Stable hybrid organic/inorganic multiple-read quantum-dot memory device based on a PVK/QDs solution

A thin-film memory device is proposed herein, based on quantum dots (QDs) with bi-stable characteristics under a positive voltage bias. The synthesized QDs had a CdSe/ZnS core/shell structure. The charge confinement effect within the QDs in the charge-storage layer was enhanced by adding (poly(9-vinylcarbazole)) (PVK). As the PVK concentration increases, the on/off ratio of the device increases. Noise was also reduced and stable I-V characteristics were demonstrated. Each thin film was fabricated by a spin-coating method, among solution process methods. The on/off ratio of the fabricated device was found to be maximum 378 × 10 ³ at 1.5 wt% PVK concentration. The initial on/off state was maintained even when a negative voltage (commonly used for the “erase” function) was applied. In addition, the write voltage of the fabricated device using the conductive polymer poly-TPD was reduced from 2.8 to 1.7 V. By optimizing PVK concentration and forming the poly-TPD thin film, the fabricated memory device had an on/off ratio of about 4 × 10 ³ at 0.5 V and the stored current maintained the initial value even after 200 h. Even with a single write process, the initially formed high state is maintained for more than 200 h, and it is possible to read repeatedly.