标题: 高密度可擦拭磁光碟片的读取方法
Reading in Achieving High Density in Magneto-Optical Disks
作者: 陈炳茂
Bing-Mau Chen
谢汉萍
Han-Ping D. Shieh
光电工程学系
关键字: 热磁超解析法;磁通量读光写;magnetically induced super-resolution;magnetic flux reading optical writing
公开日期: 2000
摘要: 由于电脑、网路和多媒体的迅速发展,大量的资讯随之产生,为了满足高达数十亿位元(Gbytes)资料储存需求,可擦拭型光碟(erasable optical disks)需要具备更高的记录密度与更大的容量。在过去十几年来,许多研究致力于提升记录容量及资料存取速度(data transfer rate):例如中央孔径检测热磁超解析法(magnetically induced super-resolution by center aperture detection, MSR-CAD)碟片可以产生小于绕射极限的等效检出孔径 (effective aperture)以读取微小的记号,进而提升记录密度;另外,如果能有效降低记录时所需的外加磁场(recording bias field, Hb),则可藉由磁调变直接覆写(magnetic field modulation direct overwrite)技术,同时提升磁光系统的记录容量及资料存取速度(data transfer rate)。本研究深入探讨其中两种新型方法:利用脉冲雷射读取法(pulsed-laser readout scheme)具有较为陡峭的温度分布(temperature profile)的特性,以提升MSR-CAD的读出效果;以磁通量读光写(magnetic flux reading optical writing)的交互耦合双层(exchange-coupled double-layer, ECDL)碟片,使得系统在更高记录密度运作时,仍能以磁通量方法(magnetic flux detection)检测微小的记号。
在脉冲雷射光读取法的研究中,模拟的结果显示:此种读取法可产生较窄小的孔径磁壁宽度(aperture wall),因而有效降低读取杂讯(readout noise),同时此种读取法可产生较为陡峭的温度分布,进而降低轨间串讯(intertrack crosstalk),提升光碟的记录容量。实验结果也证实:使用脉冲雷射检读法所得的载波杂讯比(carrier-to-noise ratio, CNR)可比直流雷射(dc laser)读出法提升2.5 dB。因此,使用脉冲雷射光读取法可以进一步改善MSR-CAD的读出特性,故为一先进之高密度读出方法。
“磁通量读光写”碟片有两个基本要求,一是高磁化量(magnetization)可产生高磁通量;二是高矫顽场(coercivity)能提高记号的稳定性,故我们研究以具有高磁化量TbFeCo读出层与另一记录层所组成之ECDL碟片的磁性质与记录特性,使其符合磁通量读光写的需求。实验结果显示:藉由磁性薄膜间的磁交互耦合作用力,交互耦合双层薄膜的等效矫顽场(effective coercivity)可从1.7 kOe 提高至7.6 kOe,且该作用力使得ECDL碟片所需的记录磁场从250 Oe 降至100 Oe。因此,交互耦合双层薄膜具有超过300 emu/cm3的磁化量、高稳定性及低记录磁场,故ECDL碟片能成为“磁通量读光写”记录方式具备高记录密度与速度的记录材料。
With the rapid progress of computer, network, and multimedia applications, the huge information is produced and continuously increased. To meet the great demand of multi-Gbyte recording media, erasable optical disk technologies should gear up for even higher density and capacity. Many techniques have been proposed to increase areal density and data rate during the past decade of years. For example, in the magnetically induced super-resolution by center aperture detection (MSR-CAD) disks, a below-diffraction-limited effective aperture is produced to read the smaller mark to increase the areal density of MO disks. Besides, if the recording bias field (Hb) of MO disks can be reduced, the areal density and data transfer rate of MO systems can be improved simultaneously by magnetic field modulation direct overwrite technique. Two of those advanced techniques have been studied in this study. The first technique is the pulsed-laser readout scheme to improve the readout characteristics of MSR-CAD disks. The other is the exchange-coupled double-layer (ECDL) disks for magnetic flux reading optical writing to resolve the low signal level resulted from small mark size in high density recording.
In the study of pulsed-laser readout scheme, the simulation results indicated that the narrower aperture wall induced by pulsed laser readout results in lower readout noise than that by DC laser readout. The sharp temperature profile resulted in pulsed readout induces less crosstalk to adjacent data tracks, thus track-pitch can be reduced to reach higher density. The experimental results demonstrated that pulsed laser readout scheme produced CNR of about 2.5 dB higher than that of conventional DC readout. It can be concluded that pulsed-laser readout can further improve the readout characteristics, potentially leading to higher recording density than DC readout in MSR-CAD MO disks.
As high magnetization for magnetic flux sensing and large coercivity for stable domains are desirable characteristics for magnetic flux detection, the ECDL disks consisting of a high-magnetization transition-metal (TM)-rich TbFeCo readout layer and a recording layer were studied for magnetic flux reading optical writing. The effective coercivity of ECDL with rare-earth (recording)/TM-rich (readout) films could be greatly enhanced from 1.7 to 7.6 kOe through exchange coupling between the two active layers. Moreover, the recording bias field of the ECDL disks could be reduced from 250 to 100 Oe by the exchange coupling effect. Therefore, the ECDL disks with magnetization over 300 emu/cm3, high stability and low recording bias field are potentially applicable for magnetic flux readout toward high density recording at a high writing rate.
URI: http://140.113.39.130/cdrfb3/record/nctu/#NT890614028
http://hdl.handle.net/11536/67910
显示于类别:Thesis