Development of Pure Torsion Test System for Micro Torsion Bars

Abstract

MEMS scanners use micro torsion bars made of single crystal silicon. The push-in method is used to measure the mechanical properties of these micro torsion bars, in which a lever connected to the torsion bar is pushed. In the push-in method, the sliding force increases as the indentation amount increases, decreasing measurement accuracy. As a method to reduce the sliding force, we proposed to generate pure torsion in the torsion bar section by rotating a sample holder with a test sample attached. The proposed method can maintain the load detection axis of the load cell and the lever part at almost a right angle regardless of the degree of torsional angle, preventing slip at the contact point between the load cell and the lever part. The torsional spring constants of test samples were obtained and compared by three different methods: a testing system using this principle, a resonance frequency method, and a theoretical calculation. The accuracy of the developed testing system is -17.5 % to 12.7 % of the measurement error compared to the torsion beam spring constant obtained from the resonance frequency, and -15.6 % to 7.2 % compared to the theoretical calculation value, thus verifying the effectiveness of the proposed test method.