Surface Modification of Polyimide Films for Inkjet-Printing of Flexible Electronic Devices

Abstract

Kapton polyimide films are one of the most commonly used flexible and robust substrates for flexible electronic devices due to their excellent thermal, chemical, mechanical, and electrical properties. However, such films feature an inert and highly hydrophobic surface that inhibits the deposition of functional materials with water-based fluids (solutions, suspensions, inkjet inks, etc.), which raise the need for their surface modification to reduce their inherent surface inertness and/or hydrophobicity in order to allow for the fabrication of electronic devices on the substrates. Traditional Kapton surface modification approaches use harsh conditions that not only cause environmental and safety problems but also compromise the structural integrity and the properties of the substrates. This chapter focuses on two recently-developed mild and environmentally friendly wet chemical approaches for surface modification of Kapton HN films. Unlike the traditional methods that target the polyimide matrix of Kapton films, these two methods target the slip additive embedded in the polyimide matrix. The surface modified Kapton films resulted from these two methods allowed for not only great printability of both waterand organic solvent-based inks (thus facilitating the full-inkjet-printing of entire flexible electronic devices) but also strong adhesion between the inkjet-printed traces and the substrate films.

Microfabrication of functional polyimide films and microstructures for flexible MEMS applications

“…Due to the hydrophobic properties of polyimide films [37][38][39] , surface modification of a polyimide substrate is usually required to ensure the continuous and uniform deposition of functional materials and robust bonding with other layers. Surface modification methods vary from plasma radiation 40,41 , ion radiation 42,43 , UV/ozone exposure 40,44 , acid treatments 40,45 and/or base treatments 46,47 .…”

Graphene Inkjet-Printed Ultrawideband Tapered Coplanar-Waveguide Antenna on Kapton Substrate

“…It reaches conductivity values of 2.5 × 10 4 ± 0.2 × 10 4 S/m, after optimizing an annealing time of 20/30 min at 250/350 °C [17]. For the antenna realization, Kapton polyimide-based substrate has been chosen due to their excellent thermal, chemical, mechanical, and electrical properties [18][19][20]. It can withstand the temperatures for the annealing process, but such films feature an inert and highly hydrophobic surface so a pre-treatment with plasma is necessary.…”

Antidelaminating, Thermally Stable, and Cost-Effective Flexible Kapton Platforms for Nitrate Sensors, Mercury Aptasensors, Protein Sensors, and p-Type Organic Thin-Film Transistors

“…Although Kapton films exhibit extraordinary mechanical, chemical, and electrical features, it has been reported that the surface of Kapton, which has a complex composition including a polyimide matrix and slip additive, is hydrophobic and inert, which prevents materials (e.g., metal inks and biomaterials) from being deposited on the film (causing delamination to frequently happen). Therefore, different surface modifications are necessary for various applications and are difficult to avoid. − In addition to the troublesome pretreatments used during the manufacturing process of inkjet-printing technologies, many reported post-treatments related to metal ink sintering, such as laser sintering, ohmic curing, microwave sintering, and infrared sintering, are also very expensive and time-consuming. , Therefore, a thorough study on eliminating or alleviating these issues of pre- and post-treatments is required to advance the development of nano- and microflexible electronics in applications of Kapton films, and selecting appropriate inks that are premodified commercially is key and of critical importance.…”