Modified Stoichiometry in Homogeneous Indium–Zinc Oxide System as Vertically Graded Oxygen Deficiencies by Controlling Redox Reactions

Abstract

several issues such as reliability and device performance. [ 4 ] To solve these problems, research has focused on material engineering, [ 5 ] post treatment engineering, [ 6,7 ] and structural engineering [ 8,9 ] approaches. However, the optimal structure for AOS TFTs has not been established, whereas amorphous and polycrystalline Si TFTs are generally manufactured with bottom-and top-gate structures, respectively.In AOS TFTs with a top-gate structure, the back-channel is not exposed to the environment because the gate dielectric acts as a passivation layer that prevents interaction with ambient gases. [ 10 ] Furthermore, the top-gate structure effectively reduces resistance-capacitance (RC) delay by decreasing overlap of the source/drain and gate electrodes via a self-alignment process. [ 11 ] Hence, the top-gate structure has also been suggested for the AOS TFT back-plane technology for high resolution and large displays. However, the top-gate structure is relatively diffi cult to manufacture using current production lines that use conventional fabrication processes designed for amorphous Si TFTs; many process steps are required. Although AOS TFTs with a bottom-gate structure could be manufactured more easily with existing processes, an additional etch stopper layer must be deposited to prevent chemical damage from occurring during the metal etching process, when the back-channel etch structure is employed. [ 12 ] Furthermore, a true passivation layer is needed because of the exposure of the back-channel to the external environment, [ 12,13 ] and the overlap between the source/ drain and gate electrodes causes poor device performance. [ 14 ] For these reasons, a hetero multi-stacked structure has recently been suggested. [ 8,9 ] This structure could improve the electrical characteristics and enable self passivation, without an additional passivation layer, by depositing channel material repeatedly during channel layer fabrication. In a hetero multi-stack structure, the front-channel has high conductivity and the backchannel has low conductivity because each layer leads to a moderate current fl ow and self passivation, respectively. However, a hetero multi-stack structure has several issues: the presence of interfaces in the middle of the channel layer, complicated diffusion effects among the channel layers, and high fabrication cost because of the need to use several depositions of rare materialsThe present study suggests a way to improve electrical characteristics and stabilities by forming a different stoichiometry in a homogeneous system without using a multiple deposition process. Post treatment by sequential pressure annealing (SPA) of a homogeneous indium-zinc oxide system is carried out to fabricate vertically graded oxygen defi ciencies via redox reactions. The SPA treatment consists of several steps. First, hydrogen pressure annealing is performed to chemically expedite the reduction reaction of weak chemical bonds in the overall channel region and thereby make the material highly conducting. Second, o...

Synergistic effects of water addition and step heating on the formation of solution-processed zinc tin oxide thin films: towards high-mobility polycrystalline transistors

“…During PBS test, the applied constant V G and V DS were 5.0 V and 2.5 V, respectively. A parallel shift of transfer plot was observed, and the positive shift of threshold voltage reached 2.80 V after 3600 s. The shift of threshold voltage in our case could be mainly ascribed to the following two reasons: (1) trapping of carriers at the dielectric/semiconductor interface; (2) absorbed ambient gases on back channel region [49,50]. To further address these instability issues, our works focusing on removing mobile ions in the dielectric layer and passivating back channel are under progress.…”

Highly stable low-temperature aqueous solution-processed oxide thin-film transistors by the hydrogen injection and oxidation method

“…In previous annealing processes related to hydrogen, hydrogen increases the carrier concentration via the formation of donor states and oxygen vacancies by a reduction reaction with weak chemical bonds [34]. We considered that the reduction reaction of hydrogen is effective at decomposing residual species in lowtemperature solution-processed oxide films.…”

“…Different ligand-based precursor systems [27], a selection of solvent techniques using water-induced synthesis [28,29], and combustion precursors have been proposed [23]. Various methods associated with processing, such as UV-ozone treatment, deep-ultraviolet light irradiation [30,31], high-pressure annealing [32], oxygen plasma treatment [33], and redox reactions using sequential hydrogen and oxygen pressure annealing [34] have also been proposed. In previous research, however, mostly binary (InO x , ZnO) or ternary oxide semiconductors (IZO, ZTO) that exhibit relatively higher mobility due to lower decomposition characteristics have been investigated.…”

Atomic Structure Evaluation of Solution-Processed a-IZO Films and Electrical Behavior of a-IZO TFTs

“…Eventually, the electrical properties of AOS TFTs are significantly affected by the bonding structure and composition ratio of the atoms constituting the semiconductor material [ 24 , 25 ]. AOS films manufactured by vacuum deposition form a relatively uniform amorphous random-network structure, whereas solution-processed AOS films are accompanied by many impurities/defects because the metal oxide is chemically rearranged while the solvent/by-product is removed [ 26 ]. Thus, the bonding structure/composition of the AOS film may vary depending on the annealing conditions, including the precursors, solvents, and catalysts used.…”