Focused ion beam milling of microchannels in lithium niobate

We present experimental and simulation results for focused ion beam (FIB) milling of microchannels in lithium niobate in this paper. We investigate two different cuts of lithium niobate, Y- and Z-cuts, and observe that the experimental material removal rate in the FIB for both Y-cut and Z-cut samples was 0.3 μm³/nC, roughly two times greater than the material removal rate previously reported in the literature but in good agreement with the value we obtain from stopping and range of ions in matter (SRIM) simulations. Further, we investigate the FIB milling rate and resultant cross-sectional profile of microchannels at various ion beam currents and find that the milling rate decreases as a function of ion dose and correspondingly, the cross-sectional profiles change from rectangular to V-shaped. This indicates that material redeposition plays an important role at high ion dose or equivalently, high aspect ratio. We find that the experimental material removal rate decreases as a function of aspect ratio of the milled structures, in good agreement with our simulation results at low aspect ratio and in good agreement with the material removal rates previously reported in the literature at high aspect ratios. Our results show that it is indeed easier than previously assumed to fabricate nanochannels with low aspect ratio directly on lithium niobate using the FIB milling technique.