Electrical properties and crystal structure of (Ba,Sr)TiO3 films on metallic oxide bottom electrodes

• Main Authors: Chung Ming Chu, 朱聰明
• Other Authors: Pang Lin
• Format: Others
• Language: zh-TW
• Published: 1999
• Online Access: http://ndltd.ncl.edu.tw/handle/99970414616009268052

博士 === 國立交通大學 === 材料科學與工程系 === 87 === There are three part of discussions were included in this study. In chapter 2, (Ba,Sr)TiO3 (BST) films on Pt electrode were fabricated with different Ba/Sr ratio BST ceramic as targets by radio-frequency (rf) magnetron sputtering at various substrate temperatures and O2/(Ar+ O2) mixing ratios (OMR). In chapter 3, BST films were deposited on (100) prefer orientation LaNiO3 elctrodes, Which were prepared by rf magnetron sputter deposition, the effects of LaNiO3 electrode on BST electrical and structure characteristics were discussed. In chapter 4, BST films were deposited on (110) prefer orientation BaRuO3 elctrodes, Which were prepared by rf magnetron sputter deposition, the effects of BaRuO3 electrode on BST electrical properties and crystal structure were discussed. We have some comparsions and conclusions in chapter 5. In chapter 2, We were using different Ba/Sr ratio BST ceramic as targets, (Ba1-xSrx)TiO3, x = 0.3 ~ 0.7, to fabricate BST films on Pt electrode by rf sputtering. As x=0.5, The BST films compositions was, (Ba+Sr)/Ti=1.007, Ba/Sr=0.42/0.58, with good composition stoichio-metric and dielctric properties. The crystallinity, dielctric constant, and leakage current characteristic of BST films were inceased with deposition OMR and deposition temperature (Td). The film deposited at Td= 550℃ and 50% OMR had a dielectric constant of 450, equivalent silicon-oxide thickness was 0.76nm, and the leakage current density was about ~5×10-7A/cm2 at an electric field of 150KV/cm. In chapter 3, BST films on a LaNiO3 underlayer were prepared by radio frequency magnetron sputter deposition. The onset of crystallization of the BST films occurred at a deposition temperature (Td) as low as 200℃. Good crystallinity was observed at Td  350℃. A moderate high dielectric constant (r ~ 170-250) of the films was obtained at relatively low Td ~ 200-300℃. The value of r showed a much slower increase with Td  350℃ than that expected from the progress of crystallinity. The deviation was attributed to an interdiffusion layer formed between the film and underlayer, which also caused an abnomal contact potential barrier and decilne of the r value of the samples postannealed at 350℃. Annealing at 300℃ under O2 atmosphere lessened the oxygen deficiency in the film and enhanced the dielectric constant without forming an interfacial layer. In chapter 4, BST films were synthesized on BaRuO3 (BRO) using radio-frequency magnetron sputter deposition. Conductive (~1mΩ-cm) BRO layers of (110) texture were produced at a deposition temperatured 400℃, about 200℃ lower than that of SrRuO3. The BST (100nm) deposited on BRO showed a (110) prefer orintation and crystallization formation at temperatures as low as 200℃. An interfacial layer and the local epitaxial growth of BST on BRO layers within columnar grains were confirmed by high-resolution transmission-electron microscopy studies. Uniform I-V characteristics (J < 5×10-7A/cm2 ) for bias voltages in the range 0.0-3.0V of all the BST films deposited within Td=300-500℃ were observed. The dielectric constants of the BST films (e.g., r = 300 at Td = 400℃) are considerably higher than generally achievable for the same Td by using Pt bottom electrodes. The dependence of the annealing atomsphere (N2 and O2) of the dielectric constants was studied and attributed to a diffused BST/BRO interfacial layer which is semiconductive in a reduced state and insulating in an oxidized state. In summery, Dielectric properties of the BST films were found to be closely correlated with the film’s structure or its crystallinity. A significant improvement in crystallization and electrical properties of BST films which were deposited at low temperature (Td = 350℃) through the perovskite type LNO and BRO electrodes. The interfacial diffusion layer on BST/LNO, and BST/BRO interfaces were avoidless, because the crystal structures and ionic radius of BST were similar to LNO and BRO. So the control of processes temperature were very important.