Reversible optival information-recording medium

Abstract

Phase-change type, reversible optical information recording medium, being possible for recording, reproducing, erasing, and rewriting of information, by use of a laser beam. This invention, consists of recording thin film of ternary elements, for example, containing Ge, Te, Sb/or Bi or quaternary elements containing the fourth element of Se with which a part of Te is replaced, which is established on such surface—flat substrates as glass or plastics. In this case, the component ratio of Te and Se is selected not to be excess for other elements, such as Ge, Sb/or Bi so as to be fixed as stable compounds of stoichiometric compositions of GeTe, Sb 2 Te 3 /or Bi 2 Te 3 , or GeSe, Sb 2 Se 3 /Bi 2 Se 3 when crystallized. Strictly speaking, a concentration of each component is selected to have proper ratio of the number of atoms each other so as to represent whole composition as the sum of each component. By this treatment, it is possible to have high crystallization speed and long cyclability of recording/erasing. The effect of Se is to increase the viscosity of the system and to make easily to obtain amorphous state; and moreover, by selecting of proper amount diplaced with Te, it is possible to obtain the composition of recoding film superior in both characteristics of recording (amorphization) and erasing (crystallization).

1. A rewritable optical information storage medium comprising a substrate and an information storage film of phase change material producing reversible phase changes between amorphous and crystalline state by laser irradiation,
 wherein said information storage film is a ternary stoichiometric compound selected from the group consisting of GeSb 4 Te 7 , GeSb 2 Te 4  and Ge 2 Sb 2 Te 5  in the crystalline state and sandwiched between dielectric thin films comprising ZnS.  
 
     
     
       2. A rewritable optical information storage medium comprising a substrate and an information storage film of phase change material producing reversible phase changes between amorphous and crystalline state by laser irradiation,
 wherein said information storage film is a mixture of two or more stoichiometric compounds selected from the group consisting of GeSb 4 Te 7 , GeSb 2 Te 5 , and Ge 2 Sb 2 Te 5  in the crystalline state and sandwiched between dielectric thin films comprising ZnS.  
 
     
     
       3. A rewritable optical information storage medium comprising a substrate and an information storage film of phase change material producing reversible phase changes between amorphous and crystalline state by laser irradiation,
 wherein said information storage film is a ternary stoichiometric compound of Ge 2 Sb 2 Te 5  in the crystalline state and sandwiched between dielectric thin films comprising ZnS.  
 
     
     
       4. An optical information recording medium comprising:
   a substrate,        a dielectric layer,        an information recording layer comprising Ge, Te, and Bi formed on the substrate; and a composition of the information recording layer is included in an area surrounded by a quadrangle having vertexes of composition points A   1 ( Te   38   ,Ge   59   ,Bi   3 ) , A   3 ( Te   44.5   ,Ge   52.5   ,Bi   3 ) , B   3 ( Te   55   ,Ge   2   ,Bi   43 ) , and B   1 ( Te   50   ,Ge   2   ,Bi   48 )  in a triangle diagram showing a range of composition of Ge, Te, and Bi.     
     
     
       5. The optical information recording medium according to  claim 4 , wherein a composition of the information recording layer is included in an area surrounded by a quadrangle having vertexes of composition points A 1 ( Te   38   ,Ge   59   ,Bi   3 ) , A   2 ( Te   42   ,Ge   55   ,Bi   3 ) , B   2 ( Te   53   ,Ge   2   ,Bi   45 )  and B   1 ( Te   50   ,Ge   2   , Bi   48 )  in a triangle diagram showing a range of composition of Ge, Te, and Bi.   
     
     
       6. The optical information recording medium according to  claim 4 , wherein a composition of the information recording layer is included in an area surrounded by a quadrangle having vertexes of composition points A 2 ( Te   42   ,Ge   55   ,Bi   3 ) , A   3 ( Te   44.5   ,Ge   52.5   ,Bi   3 ) , B   3 ( Te   55   ,Ge   2   ,Bi   43 ) , B   2 ( Te   53   ,Ge   2   ,Bi   45 )  in a triangle diagram showing a range of composition of Ge, Te, and Bi.   
     
