Experimental verification of lithium niobate cutting phenomena from the view point of crystallographic orientation

Lithium niobate (LiNbO₃) has many characteristics including piezoelectric and nonlinear optical effects. It is used for making low-path filters, light modulation devices and surface acoustic wave (SAW) elements. A processing method using the lithographic technology is generally used for various semiconductor materials, including LiNO₃. However, this method entails high production cost and has low flexibility. Moreover, LiNbO₃ is a brittle material with crystal anisotropy. In a previous study, direct processing of LiNbO₃ using an end-mill and diamond cutting tool was used to improve production flexibility. However, the processed LiNbO₃ suffered surface deterioration and brittle destruction under normal tool cutting conditions. Therefore, the aim was to achieve ductile mode cutting of LiNbO₃ in relation to the critical depth of the cut for various cutting directions. Investigation of the SAW phenomena such as propagation on the LiNbO₃ substrate revealed that SAW reflection and transmission depends on the edge quality and cross-section shape of the micro-grooves. The SAW reflection diffusion was controlled by forming micro-grooves in the LiNbO₃ surface. However, the use of end-milling to form the grooves caused many cracks and fractures. To avoid this problem, the diamond cutting tool was operated in a planner-type line direction, and the micro-grooves were cut in the same way. However, micro-grooves with fine surface integrity could not be obtained. In the study reported here, the effect of the crystallographic orientation of the LiNbO₃ for planer-type line direction cutting with a diamond tool was examined in an effort to obtain fine surface integrity. The processing conditions needed to obtain ductile mode cutting and the mechanism generating brittle fractures of the LiNbO₃ surface were investigated by comparing the crystal construction calculated from visualization of the electronic and structural analysis results. Ductile mode cutting experiments demonstrated that 0° and 90° in relation to the flat orientation are more ductile directions.