Tokyo University Realizes Ultra-High-Performance Heat Spreader ― Using graphite to control heat flow in three dimensions

A research group including Professor Junichiro Shiomi, specially appointed Assistant Professor Bin Xu , and specially appointed Researcher Yuxuan Liao of the Graduate School of Engineering, the University of Tokyo, has succeeded in isotropically converting the anisotropic heat conduction of graphite by developing a heat spreader in which graphite materials of different orientations are bonded in a double decker structure to realize the high heat dissipation performance of power semiconductors. A heat dissipation test was carried out using this heat spreader, and a performance equivalent to that of an isotropic material with a thermal conductivity of 900 W/m·K was achieved.

With the advancement in sophistication and integration of semiconductors, a heat spreader with high thermal conductivity that efficiently dissipates the high-density heat generated by these devices has become essential. Owing to its high in-plane thermal conductivity, graphite is gaining attention as a promising low-cost material for this purpose. Prof. Shiomi reported, "The thermal conductivity of graphite is high in the basal plane direction (horizontal) but low in the 'c axis' direction (vertical); this makes it difficult to use in the thermal management of power semiconductors, which require isotropic heat dissipation."

From this background the research group devised a method for realizing isotropic and high thermal conduction by controlling the heat flow three-dimensionally using a structure in which graphite materials of different orientations are assembled. First, the effect of heat flow caused by the three-dimensional structure of graphite on the heat dissipation performance of the heat spreader was theoretically simulated using the finite element method, and it was verified that the structure in which two graphite specimens with different axis orientations were stacked was the optimal structure. From this, through high-temperature firing in a vacuum chamber, the heat spreader was successfully assembled by bonding the graphite materials with microparticles of copper as the binder layer, and a heat dissipation performance equivalent to that of an isotropic material with a thermal conductivity of 900 W/m·K was experimentally realized.

It is expected that the heat spreader developed using this three-dimensional composite structure of graphite, which is both low cost and has a high heat dissipation efficiency, can be utilized in various industries by effectively improving the thermal management of power semiconductors. Prof. Shiomi commented, "We found that this type of three-dimensional structure achieves satisfactory performance for the thermal management of high-end power semiconductors, the challenge now is to manufacture it at a low cost. To do this, we can further refine the thermal bonding to produce a similar structure from thinner graphite or synthesize three-dimensional structures directly on one piece."

■ Heat spreader: A structure that improves the effective contact area with a radiator and increases heat dissipation efficiency when inserted between the heating element and the radiator.