Effects of nano mechanical properties on LiNbO3 fixed abrasive lapping

The nano mechanical properties of brittle materials are the key factors affecting nano machining performance. Lithium niobate (LN) single crystal is the typical anisotropic brittle material. The hardness H and crack length of LN crystals on X-cut wafers were measured through indentation experiments, and the fracture toughness K-IC and the critical cutting depth d(c) along <001> orientations were estimated. A set of fixed-abrasive (FA) lapping pads mixed with diamond grains of different sizes were prepared for lapping on X-cut wafers. The effects of abrasive cutting depth and d(c) on material removal rate (MRR) and surface roughness were discussed. Results indicate that: the surface hardness H of X-cut is about 6 GPa. And the minimum K-IC and d(c) on X-cut are 0.67 MPa(.)m(1/2) and 63.6 nm (along <001> orientation), respectively. Lapping tests show that when the abrasive cutting depth exceed the d(c), MRR will increase significantly, accompanied with brittle material removal and low surface quality.