In this work, depletion-mode magnesium doped zinc-oxide (MgZnO) channel thin film transistors (TFTs) with zirconium oxide (ZrO 2 ) gate insulator were fabricated using radio frequency magnetron sputtering deposition. Sputtered MgZnO TFT channel layer performed an average transmittance of 90% and an improved energy bandgap of 5.02 eV after 700 C post annealing. X-ray photoelectron spectroscopy (XPS) results indicated that the binding energy of Zn-O bonds and Mg-O bonds were enhanced following with the increasing of the post annealing temperatures. The low frequency noise spectra also indicated that the ZrO 2 /MgZnO was dominated by flicker noise and gate leakage induced noise was suppressed.Recently, ZnO and MgZnO attract considerable attention because they performed promising properties for short-wavelength optoelectronic and high breakdown voltage electronics devices due to their wide band gaps and large excitation binding energies. Compared to ZnO, MgZnO ternary alloy material provides several advantages, including continuously tunable bandgaps from 3.3 to 7.8 eV, which facilitated heterostructure with traditional ZnO-based material. 1-3 Magnesium atoms in MgZnO compound also exhibited slight lattice mismatch with ZnO because similar ionic radii between Mg 2þ and Zn 2þ . Moreover, Mg also acts as a donor, reducing the Madelung in MgZnO, and supporting the potential for development of p-type MgZnO thin films. For reasons concerning channel current density and breakdown voltage, the MgZnO channel TFT with a high energy bandgap and a high dielectric constant gate insulator is more promising compared to traditional Schottky gate contact TFT. In order to further enhance gate modulation ability of channel with the continuous scaling down of submicron thin-film transistors, the high-k dielectric insulator has become an essential issue owing to the strong demand for a low operating voltage and a low gate leakage current. Based on these considerations, ZrO 2 is a suitable candidate for gate dielectrics because ZrO 2 exhibited a large band gap (5.2-7.8 eV), a relatively high dielectric constant (>25), a high breakdown electric field (>5MV/cm) and an extreme high melting point (2750 C). 4 In addition, the ZrO 2 was deposited by electron beam evaporation at room temperature. Therefore, plasma induced surface damage and high-temperature high-k deposition processes can be avoided simultaneously because some specific substrates of TFT such as glass and polymer materials were extreme thermally sensitive. Figure 1 shows the cross sectional structure and top-view photography of top-gate MgZnO TFT with ZrO 2 gate insulator. The device gate length (L g ) and gate width (W g ) were 1 and 200 m, respectively. The MgZnO channel films used in this study were grown at room temperature by the RF sputtering method on c-face sapphire substrates. The MgZnO films were formed by a 6-inch ZnO/MgO (80/20 wt %) target. The channel thickness of the deposited MgZnO was 50 nm. After 1 minute post deposition annealing (PDA) at 700 C in an N 2 flow,...
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