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

At a Glance

Metadata	Details
Publication Date	2024-01-01
Journal	Acta Physica Sinica
Authors	Zi-Yi Liu, Fuqiang Chu, Junjun Wei, Yan-Hui Feng
Citations	1
Analysis	Full AI Review Included

Executive Summary

This study utilizes Reverse Non-Equilibrium Molecular Dynamics (RNEMD) and Orthogonal Testing to optimize the Interface Thermal Conductance (ITC) of a Diamond/Carbon Nanotube (CNT) heterostructure, proposing a superior Thermal Interface Material (TIM) for high-power diamond electronics.

Core Achievement: A record-high ITC of 2.65 GW/(m²K) was achieved under optimal conditions (900 K, 6 CNT layers, 5 nm length), significantly exceeding current general semiconductor/metal interface values.
Value Proposition: Combining diamond’s high bulk thermal conductivity (up to 3.9 kW/mK) with CNT’s superior interfacial properties solves the critical heat dissipation bottleneck in ultra-high-power diamond semiconductor devices.
Mechanism of Enhancement: Increasing the number of CNT layers enhances the overall Vibration Density of States (VDOS) and shifts the peak towards the low-frequency band, which is crucial for effective phonon coupling and heat transfer across the interface.
Optimization Strategy: Orthogonal testing identified the CNT layer count as the most significant factor influencing ITC (P < 0.01), followed by CNT length and system temperature.
Temperature Effects: While ITC generally increases with temperature due to non-harmonic effects, the structural integrity of the CNT (chirality (6, 6)) limits performance above 500 K for fixed structures, though the absolute optimum was found at 900 K under specific structural parameters.

Technical Specifications

Parameter	Value	Unit	Context
Optimal Interface Thermal Conductance (ITC)	2.65	GW/(m²K)	Achieved under optimal structural conditions (900 K, 6 layers, 5 nm).
Peak ITC (Temperature Sweep)	318.55	MW/(m²K)	Observed at 500 K during temperature variation study.
Optimal System Temperature	900	K	Highest ITC achieved in orthogonal test.
Optimal CNT Layer Count	6	layers	Most significant factor (P = 0.003009).
Optimal CNT Length	5	nm	Corresponds to an L/d ratio of 6.0.
Diamond Bandgap	5.5	eV	Ultra-wide bandgap property.
Diamond Breakdown Field	5-15	MW/cm	High electrical stability.
Diamond Thermal Conductivity (Bulk)	2.6-3.9	kW/(mK)	High bulk thermal performance.
CNT Thermal Conductivity (Bulk)	~6000	W/(mK)	Highest known natural thermal conductivity.
Factor Significance Ranking (R-value)	823.75 > 287.55 > 264.73 > 156.08	N/A	Layers > Temperature > Length > Diameter.

Key Methodologies

The study relied on advanced computational modeling and statistical optimization techniques to analyze thermal transport at the nanoscale interface.

Model Construction: Diamond/CNT heterostructure models were created using Materials Studio. The diamond substrate was oriented along the <111> direction. The interface gap (van der Waals distance) was set to 3.4 A.
Interatomic Potentials: The Tersoff potential was used to describe C-C bonding within the diamond and CNT structures. The 12-6 Lennard-Jones (L-J) potential was used to model the non-bonded interactions between the diamond and CNT carbon atoms across the interface.
Thermal Transport Simulation: The Reverse Non-Equilibrium Molecular Dynamics (RNEMD) method (Jund and Jullien constant heat flow method) was implemented in LAMMPS. Heat flux (Q) was imposed by exchanging kinetic energy between hot and cold regions, and the resulting temperature gradient (ΔT) was measured to calculate ITC (G = Q / (AΔT)).
Phonon Analysis: Phonon coupling was analyzed by calculating the Vibration Density of States (VDOS), derived from the Fast Fourier Transform (FFT) of the Velocity Auto Correlation Function (VACF). Overlap Energy was used to quantify the degree of VDOS matching between the two materials.
Orthogonal Optimization: An L₁₆(4⁵) Orthogonal Test design was employed to efficiently explore the parameter space. Five factors (Temperature, Chirality/Diameter, CNT Layers, CNT Length, and Interface Gap) were tested at four levels each to determine the optimal combination for maximizing ITC.
Boundary Conditions: Periodic boundary conditions were applied in the x and y directions. Fixed layers were used at the ends of the z-axis (heat transfer direction), adjacent to the hot and cold reservoirs.

Commercial Applications

This research provides fundamental guidance for designing next-generation thermal management solutions, particularly for devices operating under extreme power and temperature loads.

High-Power RF and Microwave Devices: Essential for cooling diamond-based high-electron-mobility transistors (HEMTs) used in radar, satellite communications, and 5G/6G infrastructure, where high local heat flux is critical.
Aerospace and Military Electronics: Applicable to high-temperature, high-frequency chips used in harsh environments (e.g., radar systems, avionics) that require materials with high Figure of Merit (FOM).
Advanced Chip Packaging: Enables device miniaturization and increased power density by providing ultra-efficient TIMs between the diamond substrate and the heat sink.
Optoelectronics: Relevant for thermal management in short-wave light-emitting devices and high-power laser diodes built on diamond substrates.
Thermal Interface Materials (TIMs): Direct application in the development of composite TIMs that utilize CNTs or graphene layers to bridge the thermal mismatch between high-conductivity substrates and cooling hardware.

View Original Abstract

<sec>Diamond, an ultra-wide band gap semiconductor material, is an ideal material for high-power, high-frequency, 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.</sec><sec>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-to-diameter 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<sup>2</sup>·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 P-value 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.</sec><sec>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.</sec>

Tech Support

Original Source

DOI: https://doi.org/10.7498/aps.73.20240323