相變型光記錄媒質之性質研究

A study of properties of phase-change optical recording medium

鄭國柔(Gwo-Rou Jeng)

指導教授 ： 劉宗平

共同指導教授 ： 黃信二(Hsin-Erh Huang)

元智大學/電機通訊學院/電機工程學系/博士(2008年)

https://doi.org/10.6838/YZU.2008.00183

摘要

摘 要

本文首先針對Ag8In13Sb49Te30 薄膜之晶化行為進行研究，以磁控濺鍍方式，將此種四元合金濺鍍於聚碳酸乙脂基板上，以其作為DVD (digital versatile disc)光記錄媒質之用。其次，在不同的升溫速率下，利用DSC (differential scanning calorimetry) 技術量測結晶化溫度以及晶相所對應之活化能。經由計算後，所得到的活化能之值為1.63 eV。依照五個不同升溫速率所得的DSC數據，利用外插法可推知在升溫速率可高達109 ℃/min下的情形。由SEM (scanning electron microscope)照片得悉，樣品之晶粒大小約為5-30 μm。結晶區為晶相與非晶相共存，沒有較大的晶粒產生，可適用於記錄較小位元長度之資料。由量測此記錄材料之活化能及晶化溫度得知，此材料在非晶態之熱穩定性，符合目前CD-RW、DVD-RW之應用要求。
在DVD-RAM光碟中，將記錄層Ge2Sb2Te5合金內分別添加1、3或5wt %之銀元素，以探討添加元素對DVD-RAM相變記錄層物理特性之影響。在此研究中，首先以磁控濺鍍的方式，將DVD 光記錄層中所需要的靶材1 (Ge2Sb2Te5)、靶材2 (Ge2Sb2Te5+1wt%Ag)、靶材3 (Ge2Sb2Te5+3wt%Ag)及靶材4 (Ge2Sb2Te5+5wt%Ag)分別濺鍍於基板上。在不同的升溫速率下，利用DSC技術進行記錄層熱性質之量測。然後，利用Kissinger方程，來獲得記錄材料的活化能。再以此活化能為基礎，藉助外插法，求出加熱時的相對結晶溫度，藉以評估光記錄媒質的適用性。經由X-ray繞射儀，分析記錄層材料的晶相，可以推知其實際的寫擦測試過程為：非晶態先轉變為亞穩態的FCC (face center cubic)晶態，再由FCC晶態轉變成HCP (hexagonal closed packing)晶態。從四個不同的升溫速率所得到之DSC數據，可以推知其升溫速率可達到1011 °C/min。在這些樣品中，以記錄層摻雜1wt %銀之樣品的非晶態之熱穩定性最好，而記錄層摻雜3 wt%銀之樣品在非晶態與晶態間變換之靈敏度較
高。
對GeSbSn之相變化材料系統而言，倘若調整Sb/Sn之比例，則可探討Sb/Sn比例與晶化速度間之關係。透過光學、熱學與動態性能等之測試量度，可研究將材料應用於高倍速DVD及藍光光碟之可行性。首先，從熱性質的DSC量測來看，GeSbSn 相變材料樣品（它們分別是GSS01~GSS04）在Sn含量較高的情況下，其升溫過程中會出現兩個結晶放熱峯，而且熔點約在400oC左右。當Sb/Sn之比值越低時，第一結晶放熱峯之溫度越低，它可降低高倍速碟片的寫入功率。然而，因其結晶活化能為Ea=1.85~4.79eV，使得它的熱穩定性會隨著Sb/Sn之比值增加而增加。其次，在光學對比度及結晶速率方面，GeSbSn相變化材料系統的晶化速度皆大於四倍速DVD之規格要求。而且，當波長為650 nm時，光學對比值＞0.6，而當波長為405nm時，其光學對比值＞0.5。在動態測試方面，當Sb/Sn之比值太低（樣品GSS01-GSS02）時，其調制 （modulation）小於0.5。而當Sb/Sn之比值太高（樣品GSS04）時，14T的 jitter > 12%，致使其動態測試之效果不佳。由樣品GSS03 （Ge14Sb64Sn22 (at%)）的動態測試結果顯示，它可適用於4~12倍速的DVD-RW或1~3倍速的藍光光碟。
關鍵詞：相變型記錄媒質DVD-RAM光碟，記錄層，活化能，結晶溫度

