ZnO-based Thin Film Transistors Employing Aluminum Titanate Gate Dielectrics Deposited by Spray Pyrolysis at Ambient Air

Abstract

The replacement of SiO2 gate dielectrics with metal oxides of higher dielectric constant has led to the investigation of a wide range of materials with superior properties compared with SiO2. Despite their attractive properties, these high-k dielectrics are usually manufactured using costly vacuum-based techniques. To overcome this bottleneck, research has focused on the development of alternative deposition methods based on solution-processable metal oxides. Here we report the application of spray pyrolysis for the deposition and investigation of Al2x-1·TixOy dielectrics as a function of the [Ti(4+)]/[Ti(4+)+2·Al(3+)] ratio and their implementation in thin film transistors (TFTs) employing spray-coated ZnO as the active semiconducting channels. The films are studied by UV-visible absorption spectroscopy, spectroscopic ellipsometry, impedance spectroscopy, atomic force microscopy, X-ray diffraction and field-effect measurements. Analyses reveal amorphous Al2x-1·TixOy dielectrics that exhibit a wide band gap (∼4.5 eV), low roughness (∼0.9 nm), high dielectric constant (k ∼ 13), Schottky pinning factor S of ∼0.44 and very low leakage currents (<5 nA/cm(2)). TFTs employing stoichiometric Al2O3·TiO2 gate dielectrics and ZnO semiconducting channels exhibit excellent electron transport characteristics with low operating voltages (∼10 V), negligible hysteresis, high on/off current modulation ratio of ∼10(6), subthreshold swing (SS) of ∼550 mV/dec and electron mobility of ∼10 cm(2) V(-1) s(-1).

Low-temperature solution-processed alumina dielectric films for low-voltage organic thin film transistors

“…Among them, Al 2 O 3 dielectrics have attracted intense interest due to its high k value (7.0-9.0) and big band-gap (8.45-9.9 eV) [15][16][17][18][19]. Moreover, Al 2 O 3 based dielectrics, such as sodium beta-alumina [20], Al 2 O 3 /polymer nanocomposite [21], aluminum titanate [22] have also widely employed for TFTs. Recently, Al 2 O 3 have also been employed as high-performance dielectrics for transparent oxide TFTs, indicating the universal functionality [23][24][25].…”

Solution‐Processed Neodymium Oxide/ZnO Thin‐Film Transistors with Electron Mobility in Excess of 65 cm V−1 s−1

“…The transfer and output characteristics of a typical ZnO TFT employing a 36 nm Nd2O3 gate dielectric (Cox = 270 nF/cm 2 ) are illustrated in Figure 3g and , comparable with those reported for equally solution processed TFTs. [55,57,59] TFT devices employing gold source and drain contacts showed excellent stability under constant bias stress (3000 s at VDS and VGS =4 V, data not shown). VTH increased by 12 % and field effect mobility decreased by less than 10 %.…”

“…Extrapolation of the linear region of the Tauc plot to the xaxis yields the direct optical band gap of 6 eV comparable with that of 5.8 eV reported for epitaxial Nd2O3. [36,64] The Urbach tail energy of Nd2O3was found to be relatively low (about 200 meV) for solution processed dielectrics, [57,59] indicating high static order perhaps due to the formation of crystalline Nd2O3. Furthermore, the optical properties of Nd2O3 films on c-Si were investigated by ex-situ UV-visible spectroscopic ellipsometry in the range of photon energies between 1.5 to 4.5 eV.…”

Electrical characteristics of InGaZnO thin film transistor prepared by co-sputtering dual InGaZnO and ZnO targets

“…5 In turn, bilayer ZnO (60 nm)/IGZO (50 nm) thin film has recently been deposited at 450°C in Ar: O 2 ambient for resulting a better TFT with µ FE ~ 2.2 cm 2 /Vs, SS ~ 0.52V/decade, V th ~ 1.3V. 6 9,10 However, there is still a challenge for finding a way to attain improved stability while maintaining high-performances via novel oxide materials and post-treatment. 11,12 In this work, three types of oxide thin films as the channel layer for TFT device are proposed to study their structural, roughness, electrical and chemical analysis for flat panel displays (FPDs) applications.…”