|关键词||尖晶石 磁控溅射 薄膜 光学性质 电学性质 拉曼 椭偏|
Mn-Co-Ni-O系热敏薄膜的制备工艺的改进对于薄膜微观结构及表面形貌的改善和薄膜电学性能及光学性能优化具有重要的意义。本文针对常见的制备Mn-Co-Ni-O系热敏薄膜的磁控溅射法和化学溶液沉积法，分别对其基本工艺参数条件进行优化，为制备Mn-Co-Ni-O系热敏薄膜器件提供了一定参考。具体来说，为了获得纯度较高，稳定性好，灵敏度高，致密单一的尖晶石相的锰钴镍的陶瓷薄膜，采用射频磁控溅射的方法生长Mn-Co-Ni-O热敏薄膜。通过优化磁控溅射制备薄膜的工艺参数，提高薄膜的致密度，探讨各参数对薄膜的影响。例如，溅射过程中氧的含量、不同衬底材料、退火条件和溅射功率等对Mn-Co-Ni-O系薄膜微观结构，表面形貌和光学电学性能有何影响。为了降低Mn-Co-Ni-O系热敏薄膜的室温电阻，同时探究阳离子分布对薄膜性能的影响，我们选择了易于改变薄膜组分的化学溶液沉积法，制备了（Mn1.56Co0.96Ni0.48O4）1-x（LaMn0.6Al0.4O3）x复合薄膜材料。Al离子的掺入，有利于提高复合薄膜的吸收系数，提高红外探测的灵敏性。研究结果主要表现在以下几个方面：（1）采用射频磁控溅射法生长Mn1.56Co0.96Ni0.48O4薄膜热敏材料。经过参数优化，发现在SiOx/Si（100）衬底上制备Mn1.56Co0.96Ni0.48O4薄膜热敏材料时，靶材为Mn1.56Co0.96Ni0.48合金靶，衬底温度为150 ℃，溅射功率为40 W时，薄膜具有单一的尖晶石结构，且薄膜的结晶性最好。（2）在不同氩氧比条件下，通过溅射锰钴镍的合金靶材，都能得到具有尖晶石结构的Mn-Co-Ni-O热敏薄膜。对氩氧比为10:2时所获得的样品进行变温椭偏测试，然后利用Tauc-Lorentz方程拟合，获得了薄膜材料随温度变化的光学常数曲线。发现随温度的升高，短波区折射率和消光系数的峰值均出现明显红移现象。当温度上升时，薄膜中载流子浓度增加，折射率n和消光系数k在短波段出现红移；当载流子减少，折射率n和消光系数k峰位则会出现“蓝移”。 对不同氧分压条件下制备的薄膜样品进行室温椭偏测试，发现当氧含量较高时，Mn-Co-Ni-O薄膜材料中电荷转移跃迁主要表现为O → Co离子的电荷转移跃迁（2.5-3.0 eV），其中主要体现在氧与Co2+之间的电荷转移跃迁。即，薄膜中不同阳离子浓度分布与薄膜的共振吸收峰直接相关。电学结果表明，随氧含量的增加，薄膜的室温电阻显著下降，薄膜的厚度减小。（3）采用射频磁控溅射法，在不同氩氧比条件下，在单面抛光的Al2O3的陶瓷衬底上沉积Mn1.56Co0.96Ni0.48O4薄膜热敏材料。研究结果表明，氩氧比对Mn-Co-Ni-O薄膜材料的结晶度，微观结构，拉曼和电学性能都有较大的影响。随着氧分压的增大，薄膜厚度明显减小，结晶度提高，表面孔隙率增大，致密性减弱，平滑度提高。电学性能的测试结果表明，无氧条件下的B值和激活能远高于有氧条件下的薄膜，且分别为5999K和0.52 eV。这是由于无氧条件下，薄膜疏松的内部结构和致密的表面形貌造成的。结合拉曼和椭偏的测试结果可知，随着溅射过程中氧含量的增加，薄膜中的Mn3+和Mn4+含量都有所提高。（4）采用射频磁控溅射法，SiO2/Si（100）衬底上制备Mn-Co-Ni合金薄膜，并在不同压强的氧条件下退火，发现在不同氧压条件下退火时，所有薄膜样品均可形成致密的Mn-Co-Ni-O热敏薄膜。当氧压强为90 kPa时，薄膜的择优取向性较好。XPS结果说明：退火过程中，氧含量对薄膜中阳离子的分布有较大的影响。当退火氧压从10 kPa增加到50 kPa时，薄膜电阻迅速下降（由183降至11.29 MΩ）；而由50 kPa增加到90 kPa时，薄膜阻值仅轻微的减少(由11.29降至6.85 MΩ)。这是因为Mn在不同退火气氛下，氧化状态的不同而造成的。（5）采用化学溶液沉积法在单晶Si（100）衬底上沉积（Mn1.56Co0.96Ni0.48O4）1-x（LaMn0.6Al0.4O3）x复合薄膜。复合薄膜包含Mn-Co-Ni-O立方尖晶石相与La-Mn-Al-O钙钛矿相，且随着x数值的增大，钙钛矿相由纯立方相转变为四方相。薄膜的表面平滑度和致密性也随着La-Mn-Al-O的增多而提高。电学测试结果表明，复合膜具有显著的负温度系数（NTC）热敏特性。当x=0.4时，室温电阻最小（7.14 MΩ），B值为3526 K，激活能为0.3 eV。椭偏光学测试结果证明， Al3+进入Mn-Co-Ni-O尖晶石结构中，极大促进了Mn-Co-Ni-O薄膜的光学吸收，对于波长为2000 nm的红外光，薄膜的k值明显增大(由0.3增致0.9)。该实验结果对开发覆盖光谱范围更广，灵敏度更高的新型红外热敏探测器材料具有一定的参考价值。;
It is very important that the synthesis processing optimization for Mn-Co-Ni-O thermistor films can greatly help the improvement in film microstructure and surface morphology as well as the electrical and optical properties. In this work the magnetron sputtering and chemical solution deposition method were mainly used to synthesize the Mn-Co-Ni-O films; the foundamental processing parameters were systematically optimized, which is meaningful to the fabrication of Mn-Co-Ni-O thermistor films in industry. In order to obtain high quality cubic phase spinel-structured Mn-Co-Ni-O films with higher purity, better stablility, larger sensitivity, more uniform and higher density, the rf magnetron sputtering method was adopted for preparation of the Mn-Co-Ni-O films. By improving film density and optimizing process parameters of the RF magnetron sputtering, the effects of the process parameters on film