Patent Publication Number: US-2005135228-A1

Title: Film structure of a rewritable compact disc

Description:
BACKGROUND OF INVENTION  
      1. Field of the Invention  
      The invention relates to a rewritable compact disc, and more particularly, to a weather-resistant film structure of a rewritable compact disc.  
      2. Description of the Prior Art  
      As the development of the digital multimedia, the 650 MB CD-ROM that can store the audio and video data in 74 minutes is insufficient for the requirement of the video quality and the capacity. The digital versatile disk (DVD) is developed to satisfy the large capacity required by the high quality video and the digital AV multimedia.  
      For providing the DVD disc with a compatible characteristic to the CD disc, the DVD disc has a 12 cm diameter and is constructed with two 0.6 mm substrates. The film structure of a conventional DVD is shown in  FIG. 1 , that the upper and lower transparent substrates  10 ,  10 ′ are bonded with a bonding layer  12  to be a data surface and a label printed surface respectively. On the lower surface of the upper transparent substrate  10 , there are sequentially a dielectric layer  13 , a recording layer  14 , a dielectric layer  16 , a barrier layer  18  and a reflective layer  20 . The recording layer  14  is a phase-change layer utilizing the thermal energy of the laser in different intensity to heat the recording layer  14 , and transforming the recording layer  14  between the crystal phase and the amorphous phase. Since the reflectivity of the crystal phase is 10%-30% higher than that of the amorphous phase, the recorded data can be read out. The material of the dielectric layer  16  and the reflective layer  20  are generally ZnS—SiO 2  and Ag alloy respectively, and the barrier layer  18  is utilized to be an insulating layer to prevent the sulfur in the dielectric layer  16  from reacting with the Ag in the reflective layer  20 .  
      However, in the film structure of the conventional DVD, the material of the barrier layer  18  is generally Si or its compound, such as SiN, SiC and so on. The sputtering process with Si or Si compound target is utilized to form the barrier layer  18 . This kind of sputtering compound is very sensitive, and the weather-resistibility is affected with a small process variation. The sputtering process is unstable and usually causes the deterioration to affect the weather-resistibility of the disc. Hence, the present invention discloses a film structure of a rewritable compact disc to overcome the above-mentioned disadvantages.  
     SUMMARY OF INVENTION  
      It is therefore a primary objective of the claimed invention to provide a film structure of a rewritable compact disc, which disusing the conventional Si compound barrier layer and using the germanium (Ge) compound instead. The process of the film structure is easily controlled, and the stability is effectively improved. The barrier layer is not easy to deteriorate and has a better barrier result to effectively overcome the unstability of the prior art.  
      It is therefore another objective of the claimed invention to provide a film structure of a rewritable compact disc, which can effectively improve the weather-resistibility of the disc to extend the lifetime and the conserving time of the disc.  
      According to the claimed invention, a film structure of a rewritable compact disc includes a transparent substrate on which sequentially laminated a phase-change recording layer, a dielectric layer and a reflective layer; and a germanium compound barrier layer located between the dielectric layer and the reflective layer to insulate the dielectric layer and the reflective layer.  
      These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       FIG. 1  is a cross-sectional view of a rewritable compact disc according to the prior art.  
       FIGS. 2-4  are cross-sectional views of a rewritable compact disc according to the present invention.  
       FIG. 5  is an inspection data of the weather-resistibility according to the present invention. 
    
    
     
       
         
           
               
               
               
             
               
                   
                   
               
               
                   
                   
               
             
            
               
                   
                 10 
                 upper transparent substrate 
               
               
                   
                 10′ 
                 lower transparent substrate 
               
               
                   
                 12 
                 bonding layer 
               
               
                   
                 14 
                 recording layer 
               
               
                   
                 16 
                 dielectric layer 
               
               
                   
                 18 
                 barrier layer 
               
               
                   
                 20 
                 reflective layer 
               
               
                   
                 30 
                 upper transparent substrate 
               
               
                   
                 30′ 
                 lower transparent substrate 
               
               
                   
                 32 
                 bonding layer 
               
               
                   
                 34 
                 dielectric layer 
               
               
                   
                 36 
                 phase-change recording layer 
               
               
                   
                 38 
                 dielectric layer 
               
               
                   
                 40 
                 barrier layer 
               
               
                   
                 42 
                 reflective layer 
               
               
                   
                   
               
            
           
         
       
