【作者】 彭静；

【导师】 揭泉林；

【作者基本信息】 武汉大学 ， 理论物理， 2013， 博士

【摘要】 铁电薄膜材料和器件的研究目前仍然面临着很多问题,如光学和光电转换系数提高优化问题、在大规模光电集成电路(OEICs)中集成化与兼容性问题、薄膜化引起的界面问题、小型化带来的尺寸效应和加工、表征问题等等。本论文以钛酸钡系铁电薄膜为研究对象,较为系统地研究钛酸钡(BTO)和钛酸锶钡(BST)薄膜的制备及表征、光学特性和应用。本论文的研究成果主要有：发展了晶态铁电薄膜低温(≤550℃)制备工艺和高度择优取向生长的制备工艺。采用溶胶—凝胶(Sol-Gel)法和金属有机分解(MOD)法于550℃成功制备出了结晶态良好的BST薄膜,采用磁控溅射法于450℃获得了(100)择优取向生长的BST薄膜,这些工艺是目前已经报道的具有较低温度制备的工艺之一。铁电薄膜的低温成功制备对其在OEICs的集成应用是十分有益的。另外,采用磁控溅射法在SiO2/Si基底上于700℃获得了高度(100)择优取向生长的晶态BST的薄膜。在非晶SiO2层上制备出高度择优取向生长的铁电薄膜一直是该领域研究的热点与难点之一较为系统地研究了单片集成即硅基底上多晶BST薄膜的光学及光电行为。SiO2/Si基底上高度(100)择优取向生长的晶态Ba0.5Sr0.5TiO3的薄膜的光带隙能Eg值与沉积温度和薄膜的厚度表现出很大相关性,主要是由于量子尺寸效应和受到薄膜结晶度,如晶界、粒度、取向生长和非晶相的存在等的影响。薄膜的这种Eg值与结晶度的相关性有望应用到集成光器件中。基于多晶(BST0.7)薄膜首次在硅衬底制备了单片集成Mach-Zehnder电光调制器,成功实现了光的调制。多晶BST0.7薄膜的电光系数为2.4pm/V。设计和制备出了铁电薄膜沟槽掩埋型光波导,并且基于双反射镜原理设计和成功制备出了小尺寸低损耗的90°直角弯曲光波导,该结构波导便于工艺制作、OEICs的光电集成和光传输损耗的定量标准测量。对于5μm宽、300nm厚的多晶BST0.7平面光波导在632.8nm波长的光传输损耗大约是17dB/cm。对于5和10μm宽的非晶态BST0.7薄膜波导在632.8nm波段的光传输损耗分别为12.8和9.4dB/cm,所制备的90°弯曲结构损耗分别为1.2和0.9dB。非晶态BST0.7薄膜波导比用于OEICs的高折射率差△的Si/SiO2波导的损耗(34dB/cm)小得多,比晶态BST0.7薄膜波导的光传输损耗也要小30%。该非晶BST0.7薄膜用于OEICs光波导是具有潜在应用价值的。通过理论分析提出了一种新的薄膜光学常数计算测量的方法。厚度约为214nm的非晶BST0.7薄膜的光学带隙能和折射率分别为：4.27eV和n=1.94。薄膜在可见光和近红外区域的消光系数远远低于多晶BST薄膜,约为10-3数量级。研究了非晶BST和BTO薄膜室温光致发光(PL)性能及其机理,用能带跃迁模型来进行了很好的解释,基于该薄膜的这种PL性能,首次应用到LED器件上,实现了基于非晶BTO薄膜白光LED器件。约150nm厚非晶BTO薄膜InGaN/GaN多量子阱LEDs呈现蓝白光,CIE坐标为(0.2139,0.1627)。基于非晶BTO薄膜白光LED器件的实现,与传统工艺比较很容易实现保形涂覆结构、在可见光波段具有高透光性能、不需要粘结剂且可以在更高的温度下使用等很多优点,为发展LED提供了一种新的思路。更多还原

