Evaluation of the Fracture Toughness of Micro-sized Single Crystal Silicon Wafers

Abstract

Reliability is one of the most critical issues for designing practical MEMS devices. In particular, the fracture toughness of micro-sized elements for MEMS is important, as micro/nano-sized flaw proved a crack initiation site and cause the final failure of such devices. By the way, MEMS components were often used Si. In this investigation, fracture toughness tests have been carried out using single crystal silicon to micro-sized specimens. Cantilever beam type specimens with notch were prepared by focused ion beam machining. Two specimens types with different notch orientations were prepared. The notch plane and direction were (100) and [010], and (110) and [110] respectively. Fracture toughness tests were carried out using a mechanical testing machine for micro-sized specimens. Fracture occurs in a brittle manner with both orientations. The provisional fracture toughness values (K_Q) are 1.05MPam^1/2 and 0.96MPam^1/2, respectively. These values are valid plane strain fracture toughness values (K_IC). These values are also equivalent to those obtained on bulk-sized specimens. This suggests that the size effect on fracture toughness is not significant for this specimen size in single crystal silicon. The results obtained in this investigation indicate that the fracture toughness measurement method used is applicable for micro-sized components of this material in MEMS devices.