Ba(Zr_0.2Ti_0.8)O₃介质薄膜生长及Mn掺杂效应研究

【作者】 接文静；

【导师】 张鹰；

【作者基本信息】 电子科技大学 ， 电子信息材料与元器件， 2008， 硕士

【摘要】 Ba(Zr_xTi_1-x)O₃ （BZT）,为Zr部分B位取代BaTiO₃（BTO）中的Ti而形成的一种BTO基钙钛矿材料。由于Zr⁴⁺比Ti⁴⁺化学稳定性更好,Zr⁴⁺取代Ti⁴⁺之后将会抑制Ti⁴⁺与Ti³⁺之间的电子跃迁,从而减小了薄膜的漏电流。因此BZT在具有较高的介电可调的同时可以保持低的介电损耗,这使得BZT得到了广泛的研究。本论文选择BZT中介电性能较好的Ba(Zr_0.2Ti_0.8)O₃,通过脉冲激光沉积设备,在氧化物衬底以及Si衬底上沉积BZT以及2% Mn受主掺杂的BZT薄膜,系统的研究了BZT薄膜的生长以及掺杂、温度、厚度、底电极等对BZT薄膜结构与性能的影响。主要包括以下内容:首先,在氧化物衬底（沉积有LaNiO₃的LaAlO₃（001）,沉积有SrRuO₃的MgO（001））上,在600℃的沉积温度下实现BZT及Mn掺杂BZT薄膜cube-on-cube的方式外延生长。通过Mn掺杂,在LAO衬底上沉积BZT薄膜可调由49.1%提高到59.4%,损耗由2.5%降低到1.8%;在MgO衬底上沉积的BZT可调由42.7%提高到52.4%,损耗由2.6%降低到2.0%。同时研究了BZT薄膜厚度与其介电性能的关系,发现介电可调随着薄膜厚度的减小,呈现先增大后减小的变化规律,这可由界面应力以及介电“死层”两种机制的竞争来解释。其次,在Pt/Ti/SiO2/Si衬底上,在700℃的沉积温度下,实现BZT及Mn掺杂BZT薄膜面外（111）取向择优生长。通过Mn掺杂,BZT薄膜结晶性能得到改善,介电可调由60.9%提高到69.0%,损耗由6.5‰降低到5.0‰。同时研究了生长温度对BZT薄膜介电性能的影响,随着生长温度的升高,介电可调增加,损耗降低,并且BZT薄膜由室温顺电相变为室温铁电相。这种随着沉积温度升高铁电性增强可能源于BZT薄膜与Si衬底间较大的热膨胀失配。论文对Mn掺杂的机理进行了初步研究。Mn掺杂改善BZT薄膜介电性能可能源于Mn掺杂改善了薄膜的结晶性能,降低了BZT的费米能级,以及Mn掺杂使得BZT薄膜电荷浓度降低,自由电子减小以及Mn T’ ’ i - VO..缺陷复合体沿着外加电场重新排列。更多还原

【Abstract】 Ba(Zr_xTi_1-x)O₃ （BZT） is obtained by substituting ions at B site of BaTiO₃ with Zr in compounds of the perovskite structure of ABO₃. This is possible because Zr4+ is chemically more stable than the Ti4+ that the substitution of Ti⁴⁺ with Zr⁴⁺ would depress the conduction caused by electronic hoping between Ti⁴⁺ and Ti³⁺. Therefore, BZT could exhibit high dielectric tunability with low dielectric loss. So BZT has been widely invested as a possible material of tunable microwave device applications. So in this thesis, Ba（Zr0.2Ti0.8）O3 （BZT） and 2 mol % additional Mn-doped Ba(Zr_0.2Ti_0.8)O₃ （Mn-BZT） thin films had been prepared on single crystal oxide substrates and Pt/Ti/SiO₂/Si by pulse laser deposition （PLD） technique. The growth of films and the effect of Mn doping, deposition temperature, thickness of films and bottom electrodes on the structural and electric properties had been systematically investigate. This dissertation had touched the following aspects:Firstly, BZT and Mn-BZT films were deposited on LaNiO3 （LNO） coated LaAlO3（001）and SrRuO3 （SRO） coated MgO（001） single crystal oxide substrate. It had been found that both films could be with a cube-on-cube arrangement on single crystal oxygen substrates at 600℃. The dielectric tunability increased from 49.1% to 59.4% and the dielectric loss at zero bias decreased from 2.5% to 1.8% by Mn doping for BZT films on LNO/LAO. The dielectric tunability increased from 42.7% to 52.4% and the dielectric loss at zero bias decreased from 2.6% to 2.0% by Mn doping for BZT films on SRO/MgO. Additionally, the effect of film thickness on the dielectric properties of BZT films was studied. With the derease of film thickness, the dielectric tanubility first increased and then decreased, whicn can be interpreted by the competition between the interface stress and dielectric“dead layer”.Secondly, BZT and Mn-BZT films were prepared on Pt（111）/Ti/SiO₂/Si（100） substrates by PLD. It indicated both films were deposited with a preferential （111） grain orientation at 700℃. And the properties of crystallization for BZT films were enhanced by Mn doping. The dielectric tunability of preferential （111）-oriented BZT film on Pt/Ti/SiO2/Si increased from 60.9% to 69.0% and the dielectric loss at zero bias decreased from 6.5‰to 5.0‰by Mn doping. Meanwhile, it was found that the dielectric properties were affected by deposition temperature. With the increase of deposition temperature, the tunability increased and the loss decreased. Furthermore, the ferroelectricity was enhanced at higher deposition temperature. It would be due to the large mismatch of themal expansion coefficient between BZT films and silicon substrates.The mechanism of Mn doping had been investigated. The enhanced dielectric behavior by Mn doping could be mainly attributed to enhanced crystallization and the lowering of Fermi levels of BZT films and the decrease of electron concentration and free electrons, and the reorientation of the defect complex of Mn T’ ’ i ? VO...更多还原