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標題: A study of optical and electrical properties and crystallization characteristics of eutectic SbxTe100-x(59<x<80)alloy.
作者: 吳俊毅
Wu, Jyun-Yi
關鍵字: 相變化;phase-change;結晶行為;記憶體;硫屬材料;crystallization characteristics;PRAM;Chalcogenide
出版社: 材料工程學系所
本論文將討論不同比例的SbTe合金薄膜,SbxTe100-x(59 < x < 80),在不同升溫速率以及恆溫下光學與電性的改變,並配合X-ray與TEM來研究其結晶行為與相變化對光學和電性的影響,藉以評估SbxTe100-x(59 < x < 80)合金應用於非揮發性相變化記憶體的可行性。
從實驗中可以發現不論哪種比例的SbTe合金薄膜在初濺鍍時均呈現非晶態,具有較低的反射率與較高的片電阻值;當溫度升到130℃~150℃時,會由非晶態轉變為Sb的結晶態,使反射率與片電阻值分別明顯的升高與下降。結晶活化能除了Sb59Te41略低至2.0eV以外,其餘組成皆在2.2eV左右,而各比例的SbTe薄膜非晶相與結晶相之間的片電阻差異均可以達到3至4個數量級,對於判別資料上,有著相當足夠的差異性。另外隨著Te比例的提升,不管非晶態或結晶態的片電阻與電子活化能均有提高,而高的電阻值對於在元件運作時,可以有效減少電流的消耗。各組成在結晶行為上,反應常數m均小於1.5,符合快速成長型材料的描述。不過SbxTe100-x合金薄膜最大的缺點在非晶態的穩定性不好,必須添加適當的合金元素來改善此一問題。總結來說,SbxTe100-x(59 < x < 80)合金系統,其非晶與結晶態之間的電阻差異夠大,可以應用於非揮發性相變化記憶體,且又屬於快速成長型材料,對於日後的高密度與高傳輸速率有ㄧ定的優勢。

Chalcogenide phase-change materials exhibiting a large difference in resistance or reflectivity between crystalline state and amorphous state have a great potential to be applied for the phase-change memory. The eutectic Sb-Te alloy is a growth-controlled phase-change material. Since the crystallization rate of Sb-Te alloy will increase when the laser spot size is reduced, Sb-Te alloy is considered as one of the promising materials for the high density and high data transfer rate memories. The object of this study is to investigate the optothermal and electothermal properties of SbxTe100-x (59 < x < 80) thin films under nonisothermal and isothermal annealing. The crystallization kinetics of SbxTe100-x thin films and the influence of constituent phases of SbxTe100-x thin films on the optical and electrical properties will be studied to evaluate the feasibility of Sb-Te alloy thin films for using in the nonvolatile phase change memory.
Based on the experimental results, it was found that the SbxTe100-x thin films in the as-deposited state were amorphous, resulting a lower reflectivity and a higher sheet resistance. When the temperature was raised to 130℃~150℃, the amorphous SbxTe100-x thin films would be transformed to crystalline phase, leading to a higher reflectivity and a lower sheet resistance. The activation energies for the SbxTe100-x thin films were all 2.2eV except that of 2.0eV for Sb59Te41. The sheet resistance of all SbxTe100-x thin films showed a large difference of about 3 or 4 orders between amorphous and crystalline state, which would be high enough for data distinguishing. In addition, as the atomic ratio of tellurium was increased, the sheet resistance and the activation energy of electron conduction of SbxTe100-x thin films in both the amorphous and crystalline states were all increased. The increase in resistance of phase change recording material will reduce the consumption current while the device is operated. The crystallization characteristics of all SbxTe100-x thin films showed that the reaction exponents were smaller than 1.5, which agree with the description of fast growth materials. However the SbxTe100-x thin films showed a disadvantage of poor thermal stability, which can be be improved by adding specific foreign elements. To sum up, the fast-growth eutectic SbxTe100-x thin films exhibiting a large difference in resistance between the amorphous and crystalline states so that they have a great potential for use in the high-density and high-data-transfer-rate nonvolatile memory.
Appears in Collections:材料科學與工程學系

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