Kavli Affiliate: Austin J. Minnich
| First 5 Authors: Ivy I. Chen, Jennifer Solgaard, Ryoto Sekine, Azmain A. Hossain, Anthony Ardizzi
| Summary:
Lithium niobate (LiNbO$_3$, LN) is a ferroelectric crystal of interest for
integrated photonics owing to the ability to impart periodic or chirped poling
via an external electric field and its large second-order optical nonlinearity
compared to other photonic materials like SiN. The introduction of thin-film
lithium niobate (TFLN) based on ion-slicing has enabled photonic circuits with
improved figures of merit on account of the greater refractive index contrast
than is achievable in bulk LN. However, TFLN device performance is presently
limited by surface roughness scattering induced by Ar$^+$ milling and the lack
of adequately precise etch depth control. Atomic layer etching (ALE) could
potentially overcome these limitations, but no ALE process has been reported
for LN. Here, we report a directional ALE process for x-cut MgO-doped LN using
sequential exposures of H$_2$ and SF$_6$ plasma. We observe etch rates up to
$1.01 pm 0.05$ nm/cycle with a synergy of $94$%. This process has the
potential to serve as a post-processing step to achieve sub-nanometer-scale
etch depth control for TFLN devices, which may both increase the photonic
performance of existing TFLN devices and ultimately enable novel devices not
attainable in other integrated photonic platforms.
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