JPH03183038A - Phase change type optical disk - Google Patents

Abstract

PURPOSE:To enable satisfactory erasing under a specified condition regardless of a radial position for recording and erasing even when a disk is used under a condition fixing the number of revolution by increasing the film thickness of a recording layer between two dielectric layers from the outer periphery to the inner periphery of the disk. CONSTITUTION:On a substrate 1, a dielectric layer 2, a recording layer 3 and a dielectric layer 4 are successively formed. The film thickness of this recording layer 3 is increased from the outer periphery to the inner periphery of the disk. Since the cooling speed of the recording layer is changed according to the size of the thermal capacity of a medium, the optical disk to vary the cooling speed in a radial direction can be obtained by changing the film thickness of the recording layer 3 in the radial direction. Therefore, even at various linear velocity, the same cooling condition can be obtained and even when the disk is used under the condition fixing the number of revolution satisfactory erasing can be executed under the fixed condition regardless of the radial position for recording and erasing.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention relates to a phase change optical disc that records information using reversible phase change by laser beam irradiation, and particularly relates to a phase change optical disc that records information using reversible phase change caused by laser beam irradiation. The present invention relates to a phase change optical disc capable of one-beam override in which new information is recorded while erasing previously used information.

[Conventional Technology] Optical disk recording systems using laser light are capable of large-capacity recording and non-contact high-speed access, so they have begun to be put into practical use as large-capacity memories. The optical disc is
Compact discs are classified into read-only types known as laser discs, write-once types that can be recorded by the user, and rewritable types that can be repeatedly recorded and erased by the user.

Write-once and rewritable optical discs are increasingly being used as external memory for computers or as document and image files.

Rewritable optical disks include phase-change optical disks that utilize phase changes in a recording film and magneto-optical disks that utilize changes in the magnetization direction of a perpendicularly magnetized film. Among these, phase change optical disks are considered promising because they do not require an external magnetic field and can be easily overridden.

2. Description of the Related Art So-called phase-change optical disks, which are rewritable and use a recording film that undergoes a phase change between crystal and amorphous upon laser beam irradiation, have been known. In phase-change optical discs, a high-power laser beam spot is irradiated on the recording film according to the information to be recorded, and the temperature of the recording film is locally increased to cause a phase change between crystalline and amorphous states. The optical constant is recorded using a low-power laser beam, and the resulting change in the optical constant is read as a difference in the intensity of the reflected light for reproduction.

For example, in a phase change optical disc using a recording film with a relatively slow crystallization time, the disc is rotated and the recording film formed on the disc is irradiated with laser light to raise the temperature of the recording film above its melting point. After the laser beam passes through it, the area is rapidly cooled to become an amorphous state and recorded. During erasing, a long oval laser beam is irradiated in the direction in which the laser beam travels to maintain the recording film temperature in the crystallization temperature range above the glass transition point and below the melting point for a sufficient period of time to allow crystallization to proceed. , crystallize. Here, when performing a pseudo override using a double-dimension method that records new information while erasing already recorded data, the elliptical laser beam for erasing is irradiated in advance of the circular laser beam for recording. Place it like this.

On the other hand, a disc using an information recording film capable of high-speed crystallization uses a single laser beam focused in a circular shape. Crystallization or amorphization is achieved by varying the power of the laser light between two levels.

That is, by irradiating the recording film with a laser beam of power capable of raising the temperature of the recording film above its melting point,
That part becomes an amorphous state when cooled, while the part irradiated with a laser beam of such power that the recording film temperature reaches a temperature above the glass transition point and below the melting point becomes a crystalline state.

[Problem to be solved by the invention] However, in the most common usage condition of recording, reproducing, and erasing information by rotating the disk at a constant rotation speed, it is extremely difficult to control the recording and erasing conditions. It is.

