| Summary: | 碩士 === 國立交通大學 === 材料科學與工程學系所 === 102 === Resistive random access memory (RRAM) has been widely recognized as the next-generation nonvolatile memory to replace conventional flash memory. This study investigates the resistive switching properties of RRAM containing aluminum (Al) as the top electrode, platinum (Pt) as the bottom electrode and hafnium oxide (HfO2) as the insulator layer prepared by sputtering deposition. Electrical measurement indicated that the thickness of HfO2 layer affects Forming voltage (VForm) of RRAM and too large VForm would permanently damage the device. As to the devices containing thin HfO2 layers, subsequent annealing treatment caused the rough surface and degraded the electrical performance. The area of electrode negligibly affected the resistance of low resistance state (LRS) whereas the resistance of high resistance state (HRS) increase with the decrement of electrode’s area.
For the HfO2 layers annealed at 300C, 500C, and 700C for 30 min in the atmospheric ambient, the effect of heat treatment on the remedy of the oxygen deficiency in HfO2 layer and surface roughness were analyzed by using x-ray photoelectron spectroscopy and atomic force microscopy, and the structure of devices were confirmed by using scanning electron microscopy. Moreover, the annealing treatments at temperatures less than 500°C insignificantly affected the electrical performance of samples. When annealing temperature was raised to 700C, the sample exhibited stable resistance of HRS and VSet as well as improved endurance and retention properties. In such a sample, amorphous HfO2 transformed to polycrystalline monoclinic structure as revealed by x-ray diffraction analysis. The improvement of electrical performance was hence ascribed to the presence of grain boundaries which provide stable formation routes of conduction filament in HfO2. However, annealing treatment seemed to reduce the interface traps at the interface of HfO2 and electrode, leading to high and unstable resistance of HRS at the initial stage of operation.
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