【作者】 朱丽丹；

【导师】 唐大伟；

【作者基本信息】 中国科学院研究生院（工程热物理研究所） ， 工程热物理， 2012， 博士

【摘要】 随着微电子等器件尺寸的减小、工作频率的提高,散热问题已成为其主要限制瓶颈之一。对微器件系统及其组成单元在特定的空间和时间尺度内的热行为的研究已极为迫切且极其关键。本文应用飞秒激光抽运-探测技术对纳米薄膜热输运特性进行研究。考虑单脉冲激光能量的累积效应,利用热反射信号满足线性时不变系统(LTI)的假设对实验数据进行拟合分析。本文第一项工作是对单波长飞秒激光抽运-探测热反射测量系统的光学系统进行了优化改进,一定程度上提高了信噪比。利用该单波长测量系统得到的热反射信号较前人的信号的质量及测量精度更高。利用该单波长测量系统,研究了不同厚度的金属纳米薄膜的非平衡传热过程。通过抛物两步模型对实验数据进行拟合,在拟合过程中还引入电子温度与声子温度对反射率影响的比例关系,从而优化了对样品热物性值的拟合结果。实验结果表明电子-声子耦合系数同时受薄膜材料的厚度以及颗粒直径的影响；在样品数十到数百纳米厚度时,样品的热导率随着厚度的增大而变大。此外,实验验证了探测光的反射率同时受电子温度与声子温度的影响。本文第二项工作在单波长测量系统基础上,建立了一种双波长飞秒激光抽运-探测热反射系统。该双波长测量系统利用倍频模块,将抽运激光束生成二次谐波,用于加热样品。在抽运光与探测光到达探测器之前使用对倍频激光的透过率为109滤光片滤除倍频后的抽运光,从而避免抽运光对信号的干扰,可实现准确高效的测量。该双波长测量系统可实现飞秒到纳秒时间域内的热输运过程的研究。利用双波长抽运-探测热反射测量系统,测量了各种不同厚度的金属／半导材料,包括：Al/Si, Ni/Si, Au/Si等样品；测量了三层纳米结构的Al/HfO2/Si薄膜样品。结合采样定理对频域信号进行分析,建立热反射信号与调制频率的关系式,最终得到多层膜结构的热传导模型。通过多层膜热传导模型与实验数据的对比,得到纳米薄膜材料的界面热阻及热导率。测量结果表明金属与半导体的界面热阻在10-8m2K/W数量级,Si的热导率接近体材料值。Al/HfO2/Si的界面热阻值与SiO2/Si的界面热阻相当。更多还原

【Abstract】 As the reduction in size and the increase in speed of microelectronic devices, heat management at nano-scale is a critical issue.It is urgent and important to study the thermal transport behavior in specific space and time domain of micro/nano devices and their components. This thesis examines the characterization of thermal transport in nanometers using femtosecond laser pump-probe method. The theory for interpreting the measurement results is developed using a linear time-invariant systems, account-ing for pulse accumulation effects.The first work of this thesis was optimized and improved the optical system of single-color of femtosecond laser pump-probe.method, which can improve the sig-nal-to-noise in a certain degree. The signal quality and measurement accuracy was higher than the former’s measurements by using this single wavelength measurement system.The experimental system was used to study the nonequilibrium heat transfer in nano metal films with different thickness. Exploring parabolic two-step model (PTS) to fit the experimental data. During the fitting process, we considered the proportional relationship with the change of electron and phonon temperature, which affect the reflectivity. The experimental results show that the electron-phonon coupling factors are affected by the film thickness and grain diameter, and in the thickness-range from tens to hundreds of nanometers, the thermal conductivity increases with the increasing thicknesses of the film. In addition, the experimental result verifies that the reflectivity of probe laser is affected by electron and phonon temperature at the same time.The second work of this thesis was established a two-color femtosecond pump-probe thermoreflectance system, which was based on the single-color pump-probe method. This experimental system used the second-harmonic generator to double the frequency of the pump pulses. Before pump and probe beams radiating the detector, a color filter which has a transmission of10-9at the wavelength around double frequency of pump beam was used to isolate the scattered pump beam. As results, it can avoid the interference of pump signal and achieve accurate and efficient measurements. In addi-tion, this two-color experimental system can be explored for the study the characteri-zation of thermal transport over time scales from femtoseconds to nanoseconds.The two-color pump-probe experimental system measured the different thickness metal/semiconductor samples with two layers nano-structure, including: Al/Si, Ni/Si and Au/Si samples; besides that, it also measured Al/HfO2/Si samples with three lay-ers nano-structure. The sampling theorem was used to analysis the frequency domain signal, establish the relationship between the thermoreflectance signals and modula-tion frequency, and finally got the heat transfer model of multilayer structure. By comparing between the experimental data and heat transfer model, the interface ther-mal resistance and thermal conductivity were obtained. The results show that the or-der of interface thermal resistances between the metals and semiconductor were at10-8m2K/W., the thermal conductivity of silicon was close to the bulk conductivity. The value of interface thermal resistances, including the three of Al/HfO2, HfO2and HfO2/Si were quite equal to the value of the SiO2/Si.更多还原