Influence of UV/Ozone Treatment on Threshold Voltage Modulation in Sol–Gel IGZO Thin‐Film Transistors

Abstract

Abstract Sol–gel indium–gallium–zinc oxide (IGZO) semiconductors are developed as active components of thin‐film transistors (TFTs) because of their high electron mobility, cost‐effective large‐area fabrication, and applicability for flexible substrates. Controlling oxygen vacancies (Vo) in the IGZO semiconductor channel is always problematic for reliable and long‐term operation. Surplus interfacial charges inside the IGZO channel cause negative shifts in threshold voltages (Vth), resulting in depletion‐mode operation and involuntary high current output. The room temperature and rapid (<3 min) modulation of Vth using a novel ultraviolet ozone (UVO) treatment of IGZO layer (In:Ga:Zn = 7:1:2) are reported. Physicochemical and electrical analysis reveals that UVO treatment enables the reduction of Vo and increases MO bonding with invariant contact resistance, resulting in the normalization of Vth close to 0 V and high operational durability under long‐term bias stress. As a proof of concept, this study demonstrates the depletion‐load n‐type inverters comprising depletion and enhancement modes (without & with UVO) on the same substrate that allow high gain (≈10) with a moderate noise margin. This UVO treatment of the active layer is advantageous for the effective modulation of Vth with stable operation under long‐term bias stress and is superior to logic inverters based on single‐mode sol–gel oxide transistors.

Keywords

• indium–gallium–zinc oxide
• inverters
• oxygen vacancy
• solution‐processed thin‐film transistors
• ultraviolet ozone treatment
• V th modulation