Patent Publication Number: US-2003223349-A1

Title: Optical recordable medium and process of recording thereon

Description:
BACKGROUND OF THE INVENTION  
       [0001] 1. Field of Invention  
       [0002] The present invention relates to an optical recordable medium and a process of recording on the same. More particularly, the present invention relates to a recordable disc made from inorganic material, which is adapted to record data by an optical method.  
       [0003] 2. Description of Related Art  
       [0004] A recordable disc has many advantages, such as high storage capacity, easy conservation, low cost and so on. Therefore, the recordable disc is gradually replacing the traditional magnetic storage medium and is becoming an indispensable storage medium for modem people. Traditionally, an organic dye is used to form a recording layer of the recordable disc. When a light beam with a specific wavelength irradiates the organic dye, the organic dye absorbs the light and then changes (vary) its property or structures. Therefore, the light beam having a specific wavelength can be used to write data onto the recordable disc. Since the environment is full of light with various wavelengths, especially the sunlight, the organic dye of the recording layer can easily absorb the light with the specific wavelength to slowly decay its property or structure. Consequently, the lifetime of the recordable disc is limited.  
       [0005] Besides, the large molecular size of the organic dye in the recording layer causes additional problems. One is that the groove and space of a future high-density recording media is going to be narrower, hence it&#39;s hard to accommodate an organic dye with a large molecular size by spin coating. Furthermore, the higher recording density requires a higher recording speed for a future high-density recording media. However, it is difficult to unite the higher recording speed and the long time stability requirements of the organic dye.  
       [0006] A data is written into an inorganic recording layer of a recordable medium by absorbing the energy of the light beam, and a optical state change of the inorganic recording layer occurs. For example, an ablation recordable disc is disclosed in U.S. Pat. No. 4,451,914 and U.S. Pat. No 4,451,915. In the ablation recordable disk, a hole is formed on a reflective recording layer by a laser beam. Moreover, alloying of a bi-layer is disclosed in U.S. Pat. No 4,499,178, in which an alloy layer is formed from two different metal-containing layers by a laser beam. Hence, the reflectivity of the recording layer is reversed. Furthermore, discontinuous metal films as an active layer in an ablative optical structure is disclosed in U.S. Pat. No. 5,188,923. in which a data is recorded by directing a focused energy to heat the discontinuous metal films to change the reflectivity of the active layer. The active layer is anti-reflective before writing and becomes strongly reflective after writing.  
       [0007] The disadvantage of the ablation recordable disc disclosed in U.S. Pat. No. 4,451,914 and U.S. Pat. No. 4,451,915 is that the material ablated by laser beam piles up around the hole. The recording layer is a reflective layer and the ablated hole is an anti-reflective position. The material piled around the hole scatters the reading light beam and thus errors occur.  
       [0008] The power used to form the alloy layer by two different metal containing layers in U.S. Pat. No. 4,499,178 is between 200 milliwatts and 400 milliwatts. It is impossible for a general commercial CD-R/RW driver or DVD-R/RW driver to provide such a large power. Other traditional materials for fabricating the recordable medium are not suitable to be used in such a high-power writing mode, neither.  
       [0009] Although the discontinuous metal films as the active layer in an ablative optical structure disclosed in U.S. Pat. No. 5,188,923 can be written in a low power mode, the reflectivity changing mode of the active layer that is anti-reflective before writing and becomes strongly reflective after writing is a disadvantage. Traditionally, the active (recording) layer is strongly reflective before writing data. If any defect exists on the disc as the disc is fabricated, it can be easily detected by any anti-reflective zone occurring. The active layer disclosed in U.S. Pat. No. 5,188,923 is anti-reflective, so it will be very difficult to detect any defects on the disc.  
       SUMMARY OF THE INVENTION  
       [0010] The disadvantages described above can&#39;t be overcome simultaneously for above independent cases. Therefore, the purpose of the optical recordable medium and a process of recording on the same disclosed in the present invention are to overcome the above disadvantages at the same time.  
       [0011] Because the recordable disc made from inorganic material has the disadvantages described above, therefore, the present invention provides an optical recordable medium and a process of recording on the same. The optical recordable medium comprises a general optical thin film material fitting with a newly designed film to solve the problems mentioned above and to achieve the purpose, recording once.  
