基于低频光热反射法的深埋界面接触热阻测量研究

随着电子器件向小型化和高功率密度化的方向发展，其工作时产生的热量呈几何倍增。如何将这一部分热量及时散发出去，从而稳定电子元器件的运行温度，实现高效热管理已逐渐成为制约当前集成电路产业发展的重要挑战。在电子元器件热管理中，热界面材料常用于填充发热器件与热沉之间的缝隙，改善界面的传热效果。热界面材料的性能优劣直接决定了器件整体热管理效率。随着热界面材料的导热系数持续提升和使役条件下厚度逐渐降低，其与工作表面之间的接触热阻在散热表现中起到越来越重要的作用。因而，研究热界面材料与常见接触表面如硅、铜、铝之间的接触热阻对优化其散热性能具有重要意义。

针对上述问题，本文开发了一种较低调制频率的频域光热反射法，来测量被深埋在数十至上百微米厚度材料下的界面的接触热阻。通过硬件搭建、光路设计和程序开发，本文建立了一种新型的光热反射测量系统，能够同步从样品前表面和后表面提取出温度变化信号。采用这套系统测量得到的光热信号保持在10 μV以上、等效噪音在0.1 μV以下，信噪比达到了40 dB。通过系统的数据采集和处理，我们不仅能够从前表面的相位拟合出热界面材料的导热系数、体积比热和接触热阻，还能从后表面的相位拟合出更精确的热扩散系数和接触热阻，有效地排除了其它因素的串扰。

基于这套测量系统，本文测得一款导热凝胶与单晶硅之间的接触热阻为1.95 mm2K/W，精确度达到了0.1 mm2K/W，相对误差在±5%以内。此外，这套系统能够用于表征深埋界面的接触热阻分布，空间分辨率在1 mm以下。因此，本系统有望实现热界面材料和芯片及热沉之间接触热阻的精确测量，助力高性能热界面材料的研发。

With the miniaturization and growing power density of electronic devices, heat generation has increased exponentially. How to disperse heat in time and control the operating temperature of electronic devices have become a challenge for thermal management in the integrated circuit industry. In order to enhance heat dissipation at the interfaces, thermal interface material (TIM) is commonly applied to fill the gap between heating unit and heat sink. Thus, the performance of TIMs directly determines the efficiency of thermal management. With the increasing thermal conductivity (TC) and decreasing thickness of TIM, thermal contact resistance (TCR) between TIM and its working surfaces is becoming dominant. Therefore, insights into TCR between TIM and its common working surfaces such as silicon, copper and aluminum are significant to the optimization of the performance of TIMs.

Herein, this thesis developed a low-frequency frequency domain thermoreflectance (FDTR) to measure the TCR at interfaces buried by materials with thickness of tens to hundred micrometers. After carefully design of system elements, optical system and software programing, this new type of FDTR can simultaneously obtain the phase signals of temperature variations at both the front and back surface. With this new measurement system, photothermal signal is kept above 10μV and noise is suppressed below 0.1μV, realizing a signal noise ratio above 40dB. With the help of the data acquisition and processing software, TC, volume heat capacity and TCR of TIMs can be extracted from phase information at the front surface. While with phase information at the back surface, the thermal diffusivity and TCR can be extracted more precisely, which overcomes crosstalk from other factors. 

Using this low-frequency FDTR system, the TCR between a thermal gel and polished silicon is measured at 1.95 mm2K/W with an accuracy of 0.1 mm2K/W and an acceptable error of ±5%. Meanwhile, the TCR at different location can be determined with a spatial resolution below 1 mm. Thus, this new system has potential application on accurate measurement of TCR between TIMs and chip or heat sink, which will facilitate the research and development of TIMs with high performances.

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