於新穎負電容閘極多功能記憶體中暫態行為之實驗探討

Abstract

近年來，隨著記憶體微縮技術的發展，揮發性與非揮發性記憶體正面臨許多技術上的挑戰，例如動態隨機記憶體的漏電與快閃記憶體的耐久性問題，但負電容鐵電記憶體具有快速的切換速度、良好的耐久性及較低的操作電壓，所以有希望成為新興記憶體候選人。而最近鐵電記憶體有重大的突破，由於商用高介電係數氧化鉿基薄膜擁有負電容鐵電特性的發現，使此新型材料製備的鐵電記憶體元件受到關注，此元件具高微縮性、低功耗、良好的耐久性以及可以突破物理極限的次臨界擺幅。因此，本論文提出結合負電容鐵電和電荷補陷兩種機制來改善新型鐵電記憶體元件特性，研究內容包含基本的鐵電特性、鐵電效應與電荷補陷之間的交互作用以及記憶體電性。 為了改進鐵電記憶體的記憶視窗與資料保存力，製作設計了鐵電材料層(HfZrO)和電荷補陷層(HfON)堆疊結構。首先，我們介紹電流電壓量測方法來獲得鐵電電容的暫態開關電流。我們應用無掃描和測量延遲的快速三角電壓波形去產生暫態開關電流，並且藉由暫態開關電流的積分方法得到鐵電極化-電壓(P-V)遲滯環。同時我們瞭解到經由三角電壓脈衝的激勵，鐵電電容的電流反應會出現明顯的波峰，以及參雜物鋯(Zr)會促進 HfO2的結晶從單斜晶相(monoclinic)轉變為正交晶相(orthorhombic)。我們驗證了鐵電極化量與外加電場的大小和時間呈正相關，還有也驗證沉積在電荷補陷層(HfON)上的鐵電層(HfZrO)是確實擁有正交晶相的結晶以及鐵電極化的特性。而更重要的是，利用電容的暫態電流反應，我們考究鐵電效應與電荷補陷之間的相互作用，然後提出界面偶極的概念，並且證實了我們新穎的記憶體在經過寫入與抹去的操作後，其鐵電效應仍持續存在。 為了改善鐵電記憶體的資料保存，我們運用擁有深層補陷特性的HfON材料當作電荷補陷結構，這種新穎混合式記憶體展現出優良的記憶體特性，它具有在正負10伏特直流掃描電壓下4.85伏特的記憶視窗、大於1010次操作的優異耐受力、比傳統鐵電記憶體優良的資料保存力以及500奈秒的快速寫入/抹除速度。根據實驗結果，我們所提出的新穎鐵電多功能型記憶體，有成為下一代記憶體應用的潛力。

In recent year, along with the development of memory scaling down technology, the volatile and non-volatile memories are facing many technological challenges such as the leakage power issue in DRAM and the endurance issue in Flash memory. The negative capacitance ferroelectric memory (NC-FRAM) is considered as a promising candidate among emerging memories due to its fast switching speed, long endurance and low operation voltage. Recently, the discovered ferroelectric properties of HfO2-based thin film open up an interesting pathway to establish highly scalable FRAM. Our studies have demonstrated one-transistor (1T) ferroelectric hybrid memories with ferroelectricity and charge-trapping mechanisms. To improve the memory window and retention of 1T ferroelectric memory, the ferroelectric dielectric layer modulation scheme of HfZrO and HfON film stack layer was proposed. We experimentally demonstrated a novel hybrid ferroelectric/charge-trapping memory structure using HfZrO and HfON film stack. We introduced the current-voltage measurement method to obtain the transient switching current for the ferroelectric capacitors. By applying fast triangular voltage waveforms without sweeping and measuring delay, the ferroelectric polarization-voltage (P-V) hysteresis loop could be got through an integral calculation from the transient switching current. We realized the one peak of current response for each ramps will occur for ferroelectric capacitors applied by triangular pulses voltages excitation and the zirconium (Zr) can help the crystallinity of HfO2 transform from monoclinic phase to orthorhombic phase. We also confirmed the ferroelectric polarization depends on applied voltage and time, and the HfZrO film deposited on HfON trapping layer still owns the crystallinity of orthorhombic phase and ferroelectric characteristics. Importantly, the interaction between ferroelectricity and charge-trapping mechanisms was investigated by transient current response. We proposed the interface dipoles concept and verified the ferroelectric effect still exist in our memory after the program and erase operation. The deep-trapped HfON employed as a charge-trapping structure to improve the data retention of ferroelectric HfZrO memory was investigated. This novel hybrid memory exhibited much better memory characteristics, it has a large memory window of 4.85V under ±10V DC sweep voltages, an excellent endurance of >1010 cycles, a better retention than conventional ferroelectric memory, and a fast 500ns program/erase speed. The novel ferroelectric versatile memory has the potential for the next generation memory application.