Damage-free hybrid encapsulation of organic field-effect transistors to reduce environmental instability

Abstract

Damage-free hybrid encapsulation layers have been fabricated and optimized to improve the structural reliability and operational stability of organic field-effect transistors (OFETs); this reduction in instability was systematically demonstrated under various environmental conditions. The introduction of a 150 nm thick SiO_x layer onto 50 nm thick pentacene OFETs on polymer/SiO₂ dielectrics was found to impart strong structural constraints against morphological and polymorphic changes of pentacene crystals in the OFETs exposed to physicochemically active species or elevated temperatures up to 180 °C. In contrast, under the same environmental conditions unpassivated pentacene OFETs were found to undergo a drastic decrease in the quality of the π overlap of pentacene molecules, causing unfavorable charge-carrier transport within the semiconductor. The deposition of either complementary CYTOP™ polymer or AlO_x layer was found to successfully prevent the diffusion of H₂O and O₂ into the pentacene films and thus to enhance the barrier properties of the SiO_x layer, in particular, against H₂O and O₂.