掺杂（O_2，Sn，Ag）Ge-Sb-Te相变薄膜的制备和性能研究
文献类型：学位论文
| 作者 | 顾四朋 |
| 学位类别 | 博士 |
| 答辩日期 | 2003 |
| 授予单位 | 中国科学院上海光学精密机械研究所 |
| 导师 | 侯立松 |
| 关键词 | 相变薄膜材料 氧掺杂 锡掺杂 银掺杂 反射率对比度 结晶动力学 光存储性能 |
| 其他题名 | Studies on the preparation and properties of O_2-, Sn- and Ag-doped Ge-Sb-Te phase-change thin films |
| 中文摘要 | 相变光存储材料良好的可擦重写性能确立了它在可擦光盘研究中的地位，Ag-In-Sb-Te和Ge-Sb-Te材料已经被成功的应用于CD和DVD可擦光盘中。为了进一步提高存储密度，使用的激光波长正向蓝光甚至紫外光移动，这就要求相变光存储材料对短波长激光有足够高的响应。同时，为了提高数据传输速率，材料的相变速度也应越快越好。因此，对短波长敏感、相变速度快的新型相变材料是一个重要的研究课题。除了开发新的相变材料体系外，通过掺杂对材料进行改性是提高相变光存储性能的一条有效途径。本文全面综述了光盘存储技术和光存储材料的研究现状和发展趋势，并对可擦重写相变光盘材料的工作原理、制备和性能研究作了重点的介绍。以发展对短波长敏感、相变速度快的新型光存储材料为目标，选取Ge_2Sb_2Te_5相变材料（以下简称Ge-Sb-Te）为基础，分别掺杂O_2、Sn和Ag制备成薄膜，用示差扫描量热（DSC）、X射线衍射（XRD）、椭圆偏振仪以及紫外可见光谱仪等研究了掺杂后相变薄膜在热处理作用下的结晶行为和结构变化、光学和光谱性质变化，并通过静态或动态测试研究了它们的光存储性能。采用反应气氛溅射法制备了不同氧含量（0、4.1、8.7、14.3和19.4at％）的Ge-Sb-Te-O薄膜。XRD测试表明，经275℃、30min真空热处理后所有样品都实现了从非晶态到品态的转变。发现氧掺杂量较小时（0、4.1、8.7at％）薄膜均变为面心立方（FCC，face-centered cubic）结构且没有发现氧化物的存在，而氧含量大于14.3at.％时，有氧化物相出现而且薄膜为六方（HEX，hexagonal）结构。基于DSC数据，用J-M-A方程计算出了Ge-Sb-Te和Ge-Sb-Te-O（O_2 4.1at.％）材料的结晶活化能分别为2.25eV和2.39eV，因此后者更易结晶，结晶速率更快。适当掺氧明显改善薄膜的短波长光学特性。在氧含量为4.1at.％时，薄膜热处理前后的反射率对比度最大，在510nm处为35％，在410nm处还高达32％，而未掺氧薄膜的相应数据分别为22％和14％。用含氧量4.1at.％的Ge-Sb-Te薄膜制备的光盘，初始化后使用激光波长780nm进行动态测试，写入功率13.5mW，脉宽500ns，载噪比达42dB，而未掺氧的Ge-Sb-Te光盘最高载噪比为38dB。在Ge-Sb-Te靶上均匀排布Sn薄片，用直流磁控溅射法制备不同Sn掺杂量（0、2.1、3.8和5.8 at.％）的Ge-Sb-Te-Sn薄膜。掺Sn后，沉积态Ge-Sb-Te薄膜的反射率有较大提高，热处理后反射率进一步增大。在405nm和300nm处分别达到78％和65％（未掺Sn样品相应数据分别为54％和30％）。薄膜的反射率对比度在Sn含量为2.1at.％时最高，在300～50Onm范围内达到36～38％，而未掺Sn样品在这一波长范围最大的反射率对比度为14％。用514.5nm激光静态测试：写入功率11mW，脉宽350ns，掺Sn2.1at.％使薄膜写入前后的反射率对比度由38％提高到66％。在擦除功率5mW，脉宽350ns时，掺入3.8at.％的Sn使薄膜擦除前后的反射率对比度由12％提高到36％。Sn的最佳掺入量为2.1at.％-3.8at.％。Sn的掺入大大提高了Ge-Sb-Te材料的结晶活化能（由未掺杂时的2.25eV提高到3.8at．％掺杂时的2.96eV）。这说明：Ge-Sb-Te-Sn是一种有前途的蓝光快速相变光存储材料。采用与掺Sn相同的方法向Ge一sb一Te薄膜中掺入不同浓度的Ag（0、3.6、7.5和10.1at.％）。Ag的掺入也提高了薄膜在405nm～300nm的反射率。当Ag的掺入量为3.6at.％时，热处理后的反射率对比度在300～600nm范围内最高，在405nm和300nm处分别为32％和25％，而未掺杂薄膜的相应数据分别为14％和-12％。当写入激光波长为514.5nm，写入功率12mw，脉宽35Ons时，样品（Ag，3.6 at.%）的激光写入反射率对比度为46％（未掺杂样品为40％）。写入后，擦除功率7mW，擦除脉宽35Ons，擦除反射率对比度为21％（未掺杂样品为15％）。Ag的掺杂同样使薄膜的结晶活化能得到提高，最高达3.00eV（Ag，10.1at.％）。可以看出，Ag的含量越高，晶化速度越快。本工作创新之处在于：首次较系统的研究了 O_2、Sn和Ag的掺杂对Ge_2Sb_2Te_5相变薄膜结晶行为和结构变化、光学和光谱性质以及光存储性能的影响：发现当掺氧量超过一定的浓度（＞ 14.3at.％）时薄膜结晶后形成氧化物，同时结构变成六方晶系，不利于可擦光存储，而掺氧量小（＜8.7at.％）时结晶后呈面心立方结构（FCC），有利于快速可擦光存储；掺杂适量的Sn或Ag，都能改善Ge_2Sb_2Te_5薄膜的短波长光存储性能，使其在＜400nm范围的相变反射率对比度大大提高，找出了sn和Ag的最佳掺杂浓度，成为有应用前景的高密度可擦光存储材料；结晶动力学的研究发现，适量掺杂上述三种元素后，Ge_2Sb_2Te_5薄膜的结晶活化能都有明显提高，从而改善相变速度，为发展快速相变光存储材料奠定实验基础。 |
| 英文摘要 | Phase-change optical storage media have become a major technology for rewritable data storage systems because of their good overwriting performance. Ag-In-Sb-Te and Ge-Sb-Te materials have been successfully used in rewritable CD and DVD discs. In order to improve the storage density further, the wavelength of laser used is moving to blue light and even ultraviolet (UV) region, which demands that the storage materials have high enough response to short-wavelength laser beam. Meanwhile, the increasing demand for higher data transfer rate has posed a severe challenge to the phase-change speed of the recording materials. Therefore, research and development of new phase change materials for short-wavelength and high-speed rewritable optical storage are an important, subject. Besides the development of novel phase-change systems, manipulation of the chemical