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题名: Mn1.56Co0.96Ni0.48O4薄膜的激光分子束外延制备及结构与电学性能研究
作者: 吉光
答辩日期: 2014-05-28
导师: 常爱民
专业: 微电子与固体电子学
授予单位: 中国科学院大学
授予地点: 北京
学位: 博士
关键词: 薄膜 ; 激光分子束外延 ; 负温度系数热敏电阻 ; 结构特性 ; 电学性能
摘要: 负温度系数(NTC)热敏电阻以其测温精度高、互换性好、可靠性高等优点被广泛应用于生产生活的诸多方面。近年来,在尖晶石型Mn-Co-Ni-O 薄膜NTC 热敏电阻的制备方面,虽然已经取得较大进展,但是要实现其在Si 基半导体器件工艺中的集成,首先需要解决晶态Mn-Co-Ni-O 薄膜制备温度过高的关键技术障碍。另外一方面,已有文献报道的Mn-Co-Ni-O 薄膜或为非晶态或为无择优取向的多晶态,未见单取向Mn-Co-Ni-O 薄膜的制备研究。然而,薄膜的许多电学、磁学及光学特性均为各向异性,与其生长取向密切相关,因此有必要研究和探索不同取向Mn-Co-Ni-O 薄膜的制备、生长机理及其特性差异。此外,由于尖晶石型Mn-Co-Ni-O 材料结构复杂、熔点高、且容易在高温结晶过程中产生第二相,故较难实现高质量外延薄膜的生长,目前尚无关于Mn-Co-Ni-O 薄膜外延生长的报道。然而,外延薄膜因其具有近乎完美的结晶质量、极低的缺陷密度、以及原子级平整的表面,故对于半导体薄膜器件性能及可靠性与稳定性的提升至关重要,因而有必要探索外延Mn-Co-Ni-O 薄膜的生长方法并对其性能进行研究。本论文首次将激光分子束外延(LMBE)技术应用于尖晶石型Mn-Co-Ni-O 薄膜的制备,以Mn1.56Co0.96Ni0.48O4 薄膜为研究对象,通过对制备工艺参数的优化,大幅降低了晶态Mn1.56Co0.96Ni0.48O4 薄膜的制备温度; 首次生长出[100] 单取向Mn1.56Co0.96Ni0.48O4 薄膜,并较为系统地研究了制备工艺参数对其结构与电学性能的影响;首次成功实现了外延Mn1.56Co0.96Ni0.48O4 薄膜的制备,并对其外延结构和电学性能进行了详细的表征和分析,同时发现了其电学性能的厚度效应。研究结果表明:(1) 采用LMBE 方法制备[100]单取向Mn1.56Co0.96Ni0.48O4 薄膜时,通过增大脉冲激光能量至275 mJ,提高背景真空度至1×10-6 Pa,可以将薄膜的最低晶化温度降至室温25 °C,远低于此前文献报道的最低晶化温度600 °C;入射激光与靶材表面之间夹角的最佳值为45°;靶衬间距应保持在40 ~ 60 mm 范围内;当脉冲激光频率在1~ 5 Hz 时薄膜呈现二维层状生长模式,当脉冲激光频率大于6 Hz 时薄膜的生长逐渐转变为三维岛状生长模式;原位退火处理可以使薄膜表面平整度显著提高,最佳原位退火处理时间为1 h;在空气气氛下对薄膜进行后退火处理可以有效降低薄膜内部应力,并显著提升薄膜的结晶质量,但后退火处理会导致薄膜表面粗糙度增大并呈现岛状起伏,后退火处理的最佳温度为800 °C,最佳持续时间为2 h。(2) 在0 ~ 100 °C 温区内,[100]单取向Mn1.56Co0.96Ni0.48O4 薄膜的电流电压关系在-10 ~ +10 V 测量电压范围内呈现良好的欧姆特性;其阻温关系呈现典型的NTC特性,可以由小极化子模型描述;其微观导电机制为最近邻跳跃导电(NNH)。(3) 通过改变制备工艺参数,可以调节[100]单取向Mn1.56Co0.96Ni0.48O4 薄膜的电学性能参数:当衬底温度低于400 °C 时,提高衬底温度可以降低薄膜的室温电阻R25,并提高其特征温度T0、激活能Ea 以及300 K 时的电阻温度系数αT,但当衬底温度高于400 °C 时,这四个电学性能参数基本不随衬底温度的升高而改变;减小脉冲激光能量可以降低R25,并提高T0、Ea 以及300 K 时的αT;提高背景真空度可以降低R25,并提高T0、Ea 以及300 K 时的αT;在空气气氛下对薄膜进行后退火处理可以有效降低R25,并显著提高T0、Ea 以及300 K 时的αT,且后退火温度越高,R25 越小,T0、Ea 和300 K 时的αT 越大。(4)在热氧化Si(100)衬底上生长的外延Mn1.56Co0.96Ni0.48O4 薄膜具有较高晶格完整性,其外延取向为[100]方向,晶格常数为8.28 Å。(5) 在0 ~ 100 °C 温区内,外延Mn1.56Co0.96Ni0.48O4 薄膜的电流电压关系在-10~ +10 V 测量电压范围内呈现良好的欧姆特性;其阻温关系呈现典型的NTC 特性,可以由小极化子模型描述;其微观导电机制为NNH。(6) 外延Mn1.56Co0.96Ni0.48O4薄膜的室温电阻率(25 °C)ρ25、特征温度T0、激活能Ea以及300K时的电阻温度系数αT均与薄膜厚度t密切相关,且都随着t的增加而减小;特别地,ρ25与1/t2之间存在着近似的线性关系,可由式ρ25(t)=211.7+119.1×104/t2 (t以nm为单位;ρ25以Ωcm为单位) 进行定量描述。
英文摘要:
Negative Temperature Coefficient (NTC) thermistors are extensively utilized in many aspects of domestic and industrial applications for their advantages of high accuracy, good interchangeability, and high reliability. In recent years, considerable progress has been made in the fabrication of spinel-type Mn-Co-Ni-O thin film NTC thermistors, however, to satisfy the requirements for Si-based semiconductor integration technology, the growth temperature of crystalline Mn-Co-Ni-O thin films must be lowered down to a reasonable level. On the other hand, the previously reported Mn-Co-Ni-O thin films were all amorphous or polycrystalline with all grain orientations rather than single-oriented. However, some electrical, optical, and magnetic properties of the films are sensitive to the crystallographic orientation. Thus, growing Mn-Co-Ni-O thin films with specific crystallographic orientation is needed in order to better control the properties. Moreover, for spinel-type Mn-Co-Ni-O materials, it is difficult to