Effect of leakage current and dielectric constant on single and double layer oxides in MOS structure

MOS structure of Al/Al2O3/n-Si, Al/TiO2/n-Si and Al/Al2O3/TiO2/n-Si was obtained by deposition of Al2O3 and TiO2 on silicon substrate by RF Magnetron Sputtering system. The total thickness of the oxide layer ~ 40 ± 5 nm in the MOS structure was kept constant. Samples were characterized by X-Ray diffraction (XRD), X-Ray photoelectron spectroscopy (XPS), Impedance analyzer and Current–voltage (J–V) characteristics. The variations in the dielectric constant and tan δ of the MOS capacitor in the frequency range of 1000Hz–1MHz were measured by impedance analyzer. The variation in dielectric constant of the Al/Al2O3/TiO2/n-Si multilayer compared to single layer of Al/Al2O3/n-Si and Al/TiO2/n-Si is due to high probability of defects, lattice mismatch and interface interactions. The steep rise of Tan δ values in the Al/Al2O3/TiO2/n-Si structure is due to the resonance effect of both Al2O3 and TiO2 layers. The leakage current mechanisms of MOS structures were extracted from Schottky coefficient and Poole–Frenkel coefficient. Theoretical values of Schottky coefficients (βSC) and Poole–Frenkel coefficients (βPF) for each sample were estimated using the real part of the dielectric constant. The experimental values were calculated from J–V characteristics and compared with theoretical values. The appropriate model has been proposed. It was found that Schottky and Poole–Frenkel mechanisms are applicable at low and high field respectively for all MOS structures. The combination of Al/Al2O3/TiO2/n-Si is found to be a promising structure with high dielectric constant and low leakage current suitable for MOS devices.