Factor Effect Study for the High Cyclic Bending Fatigue of Thin Films on PET Substrate for Flexible Displays Applications

Flexible displays is an emerging technology in which devices are mounted on flexible substrates, generally plastic substrates rather than glass ones. Flexible displays have a compliant structure, very-thin profile, low weight, and ultimately low cost. However, although this technology shows a great promise, it is still nascent and therefore faces many challenges. One of the main challenges that results in performance degradation is sensitivity to ambient conditions. Flexible displays are susceptible to many types of stresses during processing and usage including mechanical, thermal, and chemical stresses. Tension, compression, and bending are examples of mechanical stresses that might cause failures when applied repeatedly during processing. In this work, design of experiments (DOE) methods were used to study the factors affecting the high cyclic bending fatigue of uniform copper thin films forming the back planes of flexible displays on polyethylene terephthalate (PET) substrates. A 2^k-1 fractional factorial design was implemented to investigate the significant parameter effect. The parameters investigated were temperature, humidity, bending radius, film thickness, and frequency. Initial results showed a great effect of temperature and bending radius on the bending fatigue life of such structures.