KR100319839B1 - Phase change fluorescent disks and recording methods suitable for them - Google Patents

Abstract

To a phase change type optical disk suitable for high density recording and a recording method suitable therefor.

The recording method according to the invention and in sequence-free heating pulse T _P, recording pulse T _W, a multi-pulse T _M, the last pulse T _L, an off-pulse using a multi-pulse patterns that are separated by T _off for recording a recording mark a recording method of a phase-change optical disc, the recording pulse length of T to _W is referred to as route of the record mark for the X in the length T of the reference clock XT- {(pre-heating pulse T _P + T _M + multi-pulse last Pulse T _L + off pulse T _off )} and has a recording power P _W.

Since the recording method according to the present invention has an improved multi-pulse pattern, it is possible to reduce the laser power required for erasing and recording by improving the C / N ratio characteristic according to the recording and erasing powers, thereby improving the recording sensitivity .

Description

Phase change type optical disc and recording method suitable therefor

The present invention relates to a phase change type optical disk suitable for high density recording and a recording method suitable therefor.

In general, an optical disc is employed as an information recording medium of an optical pickup apparatus for recording / reproducing information in a non-contact manner. This optical disk can be classified into a phase change type, a pit type, and a photon type according to the information recording format.

The phase change type optical disc has a property that a recording film in a portion irradiated with a laser beam becomes a crystalline state or an amorphous state depending on a temperature and a cooling rate. That is, the information is recorded by changing the state of the recording film to the crystalline phase and the non-crystalline state, and associating the state of the crystalline phase with "1" (or "0") and the state of the non-crystalline state to "0" do.

Here, the temperature of the recording film is controlled by the power of the incident laser beam and time, and the cooling rate must be sufficiently large in order to be in an amorphous state, and the cooling rate must be sufficiently small in order to be in a crystalline state. Also, the reflectance difference between the crystalline state and the amorphous state must be large.

This phase change type optical disk is widely used as a DVD-RAM because it can record and erase information by controlling the power of the laser beam incident on the recording film, the time, and the cooling rate.

The DVD-RAM adopts EFM + (Eight to Fourteen modulation plus), and has recording marks of 3T to 11T and 14T size. In a phase-change type optical disc, such a recording mark is recorded by a mark edge recording method or a mark position recording method or the like. Here, 1T represents the clock period of the recording mark.

The mark edge recording method is a method capable of high density recording compared with the mark position recording method, but the end portion of the recording mark, that is, the trailing edge is formed larger than the first portion of the recording mark, that is, the reading edge So-called water droplet phenomenon occurs, so that the recording / reproducing characteristics are degraded.

In view of this, a method of forming a recording mark using a multi-pulse pattern has been proposed. This multi-pulse pattern is used by dividing the power level of each pattern into three levels, that is, a recording power P _W , an erasing power P _e , and a bias power P _b .

FIG. 1 is a waveform diagram showing a conventional multi-pulse pattern corresponding to a recording mark of 3T, and FIG. 2 is a waveform diagram showing a conventional multi-pulse pattern corresponding to 14T.

As shown in the figure, the multi-pulse patterns recorded in each of the 3T and 14T recording marks include a preheating pulse T _P , a recording pulse T _W , a multi pulse T _M ), A last pulse (T _L ), and an off pulse (T _off ).

The time of the preheating pulse (T _P ) is 1/2 T, and has an erase power level P _e . This preheating pulse T _P is for preheating the recording film before the recording pulse T _W.

The recording pulse Tw time is 3/2 T, and has a recording power level Pw. The recording pulse Tw is for forming a leading edge of a recording mark and is also referred to as a first pulse.

The multi-pulse T _M is inserted between the recording pulse Tw and the last pulse T _L when the recording mark of 4T or more is generated, and the erasing power level P _e and the recording power level P _W are 1/2 T units Periodically. The number of times of the multi-pulse (T _M ) is formed in a number corresponding to the length of the recording mark. This multi-pulse (T _M ) is formed by alternately repeating the recording powers P _W and the erasing powers P _e in order to reduce the non-uniformity of recording marks caused by heat accumulation in long recording marks.

The length of the last pulse T _L is 1T for forming the trailing edge of the recording mark _and has the recording power level P _W.

The length of the _off -pulse T _off is 1 T, and has a bias power level P _b . The off-pulse T _off is a pulse positioned after the last pulse T _L , in which the laser power is turned off to prevent the mark from being formed too long.

Table 1 shows the multiple pulse patterns for the case where the recording mark length is 3T to 11T and 14T, respectively.

