- 學位論文
相變材料銦鍺銻碲合金薄膜之金屬－絕緣體轉變 導電機制之研究
Metal-Insulator transition in In-Ge-Sb-Te thin films
摘要
本論文主要探討相變化材料In2Ge5Sb73Te21合金之薄膜會隨著其結構由無序狀態轉變成為有序狀態，其電子傳輸特性由絕緣體行為逐漸轉變為金屬行為。 In2Ge5Sb73Te21合金樣品是將四種元素依照其比例混合，然後放入石英管後抽真空，使其在真空的環境下燒熔後，製作成In2Ge5Sb73Te21合金的塊材，再利用濺鍍(sputter)的方式，將In2Ge5Sb73Te21合金塊材當做靶材鍍在玻璃基板上，即可得到In2Ge5Sb73Te21合金箔膜。剛鍍好的合金薄膜在未經過熱退火處理之前，由室溫(300K)升溫至520K(約250℃)，其電阻值隨著溫度上升而下降，在440K(約170℃)時，其電阻值會有個急遽的變化，則此溫度即為此樣品之相轉變溫度，亦稱之為結晶化溫度。同樣在變溫XRD分析的結果裡，也可以看到約略在440K時，其結構由無序狀態傳變成為有序狀態。 In2Ge5Sb73Te21合金樣品不管是在無序狀態或是有序狀態，其I-V曲線都是線性的。無序狀態的In2Ge5Sb73Te21合金樣品，在還沒有做任何熱退火處理之前，其電子傳輸特性屬於跳躍式傳導(hopping)。經過初步熱退火處理，但是還不至於使其發生相轉變的合金樣品其電子傳導特性也是屬於跳躍式傳導，只是相較還沒做過熱退火處理的，其晶格結構變得較有序，使得整體電阻率都下降。而經過長時間退火處理後，其電子傳輸特性轉變成屬於金屬的傳導特性，並且可以利用Bloch-Grüneisen law去找出去其Debye溫度為157.79K。
並列摘要
We have measured the electron transport of the In2Ge5Sb73Te21 (IGST) alloy, which is a kind of phase change material, for studying a metal-insulator transition behavior. The IGST alloys were fabricated by a method of the melt in slow shake, and then sputtered onto glass substrates. The thickness of sputtered films is 100nm, and the lattics structures are demonstrated by X-ray diffraction measurement. The IGST thin films were annealed at from room temperature to 520 K (about 250 ℃) to be observed the resistance increased with increasing temperature and with a variation of step around 440 K (about 170 ℃) to occur phase change behavior. After annealing, the X-ray diffraction patterns show the structure of polycrystalline. On the other hand, we made a serious annealing sample, and the condition of annealing time is from 0.5 to 7.5 hour at 520K (about 250 ℃). After each annealing, the temperature dependence of resistance R(T) is measured between 5 and 300 K. We have found the behaviors of serious curves of R(T) to show a transition from insulator behavior to metallic behavior. On the side of insulator behavior, the R(T) of IGST thin films can be described by hopping theory. On the side of metallic behavior, the R(T) of IGST thin films can be described by Bloch-Grüneisen law, and the Debye temperature is 157.79K.