A high quality factor and low power loss micromachined RF bifilar transformer for UWB RFIC applications

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 (NFmin) were achieved at 5.2 and 10 GHz, respectively, for a bifilar transformer with overall dimension of 240 x 240 mu m(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.