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

Diamond/Carbon Nanotube Interface Thermal Transport: 6CCVD Technical Analysis

This document analyzes the findings of the research paper “Interface thermal conductance and phonon thermal transport characteristics of diamond/carbon nanotube interface” to provide technical specifications and highlight how 6CCVD’s advanced MPCVD diamond materials can accelerate research and commercialization in high-performance thermal management.

Executive Summary

This research validates the use of diamond/carbon nanotube (CNT) composites as a superior Thermal Interface Material (TIM) for ultra-high heat flux applications, directly supporting the need for high-quality diamond substrates.

Application Focus: Diamond is confirmed as the ideal ultra-wide band gap semiconductor for high-power, high-frequency electronics, requiring advanced thermal management solutions.
Core Achievement: Molecular Dynamics (MD) simulation successfully optimized the Interface Thermal Conductance (ITC) of the Diamond/CNT heterostructure.
Peak Performance: A maximum ITC of 2.65 GW/(m²·K) was achieved, significantly exceeding the performance of current general semiconductor/metal interfaces.
Optimal Conditions: The highest ITC was found under specific conditions: 900 K system temperature, (6, 6) armchair CNT chirality, 6 CNT layers, and 5 nm CNT length.
Mechanism Identified: Enhanced heat transfer is driven by increased phonon coupling and spectral overlap, with the number of CNT layers identified as the most significant factor influencing ITC.
Commercial Impact: These findings provide a clear pathway for optimizing thermal transport at the diamond interface, crucial for next-generation device thermal management and chip material design.

Technical Specifications

The following hard data points were extracted from the simulation results and literature review presented in the paper.

Parameter	Value	Unit	Context
Optimal Interface Thermal Conductance (ITC)	2.65	GW/(m²·K)	Achieved at optimal conditions (900 K, 6 layers, 5 nm length)
Diamond Thermal Conductivity (Literature)	2.6-3.9	kW/(m·K)	Intrinsic thermal performance of diamond
CNT Thermal Conductivity (Literature)	6000	W/(m·K)	Highest known natural material conductivity
Optimal System Temperature	900	K	Temperature yielding peak ITC
Optimal CNT Layers	6	Layers	Most significant factor influencing ITC (P < 0.01)
Optimal CNT Length	5	nm	Length parameter for optimal ITC
Diamond Band Gap (Literature)	5.5	eV	Ultra-wide band gap semiconductor property
Diamond Simulation Dimensions	100 Å × 100 Å × 25 Å	-	Simulation cell size (1 Å = 0.1 nm)
ITC Range (Orthogonal Test)	33.73 to 1264.37	MW/(m²·K)	Range observed across various Length/Diameter ratios
VDOS Cutoff Frequency (Optimal 500 K)	30	THz	Diamond VDOS cutoff frequency at 500 K
VDOS Cutoff Frequency (Optimal 500 K)	40	THz	CNT VDOS cutoff frequency at 500 K

Key Methodologies

The study utilized advanced computational techniques to model and optimize the thermal interface performance.

Modeling and Orientation: The Diamond/CNT heterostructure was built using Materials Studio. The diamond substrate was oriented along the <111> direction.
Simulation Platform: Molecular Dynamics (MD) simulations were performed using the open-source LAMMPS software.
Interatomic Potentials:
- Tersoff potential was used for C-C interactions within the diamond and CNT structures.
- The 12-6 Lennard-Jones (L-J) potential was used to describe the long-range van der Waals forces between the diamond and CNT carbon atoms.
Thermal Transport Calculation: The Reverse Non-Equilibrium Molecular Dynamics (RNEMD) method (specifically, the Jund and Jullien constant heat flow method) was employed to calculate the ITC (G).
Boundary Conditions: Periodic boundary conditions were applied in the lateral (x and y) directions. Fixed layers were used at the ends, with hot and cold reservoirs applied in the heat transfer (z) direction.
Optimization Strategy: An L₁₆(4⁵) Orthogonal Test Simulation was conducted to efficiently determine the optimal combination of five factors (Temperature, Layers, Diameter, Length, Chirality) at four distinct levels.
Mechanism Analysis: Phonon Vibration Density of States (VDOS) and Overlap Energy (E_overlap) were calculated via Fast Fourier Transform (FFT) of the Velocity Auto Correlation Function (VACF) to analyze the phonon coupling and spectral matching mechanisms.

6CCVD Solutions & Capabilities

The research confirms that high-quality diamond is essential for next-generation thermal management. 6CCVD is uniquely positioned to supply the necessary MPCVD diamond materials and customization services required to replicate, extend, and commercialize this research.

Applicable Materials

To replicate or extend this high-performance thermal interface research, 6CCVD recommends the following materials:

Material Grade	Application Relevance	6CCVD Capability Match
Optical Grade Single Crystal Diamond (SCD)	Required for high-power device substrates where maximum intrinsic thermal conductivity (up to 3.9 kW/(m·K)) is critical for heat spreading prior to the TIM layer.	SCD wafers available in thicknesses from 0.1 µm to 500 µm.
High-Purity Polycrystalline Diamond (PCD)	Ideal for large-area thermal spreaders and packaging components where the Diamond/CNT composite TIM will be applied.	PCD plates/wafers available up to 125mm in diameter.
Custom Substrates	Required for testing various thermal boundary conditions and mechanical stability at high temperatures (up to 900 K).	Substrates available up to 10 mm thick.

Customization Potential

The success of the Diamond/CNT interface relies heavily on the quality and preparation of the diamond surface. 6CCVD offers comprehensive services to meet these exacting requirements:

Precision Polishing: Achieving optimal phonon coupling requires extremely smooth surfaces. 6CCVD provides:
- SCD polishing to Ra < 1 nm.
- Inch-size PCD polishing to Ra < 5 nm.
Custom Dimensions and Shaping: We provide custom laser cutting and shaping services to match specific device geometries, ensuring the diamond substrate fits seamlessly into complex high-power packages.
Metalization Services: While the paper focuses on the C-C interface, device integration often requires electrical contacts or bonding layers. 6CCVD offers internal metalization capabilities, including deposition of Au, Pt, Pd, Ti, W, and Cu layers, allowing for complex heterostructure fabrication.

Engineering Support

The optimization of the Diamond/CNT interface requires precise control over material properties and surface preparation.

Material Selection: 6CCVD’s in-house PhD team specializes in MPCVD growth parameters and can assist researchers in selecting the optimal SCD or PCD grade (e.g., specific crystallographic orientation or nitrogen content) to maximize thermal performance for similar High-Power Thermal Management projects.
Global Logistics: We ensure reliable, global delivery of sensitive diamond materials, offering DDU (Delivered Duty Unpaid) as default, with DDP (Delivered Duty Paid) available upon request.

Call to Action

To achieve the 2.65 GW/(m²·K) ITC demonstrated in this research, high-quality, precisely prepared MPCVD diamond substrates are non-negotiable.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.

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