【Abstract】 The study of ferroelectric thin film materials and devices is still facing a lot of problems, such as improvement and optimization problems of optical and optoelectronic conversion factors, integration and compatibility problems in large-scale optoelectronic integrated circuits(OEICs), interface problems caused by thin film, and size effect, processing and characterization problems brought by small size, etc. In this paper, we take barium titanate-based ferroelectric thin films as the research object and relatively systematically study the preparation and characterization, optical performance, application of barium titanate (BTO) and barium strontium titanate (BST) thin films.The main research results in this paper are as follows:Developments of the preparation process of ferroelectric thin film at low temperature (≤550℃) or highly preferred oriented growth have been implemented. We successfully prepare crystalline BST thin films at550℃by using Sol-Gel method and metal organic decomposition (MOD) method. The crystalline BST thin film with (100)-oriented growth have been fabricated at700℃by the magnetron sputtering. These processes are one of preparation processes at lower temperature reported so far. The preparation of ferroelectric thin film at low temperature can be very useful for integrated application of OEICs. Besides, we obtained crystalline BST thin film with highly (100)-oriented growth on SiO2/Si substrate at700℃by the magnetron sputtering. The preparation of ferroelectric thin films with highly oriented growth on amorphous SiO2layer has been a hot spot and one of the difficulties of researches in this field.We relatively systematically studied the optical and optoelectronic behaviors of polycrystalline BST thin film monolithically integrated on silicon substrate. The optical band gap Eg of crystalline Ba0.Sro.5TiO3film with highly oriented growth on SiO2/Si substrate showing great correlation with the deposition temperature and the thickness of film, which is mainly due to the quantum size effect and influenced by crystallinity of thin film, such as grain boundaries, size, orientation growth and the presence of amorphous phase, etc. It is believed that dependence of the band-gap energies of the thin films on the crystallinity such as deposition temperature and film thickness should find applications in integrated optical devices. We firstly prepare the monolithically integrated Mach-Zehnder electro-optic modulator on silicon substrate based on the polycrystalline Ba0.5Sr0.5TiO3(BST0.7) thin film. The modulation of light has been successfully achieved. The electro-optic coefficient of the polycrystalline BST0.7film is2.4pm/V.We successfully designed and prepared a ferroelectric thin film groove-buried optical waveguide. The90°bent structures with a small curvature of micrometers have been also designed on the basis of a double corner mirror structure. It is easy for the waveguides with the designed structures to be fabricated and integrated in OEICs. The quantitative standard measurement of the light transmission loss also becomes easy. The optical propagation losses were about17dB/cm for the5μm wide and300nm thick polycrystalline BST0.7film waveguides at the wavelength of632.8nm. It was found that the optical propagation losses were about12.8and9.4dB/cm and the90°bend losses were about1.2and0.9dB respectively for5and10μm wide waveguides at the wavelength of632.8nm., which are much smaller than that in high index contrast polycrystalline Si/SiO2waveguides for the optical interconnection in monolithic OEICs (34dB/cm) and30%smaller than the optical propagation losses of crystalline BST0.7thin film waveguide. It is obvious that amorphous BST0.7thin film groove-buried type waveguides can be promised in being applied not only for the optical interconnection in monolithic OEICs but also for active waveguide devices on the Si chip despite the optical losses are not very small at present.We proposed a new method for thin film optical constants measurement by theoretical analysis. For the amorphous BST0.7film with the thickness of about214nm, the optical band gap is4.27eV and refractive index n=1.94. The extinction coefficient of the film in the visible and near-infrared region is far below the polycrystalline BST film, approximately the magnitude order of10"3. We studied the room temperature photoluminescence (PL) properties and mechanism of the amorphous BST and BTO films. The PL phenomenon was well explained by using the model of band to band transition. Due to the PL performance of film, we firstly applied it to LED devices and obtained white LED devices based on the amorphous BTO film. The InGaN/GaN multi-quantum well LEDs based on the150nm thick amorphous BTO film display a blue-white light. The coordinates value of CIE is (0.2139,0.1627).Compared with the traditional process, it is more easy for the white LED devices based on the amorphous BTO film to implement the structure of conformal coating. The BTO thin film has high transparent performance in the visible wavelength. The binders were not used in the fabrication of the LEDs based on the amorphous BTO film. So, they could be used at higher temperature. It provides a new way to study LEDs.更多还原