Experimental Study On Thermal Interface Properties Of Vertical Aligned Carbon Nanotube Arrays

With the continuous shrinking of feature size and improvement of device performance in the microelectronics,the resulted large amount of heat gathered in a short time within the device will lead to the degradation or even failure of the device performance.Therefore,heat dissipation of the chip is one of the most significant issues which limiting the development of microelectronics technology.Since traditional thermal materials has failed to solve the problem of chip heat dissipation in a better way,carbon nanotubes(CNTs)with advantages of high thermal conductivity,thermal stability and flexibility,are expected to solve the problem of chip heat dissipation as excellent thermal management materials.In the applications of thermal interface materials,CNTs are subject to compressive stress in some degree,so it is of great significance to study the thermal properties of CNTs under compressive stress.In this paper,the thermal interface properties of vertically aligned CNT arrays are studied using a transient thermal reflection technique.Firstly,the experimental system of transient thermal reflection for measuring the thermal conductivity of CNT films is constructed and introduced.Factors which may have influence on the measured results are analyzed and the selection of parameters used in the experiments are given.Secondly,the thermal conductivity of deionized water is measured by the transient thermal reflection technique based on the bidirectional heat flow model,which verifies the feasibility of the experimental system.Then,the thermal interfacial resistance(TIR)between the 860?m CNT array and the gold(Au)thin film is measured by using a SiO2/CNT/Au three-layer sample.When the stress of 1.49 MPa is applied to the CNT array in the vertical direction,the TIR of the Au-CNT array is about 1.90~3.26×10-6m2·K/W,which is much smaller than the thermal resistance under small stress.This is because the contact area of the carbon nanotube array and the Au is increased as a consequence of the large stress applied,so that the contact thermal resistance is reduced.In addition,due to the absence of a transition layer between the Au and the glass,the TIR is about 1.12×10-7m2·K/W,which is slightly larger compared to the theoretical contact resistance(10-8-10-7m2·K/W)between metal and dielectric layer.It is found that higher sensitivity is achieved using the transient thermalreflection technique based on the bidirectional heat flow model when the TIR value of the sample is larger.Finally,according to the experimental results of the SiO2/CNT/Au three-layer sample,the NaCl /Au/ CNT double-layer structure with soluble substrate is used to measure the TIR between Au and CNT arrays with different heights.When 2Mpa stress is applied to the CNT arrays in the vertical direction,the TIR value is 4.63±1.02×10-6 m2·K/W and 2.04±0.37×10-6m2 · K/W for 230?m and 860?m CNT arrays,respectively.In addition to the influence of contact area on the TIR,the results show that the TIR also has a dependence on the length of the CNT arrays,and CNT arrays with a larger longitudinal length has a smaller TIR value.In short,as a novel and promising thermal interface materials,CNTs have advantages of no contamination and good thermal stability at high temperatures.However,the large contact thermal resistance at the CNTs/metal interface has been one of the important problems in the practical applications so far.Researches in this paper have valuable references for further reducing the TIR between CNTs and metals.