Diagnostic microstructures for the measurement of intrinsic strain in thin films

Abstract

Freestanding flexible microstructures fabricated from deposited thin films become mechanically unstable when internal stresses exceed critical values. A series of structures with varying geometries is used to determine the critical geometry at which buckling occurs. Observation with an optical microscope quickly reveals qualitative and quantitative information about the internal strain in the film. Strain values between +or-1.5% can be measured for a 2.0 mu m thick film using doubly-supported beams for compressive strain fields, and ring and beam structures for tensile strain fields. Parametric formulae are developed for diagnostic structure response with selected verification by finite element computations.