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  • 學位論文

奈米光儲存複合結構之鍺銻碲材料的熱相變行為之研究

A Research Study on Thermal Phase Transition of GeSbTe in Optical Nano-storage Composite Materials

指導教授 : 張建成
共同指導教授 : 蔡定平

摘要


本論文以合金材料(Ge2Sb2Te5)的熱相變行為,來探討奈米複合結構之雷射光致記錄點的問題。此複合結構的製作,是在一預刻溝軌之聚碳酸酯基板上,依序濺鍍上介電層,相變化記錄層,以及下介電層,反射層,最後再包夾聚碳酸酯基板薄膜為保護層。 以往處理本問題時,都由分析實驗數據所獲得之記錄點斑跡,而未能探討雷射光致記錄點在生成時期的品質及其影響因素。本論文以相變化層受熱期間之溫度變化,配合其對應之熔化與結晶行為,直接探討最終穩定記錄點之大小,形狀及邊緣平整性,這些特性對於資料讀取時之品質有著莫大的關係。 在熱相變行為之探討上,我們以三維熱擴散方程式做為本問題之統馭方程,並使用"改進式交替方向隱式差分法",做數值離散式的主要工具;在處理雷射光通過奈米複合結構之問題,本論文以馬克士威方程式為基礎,配合相應之邊界條件,解析結構中之電場、磁場以及能量流率。最後並將光、熱效應耦合,以應用在實際問題。 透過本文的分析,我們可以很精準地計算出控制光碟讀寫時的種種特性因素與參數,譬如:紀錄點的大小、形狀、邊緣平整性以及加熱時溫度與施加雷射功率的調控。一般而言,控制欲寫下記錄點之區域的溫度,必須適當的高於Ge2Sb2Te5材料的熔點之上,且避免將材料處於熔點觸過長的時間,否則邊緣處過多的固液兩相共存態,會影響到記錄點的平整性。此外,在施加超過誘入功率的能量時,雷射光致記錄點的長度將會快速上升,所以必須控制雷射光於適當功率,避免形成之記錄跡過大,過度消耗光儲存之容量。 在與相關之文獻比較後,獲知本論文所計算得之溫度、熱傳速率、相變化材料之相態、記錄點的形成時間,皆與實驗結果相當穩合。可確認此光、熱效應耦合分析是可靠的。 光儲存技術是臺灣很重要的光電產業之一。本論文所發展之模組分析,可提供相關產業在工業上設計上提升光儲存效能之參考,對此我們深具信心。

並列摘要


In this thesis, we made use of thermal phase transition of Ge2Sb2Te5 to investigate the problem of laser induced bit marks in nanoscale composite materials. The composite materials was fabricated as follows. On a pre-grooved polycarbonate substrate, sputtered in order are the upper dielectric layer, thermal phase transition layer, lower dielectric layer, reflection layer and the protection layer. In the past, all the previous studies obtained traces of bit marks by processing data from experiments without being able to characterize bit marks in their formation. In this study, we carried out theoretical/ numerical analysis to obtain the temperature history of the thermal layer, and its melting and crystallizing behaviors during the heating period. The size and edge smoothness of the bit marks can be determined very precisely; these qualities are closely related to the sensitivity to jitters in reading optical disks. For the study of thermal behavior, we used the three-dimensional heat conduction equation. An improved ADI (alternating-direction- implicit) method was developed to discretize the equation. In discussing laser light through the composite materials, we obtained the layer solution for Maxwell's equations by matching boundary conditions at the layer interfaces. The coupled optical and thermal equations enable as to study realistic/practical problems. Through the analysis in this thesis, we can very precisely determine the factors and parameters that influence reading and writing optical disks. These include the size, shape, and edge smoothness of bit marks, and the temperature control and determination of the applied laser power during the heating process. For example, the temperature in Ge2Sb2Te5 layer should be higher than the melting point appropriately to avoid maintaining the temperature at the melting point for a long time. Otherwise, the edge of bit marks would have a bad quality in smoothness because of the solid-liquid coexistence zone. In addition, if the applied power of laser exceeds the inducing power, the length of bit marks increases rapidly, and thus the applied power should be controlled appropriately to avoid over-consumption of the storage volume. In comparison with existing experimental data, we found that the simulated results in the temperature, rate of heat conduction, phase state, and formation time of bit marks are in close agreement, which adds confidence in our simulations. The technology of optical data storage is a very important industry in Taiwan. The module presented in this thesis may provide a useful tool that helps design and analysis to improve the quality/performance of optical storage.

參考文獻


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