composition by doping a small amount of other elements into the current phase-change materials is also an effective method for this purpose. In the present work, the current status and development trends of optical storage techniques and recording materials, especially the principle, preparation and performance of phase change materials used in reversible optical recording disks are reviewed. Aiming to develop new optical storage materials with high sensitivity to short-wavelength and fast phase change speed, O_2-, Sn- and Ag- doped Ge2Sb2Te5 (Ge-Sb-Te) thin films were prepared by RF-sputtering technology. The effect of doping on the crystallization behavior, structural, optical and spectral properties due to heat treatment was measured and analyzed by using Differential Scanning Calorimetry (DSC), X-ray Diffraction (XRD), Spectroscopic Ellipsometry (SE) and UV/VIS/NIR spectrophotometer. The static optical storage performance of the phase-change films and the dynamic optical storage performance of the phototype disks were also studied and reported. Ge-Sb-Te-O thin films with various O_2 contents (0、4.1、8.7、14.3 and 19.4 at.%) were deposited by reactive magnetron sputtering in a RF planar magnetron sputtering equipment. The XRD test indicated that all the samples realized transformation from amorphous to crystallization states after vacuum heat-treatment at 275 ℃ for 30min. The samples with low oxygen-doping(O、4.1、 8.7 at.%) turned into FCC(face-centered cubic)structure and no oxides were found, but when the oxygen contents is higher than 14.3 at.% oxides appeared and the film structure became HEX (hexagonal). The crystallization activation energies of Ge-Sb-Te and Ge-Sb-Te-O (O_2 4.1 at.%) films calculated using J-M-A equation and DSC data are 2.25 eV and 2.39 eV, respectively, suggesting that the latter has higher speed of crystallization than the former. The films containing 4.1 at.% oxygen has the highest reflectivity contrast, 35% at 510nm and 32 % at 410nm, whereas the reflectivity contrasts of the Ge-Sb-Te films are 22% and 14% at the two wavelengths, respectively, indicating that proper oxygen-doping can improve the short-wavelength optical characteristics of the Ge-Sb-Te materials. After initialization, the disk prepared using Ge-Sb-Te-O (4.1 at.%) as the recording material possessed a CNR of 42 dB at 780nm with the writing power of 13.5 mW and writing pulse width of 500ns, while the maximum CNR of the disk using Ge-Sb-Te was only 38 dB. Ge-Sb-Te thin films with or without Sn-doping were deposited using DC sputtering method by arranging certain number of Sn thin slices on the Ge-Sb-Te target to control the concentration of Sn in the films(0、2.1、3.8 a and 5.8 at.%). The reflectivity of the as-deposited Ge-Sb-Te films had been increased by Sn-doping, and further increased after heat treatment, up to 78% and 65% at 405nm and 300nm, respectively. But the corresponding reflectivities of Ge-Sb-Te thin films were 54% and 30%, respectively. The reflectivity contrast of the Ge-Sb-Te-Sn (2.1 at.