Solution-processed Indium Oxide Thin-film Transistors Research Articles

Effects of iodine doping on structural and electrical characteristics of solution-processed indium oxide thin-film transistors and its potential application for iodine sensing

Effects of iodine doping on structural and electrical characteristics of solution-processed indium oxide thin-film transistors and its potential application for iodine sensing

Anodization-induced ZrOx/AlOx stacked films for low-temperature, solution-processed indium oxide thin-film transistors

In this study, anodization is introduced to induce dehydroxylation and condensation of solution-processed ZrOx films as well as growth of AlOx films. The anodization-induced ZrOx/AlOx stacked films are systematically studied in structure, surface morphology, density, chemical composition, dielectric and electrical properties. X-ray diffraction and atomic force microscopy reveal that anodization-induced ZrOx/AlOx stacked films exhibit amorphous structure and smooth surface roughness (<1 nm). X-ray reflectivity and x-ray photoelectron spectroscopy reveal that the solution-processed ZrOx films exhibit a higher density and a lower content of hydroxyl groups after anodization, suggesting the anodization can induce dehydroxylation and condensation for the ZrOx films. The synergistic effect of collision inducing dissociation and the self-heating from anodization of Al film is proposed to explain the dehydroxylation of the ZrOx films. Dielectric and electrical measurements illustrate that the anodization-induced ZrOx/AlOx stacked films exhibit a lower leakage current, a higher breakdown voltage and a slighter capacitance dispersion on frequency comparing with that of solution-processed ZrOx films without anodization. To verify the possible applications of anodization-induced ZrOx/AlOx stacked films as the gate dielectric in metal-oxide (MO) thin-film transistors (TFTs), they were integrated in low-temperature, directly photopatternable InOx TFTs. Remarkably, with a low process temperature of 200 °C, the InOx TFTs based on the optimized ZrOx/AlOx dielectrics exhibit an average mobility of 8.94 cm2 V−1 s−1, an I on/I off of large than 105 and negligible hysteresis in transfer curves. These results demonstrate the potential application of anodization-induced solution-processed MO dielectric films for low-temperature TFTs.

Impact of NH3 plasma treatment for solution-processed indium oxide thin-film transistors with low thermal budget

The challenges associated with low-temperature solution-processed metal oxide thin-film transistors (TFTs) have hindered the realization of flexible oxide electronics at temperatures lower than 200 °C. NH3 plasma treatment is embarked upon as a route to effectively transform the chemical precursors to semiconducting metal oxides with high electrical quality. NH3 plasma-activated indium oxide (InOx) TFTs with saturated mobility 2.48 cm2V−1s−1 have been obtained at temperature as low as 150 °C. The low-temperature activation mechanism of NH3 plasma treatment for InOx films and the role of post-annealing in the fabrication process of InOx TFTs have been explored. Research shows that NH3 plasma treatment activates InOx films based on plasma bombardment, radicals doping and radical reactions; then, unreacted radicals and interstitial radicals were effectively removed by extra thermal energy from post-annealing. In comparison to thermal annealing, NH3 plasma treatment with moderate post-annealing is capable of achieving high degrees of condensation and densification reactions for InOx film and modulating the carrier concentration in a manner suitable for high-performance semiconducting behavior with low thermal budget. However, The InOx film after NH3 plasma treatment exhibited a non-uniform geometry due to the effect of plasma-induced damage in the local regions of InOx film, which restricts its commercial application. Some strategies were reported to eliminate the effect of plasma-induced damage by changing plasma conditions or pre-annealing temperature. The results demonstrated that changing plasma conditions by decreasing the plasma chamber temperature or the plasma power can eliminate plasma-induced damage, but attenuate the electrical performance of InOx TFT; nevertheless, changing pre-annealing temperature to 30 °C not only effectively eliminate plasma-induced damage, but also further improve the electrical performances of InOx TFT. These results provide a way for fabricating low-temperature oxide circuitry and supply an effective idea for avoiding plasma-induced damage.

Electrical stability of solution-processed indium oxide thin-film transistors under illumination stress

ABSTRACTWe investigated the variation in the electrical characteristics of solution-processed indium oxide (In2O3) thin-film transistors (TFTs) under monochromatic illumination conditions at different wavelengths of 1240, 800, 600, 500, 400, and 350 nm. In our results, there was no discernible difference between the characteristics of the TFT measured in the dark state and those obtained under light illumination at the wavelengths of 1240 nm and 800 nm. On the other hand, the TFT performance was remarkably changed when light having a wavelength of 600 nm or less was illuminated. It is found that the photon energy, which causes the characteristic degradation in the solution-processed In2O3 TFTs, is much lower than the direct band gap energy of In2O3. Consequently, illumination-induced instability in the performance of solution-processed In2O3 TFTs can be explained with the transition phenomena of neutral oxygen vacancies to ionized ones in the In2O3 semiconductor film.

