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

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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.