(100)-取向BiFeO3-基薄膜自极化调控

The ferroelectric thin films have to be polarized for their applications in piezoelectric micro-electro-mechanical and pyroelectric imaging systems. It has been demonstrated that the self-polarized ferroelectric thin films possess more excellent and stable piezoelectric and pyroelectric properties. As a promising lead-free material, BiFeO3 in thin film form has been investigated extensively for a decade. However, the high coercive field make the self-polarization more difficult to be formed in BiFeO3 thin films compared with the conventional PZT thin films. For solving this issue, (100)/(001)-oriented BiFeO3 thin films will be epitaxially grown on single crystalline substrates including MgO, SrTiO3, LaAlO3 and YSZ. The effects of the contact potential, epitaxial strain gradient, oxygen vacancies and structure change on the internal field as well as the interaction mechanism between these factors will be investigated based on tailoring the doping ions, thickness and stoichiometry of LaNiO3 electrode and BiFeO3 films as well as the annealing temperature and times. The key factors and processing conditions for maintaining the self-polarization during the thickening of the films will be identified. We will try our best to obtain the BiFeO3-based thin films with the controllable self-polarization in orientation and uniformity. In addition, the method to control the self-polarization of BiFeO3 thin film will be reproduced on Si substrates.

用于压电微机电系统和热释电红外成像系统中的铁电薄膜通常要先极化才能工作。研究表明，具有自极化的铁电薄膜往往表现出更优异的压电和热释电性能。作为一种具有广阔应用前景的无铅压电材料，BiFeO3薄膜已被广泛研究了近十年。然而，非常高的矫顽电场使BiFeO3薄膜与传统的含铅PZT薄膜相比更难产生自极化。针对这一难题，本课题拟以沉积在MgO、SrTiO3、LaAlO3和YSZ等单晶衬底上的(100)-或(001)-取向BiFeO3-基薄膜为研究对象，通过离子掺杂、改变LaNiO3电极和BiFeO3薄膜厚度和化学计量比、退火温度和气氛等方法揭示接触电势、外延应变梯度、氧空位、结构相变等因素对薄膜内偏场的影响和相互作用机制。确定影响自极化在薄膜增厚过程中得以维持的关键因素和工艺条件。努力获得自极化均匀性和方向均能可控的BiFeO3-基薄膜，并争取将自极化调控技术移植到硅基衬底上。

压电微机电系统和红外成像系统中的铁电薄膜通常要先极化才能工作，具有自极化的铁电薄膜往往表现出更优异的压电和热释电性能。作为一种具有广阔应用前景的无铅压电材料，BiFeO3薄膜已被广泛研究了近十年。然而，非常高的矫顽电场使BiFeO3薄膜与传统的含铅PZT薄膜相比更难产生自极化。针对这一难题，本课题以沉积在LaNiO3（100）/Si 、Pt(111)/TiO2/SiO2/Si等衬底上的(100)-取向BiFeO3-基薄膜为研究对象，通过离子掺杂、改变LaNiO3氧化电极和BiFeO3薄膜厚度和化学计量比、采用三明治结构、退火温度和气氛等方法揭示接触电势、外延应变梯度、氧空位、结构相变等因素对BiFeO3-基薄膜内偏场的影响以及这些因素的相互作用机制。我们的研究发现，在晶格匹配度较高的(100)-取向LaNiO3电极上容易实现BFO基薄膜(100)取向生长。在LaAlO3单晶衬底的成功获得了(100),(110)和(111)三种单一取向的Sm掺杂BFO薄膜。在Pt(111)/TiO2/SiO2/Si衬底上制备出具有自极化性能且压电性能非常优异的薄膜。上述这些发现为实现铁电薄膜的自极化和保持自极化的稳定性提供了新的途径。实现了在自极化均匀性和方向均能可控的BiFeO3-基薄膜，并成功在硅片上实现自极化薄膜的制备。