锆钛酸钡钙压电薄膜的界面优化与疲劳特性研究

Fatigue failure is the key issues to the final application of piezoelectric thin film, and, mutual diffusion between thin film and electrode was regarded as an important factor to cause the fatigue failure. In addition, it was very necessary to elaborate the relationship between texture and fatigue characteristic at low crystallization temperature which the silicon circuit can support. In our project, 0.5(Ba0.7Ca0.3)TiO3-0.5Ba(Zr0.2Ti0.8)O3 (BCZT50) piezoelectric thin film was selected as the object of study, in order to solve a series of issues which should be solved immediately such as higher crystallization temperature, serious mutual diffusion in the process of the preparation of lead-free piezoelectric thin film, the seed layer was introduced between film and electrode, which is expected to control the thin film orientation at low temperature. Meanwhile, the relationship between interface diffusion and crystallization temperature was studied in detailed. Furthermore, the influences of crystallization behavior, interface diffusion, orientation and on fatigue and leakage current behavior of the film were investigated, and it is further clarify that the mechanism for fatigue failure which was influenced by some factors such as interface and orientation, and it also developed an best craftwork to improve the anti-fatigue property of the thin film, which will establish the experimental and theoretical basis for the monolithic integration of piezoelectric thin film.

疲劳失效是压电薄膜应用必须要解决的关键问题之一，而薄膜与底电极之间的相互扩散被认为是引起疲劳时效的重要因素。另外，在硅基电路能承受的较低结晶温度下，阐述取向类型与疲劳特性之间的关系也是非常必要的。本项目选取0.5(Ba0.7Ca0.3)TiO3- 0.5Ba(Zr0.2Ti0.8)O3 压电薄膜为研究对象，针对薄膜在制备过程中晶化温度过高、界面扩散严重等一系列亟待解决的问题，提出在薄膜-基底处引入界面层的研究方案，以期在较低的结晶温度下，实现薄膜的取向调控；同时对界面扩散进行表征，建立结晶温度与界面扩散之间的有机联系，最终达到优化界面的目的。在此基础上，研究薄膜晶化行为、界面扩散程度、取向类型等对薄膜疲劳、漏电流特性的影响规律，从根本上阐明界面、取向等因素对薄膜疲劳失效的影响机理，并探索出一种提高薄膜抗疲劳性能的最优方案，为无铅压电薄膜的单片集成奠定实验与理论基础。

在准同型相界处于室温附近时，锆钛酸钡钙(BCZT)具有与铅基材料相媲美的优异压电性能。BCZT陶瓷和薄膜被认为是最有潜力的无铅压电材料，也是压电集成器件的最佳选择之一。项目利用固相反应法制备了LiNbO3、MgF2、NaF与CaCl2助烧和Y2O3、Ta2O5与Tb4O7掺杂改性的BCZT陶瓷，建立了结构和压电性能的关系规律，获得了降低陶瓷烧结温度并改善压电性能的有效途径；以BCZT陶瓷为靶材，采用脉冲激光沉积法（PLD）在Pt(111)/Si衬底上生长了BCZT薄膜，通过等离子羽辉输运理论研究，阐明了Ba、Ca、Ti和Zr粒子的迁移和分布规律，通过退火温度、界面层和Tb4O7掺杂改性优化，探索了改善薄膜漏电流、铁电压电性能和疲劳特性的方法和机制。研究结果表明：1、低浓度助烧剂的引入，有利于改善BCZT的结构、致密度和铁电、压电性能，仅0.3wt%浓度的烧结助剂即可使BCZT的最佳烧结温度降低60℃；2、三价Y3+、Tb3+离子和五价Ta5+离子在BCZT晶胞中分别属于A位和B位施主掺杂， Y2O3、Ta2O5与Tb4O7的最佳掺杂浓度均为0.2~0.3mol%，能够将BCZT陶瓷的剩余极化强度提高至10μC/cm2以上；3、BCZT薄膜PLD生长羽辉中Ca粒子的迁移速率和膨胀尺寸大于Ba、Ti和Zr粒子，更易偏离化学计量比；4、BCZT薄膜的最佳生长温度为约650℃，激光能量为约2J/cm2，氧气分为15~30Pa；5、退火处理能够促进BCZT薄膜的晶粒生长、致密化和漏电流的降低，进而显著改善薄膜的铁电和压电性能；6、0.4mol%的Tb4O7掺杂可以使BCZT薄膜的漏电流降低2个数量级以上，不仅可以提高其相对介电常数和降低介电损耗，且能够显著改善陶瓷的铁电、压电和疲劳特性。本项目的研究提供了有效改善BCZT陶瓷和薄膜性能的方法和机制，对促进BCZT无铅压电陶瓷的实用化和推动无铅压电薄膜单片集成，均有着重要理论和实验价值。