Dielectric dispersion and tunability of sol-gel derived BaxSr1-xTiO3 thin films

Abstract

Ba0.5Sr0.5TiO3, Ba0.6Sr0.4TiO3, Ba0.7Sr0.3TiO3 and Ba0.8Sr0.2TiO3 thin films were fabricated by a modified sol-gel technique on Pt(111)/Ti/SiO2/Si(100) substrates. All BaxSr1-xTiO3 films crystallized in the perovskite structure with a crack free microstructure and clear grain boundaries. Highest relative permittivity and dielectric tunability was observed in the Ba0.7Sr0.3TiO3 thin film. Ba0.7Sr0.3TiO3 and Ba0.8Sr0.2TiO3 compositions demonstrated ferroelectric hysteresis loops indicating the presence of ferroelectricity at room temperature. The paraelectric compositions of Ba0.5Sr0.5TiO3 and Ba0.6Sr0.4TiO3 showed significant tunability with negligible loss tangent. The tunability of Ba0.5Sr0.5TiO3 thin film decreased with the increase of frequency from 100 kHz to 100 MHz. As the frequency increases, especially above 10 MHz, the relative permittivity decreases while the loss tangent increases. Since Ba0.5Sr-.5TiO3 thin film is paraelectric at room temperature, relaxation due to ferroelectric domains cannot occur. Therefore this behaviour has originated from the contact resistance and finite sheet resistance of both the bottom and top electrodes. To analyse the thin film capacitor, the parallel plate capacitor structure can be modeled based on an equivalent circuit, which contain electrode and contact resistance.

Hong Kong Polytech Univ, Dept Appl Phys, Kowloon, Hong Kong, Peoples R China; Hong Kong Polytech Univ, Mat Res Ctr, Kowloon, Hong Kong, Peoples R China; Univ Moratuwa, Dept Mat Engn, Moratuwa, Sri Lanka