The Study On Organic Diode Memory Devices And Its Working Mechanism

Comparing with the conventional memory technology, organic diode memory devices have anumber of advantages, including simple and designable structure, thin-film form,3D stackingcapability for high-density data storage and flexibility. As the next-generation data storagetechnology to replace or supplement existing inorganic semiconductor memory technology, theorganic diode memory has great research value and economic prospects. However, the developmentwork of the organic diode memory is still in its infancy, and the stability of the performance of thememory devices as well as the memory mechanism problem still need urgently to be solved.Therefore, the designing and fabricating of the stable memory devices as well as the study of theirworking mechanism are very significant.In this thesis, a series of organic diode memory devices with stable performance are fabricatedand their respective working mechanism is analysed in detail, which supply a technologyforeshadowing in puting forward a universal and quantitative physical model of the description ofthe organic diode memory mechanism to guide the design of devices and achieve their massproduction.（1） A nonvolatile write-once-read-many-times memory device based onITO/Poly（N-vinylcarbazole）/SiO₂nanoparticles/Poly（N-vinylcarbazole）/Aluminium structure isdemonstrated. By the employing of SiO₂nanoparticles, the ON/OFF current ratio of the device isenlarged from20to7×10²at the low voltage, and the device shows obvious negative differentialresistance （NDR） phenomenon at the high electric field. Comparing with the ITO/PVK/Al andITO/PVK/PVK/Al devices, it is found that the size of the SiO₂nanoparticles sandwiched betweentwo PVK layers plays an important role in enhancing the reproducibility and the ON-state retentiontime of the WORM memory device. The WORM memory mechanisms of the device areinvestigated on the basis of the current-voltage characteristics and scanning electron microscopyimage. Here, the strength of the NDR effect in our devices is only related to the charge defects andtraps of PVK films, and it can be enlarged by embedding charge traps into PVK films.（2） The memory properties of the ITO/Graphene Oxide/Al diode are investigated. It is foundthat the devices show different memory behaviors with the diverse geometry and thickness of Al.When the thickness of Al electrode is relatively thick, the device of cross-point Al electrode showsthree-level memory effect, and the counterpart device of cross-bar Al electrode exhibits volatile static random access memory effect. When the thickness of Al electrode is thinner, the abovedevices demonstrate flash memory effect. The different memory behaviors of ITO/GO/Al diodesare ascribed to the mode and degree of reduction and oxidation of GO.（3） The organic diode memory devices with a small molecule material synthesized by our group,as well as the commercialized polymethylmethacrylate material are investigated. The devices of“Electrode/Organic small molecule/Electrode” using different kinds of electrode material, devicearray, or compliance current would result in different memory behaviors. The device with astructure of Indium Tin Oxide/Polymethylmethacrylate/Aluminium exhibits stable flash memorycharacteristics. The scanning electron microscope results show that there is a lot of microporesdistribution on the thin film of the polymethylmethacrylate material, which is the main origin of thememory effect revealing by the control experiment.