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) x 10(-7) Omega center dot cm(2). 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 x 10(18) /cm(3), 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(2)/Vs.