Charge Injection Engineering of Ambipolar Field-Effect Transistors for High-Performance Organic Complementary Circuits

Abstract

Ambipolar pi-conjugated polymers may provide inexpensive large-area manufacturing of complementary integrated circuits (CICs) without requiring micro-patterning of the individual p- and n-channel semiconductors. However, current-generation ambipolar semiconductor-based CICs suffer from higher static power consumption, low operation frequencies, and degraded noise margins compared to complementary logics based on unipolar p- and n-channel organic field-effect transistors (OFETs). Here, we demonstrate a simple methodology to control charge injection and transport in ambipolar OFETs via engineering of the electrical contacts. Solution processed caesium (Cs) salts, as electron injection and hole blocking layers at the interface between semiconductors and charge injection electrodes, significantly decrease the gold (Au) work function (similar to 4.1 eV) compared to that of a pristine Au electrode (similar to 4.7 eV). By controlling the electrode surface chemistry, excellent p-channel (hole mobility similar to 0.1-0.6 cm(2)/(Vs)) and n-channel (electron mobility similar to 0.1-0.3 cm(2)/(Vs)) OFET characteristics with the same semiconductor are demonstrated Most importantly, in these OFETs the counterpart charge Carrier currents are highly suppressed for depletion mode operation (I(off) < 70 nA when I(on) > 0.1-0.2 mA). Thus, high-performance; truly complementary inverters (high gain > 50 and high noise margin > 75% of ideal value) and ring oscillators (oscillation frequency similar to 12 kHz) based on a solution-processed ambipolar polymer are demonstrated.