[Table 1]

The first factor represents the length of the preheating pulse T _P , the second pulse represents the length of the recording pulse Tw, and the last factor represents the length of the off pulse < RTI ID = 0.0 > (T _off ). Then, after 4T, the last second factor indicates the length of the last pulse T _L , and the other factors indicate the length of the multi-pulse T _M.

The recording of the information is performed by adjusting the power of the laser beam (recording power Pw, erasure power P _e , bias power P _b ) and the period T of the reference clock.

That is, in order to make the recording film crystalline, the temperature of the recording film is increased to about 200 ° C by regulating the power of the laser beam, followed by slow cooling. The temperature and cooling rate may be slightly different depending on the material of the recording film. In order to make the recording film into amorphous state, the temperature of the recording film is increased to about 600 ° C by adjusting the power of the laser beam and quenched.

As for the information erasing and recording, a direct rewriting method in which recording and erasing are possible at the same time. When the recorded state is an amorphous state, when the temperature of the recording film is increased up to about 200 ° C (crystallization temperature) If the state is crystalline phase, the temperature is increased to about 600 ° C (melting point) and quenched to amorphous phase. That is, the previously recorded state transitions to the crystalline or amorphous state by controlling the power of the laser beam irrespective of crystalline or amorphous state.

In the conventional phase-change type optical disc constructed as described above, when the size of the recording mark having the above-described pattern is reduced in consideration of the recording density, that is, when the period T of the reference clock is reduced, the Carrier to Noise Ratio (CNR) There is a problem that the characteristics are deteriorated.

Further, as the wavelength of the laser beam to be irradiated becomes shorter than about 450 nm, the recording mark in the amorphous phase tends to become larger than the recording mark in the crystalline as the crystallization linear velocity increases during recording / reproduction, .

SUMMARY OF THE INVENTION Accordingly, the present invention has been made in view of the above problems, and it is an object of the present invention to provide a phase change type optical disk suitable for high density recording.

It is another object of the present invention to provide a recording method suitable for high density recording.

1 is a waveform diagram showing a conventional multi-pulse pattern corresponding to a recording mark of 3T.

2 is a waveform diagram showing a conventional multi-pulse pattern corresponding to 14T.

3 is a cross-sectional view showing the structure of a phase change type optical disc according to the present invention.

4 is a block diagram showing a configuration of a general optical disc system.

5 is a waveform diagram showing a multiple pulse pattern according to the recording method of the present invention corresponding to a recording mark of 3T.

6 is a waveform diagram showing a multiple pulse pattern according to the recording method of the present invention corresponding to 14T.

FIG. 7 is a graph showing a C / N ratio according to a recording power P _W for a case of 3T.

FIG. 8 is a graph showing a C / N ratio according to a recording power P _W for a case of 11T.

9 is a graph showing a jitter amount according to a recording mark.

Description of the Related Art

11 ... substrate 12 ... first dielectric film

13 ... recording film 14 ... complementary layer

15 ... second dielectric film 16 ... reflective film

17 ... Shield

T _P ... preheating pulse T _W ... recording pulse

T _M ... Multipulse T _L ... Last pulse

T _off ... Off pulse

According to an aspect of the present invention, there is provided a phase change type disk comprising: a substrate; A first dielectric film formed on the substrate; A recording film formed on the first dielectric film and capable of being converted into substantially an amorphous state and a substantially crystalline state by an incident laser beam; A supplementary layer formed on the recording film to control heat absorption; A second dielectric film formed on the complementary layer; And a reflective film formed on the second dielectric film.

The recording method according to the invention, another aspect of the above sequence to the pre-heating pulse T _P, the write pulse Tw, a multi-pulse T _M, the last pulse T _L, an off-pulse using a multi-pulse patterns that are separated by T _off the recording A recording method of a phase change type optical disc for recording marks,

The length of the recording pulse Tw is given by XT- (pre-heating pulse T _P + multi pulse T _M + last pulse T _L + off pulse T _off ) when X is the length of the recording mark with respect to the length T of the reference clock , And a recording power Pw. Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

Compounds such as Ge ₁ Sb ₂ Te ₄ , Ge ₂ Sb ₂ Te ₅ , and Ge ₁ Sb ₄ Te ₇ have been known to have good properties as recording films that have been extensively studied as phase change type optical discs. have. I. Morimoto published the possibility of Ge-Sb-Te as a high density recording film in SPIE Vol.1663 OPTICAL DATA STORAGE (1992). Further, regarding In-Ag-Te-Sb as a reproducible phase change recording medium, T. Handa, Jpn. J. Appl. Phys. Vol.32 (1993) reports the improvement of C / N.

