相变存储材料的激光诱导晶化过程研究
文献类型：学位论文
| 作者 | 梁广飞 |
| 学位类别 | 博士 |
| 答辩日期 | 2013 |
| 授予单位 | 中国科学院上海光学精密机械研究所 |
| 导师 | 王阳 |
| 关键词 | 相变存储材料 晶化过程 泵浦-探测技术 晶化机制 激光脉冲 |
| 其他题名 | Laser-induced crystallization process of phase change memory materials |
| 中文摘要 | 以GeSbTe和AgInSbTe为代表的相变薄膜是目前商品化可擦重写光盘（如CD-RW、DVD-RW和BD-RE）和研发中的相变随机存储器（PCRAM）的主要记录介质，其基本的结构、光电性质和相变特性虽然都已经为大家所熟知，但是对其短脉冲（纳秒或更短）诱导下的极端非平衡相变过程和快速晶化机制的认识还远不够深入，对高性能新材料的探索仍然是目前的主要工作之一。 在本论文中，我们利用泵浦-探测技术系统研究了GeSbTe和AgInSbTe相变存储材料在不同时间尺度激光脉冲（纳秒，皮秒和飞秒）诱导下的晶化动力学过程，重点分析了同一晶化过程中光、电瞬态响应的差异性和不同晶化机制（形核主导与生长主导）引起的相变过程差异性。此外，初步探索了一类新型快速相变材料MSb（M=Al、Cu、Zn和AlCu）。具体研究内容和结果简述如下： 建立时间分辨泵浦-探测系统，采用单脉冲纳秒激光（波长532nm，脉宽8ns）作为泵浦源，连续红光（波长632.8nm）和参考电阻电压作为探测源，研究了GeSbTe薄膜的激光诱导晶化动力学过程。研究发现晶化过程中光学反射率和电阻变化的瞬态响应存在显著差异，建立了2维渗透模型，对此种差异性进行了合理的解释。这种直接对比在相变过程中光学和电学性质的实时演化，将对深入了解极端非平衡条件下的相变机制提供有力的帮助。 建立时间分辨泵浦-探测系统，采用单脉冲皮秒激光（波长532nm，脉宽30ps）作为泵浦源，连续红光（波长632.8nm）和参考电阻电压作为探测源，实时探测研究了AgInSbTe薄膜的晶化动力学过程。研究分析表明，单脉冲皮秒脉冲诱导下，沉积态AgInSbTe薄膜仅能发生非完全晶化。基于涉及到复辉过程的非完全晶化过程，构建了电阻-电容模型对电学响应曲线的延迟现象进行了合理的解释。计算得出的RC电路的充电时间和实验测得的电学响应曲线的延迟时间在同一时间量级。研究结果对快速相变材料和结构的设计与应用具有重要参考价值。 采用皮秒激光（波长532nm，脉宽30ps）作为泵浦源，连续红光（波长632.8nm）作为探测源，利用时间分辨光学泵浦-探测方法研究比较了GeSbTe和AgInSbTe薄膜在激光作用下晶化动力学过程。研究发现形核主导型相变材料GeSbTe和生长主导型相变材料AgInSbTe在皮秒激光脉冲作用下的晶化动力学过程存在显著差异。对生长主导型晶化机制的沉积非晶态相变薄膜，单脉冲皮秒脉冲激光诱导晶化的前提是必须有表面熔化态的出现，然后由复辉驱动晶体生长；而对于形核主导型晶化机制的相变材料，其沉积非晶态薄膜的晶化过程则可以通过皮秒脉冲激光诱导固态结晶逐步完成。这种直接对比超快激光脉冲诱导下的不同晶化机制材料的相变过程将对深入了解极端非平衡条件下的超快相变机制，以及对快速相变材料的设计与应用具有重要意义。 建立时间分辨泵浦-探测系统，采用飞秒激光（波长800nm，脉宽130fs）作为泵浦源，连续红光（波长650nm）和参考电阻电压作为探测源，实时探测研究了GeSbTe和AgInSbTe薄膜的晶化动力学过程。研究发现单脉冲飞秒激光可以诱导沉积非晶态GeSbTe和AgInSbTe薄膜发生完全晶化，晶化过程都表现为包含复辉的多态过程。当脉冲能量密度达到完全晶化阈值（分别为57.9时和46.3 mJ/cm2）时，反射率对比度达到最高值（分别为44%和42%），此时，所对应的晶化时间分别为569ns和497ns。研究结果将对深入了解极端非平衡条件下的超快相变机制，以及对快速相变材料的设计与应用具有重要参考价值。 通过磁控溅射（两靶共溅）的薄膜制备方法，制备出了不同掺杂浓度的Sb基二元合金（AlSb、CuSb和ZnSb）和三元合金（AlCuSb）。采用静态记录、泵浦-探测等方法研究了这些薄膜的结晶特性和晶化过程。研究发现通过掺杂Al、Cu、Zn等元素可以有效改善纯Sb薄膜的非晶态稳定性，得到室温下稳定的非晶态Sb基相变薄膜。这些Sb基薄膜的晶化速率（10-50ns）明显优于常用的GeSbTe和AgInSbTe相变材料的晶化速率（在相同条件下约200ns左右），其中AlSb、ZnSb和AlCuSb薄膜还具有较高的反射率对比度。是快速相变材料的优良候选材料。 |
| 英文摘要 | Phase change materials (such as GeSbTe and AgInSbTe), as the recording media, have been widely used in rewritable optical disk (such as CD-RW, DVD-RW and BD-RE), and nonvolatile phase change random access memory (PCRAM). Its microscopic structure, optical, electrical, and phase transition characteristics have been well studied. However, the understanding of the extra-non-equilibrium phase transition dynamics driven by short pulses (such as nanosecond, picosecond or femtosecond laser pulses) is far from enough. It is still one of the most important jobs to explore new phase change materials with high performances. In this dissertation, the laser-induced crystallization process of GeSbTe and AgInSbTe thin films were studied by using pump-probe technique with different pumping sources (nanosecond, picosecond, and femtosecond laser). The difference between the optical and electrical transients during crystallization and the different crystallization processes driven by nucleation- and growth-dominated mechanisms were discussed in detail. Furthermore, a new kind of fast phase change material MSb (M=Al, Cu, Zn, or AlCu) was studied. The detailed contents and results are described briefly as follows. The nanosecond laser pulse (wavelength: 532 nm, pulse width: 8 ns) induced crystallization dynamics of as-deposited amorphous GeSbTe thin films were synchronously monitored by the optical and electrical signals in real time. We found that the transient optical reflectivity and electrical resistivity showed a very different evolution. A 2-dimensional percolation model was established to explain the difference between the