氧化鋁覆蓋層效應於堆疊型與混合型氧化鉿鋯鐵電記憶體之電性分析與切換可靠度探討

Abstract

鐵電記憶體(Ferroelectric Random-Access Memory)具有低耗能以及高讀寫次數等優點，對於元件效能優化與高可靠度保有競爭優勢；隨著科技日新月異，電子元件朝向微小化，而傳統鐵電材料面臨厚度微縮限制且有元素擴散等問題，因而近年來發展以二氧化鉿(Hafnium-Oxide, HfO2)為基底之新興鐵電材料，其有利於元件微縮並優化製程相容度。二氧化鉿能透過元素摻雜方式使得晶格相轉，改變鐵電特性，其中與鋯元素所形成之氧化鉿鋯(Hafnium-Zirconium-Oxide, HfZrO)由於能夠摻雜的濃度範圍較廣，相對易於呈現優良之鐵電極化，對於元件應用具有潛力；於先前研究得知適量的鋯元素能增益極化，因此本實驗選用之摻雜比例為50 %，以達到較佳的極化量。而鋯元素在高溫下之穩定度不盡理想，容易因介面缺陷增加而導致漏電流上升現象。因而本實驗以堆疊(Stacked)形式沉積鐵電層並比較混合(Mixed)沉積形式，期望透過堆疊型結構來改善鋯元素的不穩定度對於電性與鐵電極化之影響。於覆蓋層效應對於鐵電特性與電性變化，在沉積後退火(Post-Deposition-Annealing, PDA)溫度條件450℃，堆疊型與混合型結構皆於增加錶值厚度3 nm氧化鋁覆蓋層後，呈現鐵電極化增益，其兩倍殘餘極化量(2Pr)分別為34.66 μC/cm2以及41.57 μC/cm2，並提升電容數值，於漏電流則分別由8.17×10-9 A與1.01×10-7 A抑制為4.22×10-9 A與9.33×10-9 A；在可靠度分析耐久度(Endurance)測試結果，操作電壓為±2.9 V時，經過循環操作次數10 5後，透過增加氧化鋁覆蓋層有助於鐵電電容保有較佳殘餘極化量並提高可承受之操作次數至10 7循環，延後元件崩潰(Breakdown)。於類神經型態分析，兩種結構皆以增加氧化鋁覆蓋層後呈現較低的非線性度數值(α)，意即提高鐵電電容之線性程度，因而說明增加覆蓋層對於元件未來之應用有所助益。關鍵詞：氧化鉿鋯、覆蓋層效應、可靠度測試、類神經應用Ferroelectric random-access memory has the advantages of low power consumption and high operating cycles. It has a competitive advantage of device performance optimization and high reliability. With the rapid development of technology, electronic devices are toward from miniaturization, while traditional ferroelectric materials are confronted with the limitation of thickness reduction and element diffusion. Therefore, the novelly ferroelectric material of HfO2-based has been developed in recent years, which is beneficial to device miniaturization and process compatibility optimization.The ferroelectric properties and phase transition of HfO2 can be induce by element doping. The HfZrO which doped by zirconium is liable to exhibit excellent ferroelectric polarization due to its wide range of doping ratio, it has potential for device applications. It is known from previous research that the polarization can be increased by appropriate zirconium dopant, thus the ratio of 50 % zirconium is selected in this experiment to achieve the better polarization. The stability of zirconium at high temperature is not ideal, it is liable to increase the leakage current due to the increase of interface defects. Therefore, the ferroelectric layer is deposited by stacked form and compared with the mixed deposition. It is expected that the influence of the instability of zirconium on the electrical characteristics and ferroelectric polarization can be improved through the stacked structure.Under the post-deposition annealing temperature of 450℃, the change of the ferroelectric properties and electrical characteristics caused by the capping layer effect have be discussed. After adding the 3 nm aluminum capping layer, the ferroelectric polarization have be increased in both structures. The remanent polarization (2Pr) of stacked and mixed structure are 34.66 μC/cm2 and 41.57 μC/cm2 respectively, and the capacitance values have be improved. The leakage current can be suppressed from 8.17×10-9 A and 1.01×10-7 A to 4.22×10-9 A and 9.33×10-9 A, respectively. From the results of the endurance test, after 10 5 cycles of operation under the operating voltage of ±2.9V, it is clearly found that adding the aluminum capping layer can helps the ferroelectric capacitor to maintain a better remanent polarization, increases the number of operations that can be withstand to 10 7 cycles, and delays the breakdown of the device. From the neuromorphic analysis, it can be found that both structures show lower nonlinearity values (α) after adding the aluminum capping layer, which mean that the linearity of the ferroelectric capacitor have be improved. According to above results, we known that adding the capping layer is beneficial for future applications of the device.Keywords: Hafnium Zirconium Oxide、Capping layer effect、Reliability test、Neuromorphic application