No abstract

No abstract

Phone: +81-44-548-5359 ' Toshiba Intelligent Technology Corporation Phone: +81-44-548-5710 1. Introduction A high density recording was investigated by using a mark-edge recording method forAgTe-C hlm [l], where an ablative recording was carried out to form a pit. The tracking servo control was pointed out to be influenced by the decrease of reflectivity, which was brought about by the long length pits formed repeatedly. Ge-Sb-Te/Bi-Te write-once disk was developed as a nonablative type media, where data were recorded by the alloying process between the two layers, to keep the tracking servo controlbeing stable.We will report the mark-edge recording charicteristics and the reliability of the disk using an alloying process 2. Experimental Figure 1 exhibits the cross sectional view of the recording layers. These two layers were prepared by an rf-magnetron sputtering onto a polycarbonate substrate having a pregrmve of 1.6 um track pitch. The surface of Bi-Te layer was covered with a layer of W light cured resin. The laser beam of 830 nm in wavelength was focused by an objective lens with a numerical aperture (NA) of 0.55. Carrier to noise ratio (CNR) was measured at a recording frequency of 3.7 M H z and a linear velocity of 5.7 m/s. The measurements of byte erorr rate (BER) were carried out for the random data recorded by using a (1,7)RLL code without waveform equalization. 3. Results and Discussion Figure 2 shows the dependencre of the CNR on the recording power. With 50 ns pulse width, the CNR reached 50 dB at 5 mW; the CNR of more than 50 dB was obtained up to 15 mW. With 100 ns pulse width, 50 dB was obtained at 4 mW; the CNR reached the peak level of 56 dB, then decreased to less than 50 dB because of the readout interference. Figure 3 indicates the dependence of the BER on the recording power at the linear velocity of 5.7 m/s. For the linear density of 0.68 um/bit, the BER was about 2E-5 in the recording power region from 7 to 14 mW. It is recognized that the Ge-Sb-Te/Bi-Te disk has a wide recording power tolerance of +33% at the center power of 10.5 mW. The leveled off value of the BER curve, 2E-5, for 0.68 um/bit was approximately equal I uv light curing resin I I I Polycarbonate substrate Fig.1 Cross sectional view of the disk 60 -0-lOOnsec t-50nsec Linear Velocity : 5.7 m/s Recording Frequency : 3.7 ,WIZ 5 10 15 Recording Power (mW) Fig.2 CNR vs. recording power