     
     DETAILED DESCRIPTION  
      The present invent relates to a barrier layer in the film structure of the compact disc, and the feature is that the barrier layer is composed of a germanium compound to improve the process stability and the weather-resistibility.  
      FIGS.  2  to  4  are cross-sectional views of a rewritable compact disc according to the present invention. Please refer to  FIG. 4 , which is a cross-sectional view of the present invention. The rewirtable compact disc includes upper and lower transparent substrates  30 ,  30 ′ bonded with a bonding layer  32 . The upper transparent substrate  30  is a data area and the lower transparent substrate  30 ′ is a label printed area. On the lower surface of the upper transparent substrate  30 , there are sequentially a dielectric layer  34 , a phase-change recording layer  36 , a dielectric layer  38 , a barrier layer  40  and a reflective layer  42 . The barrier layer  40  is used for insulating the dielectric layer  34  and the reflective layer  42 , and the barrier layer  40  is composed of a germanium compound.  
      After explaining the entire structure, the structure and manufacturing method of each layer will be described following. Please refer to FIGS.  2  to  4 . Firstly, as shown in  FIG. 2 , the transparent substrate  30 , which is made by plastic material with the injection molding method, is provided. The plastic material is generally the polycarbonate (PC), and the transparent substrate  30  is in a 0.6 mm thickness. Then, as shown in  FIG. 3 , with the sputtering method that the vacuum sputtering is commonly used, the dielectric layer  34 , the phase-change recording layer  36 , the dielectric layer  38 , the barrier layer  40  and the reflective layer  42  are sequentially coated on the transparent substrate  30 , and the semi-product of the disc is finished. The material of the dielectric layers  34 ,  38  is generally ZnS—SiO 2 , and the phase-change recording layer  36  is composed of silver (Ag), indium (In), antimony (Sb) and tellurium (Te). When irradiated by the laser, the phase-change recording layer  36  is transformed between the crystal phase and the amorphous phase, and the 0 and 1 signals are distinguished in accordance with the high reflectivity of the crystal phase and the low reflectivity of the amorphous phase. The barrier layer  40  is composed of the germanium compound, and the germanium compound is generally GeN or GeCrN. The material of the reflective layer  42  is generally Ag or Ag alloy to reflect the laser signal.  
      After finishing the semi-product of the disc, as shown in  FIG. 4 , the lower transparent substrate  30 ′ is faced to the reflective layer  42  of the upper transparent substrate  30 , and these two transparent substrates  30 ,  30 ′ are bonded together to be a DVD disc in a 1.2 mm thickness. The lower transparent substrate  30 ′ is also a transparent plastic substrate which is also commonly composed of polycarbonate, and the lower transparent substrate  30 ′ is printed a label.  
      Then, an initializing process of the DVD disc is performed to crystallize the phase-change recording layer  36 . The DVD disc is finished.  
      In the above-mentioned structure, the barrier layer  40  is used for preventing the sulfur in the dielectric layer  38  from reacting with the Ag in the reflective layer  42 . The prior art using the Si or the Si compound to be the target is unstable for sputtering process and usually causes the deterioration to affect the weather-resistibility of the disc. In the claimed invention, germanium (Ge) is utilized to be the main material of the target and effectively improves the process stability. The process is easy to control and the barrier layer has a better barrier result that can substantially enhance the weather-resistibility of the disc and improve the quality stability.  
      The claimed invention is verified in the aging test with the 80° C. temperature and the 85% relative humidity, and the specimens are the claimed disc with the Ge compound barrier layer and the conventional disc with the Si compound barrier layer. Table 1 is the test result, and the relative curve is shown in  FIG. 5 . In Table 1, PI 8  is PI sum  8  that means the sum of the data error in 8 continuous blocks, and the larger number means the more mistakes (1 block=32 Kbyte). Jitter means the stability of the written mark position and length, and the smaller number means the more accurate result.  
      According to the inspection result, the weather-resistibility of the claimed disc is more than 700 hours, and that of the conventional disc is less than 50-300 hours. The weather-resistibility is obviously improved.  
                           TABLE 1                                      PI8   Jitter                                 Time   Si compound   Ge compound   Si compound   Ge compound       (hr)   barrier layer   barrier layer   barrier layer   barrier layer                                         0   15   12   8.3   8.9       22   22   20   9.2   9.0       44   21   25   8.9   9.6       62   22   25   9.3   9.7       78   21   27   9.0   9.6       102   26   31   9.3   9.6       134   33   34   9.5   9.7       150   44   35   9.8   9.5       170   45   40   9.2   9.4       235   84   51   9.7   9.5       283   123   59   9.4   9.5       327   198   67   9.8   9.4       482   389   91   10.4   9.4       610   798   112   12.6   10.1       755   1362   218   14.5   10.6                  
 
      Hence, the barrier layer in the film structure of the rewritable compact disc of the claimed invention is altered from the Si compound to the Ge compound, and can effectively improve the process stability and the weather-resistibility of the disc to extend the lifetime and the conserving time of the disc.  
      Those skilled in the art will readily observe that numerous modifications and alterations of the device may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.