       [0012] It is therefore an objective of the present invention to provide an optical recordable medium and a process of recording on the same, wherein data can be written onto the medium with a low writing power.  
       [0013] It is another an objective of the present invention to provide an optical recordable medium and a process of recording on the same, which meets the requirements of the specifications of current CD formats or DVD formats and that of a higher density recordable media in the future.  
       [0014] It is still another an objective of the present invention to provide an optical recordable medium and a process of recording on the same, which can have high reflectivity, low writing power, high signal modulation, and the same modulation polarity as the commercial optical discs.  
       [0015] In accordance with the foregoing and other objectives of the present invention, the present invention provides an optical recordable medium and a process of recording on the same. An optical recordable medium at least comprises a recording layer. The recording layer is formed on a transparent substrate. The recording layer sequentially comprises a transparent layer, a first semi-reflective layer, a dielectric layer, a reflective layer and a material layer from bottom to the top.  
       [0016] When a modulated writing beam irradiates the recording layer and data is written in a recorded area, the transparent layer and the first semi-reflective layer react to form a second semi-reflective layer. When a reading light irradiates the recorded area, the light wave phase shift from its initial state and the recorded area becomes an anti-reflective state.  
       [0017] The theory applied to the present invention is that the transmittance (reflectivity) of a light beam depends on the thickness of a material layer. While a modulated writing beam irradiates the recording layer and data is written in a recorded area, the transparent layer and the first semi-reflective layer react to form a second semi-reflective layer. When a reading light beam irradiates the unrecorded area, the reflective layer, the first semi-reflective layer, and the transparent layer reflect the light beam. However, when the reading light beam irradiates the recorded area, the light beam is only reflected by the reflective layer and the second semi-reflective layer. The total thickness of the second semi-reflective layer and the dielectric layer shift the phase of the reflected reading light beam, hence the reflectivity of the recorded area is changed.  
       [0018] In order to improve the thermal conducting character of the recording layer and to decrease the misjudgment of the recorded marks on the recording layer, a dielectric layer can be formed prior to the transparent layer to enhance the modulation of thermal profile of the recording layer.  
       [0019] Furthermore, for the purpose of increasing the reflectivity of the recording layer, a semi-reflective layer can be formed prior to the transparent layer.  
       [0020] Additionally, a transparent layer can also be formed between the dielectric layer and the semi-reflective layer to improve the thermal conducting character of the recording layer and to decrease the misjudgment of the recorded marks on the recording layer.  
       [0021] It is to be understood that both the foregoing general description and the following detailed description are by examples, and are intended to provide further explanation of the invention as claimed. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0022] The invention can be more fully understood by reading the following detailed description of the preferred embodiment, with reference made to the accompanying drawings as follows:  
     [0023] The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. In the drawings,  
     [0024]FIG. 1 is a schematic, cross-sectional diagram showing the optical recordable medium disclosed in first, second and third embodiments of the present invention;  
     [0025]FIG. 2 is a schematic, cross-sectional diagram showing the recorded optical recordable medium disclosed in the present invention;  
     [0026]FIG. 3 is a schematic, cross-sectional diagram showing the recorded optical recordable medium according to a fourth preferred embodiment of this invention;  
     [0027]FIG. 4 is a schematic, cross-sectional diagram showing the recorded optical recordable medium according to a fifth preferred embodiment of this invention; and  
     [0028]FIG. 5 is a schematic, cross-sectional diagram showing the recorded optical recordable medium according to a sixth preferred embodiment of this invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
     [0029] Reference will now be made in detail to the present preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers are used in the drawings and the description to refer to the same or like parts.  
     [0030] Reference is made to FIG. 1. FIG. 1 is a schematic, cross-sectional diagram showing the optical recordable medium disclosed in the present invention. An optical recordable medium at least comprises a recording layer  200 . The recording layer  200  is formed on a transparent substrate  202 . The recording layer  200  sequentially comprises a transparent layer  204 , a semi-reflective layer  206 , a dielectric layer  208 , a reflective layer  210  and a material layer  212 . The material used to form the transparent layer  204  comprises metal alloy, semi-conductive material, metal phosphine and metal arsenide. Specially, the material of the transparent layer  204  is silicon, germanium, germanium phosphine, indium phosphine, gallium arsenide, indium arsenide, bismuth gallium alloy, bismuth indium alloy or a combination thereof. The thickness of the transparent layer  204  is between about 1 nm and 200 nm.  
