氧化物半導體電阻式記憶體與薄膜電晶體技術整合之研究

Abstract

隨著科技的日新月異，不同種類的消費性電子產品都需要大容量的記憶體，其中以非揮發性記憶體的需求量為最大宗，加上快閃記憶體的微縮極限，造成非揮發性記憶體的研究更加的蓬勃發展。電阻式記憶體具有結構簡單、操作速度快、低耗能、高密度和非破壞性讀取等優點，非常有可能成為下一世代非揮發性記憶體的主流。 本論文的研究是著重於利用一種新的非晶態鋅錫氧化物半導體(a-AlZnSnO)同時作為電阻式記憶體的電阻切換層與薄膜電晶體的主動層通道，並將兩者結合以製成電阻式記憶體串聯薄膜電晶體(1T1R)的結構；不論是對於電阻式記憶體亦或是薄膜電晶體，在以往的許多研究當中都指出非晶態銦鎵鋅氧化物(a-IGZO)展現出高載子遷移率與透明性等良好的特性並且被認為擁有足夠的潛力應用於次世代的顯示器中，例如電阻式記憶體、LED顯示器、3D顯示器等。因此，若發展此類型的電阻式記憶體整合於相同材料的電晶體中，將在未來系統面板(SOP)的應用上有很大的幫助。然而，含有銦與鎵的材料大量的應用在許多光電元件上，例如:薄膜電晶體、LED、太陽能等，使得含有銦與鎵的材料在不久的未來將越來越貴，甚至貧瘠。鑒於上述的原因，我們提出一種新的非晶態鋁鋅錫氧化物半導體(a-AlZnSnO)同時作為電阻式記憶體的電阻切換層與薄膜電晶體的主動層通道，並將兩者結合以製成電阻式記憶體串聯薄膜電晶體(1T1R)的結構，由於不含大量消耗的銦與鎵，將能有效的降低成本。此外，由於電阻切換層與薄膜電晶體的主動層通道是使用相同材料，於系統整合之顯示面板亦可達成簡化製程、減少成本的目的。 論文主要分兩部分，第一部分是利用在AZTO電阻式記憶體的轉態層與底電擊間插入一層氧化鉿薄膜來更加優化轉態特性，第二部分則是藉由減少電阻式記憶體內部的氧空缺使其能與薄膜電晶體完美結合。其中，雙層氧化層電阻式記憶體與單層AZTO電阻式記憶體相比有較低的功耗及較均勻的電壓與電阻態分佈，耐久度與非揮發性測試也有良好的表現，我們也藉由X光光電子儀來分析可能造成此優量表現的原因。最後我們進一步透過改變製程條件(包含改變製程中氣氛與氧化層的厚度)來使得電阻式記憶體能與薄膜電晶體完美搭配。第二部分則將電阻式記憶體與薄膜電晶體結合。此元件成功的消除單一電阻式記憶體可能產生的電流驟升現象，且其電特性展現出低功耗(~μA)、高複寫次數(可達〖10〗^7 次)、良好的非揮發性(85℃測試下電阻能維持〖10〗^4秒)；此外，我們也藉由控制薄膜電晶體的閘極偏壓使得電晶體輸出的電流產生變化，進而造成記憶體轉換的阻值不同來達成良好的多階操作特性。最後，由於元件的所有製程都是在低溫下完成(薄膜電晶體約攝氏450度，電阻式記憶體於室溫下製成)，非常具有潛力應用於軟性電子領域，且由於薄膜電晶體之通道主動層與電阻式記憶體之電阻切換層皆為非晶態鋁鋅錫氧化物半導體，除了因為具有新穎的透明特性、高載子遷移率與非晶態大面積均勻之特性使得適合應用於下一世代系統面板上以外，若以同樣材料應用在系統面板，還可達成簡化製程、減少成本的目的。

Many types of consumer electronics products require high-capacity memory with the development of the technology, in which demanding for non-volatile memory is the largest. Flash memory face the issue of scale limit, so the research of next generation non-volatile memory is booming. The resistive switching random access memory (RRAM) have these advantages, such us high operation speed, low power consumption, high cell density, and lower scale limit and non-destructive readout, rhich have the opportubity to become the mainstream of next generation non-volatile memory. The purpose of this thesis is to develop a reliable 1T1R of a-AlZnSnO based resistive switching memory and thin-film transistor. No matter we focus on resistance random access memory of thin-film transistor, many study show that the well-known amorphous InGaZnO (a-IGZO) film exhibit remarkable characteristics on both filed. It is expected to be the potential candidate for thin film transistors in next-generation flat-panel displays, including resistive random access memory, light-emitting diode displays and three-dimensional displays, due to its high mobility and good transparency to visible light. Therefore, RRAM devices using IGZO films as switching layer are worthy of developing for future system-on-panel (SOP) applications. However, the target materials that comprise indium (In) and gallium (Ga) are in great demand for use in the manufacture of optoelectronic devices, such as thin film transistors, light-emitting diodes, lasers, solar cells, and radio-frequency (RF) circuits. From these considerations, In- and Ga-free TAOS materials(AZTO) are utilized to demonstrated Characteristics of 1T1R of a-AZTO based RRAM and TFT for the lower material cost. In addition, it also has the benefit of simplifying the flow, and cuting down the cost for future system-on-panel (SOP) applications. This thesis divides two parts. First part, we improve the resistive switching uniformity for Al-Zn-Sn-O-based memory device with inserting HfO2 layer. Second part, we perfectly integrate a-AZTO based Resistive Switching Memory and thin-film transistor through localizing the oxygen vacancy of RRAM. A lower power consumption and superior uniform statistical distribution of resistance states and operation voltage on HRS and LRS are shown for the bi-layer structure. Besides, it also shown good cycling endurance and data retention. We also analyze the mechanism through the XPS spectrum. In the final of the first part, we further optimize the resistive memory to perfectly combine with the thin-film transistor (including the ambient of manufacture process and the thickness of switching layer). In the second part, our 1T1R device could efficiently control overshoot current and show low power consumption (~μA), repeated endurance cycles (〖10 〗^7 times), and stable retention characteristics (over 〖10〗^4 seconds for 85℃). In addition, we demonstrate the multi-level operation through control the gate voltage, which changethe drain current and caus e different resistance of RRAM. Finally, because the whole fabricating process of the RRAM device is under low temperature, (the annealing temperature of thin-film transistor is 450℃, RRAM is prepared at room temperature.) it holds the potential for flexible electronics applications. Furthermore, due to the resistive switching memory and thin-film transistor are both a-AlZnSnO base, it has the ability to develop future system-on-panel (SOP) because of the transparence, high mobility, uniformity of amorphous state. Beside, it also has the benefit of simpler flow, and lower cost.