Aluminium Oxide

Physics / mechanism

Aluminium oxide (Al₂O₃, corundum/sapphire phase) is a wide-bandgap ceramic (~9 eV) with high dielectric constant (ε ~9–10), thermal conductivity up to 30 W/m·K (single-crystal), breakdown field ~10 MV/cm, and near-zero optical absorption from UV (~150 nm) through mid-IR. As a gate dielectric it delivers EOT scaling; as ALD-deposited Al₂O₃ it passivates III-V and GaN surfaces with interface trap densities Dit ~10¹⁰ cm⁻²eV⁻¹. Sapphire substrates (c-plane, r-plane) are the dominant GaN-on-sapphire epitaxy platform. ALD Al₂O₃ at 1–10 nm is standard in DRAM capacitor stacks and advanced node back-end passivation. HVM ALD cycle times now sub-2 s at 200–300 °C.

Competitive landscape

Competes with HfO₂ and ZrO₂ (higher-k, preferred for CMOS gate dielectrics), SiO₂/SiON (mature, lower interface quality on III-V), and Si₃N₄ (passivation, lower thermal conductivity). For substrates, SiC displaces sapphire in high-power GaN-on-SiC RF; AlN challenges it for UV-C epitaxy. In thermal management ceramics, AlN (180 W/m·K) wins on conductivity. Al₂O₃ holds where cost, optical transparency, and ALD conformality dominate.

Companies using

Connected ideas

Sources

Frontier (open questions)

• To be added.