Dielectric Tunability Properties and Thermal Stability of (Ba,Sr,Ca)TiO 3 Thin Films Prepared by the Sol-Gel Method
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0966-T10-14
Dielectric Tunability Properties and Thermal Stability of (Ba,Sr,Ca)TiO3 Thin Films Prepared by the Sol-Gel Method Wei Qin, Wanhai Chen, Wenbiao Wu, Jinrong Cheng, and Zhongyan Meng School of Materials Science and Engineering, Shanghai University, 149 Yanchang Road, Box 32, Shanghai, 200072, China, People's Republic of ABSTRACT A new family of (Ba1-x-ySrxCay)TiO3 (BSCT) thin films was prepared on Pt(111)/TiO2/SiO2/Si substrates by using sol-gel techniques. BSCT thin films with Ba/Sr/Ca ratio of 15/55/30, 20/45/35 and 25/35/40 were investigated, which were selected at the cubic region in the vicinity of the cubic-tetragonal phase boundary according to the ternary phase diagram of BaTiO3SrTiO3-CaTiO3. X-ray diffraction analysis indicates that BSCT thin films are of the cubic perovskite structure. No hysteresis window can be observed from the capacitance-voltage curves, reflecting that BSCT thin films are in the paraelectric phase. The dielectric constant and tunability of BSCT thin films were investigated in the temperature range of 200-370 K. The Curie temperature Tc increases with increasing Ba concentration. INTRODUCTION Thin films of perovskite-type barium strontium titanate (BST) have attracted extensive attention in the past decades due to the promising applications in tunable microwave devices [13]. For this application, BST thin films are required to have low dielectric constant, large tunablity, low dissipation factor and low temperature dependence [4]. Substitution of Mn2+, Ni2+, and Mg2+ for Ba2+ ions are utilized to reduce the dielectric loss of BST thin films [5,6]. The compositional gradient structure of BST thin films is investigated to improve the dielectric stability with temperature, whereas involving the complex processing to prepare the multilayer structures [7]. But the method of complex oxide thin films preparation and the enhanced strong polarization in asymmetric three-component ferroelectric superlattices have been reported [8,9]. It has been reported that the proper ratio of Ba/Sr/Ca in the (Ba,Sr,Ca)TiO3 ternary system produce the comparable dielectric tunability without causing the dielectric loss to increase. The addition of CaTiO3 may suppress the dielectric loss and the temperature dependence of BST simultaneously, without causing the significant variation of Curie temperature [10]. The substitution of Ca ions for the A-site cation of BST thin films can set the temperature of phase transition over a wide range. The BaTiO3, SrTiO3 and CaTiO3 ternary system is expected to be more stable in a certain temperature range [11]. There are some papers to investigate the effect of Ca-doping on the structure and dielectric properties of BST ceramics. The Ca-doped BSCT ternary system is of particular interest as novel microwave tunable materials [12-16]. However, most of these studies focus on bulk materials and thick films. To authorsí knowledge, it is lack of reports on BSCT thin films. In this paper, (Ba0.15Sr0.55Ca0.3) TiO3, (Ba0.2Sr0.45Ca0.35) TiO3 and (Ba0.25Sr0.35Ca0.4) TiO3 thin
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