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Single-Crystal vs Polycrystalline Diamond for Thermal Management
Behind the near-2× thermal conductivity gap lies grain-boundary scattering — the materials science of why single-crystal wins for high-end thermal management.
01The Conductivity Gap
At room temperature, single-crystal CVD diamond reaches 1800-2500 W/m·K (near the theoretical limit), while polycrystalline CVD diamond typically delivers 500-1800 W/m·K — nearly a 2× gap. Copper is ~400 W/m·K and AlN ~200 W/m·K, making single-crystal diamond the most thermally conductive material known.
02The Root Cause: Grain-Boundary Scattering
Polycrystalline diamond consists of countless small grains; phonons (the carriers of heat) scatter at grain boundaries, so conductivity falls as grain size shrinks. Single-crystal diamond has no grain boundaries, giving phonons a long mean free path and conductivity near the perfect-crystal theoretical value. This is why single-crystal costs more — its physical performance ceiling is higher.
03TBR & GaN Integration
In GaN-on-Diamond RF and power devices, thermal boundary resistance (TBR) matters just as much. Direct bonding of single-crystal diamond cuts TBR to ~3 m²K/GW; combined with its conductivity, this lets GaN HEMTs exceed 40 W/mm power density (vs ~5-10 W/mm for Si/SiC). MIT's 2026 GaN-on-single-crystal-diamond amplifier exemplifies this route.
04Cost & Selection
Single-crystal size is limited by the seed and costs more — ideal for extreme thermal needs like 5G/6G GaN amplifiers, high-power data-center chips and LiDAR. Polycrystalline scales to large sizes at lower cost for less demanding uses. ENTASK makes single-crystal only, in yellow/coffee/grey, custom sizes from 20×20 to 30×30mm.
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