Phase-Separated, Flexible and Printed Organic Nonvolatile Memory Thin-Film Transistor

Abstract

In this work, we present flexible and printed organic nonvolatile memory thin-film transistors (TFTs) using a phase-separated polymer tunneling layer. On a large-area substrate of 150 by 150 mm, finely patterned electrodes are fabricated by reverse-offset printing with 15 um line width and 10 um channel length through three steps of ink coating, patterning and transfer. The memory devices are configured in a bottom-gate bottom-contact TFT structure with a high-k gate blocking insulator poly(vinylidene fluoride-co-trifluoroethylene). All functional layers are solution-processed. A blend ink containing a small-molecule p-type organic semiconductor dithieno[2,3-d;2′,3′-d′]benzo[1,2-b;4,5-b′]dithiophene and a tunneling polymer polystyrene are printed on the TFT active area using air-pulse nozzle printing. The tunneling layer is formed during the active layer printing process with the blended ink by phase separation of small-molecule and polymer. The printed nonvolatile memory TFTs with the phase-separated tunneling layer exhibited significantly improved VTH shifts (~3 times), programmed/erased current ratio (>10^3 A/A), switching speed (<100 ms) and data retention (>10 y). We believe that proposed approach shows a facile way to the printing fabrication of nonvolatile memory TFTs with improved memory characteristics, and thus demonstrates the feasibility of flexible memory into emerging applications in wearable electronics, smart Internet-of-Things devices and neuromorphic computing devices.