A high-performance micromachined RF monolithic transformer with optimized pattern ground shields (OPGS) for UWB RFIC applications

In this brief, we demonstrate that high-quality-factor and low-power-loss transformers can be obtained if the optimized pattern ground shields (OPGS) of polysilicon is adopted and the CMOS process-compatible backside inductively coupled-plasma (ICP) deep-trench technology is used to selectively remove the silicon underneath the transformers completely. OPGS means that the redundant PGS of a traditional complete PGS, which is right below the spiral metal lines of the transformer, is removed for the purpose of reducing the large parasitic capacitance. The results show that, if the OPGS was adopted and the backside ICP etching was done, a 69.3% and a 253.6% increase in quality factor, a 10.5% and a 14% increase in magnetic-coupling factor (k_Im, a 17.2% and a 51.1% increase in maximum available power gain (G_Amax, and a 0.682- and a 1.79-dB reduction in minimum noise factor (NF_min were achieved at 5 and 8 GHz, respectively, for a bifilar transformer with an overall dimension of 230 × 215 μm².