金刚石/碳纳米管异质界面热导及声子热输运特性

Interface thermal conductance and phonon thermal transport characteristics of diamond/carbon nanotube interface

碳纳米管作为新一代热界面材料,在天然材料中具有最高的热导率,有望解决金刚石半导体超高热流密度的散热问题.因此,本文提出将金刚石和碳纳米管结合,可大幅度提高器件性能及稳定性,减小封装尺寸,实现器件小型化设计.采用非平衡分子动力学方法从微观层面探究了金刚石/碳纳米管异质结构界面热特性及影响因素.研究发现碳纳米管层数增加使声子态密度峰值增大并向低频波段移动,低频声子增多更有利于界面传热,同时声子重叠能提高,声子耦合振动增强提升了界面传热效率;同时,一定范围内体系温度的升高及碳纳米管长径比的增大可以提高近界面处金刚石和碳纳米管的态密度截止频率,提升低频波段的峰值,进一步增强两侧声子的耦合振动,提高了界面热导.最后,采用正交试验模拟获得了金刚石/碳纳米管界面热导的最优值,结果远优于目前一般半导体/金属的界面热导.该工作为优化金刚石/碳纳米管异质界面的热输运提供了思路,并将有利于器件热管理和芯片材料设计.

Diamond,an ultra-wide band gap semiconductor material,is an ideal material for high-power,highfrequency,high-temperature,and low-power loss electronic devices.However,high-frequency and high-power working environment leads to ultra-high local hot spots.Thermal interface material(TIM)is urgently needed to improve interface heat dissipation.Carbon nanotube(CNT),a brand-new generation of TIM,has ultra-high thermal conductivity(6000 W/(m·K))and is expected to solve the heat dissipation problem of diamond semiconductor.Based on this,we first propose to combine diamond and CNT to improve the performance and stability of semiconductor device,reduce packaging size,and achieve miniaturized design of devices.Here we use reverse non-equilibrium molecular dynamics(RNEMD)method to study the thermal transport characteristics and interface thermal conductance(ITC)at the diamond/CNT interface.The results reveal that increasing CNT layers enhances the overall vibration density of states(VDOS)of CNT and shifts the peak value towards the low frequency band,which is more conducive to interface heat transfer.Alternatively,the enhancement of the phonon overlap energy strengthens the coupling vibration of phonon and thus improving the efficiency of the interfacial heat transfer.Moreover,in a certain range,the increase of system temperature and CNT length-todiameter ratio can raise the cutoff frequency of the VDOS of diamond and CNT near the interface and the peak value of the low frequency band.This further improves the coupling vibration of phonon on both sides.Finally,by orthogonal test simulation,the optimal value of ITC is determined to be 2.65 GW/(m~2·K)when the temperature,chirality,layers and length are 900 K,(6,6),6 layers and 5 nm respectively.This result greatly exceeds the current ITC of general semiconductors/metal.Compared with general composite materials,diamond/CNT composite material has great potential to enhance heat dissipation.Furthermore,according to Pvalue test,the number of layers has an extremely significant influence on interfacial thermal transport,while the influence of length,temperature and diameter decrease in turn.This work provides insights into optimizing heat transport at diamond/carbon nanotube interface and will be beneficial for device thermal management and chip material design.