Low switching voltage, high-stability organic phototransistor memory based on a photoactive dielectric and an electron trapping layer

An organic phototransistor memory is presented with a photoactive dielectric layer of 6-[4'-(N,N-diphenylamino)phenyl]-3-ethoxycarbonylcoumarin (DPA-CM) doped into poly(methyl methacrylate) (PMMA) and an electron-trapping layer of poly(perfluoroalkenyl vinyl ether) (CYTOP). The dielectric gate layer functioned as an insulator in the dark and as a charge generator and/or conductive layer under photoirradiation, which resulted in a low program voltage and an operation with long-term stability. A shift in the phototransistor threshold voltage could be reversibly tuned from −5.8 to 6.2 V with a low switching voltage (≤8 V) under UV irradiation. Programmed/erased states were obtained by applying gate pulse voltages of −8/5 V under UV irradiation from an external light source. The phototransistor memory exhibited high stability with a large on/off current ratio of ~10⁵ for a retention time up to 2 × 10⁶ s with a reliability greater than 10³ programming/erasing testing cycles. These findings introduce a new approach for organic phototransistor non-volatile memory with high stability.