Deterministic and continuous control of the threshold voltage and noise margin of organic thin-film transistors and organic complementary circuits using mixed phosphonic acid self-assembled monolayer gate dielectrics

Abstract

For many applications of organic thin-film transistors (TFTs), high-capacitance gate dielectrics that can be processed at low temperature are of interest. Several approaches exist, including vapor-deposited metal oxides [1], ultra-thin polymers [2], self-assembled nanodielectrics [3], and thin hybrid dielectrics based on alkyl phosphonic acid self-assembled monolayers (SAMs) on plasma-oxidized aluminum gates [4]. None of these approaches, however, provides deterministic and continuous control of the threshold voltage. A few reports of low-voltage (≤5 V) organic complementary circuits with symmetric switching threshold and large noise margins exist [5–9], but the TFTs were not air-stable and had to be operated in an inert gas, which is not practical for real applications. Here we show how the threshold voltage of air-stable, low-voltage organic TFTs and the switching threshold and noise margin of air-stable, low-voltage, low-power organic complementary circuits can be reproducibly tuned over a wide range by using a mixed alkyl/fluoroalkyl phosphonic acid self-assembled monolayer (SAM) as a high-capacitance gate dielectric.