Pentacene thin-film transistors with sol–gel derived amorphous Ba0.6Sr0.4TiO3 gate dielectric

An amorphous Ba0.6Sr0.4TiO3 (BST) film with the thickness of 200 nm was deposited on indium-tin-oxide (ITO)-coated glass substrate through sol–gel route and post-annealing at 500 °C. The dielectric constant of the BST film was determined to be 20.6 at 100 kHz by measuring the Ag/BST/ITO parallel plate capacitor, and no dielectric tunability was observed with the bias voltage varying from −5 to 5 V. The BST film shows a dense and uniform microstructure as well as a smooth surface with the root-mean-square (RMS) roughness of about 1.4 nm. The leakage current density was found to be 3.5 × 10−8 A/cm2 at an applied voltage of −5 V. The transmittance of the BST/ITO/glass structure is more than 70% in the visible region. Pentacene based transistor using the as-prepared BST film as gate insulator exhibits a low threshold voltage of −1.3 V, the saturation field-effect mobility of 0.68 cm2/Vs, and the current on/off ratio of 3.6 × 105. The results indicate that the sol–gel derived BST film is a promising high-k gate dielectric for large-area transparent organic transistor arrays on glass substrate.