Ionic nanocluster-evolved polymers for low-voltage flexible organic nonvolatile memory transistors
We demonstrate flexible nonvolatile memory organic field-effect transistors (OFETs) that can be operated at low voltages (−1 to −5 V) due to the ionic nanoclusters in the polymeric gate-insulating memory layers. The memory layers were prepared by spin-coating the aqueous solutions of poly(2-acrylamido-2-methyl-1-propanesulfonic acid) (PAMPSA) reacted with aniline (AN). The PAMPSA–AN solutions showed gradually increased pH and their films exhibited new optical absorption peaks, evidencing acid–base reactions leading to the formation of ionic pairs (–SO3−–+NH3–). The OFETs with the PAMPSA–AN layers exhibited AN ratio-dependent drain current hysteresis, which has been ascribed to the core role of highly polarized ionic nanoclusters evolved by the ionic pairs. The best transistor performance and hysteresis characteristics were measured at the AN ratio of 0.5 and by annealing at 150 °C. The OFET memory devices (glass and colorless polyimide substrates) showed excellent retention characteristics up to 10 000 cycles, even though the hysteresis characteristics of flexible memory devices were gradually lost upon repeated bending tests.