In the present invention, Ge (germanium) -Te (tellur) -Sb (antimony) -A compound was used as a recording film. Here, A is a material containing at least one element selected from Ag (silver), Al (aluminum), Au (gold), Ga (gallium), In (indium), Ti (titanium), and Pd (palladium) Lt; / RTI >

3 is a cross-sectional view showing the structure of a phase change type optical disc according to the present invention. 1 includes a substrate 11, a first dielectric film 12, a recording film 13, a complementary layer 14, a second dielectric film 15, and a second dielectric film 15 in this order from the side to which the light L is irradiated. A reflective film 16, and a protective film 17.

The substrate 11 is made of a material such as a photopolymer (photopolymer; 2P) or polycarbonate having a thickness of 0.6 mm and includes a first and a second dielectric films 12 and 15, Lt; / RTI >

A first dielectric film 12 is composed of a mixture ZnS -SiO _2, it is formed by evaporation on the substrate 11.

The recording film 13 is made of a Ge-Te-Sb-A compound and has an amorphous state and a crystalline state according to the power of the laser beam and the cooling rate of the laser beam incident thereon. Here, A indicates a substance containing at least one or more elements of Ag, Al, Au, Ga, In, and Ti.

The optical disc according to the present invention can record and reproduce information in a short wavelength light of about 450 nm or less by changing the compound composition of the recording film 13. [ For this, the thickness T _r of the recording film 13 preferably satisfies the following formula (1).

[Equation 1]

100? Tr? 300 [?]

The recording film 13 is thermally stable so as to have a low crystallization temperature and a recording capacity of 15 GByte or more. To realize a low crystallization temperature and a high crystallization rate, the composition of the recording film 13 is It is preferable to satisfy the expression (2).

&Quot; (2) "

Here, as the x ₁ decreases and the x ₂ increases, the crystallization speed at the time of recording becomes faster, and the data transfer rate due to the high-density recording can be increased. In addition, by increasing Z, the laser power required for recording and erasing can be reduced, and the recording sensitivity can be improved.

The melting point of the Ge-Te binary compound is very high at 725 ° C and the melting point of the Ge-Sb-Te ternary compound made by adding Sb is lowered to about 600 ° C. Therefore, the recording sensitivity is improved and the crystallization speed is increased to enable high-density recording. This is because the melting point of Ge is as high as 959 ° C, whereas the melting point of Sb is relatively low at 630 ° C. The Ge-Te compound contributes to prevention of deterioration of the substrate at a high temperature and stability of the recording mark at room temperature, and Sb ₂ Te ₃ has a characteristic of contributing to an increase in the crystallization rate.

In addition, by adding a small amount of Al (melting point 660 占 폚), Ga (melting point 30 占 폚), In (melting point 157 占 폚) and Ti (melting point 302 占 폚) having a relatively low crystallization temperature to lower the melting point of the recording film, The laser power can be reduced and the recording sensitivity can be improved.

The complementary layer 14 is formed by depositing Si on the recording film 13 and regulates the heat absorption so that the recording mark 13 is more easily formed on the recording film 13. The refractive index of Si is higher than the refractive index of the second dielectric film 15 (about 3.56). The thickness of the compensating layer is about 50-600 ANGSTROM.

The second dielectric film 15 is deposited on the complementary layer 14 and is composed of mixed ZnS and SiO ₂ similarly to the first dielectric film 12. A high refractive index is preferable for heat absorption. Since the refractive index of the second dielectric film 15 is 1.6 - 2.0, it is compensated by the complementary layer 14 having a higher refractive index.

The reflective film 16 is made of a material having a good reflectance such as an Al alloy (Al-Ti 1.5 wt%) or a Cu alloy, and is deposited on the second dielectric film 15. The reflective film 16 reflects the incident light transmitted through the substrate 11 and the recording film 13 toward the substrate 11.

The deposition of the first dielectric film 12, the recording film 13, the complementary layer 14, the second dielectric film 15 and the reflective film 16 on the substrate 11 is performed by sputtering do.

The protective film 17 is bonded to the reflective film 16 by a spin coating method or the like to prevent oxidation and scratching of the reflective film 16 and to maintain the strength of the entire phase change type optical disk.