electrical and optical transients. The results will be helpful to the deeper understanding of the crystallization mechanism under extra- non-equilibrium conditions. Picosecond laser pulse (wavelength: 532 nm, pulse width: 30 ps) induced crystallization process of as-deposited amorphous AgInSbTe thin films were studied by real-time reflectivity and resistance measurements. The study results showed that the crystallization of AgInSbTe films induced by picosecond laser was a non-fully crystallization process. Based on the recalescence-involved (melting-involved) non-fully crystallization process, a resistor–capacitor model was proposed to interpret the delay of electrical signals. The results will be helpful to the design and application of fast phase change materials and memory structures. Direct comparison of the real-time crystallization behaviors of as-deposited amorphous GeSbTe and AgInSbTe phase-change thin films driven by picosecond laser pulses (wavelength: 532 nm, pulse width: 30 ps) was performed by a time-resolved optical pump-probe technique with nanosecond resolution. Different optical transients showed various crystallization processes because of the dissimilar nucleation- and growth-dominated mechanisms of the two materials. The effects of laser pulse fluence, thermal conductive structure, and successive pulse irradiation on their crystallization dynamics were also discussed. A schematic model was then established to describe the different crystallization processes beginning from the as-deposited amorphous state. The results may provide further insight into the phase-change mechanism under extra-non-equilibrium conditions and aid the development of ultrafast phase-change memory materials. The femtosecond laser pulses (wavelength: 800 nm, pulse width: 130 fs) driven crystallization processes of as-deposited GeSbTe and AgInSbTe thin films were studied by the pump-probe technique. The results show that crystallization almost can be fulfilled by a single femtosecond laser pulse. The crystallization dynamics of both materials show a similar recalescence-involved multi-stage process. The crystallization times of GeSbTe and AgInSbTe thin films were determined to be 569 and 497 ns, respectively. When pumping fluence was below the threshold for full crystallization (57.9 and 46.3 mJ/cm2 for GeSbTe and AgInSbTe thin films respectively), micro-capacitance maybe will be generated, which will result in time delay in the electrical response. The results will be helpful to the further understanding of the ultrafast phase transition mechanism and the design of ultrafast phase-change memory materials. Sb-based binary (AlSb, Cusb, and ZnSb) and ternary (AlCuSb) alloy films were designed and prepared by the magnetron co-sputtering method. The crystallization characteristics of these alloys were evaluated by static recording and pump-probe methods. It was found that the room-temperature stability in as-deposited state of Sb films can be improved by doping Al, Cu, Zn and AlCu. Most of these Sb-based alloys have a high crystallization speed (10-50 ns), which is faster than traditional GeSbTe and AgInSbTe phase change materials (~200 ns) at the same conditions. AlSb, ZnSb, and AlCuSb also showed a high reflectivity contrast after laser-induced crystallization. These materials are excellent candidates for fast phase change materials. |
| 语种 | 中文 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/15748]  |
| 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 | 梁广飞. 相变存储材料的激光诱导晶化过程研究[D]. 中国科学院上海光学精密机械研究所. 2013. |
入库方式： OAI收割
来源：上海光学精密机械研究所
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