Positive gate bias instability alleviated by self-passivation effect in amorphous InGaZnO thin-film transistors

GongTan Li, Bo-Ru Yang, Chuan Liu, Chia Yu Lee, Chih-Yuan Tseng, Chang-Cheng Lo, Alan Lien, Shaozhi Deng, Han-Ping Shieh, Ningsheng Xu

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8 Scopus citations

Abstract

The threshold voltage shift (Delta Vth) under positive gate bias stress (PGBS), generally found in amorphous InGaZnO thin-film transistors (a-IGZO TFTs), has usually been suppressed by external passivation layers. We report it can also be alleviated by the self-passivation effect of the active layer, where moderately increasing the active layer thickness (d(s)) reduces Delta Vth by 82% in SiOx-passivated a-IGZO TFTs. Our experiments in conjunction with simulations show that the instability of V-th comes from ambient factors at the back channel. Larger d(s) results in lower carrier concentrations at the back channel (N-back), fewer diffusive ions affecting the front channel, and much more stable operations under PGBS. The optimal thickness of an IGZO film simultaneously obtaining a small Delta V-th, near-zero Vth, and sharp sub-threshold swing is about 80-90 nm, thicker than those usually adopted. The self-passivation effect combined with the externally deposited passivation layer can improve the overall device reliability.
Original languageEnglish
Article number475107
JournalJournal Physics D: Applied Physics
Volume48
Issue number47
DOIs
StatePublished - 2 Dec 2015

Keywords

  • InGaZnO; reliability; self-passivation; thin-film transistor; positive gate bias stress
  • CHANNEL THICKNESS

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