For example, when a phase change optical disk made using a substrate with a diameter of 5.25 inches is rotated at 1800 rl), at a radius of 30 mm, the linear velocity is 5.65 m/
s, but at the outermost radius of 60 mm, the linear velocity is 11
．． It becomes 3m/s. In this way, when a disk is used at a constant rotation speed, the linear velocity differs between the inner and outer circumferences of the disk, so under the same power conditions, there will be a difference in the amount of temperature rise due to laser irradiation between the inner and outer circumferences of the disk. I can do it. And...
Even if the power is controlled so that the amount of temperature rise of the recording film is the same, if the linear velocity changes, the cooling conditions will change because there will be a difference in the time the recording film is irradiated with the laser. That is, at high linear speeds, the time that the laser irradiates an area of the recording film is short, and the laser, which is the heat source, moves quickly, resulting in a rapid heating and cooling state.On the other hand, at low linear speeds, body heat decreases. It becomes a slow cooling state. This means that the cooling conditions that determine the erased state, that is, the crystallization conditions, vary depending on the linear velocity. For disks that have the same media configuration over the inner and outer circumferences of the disk, that is, for disks that have a configuration in which each layer including the recording layer has a constant thickness, in order to obtain a good erase condition, it is necessary to control the erase conditions for each recording radius with high precision. You are requested to do so. In other words, there is a drawback that good erasing cannot be achieved unless the erasing conditions are precisely controlled.

The purpose of the present invention is to solve the above-mentioned drawbacks, eliminate the need for highly accurate control of erasing conditions even when used under constant rotational speed conditions, and ensure good erasing under constant conditions regardless of the radial position of recording/erasing. The object of the present invention is to provide a phase change type optical disk that can achieve the above goals.

[Means for Solving the Problems] The present invention provides a phase-change optical disc that records, reproduces, and erases information by utilizing a reversible phase state change of an information recording film caused by laser beam irradiation. The disc is composed of a first dielectric layer, a recording layer, and a second dielectric layer that are sequentially formed on the disc, and the thickness of the recording layer increases from the outer circumference toward the inner circumference of the disk. This is a phase change optical disc.

[Operation When the co-disk is used at a constant rotational speed, the linear velocity becomes slower on the inner circumference of the disk and faster on the outer circumference. If the linear velocity is slow, the recording pulse will shine on one point on the disk.
The time for A tends to be longer, and the cooling rate is slower. Therefore, the cooling rate is slow on the inner circumferential side of the disk, and faster on the outer circumferential side.

On the other hand, the cooling rate of the recording layer changes depending on the heat capacity of the medium, and the larger the heat capacity, that is, the thicker the recording layer, the faster the cooling rate.

Therefore, if the thickness of the recording layer is made larger on the inner circumference side of the disk and smaller on the outer circumference side, a phase change type optical disk with constant cooling rate characteristics can be obtained.

[Example] Next, an example of the present invention will be described with reference to the drawings.

FIG. 1 is a schematic sectional view showing an embodiment of a phase change type optical disk of the present invention. A first dielectric layer 2, a recording layer 3, and a second hyperelectric decoy 4 are sequentially formed on a disk-shaped substrate 1 made of glass or plastic. Here, the first dielectric layer 2 and the second dielectric layer 4 include SiO2, Si3
N4, Aj! Materials such as N, TiO2, and SiO are used. The recording layer 3 is made of chalcogenide materials such as GeTeSb, In5bTe, InSe, and InSe.
-1e series, ASTeGe series, Tea, -GeSn series, T
e5eSn series, 5bSeBi series, [3+3eGe series, etc. are used.

In FIG. 1, the thickness of the recording layer 3 increases from the outer circumference to the inner circumference of the disk. This is a feature of the phase change optical disc according to the present invention.

Normally, the cooling rate of the recording layer varies depending on the medium configuration, that is, the heat capacity of the medium, so by changing the thickness of the recording layer, optical disks with different cooling rates in the radial direction can be obtained.

Therefore, by changing the thickness of the recording layer, it is possible to control the cooling rate and obtain equivalent cooling conditions even at different linear velocities.

FIG. 2 shows the relationship between the linear velocity during recording and the cooling rate immediately after recording when the thickness of the recording layer is <200OA and 1000A.

500A> as a parameter. For example, when recording a signal with a pulse width of 50 nS, the linear velocity is 5
m/s, the recording beam on the disk is 0.257
m, the recording beam with a leg diameter of 1.5 mm usually moves about 1.5 m.
Heat an area of 75 radians. On the other hand, linear velocity 20
At m/S, the recording beam on the disk moves by 1.0, so normally 1.5 IJ! The n-diameter recording beam is approximately 2
．． Heat a 51Jjn long area to 0. The slower the linear velocity is, the longer the recording pulse is irradiated to one point on the disk, which slows down the cooling rate. As is clear from Figure 2, the cooling rate tends to increase as the thickness of the recording layer increases, so if you change the thickness of the recording layer in accordance with the linear velocity used, you can maintain a constant cooling rate. A phase change type optical disk with characteristics can be obtained.