     [0031] The material used to form the semi-reflective layer  206  is metal or metal alloy. Specially, the material of the semi-reflective layer  206  is silver, aluminum, gold, chromium, copper, indium, iridium, nickel, platinum, rhenium, rhodium, tin, tantalum, tungsten or a combination thereof. The thickness of the semi-reflective layer  206  is between about 5 nm and 100 nm. The material used to form the reflective layer  210  is also metal or metal alloy. Specially, the material of the reflective layer  210  is silver, aluminum, gold, chromium, copper, indium, iridium, nickel, platinum, rhenium, rhodium, tin, tantalum, tungsten or a combination thereof. The thickness of the reflective layer  210  is between about 1 nm and 300 nm.  
     [0032] Additionally, the material used to form the dielectric layer  208  is an oxide or a sulfide of zinc, aluminum, indium, tin, titanium, magnesium, silicon, tantalum, tungsten or a combination thereof. Moreover, the material used to form the dielectric layer  208  further comprises an organic dielectric material. The thickness of the dielectric layer  208  is between about 1 nm and 300 nm. The material layer  212  is a protective layer to protect other material layers. The material layer  212  also can be a transparent layer for binding.  
     [0033] Reference is made to FIG. 2. FIG. 2 is schematic, cross-sectional diagram showing a recorded optical recordable medium disclosed in the present invention. When a modulated writing beam  300  irradiates the recording layer  302  and data is written in a recorded area, the transparent layer  304  and the semi-reflective layer  306  react to form a semi-reflective layer  314 . When a reading light irradiates the recorded area, the light wave phase will shift and the recorded area becomes an anti-reflective state.  
     [0034] The writing power used to write data in the optical recordable medium provided by the present invention is between about 5 milliwatts and 30 milliwatts. The magnitude of the writing power depends on the thickness of the designed material layer. The reflectivity of the recording layer is between about 0.2 and 0.65, and the largest variation of the reflectivity between before writing and after writing is sixty percent. The carrier-noise ratio (CNR) of the recordable medium is higher than 40 dB, generally speaking, the CNR value is 60 dB.  
     [0035] The theory applied to the present invention is that the transmittance (reflectivity) of a light beam depends on the thickness of a material layer. While a modulated writing beam  300  irradiates the recording layer  302  and data is written in a recorded area, the transparent layer  304  and the semi-reflective layer  306  react to form a semi-reflective layer  314 . When a reading light beam irradiates the unrecorded area, the reflective layer  310 , the semi-reflective layer  314 , and the transparent layer  304  reflect the light beam. However, when the reading light beam irradiates the recorded area, the light beam is only reflected by the reflective layer  310  and the semi-reflective layer  314 . The total thickness of the semi-reflective layer  314  and the dielectric layer  308  shift the phase of the reading light beam, hence the reflectivity of the recorded area is changed.  
     [0036] In order to improve the thermal conducting character of the recording layer and to decrease the misjudgment of the recorded marks on the recording layer, a dielectric layer can be formed prior to the transparent layer  304  to enhance the modulation of the thermal profile of the recording layer.  
     [0037] Furthermore, for the purpose of increasing the reflectivity of the recording layer, a semi-reflective layer can be formed prior to the transparent layer  304 .  
     [0038] Additionally, a transparent layer can also be formed between the dielectric layer  308  and the semi-reflective layer  306  to improve the thermal conducting character of the recording layer and to decrease the misjudgment of the recorded marks on the recording layer.  
     [0039] The thickness of the material layer disclosed in the present invention depends on requirement. Because the feature of the present invention is that the total thickness of the semi-reflective layer and the dielectric layer shifts the phase of the reading light beam and the reflectivity of the recorded area is changed, therefore, the thickness of all material layers disclosed above-mention is just an exemplification, for example, the thickness of the material layers in the recording layer is changed and the recording layer becomes anti-reflective prior to writing. The thickness of partial material layer maybe beyond the range disclosed forgoing. The writing power will be lower than about 1 milliwatt in this mode.  
