利用選擇器串接電阻式記憶體在可撓式基板上製作高密度交錯式記憶體陣列

Abstract

遵循著莫爾定律，快閃式記憶體在過去十年來不斷的微縮，但在面臨16nm以下的製程將面臨到很大的困難，除了微影技術的成本昂貴，在單一記憶細胞使用多層記憶狀態技術時，受限於每個記憶狀態提供的電子數越來越少，要清楚的分辨每一個記憶狀態也越來越難。在過去這幾年，許多前瞻性的非揮發性記憶體被大量的研究與討論，其中電阻式記憶體因具有低功率消耗、操作速度快、結構簡單可使用於交錯式陣列結構而被認為是最有競爭力。然而，使用於交錯式陣列的電阻式記憶體將面臨嚴重的串擾效應，造成記憶細胞內的資料會被錯誤的讀取。 電阻式記憶體的串擾效應可以藉由額外串接一個選擇器元件來解決，雖然雙極性電阻式記憶體的操作比較穩定，但是一直沒有適合的選擇器元件可以搭配使用。在這篇論文中，我們將利用鎳金屬和二氧化鈦製作出適合雙極性電阻式記憶體使用的選擇器元件，並發現在不同條件下製作的二氧化鈦對於改善串擾效應會有不一樣的表現，而在電性量測中我們發現，此元件改善串擾效應的能力可能是來自於蕭特基能障。 塑膠基板因為質量輕盈且可以運用在滾筒式製程等優點，在近年來被廣泛的運用在電子產品上。除了矽基板製程，我們也將此選擇器製作在塑膠基板，並搭配可撓式雙極性電阻式記憶體形成1S-1R結構。利用1S-1R結構，交錯式陣列的串擾效應確實被有效的抑制，不管是應用在2×2或是8×8的大尺寸陣列都有令人滿意的成效。

Following the Moore's law, flash memory has been aggressively scaled in the past ten years, but it is approaching the fundamental limits beyond the 16nm technology node. Besides the high cost of lithography facilities, the number of electrons stored per bit is less than 100 when using the multi level cell technology. It's difficult to distinguish the memory state without complicated error correction techniques at the expense of increased cost. In the past ten years, several emerging non-volatile memories have been widely investigated. Resistive random access memory (RRAM) has attracted the most attention because of the low power consumption, high operation speed, and simple structure is compatible to crossbar array. However, the undesired crosstalk problem may result in incorrect data reading. The crosstalk problem in crossbar RRAM may be solved by adding a selection device. Although the operation of bipolar RRAM is more stable than that of unipolar RRAM, there is no appropriate bipolar selection device available. In this thesis, we fabricate the selection device suitable for bipolar RRAM using a Ni/TiO2/Ni Metal-Insulator-Metal (MIM) structure, and investigated the effect of conditions on the selector characteristics. The observed nonlinear resistance was attributed to the Schottky barriers at the Ni/TiO2 interface. In recent years, flexible substrates have been used in many electronic products because of the advantages of light weight and compatibility to roll-to-roll process. We also fabricated the selector on a flexible polyimide substrate. Combined with the bipolar RRAM, we fabricated a vertically stacked 1S-1R structure which effectively reduced the crosstalk phenomenon in both 2×2 and 8×8 1S-1R array.