Enhancing the Bias and Illumination Stabilities of Aamorphous InGaZnO Thin Film Transistors Using a SiAlNO Passivation Layer

Abstract

This study examines the transfer stability of amorphous InGaZnO thin film transistors, with and without a SiAlNO passivation layer. The passivation layer was magnetron sputtered at ambient temperature followed by an annealing at 320 • C in air, resulting in a stoichiometric (SiAl)(NO) layer. I-V characteristics were measured under positive bias stress (PBS) in O 2 or negative bias illuminated stress (NBIS) in vacuum. Both the PBS and NBIS stabilities of the passivated TFT were substantially improved by reducing the V th of PBS from 8.1 V to 0.1 V and the V th of NBIS from −22.6 V to −0.8 V.Thin film transistors (TFTs) based on amorphous InGaZn oxide (a-IGZO) have been studied extensively for potential application on next-generation flat-panel displays. 1 Although a-IGZO TFTs exhibit superior optical and electric properties, their long-term stability and reliability under bias and/or illumination stresses is a problem that has attracted considerable attention.Previous studies have demonstrated that exposing the active layer of bottom-gate a-IGZO TFTs to the environment causes dramatic shifts in the threshold voltage under either positive bias stresses (PBS) or negative bias illumination stresses (NBIS). 2-5 Oxygen and moisture was identified as a critical factor inducing the threshold voltage instability. 6,7 Accordingly, adopting a passivation layer to protect the active layer of the a-IGZO TFTs is essential. The passivation layers suggested were mostly deposited using the plasma-enhanced chemical vapor deposition (PECVD) process at temperatures between 150 and 350 • C. [8][9][10][11] However, the PECVD technique is challenging because of the tight processing parameters required and the damages created on the surface of the active layer by plasma bombardment. [12][13][14] Magnetron sputtering is a low-energy deposition technique which is the most popular process for depositing the a-IGZO layer and the metal electrodes for TFT fabrication. It is thus desirable to find suitable passivation materials that can also be deposited by using magnetron sputtering. This paper reports the use of a SiAlNO layer to passivate the a-IGZO channel of a bottom-gate TFT. The SiAlNO layer deposited using radio-frequency (RF) magnetron sputtering at room temperature was as thin as 25 nm. Excellent PBS and NBIS stabilities were observed for the passivated TFTs.A bottom-gate coplanar structure was used for preparing the TFTs. The gate layer was composed of Ti (50 nm), Al (200 nm) and Ti (50 nm) layers deposited on glass. PECVD was used to deposit a 300 nm-thick SiO x layer at 300 • C on the patterned gate electrode as the gate dielectric. The source and drain electrodes of the same Ti/Al/Ti structure were deposited and patterned. A 15 μm-wide and 9 μm-long a-IGZO layer was then deposited using RF magnetron sputtering at room temperature, using a compound target with a In, Ga and Zn atomic ratio of 1:1:1. Sputtering was carried out in an Ar + 6.7% O 2 atmosphere at 5 mtorr. After deposition, the TFTs were annealed at 320 • C in air for 1...

Influence of Passivation Layers on Characteristics of High Mobility Amorphous Indium-Zinc-Tin-Oxide Thin-Film Transistors

“…This undesired carrier level would result in a transformation of the IZTO film from a semiconducting state to conducting one. The reason may be attributed to the generation of excess carriers and/or positively-charged traps in channel layer and/or interface between channel and passivation layer when the passivation layer was deposited, which could be explained by the creation of defects in form of oxygen vacancies [9,10]. According to Fig.…”