Growth and dielectric characterisation of large grain BiFeO 3 thin films on amorphous SiO 2 substrates

Abstract

The BiFeO3 (BFO) thin films have been grown by pulsed laser deposition technique on fused silica substrates with pre-patterned inter-digital Au electrodes. The surface images reveal that with increasing growth temperature some needle-shaped grains develop rapidly from the electrode edges in the film plane and at 600 degrees C fill up the 6 gm gap between the electrodes. The x-ray diffraction patterns reveal BFO (001) peaks and additional peaks associated with Bi and Fe oxides. The dielectric response of the BFO films is measured as a function of external dc field up to 200 kV/cm at 10 MHz, and in the frequency range 0.01-45 GHz without dc field. The capacitance-voltage dependence reveals typical ferroelectric behaviour with a coercive field approximately 60 kV/cm. The permittivity (24) of non-poled BFO films is rather frequency independent, at least up to self resonance frequency (about 15 GHz) of the inter-digital test structure including BFO film. The loss tangent increases with frequency and is less than 0.02 at 1 GHz. It is found that the normal magnetic field 0.2 T decreases permittivity of non-poled BFO films approximately by 0.3%.