     [0040] Embodiment 1  
     [0041] Reference is made to FIG. 1. The optical recordable medium at least comprises a recording layer  200 . The recording layer  200  is formed on a transparent substrate  202 . The recording layer  200  sequentially comprises a transparent layer  204 , a semi-reflective layer  206 , a dielectric layer  208 , a reflective layer  210  and a material layer  212 . The transparent substrate  202  is a polycarbonate (PC) substrate having a thickness of about 1.2 mm. The transparent layer  204  is a silicon thin layer. The thickness of the transparent layer  204  is between about 10 nm and 100 nm. The semi-reflective layer  206  is a thin gold layer. The thickness of the semi-reflective layer  206  is between about 7 nm and 30 nm. The dielectric layer  208  is a ZnS—SiO2 complex thin layer. The thickness of the dielectric layer  208  is between about 10 nm and 150 nm. The reflective layer  210  is aluminum thin layer. The thickness of the reflective layer  210  is between about 10 nm and 100 nm. The material layer  212  is a protective layer.  
     [0042] The optical recordable medium is tested with a 4× writing speed on a dynamic tester inside which is a commercial CD-R/RW drive with a 780 nm read/write wavelength. The optimum writing power is between about 14 milliwatts and 20 milliwatts. The test result is that the reflectivity of the recording layer is between about 0.2 and 0.65, and the largest variation of the reflectivity between before writing and after writing is about sixty percent. The carrier-noise ratio (CNR) of the recordable medium is higher than about 45 dB.  
     [0043] Embodiment 2  
     [0044] Reference is made to FIG. 1. The optical recordable medium at least comprises a recording layer  200 . The recording layer  200  is formed on a transparent substrate  202 . The recording layer  200  sequentially comprises a transparent layer  204 , a semi-reflective layer  206 , a dielectric layer  208 , a reflective layer  210  and a material layer  212 . The transparent substrate  202  is a polycarbonate (PC) substrate having a thickness of about 0.6 mm. The transparent layer  204  is a silicon thin layer. The thickness of the transparent layer  204  is between about 10 nm and 100 nm. The semi-reflective layer  206  is a gold thin layer. The thickness of the semi-reflective layer  206  is between about 7 nm and 30 nm. The dielectric layer  208  is a ZnS—SiO2 complex thin layer. The dielectric layer  208  also could be an organic dielectric material. The thickness of the dielectric layer  208  is between about 10 nm and 150 nm. The reflective layer  210  is gold thin layer. The thickness of the reflective layer  210  is between about 10 nm and 100 nm. The material layer  212  is also a polycarbonate (PC) substrate having 0.6 mm thickness.  
     [0045] The optical recordable medium is tested with a 1× writing speed on a dynamic tester Pulsetech DDU-1000 with a 650 nm read/write wavelength. The optimum writing power is between about 11 milliwatts and 20 milliwatts. The test result is that the reflectivity of the recording layer is between about 0.2 and 0.65, and the largest variation of the reflectivity between before writing and after writing is about sixty percent. The carrier-noise ratio (CNR) of the recordable medium is higher than about 60 dB.  
     [0046] Embodiment 3  
     [0047] Reference is made to FIG. 1. The optical recordable medium at least comprises a recording layer  200 . The recording layer  200  is formed on a transparent substrate  202 . The recording layer  200  sequentially comprises a transparent layer  204 , a semi-reflective layer  206 , a dielectric layer  208 , a reflective layer  210  and a material layer  212 . The transparent substrate  202  is a polycarbonate (PC) substrate having 1.2 mm thickness. The transparent layer  204  is a silicon thin layer. The thickness of the transparent layer  204  is between about 10 nm and 100 nm. The semi-reflective layer  206  is a gold thin layer. The thickness of the semi-reflective layer  206  is between about 7 nm and 30 nm. The dielectric layer  208  is a ZnS—SiO2 complex thin layer. The thickness of the dielectric layer  208  is between about 10 nm and 150 nm. The reflective layer  210  is also metal or metal alloy. Specially, the material of the reflective layer  210  is silver, aluminum, gold, copper, or combinations thereof. The thickness of the reflective layer  210  is between about 10 nm and 100 nm. The material layer  212  is a protective layer.  
     [0048] The optical recordable medium is tested with a 4× writing speed on a dynamic tester inside which is a commercial CD-R/RW drive with a 780 nm read/write wavelength. The optimum writing power is between about 11 milliwatts and 20 milliwatts. The test result is that the reflectivity of the recording layer is between about 0.2 and 0.65, and the largest variation of the reflectivity between before writing and after writing is about sixty percent. The carrier-noise ratio (CNR) of the recordable medium is higher than about 45 dB, and the highest value is about 64 dB.  
