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

Abstract

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 <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Amax</sub> ), 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 <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">min </sub> ) were achieved at 5.2 and 10 GHz, respectively, for a bifilar transformer with overall dimension of 240times240 mum <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> after the backside ICP etching. The values of G <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Amax</sub> 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