Improved Specific Contact Resistivity in Amorphous IGZO Transistors Using an ALD-Derived Al-Doped ZnO Interlayer
Joo Hee Jeong, Seong Hun Yoon, Seung Hee Lee, Bong Jin Kuh, Taikyu Kim, Jae Kyeong Jeong
Abstract
This study shows the effects of an ultrathin Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> -doped ZnO (AZO) interlayer inserted between the channel layer and source/drain (S/D) electrodes on the electrical contact properties of amorphous In-Ga-Zn-O (a-IGZO) thin film transistors (TFTs). In particular, Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> -doping ratio-dependent variations in electrical contacts were systemically investigated, which were modulated by adjusting the number of Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> injection cycles during atomic-layer-deposition (ALD) of AZO. Consequently, a-IGZO TFTs using a 1.8-nm-thick AZO interlayer (IL) with an Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> :ZnO sub-cycle ratio of 2:8 showed the lowest specific contact resistivity of (4.2 ± 7.3) × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-7</sup> Ω·cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . This value is three orders of magnitude lower than that of devices without the AZO IL. This substantial improvement could be attributed to the IL’s high electron concentration of 1.9 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">18</sup> /cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> , which greatly lowered the effective Schottky barrier height between IGZO and the S/D electrodes. This enhanced electrical contact led to a field-effect mobility increase from 38.8 ± 0.8 to 45. 3 ± 0.6 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> /Vs.