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

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 SiOx 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 degrees C. In contrast, under the same environmental conditions unpassivated pentacene OFETs were found to undergo a drastic decrease in the quality of the pi overlap of pentacene molecules, causing unfavorable charge-carrier transport within the semiconductor. The deposition of either complementary CYTOP (TM) polymer or AlOx layer was found to successfully prevent the diffusion of H2O and O-2 into the pentacene films and thus to enhance the barrier properties of the SiOx layer, in particular, against H2O and O-2.