Mechanical strengthening of silicon torsion bar of MEMS scanning mirror by hydrogen anneal

This paper reports on the strengthening effect of hydrogen anneal on torsional fracture strength of single crystal silicon (SCS). Moving-magnet-type MEMS mirrors were prepared by fabricating SCS and silicon on insulator (SOI) wafers via deep reactive ion etching (DRIE) as fracture test specimens. As a result of the fracture test of the torsion bar on the mirrors, the torsion bar fabricated using a SCS wafer could be strengthened to about 4 times in average by hydrogen anneal. By contrast, that using a SOI wafer was weaken to half. This mechanical strengthening effect has the potential ability to provide highly-reliable and tough SCS-based MEMS devices.