Enhancing nonvolatile write-once-read-many-times memory effects with SiO ₂ nanoparticles sandwiched by poly(N-vinylcarbazole) layers

A nonvolatile write-once-read-many-times (WORM) memory device based on the ITO/poly(N-vinylcarbazole) (PVK)/SiO ₂ nanoparticles (SiO ₂ NPs)/PVK/Al structure is demonstrated. By employing SiO ₂ NPs, the ON/OFF current ratio of the device is enlarged from 20 to 7×10 ² at a low voltage, and the device shows obvious negative differential resistance (NDR) phenomenon at a high electric field. Compared with the ITO/PVK/Al and ITO/PVK/PVK/Al devices, it is found that the size of the SiO ₂ NPs sandwiched between two PVK layers plays an important role in enhancing the reproducibility and the ON state retention time of the WORM memory device. The WORM memory mechanisms of the device are investigated on the basis of the currentvoltage (I-V) characteristics and scanning electron microscopy image. Here, the strength of the NDR effect in our devices is only related to the charge defects and traps of PVK films, and it can be enlarged by embedding charge traps into the PVK films.