Patent Grant
6906993
The invention relates to a hybrid optical disc recording medium and particularly to a hybrid optical disc recording medium that has a read-only area and a rewritable area.
Optical disc recording media are generally for recording data. The recorded data on the optical disc may be read and retrieved by commercial optical disk drives. Conventional recordable optical discs are formed by a substrate and have their surfaces coated sequentially with a dielectric layer, a recording layer, and a reflective layer, and finally are covered by a protective overcoat.
The recording materials used by the recording media mentioned above usually include Ag—In—Sb—Te, In—Sb—Te, or Ge—In—Sb—Te. The media thus made generally are called CD-RW and are available on the market, Records on flee CD-RW generally are formed by irradiating a high power semiconductor laser of the wavelength about 780 nm. A portion of the recording layer materials being irradiated are transformed from the crystallized region to the amorphous region and result in a reliable burning effect. As the crystallized region and the amorphous region have different reflectance, signals burned on the CD-RW may be read sequentially by a lower power laser beam. The substrate of the CD-RW set forth above has wobble grooves, The frequency of the wobble grooves contains Absolute Time In Pre-groove (ATMP). The noise-signal ratio of the wobble grooves is above 36 dB before burning, and above 26 dB after burning.
In contrast, conventional CD and CD-ROM discs do not have any recording layer. All of the data are engraved in advance on stampers. Then an injection principle is employed to replicate the pits on the substrate. The substrate is plated with a reflective layer to complete the CD or CDROM disc. The information formed by the pits are read to control the rotation speed of the disc and obtain time signals. The signals formed by the pits no longer contain wobble information.
Recently there are patents suggesting to make hybrid discs to combine the read-only area formed by pits and the rewritable area formed by grooves. Such discs are generally called Hybrid Discs in the Orange Book. For the hybrid discs, one of the critical techniques is to make the electric signals regenerated from the read-only area and the rewritable area to meet the standards of the Orange Book. However on the hybrid discs designed by directly adopting the conventional technical specifications of CD or CD-RW, the electric signals regenerated from the read-only area and the rewritable area are difficult to simultaneously meet the standards of the Orange Book.
In the presently known hybrid discs, the composition of the read-only area and the rewritable area differs greatly from the conventional CD or CD-RW. For instances, U.S. Pat. Nos. 5,316,814, 5,696,758, 6,115,353 and 6,212,158 disclose various types of techniques for making the hybrid disc. They directly adopt the pre-pit and pre-groove specifications of the conventional CD and CD-RW. The differences are:
Making the stamper for a conventional hybrid disc, as shown in FIG. 1(A) generally includes forming a photoresist film 11 at a thickness ranged from 30 nm to 160 nm on a glass substrate 10; then as shown in FIG. 1(B), employing a laser beam to cut the photoresist film 11 to form pits 12 with the bottom ends reaching the surface of the glass substrate 10. The maximum depth of the pits 12 is the thickness of the photoresist layer 11. Thus to cut and form the pits 12 with the required depth does not need to control the energy of the laser beam.
However, cutting the grooves 13 is different. In order to meet the Orange Book standards, in the presently known products that adopt the groove depth of the conventional CD-ROM, to cut the groove with the depth between 30 nM and 80 nm requires strict control of laser beam energy. Taking the median value of 55 nm as the basis, the upper and the lower allowance is merely 25 nm. With so small of tolerance, production yield is very low. Moreover, there is still a distance between the bottom end of the groove 13 and the surface of the glass substrate 10, and the bottom end of the groove is pointed because of We characteristics of the laser beam. The pointed bottom end of the groove results in not desirable signal regeneration and burning.
After having fished the manufacturing processes set forth above, the back surface of the finished product is plated with silver or nickel to form the master disc. The master disc then is polished on the back surface and cut to form the stamper for producing the hybrid optical discs.
For the engraving machines now available, to engrave the pits and the grooves of two different depths and widths on the same photoresist film is very difficult. As a result, production cost for such type of stamper is very high and control of the yield is very difficult. Therefore it is critical to develop an improved hybrid optical disc.
In view of the aforesaid disadvantages of the difficulty to precisely engrave two different depths and widths for the pits and the grooves on the photoresist film that incurs to the conventional manufacturing processes that employing the stamper to make the hybrid optical discs, the object of the invention is to provide a hybrid optical disc recording medium that has the same depth for the pits and the grooves.
The hybrid optical disc recording medium according to the invention has pre-pits in the read-only area with a depth ranging from {fraction (1/10)} to ⅕ of the wavelength and a width ranging from ¼ to ½ of the track pitch. In the rewritable area, the pre-grooves have a depth ranging from {fraction (1/10)} to ⅕ of the wavelength and a width ranging from ½ to ⅞ of the track pitch.
Experiments prove that electric signals regenerated in the read-only area and the rewritable area of the hybrid optical disc recording medium according to the invention all meet the standards of the specifications.
