Domains inversion in LiNbO₃ using electron beam irradiation for phononic crystals

We report here, the study of domain inversion in lithium niobate (z-cut) by electron beam irradiation without any static bias associated to wet etching, in view of the fabrication of phononic crystals. The inverted domains are revealed by HF-etching taking advantage of the large difference in etching rate between z+ and z-faces. A pertinent choice of irradiation conditions such as accelerating voltage, probe current and injected dose, (parameters of interest for the geometry and size of the obtained domains), was determined and optimized. Two dimensional structures at the micrometer scale were then realized on z-cut LiNbO₃. We demonstrate the achievement of 8μm diameter hexagons, with a very large depth close to 30μm, which depends on the etching time. The obtained structures were characterized before etching by optical microscopy to visualize the inverted domains, and after etching by field emission scanning electron microscopy. These characterisations pointed out the high occupancy rate of obtained structures. Numerical simulations of the realized phononic structure band gap show a frequency band gap around 200MHz.