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锰钴镍氧化物薄膜和超薄片的制备及其光学和电学性能研究
孔雯雯
学位类型博士
导师常爱民
2015-05-24
学位授予单位中国科学院大学
学位授予地点北京
学位专业微电子学与固体电子学
关键词薄膜 超薄片 制备方法 负温度系数热敏电阻 光电性质
摘要

尖晶石型Mn-Co-Ni-O系材料被广泛用于制造负温度系数热敏电阻器和热敏电阻型红外探测器。近年来,极端环境对器件的准确度及灵敏度提出了更高的要求;器件集成化对元件的尺寸提出了更小的要求;可持续发展对材料制备过程的环境友好性提出了更新的要求,因此,相比于传统块体材料而言,精度更高、响应更快、尺寸更小的Mn-Co-Ni-O系薄膜和超薄片材料逐渐成为了该体系的研究热点。具有良好的结晶性、低缺陷密度、原子级别平整且物理性能稳定的过渡金属氧化物薄膜是制备出高可靠性和高稳定性薄膜器件的前提。目前,国内外研究人员已采用化学沉积法、磁控溅射法、电子束蒸发法、激光脉冲沉积方法等制备出非晶态、多晶态及择优取向的Mn-Co-Ni-O系薄膜,并对其光、电、磁、热等物理性质进行了分析和研究。然而,已有文献报道中未见不同择优取向Mn-Co-Ni-O系薄膜光电性能的比较,单晶外延Mn-Co-Ni-O系薄膜制备方法的摸索,柔性Mn-Co-Ni-O系薄膜的研究和无支撑Mn-Co-Ni-O系超薄片的制备。本文采用激光分子束外延技术(LMBE)依次在Si/SiOx衬底、MgO(100)单晶衬底、聚酰亚胺衬底表面制备出以上不同类型的Mn1.56Co0.96Ni0.48O4(MCN)薄膜。与此同时,文中设计出将现代电子印刷技术与传统的陶瓷制备方法相结合的叠加工艺技术,并利用该方法制备出MCN无支撑超薄片。通过对不同类型的薄膜和无支撑超薄片进行了结构、光学和电学性质的表征,详细分析了材料结构对其光学和电学性能的影响。研究结果如下:1、采用LMBE方法在Si/SiOx衬底上制备出不同择优取向的MCN薄膜。实验发现,当氧分压为2×10-4Pa时,MCN薄膜呈现出良好的(400)晶向择优生长;当氧分压上升至2×10-3Pa时,MCN薄膜的(400)衍射峰的强度明显减弱,开始出现(113)晶向的X射线衍射峰;当氧压高于2×10-2Pa后,薄膜的(400)衍射峰消失,薄膜呈现出单一的(113)晶向择优生长,材料的结晶性随氧分压的增加而增强。650cm-1处的Raman峰仅存在于(113)取向的MCN薄膜中,原因是(113)取向薄膜的八面体位置中存在更多的[Mn3+-O]6和[Mn4+-O]6键。在测试范围内,(400)取向薄膜的折射率和消光系数均不存在明显的峰值,而(113)取向薄膜中存在峰值,说明(113) 取向的MCN薄膜的结晶性优于(400)取向的薄膜。(113)取向的禁带宽度(1.01 eV) 约为(400)取向的禁带宽度(0.47eV)的两倍。由电学测试结果可知,(113)取向薄膜属于变程跃迁导电模型(VRH),而(400)取向薄膜属于最近邻跳跃导电模型(NNH)。 (113)取向薄膜的电阻远小于(400)取向的薄膜,B值和活化能则远大于后者。这是由于(113)取向薄膜中的Mn3+和Mn4+离子含量随薄膜生长过程中氧分压的增加而逐渐增加的缘故。2、采用LMBE方法在300~600℃的衬底温度条件下制备出一系列MCN/MgO薄膜。采用XRD、AFM、RHEED、阻温测试对不同衬底温度条件制备所得薄膜进行表征。从结果可以看出在500℃时,薄膜具有最佳结晶度,呈现出(100)方向外延生长,随着生长厚度的增加,其生长模式从三维岛状生长逐渐转变为二维层状生长。所有薄膜样品均具有良好的NTC热敏电阻特性,其R值分布在10-50MΩ范围内,B值约为3300K;确定生长温度为500℃,改变MCN/MgO薄膜制备过程中的氧分压(5×10-4Pa~5×10-1Pa),所得的薄膜具有显著不同的电学性能。5×10-4Pa的氧分压条件下制备所得的薄膜不具备良好的NTC热敏电阻特性。说明超高真空度尽管有利于高质量、高平整度的薄膜的制备,但是对于过渡金属氧化物的物理性质有所抑制。3、采用LMBE方法在不同衬底温度(50℃,150℃,250℃)下制备MCN柔性薄膜,并将薄膜置于300℃条件下快速退火处理。50℃条件下制备所得薄膜是非晶态的, 150℃和250℃沉积所得薄膜呈现出(113)取向尖晶石结构。所有薄膜的原子比例均与靶材一致,且满足NTC热敏电阻特性。(113)取向薄膜的R值、B值、Ea都明显小于非晶MCN薄膜。这是由于随着衬底温度的增加,薄膜的晶格尺寸逐渐增大,弛豫频率逐渐减少。该研究为柔性NTC薄膜元件的制备提供了可能。4、对不同烧结温度下所得的薄片进行了XRD、SEM、XPS、FTIR、Raman、电阻温度关系、复阻抗谱的测试与分析,结果发现:随着烧结温度的升高,薄片的结晶性、化学计量比、致密度均有显著的改善,薄片的电阻率从2660Ω·cm迅速降低到21.9Ω·cm,这是晶界电阻降低和Mn3+/Mn4+比例增加共同决定的。当烧结温度高于1100℃后,由于薄片的致密性显著增加,1160cm-1处的红外吸收峰消失。850cm-1处的吸收峰的强度随Mn3+和Mn4+离子的含量的增加而增强。

