4μm thick fabric like flexible circuit

According to the Korea Advanced Institute of Science and Technology (KAIST), complete with substrate, an active matrix for a flexible display need only be 4μm thick. 

Initially on a sacrificial laser-reactive substrate the matrix of ultra-thin n-type transparent oxide thin-film transistors (TFTs) were fabricated for the back plane.

Laser irradiation from the backside of the substrate split off only the oxide TFT array as a result of reaction with the laser-reactive layer.

The free transistors were transferred to a 4μm  polyethylene terephthalate (PET) substrate, and then the combination was further transferred con-formally to the surface of human skin and artificial leather to demonstrate the possibility of the wearable application.

“The attached oxide TFTs showed high optical transparency of 83% and 40cm2/Vs even under several cycles of severe bending tests,” said KAIST.

The method is called inorganic-based laser lift-off (ILLO).

“By using our ILLO process, the technological barriers for high performance transparent flexible displays have been overcome at a relatively low cost by removing expensive polyimide substrates. Moreover, the high-quality oxide semiconductor can be easily transferred onto skin-like, or any flexible, substrate for wearable application,” said Professor Keon Jae Lee.

Con-formal displays are a potential application.

“With the advent of the Internet of Things era, demand has grown for wearable and transparent displays that can be applied to fields such as augmented reality and skin-like thin flexible devices,” said KAIST. “However, previous flexible transparent displays have poor transparency and low electrical performance. To improve the transparency and performance, past research efforts have tried to use inorganic-based electronics, but the fundamental thermal instabilities of plastic substrates have hampered the high temperature process, an essential step necessary for the fabrication of high performance electronic devices.”

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