Research On The Resistive Switching Of ZnO Thin Films Based On The Flexible Substrate

Although Flash technology is still the biggest part of the semiconductor memory market, it isn’t seriously considered as candidates for future memories, with the drawbacks of high operational voltage, slow operational speed, low density and so on. There are more than a dozen memories, based on different concepts, which have been considered as emerging memories. Among the memories, ferroelectric random access memories(FRAMs), phase change random access memories(PRAMs), magnetic random access memories(MRAMs) and resistance random access memories(RRAMs) have been considered as the next generation nonvolatile memories.Among the four emerging memories, RRAMs, which use two distinctive resistance states as the binary number “0” and “1”, are considered as the most promising candidates due to their good compatibility with the traditional complementary metal oxide semiconductor technology(CMOS), fast operational speed and good endurance. Reversible resistive switching has been observed in many kinds of materials, such as organics, perovskite compounds, solid electrolyte and transition metal oxides. On the other hand, flexible nonvolatile memories have attracted tremendous attentions for data storage for future electronic application, which have the advantages of thin, lightweight, foldable, printable and stretchable. Until now, a lot of the research work for the application of flexible RRAM devices has been carried out. ZnO film has been widely studied as the functional layer because of its good performance of resistive switching behavior such as coexistence of unipolar and bipolar switching behavior, reliable retention and so on. To improve the resistive switching behavior of ZnO, impurity doping and multilayer are two effective methods.In this thesis, the thin films of pure ZnO and Cu doped ZnO are deposited on the flexible PET by pulse laser deposition(PLD) at room temperature. First, the influence of different oxygen pressure, laser energy and film thickness on the resistance switching behavior of ZnO are studied, and we get the optimal process parameters of depositing ZnO film by PLD. Then the Cu doped ZnO films(n Cu=1mol%, 3mol%, 5mol%) are deposited on PET by using the same parameters. We test the structure and the electrical properties of the films. The results show that:1. The optical process parameters by PLD are 10 Pa O2 pressure, 100 mJ laser energy and 160 nm thickness;2. The ZnO films exhibit a polycrystalline pattern with a high(002) orientation, and a columnar grain structure on the PET substrate;3. The pure ZnO film has poor endurance and unstable distribution of two different resistance state; compared with the pure ZnO film, the ZnO films at various Cu concentrations have improved the resistive switching behavior, which have slightly variation of two different resistance state, good endurance and good retention performance; the ZnO film with nCu=3 mol% has the excellent resistive switching behavior;4. In order to investigate the conduction mechanism, the I-V curves are re-plotted in double-logarithmic scale, the conduction behavior in the low resistance state and the high resistance state are well fitted by Ohmic behavior and Space Charge Limited Conduction mechanism;5. To confirm the feasibility of the device for flexible memory applications, the ZnO film with n Cu=3 mol% was investigated by repeated bending, the device exhibits excellent endurance against continuous bending, and our device has the potential of the flexible memory devices.