Diamond/Aluminum Nitride Composite
May29, 2026
Diamond/Aluminum Nitride Composite
AlN-Engineered Diamond/Aluminum Nitride Composite with Multiscale Interface Architecture for Ultra-High Thermal Conductivity and Electrical Insulation
Abstract
The integration of high thermal conductivity and electrical insulation in a single material system remains a critical challenge for advanced thermal management in high-power electronics. Here, we report a hierarchical diamond–AlN composite architecture enabled by multiscale interface engineering and additive manufacturing. Diamond particles are first activated via plasma-induced surface nano-roughening to enhance interfacial bonding. A conformal AlN interlayer is subsequently deposited by plasma-enhanced atomic layer deposition (PE-ALD), followed by the formation of a thick AlN shell via chemical vapor deposition (CVD). The resulting core–shell particles are consolidated with AlN matrix powder using selective laser melting and post-densification via hot isostatic pressing. The engineered interfaces significantly reduce thermal boundary resistance while preserving electrical insulation, yielding bulk composites with thermal conductivity up to 700 W m⁻¹ K⁻¹, high density (>99%), and dielectric breakdown strength up to 14 kV. This work demonstrates a scalable pathway for architected diamond-based composites for extreme thermal management applications.
1. Introduction
The rapid evolution of high-power and high-frequency electronic systems, including GaN-based power devices, radar modules, and laser arrays, has imposed stringent demands on thermal management materials. Conventional polymer-based substrates suffer from low thermal conductivity and limited thermal stability, while metallic composites, despite their excellent heat conduction, fail to meet electrical insulation requirements. Ceramic materials such as aluminum nitride (AlN) provide intrinsic electrical insulation but are limited by moderate thermal conductivity.
Diamond exhibits the highest known thermal conductivity among bulk materials; however, its integration into composite architectures is fundamentally constrained by interfacial thermal resistance and poor wettability with ceramic matrices. Consequently, engineering a thermally efficient and electrically insulating diamond-based composite remains a key materials challenge.
2. Materials Design Concept
We propose a multiscale interface engineering strategy to construct a hierarchical diamond/AlN composite system. The design is based on three synergistic components:
Diamond thermal core High intrinsic phonon conductivity provides the primary heat transport pathway.
Conformal AlN interfacial layer (nanometer scale) Deposited via PE-ALD, this layer ensures atomic-scale continuity, enhances phonon coupling, and suppresses interfacial scattering.
AlN outer shell (micrometer scale) Formed via CVD, this layer provides structural continuity, electrical insulation, and compatibility with powder consolidation processes.
This multiscale architecture transforms discrete diamond particles into thermally integrated building blocks for bulk composites.
3. Surface Activation of Diamond Particles
Diamond powders (20–400 μm) are subjected to plasma-based surface activation using inductively coupled plasma (ICP) or an anode-layer ion source. Reactive oxygen or hydrogen plasma induces controlled surface etching, producing nano-scale roughness (Ra ≈ 5–100 nm). This process simultaneously removes organic contaminants and generates high-density surface anchoring sites.
The increased effective surface area enhances particle–coating adhesion and promotes mechanical interlocking at subsequent interface formation stages. Importantly, controlled roughening improves interfacial phonon coupling by increasing the real contact area between diamond and AlN.
4. Atomic-Scale Interface Engineering via PE-ALD
A conformal AlN interlayer is deposited using plasma-enhanced atomic layer deposition (PE-ALD) with trimethylaluminum (TMA) and NH₃ as precursors. The process yields an ultrathin (10–200 nm) yet dense AlN coating with near-unity conformality.
A graded deposition strategy is employed, wherein precursor-to-reactant ratios are systematically varied to produce a compositional gradient across the interlayer. This gradient reduces lattice and thermal mismatch between diamond and AlN, thereby minimizing interfacial thermal resistance.
The ALD-derived interlayer acts as a phonon coupling mediator, bridging the acoustic impedance mismatch between diamond and ceramic matrix.
5. Formation of Thick AlN Shell via CVD
A secondary AlN layer (>10 μm) is deposited using chemical vapor deposition (PECVD or hot-wire CVD). This layer ensures mechanical robustness and electrical insulation while preserving thermal continuity established by the ALD interface.
The CVD shell transforms individual diamond particles into electrically insulated thermally conductive units suitable for powder-based additive manufacturing.
6. Additive Manufacturing and Densification
Core–shell diamond particles are blended with AlN powder (1–40 μm) and processed via selective laser melting (SLM) under controlled inert atmosphere conditions (O₂ < 0.1%). Layer-wise laser consolidation is followed by:
Vacuum sintering (850–1100 °C)
Optional cold isostatic pressing
Hot isostatic pressing (50–200 MPa, 850–1050 °C)
This multi-step densification sequence ensures near-full density (>99%) while preserving the integrity of thermally engineered interfaces.
7. Thermal Transport Mechanism
The enhanced thermal performance originates from three coupled mechanisms:
Reduced interfacial phonon scattering due to ALD-mediated acoustic bridging
Increased real contact area from plasma-induced surface roughening
Continuous AlN matrix enabling percolative heat conduction pathways
The hierarchical architecture effectively suppresses thermal boundary resistance, which is typically the dominant bottleneck in diamond-based composites.
8. Results and Performance
The resulting bulk composites exhibit:
Thermal conductivity: 600–700 W m⁻¹ K⁻¹
Relative density: ≥99%
Dielectric breakdown strength: ~14 kV
Stable high-temperature thermal transport up to 500 °C
These values represent a significant improvement over conventional AlN or metal-based thermal substrates.
9. Conclusion
We demonstrate a multiscale interface engineering strategy for the fabrication of diamond–AlN composites with exceptional thermal and electrical performance. By integrating plasma-activated surface modification, atomic-scale ALD interface design, and CVD shell formation, we establish a scalable route to overcome long-standing interfacial limitations in diamond-based composites. This work provides a generalizable framework for designing next-generation thermal management materials for extreme electronic environments.
