Measurement of mean and gradient residual stresses in thin films using spiral microstructures

This research uses spiral microstructures to measure both the residual mean normal compressive/tensile stress and gradient stress of the thin films for MEMS devices. The relation between these two residual stresses and the resultant geometric or dimensional deformations is first established using the analytical solutions. Then based on this relation the deformations are measured and utilized to determine these two residual stresses. ANSYS simulation and experiments are conducted to verify the measurement. The deformations from ANSYS simulation for a microspiral subjected to the measured mean and gradient residual stresses agree well with those from experiments (less than 6% errors). Therefore, it can be concluded that the proposed measurement method is validated by the experimental results.