Electrical Performance Improvement of Organic Thin-Film Transistors by O2-Plasma Treatment

Abstract

We studied the enhancement of the field effect mobility and the reduction of the operating voltage in the bottom-contact organic thinfilm-transistor (OTFT) by the oxygen plasma treatment of the silver contacts. The O2-plasma treatment was selectively carried out on the Ag electrodes to decrease the work function of the metal, avoiding the degradation of the channel by oxygen. In our study, a thermally grown silicon dioxide layer on a p-doped Si wafer was used as a gate insulator. Photoresist patterns were produced on the gate insulator to define the channel region and to simultaneously protect the insulator surface from the O2-plasma treatment. Deposited silver source/drain electrodes were treated by O2-plasma for the durationof 1, 5, 10, 20, and 60 seconds. Finally, the active layer was prepared from a solution of TIPS-pentacene (TIPS-PEN). The channel length of the TIPS-PEN OTFTs was defined to be 110 μm. It was found that a linear relationship between the mobility and the plasma exposure time was observed. In addition, the threshold voltage decreased with increasing the plasmaexposure time. These results suggest that the plasma treatment on the Ag electrodes is an effective method of improving the electrical performance of solution-processed OTFTs.