Thin-film transistors based on Zinc Oxide channel layer and Molybdenum doped Indium Oxide transparent electrodes

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Thin -film transistors based on Zinc Oxide channel layer and Molybdenum doped Indium Oxide transparent electrodes Mateusz Tomasz Mądzik, Elangovan Elamurugu, Raquel Flores, and Jaime Viegas Masdar Institute, Abu Dhabi, United Arab Emirates ABSTRACT Thin-film transistors (TFT) were fabricated at room-temperature (RT) utilizing zinc oxide (ZnO) channel and indium molybdenum oxide (IMO) electrodes. The common bottom-gate TFTs were fabricated on commercially available thermal silicon oxide (100 nm thick) coated silicon wafers. A total of 100 devices were made in a 1 inch square area as 10 u 10 matrix, by varying the channel width and length, between 5 μm and 300 μm. Output and transfer characteristics of the fabricated devices were extracted from a semiconductor parameter analyzer. A threshold voltage (VTh) of 10 V and an ION/IOFF ratio of 1 u 10-5 were obtained. The impact of channel dimensions on the device performance was investigated, confirming that the saturation current (Isat) is directly proportional to the channel width (W), and inversely proportional to channel length (L), in agreement with field effect device theory. INTRODUCTION The TFTs based on transparent metal oxide (TMO) layers are widely studied due to their high current density, high carrier mobility, and high transmittance [1]. Among the available TMOs, zinc oxide (ZnO) is of central interest due to many potential applications in display technology, sensing and energy harvesting. In order to achieve an improved device performance, researchers always look for a novel material and/or improved material properties, to be implemented as channel, gate-oxide and gate-electrodes. Among the proposed compounds, In-Ga-Zn-O (IGZO) is considered to be the most promising. TFTs based on IGZO achieved high ION/IOFF ratio in the order of 1 u 10-8 and threshold voltage below 1 V [2]. Aluminum doped zinc oxide (AZO) and tin doped zinc oxide (ZTO) as active layers [3] have also been reported in the literature. In recent developments, not just the channel layers, but also the electrodes are preferred to be transparent, both for developing transparent electronics and brighter pixels in OLED displays. It is well known that indium tin oxide (ITO) is the commonly used transparent electrode. IMO is a potential ITO-alternate for transparent electrodes [4]. We have earlier reported IMO films, with a highest carrier mobility of ~50 cm2/Vs, a lowest resistivity of 4.21×10−4 Ω-cm and a work function of ~5 eV; these properties make IMO a successful alternative to the existing transparent electrodes [5]. A VTh of 10 V and ION/IOFF ratio of 1 u 10-5 were obtained from the fabricated set of TFTs. The influence of channel dimensions on the Isat was determined to be in excellent agreement with electronic device theory derived for Si devices. EXPERIMENT Commercial Si wafers with a 100 nm thick thermal SiO2 on the top side were used for the fabrication of TFTs in the present study. The bulk Si serves as the gate-electrode; and the SiO2 is the gate dielectric. This means the bulk Si is use

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