Solution processed Gadolinium Oxide : A promising gate dielectric for metal oxide-based thin film transistors

Antoniou, Giorgos and Coogan, Michael Peter and Milne, W.I. and Adamopoulos, George (2018) Solution processed Gadolinium Oxide : A promising gate dielectric for metal oxide-based thin film transistors. In: EMRS 2018, 2018-06-18 - 2018-06-22, Strasbourg.

Abstract

A wide range of rare earth metal oxides (REOs) constitute promising candidates for high-k gate dielectrics, as they combine excellent dielectric properties, i.e., high dielectric constant and low leakage currents with wide bandgaps, in the range between 3.9 and 6 eV. Yet, another attractive feature of rare earth oxides that further boosted their research is the excellent stability and interface properties with silicon. Also, their relatively close lattice constant match to silicon further enhances the possibility of epitaxial growth. Epitaxial growth of REOs (i.e., Gd2O3) on GaAs has been reported, and further investigations demonstrated their potential applications in a number of III–V-based optoelectronic devices. Due to their wide bandgaps (>3 eV) however, metal oxide based semiconductors require gate dielectrics with a relatively wide in order to inhibit conduction by the Schottky emission of electrons or holes into the oxide bands. A number of wide bandgap REOs (La2O3, Y2O3, Nd2O3) have shown promise for implementation in TFTs employing metal oxide semiconducting channels. Among those, Gadolinium oxide (Gd2O3) is the least investigated one and a small number of works have been reported. In this report we demonstrate the spray coating deposition of Gd2O3 thin films at moderate temperatures (≈400 °C) over large area, by using custom made Gadolinium tris(2-salicylaldiminoethanol) precursor. The films were deposited by spray coating at moderate substrate temperatures (440 oC) in air and characterised by UV-Vis, FT-IR, impedance spectroscopy, AFM, XRD and field-effect measurements. Data analysis revealed Gd2O3 films of cubic structure, wide band gap of about 5.5 eV and dielectric constant in the range between 9 and 13. TFTs employing Gd2O3 dielectrics and In2O3 semiconducting channels show low leakage currents (<1 nA/cm2), low subthreshold swing, high on/off current modulation ratio (>10^7) and electron mobilities in excess of 70 cm2 V−1 s−1.