利用金屬嵌入層改善氧化鋯之單極性電阻轉換特性之研究

Abstract

隨著科技的日新月異，各種消費性電子產品的發展快速，各種產品所需要的記憶體容量越來越大，而其中不需要電源供應仍能儲存資料的非揮發性記憶體，也漸漸受到矚目。快閃記憶體為現今非揮發性記憶體的主流，由於近年來元件製程不斷地微縮之下，快閃記憶體面臨了許多急欲克服之難題，如儲存在懸浮閘極中之電荷，因穿遂氧化層過薄而隨時間漸漸流失，造成儲存資料的喪失。電阻式非揮發性記憶體具有高密度、高操作速度、低功率消耗、高耐久性、可微縮化、非破壞性讀取資料、能符合現在CMOS製程以及結構簡單等特性，因此有機會取代快閃記憶體，使其成為次世代非揮發性記憶體的熱門選擇。 在這篇論文中，著重於在不同金屬及不同熱退火溫度對於氧化鋯電阻式記憶體之單極性操作影響的研究，主要分為兩個部分。第一個部分在氧化鋯上下各為10奈米厚度中間嵌入一層鈷金屬層為5奈米厚度，上下電極分別為鈦金屬與鉑金屬，在沉積上電極前經由六百度熱退火處理，可由TEM的分析，得知鈷金屬形成大約九奈米厚度的奈米球，因金屬尖端放電的影響，大幅降低形成電壓及操作電壓，並拘限轉換區域，因此有極佳之單極性轉換特性。其電性分析為:持久度可超過3000次並且還有10倍的區隔視窗，及在高溫220度環境與-0.1伏特電壓讀取下，非破壞性讀取時間可達到10000秒，對比到我們之前研究，可知在85度下有超過十年非破壞讀取的時間。並且經由電性量測結果與材料分析所建立的模型，我們可以得知此系統單極性操作會相較傳統的單極性操作會有較佳的時間耐久度。第二部分為中間金屬嵌入層為1奈米厚的鈦金屬，經由材料分析，可得知鈦金屬擴散至氧化鋯薄膜中，因而產生較多的氧空缺，經由較多缺陷的幫助，而造成極好的單極性電阻轉換特性。其電性分析為:靜態轉態特性可以超過1000次以上；時間耐久度超過105秒；然後非破壞性讀寫特性超過10000秒。

Many types of consumer electronics products require high-capacity memory with the development of the technology. The demand of nonvolatile memory (NVM) increases significantly with the years in the semiconductor industry. The mainstream of NVM nowadays is flash memory. However, the device dimensions are continuously scaled down, the flash memory faces the challenge of thin tunneling oxide that causes an unsatisfactory retention time. Resistive switching random access memory (RRAM) have these advantages, such as high operation speed, low power consumption, high cell density, and lower scale limit, non-destructive readout, and compatibility of the complementary metal oxide semiconductor (CMOS) process which have the opportunity to become the mainstream of next generation non-volatile memory. In this thesis, the research is focus on the influence of embedded different metal layer and different process temperature with thermal treatment for unipolar resistive switching characteristic in ZrO2 thin films, and it divides into two parts. First, the resistive switching characteristics are investigated based on the Ti/ZrO2(10nm)/Co(5nm)/ZrO2(10nm)/Pt structure by means of 600 ℃ in N2 ambient for 60 s post annealing condition before depositing top electrode. The cobalt layer is formed cobalt nano-particle analyzed by transmission electron microscopy observation. Due to metal point discharge with Co-cluster, forming voltage and operation voltage is reduced significantly and it localizes resistive switching area. Therefore, it exhibits robust negative bias unipolar resistive switching behavior in ZrO2 thin film. DC sweep cycle times can achieve more than 3000 times, and there is no data loss at the nondestructive readout test for over 10000 seconds under -0.1V DC voltage at 220℃. Due to the results of electrical property analyses and material analyses, the switching mechanism model is proposed. Comparison with traditional unipolar system, our new type unipolar system has better retention performance. Second, the resistive switching characteristics are investigated based on the Ti/ZrO2(10nm)/Ti(1nm)/ZrO2(10nm)/Pt structure by means of 600 ℃ in N2 ambient for 60 s post annealing condition before depositing top electrode. The XPS results indicate that the Ti diffusion into ZrO2 film can introduce more oxygen vacancies within ZrO2, leading to good unipolar resistive switching behavior. DC sweep cycle times can achieve over 1000 times; retention test is 105s; and there is no data loss at the nondestructive readout test for over 10000 seconds.