quality were discussed in detail. For example, how do the oxygen variation in sputtering gas, different substrate materials, annealing condition and sputtering power affect the microstructures, surface morphology and the electrical and optical proerties? In order to reduce the resistance of the Mn-Co-Ni-O films at the room temperature and investigate the effects of cation distribution on the film properties, the chemical solution deposition method, where it is easy to adjust the film composition, was chosen to prepare the （Mn1.56Co0.96Ni0.48O4）1-x（LaMn0.6Al0.4O3）x composite films. Doping with Al ion can facilitate the improvement in the absorption coefficient of composite films, and enhance the film sensitivity of infrared detecting ability. The results of the work mainly include the following:(1) Mn1.56Co0.96Ni0.48O4 thin films have been prepared by RF magnetron sputtering. After parameter optimization, we found the thin films have single spinel structure and better crystalline on SiO2/Si (100) with substrate temperature of 150 ℃ and sputtering power of 40 W.(2) Mn1.56 Co0.96 Ni0.48 O4 thin films have been successful prepared on alumina ceramic substrates by RF magnetron sputtering technique under different oxygen partial pressure. The results show that the oxygen partial pressure greatly effect on crystalline, microstructure, Raman spectrum and electrical properties with the increase of oxygen partial pressure, the thin films show significantly reduced thickness, improved crystalline and smoothness, porosity increases and the density decreases. Electrical performance test results show that B value and the activation energy of the thin films under free-oxygen sputtering condition are much higher than oxygen sputtering conditions, B value of 5999 K and activation energy value of 0.52 eV, respectively. This is due to the internal structure of porous and density of surface in the Mn- Co-Ni-O thin film.(3) All samples of Mn-Co-Ni-O NTC thin films are spinel-structured under the condition of different oxygen partial pressure by sputtering Mn1.56Co0.96Ni0.48 alloy target. When Ar/O2 ratio is 10：1, the sample was measured by ellipsometry, and the data were fitted by Tauc-Lorentz oscillator dispersion formula. Thus, the optical constants of MCN films with the different temperature were obtained. The results show that the peak position of refractive index n and extinction coefficient k are red shifted in the range of short wavelength with temperature (the peak position is close to the absorption resonance of thin film material). When the temperature rises, carrier concentration increased in the thin films. This lead to the peak positions of n and k appear red-shift. When carrier concentration decreased in the thin films, the peak position of n and k will appear "blue shift" in the range of short wavelength. The deposited thin film samples with different oxygen partial pressure were measured by the spectroscopic