Growth Of Oriented Ba_0.5Sr_0.5TiO₃/La_0.5Sr_0.5CoO₃ Films On SiO₂/Si Substrate By Pulsed Laser Deposition

Ferroelectric (Ba,Sr)TiO₃ thin films have excellent ferroelectric and dielectric properties, and own good application prospect in tunable microwave devices, dynamic random access devices, and pyroelectric detector devices.In this thesis, the Ba_1-X Sr_x TiO₃ (x =0.5, 0.4) targets are prepared by conventional ceramic route. The effects of sintering condition on the crystallinity and the dielectric properties of the targets are studied. The results show that the suitable temperatures of sintering should be 1350 °C for both of x = 0.5 and x = 0.4, higher or lower sintering temperature should lead to lower dielectric properties.We analyzed several traditional substrates and bottom electric materials using in BST film capacitors, and chose SiO₂ /Si as substrates for potential uses in the integration of ferroelectric materials with conventional Si process technology, and using LSCO as bottom electrodes as its better structural/chemical compatibility and a cleaner interface (less charged defects) between LSCO and BST films. The BST/LSCO/SiO₂/Si multilayered ferroelectric heterostructure were successfully prepared.Growth and structural evolution of La_0.5Sr_0.5CoO₃ thin films fabricated directly on SiO₂ / Si substrate by pulsed laser deposition (PLD) were investigated. Films deposited at 780°C and oxygen partial pressure of 2Pa showed highly c-axis orientation. Films with low electrical resistivity of 2×10^-3Ω·cm were obtained by annealing at 650 ℃ for 40 min.C-axis oriented Ba_0.5Sr_0.5TiO₃ (BST) thin film was then grown on the LSCO film. The dielectric constant of the films were about 110, loss tangent were 0.06, and large dielectric tuning (>50%) was achieved.