Low voltage operation of non-volatile flexible OFET memory devices using high-k P(VDF-TrFE) gate dielectric and polyimide charge storage layer

Flexible OFET memory devices of semiconducting poly(9,9-dioctylfluorene-alt-bithiophene) (F8T2) on PEN substrates were fabricated and characterized using a high-k poly(vinylidene fluoride-co-trifluoroethylene) (P(VDF-TrFE)) gate dielectric combined with donor–acceptor polyimide electrets of (poly[2,5-bis(4-aminophenylenesulfanyl)selenophene-hexafluoroisopropylidene diphthalimide] (APSP-6FDA) or poly[2,5-bis(4-aminophenylenesulfanyl)thiophene-hexafluoroisopropylidenediphthalimide] (APST-6FDA)). All the polymer thin films, including gate dielectric, charge storage, and semiconducting layer, possessed a smooth surface to form good contact adhesion between each layer, as confirmed by atomic force microscopy. The flexible OFET device could be operated using low gate voltage (<15V) because of the high dielectric constant of P(VDF-TrFE). In addition, the OFET memory devices exhibited a reversible non-volatile behavior with a memory window over 10V and an on/off memory ratio of 103. The data storage characteristic was mainly attributed to the charge trapping in polyimide layer under a positive or negative gate bias. The studied flexible memories, moreover, exhibited stable electrical parameters, such as charge carrier mobility, threshold voltage change, and memory window, under a bending radius of 10mm with 1000 repeating cycles, resulting in reproducible and reliable device characteristics. The experimental results indicated that a low-voltage operated non-volatile flexible OFET memory device could be simply integrated using all polymer components, including gate dielectric, charge storage electret, and semiconductor.