be achieved after the redundant PGS of a traditional complete PGS, which is right below the spiral metal lines of an RF passive device, is removed for the purpose of reducing the large parasitic capacitance. A set of test transformers has been implemented to demonstrate the partial PGS. The results show that when the partial PGS was adopted, a 56.5% (from 6.12 to 9.58) and a 55.7% (from 5.55 to 8.64) increase in Q-factor, an 18.2% (from 0.67 to 0.79) and a 21.4% (from 0.66 to 0.8) increase in maximum available power gain (GAmax), and an 18.4% (from 0.69 to 0.82) and a 21.2% (from 0.69 to 0.83) increase in magnetic-coupling factor (kim) were achieved at 4.2 and 5.2 GHz, respectively, for a bifilar transformer with an overall dimension of 230times215 mum2. Furthermore, compared with the transformer with traditional PGS, a 9.9% (from 10.1 to 11.1 GHz) increase in resonant frequency (fSR), a 38% (from 6.94 to 9.58) increase in Q-factor at 4.2 GHz, and a 5.3% (from 0.75 to 0.79) increase in GAmax at 4.2 GHz were obtained. These results demonstrate that the proposed partial PGS is very promising for high-performance RF-ICs applications