High Performance Gigahertz Flexible Radio Frequency Transistors with Extreme Bending Conditions

Abstract

In this work, ultrathin indium tin oxide (ITO) radio frequency (RF) transistors have been demonstrated for the first time, where inverted gate structure are used with a flexible polyimide substrate using magnetron sputtering at a thermal budget below 200 °C. The 160 nm channel length device exhibits excellent DC characteristics, including mobility of 26 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> /V·s and an I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</sub> /I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">off</sub> ratio of 6.6×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">8</sup> . A record-high extrinsic cut-off frequency (f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</sub> ) of 2.1 GHz and an extrinsic maximum oscillation frequency (f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</sub> ) of 3.7 GHz have also been obtained, which are more than one order of magnitude higher than previous results on flexible substrate. A high conversion gain of -20.9 dB has been achieved for the gigahertz frequency mixer based on flexible ITO RF transistor. Moreover, the stability of DC and RF performance under different bending conditions up to 50,000 bending cycles or down to 1 mm bending radius are studied without device failure.