Investigation on residual stress and stress-optical coefficient for flexible electronics by photoelasticity

For flexible electronics in manufacture, the full-field stress measurement is an important issue for the film deposited on the flexible substrate. In this work, the two-dimensional photoelasticity is proposed to measure stress-optical coefficients and an analytical derivation is carried out for investigation on full-field residual stresses under tensional forces. In experimental setup, a polarization beam splitter (PBS) is used to connect with two CCD cameras that are used to capture the intensity of right-hand and left-hand circular polarization separately. It has higher measured speed and better uniformity than a direct rotation method. Stress-optical coefficients can be calculated by extracting the slope from tensional stress versus optical retardation curve. Experimental results show that optical retardations for indium-tin-oxide (ITO)-coated PET (polyethylene terephthalate) substrates can be affected more easily than PET substrates under tensional forces. The difference of stress-optical coefficients between 0° and 90° orientations for PEN (polyethylene naphthalate) substrates is smaller than that for PET substrates. Furthermore, it shows residual stresses for ITO-coated PET substrates in 0° and 90° orientations are different under tensional stress.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Derivation on full-field residual stresses is investigated for thin-film substrate. ► Stress-optical coefficient is measured by 2D photoelasticity under tensional forces. ► Residual stresses for thin-film substrate in different orientations are different. ► Slope of stress versus retardation curve describes stress-optical coefficient.