A novel microstructure for in-situ measurement of residual stress in micromechanical thin films

Abstract

A novel microstructure for in-situ measuring residual stress in micromechanical thin films by the method of critical buckling observation was proposed and two different samples were fabricated using surface micromachining technique. The experimental apparatus was built for in-situ observation of critical buckling patterns of these microstructures during sacrificial layer etching. Then, the states of residual stresses can be distinguished directly by the buckling patterns and the magnitudes can be estimated with finite element method (FEM) when the values of critical etching length have been measured. Before the measurement, effects of various parameters on the critical buckling stress were investigated in detail with FEM in advance. After that, measurements of residual stresses using the new microstructures were carried out and the results were in good agreement with that obtained from micro rotating structures. It is consequently revealed that measurement of residual stresses by this new microstructure has evident advantages over the conventional buckling observation methods. Both compressive and tensile residual stresses in wide ranges of amplitude can be measured, just using a single appropriately designed microstructure. Therefore, the usefulness of layout space can be greatly improved.