Photo and electrically stable transparent ZnO thin-film transistors for an active matrix organic light emitting diode (AM-OLED) panel are reported. Oxide semiconductor-based thin-film transistors (TFTs) have been extensively studied mainly to replace Si-based TFTs in electrical and optical devices. [1][2][3][4][5] Therefore, there have been many reports on oxide-based TFTs: transparent oxide TFTs, [6][7][8][9][10] amorphous oxide TFTs, [11][12][13][14][15] polycrystalline oxide TFTs, [16,17] and even photo-detecting oxide TFTs. [18] In particular, transparent ZnO-TFTs have attracted much attention as display drivers that possess some evident advantages over opaque Si-based TFTs.[19] Transparent TFTs (TTFTs) with a large energy bandgap channel of $3.3 eV would transmit a visible light signal to increase the aperture ratio even in the bottom emission OLED display, which could not be anticipated from any conventional opaque TFTs. Well-designed TTFTs would result in important benefits such as longer life time and lower fabrication price of OLEDs or TFT-LCDs. However, since the ZnO-TFTs usually contain defects in the ZnO channel and deep level defects in the channel/dielectric interface that generate unwanted photo-current during light transmission and device operation, [20,21] the very advantages of the transparent ZnO-TFTs have never been fully utilized or demonstrated for display panels, to the best of our limited knowledge. We recently developed an effective fabrication methodology to greatly reduce the number of defects in the channel and interfacial charge trap defects using a low temperature (200 8C) atomic layer deposition (ALD) for a ZnO semiconductor channel and Al 2 O 3 dielectric. We found that our transparent ZnO-TFTs with defect-controlled channel and channel/dielectric interface maintain good photo-stability during device operation without generating much detectable photocurrent. Our ZnO-TFTs showed a good mobility of $4 cm 2 V À1 s À1 and an excellent high on/off ratio of $10 7. The display back panels with our photo-stable and fully transparent ZnO-TFT array demonstrate a successful operation of a 2.5 inch-sized bottom emission AM-OLED panel under 15 V, which exhibited a high aperture ratio of $60%. Figure 1a and 1b show a microscopic plan view of our 2 TFT/1 storage capacitor (2T/1C) cell structure and a circuit diagram of the cell, respectively. (Please note that the size of a pixel cell was 210 mm 230 mm as measured under an optical microscope.) Based on this back plane composed of a 2T/1C cell matrix we fabricated OLED pixels to operate in a manner of bottom emission. Our TTFT exhibited a higher than 80% transmittance in the visible range as shown in Figure 1c. The schematic but detailed cross section of the cell is shown in Figure 2a, although it only displays our top-gate driving ZnO-TFT and storage capacitor here. In Figure 2a, the driving ZnO-TFT contains an initial 9 nm thin gate dielectric and next a 176 nm thick dielectric. The first thin dielectric was deposited on a ZnO channel at 200 8C...

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.

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Bending characteristics of flexible oxide thin-film transistors could be enhanced by optimizing the barrier layers on the polyethylene naphthalate substrate.