The Resistive Switching Behavior Of ZnO Films

The final non-volatile data storage should be provided with performance such as high-density and low cost, fast write and read access, low energy operation, and high performace with respect to endurance (write cyclability) and retention. At present, the Flash memory devices based on silicon represent the most popular non-volatile memories (NVM) for the high density and low manufacturing costs of Flash memory. However, Flash suffers from low keep endurance, low write spead, and high voltages required for the write operation. In addition, further scaling, i.e., acontinution in increasing the density of Flash will run into physical limits in the near future. In order to overcome the physical limits scaling problem of NVM, scientists have proposed a new storage concept-resistance change memory (RRAM). Through applied additional voltage on RRAM devices, it is realized that the resistance of RRAM devices will be switched between high resistance state (HRS, OFF state) and low resistance state (LRS, ON state). With the further research in RRAM, it is found that RRAM can solve the further scaling problem for increasing the density of memory devices, and the power consumption of RRAM is very small, at the same time the RRAM desplay high endurance performance and outstanding data storage capacity. The research for the RRAM materials also become more and more widely. The earliest object for RRAM materials is Pr_1-xCa_xMnO₃ (PCMO) and perovskite materials. Nowadays, because of the characteristic of simple structure and easy preparation, the unit transitional metal oxide gradually becomes the principal materials for which the domestic and overseas various scientific research teams have invested lots of energy and time in the research.In this paper, the ZnO films and doped ZnO films are prepared on Pt/Ti/SiO₂/Si substrate and p-Si substrate by Sol-gel method, respectively. The top Pt and Al electrodes with a diameter of 200μm were deposited by radio-frequency sputtering with a metal shadow mask to form sandwich structure device cells. By changing the top electrode, the ZnO thin film devices will show different types of resistance change performance. Compared with the ZnO device, there was a noticeable transformation in the leakage current for the (Cu, V, La) doped ZnO device in OFF state. Then the the resistive switching (RS) performance study for the ZnLaO films include the measure of I-V characteristics, the repeatability behavior, and the retention characteristics. The study of RS mechanism by the change of different substrates has been carried out. Consider to the influence of the compliance current on the alternation between the unipolar switching and bipolar switching, we found that the reset current for switching the resistance from the ON state to OFF state will be higher with the increase of complaince current. Finally, the dependence of resistive resistance on variable thickness properties has also been reported.Although RRAM has very good storage properties, there is no explicit explanation for RS mechanism, so that this problem seriously influences the application of RRAM in practice. In this paper, we tried to understand the resistive mechanism through changing the device substrate and the top electrode materials. When the devices were switched in OFF state, the leakage current mechanism is dominated by the space charge limit current (SCLC), so the device of RS mechanism can be explained by the conductive filaments theory. If the leakage current of HRS depends on the schottky emission, then the interface effect is suggested to be responsible for the RS phenomenon.