A study of creep in polysilicon MEMS devices

Plastic deformation of polysilicon at high temperatures under stress due to creep has been demonstrated at the micro scale. This type of material behavior is generally associated with mechanical failure, however it can also be used to permanently deform or position a device. In order for creep in polysilicon to be used for MEMS applications its mechanical properties must be investigated. In this work, an experimental micro test structure is developed and measurements of high temperature plastic deformation within polysilicon are conducted. Both increases in temperature and stress are shown to increase the creep rate within the studied beams in the region of interest of the test device. Immediate plastic deformation of polysilicon has been observed to start at approximately 63% of the absolute melting temperature under moderate stress.