Direct Photochemical Patterning of Lithium Niobate Thin Films for Scalable Nonlinear Optical Metasurfaces

Lithium niobate is one of the most sought-after materials for nanophotonic devices, including frequency converters, modulators, and quantum light sources. Integration of lithium niobate into optical devices, however, is hampered by significant top-down fabrication challenges due to its exceptional chemical resistance. Scalable fabrication methods that preserve material quality while reducing fabrication complexity and cost are, therefore, crucial to advancing lithium niobate devices. We present a photochemical metal-organic decomposition technique for the scalable patterning of lithium niobate at ambient conditions, eliminating the need for harsh etching conditions and cleanroom protocols. The method utilizes a solution of a custom-prepared photosensitive organometallic precursor as a negative photoresist. The UV light exposure of the thin films of the precursor through a photomask, followed by rinsing with ethanol, yields amorphous patterns, which transform into crystalline lithium niobate after a calcination step. This method enables a scalable fabrication of a range of complex geometric shapes with a feature resolution down to $30\,\mu\mathrm{m}$. The patterned lithium niobate structures exhibit a tunable second harmonic generation activity with an isotropic optical response. This approach offers a scalable and low-cost pathway for manufacturing lithium niobate photonics and the potential to fabricate other materials (e.g., barium titanite and lithium tantalate).