A miniaturized contactless pure-bending device for in-situ SEM failure analysis

Abstract

Flexible electronic devices (flexible displays, solar cells) are subjected to large bending loads during manufacturing and use, making delamination in the underlying thin-film structure a major reliability concern. To investigate such failures, a new miniature contactless, frictionless pure-bending device is presented that enables highly sensitive moment-curvature measurements and simultaneous in-situ SEM failure analysis. Bending tests are of particular interest as they apply nonuniform loads without geometrical instabilities (necking, buckling, etc.). Most standardized bending tests (3-point, 4-point or cantilever bending) are contact-based, however, therefore they: cannot straightforwardly impose (large amplitude) cyclic or reversed loading; may introduce local deformations (indentations); typically obstruct the field of view at top or bottom surface; and typically introduce ill-defined parasitic frictional forces and moments. Contact and friction contributions particularly form a problem for cyclic testing or miniaturization and significantly complicate experimental-numerical material model identification. The here presented miniature pure-bending device overcomes these limitations. Contactless pure bending is realized through the relative rotations of two clamps, while active piezo control is use to eliminate axial and normal clamp forces and keep the area of interest in field of view for continuous SEM observation.