Automatic Measurement and Stress Analysis of ITO/PET Flexible Substrate by Shadow Moiré Interferometer With Phase-Shifting Interferometry

Phase-shifting interferometry was applied in the double beam shadow moiré interferometer, and furthermore,this technique used the automatic measurement system to catch the interferograms and calculated the residual stress of flexible electronics. As results of the shadow moiré interferometer were symmetrical, this measurement system was found to be stable and of high precision. The systematic error was less than 2% when the tolerance of the CCD view angle was between -5° and +5°. Experimental results showed that this technique can precisely determine a fraction of a fringe with a precision of 0.44% for a rigid specimen. The stress of a flexible substrate can be evaluated by the modified Stoney formula. Therefore, the residual stress of tin-doped indium oxide (ITO) films deposited on a polyethylene terephthalate (PET) was -744.1 MPa and the measurement tolerance was ±9.4 MPa of 1.26% error.