ellipsometry at room temperature, and the optical constants of the thin films were fitted using Tauc-Lorentz model. The experimental results showed that the charge transfer is mainly due to the transition by O→ Co ion in 2.5-2.5 eV. When the oxygen content is higher, which is mainly manifested the charge transfer transition between oxygen and Co2+. Cation concentration distribution is directly related to resonance absorption peaks of the Mn-Co-Ni-O films. The electrical characterization shows that the resistance of the thin film is decreased significantly with the increase of the oxygen content at the room temperature. Thus, we can control the thickness of the thin film and B value range (4423-5412 K) by controlling the oxygen content during sputtering. (4) Mn-Co-Ni alloy films were deposited on SiO2/Si (100) substrate by RF sputtering method, then annealed in different O2 ambiance to form MCN spinel films. Effects of the oxygen pressures on the structural, electrical and optical properties of Mn-Co-Ni-O films were investigated. The preferred orientation of the films was displayed at 90 kpa the pure oxygen pressure. The result of XPS shows that the oxygen content affects the cation distribution in the thin films in annealing process. When annealing oxygen content increased from 10 kpa to 50 kpa, thin film resistance drops rapidly, however thin film resistance only a slight decrease when annealing oxygen content increased by 50 kpa to 90 kpa. This is because the Mn oxidation state is different under different annealing atmosphere. Combination of Raman and ellipsometry experimental results show that the Mn3+ and Mn4+ content in the film are improved with the increase of oxygen content in the process of sputtering.(5) The (Mn1.56Co0.96Ni0.48O4)1-x (LaMnO3) x composite serial thin films were synthesized by CSD method on Si (100) substrates. It was found that the composite films include both cubic spinel MCN and cubic perovskite LMA, where the cubic perovskite LMA transforms into the rhombohedral perovskite phase with the increase of La content. At the same time, surface roughness of the composite thin film was improved too. The results of electrical performance indicate all of the films have negative temperature coefficient (NTC) characters. Especially, the film with x = 0.4 offered the lower room temperature resistance (7.14 MΩ), the B value (3526 K) and the activation energy (0.35 eV). From spectroscopic ellipsometer spectroscopy, it shows that Al3+ ion goes into the MCN Spinel structure, which greatly promotes optical absorption of the MCN thin film. This makes absorption coefficient k value increase significantly (from 0.3 to 0.9). The result is meaningful to develope new infrared thermal detector material with wided infrared spectrum coverage and higher sensitivity.
|史芹. Mn1.56Co0.96Ni0.48O4薄膜及与LaMn0.6Al0.4O3复合薄膜的制备工艺及光学电学性能研究[D]. 北京. 中国科学院大学,2017.|
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