Properties of W Electroded ZrO2-based Non-Volatile Resistive Memory
|關鍵字:||非揮發性記憶體;電阻式記憶體;氧化鋯;鎢電極;阻態轉換;Non-Volatile Resistive Memory;Resistive Random Access Memory;ZrO2;W Electrode;Resistive Switching|
The thesis mainly focuses on ZrO2-based RRAM with tungsten bottom electrode. I discuss the Ti/ZrO2/W structure with its electrical properties and find the way to improve the characteristics. Thus, I change different top electrode and study on the change of RRAM’s characteristics. I want to figure out different Gibb’s free energy of respective electrode would bring what influence on the characteristics. On the other hand, adding CoO layer would enlarge the difference of Gibb’s free energy in the interface, and I want to discuss with how to influence the original structure by adding this buffer layer. Using Al as my top electrode, I could utilize Gibb’s free energy difference to control the amount of its combination with oxygen. When I use Al as top electrode, because of Al being easy to combine with oxygen and its Gibb’s free energy greatly larger than Ti, Al would combine with oxygen in ZrO2 to form Al2O3. Furthermore, the transition region would tend to be the interface of Al electrode and ZrO2, and thus lower down the variation during transition. The structure of Al/ZrO2/W has the advantage of low power, low cost and moreover less variation during transition, and as a result I could easily judge the position where oxidation and reduction would happen. ZrO2 was deposited in the temperature of room temperature, 100℃, 150℃ and 200℃, respectively. I can control the amount of vacancies by controlling the deposition temperature of transition layer. The endurance is the best in room temperature. However, endurance and resistive ratio are tradeoff. When the deposition temperature increases, the endurance would decrease while ratio would be larger. As a result, I try to change temperature and hope to strike a balance between endurance and resistive ratio. Finally, my device has higher endurance and higher resistive ratio and can be practically applied. By means of adding CoO layer between Ti and ZrO2 as a buffer layer, I can increase the activity of Ti to react with ZrO2. Once I add this buffer layer, and the performance of this structure can be effectively developed—higher endurance, lower resistive transition variation and larger resistive ratio. Moreover, I can find the role of CoO layer by material analysis. Through enlarging the difference of Gibb’s free energy, Ti electrode would combine with oxygen ion in large quantity.