Effect of substrate bias voltage on the structure, electric and dielectric properties of TiO 2 thin films by DC magnetron sputtering

Abstract

Titanium dioxide (TiO 2) films have been deposited on glass and p-silicon (1 0 0) substrates by DC magnetron sputtering technique to investigate their structural, electrical and optical properties. The surface composition of the TiO 2 films has been analyzed by X-ray photoelectron spectroscopy. The TiO 2 films formed on unbiased substrates were amorphous. Application of negative bias voltage to the substrate transformed the amorphous TiO 2 into polycrystalline as confirmed by Raman spectroscopic studies. Thin film capacitors with configuration of Al/TiO 2/p-Si have been fabricated. The leakage current density of unbiased films was 1 × 10 −6 A/cm 2 at a gate bias voltage of 1.5 V and it was decreased to 1.41 × 10 −7 A/cm 2 with the increase of substrate bias voltage to −150 V owing to the increase in thickness of interfacial layer of SiO 2. Dielectric properties and AC electrical conductivity of the films were studied at various frequencies for unbiased and biased at −150 V. The capacitance at 1 MHz for unbiased films was 2.42 × 10 −10 F and it increased to 5.8 × 10 −10 F in the films formed at substrate bias voltage of −150 V. Dielectric constant of TiO 2 films were calculated from capacitance–voltage measurements at 1 MHz frequency. The dielectric constant of unbiased films was 6.2 while those formed at −150 V it increased to 19. The optical band gap of the films decreased from 3.50 to 3.42 eV with the increase of substrate bias voltage from 0 to −150 V.