Carbon nanotube-copper exhibiting metal-like thermal conductivity and silicon-like thermal expansion for efficient cooling of electronics

Abstract

Increasing functional complexity and dimensional compactness of electronic devices have led to progressively higher power dissipation, mainly in the form of heat. Overheating of semiconductor-based electronics has been the primary reason for their failure. Such failures originate at the interface of the heat sink (commonly Cu and Al) and the substrate (silicon) due to the large mismatch in thermal expansion coefficients (∼300%) of metals and silicon. Therefore, the effective cooling of such electronics demands a material with both high thermal conductivity and a similar coefficient of thermal expansion (CTE) to silicon. Addressing this demand, we have developed a carbon nanotube-copper (CNT-Cu) composite with high metallic thermal conductivity (395 W m(-1) K(-1)) and a low, silicon-like CTE (5.0 ppm K(-1)). The thermal conductivity was identical to that of Cu (400 W m(-1) K(-1)) and higher than those of most metals (Ti, Al, Au). Importantly, the CTE mismatch between CNT-Cu and silicon was only ∼10%, meaning an excellent compatibility. The seamless integration of CNTs and Cu was achieved through a unique two-stage electrodeposition approach to create an extensive and continuous interface between the Cu and CNTs. This allowed for thermal contributions from both Cu and CNTs, resulting in high thermal conductivity. Simultaneously, the high volume fraction of CNTs balanced the thermal expansion of Cu, accounting for the low CTE of the CNT-Cu composite. The experimental observations were in good quantitative concurrence with the theoretically described 'matrix-bubble' model. Further, we demonstrated identical in-situ thermal strain behaviour of the CNT-Cu composite to Si-based dielectrics, thereby generating the least interfacial thermal strain. This unique combination of properties places CNT-Cu as an isolated spot in an Ashby map of thermal conductivity and CTE. Finally, the CNT-Cu composite exhibited the greatest stability to temperature as indicated by its low thermal distortion parameter (TDP). Thus, this material presents a viable and efficient alternative to existing materials for thermal management in electronics.

Enhanced thermal conductivity of epoxy composites filled with silicon carbide nanowires

“…Recently, it has been reported that the fillers with high aspect ratio, such as nanowires and nanosheets, can form more continuous thermally conductive network in the polymer matrix and therefore are more efficiently in improving the heat transfer 1, 52 . In order to fabricate composites with superior thermal conductivity, beside the amount of filler, uniform dispersion in polymer matrix is the critical factor 35 .…”

“…Meanwhile, performance and versatility of electronic devices have been integrated with a decreasing dimensions. Consequently, a high level of circuit integration cause high heat, which needs to be rapidly dissipated to let the device work efficiently 1 . Epoxy resins are widely applied in the aerospace, automotive and electronic industries for supporting and adhesive, owing to their excellent mechanical properties, thermal stability, and chemical resistances 2, 3 .…”

“…Nowadays, the heat source are usually Si-based 1 . Copper and aluminum are traditional heat dissipating materials, which show large mismatch with silicon and insulating ceramics and cannot directly attach to silicon without stress compensating interlayers 34 .…”

“…Therefore, control of reinforcing fillers into the polymer can fulfill the high thermal conductivity and the lowest CTE or thermal distortion parameter (TDP, an indicator of thermal dilation) potential requirements. It will meet the requirement of thermal management and electronic packaging applications ranging from microelectronic components and devices to supercomputers 1, 35, 36 .…”

Enhanced cooling in mono-crystalline ultra-thin silicon by embedded micro-air channels

“…Scaling of device dimensions has enabled performance enhancement but as a trade-off scaled devices experience higher leakage current induced excessive power consumption in their idle state. [1][2][3][4][5][6][7] This also results into higher heat dissipation and eventually lower battery lifetime. With increased demand for ultra-mobile electronics, this rapid power draining acts as one of the main show stoppers.…”