ZnO-based Nanostructure Resistive Random Access Memory

Resistive random access memory （RRAM） which is based on resistance switching （RS）behavior is attracting much attention for its superior properties, such as high density, highspeed and simple device structure. However, the switching parameters of existing RRAMoften exhibit large variations, such as the resistance values of low-resistance state （LRS） andhigh-resistance state （HRS）. The reason of resistance’s instability may be due to the followingmechanism: It has been reported that the RS process is usually based on the formation andrupture of conducting filaments （CFs） under an electric field, the formation of CFs is randomand the CFs may not go through the same paths in each switching cycle, lead to the switchingparameters of these CFs-based RRAMs often exhibit large variations. Therefore, it is criticalto effectively control the formation and the rupture of CFs to achieve reliable and uniformswitching operations of the CFs-based RRAM. At the same time，with the improvement ofthe quality of life in the pursuit and development of electronic technology, the flexible ofelectronic devices also become a hot research today. But finding the right material hasbecome a key issue in the process of structure flexible RRAM. The paper covers thefollowing aspects:First, the nanostructure fabricated by50nm polystyrene nanospheres （PS-NS） isproposed to improve resistive switching properties in the Pt/IGZO/Al RRAM device.Compared to the Pt/IGZO/Al/SiO₂/Si common device with flat electrode, thePt/IGZO/Al/PS-NS/SiO₂/Si improved device reduces the distributions of LRS and HRS, andalso improves the stability of reset process. The percentage of direct “reset process” can beenhanced from26%to73%. The switching mechanism is believed to be related with theformation and rupture of conductive filament. The nanostructure affect the sharp of electricfield which between bottom electrode and top electrode so that it can control the conductivefilament, thus leading to high uniformity resistive switching properties.Second, flexible resistive switching memory devices fabricated on plastic substratesutilizing ZnO nanorod embedded in PMMA organic layer were fabricated by using aspin-coating technique. The device exhibits reversible and steady unipolar resistive switchingbehaviors and good electrical performance parameters. And it also shows high performance,excellent flexibility, and mechanical endurance in bending tests. No performance degradationoccurs, and the stored information is not lost after bending the device to different angles andup to105times. The resistive switching behavior may be related to the oxygen vacanciesand/or zinc interstitials confined on the surface of the ZnO nanorods. The unique switchingmechanism and flexible mechanical properties ensure stable device performance in flexibleapplications.