Multilevel characteristics and operating mechanisms of nonvolatile memory devices based on a floating gate of graphene oxide sheets sandwiched between two polystyrene layers

•Nonvolatile memory devices with graphene oxide layer embedded between two polystyrene layers were fabricated.•Capacitance-voltage curves of the fabricated devices showed multilevel characteristics.•Window margin of the devices showed no degradation until 104 cycles of repetitive stress.•Flat-band voltage shifts increased with higher sweep voltages, indicative of multilevel characteristics.