Encapsulation for Flexible Electronic Devices

Abstract

Flexible electronic devices are influenced by mechanical impacts or bending. This mechanical stress can damage brittle inorganic thin-film layers. One way to improve the stability of such devices is to encapsulate them. For this reason, we encapsulate brittle inorganic materials in our thin-film transistors (TFTs) on flexible polyimide (Kapton) substrates by gluing a second patterned flexible polyimide substrate on top. The developed encapsulation method has the advantages of low process temperatures and micrometer alignment between features on the two substrates and does not damage any thin-film device layer. We are able to bend encapsulated TFTs down to a radius of 125 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\mu\hbox{m}$</tex></formula> without loss of functionality. At this bending radius, the saturation mobility decreases by 3%, and the threshold voltage shifts by 0.2 V. Compared with nonencapsulated TFTs, we decrease the bending radius before the devices fail by an order of magnitude.