%) film was the highest, 36-38% in the range of 300-500nm, while that of the undoped one was only 14% at maximum in the same wavelength range. The static test results showed that the Sn-doping of 2.1 at. % increased the recording reflectivity contrast form 38% to 66% using 514.5nm laser with the writing power of llmW and writing pulse width of 350ns, and the erasing reflectivity contrast of Ge-Sb-Te-Sn film (Sn, 3.8 at. %) was 36%, which is much higher than that of the undoped one when the erasing power was 5mW and the pulse width was 350ns. It has been established that the optimum Sn-doping content is between 2.1 at.% and 3.8 at. %. The DSC results indicated that Sn-doping could increase the crystallization activation energy from 2.25 eV without Sn-doping to 2.96eV at the Sn-doping of 3.8 at.%. These results imply that Ge-Sb-Te-Sn is a promising short-wavelength high-density optical storage material. Employing the same method as in the case of Sn-doping, Ge-Sb-Te-Ag films were prepared with different Ag contents (0, 3.6, 7.5 and 10.1 at.%). Ag-doping could also increase the reflectivity of the films in the range of 405-300nm. The sample with Ag-doping of 3.6 at.% had the highest reflectivity contrast due to heat treatment in the range of 300-600 run. The reflectivity contrasts were 32% and 25% at 405nm and 300nm, respectively, and the corresponding results of the films without Ag-doping were 14% and -12%, respectively. At 514.5nm with the writing power of 12 mW and writing pulse width of 350 ns, the writing reflectivity contrast of the Ge-Sb-Te-Ag film (Ag, 3.6 at.%) was 46% and that of Ge-Sb-Te was 40%. The erasing reflectivity contrast of the Ge-Sb-Te-Ag film (Ag, 3.6 at.%) was 21% (that of Ge-Sb-Te was 15%) when using the erasing power of 7mW, erasing pulse width of 350 ns. Ag-doping could increase the crystallization activity energy, which could be up to 3.00 eV when Ag-doping content was 10.1 at.%. This indicates that the films containing higher contents of Ag have higher crystallization speed. There are the following innovative points in this work: For the first time, a systematic study on the effect of O_2-, Sn- and Ag-doping on the crystallization behavior and structural change, optical and spectral properties and optical storage performance of Ge_2Sb_2Te_5 phase change thin films has been carried out and some new results are reported; It was found that oxides were formed in the film after crystallization when oxygen-doping exceeds certain concentration (> 14.3 at. %), and the films turned into a hexagonal structure, while when the oxygen content was relatively low (<8.7 at. %) the films crystallized into a FCC structure without oxides formation, very favorable to high-speed optical storage; Proper Sn- or Ag-doping can improve the short-wavelength storage performance of Ge_2Sb_2Te_5 thin films, especially the reflectivity contrast in the <400nm range. The optimum doping concentrations of Sn and Ag have been established, making the materials very promising for high density optical storage. The crystallization kinetics research revealed that the above-mentioned 3 dopants at proper concentrations could increase the crystallization activation energy of Ge_2Sb_2Te_5 thin films considerably and thereby improve the crystallization rate. This lays an experimental foundation for developing high-speed optical storage materials. |
| 语种 | 中文 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/15388]  |
| 专题 | 上海光学精密机械研究所_学位论文 |
| 推荐引用方式 GB/T 7714 | 顾四朋. 掺杂（O_2，Sn，Ag）Ge-Sb-Te相变薄膜的制备和性能研究[D]. 中国科学院上海光学精密机械研究所. 2003. |
入库方式： OAI收割
来源：上海光学精密机械研究所
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