Time-Resolved Micro-Raman Stress Spectroscopy for Single-Crystal Silicon Resonators Using a MEMS Optical Chopper

A microelectromechanical systems (MEMS) optical chopper with a silicon-on-glass structure has been developed for time-resolved micro-Raman stress measurements of single-crystal silicon resonators. The chopper was inserted directly into the optics of a commercial micro-Raman spectrometer to modulate the incident laser light. The slit portion of the chopper (Ø500 μm) was actuated by electrostatic force using slanted parallel plate capacitors. The chopper was fabricated in a 15-μm-thick silicon layer on a 600μm-thick glass substrate on which aluminum shutters were formed. The stopper structure and pull-in driving realized low-voltage operation at 12 V and a quick mechanical response time of 77 μs. The modulation of incident light for measuring an out-of-plane silicon resonator made from a silicon-on-insulator wafer resonated at 1 kHz, and a 10% duty cycle and an extinction ratio of 31 were achieved. The dynamic stress was measured and its amplitude (303 MPa) was found to be in good agreement with the results of finite-element analysis.