Crack-free stoichiometric silicon nitride grown on sapphire reaches 2 μm at only 200 MPa stress
jwt0625 · x · 2026-10-15
The author shared arXiv paper 2610.15754 (NIST and collaborators): direct growth of crack-free stoichiometric silicon nitride on sapphire, up to 2 μm thick with only 200 MPa residual stress.
Conventional LPCVD silicon nitride on oxidized silicon carries 1000 MPa tensile stress and tends to crack beyond 400 nm. The author was initially puzzled by how large the CTE mismatch range was, then realized CTE is temperature-dependent — it must be matched across the whole temperature range to avoid cracks.
Fabricated photonic devices show propagation losses of 0.35 dB/cm at 780 nm, 0.37 dB/cm at 1064 nm, and 0.25 dB/cm at 1630 nm; prism-coupling indicates film losses below 1 dB/cm down to 500 nm, suiting wide-band nonlinear and quantum photonics.
Related event: NIST Grows Crack-Free Silicon Nitride on Sapphire(2 posts)→
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