Enhancement of long-term stability of pentacene thin-film transistors encapsulated with transparent SnO ₂

The long-term stability of pentacene thin-film transistors (TFTs) encapsulated with a transparent SnO ₂ thin-film prepared by ion beam-assisted deposition (IBAD) was investigated. After encapsulation process, our organic thin-film transistors (OTFTs) showed somewhat degraded field-effect mobility of 0.5 cm ² /(V s) that was initially 0.62 cm ² /(V s), when a buffer layer of thermally evaporated 100 nm SnO ₂ film had been deposited prior to IBAD process. However, the mobility was surprisingly sustained up to 1 month and then gradually degraded down to 0.35 cm ² /(V s) which was still three times higher than that of the OTFT without any encapsulation layer after 100 days in air ambient. The encapsulated OTFTs also exhibited superior on/off current ratio of over 10 ⁵ to that of the unprotected devices (∼10 ⁴ ) which was reduced from ∼10 ⁶ before aging. Therefore, the enhanced long-term stability of our encapsulated OTFTs should be attributed to well protection of permeation of H ₂ O and O ₂ into the devices by the IBAD SnO ₂ thin-film which could be used as an effective inorganic gas barrier for transparent organic electronic devices.