Sungkeun Baang

Understanding the density of state (DOS) distribution in solution-processed indium-zinc-oxide (IZO) thin-film transistors (TFTs) is crucial for addressing electrical instability. This paper presents quantitative calculations of the acceptor-like state distribution of solution-processed IZO TFTs using thermal energy analysis. To extract the acceptor-like state distribution, the electrical characteristics of IZO TFTs with various In molarity ratios were analyzed with respect to temperature. An Arrhenius plot was used to determine electrical parameters such as the activation energy, flat band energy, and flat band voltage. Two calculation methods, the simplified charge approximation and the Meyer–Neldel (MN) rule-based carrier–surface potential field-effect analysis, were proposed to estimate the acceptor-like state distribution. The simplified charge approximation established the modeling of acceptor-like states using the charge–voltage relationship. The MN rule-based field-effect analysis validated the DOS distribution through the carrier–surface potential relationship. In addition, this study introduces practical and effective approaches for determining the DOS distribution of solution-processed IZO semiconductors based on the In molarity ratio. The profiles of the acceptor-like state distribution provide insights into the electrical behavior depending on the doping concentration of the solution-processed IZO semiconductors.

The atomic composition ratio of solution-processed oxide semiconductors is crucial in controlling the electrical performance of thin-film transistors (TFTs) because the crystallinity and defects of the random network structure of oxide semiconductors change critically with respect to the atomic composition ratio. Herein, the relationship between the film properties of nitrate precursor-based indium-zinc-oxide (IZO) semiconductors and electrical performance of solution-processed IZO TFTs with respect to the In molar ratio was investigated. The thickness, morphological characteristics, crystallinity, and depth profile of the IZO semiconductor film were measured to analyze the correlation between the structural properties of IZO film and electrical performances of the IZO TFT. In addition, the stoichiometric and electrical properties of the IZO semiconductor films were analyzed using film density, atomic composition profile, and Hall effect measurements. Based on the structural and stoichiometric results for the IZO semiconductor, the doping effect of the IZO film with respect to the In molar ratio was theoretically explained. The atomic bonding structure by the In doping in solution-processed IZO semiconductor and resulting increase in free carriers are discussed through a simple bonding model and band gap formation energy.

Understanding the chemical reaction pathway of the metal–salt precursor is essential for modifying the properties of solution-processed metal-oxide thin films and further improving their electrical performance. In this study, we focused on the structural growth of solution-processed amorphous indium-zinc-oxide (a-IZO) films and the electrical behavior of a-IZO thin-film transistors (TFT). To this end, solution-processed a-IZO films were prepared with respect to the Zn molar ratio, and their structural characteristics were analyzed. For the structural characteristic analysis of the a-IZO film, the cross-section, morphology, crystallinity, and atomic composition characteristics were used as the measurement results. Furthermore, the chemical reaction pathway of the nitrate precursor-based IZO solution was evaluated for the growth process of the a-IZO film structure. These interpretations of the growth process and chemical reaction pathway of the a-IZO film were assumed to be due to the thermal decomposition of the IZO solution and the structural rearrangement after annealing. Finally, based on the structural/chemical results, the electrical performance of the fabricated a-IZO TFT depending on the Zn concentration was evaluated, and the electrical behavior was discussed in relation to the structural characteristics.

The electronic device industry has recently focused its attention towards the development of organic memory devices. This research highlights the development of organic memory devices by utilizing pentacene as a semiconductor and ferroelectric polymers, such as poly(vinylidene fluoride-hexafluoropropylene) [P(VDF-HFP)] and poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)], as a gate dielectric. 10 wt% solutions of P(VDF-HFP) and P(VDF-TrFE) were prepared individually and blended (50:50). The resultant solutions were coated on the gate electrode and subsequently annealed for 2 h at 90 °C. The fabricated field-effect transistors (FETs) were studied in terms of their hysteresis characteristics with particular emphasis on the memory window. The results show that the FETs fabricated using the P(VDF-HFP)/P(VDF-TrFE) blend have significantly improved memory characteristics. The enhancement in the memory characteristics is explained through the interface properties between the pentacene semiconductor and dielectric layers. This work provides a design of organic FETs with excellent memory characteristics using low-cost technology.

The electrical characteristics of indium zinc oxide (IZO) thin-film transistors (TFTs) fabricated by solution process are analyzed under different atmospheric conditions. Compared to the electrical properties measured in atmospheric air, a positive shift in the threshold voltage and a decrease in the off-state current invariably are observed under vacuum. During consecutive operations of the IZO TFTs, the threshold voltage shifts towards a negative direction in atmospheric air but a positive direction under vacuum. In addition, the characteristic variations in the linear operation region are more pronounced when the TFTs are operated under vacuum environment. However, the effects of O₂ and N₂ gaseous ambient on the electrical characteristics of IZO TFTs are found to be negligible. These results suggest that the environmental influence on the performance of solution-processed IZO TFTs, which is observed in atmospheric air and under vacuum, is originated mainly from the interplay between polar H₂O molecules and majority carrier electrons in the IZO film.

We report a viable method for localizing a ferroelectric poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] film by using the transfer-print process. Micro-scaled topographic P(VDF-TrFE) patterns were successfully produced by using the transfer-print method, and the transferred films exhibited inherent ferroelectric properties. The characteristic improvements in the ferroelectric field-effect transistors (FeFETs) with respect to the operation voltage and the field-effect mobility could be achieved by using the transfer-print method to fabricate a ferroelectric insulator. The results suggest that transferring a ferroelectric film would be useful for realizing high-performance nonvolatile memory devices composed of FeFETs.