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 processcompatible 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 A max ), 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 µm 2 . Index Terms-Micromachined, optimized pattern ground shield (OPGS), power gain, quality-factor, radio frequency integrated circuits (RFICs), transformer.
In this letter, the authors demonstrate that high quality factor and low power loss transformers can be obtained by using the CMOS process-compatible backside inductively coupled plasma (ICP) deep-trench technology to selectively remove the silicon underneath the transformers. A 62.4% (from 8.99 to 14.6) and a 205.8% (from 8.6 to 26.3) increase in the Q-factor, a 10.3% (from 0.697 to 0.769) and a 30.2% (from 0.652 to 0.849) increase in the maximum available power gain (G Amax ), and a 0.43-(from 1.57 to 1.14 dB) and a 1.15-dB (from 1.86 to 0.71 dB) reduction in the minimum noise figure (NF min ) were achieved at 5.2 and 10 GHz, respectively, for a bifilar transformer with overall dimension of 240 × 240 µm 2 after the backside ICP etching. The values of G Amax of 0.769 and 0.849 are both state-of-the-art results among all reported on-chip bifilar transformers. These results indicate that the backside ICP deep-trench technology is very promising for high-performance radio frequency integrated circuit applications.Index Terms-Inductively coupled plasma (ICP), isolation, power loss, quality factor, radio frequency integrated circuit (RFIC), transformer.
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