光記錄媒體之資料傳輸與容量提升之研究

Abstract

本論文研究相變化光碟之資料傳輸與容量提升的方法。資料傳輸的部分係利用氮氣（N2）摻雜於記錄層的方式提升共晶型銻-碲（Sb-Te）相變化記錄媒體之資料傳輸速率，研究項目包括氮氮摻雜對共晶型鍺-銦-銻-碲（Ge-In-Sb-Te，GIST）相變化材料的非晶-結晶轉換速率（相對應於相變化光碟之資料傳輸速率）、光學特性、熱性質及微觀結構之影響。實驗結果顯示：當濺鍍記錄層之氮氬氣比例（N2/Ar）為3%時，非晶-結晶轉換速率於藍光（波長 = 422 nm）靜態測試系統（Static Test）及紅光（波長 = 650 nm）動態測試系統（Dynamic Test）下分別可提昇1.5及1.6倍，加入氮化鍺（GeN）結晶促進層（Nucleation Promotion Layer）於GIST-(N)x記錄層兩側後，動態測試之結果顯示非晶-結晶轉換速率更可進一步提昇至3.3倍。本實驗亦利用熱差分析儀（Differential Scanning Calorimeter，DSC）、x光繞射（x-ray diffraction，XRD）、橢圓偏光儀（Ellipsometry）、電子能譜儀（Electron Spectroscopy for Chemical Analysis，ESCA）及穿透式電子顯微鏡（Transmission Electron Microscopy，TEM）對GIST-(N)x之光學特性、熱性質及微觀結構加以研究，結果顯示：經適量氮氣摻雜的GIST不僅其相對應之活化能有降低的趨勢，而且有助於提昇光碟之訊號特性。氮氣摻雜將使得記錄層中產生均勻分佈的氮化物，而氮化物與非晶處的界面則成為有利於相變化發生的位置（site），因而使得相變化不僅於非晶與結晶處的界面，亦在氮化物與非晶處的界面發生，如此一來，非晶-結晶轉換速率得到有效的提昇。 在光碟容量提升之研究部分則是以奈米硒化鎘（CdSe）摻雜之半導體玻璃（Semiconductor-doped Glass，SDG）為光碟的光學遮罩層材料，並以此進行超解析結構光碟之研究。實驗結果顯示：於讀取功率為4 mW的條件下，可解析出69 nm之訊號，其載波雜訊比（Carrier-to-noise Ratio，CNR）值為13.56 dB，且當訊號長度大於100 nm時，CNR值更可高達約40 dB。除此之外，在4 mW的讀取條件下，含CdSe-SiO2 SDG超解析層之光碟經105的讀取次數後，仍然具相當程度的穩定性及可靠度。

This thesis work studies the methods to enhance the data transfer rate and storage capacity of optical recording media. In the part of data transfer rate enhancement, appropriate amount of nitrogen (N2) doped in the eutectic Sb-Te phase change recording layer is able to accelerate the data transfer rate of optical disks containing Ge-In-Sb-Te (GIST) recoding media. The speed of the amorphous-to-crystalline phase transformation, thermal properties, optical properties and microstructure induced by nitrogen doping in GIST recording layer were investigated and discussed in this work. The experimental results show that for the GIST recording layer doped at the condition of sputtering gas flow ratio of N2/Ar = 3 %, the data transfer rate increases up to 1.5 and 1.6 times as revealed by a static tester containing blue-light laser (λ = 422 nm) and a dynamic tester containing red-light laser (λ = 650 nm). When thin GeNx nucleation promotion layers were further added in below and above the GIST-(N)x recording layer, an overall enhancement up to 3.3 times in data transfer rate was achieved. The nitrogen contents corresponding to various N2/Ar flow ratios (N2/Ar = 0 % ~ 10 %) were calibrated by electron spectroscopy for chemical analysis (ESCA). The changes of thermal, optical and phase constitution of GIST layer resulted from N2 doping were investigated by using differential scanning calorimetry (DSC), ellipsometry, and x-ray diffraction (XRD). These analyses indicated that when appropriate amount of nitrogen was added, the activation energy (Ea) of amorphous-crystalline phase transition of GIST decreased and the optical constants of amorphous and crystalline phases (except the k value of amorphous phase) gradually reduced with the increase of wavelength in the range of 600 to 750 nm. Modulation simulation based on the reflectively of doped GIST layers obtained from static test indicated that appropriate nitrogen doping benefited the signal characteristics of optical disks. Transmission electron microscopy (TEM) revealed that nitrogen doping was able to promote the phase transformation by generating numerous nucleation sites uniformly distributed in the recording layer and hence increased the recrystallization speed. In the part of storage capacity enhancement of optical disks, we demonstrate a distinct super-resolution phenomenon and signal properties of optical disk with a semiconductor-doped glass (SDG) mask layer containing CdSe nanoparticales. It was found that the 69-nm marks could be consistently retrieved at reading power (Pr) = 4 mW with carrier-to-noise ratio (CNR) = 13.56 dB. The signals were clearly resolved with CNRs nearly equal to 40 dB at Pr = 4 mW when the recorded mark sizes were over 100 nm. The cycleability test indicated that the CdSe-SiO2 SDG layer may serve as a stable and reliable optical mask layer in 105 readout cycles.