     
       7. The optical information recording medium according to  claim 4 , wherein the dielectric layer comprises ZnS. 
     
     
       8. A method of one of recording, erasing, and rewriting information on a recording layer of an optical information recording medium, comprising a dielectric layer, comprising the steps of:
   changing a phase of the recording layer, which comprises Ge, Te, and Bi and a composition of the information recording layer is included in an area surrounded by a quadrangle having vertexes of composition points A   1 ( Te   38   ,Ge   59   ,Bi   3 ) , A   3 ( Te   44.5   ,Ge   52.5   ,Bi   3 ) , B   3 ( Te   55   ,Ge   2   ,Bi   43 ) , and B   1 ( Te   50   ,Ge   2   ,Bi   48 )  in a triangle diagram showing a range of composition of Ge, Te, and Bi, between amorphous phase and crystalline phase.     
     
     
       9. The optical information recording method according to  claim 8 , wherein a composition of the information recording layer is included in an area surrounded by a quadrangle having vertexes of composition points A 1 ( Te   38   ,Ge   59   ,Bi   3 ) , A   2 ( Te   42   ,Ge   55   ,Bi   3 ) , B   2 ( Te   53   ,Ge   2   ,Bi   45 ) , and B   1 ( Te   50   ,Ge   2   ,Bi   48 )  in a triangle diagram showing a range of composition of Ge, Te, and Bi.   
     
     
       10. The optical information recording method according to  claim 8 , wherein a composition of the information recording layer is included in an area surrounded by a quadrangle having vertexes of composition points A 2 ( Te   42   ,Ge   55   ,Bi   3 ) , A   3 ( Te   44.5   ,Ge   52.5   ,Bi   3 ) , B   3 ( Te   55   ,Ge   2   ,Bi   43 ) , and B   2 ( Te   53   ,Ge   2   ,Bi   45 )  in a triangle diagram showing a range of composition of Ge, Te, and Bi.   
     
     
       11. The method for one of recording, erasing, and rewriting information on a recording layer of an optical information recording medium according to  claim 8 ,
   wherein the dielectric layer comprises ZnS.     
     
     
       12. An optical information recording medium comprising:
   a substrate,        a dielectric layer,        an information recording layer comprising Ge, Te and Bi formed on the substrate; and wherein        a composition of the information recording layer shown by Te   (60-10x)   Ge   50x   Bi   (40-40x)  ( wherein  0 . 05 ≦x≦ 0 . 8   ) ; showing a range of composition of Ge, Te, and Bi.     
     
     
       13. The optical information recording medium according to  claim 12 , wherein the dielectric layer comprises ZnS. 
     
     
       14. A method for one of recording, erasing, and rewriting information on a recording layer of an optical information recording medium comprising a dielectric layer;
   comprising the steps of:        changing a phase of the recording layer, which comprises Ge, Te, and Bi and a composition of the information recording layer is shown by Te   (60-10x)   Ge   (50x)   Bi   (40-40x)  ( wherein  0 . 05 ≦x≦ 0 . 8   ) ; in a triangle diagram showing a range of composition of Ge, Te and Bi, between amorphous phase and crystalline phase.     
     
     
       15. The method for one of recording, erasing, and rewriting information on a recording layer of an optical information recording medium according to  claim 14 ,
   wherein the dielectric layer comprises ZnS.     
     
     
       16. An optical information recording medium comprising:
   a substrate;        a dielectric layer,        an information recording layer consisting of Ge, Te, and Bi formed on the substrate; and        a composition of the information recording layer is included in an area surrounded by a quadrangle having vertexes of composition points A   1  ( Te   38   ,Ge   59   ,Bi   3 )  D   1  ( Te   63   ,Ge   34   ,Bi   3 )  C   1  ( Te   70   ,Ge   2   ,Bi   28 ) , and B   1  ( Te   50   ,Ge   2   ,Bi   48 )  in a triangle diagram showing a range of composition of Ge, Te, and Bi.     
     
     
       17. The optical information recording medium according to  claim 16 , wherein the dielectric layer comprises ZnS. 
     
     
       18. A method of one of recording, erasing, and rewriting information on a recording layer of an optical information recording medium, comprising a dielectric layer,
   comprising the steps of:        changing a phase of the recording layer, consisting of Ge, Te and Bi and a composition of the information recording layer is included in an area surrounded by a quadrangle having vertexes of composition points A   1  ( Te   38   ,Ge   59   ,Bi   3 ) , D   1  ( Te   63   ,Ge   34   ,Bi   3 ) , C   1  ( Te   70   ,Ge   2   ,Bi   28 ) , and B   1  ( Te   50   ,Ge   2   ,Bi   48 )  in a triangle diagram showing a range of composition of Ge, Te, Bi, between amorphous phase and crystalline phase.     
     
     
       19. The method for one of recording, erasing, and rewriting information on a recording layer of an optical information recording medium according to  claim 18 , wherein the dielectric layer comprises ZnS.