Highly Flexible Microcrystalline Silicon n-Type TFT on PEN Bent to a Curvature Radius of 0.75 mm

Electrical and mechanical performances of microcrystalline silicon top-gate thin-film transistors (TFTs) on flexible substrate under high bending is presented. These devices are directly fabricated on 25-μm-thick Polyethylene naphthalate (PEN) at a maximum temperature of 180 °C. Tensile and compressive bending are performed and revealed that the TFTs can hold curvature radii of 1.5 mm without losing their performance and 0.75 mm with lower electrical performances. The limiting factor on the flexibility is shown to be the mechanical behavior of silicon nitride film used as a gate insulator. These extremely high curvatures demonstrate the possibility to use silicon technology in foldable electronics. TFTs are also shown to fully recover their characteristics when reflattened after such very low curvature radii. It opens the way to fold in half an electronic circuit to be stored and reused when reflattened.