4 is a block diagram showing a configuration of a general optical disc system. 4, the recording system comprises an analog / digital converter 41, a digital signal processor (DSP) encoder 42, a recording compensation unit 43, and an optical wave controller 44, And records the inputted video signal and audio signal on the optical disc 51. [

The analog / digital conversion section 41 converts the video signal and the audio signal, which are analog signals to be recorded, into a digital signal. The DSP encoder 42 converts the input data bit stream consisting of binary information "0" and "1" into a recording section sequence according to the modulation method. The write compensator 43 performs write pulse compensation to improve the recording density characteristic and reduce the waveform interference at the time of reproduction. The optical power control unit 44 converts the recording pulse into an optical signal and records the optical signal on the optical disc 11.

4, the reproduction system includes a photodetector 45, a reproduction amplifier 46, a reproduction equalizer 47, a synchronization circuit 48, a DSP decoder 49, and a digital / analog converter 50, and reproduces and reproduces the data read from the optical disc 51 using the original video signal and audio signal.

The photodetector 45 converts the optical signal reflected from the optical disc 51 into a current signal. The reproduction amplifier 46 amplifies the reproduction signal converted into the current signal. The reproduction equalizer 47 eliminates distortion and noise of the reproduction signal and performs waveform shaping. The synchronization circuit section 48 restores the synchronization signal and the reproduction data from the reproduction signal. The DSP decoder 49 detects whether there is a reproduction pulse signal of light during a time zone determined by using the synchronization signal output from the synchronization circuit unit 48, that is, during a detection window, and outputs the detected code string as data Demodulate into a bit stream. The digital / analog converter 50 converts the demodulated data bit stream into an analog video signal and an audio signal and outputs the analog video signal and the audio signal.

The recording method and effect according to the present invention will be described in detail with reference to Figs. 5 to 9. Fig. The recording method according to the present invention irradiates a recording beam 13 of a phase change type optical disc as shown in FIG. 3 with a laser beam of a predetermined power to record marks having a minimum size of 3 T and a maximum size of 14 T .

The multiple pulse pattern for forming the recording mark has a preheating pulse TP, a recording pulse Tw, a multi pulse T _M , a last pulse T _L , and an off pulse T _off in sequence.

FIG. 5 is a waveform chart showing a multiple pulse pattern according to the recording method of the present invention corresponding to a recording mark of 3T, and FIG. 6 is a waveform diagram showing a multiple pulse pattern according to the recording method of the present invention corresponding to 14T.

5 and 6, the preheating pulse T _P is positioned before the recording pulse Tw and is for preheating the recording film. In the recording method according to the present invention, T, and has an erasure power P _e of about 1.0 mW or less.

The recording pulse Tw is {3T- (T _p + T _off )} when the time of the waveform is 3T and {14T - (T _P + T _M + T _L + T _off ) And a recording power Pw in the range of approximately 10 to 14 mW.

The multi-pulse T _M is formed on a recording mark whose size is 4T or more, and the erasure power level P _e and the recording power level P _W are periodically formed to correspond to the length of the recording mark in units of 1/2 T . Also, the number of multi-pulses T _M is optional.

In the example of the present invention, the length of the multi-pulse (T _M ) is 0 - 10.5T. As described above, in the recording method according to the present invention, by making the waveform time of the recording pulse T _W longer, the recording mark is relatively well formed as compared with the conventional recording method, and the carrier-to-noise ratio (C / N ratio) ratio is improved. In addition, the recording sensitivity is improved and the C / N ratio is excellent even in a recording power relatively lower than the conventional recording method.

The last pulse T _L is formed in a recording mark whose size is 4 T or more _and has a recording power P _W.

The off-pulse T _off has a bias power P _b in the range of approximately 4 to 6 mW.

In an embodiment of the invention, the combined length of the length of the last pulse T and the off pulse length _L of the T _off is 2T, the length of the last pulse T _L T and the off pulse _off is optional. Here, the length of the _off -pulse T _off is 1 / 4T-7 / 4T.

That is, when the length of the _off -pulse T _off is 1/4 T, the length of the last pulse T _L is 7/4 T, and when the length of the off-pulse T _off is 7/4 T, the length of the last pulse T _L is 1/4 T.

Table 2 shows the multiple pulse patterns for each recording mark when the length of the preheating pulse T _P is 0.25 T and the length of the multi-pulse T _M is zero.

[Table 2]

The first factor represents the length of the preheating pulse T _P , the second factor represents the length of the recording pulse T _W , the last factor represents the length of the recording pulse T _W , Represents the length of the last pulse T _L plus the length of the off-pulse T _off .

In the recording method according to the invention shown in Figure 1 and the conventional recording method in FIG 5 to FIG. 6 described with reference to Figure 2, C / N ratio according to the recording pawooeo Pw and, erasing pawooeo according to P _e C / N ratio is as follows.

