Mixed self-assembled monolayer gate dielectrics for low-voltage solution-processed polymer field-effect transistors

Abstract

Ultrathin hybrid gate dielectrics based on aluminum oxide (AlOx) and mixed-type phosphonic-acid self-assembled monolayers (PA-SAMs) are studied with a high performance liquid-crystalline semiconducting polymer, viz. poly(2,5-bis(3-alkylthiophen-2-yl)thieno[3,2-b]thiophene) (pBTTT). We present a simple assembly procedure to obtain mixed-type PA-SAMs terminated by methyl and carboxylic acid groups. Tunable surface energy in combination with excellent insulating properties was allowed by this unprecedented mixed monolayer. pBTTT morphology is dramatically affected by the presence of sparse functional groups at the surface. Lithographically defined field-effect transistors operating at low-voltage (<3 V) are demonstrated utilizing the mixed-type SAM-based dielectrics. Lower leakage currents, higher on/off ratios, and steeper subthreshold swing are obtained with the mixed-type monolayer, as compared to monolayers fully assembled with carboxylate-containing molecules.