銀電極搭配鍺銻碲薄膜之電阻轉換現象研究

Abstract

電阻式記憶體（Resistive Random Access Memory，RRAM）被視為取代快 閃記憶體的次世代記憶體之一。本研究使用銀（Ag）及鎢-鈦（W-Ti）為含鍺銻 碲（Ge 2 Sb 2 Te 5 ，GST）固態電解質層薄膜的導電橋接式記憶體（Conductive Bridge Random Access Memory，CBRAM）之活性電極與惰性電極，並研究其電阻轉換（Resistive Switching）性質。 電流-電壓（I-V）特性之量測顯示含經 250C 退火之 GST 薄膜的試樣具備 CBRAM 的特性，但歐傑電子奈米顯微鏡（Auger Electron Nanoscope）之分析顯示 GST 層中的 Ag 擴散相當嚴重。在 Ag 電極與 GST 層間置入一硫化鋅 （ZnS-SiO 2 ）層雖可抑制 Ag 擴散，但卻使得元件的 CBRAM 特性劣化；惟此一試片再經 250C 退火後，其電性可獲改善，V Set 、V Reset 與 R Off /R On 比等皆較原有試片為佳，且 I-V 曲線顯示其出現極性反轉（Polarity Reversal）的現象。以電子顯微鏡（Transmission Electron Microscopy，TEM）及歐傑電子能譜（Auger Electron Spectroscopy，AES）分析對 GST 層內 Ag 元素的分析發現正常極性的試片 GST 層內 Ag 元素係往 W-Ti 電極端呈遞減分佈，而極性反轉的試片 GST 層內 Ag 元素則往 W-Ti 電極端呈遞增分佈。我們推測在這兩種試片中 Ag 導電絲（Conductive Filament）之破斷/生成處應在 GST 層相反的兩側，此使得在所施加偏壓時 Set 及 Reset 步驟相反，因而呈現極性反轉的現象。

Resistive random access memory (RRAM) has been widely recognized as the next-generation nonvolatile memory to replace the flash memory. This study investigates the resistive switching property of conductive bridge random access memory (CBRAM) containing Ge 2 Sb 2 Te 5 (GST) as the solid-state electrolyte layer, Ag as the active electrode and W-Ti as the counter electrode. As revealed by the I-V measurement, the CBRAM characteristics were observed in the sample containing GST layer subjected to 250C annealing. However, the Auger electron nanoscope analysis indicated a severe Ag diffusion into the GST layer. Though the insertion of ZnS-SiO 2 layer in between Ag and GST layers might alleviate the Ag diffusion, it degraded the CBRAM performance. Subsequent study found that a further annealing at 250C may improve the electrical properties of device samples. In addition to the improvement of V Set , V Reset and R Off /R On ratio, the polarity reveral phenomenon was also observed by the I-V measurement. Transmission electron microscopy (TEM) and Auger electron Spectroscopy (AES) analyses on the Ag distribution in GST layer found that the segregation of Ag elements toward the W-Ti electrode side in the samples with normal polarity and the accumulation of Ag elements at the Ag electrode side in the samples with reveral polarity. It is speculated that the formation and rupture sites of Ag conductive filaments are reverse in these two distinct sample types. This set and reset processes were hence reversed when external bias was applied, leading to the polarity reveral phenomenon.