achieve high-quality epitaxial thin film growth because of their complicated structure, high melting point, and the strong possibility of second phase generating during the high temperature crystallization process, and there has been no report for epitaxial growth of Mn-Co-Ni-O thin films. Nevertheless, epitaxial thin films with improved crystalline quality and homogeneity are essential to the reliability and stability of semiconductor thin film devices, thus it’s of great technological importance to fabricate high-quality epitaxial Mn-Co-Ni-O thin films and investigate their properties. In this thesis, laser molecular beam epitaxy (LMBE) technique is applied in the fabrication of spinel-type Mn-Co-Ni-O thin films for the first time, taking Mn1.56Co0.96Ni0.48O4 thin films as the research object. Through optimizing the parameters in the LMBE process, the growth temperature of crystalline Mn1.56Co0.96Ni0.48O4 thin films is significantly reduced. Single-[100]-oriented Mn1.56Co0.96Ni0.48O4 thin films are successfully grown for the first time, and the influence of the growth conditions on the structural and electrical properties of the films are investigated. Epitaxial growth of Mn1.56Co0.96Ni0.48O4 thin films is achieved for the first time, and the epitaxial structure and electrical properties of the films are characterized and analyzed in detail. Moreover, thickness effects on the electrical properties are found for epitaxial Mn1.56Co0.96Ni0.48O4 thin films. The main results are summarized as follows. (1) For single-[100]-oriented Mn1.56Co0.96Ni0.48O4 thin films grown using LMBE technique, by raising the laser pulse energy to 275 mJ and pumping the vacuum chamber to 1×10-6 Pa, the lowest crystallization temperature of the films can be reduced to room temperature (25 °C), which is much lower than the previously reported crystallization temperature of 600 °C. The optimum angle between the incident laser and the surface of the target is 45°. The optimum distance between the target and the substrate is 40 ~ 60 mm. The films grow in 2-dimensional layer mode when the laser pulse repetition frequency is in the range of 1 ~ 5 Hz, while the growth mode gradually turns into 3-dimensional island mode when the repetition frequency is over 6 Hz. The surface smoothness of the films can be greatly improved through in situ annealing, and the optimum in situ annealing time is 1 h. After post annealing in air, the stress in the films is significantly reduced and the crystalline quality of the films is greatly improved; while the surface roughness of the films is increased and islands begin to appear on the surfaces of the films. The optimum post annealing temperature and time are 800 °C and 2 h, respectively. (2) In the temperature range of 0-100 °C, the current-voltage characteristics of single-[100]-oriented Mn1.56Co0.96Ni0.48O4 thin films show Ohmic behavior in the voltage range of -10 ~ +10 V, and the resistance-temperature re
内容类型: 学位论文
URI标识: http://ir.xjipc.cas.cn/handle/365002/3445
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作者单位: 中国科学院新疆理化技术研究所

Recommended Citation:
吉光. Mn1.56Co0.96Ni0.48O4薄膜的激光分子束外延制备及结构与电学性能研究[D]. 北京. 中国科学院大学. 2014.
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