JPH0445896B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical recording medium for optically recording and reproducing information.

Conventionally, this type of optical recording medium has been prepared by providing an undercoat layer on a plastic substrate such as glass or PMMA or polycarbonate, and coating it with phthalocyanine dyes, naphthoquinone dyes, Te alloys, etc.
A recording layer such as a mixture containing Te is provided.
Subbing layers are used to obtain an optically defect-free surface or for thermal insulation.

When a large number of media with such a configuration are manufactured and recorded/reproduced, there is a problem in that some media have small read signals.

An object of the present invention is to provide an optical recording medium that does not have the above-mentioned problems.

That is, the present invention provides an optical recording medium in which a recording layer is disposed on a transparent substrate via an undercoat layer, in which the thickness of the undercoat layer is an integral multiple of λ/2n (λ is the wavelength of readout light, and n is The refractive index of the undercoat layer).

This will be explained in detail below using figures.

FIG. 1 is a sectional view of an optical recording medium, in which a recording layer 3 is arranged on a transparent substrate 1 with an undercoat layer 2 interposed therebetween, and light 4 for recording and reading is incident from the substrate 1 side. As the substrate material, synthetic resins such as PMMA and polycarbonate, glass, etc. are used. As the recording layer, a Te alloy, a mixture of Te and carbon, a plasma polymerized film containing Te, and an organic dye such as a phthalocyanine dye, squarylium dye, or naphthoquinone dye are used. As the undercoat layer, photoresist, polyimide resin, etc. are used to obtain a surface free of optical defects or for heat insulation, but the thickness of the layer has not been strictly regulated.
The inventors of the present invention produced a large number of optical recording media having such a configuration, and when performing recording and reproduction, they experienced the problem that the magnitude of the read signal varied.
When we investigated this problem, we found that the cause was as follows. Figure 2 shows the reflectance undercoat layer film thickness of a medium with a configuration in which an undercoat layer with a refractive index of 1.6 is provided on a substrate with a refractive index of 1.5, and a 70 nm recording layer with a complex refractive index of 2.3−i0.8 is provided on top of the undercoat layer. It depends. The wavelength of light incident from the substrate is 830nm,
R indicates the reflectance where the recording layer is present, and R' indicates the reflectance where the pits are formed.
It can be seen that the signal (=R-R') decreases for every odd number multiple of 130 nm, which is λ/4n (λ is the wavelength of light, and n is the refractive index of the undercoat layer). Also, it can be seen that the maximum signal is obtained at every integer multiple of 259 nm, which is λ/2n.
Figure 3 shows the dependence of medium reflectance on the thickness of the undercoat layer when the refractive index of the undercoat layer is 1.7. It can be seen that the signal becomes smaller at every odd multiple of 122 nm, which is λ/4n, and the maximum signal is obtained at every integer multiple of 244 nm, which is λ/2n.

In other words, when the refractive index of the undercoat layer is larger than that of the substrate, the signal becomes the smallest for each integer multiple of λ/4n in thickness of the undercoat layer, and the maximum signal is obtained in the undercoat layer. This is when the film thickness is an integral multiple of λ/2n.

Hereinafter, it will be explained in more detail using Examples.

Example 1 Polyimide resin (n=1.7) was coated on a glass disk with a thickness of 1.2 mm and a diameter of 200 mm, and 5-
Amino-2,3-dicyano-8-[(4-ethquin)anilino]-1,4-naphthoquinone dye (n
-ik=2.3-i0.8) was deposited to a thickness of 70 nm to fabricate an additionally writable optical disk. Four types of disks were fabricated with polyimide film thicknesses of 980 nm, 1100 nm, 1220 nm, and 1340 nm, and recording was generated by irradiating semiconductor laser light with λ = 830 nm from the substrate side, resulting in 980 nm and 1220 nm, which are integral multiples of λ/2n. The output signal was the largest and had good characteristics.

Example 2 Photoresist AZ1350 (trade name, manufactured by Shippray, n.
= 1.67) and 5-amino-2,3
-dicyano-8-[(4-ethchin)anilino]-
1,4-naphthoquinone dye (n-ik=2.3-i0.8)
was deposited to a thickness of 70 nm. When recording and reproducing were performed by irradiating a semiconductor laser beam of λ=830 nm from the substrate side, the signal output was the largest even though the photoresist film thickness was an integral multiple of λ/2n, and the characteristics were good.

As described above, according to the present invention, an optical recording medium with good characteristics can be obtained.

[Brief explanation of drawings]

Figure 1 is a cross-sectional view showing a partial structure of an optical recording medium, Figure 2 is a diagram showing the dependence of the reflectance of an optical recording medium on the thickness of the undercoat layer, and Figure 3 is a diagram showing the dependence of the reflectance of the optical recording medium on the thickness of the undercoat layer. It is a figure showing thickness dependence. In the figure, 1 is a transparent substrate, 2 is an undercoat layer, 3 is a recording layer, and 4 is a reproduction light.

Claims (1)

[Claims] 1. In an optical recording medium in which a recording layer is disposed on a transparent substrate via an undercoat layer, the thickness of the undercoat layer is an integral multiple of λ/2n (λ is the wave number of the readout light, 1. An optical recording medium, wherein n is a refractive index of an undercoat layer.