Improved Specific Contact Resistivity in Amorphous IGZO Transistors using an ALD-Derived Al-Doped ZnO Interlayer

Abstract

This study shows the effects of an ultrathin Al2O3-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, Al2O3-doping ratio-dependent variations in electrical contacts were systemically investigated, which were modulated by adjusting the number of Al2O3 injection cycles during atomic-layer-deposition (ALD) of AZO. Consequently, a-IGZO TFTs using a 1.8-nm-thick AZO interlayer (IL) with an Al2O3:ZnO sub-cycle ratio of 2:8 showed the lowest specific contact resistivity of (4.2 ± 7.3) × 10-7 Ω·cm2. 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 × 1018 /cm3, 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 cm2/Vs.