A comparative study on the electrical properties of Ba0.6Sr0.4TiO3 film capacitors with different top electrodes

Au/Ba_0.6Sr_0.4TiO₃ (BST)/La_0.5Sr_0.5CoO₃ (LSCO) and Pt/BST/LSCO ferroelectric capacitors were successfully constructed on (001) LaAlO₃ substrates via off-axis magnetron sputtering. X-ray diffraction (XRD) and Phi scan patterns confirmed that the BST film was epitaxial with an out-of-plane tetragonal phase. The ferroelectric and dielectric measurements reveal that, compared with the Pt/BST/LSCO capacitor, the Au/BST/LSCO capacitor exhibits a larger coercive field (∼139.7 kV/cm), smaller permanent polarization (∼2.94 $\mu C/{cm}^2$), and lower tunability (∼65.22 %), which may be attributed to the higher difference in work function and weaker depolarization field screen effect of the top electrode, as well as smaller interfacial capacitance of the Au/BST interface than those of the Pt/BST interface. Therefore, based on series capacitor model and leakage behavior analysis, the thickness and dielectric constant of interfacial layer are quantitatively determined to be 3.52 nm and 12.13 for Pt/BST, and 4.42 nm and 5.82 for Au/BST, respectively. Our results pave a way for improving the dielectric performance in electrically tunable microwave devices.