Residual stress

• Has an important effect to the mechanical behaviour of MEMS structures

 

• Stress appearing after the fabrication process

• Can be decomposed into two components
  
• Thermal mismatch stress
  Created by the deposition of thin layers to the substrate at the higher temperature and by cooling to room temperature
  
• Intrinsic stress
  Covers all other types of stresses as that occurring during
• chemical reactions,
• doping,
• epitaxial growth,
• evaporation,
• sputtering,
• and other processes

• Residual stresses can have three important effects on beams
  • Residual stresses in some cases modify the bending stiffness
  • Nonuniform residual stresses can cause beams to curl
  • Compressive residual stresses are source of beam buckling

• Residual stresses and thus their effect on the beam properties can be modified by thermal processes such as annealing