Study on Microscale Heat Transfer in Microelectronic Devices and Effective Cooling using Boiling Heat Transfer

从微电子器件冷却技术的角度，研究了基板中极小加热元件的微尺度传热问题。采用区域分解技术对微尺度基底内热传导和宏观尺度流体强制对流冷却的共轭传热进行了数值分析。利用傅里叶变换也考虑了周期性加热的影响。计算出的加热器温度与雷诺数、比奥数、傅立叶数、加热元件与衬底的长度比等无量纲参数相关，并提出了在一定范围内无量纲参数下加热元件温度的简化模型。在池沸腾和强制对流沸腾的情况下，还研究了基底中非常小的加热元件的沸腾传热。随着加热器尺寸的减小，热传导效应占主导地位。此外，由于加热元件小于气泡直径，元件温度随气泡的生长和离开而波动，这表明在气泡离开的时刻，表面传热非常大。通过对基材传导的数值分析，估算了有效表面换热系数。最后，作为微尺度温度测量的一项基本技术，通过考虑电子穿过表面氧化层的隧道效应和点接触处的非平衡效应，对针与表面点接触产生的热电功率进行了分析。分析结果很好地解释了实验结果。

Microscale heat transfer from very small heating elements in a substrate has been investigated from the view point of cooling technology of microelectronic devises. Conjugate heat transfer of microscale heat conduction in the substrate and macroscale forced convective cooling by fluid was numerically analyzed by using a domain decomposition technique. The effect of periodic heating was also taken into account by using the Fourier transforms. The calculated heater temperature was correlated with nondimensional parameters such as Reynolds, Biot, Fourier numbers, length ratio of the heating element and substrate, etc.A simplified model was proposed to predict the element temperature in a certain range of nondimensional parameters. Boiling heat transfer from very small heating elements in a substrate was also investigated both for pool boiling and forced convective boiling. With the decrease of heater size, the effect of heat conduction becomes dominant. Further, because the heating element is smaller than the bubble diameter, the element temperature fluctuates corresponding to the bubble growth and departure, which indicates an extraordinary large surface heat transfer at the moment of the bubble departure. The effective surface heat transfer coefficient was estimated with the aid of numerical analysis of the substrate conduction. Finally, as a fundamental technique of temperature measurement in the microscale, thermoelectirc power due to the point contact of a needle to the surface was analyzed by considering both the electron tunneling effect through the surface oxide layr and the nonequilibrium effect at the point contact. The analysis well explained the experimental results.