GaN衬底上复合缓冲层诱导BST类钙钛矿结构氧化物薄膜外延生长的研究

【作者】 经晶；

【导师】 李言荣； 朱俊；

【作者基本信息】 电子科技大学 ， 材料科学与工程， 2010， 硕士

【摘要】 以BST为代表的钙钛矿结构（ABO3）的多元氧化物是当今最热门的电子材料之一。作为微波及射频电路中无源器件的关键材料,它集铁电、介电等多种功能性能与一身。将这种功能材料与以GaN为代表的第三代半导体材料通过固态薄膜的形式集成,并利用这种集成的一体化及耦合特性,可以实现有源-无源的多功能器件集成化和模块化,增强系统功能,提高集成度。然而,由于两者在生长机制及晶体结构上存在巨大的差异,不易实现高质量的外延生长;同时,由于钙钛矿氧化物材料的各向异性,在GaN衬底上实现氧化物薄膜的取向控制尤为重要。因此,探索GaN衬底上钙钛矿结构的氧化物薄膜的生长行为并且实现取向控制对多功能集成元器件有十分重要的指导意义。本论文正是针对上述问题,以立方钙钛矿结构的SrTiO3（STO）主要的研究对象,利用TiO₂、YSZ、CeO₂以及YBCO等氧化物材料作为缓冲层,实现了GaN衬底上外延高质量的STO薄膜以及对其进行取向控制,分别得到了[001]、[110]、[111]三种典型取向的STO薄膜。并且,利用相同工艺实现了这三种取向的BST薄膜与GaN集成一体化。首先,采用脉冲激光沉积法,研究了沉积温度、氧分压和激光能量密度对薄膜生长相与取向的影响,得到了a轴取向的萤石相YSZ及CeO₂薄膜的择优工艺条件,达到取向生长可控。其次,通过复合缓冲层的诱导使STO薄膜实现c轴取向及[110]取向的外延生长,并且探求了STO薄膜在复合缓冲层上生长动力学模型。其中,利用YSZ/ TiO₂缓冲层诱导生长了（110）取向的STO薄膜;利用YBCO作为模板层,CeO₂/YSZ为缓冲层,TiO₂为种子层的复合结构外延生长了具有面内旋转畴结构的单一c轴取向SrTiO3薄膜,并确定外延关系为STO （200） [110]// YBCO（001）[110] //CeO₂ （200） [010]// YSZ （200）[010] //GaN（0001）[11-20]。并且,发现STO薄膜在萤石结构上生长时,其生长行为由晶格应力及离子键合作用两者共同决定。最后,通过复合缓冲层有效的诱导BST铁电薄膜沿三种典型取向生长,实现了BST/GaN的集成,并对原型器件的电学性能进行了探索。更多还原

【Abstract】 Pervoskite complex oxide materials such as BST- series materials are one of the most important functional materials. Such material is the key part of passive devices in microwave and RF circuits due to its outstanding multifunctional properties in ferroelectric, dielectric field. The heterostructure, which integrated the pervoskite thin films with GaN substrate （as the third generation semiconductor）, can fulfill the passive-active integrated devices, leading to the high multifunctional performance and increasing the level of integration. However, because of the large difference both in growth behavior and crystal structure between the pervoskite oxide and gallium nitride material, it is difficult to obtain the epitaxial thin films; Moreover, due to the anisotropy properties of pervoskite materials, it requires to control of the orientations of epitaxial films on GaN substrate. Therefore, it is crucial to explore a method to fulfill the epitaxial growth and orientation control of the pervoskite films on GaN substrate.In this thesis, SrTiO3 with cubic pervoskite have been analyzed. Then, using the multi-oxide-buffer-layer as TiO₂, YSZ, CeO₂ and YBCO layers, STO in three typical orientations had been epitaxially grown on GaN substrate, which was in [001], [110] and [111] respectively. Further, BST films in such orientations were integrated with GaN using same process conditions.Firstly, the a-axial oriented YSZ and CeO₂thin films with fluorite structure were prepared by pulsed laser deposition method. The dependence of the crystalline quality and crystal orientation of such films upon the process parameters （deposition temperature, oxygen pressure, pulse laser energy intensity） were systematically studied.Secondly, the STO films in [001] and [110] orientations have been grown on GaN substrate using multi-buffer-layers. The modeles in growth kinetics of STO films have been build up. Further, （110）-oriented STO films were obtained using YSZ/TiO₂ buffer layers; （001）-oriented STO films were prepared using YBCO/CeO₂/ YSZ/TiO₂ buffer layers, and the epitaxial orientation has been confirmed: STO （200） [110]// YBCO（001）[110] //CeO₂ （200） [010]// YSZ （200）[010] //GaN（0001）[11-20]. Moreover, the growth behavior of STO has been determined by both of the interface stress and ionic bonding when STO growing on fluorite surface.Finally, BST films in three typical orientations have been integrated with GaN substrate using the multi-oxide-buffer-layers technique. Further, the electric properties of such original integrated devices have been anglicized.更多还原