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...

Direct quantitative mapping of the density‐of‐states, named the photo‐excited charge‐collection technique, for the interface traps at the n‐ZnO and/or p‐pentacene thin‐film transistor channel is implemented by using monochromatic photons which are carried by optical fibers and are probed onto thin‐film transistors.

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The effects of electrode materials on the device stabilities of In-Ga-Zn-O (IGZO) thin-film transistors (TFTs) were investigated under gate- and/or drain-bias stress conditions. The fabricated IGZO TFTs with a top-gate bottom-contact structure exhibited very similar transfer characteristics between the devices using indium-tin oxide (ITO) and titanium electrodes. Typical values of the mobility and threshold voltage of each device were obtained as 13.4 cm(2) V(-1) s(-1) and 0.72 V (ITO device) and 13.8 cm(2) V(-1) s(-1) and 0.66 V (titanium device). Even though the stabilities examined under negative and positive gate-bias stresses showed no degradation for both devices, the instabilities caused by the drain-bias stress were significantly dependent on the types of electrode materials. The negative shifts of the threshold voltage for the ITO and titanium devices after the 10(4)-s-long drain-bias stress were estimated as 2.06 and 0.96 V, respectively. Superior characteristics of the device using titanium electrodes after a higher temperature annealing process were suggested to originate from the formation of a self-limiting barrier layer at interfaces by nanoscale observations using transmission electron microscopy.

DC-DC converters integrated into a panel are proposed for mobile display applications using indium gallium zinc oxide (IGZO) thin film transistors (TFTs). The proposed positive DC-DC converter uses cross-coupled and diode-connected structures for a high output voltage and a high power efficiency, while the proposed negative DC-DC converter uses also a cross-coupled structure but with separated pumping capacitors for a negative output voltage and a high power efficiency. The simulated results show that the output voltage and power efficiency are 21.3 V and 69.5% for the positive DC-DC converter and À5:1 V and 56.1% for the negative DC-DC converter, respectively, at a supply voltage of 10 V and a load current of 250 mA. The measured results show that the output voltage and power efficiency of the proposed positive DC-DC converter are 20.8 V and 66.6%, respectively, under the same conditions as those for the simulated results.