Thermal Interface Materials Based On Carbon Nanotube And Copper Nanowire Arrays

With rapidly increasing power densities in electronic devices,thermal management is becoming a crucial issue in maintaining the reliability and performance.Inadequate power dissipation will raise the device temperature and shorten device lifetime.The microscopic asperities between contact surfaces impede heat transfer from a chip to the heat sink,which contribute to the prominent thermal resistance.The thermal interface materials(TIMs)are used to replace air gaps between the contact surfaces to enhance thermal conduction.Vertically aligned carbon nanotube(CNT)arrays and copper nanowires are promising candidates for advanced thermal interface materials(TIMs)since they possess high mechanical compliance and high intrinsic thermal conductivity.Some of the previous works indicate that the CNT arrays in directly dry contact with the target surface process low contact thermal conductance which is the dominant thermal resistance.In this study,the vertical pressure experiment was carried out on the carbon nanotube array,and the side and top of the array were characterized by electron microscope(SEM)and atomic force microscope(AFM).Using a phase sensitive transient thermo-reflectance(PSTTR)technique,we measure the thermal conductance between CNT arrays and copper(Cu)surface under different pressure.We demonstrated that the contact force is one of the crucial factors for optimizing the thermal performance of CNT arrays TIMs.The experimental results suggest that the Cu-CNT arrays contact thermal conductance has a strong dependence on the surface deformation and has an order of magnitude rise as the contact pressure increases from 0.05 to 0.15MPa.Besides,the pressure has little effect on the contact thennal resistance after it reaches 0.15MPa.This work could provide guidelines to determine the minimum requirement of packaging pressure on CNT TIMs.Since the large thermal contact resistance when using CNTs limits their potential for TIMs because their ends are highly entangled.While the copper nanowires grown from alumina membranes have recently been measured to have a thermal conductivity as high as 70 W/m K,most importantly they can achieve much higher array density and free of entanglement between the wires.Therefore,CuNW array TIMs are expected to have a better thermal performance than CNT array TIMs.Mechanical testing of copper nanowire arrays shows that its Young's modulus is on the order of tens of megapascals,which means it has a good mechanical compliance.However,the results of thermal measurement show that dry contact between copper nanowires and gold has pretty high contact thermal resistance.It may be that the copper wires do not have the same height due to nonuniform growth.Welding copper nanowire array and target interface with indium may be the direction to further improve contact thermal conductivity in the future.