Improvement of Thermal and Environmental Stabilities of Short Channel Coplanar Amorphous InGaZnO Thin-Film Transistors by Introducing Amorphous ZrAlO_x Interlayer

The short channel coplanar amorphous indium gallium zinc oxide (a-IGZO) thin-film transistor (TFT) is reported by introducing a ZrAlO_x (ZAO) interlayer deposited by spray pyrolysis at the substrate temperature of 350 °C. The atomic ratio (at. %) of In:Ga:Zn:O is 1:2.5:1.2:5.2 in the a-IGZO film deposited by sputtering. The a-IGZO TFT with ZAO layer with 0.87 μm channel length exhibits the field-effect mobility of 6.44 cm² V⁻¹ s⁻¹, the threshold voltage of −2.16 V, and on/off current ratio of 7.6 × 10⁷. It is found from the X-ray photoelectron spectroscopy depth profile and high-resolution transmission electron microscope analysis that some Zr atoms diffuse into the a-IGZO underlayer. The formation of Zr O bonds on a-IGZO surface region reduces the carrier concentration in the a-IGZO TFT offset region, between source/drain contact and the channel, and blocks the carrier diffusion into the channel. This reduces the field-effect mobility of 10 μm channel length TFT from 21.86 to 14.01 cm² V⁻¹ s⁻¹, but the ZAO layer protects the a-IGZO from the diffusion of H₂O and O₂. As a result, 0.87 μm TFT shows high on/off current ratio and stable under 85 °C and 85% relative humidity test for 2 days.