Structural and Electrical Characterization of SiO₂ Gate Dielectrics Deposited from Solutions at Moderate Temperatures...

Silicon dioxide (SiO₂) is the most widely used dielectric for electronic applications. It is usually produced by thermal oxidation of silicon or by using a wide range of vacuum-based techniques. By default, the growth of SiO₂ by thermal oxidation of silicon requires the use of Si substrates whereas the other deposition techniques either produce low quality or poor interface material and mostly require high deposition or annealing temperatures. Recent investigations therefore have focused on the development of alternative deposition paradigms based on solutions. Here, we report the deposition of SiO₂ thin film dielectrics deposited by spray pyrolysis in air at moderate temperatures of ≈350 °C from pentane-2,4-dione solutions of SiCl₄. SiO₂ dielectrics were investigated by means of UV-vis absorption spectroscopy, spectroscopic ellipsometry, XPS, XRD, UFM/AFM, admittance spectroscopy, and field-effect measurements. Data analysis reveals smooth (R_RMS < 1 nm) amorphous films with a dielectric constant of about 3.8, an optical band gap of ≈8.1 eV, leakage current densities in the order of ≈10^-7 A/cm² at 1 MV/cm, and high dielectric strength in excess of 5 MV/cm. XPS measurements confirm the SiO₂ stoichiometry and FTIR spectra reveal features related to SiO₂ only. Thin film transistors implementing spray-coated SiO₂ gate dielectrics and C₆₀ and pentacene semiconducting channels exhibit excellent transport characteristics, i.e., negligible hysteresis, low leakage currents, high on/off current modulation ratio on the order of 10⁶, and high carrier mobility.