Encapsulation of organic field-effect transistors with highly polarizable transparent amorphous oxide

To enhance the stability of pentacene field-effect transistors, a highly polarizable amorphous oxide is used as a gas barrier due to the strong chemical interaction between permeating polar water molecules and an oxide. For a more reliable barrier function, in addition to chemical effects, a dense amorphous microstructure of a barrier is also preferred and achieved by ion-beam-assisted deposition (IBAD) at room temperature in this study. Our OTFTs encapsulated with IBAD SnO₂ showed a degraded field-effect mobility of 0.5cm ²/(V s) after encapsulation. However, the field-effect mobility was surprisingly sustained up to one month and then gradually degraded down to 0.35 cm²/(V s) after 100 days in air, which was still three times higher than that of an OTFT without an encapsulation layer. The encapsulated OTFTs also exhibited a superior on/off current ratio of more than 105 to that of the unprotected device (∼ 10⁴), which was reduced from ∼10 ⁶ before aging. The effects of encapsulation on the electrical properties of OTFTs are discussed in terms of the physical and chemical properties of barrier films.