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Herein, we propose an ionic liquid–polymer dielectric layer for flexible electronics reinforced by a chemical interaction between the polymer matrix (PVP) and the ionic liquid. Due to the robust structures of the cross-linked PVP matrix and hydrogen bonding between the ionic liquid and PVP, the ionic liquid–PVP (IL–PVP) layer exhibited a good mechanical strength when bending up to 1000 times and a stable thermal behaviour up to 300 °C. Furthermore, the IL–PVP dielectric layer showed a high capacitance value of ∼2 μF cm−2 and was operated well as a gate insulator for flexible ZnO thin film transistors with a linear field-effect mobility of ∼3.3 cm2 V−1 s−1 at a gate bias of 3 V.

Solution-processed high-K dielectrics for oxide thin-film transistors (TFTs) have been widely studied with the objective of achieving high performance and low-cost TFTs for next-generation displays. In this study, we introduce an amorphous hafnium-lanthanum oxide (HfLaOx) gate insulator with high electrical permittivity which was fabricated by the simple spin-coating method. In particular, the solution-processed HfLaOx dielectric layer, which was achieved by a mixture of two Hf and La metal hydroxide precursors, showed amorphous properties, a low leakage current and a high dielectric constant. The solution-processed HfLaOx dielectric layers showed a breakdown voltage as high as 5 MV cm−1 in strength and a dielectric constant above 22. Based on their implementation as a gate insulator, the solution-processed ZnO/HfLaOx TFTs showed good and stable performances during operation at a low voltage. A mobility of μ = 1.6 cm2 V−1 s−1, an on/off current ratio of 106, and a threshold voltage of 0.0015 V were obtained under a 5 V gate bias. Our results show the possibility of the solution-processed amorphous HfLaOx dielectric layer as a gate insulator for oxide TFTs. We believe that this amorphous HfLaOx dielectric has good potential for next-generation high-performance TFT devices.

We fabricated zinc oxide (ZnO) TFTs using a zinc ammine complex with various zinc oxide sources such as ZnO, intrinsic Zn(OH)2, and precipitated Zn(OH)2. From the analyses of the reaction mechanism, surface morphology, crystal structure, and oxygen vacancy in the ZnO films, we confirmed the same intermediate in ZnO semiconductor films irrespective of the type of zinc oxide source in the zinc ammine complex precursor. The results showed the analogous value of the average field effect mobility, on/off current ratio, and turn-on voltage in all solution-processed ZnO TFTs. In conclusion, we confirmed that directly dissolving pristine ZnO into ammonia water is the most efficient method for preparing the ZnO semiconductor precursor, the zinc ammine complex, for low-temperature, solution-processed, and high performance ZnO TFTs.

Chemical imprinting was conducted on ZnO semiconductor films via a chemical reaction at the contact regions between a micro-patterned PDMS stamp and ZnO films. In addition, we applied the chemical imprinting on Li doped ZnO thin films for high performance TFTs fabrication. The representative micro-patterned Li doped ZnO TFTs showed a field effect mobility of 4.2 cm(2) V(-1) s(-1) after sintering at 300 °C.

Flexible and transparent thin film transistors (FTTFTs) can lead to next generation displays that involve large area, future-oriented flexible and transparent displays. In order to achieve stable FTTFTs, solution processes of organic and inorganic compounds have received significant attention. Above all, transparent oxide semiconductors such as ZnO have been studied to enhance flexibility with high electrical performance by integration with organic dielectrics. However, interfacial traps between inorganic and organic compounds are derived by interface dipole, which induce a considerable flat band shift. Herein, we have developed a self-assembled inorganic layer (SAIL) via the photo-induced transformation of a mono-poly(dimethylsiloxane) (PDMS) layer as interface engineering. Especially, the shifting of flat band voltage (VFB) was effectively suppressed by the SAIL process, which was analyzed with a single-piece analytical model for ZnO TFTs. In addition, flexible ZnO/SAIL/polymer dielectric TFTs with low process temperature as high as 200 °C exhibited a good field-effect mobility μ = 0.28 cm2 V−1 s−1, more than 106 on–off current ratio and excellent device operational stability and flexibility.

