以氧化鋯製備雙層結構電阻式記憶體於單極性電阻轉態特性之研究

Abstract

由於消費性電子產品的發展快速，所需的記憶體容量也與之俱增。在 眾多種類的記憶體之中，以非揮發性記憶體中的電阻式記憶體最具有發展 性。電阻式記憶體具備了結構簡單，操作速度快，低耗能，高密度和非破 壞性讀取的優點，因此可以取代其他類型的記憶體(DRAM, FRAM, FLASH) 而成為次世代非揮發性記憶體的主流。 本篇論文主要著重於兩個部分：雙層氧化鋯電阻式記憶體以及利用氧化鈷與氧化鋯所製成的電阻式記憶體和氧化物二極體。從雙層氧化鋯電阻式記憶體的電性量測中，我們發現三種製程的因素會使記憶體的操作次數獲得明顯的改善。第一個是在用濺鍍機沉積氧化鋯上下兩層的薄膜時，氬氣與氧氣的比例越懸殊越好。第二個為上層的厚度要薄(約5 奈米) ，而下層的厚度要厚(約30 奈米)。第三個條件則為上層的氧化鋯薄膜在氧缺的環境下沉積且下層的氧化鋯薄膜在氧含量多的情況下沉積，會得出最佳的操作次數。在可靠度的量測中，此雙層氧化鋯電阻式記憶體的非破壞性讀取量測中能在施加0.3V 直流電壓下可維持10000秒而無改變、資料保存能力在常溫及 150℃下到達105 秒、操作次數可達1000 次以上。 我們利用氧化鈷與氧化鋯之雙層結構來製作出電阻式記憶體及氧化物二極體。氧化物二極體的製程關鍵在於適當的氬氣與氧氣的比例，使得氧化鈷成為P 型的半導體且氧化鋯成為N 型的半導體。此氧化物二極體在正負3 伏特時具有1000 倍的整流特性。如果在沉積氧化鈷時所用的氣體比例不能使氧化鈷變成P 型半導體，此時的氧化鈷與氧化鋯之雙層結構可以具有電阻式記憶體的特性，並且其操作次數也可達400 次以上。

Due to the development of electronic products, the larger capacity of memory is needed. Among all kinds of memories, the most promising volatile memory is resistive memory. Resistive memory has simple structure, fast operation speed, low power consumption, high cell density and non-destructive readout, therefore it is possible to replace other memories such as DRAM, FRAM and FLASH to be the next-generation non-volatile memory. From the electrical measurements of ZrO2 double-layer memory, we find that there are three factors in the improvement of endurance during fabrication.The first one is the ratio of Ar to O2 is better to be kept at 2: 16 or 16: 2 when we sputter the double-layer films. Another factor is the upper ZrO2 layer has to be thinner(5nm) while the bottom layer has to be thicker(30nm). The final factor is that the best switching cycles occur when the upper ZrO2 layer is deposited in OD atmosphere while the bottom layer is deposited in OR atmosphere. As for reliability test, the sample was stable over 10000s during non-destructive readout at -0.3V. Retention test showed that our samples could remain 105s without degradation at RT and 150℃. Beside, the switching cycles was more than 1000 cycles. We also constructed CoO and ZrO2 double-layer structure to fabricate resistive memory and oxide diode. The key point for oxide diode is proper ratio of Ar to O2 in order to make CoO become P-type material while ZrO2 become N-type material. Such oxide diode had rectifying ratio = 1000 at 3V. If the Ar/O2 ratio could make CoO become P-type material, the double-layer structure of CoO and ZrO2 would show the characteristics of resistive memories. Moreover, the endurance was up to 400 cycles.