Transparent flexible fluorine-doped indium zinc oxide (IZO:F) thin-film transistors (TFTs) were demonstrated using the spin-coating method of the metal fluoride precursor aqueous solution with annealing at 200°C for 2 hrs on polyethylene naphthalate films. The proposed thermal evolution mechanism of metal fluoride aqueous precursor solution examined by thermogravimetric analysis and Raman spectroscopy can easily explain oxide formation. The chemical composition analysed by XPS confirms that the fluorine was doped in the thin films annealed below 250°C. In the IZO:F thin films, a doped fluorine atom substitutes for an oxygen atom generating a free electron or occupies an oxygen vacancy site eliminating an electron trap site. These dual roles of the doped fluorine can enhance the mobility and improve the gate bias stability of the TFTs. Therefore, the transparent flexible IZO:F TFT shows a high mobility of up to 4.1 cm2/V·s and stable characteristics under the various gate bias and temperature stresses.

Novel fluorine-doped zinc tin oxide (ZTO:F) thin-film transistors (TFTs) have been fabricated using an aqueous solution process. Exploiting hydrolysis and condensation reactions in an aqueous solution process, organic-free ZTO:F thin films were fabricated at a low temperature of 250°C. The fabricated TFT device shows a field-effect mobility of 2.85 cm 2 /V s, on-to-off current ratios exceeding 10 7 , and sub-threshold swings of 0.83 V/dec. The ZTO:F TFT also displays high operational stability of ΔV th = 1.73 V despite incorporation of a large amount of fluorine and use of a low-temperature annealing process. This is attributed to effective passivation of oxygen vacancy diffusion by metal fluoride bonds at the ZTO:F channel/gate dielectric interface.Amorphous metal oxide semiconductors have attracted much attention as candidates for the backplanes of active-matrix organic light-emitting diode displays owing to their high field-effect mobility. [1] To date, outstanding progress has been made in the area of solution processing for oxide semiconductors, [2][3][4] as researchers attempt to meet the requirements of low-cost fabrication and printed electronics. Recently, a highperformance InZnO semiconductor fabricated under 250°C using metal alkoxide precursors was reported. [4] However, fabrication steps requiring anhydrous conditions are very expensive and complicated. [5] Recently, solution processed ZnSnO (ZTO) thin films have been investigated for low-cost fabrication of oxide thin-film transistors (TFTs). Amorphous ZTO semiconductor exhibits excellent semiconducting properties and enables low-cost fabrication without an indium composition. [6] The conventional solution process for producing ZTO semiconductors utilizes a non-aqueous solvent such as acetonitrile or 2-methoxyethanol and metal chloride precursors. However, non-aqueous solutions with chloride precursors have a high decomposition temperature of more than 400°C in order to obtain good electronic characteristics and also effect of chlorine residue is vague. [7,8] In this study, we report a low-temperature-processed, novel fluorine-doped zinc tin oxide (ZTO:F) TFT using a simple aqueous solution process. The aqueous solution process utilizing rapid hydrolysis and condensation reactions enables the lowenergy kinetics of M-O-M network formation without any organic residues. In particular, we emphasize that the overall fabrication cost is cheap for several reasons: (i) the process uses an inexpensive solvent (water) and affordable metal precursors and (ii) all ZTO:F film fabrication steps including stirring, spin coating, and annealing were performed under ambient air conditions. The ZTO:F TFT with fluorine of more than 5%, which was annealed at low temperature of 250°C in an ambient atmosphere, shows a field-effect mobility of 2.85 cm 2 /V s and ΔV th of less than 1.73 V under long-term positive bias stress. We conjecture that fluorine, which has similar ionic size with oxygen, is responsible for the enhanced electrical characteristics of the suggested ZTO...

Novel fluorine doped zinc tin oxide (ZTO:F) thin-film transistor (TFT) was fabricated by an aqueous sol-gel method and their bias-temperature-illumination stability were observed. ZTO:F TFT optimized at Sn:Zn = 1:1 composition exhibits high field-effect mobility of 11.52 cm 2 /V · s at a process temperature of 350 • C. In particular, the TFT displays a small negative threshold voltage shift of approximately 1 V under positive bias-temperature-illumination stress. This is attributed to asymmetry of the recombination for photo-generated holes with the free electrons at the ZTO:F channel/gate dielectric interface due to the substitution of oxygen by fluorine with different electrovalence.Amorphous oxide thin film transistors (TFTs) are attractive switching devices for active matrix displays due to their superior performance and good uniformity compared to Si-based TFTs. 1 Another advantage of oxide semiconductors is that they can be produced using a solution process such as spin-coating or inkjet-printing thus enable simple and low cost fabrication. Solution processed oxide TFTs have exhibited the remarkable performances such as high mobility, bias stability, and low annealing temperature although they basically require an annealing process to obtain a dense oxide structure. 2-6 Seo et al. attempted to obtain the high performance, 2 to lower the annealing temperature 3 and to ensure the bias stability under humidity and bias stress. 4 Park et al. and Avis et al. demonstrated bias stability of oxide TFTs for application to electronic device such as organic light emitting diodes (OLEDs) utilizing a patterned structure 5 and the use of an inkjet process, 6 respectively. The poor stability of oxide TFT devices leads to deterioration of the current-voltage (I-V) characteristics under prolonged current and gate bias, resulting in a threshold voltage shift which can affect the brightness of OLED devices. 7 In this study, we present a fluorine doped zinc tin oxide (ZTO:F) TFT with a very high mobility of 11.52 cm 2 /V · s by applying an aqueous solution process using metal fluoride precursors. The stability test of ZTO:F TFT was investigated with applying a methacrylate hybrid material passivation layer that has an excellent gas barrier property. 8,9 Interestingly, the small negative threshold voltage shift ( V th ) less than 1 V under positive bias-temperature-illumination stress condition was observed. It is thought that the dominant factor of the extraordinary result to the conventional report is due to the M-F bonds at the ZTO:F channel/gate dielectric interface.The ZTO:F solution is prepared by using zinc fluoride hydrate (ZnF 2 · xH 2 O) and tin fluoride (SnF 2 ), with water as a solvent. The concentration of metal precursors was 0.2 M, and the molar ratio of (Sn/Sn+Zn) was 0.5. The solution was stirred for 4 hr at room temperature in a glass vial and a clear colorless solution was obtained. The heavily boron doped (p + ) Si substrate with a thermally grown 100 nm thick SiO 2 was ultra-sonicated in deionized water for...

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