Operational stability of solution-processed indium-oxide thin-film transistors: Environmental condition and electrical stress

We investigate the operational stability of bottom-gate/top-contact-structured indium-oxide (In2O3) thin-film transistors (TFTs) in atmospheric air and under vacuum. Based on the thermogravimetric analysis of the In2O3 precursor solution, we utilize a thermal annealing process at 400 °C for 40 min to prepare the In2O3 films. The results of X-ray photoemission spectroscopy and field-emission scanning electron microscopy show that the electron is the majority carrier in the In2O3 semiconductor film prepared by a spin-coating method and that the film has a polycrystalline morphology with grain boundaries. The fabricated In2O3 TFTs operate in an n-type enhancement mode. When constant drain and gate voltages are applied, these TFTs in atmospheric air exhibit a more acute decay in the drain currents with time compared to that observed under vacuum. In the positive gate-bias stress experiments, a decrease in the field-effect mobility and a positive shift in the threshold voltage are invariably observed both in atmospheric air and under vacuum, but such characteristic variations are also found to be more pronounced for the atmospheric-air case. These results are explained in terms of the electron-trapping phenomenon at the grain boundaries in the In2O3 semiconductor, as well as the electrostatic interactions between electrons and polar water molecules.

High-Performance, Solution-Processed Indium-Oxide TFTs Using Rapid Flash Lamp Annealing

In this letter, we discuss the temperature distribution of light-illuminated Si substrates with time and the successful fabrication of high-performance, solution-processed indium-oxide thin-film transistors within an annealing time of 2 min using a high-power flash lamp under ambient conditions. The precursor films are completely converted into oxide films within 30 s using flash lamp annealing (FLA). As a result, we obtained the high performance of indium-oxide TFTs with the mobility of impressive 38.9 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> V <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> s <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> with the on/off ratio of ~104 for the irradiation time of 2 min and the mobility of 10.3 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> V <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> s <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> with the on/off ratio of ~5 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup> for the irradiation time of 10 s for three times, which is the highest mobility ever reported using FLA. This result will be helpful for breaking the barrier in the mass production of the next-generation semiconductors.

Low-temperature, solution-processed indium-oxide thin-film transistors fabricated by using an ultraviolet-ozone treatment

For the fabrication of low-temperature solution-processed metal-oxide thin-film transistors (TFTs), alternative annealing processes have recently been studied for reduced fabrication cost and applications to flexible devices. Indium nitrate solution has been proposed as a precursor for the low-temperature solution-processed TFTs. However, due to its high decomposition temperature, achieving a high-performance indium-oxide (In2O3) TFT at temperatures below 200°C is still difficult. In this study, for improved metal-oxide formation in low-temperature solution-processed In2O3 TFT, indium nitrate film was exposed to UV-ozone for 30 min before annealing at 200°C. The smooth scanning electron microscopy (SEM) image of the UV-ozone treated film implies that the indium nitrates are condensed after treatment. In addition, X-ray photoemission spectroscopy (XPS) data suggest that UV-ozone decreases the number of oxygen vacancies and increases the number of metal-oxygen-metal bonds in the indium-oxide films. As a result, high electrical device performance was achieved with an improved Ion/off ratio (∼107) and mobility (1.25 cm2V −1s −1).

Hydroxyl radical-assisted decomposition and oxidation in solution-processed indium oxide thin-film transistors

Solution-processed indium oxide TFTs were fabricated by hydroxyl radical-assisted (HRA) decomposition and oxidation.

Effect of Aluminum and Gallium Doping on the Performance of Solution-Processed Indium Oxide Thin-Film Transistors

Thin-film transistors (TFTs) with indium gallium oxide and aluminum indium oxide as a channel layer were fabricated via an aqueous route with low temperature annealing. The effects of chemical composition on electrical performance were examined. The fabricated IGO and AIO TFTs exhibited mobility in the range of 3.9-10.7 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ·V <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> ·s <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> with an on-to-off current ratio over 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup> and a sub-threshold swing of below 0.7 V/dec at the optimized composition. The optimized IGO and AIO thin-films were in an amorphous phase, which has an advantage in large area uniformity. Finally, we performed a positive and negative bias test on the optimized IGO and AIO TFTs to understand the resistance to external bias stress. The turn-on voltage shift of the optimized IGO and AIO TFTs, annealed at 300 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> C, were 1.45 V (negative bias stress), and 1.56 V (positive bias stress) with 3600 s stress, respectively.