Effects of the alkyl chain length in phosphonic acid self-assembled monolayer gate dielectrics on the performance and stability of low-voltage organic thin-film transistors

We have fabricated pentacene organic thin-film transistors (TFTs) using self-assembled monolayers (SAMs) based on alkyl-phosphonic acids with five different alkyl chain lengths as the gate dielectric and investigated the relationship between the SAM chain length and the electrical performance and stability of the transistors. A SAM chain length of 14 carbon atoms provides a maximum TFT mobility of 0.7 cm(2)/V s, along with an on/off current ratio greater than 10(5). We have also investigated the bias stress effect in these TFTs and found that the change in drain current is substantially less severe than in pentacene TFTs with polymer gate dielectrics.