The foregoing, as well as additional objects, features and advantages of the invention will be more readily apparent from the following detailed description, which proceeds with reference to the accompanying drawings.
FIG. 1(A) is a cross section of a glass substrate for a conventional hybrid optical disc before making the master mold, with a photoresist film formed thereon.
FIG. 1(B) is a cross section of a glass substrate for a conventional hybrid optical disc with the photoresist film etched to form pits in the read-only area and the grooves in the rewritable area. The depths of the grooves do not reach the glass substrate, thus result in difficult control of the cutting depth by the laser, and pointed bottom ends.
Referring to
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The width FWHM1 of the pre-pits 26 may be in the range between {fraction (3/16)} and ½ of the track pitch (or from 300 nm to 800 nm), and the width FWHM2 of the pre-groves 29 may be in the range between ½ and ⅞ of the track pitch (or from 800 nm to 1400 nm).
Preferably, the width FWHM1 is in the range between ¼ and {fraction (7/16)} of the track pitch (or from 400 nm to 700 nm), and the width FWHM2 is in the range between {fraction (9/16)} and ¾ of the track pitch (or from 900 nm to 1200 nm).
Referring to
Refer to
Test results of the embodiments:
The actual example being made for the hybrid optical disc medium:
A substrate is made by injection molding and has the radius of 120 mm, the thickness of 1.2 mm and the reflective index 1.58. There are wobble grooves formed on the substrate with the track pitch of 1.6 nm between the centers of a pair of adjacent tracks. The depth of the pits and the grooves in the read-only area is 100 nm. The width of half depth of tile pits in the read-only area is 600 nm, while the width of half depth of the grooves in the rewritable area is 800 nm. The diameter of the whole rewritable area is in the range between 60 and 118 mm.
The laminated layers is made by commercial sputtering machines. The operation vacuum is 7.0×10−3 mbar and is filled with argon gas during sputtering. The laminated layer structure formed on the substrate includes, sequentially, a lower dielectric layer, a recording layer, an upper dielectric layer, and a reflective layer, and finally a protective overcoat. The material of the dielectric layers is the alloy of ZnS—SiO2 and is coated with the sputtering power of 3 kW. The material of the recording layer is the alloy of Ag—In—Sb—Te and is coated with the sputtering power of 0.5 kW. The material of the reflective layer is Al-alloy and is coated with the sputtering power of 6 kW. The material of the protective overcoat is a resin curable by ultraviolet light and laid on the reflective layer by spin coating, and is formed by exposing through an ultraviolet light exposing machine. Finally, the disc is initialized by means of an initializer.
(Testing of the Hybrid Optical Disc Recording Medium)
EFM signals are written on the rewritable area of the hybrid optical disc recording medium by means of a commercial burner (YAHAMA 8824S). Then a CD-CATS testing machine is used to test signals in die read-only area and the written rewritable area. Test items include the error rate (BLER), high frequency modulation rate (I11/Itop), reflectance, push-pull, jitter, and average wobble amplitude (NWA). The test values of the parameters set forth above are shown in Table 1 below.
Methods of making and testing the disc are same as the ones of the example 1. The pre-pits in the read-only area also are not connected by connecting grooves. However, the depth of the pits is changed to 80 nm, and the width of the half-depth groove in the rewritable area is 900 nm. The finished disc thus made is written and read by means of the same optical disc burner.
Methods of making and testing the disc are same as the ones of the example 1. However, the depth of the pits is changed to 120 nm, and the width of the half-depth groove in the rewritable area is 1200 nm. The pits in the read-only area are connected by connecting grooves which have a depth of 30 nm. The finished disc thus made is written and read means of the same optical disc burner.
Methods of making and testing the disc are same as the ones of the example 1. The pre-pits in the read-only area also are not connected by connecting grooves. However, the depth of the pits is changed to 160 nm, and the width of the half-depth groove in the rewritable area is 1400 nm. The finished disc thus made is written and read by means of the same optical disc burner.
Methods of making and testing the disc are same as the ones of the example 1, however the half-depth groove in the rewritable area decreases to 600 nm.
Actual test conditions and results are shown in Table 1 and Table 2 below:
Test results in the above tables indicate that, except for the example 5, for those examples that have the same depth of grooves and pits, all of the regenerated electric signals meet the specifications of the Orange Book. Only example 5 fails. It is caused by the width of the half-depth pre-grooves being only 600 nm and resulting in too low of reflectance. As a result, it could not be written by the commercial burner.
While the preferred embodiments of the invention have been set forth for the purpose of disclosure, modifications of the disclosed embodiments of the invention as well as other embodiments thereof may occur to those skilled in the art. Accordingly, the appended claims are intended to cover all embodiments which do not depart from the spirit and scope of the invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 90114596 A | Jun 2001 | TW | national |
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| Number | Date | Country |
|---|---|---|
| 09106577 | Apr 1997 | JP |
| Number | Date | Country | |
|---|---|---|---|
| 20030007447 A1 | Jan 2003 | US |
