Fabrication of ultra-high-Q Ta₂O₅ microdisks by photolithography-assisted chemo-mechanical etching

Tantalum pentoxide (Ta₂O₅) is widely recognized as a promising material platform for photonic integration. This is primarily attributed to its exceptional properties including large bandgap of 3.8 eV, broad transparency window ranging from 300 nm to 8000 nm, high nonlinear refractive index of ∼7.2 × 10⁻¹⁹ m²/W, low optical loss, moderate refractive index of 2.05, low intrinsic material stress, compatibility with CMOS technology, and high solubility for rare-earth ions. However, dry etching of Ta₂O₅ is challenging and typically results in sidewall roughness with substantial scattering losses. Here, we report on fabrication of a high-Q whispering gallery mode (WGM) microdisk with a diameter of 120 µm and a loaded Q factor of 1.92 × 10⁶ by femtosecond laser photolithography assisted chemo-mechanical etching (PLACE) on amorphous Ta₂O₅ film. Thanks to the suppression of sidewall scattering, the loaded Q factor is two orders of magnitude higher than the best reported value in dispersion engineered Ta₂O₅ microresonators.