A UV-ozone treated amorphous barium-strontium titanate dielectric thin film for low driving voltage flexible organic transistors

Reducing the operating power and making them suitable for portable and wearable electronic applications are critical steps for the further development of organic field effect transistors (OFETs). One of the possible approaches to achieve this is by using a high dielectric constant (high-k) dielectric layer. Here, we propose a new kind of high-k amorphous Ba0.7Sr0.3TiO3 (BST) material derived by a layer-by-layer sol-gel method and solidified by UV-ozone treatments under atmospheric air and pressure. The dielectric constant of the amorphous BST thin film is around 11. Without employing the self-assembled monolayers (SAMs), the pentacene OFET on a polyethylene naphthalate (PEN) substrate shows saturation under -2.5 V, the saturation mobility of 0.252 cm(2) V-1 s(-1) with negligible hysteresis effects. The chemical composition of the dielectric film and the morphology structure are studied by X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) respectively. We also performed compressive and tensile bending tests on the OFETs and the dielectric layer. Due to the amorphous nature of the BST thin film, it shows a constant C-f relationship in both compressive and tensile bending up to a bending radius of 3.3 mm. It demonstrates high application potential of the current BST thin film in flexible electronics and circuits. To confirm the application potentials, we develop an organic inverter based on the transistor and a resistor, and a gain as high as 20 can be achieved.