Failure of micron scale single crystal silicon bars due to torsion developed by MEMS micro instruments

A single crystal silicon (SCS) bar subjected to pure torsion using MicroElectroMechanical Systems (MEMS) micro instruments is experimentally studied. The bar is in the form of a pillar, anchored at one end to the silicon substrate and the other end to a lever arm. With the application of forces by the two micro instruments, a torque is generated which twists the pillar. The angular twist at different applied voltages are recorded using an angular scale. The corresponding torques are determined from the calibration parameters of the actuators. Torque is applied until the pillar fractures. In two samples designated as 1 and 2, it is found that both the pillars behave linearly until failure. The stresses prior to fracture are evaluated based on anisotropic theory of elasticity. Samples 1 and 2 fail at shear stresses of 5.6 and 2.6 GPa. The fracture surfaces coincide with the (111) plane of SCS.