Recording medium having resin substrate

1. A recording medium comprising:

a resin substrate having a first thermal expansion coefficient, a center hole, a first surface, and a second surface opposite to said first surface;

a recording layer formed on said first surface of said resin substrate, said recording layer having a recording region, an inner nonrecording region formed inside the inner periphery of said recording region, and an outer nonrecording region formed outside the outer periphery of said recording region;

a protective layer formed on said first surface of said resin substrate so as to cover said recording layer; and

a thermal deformation suppressing layer formed on said second surface of said resin substrate except in an inner peripheral region having a predetermined range from said center hole, a region corresponding to said recording region, and a region corresponding to said outer nonrecording region,

said thermal deformation suppressing layer having a second thermal expansion coefficient smaller than said first thermal expansion coefficient.

2. A recording medium according to claim 1 , wherein said resin substrate is circular.

3. A recording medium according to claim 2 , wherein said thermal deformation suppressing layer is formed in the range of 13.5 to 22 mm along the radius of said resin substrate from the center thereof.

4. A recording medium according to claim 3 , wherein said thermal deformation suppressing layer is formed in the range of 17 to 22 mm along the radius of said resin substrate from the center thereof.

5. A recording medium according to claim 1 , wherein said recording layer is optically recordable.

6. A recording medium according to claim 1 , wherein said recording layer has a third thermal expansion coefficient smaller than said first thermal expansion coefficient.

7. A recording medium according to claim 6 , wherein said second thermal expansion coefficient is smaller than said third thermal expansion coefficient.

8. A recording medium according to claim 7 , wherein said thermal deformation suppressing layer is formed of SiN.

9. A recording medium according to claim 1 , further comprising a second protective layer formed on said second surface of said resin substrate so as to cover said thermal deformation suppressing layer.

10. A recording medium according to claim 1 , wherein said thermal deformation suppressing layer is bonded to said resin substrate.

11. A recording medium according to claim 1 , wherein said thermal deformation suppressing layer is formed by any one of sputtering, evaporation, and printing.

12. A recording medium comprising:

a resin substrate having a first thermal expansion coefficient, a first center hole, a first surface, and a second surface opposite to said first surface;

a recording layer formed on said first surface of said resin substrate, said recording layer having a recording region, an inner nonrecording region formed inside the inner periphery of said recording region, and an outer nonrecording region formed outside the outer periphery of said recording region;

a thermal deformation suppressing layer formed on said second surface of said resin substrate except in an inner peripheral region having a predetermined range from said first center hole, a region corresponding said recording region, and a region corresponding to said outer nonrecording region,

said thermal deformation suppressing layer having a second thermal expansion coefficient smaller than said first thermal expansion coefficient; and

a dummy resin substrate bonded to said first surface of said resin substrate, said dummy resin substrate having a second center hole aligned with said first center hole.

13. A recording medium comprising:

a resin substrate having a first thermal expansion coefficient, a first center hole, and a first surface;

a recording layer formed on said first surface of said resin substrate, said recording layer having a recording region, an inner nonrecording region formed inside the inner periphery of said recording region, and an outer nonrecording region formed outside the outer periphery of said recording region;

a dummy resin substrate bonded to said first surface of said resin substrate, said dummy resin substrate having a surface opposed to said first surface of said resin substrate and a second center hole aligned with said first center hole; and

a thermal deformation suppressing layer formed on said opposed surface of said dummy resin substrate except in an inner peripheral region having a predetermined range from said second center hole, a region corresponding to said recording region, and a region corresponding to said outer nonrecording region,

said thermal deformation suppressing layer having a second thermal expansion coefficient smaller than said first thermal expansion coefficient.

14. An optical storage device capable of at least reading information recorded on an optical recording medium, comprising:

a light source for emitting a light beam;

an optical head for focusing said light beam on said optical recording medium; and

a photodetector for generating a reproducing signal from light reflected on said optical recording medium according to said light beam;

said optical recording medium comprising:

a resin substrate having a first thermal expansion coefficient, a center hole, a first surface, and a second surface opposite to said first surface;

a recording layer formed on said first surface of said resin substrate, said recording layer having a recording region, an inner nonrecording region formed inside the inner periphery of said recording region, and an outer nonrecording region formed outside the outer periphery of said recording region;

a protective layer formed on said first surface of said resin substrate so as to cover said recording layer; and

a thermal deformation suppressing layer formed on said second surface of said resin substrate except in an inner peripheral region having a predetermined range from said center hole, a region corresponding to said recording region, and a region corresponding to said outer nonrecording region,

said thermal deformation suppressing layer having a second thermal expansion coefficient smaller than said first thermal expansion coefficient.

15. An optical storage device capable of at least reading information recorded on an optical recording medium, comprising:

a light source for emitting a light beam;

an optical head for focusing said light beam on said optical recording medium; and

a photodetector for generating a reproducing signal from light reflected on said optical recording medium according to said light beam;

said optical recording medium comprising:

a resin substrate having a first thermal expansion coefficient, a first center hole, a first surface, and a second surface opposite to said first surface;

a recording layer formed on said first surface of said resin substrate, said recording layer having a recording region, an inner nonrecording region formed inside the inner periphery of said recording region, and an outer nonrecording region formed outside the outer periphery of said recording region;

a thermal deformation suppressing layer formed on said second surface of said resin substrate except in an inner peripheral region having a predetermined range from said first center hole, a region corresponding to said recording region, and a region corresponding to said outer nonrecording region,

said thermal deformation suppressing layer having a second thermal expansion coefficient smaller than said first thermal expansion coefficient; and a dummy resin substrate bonded to said first surface of said resin substrate, said dummy resin substrate having a second center hole aligned to said first center hole.

16. An optical storage device capable of at least reading information recorded on an optical recording medium, comprising:

a light source for emitting a light beam;

an optical head for focusing said light beam on said optical recording medium; and

a photodetector for generating a reproducing signal from light reflected on said optical recording medium according to said light beam;

said optical recording medium comprising:

a resin substrate having a first thermal expansion coefficient, a first center hole, and a first surface;

a recording layer formed on said first surface of said resin substrate, said recording layer having a recording region, an inner nonrecording region formed inside the inner periphery of said recording region, and an outer nonrecording region formed outside the outer periphery of said recording region;

a dummy resin substrate bonded to said first surface of said resin substrate, said dummy resin substrate having a surface opposed to said first surface of said resin substrate and a second center hole aligned to said first center hole; and

a thermal deformation suppressing layer formed on said opposed surface of said dummy resin substrate except in an inner peripheral region having a predetermined range from said second center hole, a region corresponding to said recording region, and a region corresponding to said outer nonrecording region,

said thermal deformation suppressing layer having a second thermal expansion coefficient smaller than said first thermal expansion coefficient.

17. A recording medium comprising:

a resin substrate having a first thermal expansion coefficient, a center hole, a first surface, and a second surface opposite to said first surface;

a recording layer formed on said first surface of said resin substrate, said recording layer having a recording region, an inner nonrecording region formed inside the inner periphery of said recording region, and an outer nonrecording region formed outside the outer periphery of said recording region;

one of a protective layer or a dummy resin substrate formed on said first surface of said resin substrate so as to cover said recording layer; and

a thermal deformation suppressing layer formed on one of said second surface of said resin substrate or said dummy resin substrate, wherein said thermal deformation suppressing layer is spaced a predetermined distance from said center hole, such that an inner circumferential region lacks said thermal deformation suppressing region,

said thermal deformation suppressing layer having a second thermal expansion coefficient smaller than said first thermal expansion coefficient.