Optical information recording medium and methods for recording, reading, and erasing information thereupon

An optical information recording medium having a light transmitting substrate and phase-change optical recording layers formed on the light transmitting substrate, each of the phase-change optical recording layers comprising:

• a phase-change recording film for recording and erasing information by a phase change caused by illumination of laser light;
• a transparent upper protective film formed on top of the phase-change recording film and for protecting the phase-change recording film against thermal deformation during recording and erasing of information;
• a transparent lower protective film formed under the phase-change recording film and for protecting the phase-change recording film against thermal deformation during recording and erasing of information;
• and
• a foundation interference film formed under the transparent lower protective film and for adjusting the transmittance of the phase-change recording film for the laser light,
• wherein recorded regions of the phase-change recording film show a transmittance that is 0.90 to 1.10 times the transmittance of unrecorded regions.

A method for recording information on an optical information recording medium having a light transmitting substrate comprising the step of:

• forming plural phase-change optical recording layers over the light transmitting substrate via transmission spacers,
• each of the phase-change optical recording layers having a top phase-change optical recording layer and non-top phase-change optical recording layers, the top phase-change optical recording layer having a first phase-change recording film for recording, reading, and erasing information by a phase change caused by illumination of laser light, and having a first transparent upper protective film formed on top of the first phase-change recording film and acting to protect the first phase-change recording film against thermal deformation during recording and erasing of information, and having a first transparent lower protective film formed under the first phase-change recording film and acting to protect the first transparent lower protective film against thermal deformation during recording and erasing of information,
• each of the non-top phase-change recording optical recording layers having a second phase-change recording film for recording and erasing information by a phase change caused by illumination of the laser light, and having a second transparent upper protective film formed on top of the second phase-change recording film and acting to protect the second phase-change recording film against thermal deformation during recording and erasing of information, and having a second transparent lower protective film formed under the second phase-change recording film and acting to protect the second transparent lower protective film against thermal deformation during recording and erasing of information, and having a foundation interference film formed under the second transparent lower protective film and acting to adjust transmittance of the second phase-change recording film for the laser light, the method further comprising the step of:
• directing laser light to the optical information recording medium from a side of the light transmitting substrate while varying focal point of the laser light, thus causing a phase change in at least one of the first and second phase-change recording films.

A method for reading information from an optical information recording medium having a light transmitting substrate comprising the step of:

• forming plural phase-change optical recording layers over the light transmitting substrate via transmission spacers,
• each of the phase-change optical recording layers having a top phase-change optical recording layer and on-top phase-change optical recording layers, the top phase-change optical recording layer having a first phase-change recording film for recording, reading, and erasing information by a phase change caused by illumination of laser light, and having a first transparent upper protective film formed on top of the first phase-change recording film and acting to protect the first phase-change recording film against thermal deformation during recording and erasing of information, and having a first transparent lower protective film formed under the first phase-change recording film and acting to protect the first transparent lower protective film against thermal deformation during recording and erasing of information,
• each of the non-top phase-change recording optical recording layers having a second phase-change recording film for recording and erasing information by a phase change caused by illumination of the laser light, and having a second transparent upper protective film formed on top of the second phase-change recording film and acting to protect the second phase-change recording film against thermal deformation during recording and erasing of information, and having a second transparent lower protective film formed under the second phase-change recording film and acting to protect the second transparent lower protective film against thermal deformation during recording and erasing of information, and having a foundation interference film formed under the second transparent lower protective film and acting to adjust transmittance of the second phase-change recording film for the laser light, the method further comprising the step of:
• directing laser light to the optical information recording medium from a side of the light transmitting substrate while varying focal point/of the laser light, thus causing a phase change in at least one of the first and second phase-change recording films.

A method for erasing information from an optical information recording medium having a light transmitting substrate comprising the step of:

• forming plural phase-change optical recording layers over the light transmitting substrate via transmission spacers,
• each of the phase-change optical recording layers having a top phase-change optical recording layer and non-top phase-change optical recording layers, the top phase-change optical recording layer having a first phase-change recording film for recording, reading, and erasing information by a phase change caused by illumination of laser light, and having a first transparent upper protective film formed on top of the first phase-change recording film and acting to protect the first phase-change recording film against thermal deformation during recording and erasing of information, and having a first transparent lower protective film formed under the first phase-change recording film and acting to protect the first transparent lower protective film against thermal deformation during recording and erasing of information,
• each of the non-top phase-change recording optical recording layers having a second phase-change recording film for recording and erasing information by a phase change caused by illumination of the laser light, and having a second transparent upper protective film formed on top of the second phase-change recording film and acting to protect the second phase-change recording film against thermal deformation during recording and erasing of information, and having a second transparent lower protective film formed under the second phase-change recording film and acting to protect the second transparent lower protective film against thermal deformation during recording and erasing of information, and having a foundation interference film formed under the second transparent lower protective film and acting to adjust transmittance of the second phase-change recording film for the laser light, the method further comprising the step of:
• directing laser light to the optical information recording medium from a side of the light transmitting substrate while varying focal point of the laser light, thus causing a phase change in at least one of the first and second phase-change recording films.