Low-Voltage Organic Nonvolatile Memory Transistors with Water-Soluble Polymers Containing Thermally Induced Radical Dipoles

A water-soluble acidic polymer, poly­(2-acrylamido-2-methyl-1-propanesulfonic acid) (PAMPSA), was applied as a gate-insulating layer for organic field-effect transistors (OFETs). Before depositing the poly­(3-hexylthiophene) (P3HT) channel layers, the PAMPSA layers were subjected to thermal treatment at various temperatures from 140 to 230 °C. The OFET performance was greatly enhanced by thermal treatment between 140 and 170 °C, whereas it became very poor at higher temperatures (200–230 °C). In particular, the transfer curves showed pronounced hysteresis phenomena at 170 °C. Various measurements including thermogravimetric analysis and X-ray photoelectron spectroscopy disclosed that the PAMPSA chains underwent thermal degradation from ca. 160 °C and could generate carbon radicals leading to the formation of dipoles with the nitrogen lone pair electrons. The carbon–nitrogen dipoles delivered hysteresis phenomena to the OFETs with the PAMPSA layers treated at 170 °C, which exhibited excellent memory retention characteristics up to 10 000 cycles even at −1 V. Hence, it is expected that the thermally treated PAMPSA layers can be used as one of the viable gate-insulating memory materials for low-voltage transistor-type organic memory devices (TOMDs).