Electronic Structure of Low‐Temperature Solution‐Processed Amorphous Metal Oxide Semiconductors for Thin‐Film Transistor Applications

Abstract

The electronic structure of low temperature, solution-processed indium–zinc oxide thin-film transistors is complex and remains insufficiently understood. As commonly observed, high device performance with mobility >1 cm2 V−1 s−1 is achievable after annealing in air above typically 250 °C but performance decreases rapidly when annealing temperatures ≤200 °C are used. Here, the electronic structure of low temperature, solution-processed oxide thin films as a function of annealing temperature and environment using a combination of X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy, and photothermal deflection spectroscopy is investigated. The drop-off in performance at temperatures ≤200 °C to incomplete conversion of metal hydroxide species into the fully coordinated oxide is attributed. The effect of an additional vacuum annealing step, which is beneficial if performed for short times at low temperatures, but leads to catastrophic device failure if performed at too high temperatures or for too long is also investigated. Evidence is found that during vacuum annealing, the workfunction increases and a large concentration of sub-bandgap defect states (re)appears. These results demonstrate that good devices can only be achieved in low temperature, solution-processed oxides if a significant concentration of acceptor states below the conduction band minimum is compensated or passivated by shallow hydrogen and oxygen vacancy-induced donor levels.

Field‐Driven Athermal Activation of Amorphous Metal Oxide Semiconductors for Flexible Programmable Logic Circuits and Neuromorphic Electronics

“…And, the peak at high binding energy (≈532.2 eV) was assigned to the presence of loosely bound oxygens (adsorbed oxygen) associated with the presence of hydroxyl groups on the surface. [33] The percentage area of MOM peak, oxygen vacancy peak, and adsorbed oxygen peak was changed from 74.2% to 41.4%, from 21.2% to 46.3%, and from 4.7% to 12.3%, respectively. XPS analyses revealed an increase in the concentration of oxygen vacancies for thin films that were biased at +1 V for 1200 s, authenticating the current transient measurements and hypothesis of oxygen vacancies modulation using the high electric field present due to EDL at the interface of the ionic liquid and channel.…”

“…The mid‐peak at ≈531.1 eV was assigned to oxygen ions in the oxygen‐deficient region (indicative of oxygen vacancy concentration). And, the peak at high binding energy (≈532.2 eV) was assigned to the presence of loosely bound oxygens (adsorbed oxygen) associated with the presence of hydroxyl groups on the surface . The percentage area of MOM peak, oxygen vacancy peak, and adsorbed oxygen peak was changed from 74.2% to 41.4%, from 21.2% to 46.3%, and from 4.7% to 12.3%, respectively.…”

Effects of Mechanical Stress on Flexible Dual‐Gate a‐InGaZnO Thin‐Film Transistors

“…The structural defects are considered to be deep defects, such as voids. In addition, it is well known there are three kinds of defects related to the oxygen vacancy, namely Vo 2+ near the CBM as the shallow donor, singly ionized Vo + at the mid‐gap and non‐ionized neutral Vo 0 near the VBM as deep localized state . The slightly increased S.S. value indicates an increase in deep states.…”

“…In addition, it is well known there are three kinds of defects related to the oxygen vacancy, namely Vo 2þ near the CBM as the shallow donor, singly ionized Vo þ at the mid-gap and non-ionized neutral Vo 0 near the VBM as deep localized state. [17][18][19][20] The slightly increased S.S. value indicates an increase in deep states. The atoms, withstanding a certain pressure, cause a small dislocation in IGZO or at the IGZO/GI interface, resulting in an increase of Vo 0 and Vo þ .…”

P‐23: Fabrication of Eco‐Friendly Solution‐Processed Indium Zinc Oxide Thin‐Film Transistors through Recycling Based on Photocatalytic Reactions of TiO2

“…), especially solution processes are effective fabrication methods for precise active channel formation in the regions of interest. [3][4][5] Contrary to this advantage, some obstacles such as low electrical properties and necessity of high temperature during annealing process must be overcome to be implemented for next-generation flexible displays. In this study, to improve the problem such as low electrical properties and high annealing temperature, we suggest new method of solution-processed AOSs via photocatalytic reaction of TiO 2 (PRT method).…”