【作者】 王新昌；

【导师】 叶志镇；

【作者基本信息】 浙江大学 ， 材料物理与化学， 2005， 博士

【摘要】 LiNbO₃因具有优异的电光、压电、非线性光学等特性,已被广泛应用于声表面波及集成光学器件中。制备集成光学器件常需将LiNbO₃制成各种形式的光波导结构,但传统方法制备的光波导薄膜存在较多的缺点,因而异质LiNbO₃薄膜引起了人们的关注。与体单晶相比,异质LiNbO₃薄膜具有明显的优势,如可以获得较大的波导膜与衬底折射率差。至今人们已经采用多种薄膜生长技术来制备异质LiNbO₃薄膜,相比其它薄膜生长技术,脉冲激光沉积法具有能保持靶与薄膜组分一致的优点,在多元氧化物薄膜制备方面有着独特的优势。硅材料作为半导体微电子工业的基石,在硅衬底上生长LiNbO₃薄膜与目前半导体工艺兼容,有利于光电集成且价格低廉,具有广阔的应用前景。因而,开展硅基LiNbO₃薄膜的研究具有非常重要的意义。 本文在总结了LiNbO₃薄膜制备研究现状的基础上,利用PLD技术对硅基LiNbO₃薄膜的生长及性能进行了研究,为了与硅基上制备的LiNbO₃薄膜进行比较,作者还对蓝宝石衬底上制备的LiNbO₃薄膜的质量及性能进行了研究。通过研究得出以下主要结果: 1.首次在未施加诱导电场和缓沖层的情况下采用PLD技术在SiO₂/Si衬底上生长出了具有良好晶体质量的完全c轴取向LiNbO₃薄膜。系统研究了工艺参数对LiNbO₃薄膜质量的影响,获得了生长LiNbO₃薄膜的最佳工艺参数:衬底温度约为600℃,氧压约为30Pa,激光能量密度为3.2-3.7J/cm²,激光频率约为3Hz,靶材与衬底距离约为4cm,非晶SiO₂过渡层厚度约为230nm。 2.等化学计量比LiNbO₃薄膜的生长是薄膜制备中的难点。作者借助XPS、SIMS测试,发现通过优化工艺参数采用等化学计量比的LiNbO₃陶瓷靶材在SiO₂/Si衬底上生长出了等化学计量比的LiNbO₃薄膜,且薄膜组分随深度变化均匀。初步探讨了SiO₂/Si衬底上LiNbO₃薄膜的生长机制,提出了其生长模型。 3.成功地在SiO₂/Si衬底上制得低传输损耗的LiNbO₃薄膜,最低传输损耗为1.14dB/cm,优于文献报道硅基LiNbO-3薄膜的传输损耗。表面形貌作为影响传输损耗的一个重要因素,本文分析了衬底温度和激光频率对薄膜粗糙度的更多还原

【Abstract】 As an important ferroelectric material for fabrication of SAW and integrated optical devices, LiNbO₃ exhibits excellent electro-optical, piezoelectric and nonlinear optical properties. Generally speaking, LiNbO₃ wave-guided structures are demanded in the optical devices. However, there are several problems in the traditional wave-guide films so that there are increasing interests on the fabrication hetero-structure LiNbO₃ films. Compared with bulk materials, hetero-structure LiNbO₃ films possess a series of advantages, like available step index profiles in the multilayer structures. Up to now, there have been various techniques which were used to prepare the hetero-structure LiNbO₃ films. Among them, pulsed laser deposition （PLD） method shows some advantages over the others, for example, it is easier to prepare epitaxial stoichiometric films due to the high compositional consistency with the target. As the base in the microelectronic technology, Si is an interesting host for preparing LiNbO₃ films, because it provides an ideal and cheap substrate for large area processing of devices which can be integrated in the current semiconductor technology, and this will make it possible to develop integrated electro-optics technology. Therefore, this work on Si-based LiNbO₃ films is of great interests and potentials.In this paper, besides the introduction of past and current research on LiNbO₃ films, we investigated growth and properties of Si-based LiNbO₃ films by PLD. Comparing with Si-based LiNbO₃films, we also investigated growth of LiNbO₃thin films on sapphire substrate, and obtained the following results:1. Without the application of induced electrical field and any buffer layer, we firstly prepared the high-quality c-axis oriented LiNbO₃ films on SiO₂/Si substrate by PLD. Through systematically analyzing the influence of experimental parameters on the films growth, the optimal growth conditions were determined: substrate temperature （T_S） is ⁶00℃, oxygen pressure （P_o） is ³0 Pa, laser energy density is 3.2-3.7 J/cm², laser frequency is ³ Hz, substrate-to-target distance （L）is 4 cm, and the thickness of amorphous SiO2 layer is 230nm.2. Stoichiometric LiNbO3 film is a key factor during the investigation. From the results of XPS and SIMS, the as-grown films originated from the stoichiometric ceramic target in the optimal growth conditions exhibit ideal stoichiometric composition and uniform in the cross-sectional profile. Moreover, the film growing mechanism was also discussed, and the growth pattern was supposed.3. The as-grown film deposited on SiCVSi substrate exhibits a very low optical loss （1.14 dB/cm）, which is lower than those reported earlier. Moreover, because the surface morphology is believed to be an important factor on the optical loss, we also investigate the effect of the Ts and laser frequency on the film surface morphology.4. High-quality LiNbO3 films for SAW devices were firstly deposited on Si （111） substrate by PLD. Through the investigations of the growth parameters, the film surface morphology and the refractive index, we found that the films exhibited a smooth surface with the rms of 4.87 nm and the refractive index （no） were 2.279, when the Ts was higher than 600 °C. Moreover, the effects of post-annealing were also investigated.5. High-quality c-axis oriented LiNbC>3 films were firstly deposited on ZnO/Si substrates. Compared with the films deposited on SiCVSi and Si （111） substrates, the films on ZnO/Si substrates also exhibited good crystalline quality in the same optimal growth condition. However, the films on ZnO/Si substrates exhibits worse surface morphology than those on SiCVSi and Si （111） substrates and the value of rms are 6.67 nm. The refractive index （no） was 2.255.6. The fabrications of LiNbC>3 films on sapphire were investigated and the effects of Ts on the film growth were analyzed. The results of XRD <￡-scan show that the films deposited at sapphire exhibit 3-fold symmetry and epitaxial growth with the relationships of （001） LiNbC>3 II （001） AI2O3. Through analyzing the film surface morphology and optical properties, we found the film deposited at 600 °C has the stoichiometric composition and the value of rms is 2.71 nm which is smoother than that deposited on Si substrate. The refractive index of the film was measuredby UV-VIS spectrum as 2.283. Finally, we compared with the effects of different substrates such as SiCVSi, Si （111）, ZnO/Si, and sapphire on the crystal quality and the surface morphology of the film.更多还原