Ambipolar Organic Field Effect Transistor Using Top-gate Style Split-gate Structure

Abstract

Ambipolar organic semiconductors have received scientific interest due to their great potential for low-cost and large area electronics. Both holes and electrons can be injected in a single semiconductor layer, which significantly reduces the fabrication process and thus manufacturing cost. Recent advancements in ambipolar organic transistors using multi-gate techniques such as split-gate and tri-gate structures enabled ambipolar device to operate as unipolar p-type or n-type. However, all previous split-gate ambipolar OTFTs showed electrical hysteresis or reported single voltage-sweep curves only. To achieve practical application based on ambipolar transistors, the electrical hysteresis should be eliminated. Here, I present top-gate style ambipolar organic filed effect transistors using split gate structure. By adopting Cytop as a hydrophobic buffer layer and Parylene-C as an insulating polymer dielectric, I show that the device can operate as unipolar p-type or n-type transistor selectively without having I-V hysteresis. Moreover, hydrophobic channel with the Cytop buffer layer offered the higher carrier mobilities for both hole and electron carrier than previous split-gate OTFTs. In the proposed device, the additional gate electrode suppressed the charge injection from the drain electrode. Thus, the current on/off ratio was increased as high as 1,000 times for both n-type and p-type operations.