Solution processed lanthanum aluminate gate dielectrics for use in metal oxide-based thin film transistors

We report on ZnO-based thin-film transistors (TFTs) employing lanthanum aluminate gate dielectrics (La_xAl_1-xO_y) grown by spray pyrolysis in ambient atmosphere at 440 °C. The structural, electronic, optical, morphological, and electrical properties of the La_xAl_1-xO_y films and devices as a function of the lanthanum to aluminium atomic ratio were investigated using a wide range of characterization techniques such as UV-visible absorption spectroscopy, impedance spectroscopy, spectroscopic ellipsometry, atomic force microscopy, x-ray diffraction, and field-effect measurements. As-deposited LaAlO_y dielectrics exhibit a wide band gap (∼6.18 eV), high dielectric constant (k ∼ 16), low roughness (∼1.9 nm), and very low leakage currents (<3 nA/cm²). TFTs employing solution processed LaAlO_y gate dielectrics and ZnO semiconducting channels exhibit excellent electron transport characteristics with hysteresis-free operation, low operation voltages (∼10 V), high on/off current modulation ratio of >10⁶, subthreshold swing of ∼650 mV dec^-1, and electron mobility of ∼12 cm² V^-1 s^-1.