其他摘要

The Mn-Co-Ni-O spinel materials have been extensively used in negative temperature coefficient (NTC) thermistors and the infrared detectors. Recently, the smaller size Mn-Co-Ni-O thin films and ultrathin chips become the newest research focus. It is due to their high accuracy, sensitivity, integrated and environmentally friendly. Generally, the thin film growth of the transition metal oxides with no obvious defects and stable properties is desired since the smoothness of the films is vital to the stability and reliability of the devices. Previously reported that the Mn-Co-Ni-O amorphous, polycrystal and preferred orientation thin films has been prepared by chemical deposition method, RF sputtering, electron evaporating method and pulsed laser deposition method. The electrical, magnetic, thermal, optical and mechanical properties of the Mn-Co-Ni-O thin films have been studied in detail. In present study, the Mn1.56Co0.96Ni0.48O4(MCN)thin films with different preferred orientation, MCN epitaxial single crystal films and MCN flexible films are prepared on Si/SiOx substrate, MgO(100) single-crystal substrate and polymide substrate by adopting the laser molecular beam epitaxy (LMBE) method. In addition, we also fabricate the free-standing MCN ultrathin chips based on screen printing and traditional ceramic fabricating technology. The structure, optical and electrical properties of different films and ultrathin chips are studied and the main results are summarized as follows. 1. Mn1.56Co0.96Ni0.48O4 (MCN) thin films with different preferred orientation have been grown on Si/SiOx substrate using LMBE technique. When the oxygen partial pressure (Po2) is 2×10-4 Pa, only the (400) diffraction peak appears in the MCN films. As Po2 increases to 2×10-3 Pa, the (400) peak intensity gradually diminishes while the (113) diffraction peak starts to dominate. When Po2 is above 2×10-2 Pa, the (113) peak intensity further increases, which generally means the improvement of crystallinity of the films. The Raman active mode (around ca. 650 cm-1) of (400) films almost disappears, whilst the active mode in (113) films remains. It is ascribed to the increase of Mn3+-O and Mn4+-O stretching vibration in the octahedral lattice sites. From spectroscopic ellipsometer spectroscopy, it is found that both the refractive index n and extinction coefficient k of the (400)-oriented films have no obvious peaks, whereas in the (113)-oriented films, peaks exist. This feature typically originates from a change in the crystal structure as oxygen pressures increase. The Eg of the (113) film is 1.01 eV, which is twice as large as that of the (400) film (0.47 eV). The resistance of the (113)-oriented films is found to decrease compared to those of the (400)-oriented ones. Meanwhile, the activation energy Ea increases dramatically. This is because that higher oxygen partial pressure during deposition should be responsible for the preferred (113) plane growth and the greatly elevated amount of Mn3+ and Mn4+, which can result in decrease of the resistance. 2. The MCN/MgO thin films are prepared by LMBE process at a set of substrate temperatures from 300 to 600 oC. The effect of growth temperature on microstructure and electrical properties as well as the growth mode were studied using XRD, RHEED, AFM and resistance–temperature measurements. The results show that all prepared thin films underwent epitaxial growth along the single-(100) orientation direction of the MgO substrate from 3D-island mode to 2D layer-by-layer mode, exhibit good crystallinity and NTC thermistor behavior. Their resistance at room temperature can be in the range of 10–50 MΩ together with a B-value of about 3300 K, which is desirable for a wide range of practical applications of the NTC thermistors. However, the electrical properties of MCN/MgO thin films are different by changing the oxygen pressures (5×10-4~5×10-1Pa). The thin films deposited at 5&tim

文献类型学位论文
条目标识符http://ir.xjipc.cas.cn/handle/365002/4255
专题材料物理与化学研究室
作者单位中国科学院新疆理化技术研究所
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孔雯雯. 锰钴镍氧化物薄膜和超薄片的制备及其光学和电学性能研究[D]. 北京. 中国科学院大学,2015.
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