Development of a thin-film residual-stress measurement device using multi-folded structures

Abstract We developed an on-chip residual-stress measurement device with a multi-folded spring to evaluate a 10 μm thick Ni–Nb–Zr thin-film metallic glass. To address the reduced critical buckling load in thin films, we tailored the stiffness anisotropy by decreasing the axial stiffness ( k x ) to suppress buckling while maintaining a high out-of-plane stiffness ( k z ) for structural stability. The device enabled in situ measurements of high compressive stress while maintaining a flatness of <2.4 μm. The as-sputtered stress agreed with Stoney’s method, whereas a pronounced discrepancy (approximately 140 MPa) emerged after annealing. We attribute this to the difference in mechanical boundary conditions: the biaxial stress state in substrate curvature methods versus the predominantly uniaxial state in released MEMS beams, together with the Poisson effect. These results suggest that Stoney’s method can overestimate the stress change during structural relaxation and that the proposed device provides a more representative stress evaluation for patterned MEMS structures.