關鍵字

相變型記錄煤質 記錄層 活化能

並列摘要

ABSTRACT

This study first the researched crystalline behavior of a thin film (Ag8In13Sb49Te30 ) in which a DVD (digital versatile disc) optical recording film is deposited on a polycarbonate (PC) substrate by sputtering technique. At different rates of increasing temperature, an activation energy of 1.63 eV, is obtained from the crystallizing temperature data by using DSC technique. We can obtain the increasing temperature in a real case at a high rate of 109℃/min by regression, from the DSC data at five rate, increasing of temperature. From the SEM (scanning electron microscope) figure, we can see their grain size, were about 5-30 μm, their crystalline regions were eutectic that with crystalline and amorphous which size were small, satisfied for smaller bits’ recording. The thermal stasblity of the material can match with the requirement of CD-RW (rewritable) and DVD-RW due to the data of their activation energy and crystallizing temperature.
Doped with a small amount of Ag atoms (1, 3, 5 wt % of Ag, respectively) Ge2Sb2Te5 alloys can be used as the recording layer of DVD-RAM discs. Doping can effect the physical properties of phase-change recording layer in DVD-RAM disc. For DVD the four different targets were used to deposite the recording medium on a PC substrate by RF sputtering process. The activation energy can be obtained from DSC measurements combined with the Kissinger equation. At different rates of increasing temperature, we use DSC technique to measure the crystallization temperature and the activation energy corresponding to crystalline phase, and take the activation energy as a basis to obtain the relative crystallization temperature in heating by extrapolation, then, by means of dynamic test which can be used to simulate the practical condition in dynamic writing and erasing and assess adaptability of optical recording media. Through the analysis of the variations of crystalline phase by X-ray diffracter (XRD), we can see that the actual testing process in writing and erasing are as follows: the amorphous state has been transformed into the meta-stable state that we call the FCC (face center cubic) crystalline state, then, transformed again from FCC crystalline state to HCP (hexagonal closed packing) crystalline state. Recourse to the DSC data obtained from four diverse rates of increasing temperature, together with extrapolations, we can get the condition when the rate of increasing temperature being promoted at a high speed to 1011 °C/min. The amorphous state of that mixed with 1wt% of Ag in recording layer has the best thermal stability. Among the four targets, the one mixed with 3wt% of Ag has the best sensitivity of amorphous-to-crystalline transition.
Through a series of optical, thermal, and dynamic testings, the properties of phase-change material of GeSbSn used in blue-ray disks and high-speed DVDs, can especially be studied on different ratios between Sb and Sn, as well as their crystallization rates. For GeSbSn material system, there are two exothermal peaks under a condition of high Sn content in the material. For our four samples of GSS01-GSS04, the smaller the ratio of Sb/Sn, the lower the temperature of first exothermal peak. It means that the write-in power of high-speed DVD disk can be apparently decreased. However, the thermal stability due to the activation energy of crystallization increases with the Sb /Sn ratio. By optical measurements for these samples, the optical contrast is greater than 0.6 at a wavelength of 650 nm and that than 0.5 at a length of 405 nm. All of them are meet the requirements of 4X speed DVD. In dynamic test, the modulation of readout signal for GSS01-GSS02 decresses below 0.5 as the ratio of Sb/Sn becomes lower, while the jitter at 14T for GSS04 is over 12 ﹪as the ratio of Sb /Sn is too large. Consequently, only GSS03（Ge14Sb64Sn22(at%)）can be used in 4-12X speed DVD-RW or 1-3 X speed blue-ray disk.
Keywords: phase-change recording medium DVD-RAM optic disc, recording layer, activation energy, crystallization temperat

並列關鍵字

phase-change recording layer action energy

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