Vacuum thermally evaporated polymeric zinc acrylate as an organic interlayer of organic/inorganic multilayer passivation for flexible organic thin-film transistors

Abstract

Polymeric zinc acrylate (pZA) was introduced as an organic interlayer for the inorganic/organic multilayer passivation of flexible organic thin film transistors (OTFTs). The pZA film was deposited by thermally evaporating a zinc diacrylate (ZDA) monomer under high vacuum (<10⁻⁵ Torr) and applying UV irradiation. The conversion of ZDA into a polymeric phase was confirmed by FTIR analysis, breakdown voltage measurements and the photopatternability of the film before and after UV irradiation. Vacuum-thermally evaporated pZA film showed good surface smoothness and a high permeation activation energy (53 kJ mol⁻¹) compared to conventional polymeric films. As an interlayer for multilayer passivation, vacuum-thermally evaporated silicon monoxide (SiO) was introduced as the inorganic counterpart of the pZA interlayer. A multilayer film comprising 6.5 pairs of layers showed a water vapor transmission rate (WVTR) of 0.055 g m⁻² per day, a 25-fold improvement over the WVTR of a single SiO film (1.207 g m⁻² per day). OTFTs encapsulated with 6.5 pairs of polymeric zinc acrylate/silicon monoxide layers showed prolonged stability over 97 days. In addition, the passivation layer did not show crack formation, and sustained barrier characteristics, even after 500 bending tests.