Dual Active Layer Mg-Doped InZnO Thin-Film Transistors with Ultra-Low Indium Doping

Dual active layer (DAL) Mg-doped InZnO thin film transistors (TFTs) are fabricated with ultralow usage of the rare metal In. Optimized DAL MIZO TFTs are obtained by adjusting In-doping, Mg content, and the thickness of two active layers. Compared with conventional single active layer TFTs, the DAL MIZO TFTs showed improved performance in terms of carrier mobility, threshold voltage (V <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</inf> ), ON-state current (I <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ON</inf> ), and leakage current (I <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">OFF</inf> ). The front channel near the gate oxide has a lower Mg-doping and a higher In-doping compared with that of back channel, providing a high carrier concentration (n <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">e</inf> ) to increase I <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ON</inf> . The back channel has a higher Mg-doping and a lower In-doping, providing a low n <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">e</inf> to suppress I <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">OFF</inf> . Furthermore, the heterojunction potential barrier formed between the two channel layers also helps to suppress the I <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">OFF</inf> of the DAL TFTs.