Yunnan Fang

By Yunnan Fang and Manos M. Tentzeris

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 water- and 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.

Part of the book: Flexible Electronics

By Yunnan Fang

This chapter describes a strategy for sensitivity and chemical stability enhancement of chemiresistive gas sensors via electrode engineering. In this strategy, flexible chemiresistive gas sensors were fabricated by uniformly depositing functionalized semiconducting carbon nanotubes (CNTs) on a polyimide substrate via a novel layer-by-layer wet chemical method, followed by inkjet printing fine-featured silver interdigitated electrodes (IDEs) on the substrate. The electrode engineering was realized by converting the inkjet-printed IDEs into their highly porous and chemically stable gold counterparts via a mild and facile two-step process, with the substrate-IDE adhesion retained. As a proof-of-concept demonstration, a diethyl ethylphosphonate (DEEP, a simulant of the nerve agent sarin) sensor equipped with inkjet-printed dense silver IDEs was converted into its counterpart equipped with highly porous gold IDEs. The resulting gold-electrode gas sensor exhibited sensitivity to DEEP of at least fivefold higher than a similar sensor electrode with the dense silver IDEs. The sensitivity enhancement was probably due to the catalytic activity of the resulting gold IDEs, as well as the creation of the nano−/micro-scale pores in the gold IDEs that increased the Schottky contacts between the gold IDEs and the semiconducting CNTs.

Part of the book: Gold Nanoparticles and Their Applications in Engineering