Phase-change optical disks are manufactured by film-forming methods such as resistance heating vacuum evaporation, electron beam vacuum evaporation, and sputtering. The film thicknesses of the first dielectric layer 2 and the second dielectric layer 4 are set in a range of 10 m to 200 nm. The thickness of the recording layer 3 is set in a range of 20 nm to 200 nm.

For film formation, as shown in FIG. 3, a film formation equipment having an evaporation source or sputter source 11 in a vacuum chamber 10 is used. In the figure, 12 is an exhaust system, and 13 is a gas inlet during film formation. The disk 5 is rotated by a motor 14 to form a film. 1st. The second dielectric layer is formed to have a uniform thickness, but the recording layer is formed to have a thickness that varies in the radial direction. By setting the source 11 for the recording layer at a position eccentric to the disk 5 during film formation and forming the film while rotating the disk 5, the film can be formed so that the film thickness changes in the radial direction of the disk.

Next, the manufactured disk will be explained with reference to FIG. 1. The substrate 1 is a glass substrate with a diameter of 5.25 inches (thickness 1.2 mm, with a pre-group of 1.6 pitch), and the first dielectric layer 2 and the second dielectric layer 4 are S
i3N4 was used. The recording layer 3 contains GeTe and 5bT.
A GeTeSb film formed by a magnetron sputtering method using a composite target of E was used. Si3
N4 was continuously formed into a film by magnetron sputtering in the same vacuum chamber as GeTeSb. The first dielectric layer 2 and the second dielectric layer 4 each have a thickness of 100 mm.
nm, set at 190 nm. The thickness of the GeTe5b recording layer 3 is 100 nm at a radius of 30 mm.

The film was formed to have a length of 601 m at a radius of 60 mm.

Attempts were made to record, reproduce, and erase data on the resulting disc. The disk was rotated at a constant rotational speed of 240 rpm, and override was performed using modulated laser power as shown in FIG. The recording frequencies were 4MH2 and 5MH2, and the recording power level was 20mW.

The erase power level was set to 8 mW. When A--parite was applied to the innermost and outermost peripheries of the disk, characteristics with an erasure rate of 25' CIB or more were obtained in both cases.

On the other hand, in a conventional disk having a recording layer having a constant thickness in the radial direction of the disk, that is, a constant cooling rate, the erasure rate decreased at the outer periphery at the constant recording/erasing power level used here.

[Effects of the Invention] As explained above, the phase change optical disc of the present invention has the following effects:
Since the thickness of the recording layer changes in the radial direction of the disk, the cooling rate changes in the radial direction.

Therefore, when used at a constant rotational speed, the difference in cooling rate caused by the difference in linear velocity between the inner and outer sides of the disk is compensated for by varying the thickness of the recording layer. There is no need to change the recording/erasing conditions in accordance with the radial position of the disk, which has the effect of significantly reducing the burden on the optical disk device.

[Brief explanation of drawings]

FIG. 1 is a schematic sectional view of an embodiment of the present invention, FIG. 2 is a characteristic diagram showing the relationship between linear velocity and cooling rate during recording using the thickness of the recording layer as a parameter, and FIG. 3 is a phase change diagram of the present invention. FIG. 4 is a schematic configuration diagram of an example of a film forming apparatus used for manufacturing a molded optical disk, and FIG. 4 is a diagram showing an example of a laser power drive waveform during an override operation. 1... Substrate 2... First dielectric layer 3.
...Recording layer 4...Second dielectric layer 5...
Disk 10... Vacuum chamber 11... Evaporation source (
Sputter source> 12... Exhaust system 13... Gas inlet 14
···motor

Claims (1)

[Claims] (1) In a phase-change optical disk that records, reproduces, and erases information by utilizing a reversible phase change of an information recording film caused by laser beam irradiation, the optical disk consists of a first dielectric film sequentially formed on a substrate. 1. A phase change optical disc comprising a body layer, a recording layer, and a second dielectric layer, the thickness of the recording layer increasing from the outer circumference toward the inner circumference of the disk.