A solution-processed ionic amorphous Al2O3 dielectric with a low temperature annealing process at 350 °C shows good compatibility and high performance in metal oxide semiconductor thin film transitors (TFTs) such as Li–ZnO TFTs and In–ZnO TFTs. The Li–ZnO/Al2O3 and In–ZnO/Al2O3 TFTs, with solution-processability and low temperature annealing at a maximum of 350 °C, exhibited field-effect mobilities of 46.9 cm2 V−1 s−1 in crystalline Li–ZnO/Al2O3 TFTs and 44.2 cm2 V−1 s−1 in amorphous In–ZnO/Al2O3 TFTs with an on/off current ratio of more than 105. The proton mobile ion, such as hydrogen ion (H+) from chemisorbed water, in the ionic Al2O3 dielectric remarkably induces a high performance capacitance by the formation of an electrical double layer. The chemisorbed water was monitored by FT-IR and ellipsometric porosimetry measurements. Furthermore, the addition of H2O2 to the ionic Al2O3 dielectric precursor successfully suppressed the oxygen vacancies in the dielectric layer, which caused the electrical trap and pass, and confirmed the stable operation. These ionic amorphous Al2O3 dielectrics show good potential as switching TFTs devices in advanced displays, because they can satisfy the various demands of next-generation high-performance TFTs, such as low-cost, solution-processability, and a relatively low-temperature process.

The structural, electrical and optical properties of high-performance, low-temperature and solution-processed alkali metal-doped ZnO TFTs were studied using various analytic instruments, including HR-TEM, AFM, XPS, EDS, electrical bias stability test and UV-vis spectroscopy. Furthermore, we successfully demonstrated that a change in the optical bandgap energy of Li-doped ZnO semiconductor films supported by Burstein–Moss theory can show a trade-off relationship between the field effect mobility of Li-ZnO TFTs and the Li doping concentrations. The relative broadening of the Eopt values, which are strongly related to the amount of excited electrons from the Fermi level in the valance band to the conduction band, was observed from the undoped ZnO film to the Li-doped ZnO film (10 mol%). The increase in the electron donor concentration was the dominant reason for the enhancement in the electron mobility of the alkali metal-doped ZnO TFTs.

We introduce high performance, low-temperature (

A transparent thin film transistor (TTFT), including zinc oxide (ZnO), has come into the spotlight as an innovative TFT that has the potential to drive the future of the information technology industry. Herein, we developed a new direct patterning method, drop-casting with a new developing method, through the combination of an aqueous ammonia–ZnO process with the doping of Na ions and surface engineering for high n-type semiconducting performance with good operational stability at low temperature. In particular, the effective decomposition and removal of the residual ammonia compounds using methanol have a successful effect on both intrinsic and Na doped ZnO precursor processes for TFTs and they showed the extensive possibility of ammonia based metal oxide precursor solutions. In this method, the Na doped ZnO TTFTs showed good operational stability even with the process of low temperature sintering. The mobility μ = 0.80 cm2 V−1 s−1 was obtained at 200 °C sintering and the mobility μ = 0.10 cm2 V−1 s−1 at 100 °C sintering. In addition, in ambient conditions, the patterned Na doped ZnO TTFT exhibited high electron mobility μ = 1.84 cm2 V−1 s−1 with excellent device operational stability and scant hysteresis with sintering at 300 °C. This method is not only simple as compared with photolithography and inkjet printing, but is also a sophisticated patterning process with good fidelity for solution-processed ZnO TFTs. Moreover, the proposed method can be extended to plastic substrates on a large scale because of the low temperature development process of the ammonia–ZnO precursor using methanol and continuous patterning at ambient conditions. We believe that this method can be adapted to the advanced process toward future printed transparent electronic devices.