Silicon Nitride

Physics / mechanism

Silicon nitride (Si₃N₄) is a wide-bandgap ceramic dielectric (bandgap ~5 eV) with exceptional mechanical hardness (~30 GPa), thermal stability (>1400°C), and low optical absorption in the visible through mid-IR. In photonics, stoichiometric Si₃N₄ waveguides exhibit propagation losses <0.1 dB/m at 1550 nm, negligible two-photon absorption at telecom wavelengths, and a moderate Kerr nonlinearity (n₂ ≈ 2.4 × 10⁻¹⁹ m²/W) — enabling frequency combs, LiDAR PICs, and low-noise microwave photonics. In semiconductors, LPCVD Si₃N₄ films serve as hard masks, etch stops, and stress-engineering layers (tensile ~1 GPa). Damascene-process Si₃N₄ photonics (EPFL/Ligentec lineage) is the current state of the art for ultra-low-loss PICs.

Competitive landscape

Silicon nitride competes with silicon-on-insulator (SOI) for photonic integration — SOI wins on CMOS compatibility and high-index contrast but loses on two-photon absorption and loss at visible wavelengths. Lithium niobate (TFLN) competes for electro-optic modulation (Pockels effect) where Si₃N₄ has no native EO response. Aluminium nitride (AlN) offers EO capability plus UV transparency. Silica (SiO₂) planar waveguides offer lower loss but massive footprint. For structural/ceramic applications, SiC and Al₂O₃ are the principal substitutes.

Quantum computing on SiN

Companies using

Connected ideas

Sources

Frontier (open questions)

• To be added.