Freestanding HfO2 resonant grating fabricated by ion beam etching

We report here the design and fabrication of freestanding Hafnium dioxide (HfO₂) resonant gratings. The proposed freestanding HfO₂ gratings are implemented on the prepared HfO₂/Silicon wafer by combining ion beam etching (IBE) of HfO₂ film with deep reactive ion etching (DRIE) of silicon substrate. The grating patterns are defined by electron beam lithography and then transferred to HfO₂ film by IBE. The silicon substrate beneath the HfO₂ grating region is removed to make the HfO₂ grating suspend in space with air as low refractive index materials on the top and bottom. The optical responses of the freestanding HfO₂ gratings are analyzed by the rigorous coupled-wave analysis (RCWA) method. In the simulation result, the strong resonant peaks indicate that the resonant effects are tunable as the grating period increases and the filling factor varies at visible wavelengths. The simple process is feasible for fabricating HfO₂ resonant grating that can be exploited in arrays of optical switches or modulators and narrowband spectral filters, for use in advanced optical signal processing and communication systems.