FIG. 7 is a graph showing a C / N ratio versus a recording power Pw for a case of 3T, where A is a C / N ratio vs. recording power ratio according to a conventional recording method in which a recording pulse T _W has a length of 1T And B represents the C / N ratio versus recorded power of the recording method of the present invention in which the length of the recording pulse Tw is 1.75T. In the graph shown in Fig. 6, 4.5 mW was used for the erasure power.

As shown in FIG. 7, since the C / N ratio according to the recording powers is almost constant, the recording sensitivity can be improved by reducing the power required for recording.

8 is a graph showing a C / N ratio versus a recording power Pw of 11T, where A is a C / N ratio versus recording power of a conventional recording method in which the recording pulse Tw has a length of 1T And B is a C / N ratio versus recording power according to the recording method of the present invention in which the length of the recording pulse Tw is 5.25T. In the graph shown in Fig. 7, 4.5 mW was used for the erasure power.

As shown in FIG. 8, since the C / N ratio according to the recording power is almost constant, the recording sensitivity can be improved by reducing the power required for recording.

9 is a graph showing a jitter amount according to a recording mark, where A is a length of a recording mark according to a conventional recording method in which the length of the recording pulse Tw is 1T (1.5T in the case of a recording mark of only 3T) And B indicates the amount of jitter in the case where the length of the recording pulse Tw is 1.75T (3T), 2.5T (4T), 3.5T (5T), 3T (6T), 3T The length of the recording mark by the conventional recording method with 4T (9T), 4T (10T), 5T (11T), and 5T (14T).

As shown in FIG. 9, according to the recording method of the present invention, it can be seen that the length of the recording mark versus the amount of jitter is significantly reduced.

As described above, the phase change type optical disc according to the present invention has a low melting point of the recording film, which allows a good exchange of the crystalline and amorphous materials, a high crystallization rate, a low temperature, an improved C / N ratio and improved jitter characteristics . Therefore, the data transfer time can be shortened.

Further, since the recording method according to the present invention has an improved multi-pulse pattern, it is possible to reduce the laser power required for erasing and recording by improving the C / N ratio characteristic according to recording and erasing powers, .

In addition, by making the recording pulse time relatively long, uniform recording marks can be formed, and the size of the reproduction signal can be greatly improved.

Further, the hardware for creating a multi-pulse pattern can be simplified in comparison with the conventional recording method, and the leading edge and the trailing edge of the recording mark can be optimally improved.

Claims (11)

Board; A first dielectric film formed on the substrate; A recording film formed on the first dielectric film and capable of being converted into substantially an amorphous state and a substantially crystalline state by an incident laser beam; A supplementary layer formed on the recording film to control heat absorption; A second dielectric film formed on the complementary layer; And And a reflective film formed on the second dielectric film. The phase change type disk according to claim 1, wherein the complementary layer is a Si layer. 3. The phase change type disk according to claim 2, wherein the thickness of the complementary layer is 50-600 angstroms. The method of claim 1 wherein said recording film comprises Ge (germanium) -Te (tellur) -Sb (antimony) -A compound wherein A is selected from the group consisting of Ag, Al, Au, Gallium), In (indium), Ti (titanium), and Pd (palladium). 5. The phase change type optical disc according to claim 4, wherein the thickness T _r of the recording film satisfies the following equation. 100? Tr? 300 [?] The recording film according to claim 5, wherein each of x ₁ , x ₂ , Y and A satisfies the following conditional expression, and the recording film is {(GeTe) x ₁ (Sb ₂ Te ₃ ) x ₂ } _Y A _Z Phase change type optical disc. A recording method of a phase change type optical disk for recording a recording mark by using a preheating pulse T _P , a recording pulse Tw, a multi pulse T _M , a last pulse T _L , and an off pulse T _off , As a result, The length of the recording pulse Tw is given by XT- (pre-heating pulse T _P + multi pulse T _M + last pulse T _L + off pulse T _off ) when X is the length of the recording mark with respect to the length T of the reference clock , And a recording power Pw. 6. The recording method according to claim 5, wherein the preheating pulse T _{P has} a length of 1/4 T - 1 / 2T and an erase power P _e . 8. The recording method according to claim 7, wherein the length of the multi-pulse T _M is 0 - 10.5T. The method of claim 8, wherein the off-pulse T _{off has} a length of 1/4 T - 7 / 4T. The method of claim 9 or 10, wherein the length of the last pulse T _L plus the length of the _off -pulse T _off is 2T.