氧化鋅摻雜鈷應用於透明電阻式記憶體之電阻開關特性研究

Abstract

In conclusion, resistance switching of various amounts of Co dopant in ZnO resistive layer is investigated. The undoped and Co doped ZnO films were deposited using RF magnetron sputtering at room temperature. The fabricated powder targets, both undoped and Co doped ZnO powders were heat-treated at the same annealing treatment, and found that the doping process is succesful which confirmed by XRD. Different concentration of Co doped ZnO; 0, 2 and 5 mol % Co-doped ZnO films are used as a resistive switching layer for TRRAM devices. Introduction of Co doping is found to increase the bulk resistance of the resistive layer as compare to the pure ZnO device which shows much lower leakage current during both negative and positive sweep. The switching performance is increased after 2 mol% of Co doped ZnO. However, higher concentration of Co may deteriorate the grown structure and affect the resistance switching. The 2 mol% doped ZnO device also demonstrated reasonable bipolar resistive switching behavior with a low operation voltage, and good endurance up to 4500 cycles with a HRS/LRS ratio of about 20 times are achieved at low operating voltage. The ITO/Co:ZnO/ITO/glass device was highly transparent (~85%) over the visible wavelength range 400 to 800nm.

In this thesis, various Cobalt doped Zinc oxide (Co: ZnO) thin film as a resistive switching layer for transparent resistive switching random access memory (T-RRAM) devices was investigated. The influence of Co doping concentrations (0, 2 and 5 mol%) on structural and electrical properties of Co-doped ZnO T-RRAM have been studied. Co doped Zinc Oxide was synthesized using oxide mixing and calculation methods to fabricate sputter target. X-ray diffraction analysis indicated that the undoped and doped ZnO and Co: ZnO thin film has a hexagonal wurtzite structure with (002) preferential orientation crystalline nature. The maximum average crystallite size of Co: ZnO were 55.47 nm at a concentration of 2%, indicating that the crystallinity of doped powders were improved after doping. Approximately 38 nm thick of Co: ZnO films were deposited on the ITO / glass substrate using RF-magnetron suppter. ITO top electrode was deposited in order to fabricate sandwich structures. The optical transmittance exhibits that all undoped and doped devices are fully transparent (approximately 85% in the visible wavelength region) and demonstrate bipolar switching behavior. Resistive switching performance was enhanced after doping 2 mol% of Co. Good endurance of 4500 DC stable switching cycles with a resistance ratio of HRS/LRS about 20 times are achieved at a low operating voltage and data retention up to 104 sec in room temperature have achieved. The conduction mechanism of Co: ZnO RRAM was also discussed. These results indicate that Co: ZnO resistive layer is a promising candidate for the transparent resistive switching device. It has good potential for next generation non-volatile applications and as an embedded in transparent electronic devices.