High Mobility and Photo‐Bias Stable Metal Oxide Thin‐Film Transistors Engineered by Gradient Doping

Abstract

Doping of oxygen‐deficient binder is an efficient way to alleviate the photo‐bias instability issue of oxide thin‐film transistors (TFTs). However, almost all dopants are working as electron suppressors and degrading mobility. Here we report an effective three‐level O‐anti|O|O‐N (OI|OII|N) gradient doping solution to overcome the adverse mobility‐stability trade‐off in N‐doped InGaZnO (IGZO:N) TFTs. 100 nm‐thick IGZO:OI|IGZO:OII|IGZO:N (IGZO:OI|OII|N) junctionless channel layers are fabricated by varying the partial pressures of oxygen and nitrogen doping gases. Best balance between improved performance and negligible degraded stability is first engineered by reducing the back‐channel IGZO:N depth close to the theoretical diffusion length of photo‐excited holes and forming two‐level graded IGZO:OII|N (40 nm|60 nm) TFTs. Much improved performance and comparable stability are further induced by incorporating ~1.5 nm percolation conduct IGZO:OI at the front‐channel to enhance accumulation. The three‐level graded IGZO:OI|OII|N TFTs exhibit high mobility (34.25 cm2 V−1 s−1) and good photo‐bias stability (∆Vth = −0.85 V@10 000 cd m−2, 3.0 h), which are 2~5‐fold superior to those of the controlled two‐level graded IGZO:OI|N TFTs, IGZO:OII|N TFTs, and homogeneous IGZO:OII TFTs, IGZO:N TFTs. The fabrication of high mobility and photo‐bias stable IGZO TFTs paves the way to future high‐performance oxide electronics.

Investigation on Atomic Bonding Structure of Solution-Processed Indium-Zinc-Oxide Semiconductors According to Doped Indium Content and Its Effects on the Transistor Performance

“…With increasing interest in solution-processed oxide semiconductors, TFTs with high electrical mobilities of over 30 cm·V −1 s −1 and low driving voltages of less than 2 V have been reported [ 10 , 11 ]. Moreover, studies on process developments such as atomic composition ratio, doping, and chemical treatment have remarkably improved TFT performance [ 12 , 13 ].…”

“…In these cases, the morphological and film thickness characteristics play a more decisive role, depending on the crystal structure. Although studies on the solution-processed IZO TFT have focused on the electrical improvement [ 10 , 11 , 12 , 13 ] in solution-processed oxide semiconductors, because the atomic bonding structure is rearranged via processes such as solvent evaporation, thermal decomposition, and condensation reactions, the crystallinity is further influenced by the reaction pathways [ 30 ]. Therefore, to discuss a one-step forward analysis such as bias-stress mechanisms of TFT, it is essential to understand the trap state distribution and charge transport mechanism based on the atomic bonding structure; however, such an understanding has not been adequately investigated.…”

Illuminating Trap Density Trends in Amorphous Oxide Semiconductors with Ultrabroadband Photoconduction

“…Exploring nonstoichiometric compositions of a-IGZO (with greater or lesser relative concentrations of the In, Ga, and/or Zn metal constituents compared to 111 a-IGZO) is an active area of research for improving upon a-IGZO TFT characteristics such as field effect mobility. [40][41][42][43][44][45] These efforts are sometimes linked to the deposition of bilayer [46][47][48][49][50] (or trilayer) [51][52][53] active channels. These bilayer TFTs often contain a stoichiometric or near-stoichiometric stability layer [43] with a boost layer that is richer in certain constituent elements such as In, [45,49] doped with metals such as Ti, [54] or composed of a conductive material such as ITO [55] ) intended to enhance the TFT electrical performance.…”

A chemically treated IGZO-based highly visible-blind UV phototransistor with suppression of the persistent photoconductivity effect

“…15 It has been reported that the electronegativity difference between nitrogen (N, 3.04) and oxygen (O, 3.44) results in a higher binding energy of the In 3d, Ga 2p, and Zn 2p spectra when binding nitrogen with the corresponding metal. 63 A more detailed discussion on this will be presented later in this paper.…”