Investigation of fabricating a LiNbO3 ultrasonic phased array transducer of more than 100 MHz

36°/Y-cut lithium niobate (LiNbO₃) single crystals have been patterned by means of Inductively Coupled Plasma (ICP) deep etching to create ultrasonic arrays resonating in the frequency range of 100-200 MHz. The limitation of etching aspect ratio and the minimum pitch are explored under the optimized ICP parameters. The experimental results demonstrate that the minimum pitch could be obtained at about 25 μm, equivalent to a pitch of 1.6 λ, with a kerf depth of 16 μm. Focusing Ion Beam (FIB) technique is also studied to etch LiNbO₃ crystals. The aspect ratio is up to as high as 6. A pitch of 0.5 λ can be obtained for a 100 MHz half-kerfed LiNbO₃ array.