     [0049] Embodiment 4  
     [0050] Reference is made to FIG. 3. The optical recordable medium at least comprises a recording layer  400 . The recording layer  400  is formed on a transparent substrate  402 . The recording layer  400  sequentially comprises a dielectric layer  403 , a transparent layer  404 , a semi-reflective layer  406 , a dielectric layer  408 , a reflective layer  410  and a material layer  412 . The transparent substrate  402  is a polycarbonate (PC) substrate having a thickness of about 0.6 mm. The transparent layer  404  is a silicon thin layer. The thickness of the transparent layer  404  is between about 10 nm and 100 nm. The semi-reflective layer  406  is a gold thin layer. The thickness of the semi-reflective layer  406  is between about 7 nm and 30 nm. The dielectric layer  408  is a ZnS—SiO2 complex thin layer. The dielectric layer  408  also could be an organic dielectric material. The thickness of the dielectric layer  408  is between about 10 nm and 150 nm. The reflective layer  410  is gold thin layer. The thickness of the reflective layer  410  is between about 10 nm and 100 nm. The material layer  412  is also a polycarbonate (PC) substrate having a thickness of about 0.6 mm.  
     [0051] The material of the dielectric layer  403  is same as the material of the dielectric layer  408  but the thickness is between about 5 nm and 200 nm. The purpose of the dielectric layer  403  is to improve the thermal conductingcharacter of the recording layer and to decrease the misjudgment of the recorded marks on the recording layer.  
     [0052] The optical recordable medium is tested with a 1× writing speed on a dynamic tester Pulsetech DDU-1000 with a 650 nm read/write wavelength. The optimum writing power is between about 11 milliwatts and 20 milliwatts. The test result is that the reflectivity of the recording layer is between about 0.2 and 0.65, and the largest variation of the reflectivity between before writing and after writing is about sixty percent. Compared with the character of the optical recordable medium described in embodiment 2, the jitter of the recorded marks decreases by about 0.5-2%.  
     [0053] Embodiment 5  
     [0054] Reference is made to FIG. 4. The optical recordable medium at least comprises a recording layer  500 . The recording layer  500  is formed on a transparent substrate  502 . The recording layer  500  sequentially comprises a semi-reflective layer  503 , a transparent layer  504 , a semi-reflective layer  506 , a dielectric layer  508 , a reflective layer  510  and a material layer  512 . The transparent substrate  502  is a polycarbonate (PC) substrate having a thickness of about 0.6 mm. The transparent layer  504  is a silicon thin layer. The thickness of the transparent layer  504  is between about 10 nm and 100 nm. The semi-reflective layer  506  is a gold thin layer. The thickness of the semi-reflective layer  506  is between about 7 nm and 30 nm. The dielectric layer  508  is a ZnS—SiO2 complex thin layer. The dielectric layer  508  also could be an organic dielectric material. The thickness of the dielectric layer  508  is between about 10 nm and 150 nm. The reflective layer  510  is gold thin layer. The thickness of the reflective layer  510  is between about 10 nm and 100 nm. The material layer  512  is also a polycarbonate (PC) substrate having 0.6 mm thickness.  
     [0055] The material of the semi-reflective layer  503  is the same as the material of the semi-reflective layer  506  but the thickness is between about 5 nm and 100 nm. The purpose of the dielectric layer  503  is to increase the reflectivity of the recording layer and to improve the thermal conducting character of the recording layer.  
     [0056] The optical recordable medium is tested with a 1× writing speed on a dynamic tester Pulsetech DDU-1000 with a 650 nm read/write wavelength. The optimum writing power is between about 11 milliwatts and 20 milliwatts. The test result is that the reflectivity of the recording layer is between about 0.2 and 0.65, and the largest variation of the reflectivity between before writing and after writing is about sixty percent. Compared with the character of the optical recordable medium described in embodiment 2, the reflectivity of the recording layer increases by about 3-10%.  
     [0057] Embodiment 6  
     [0058] Reference is made to FIG. 5. The optical recordable medium at least comprises a recording layer  600 . The recording layer  600  is formed on a transparent substrate  602 . The recording layer  600  sequentially comprises a transparent layer  604 , a semi-reflective layer  606 , a transparent layer  607 , a dielectric layer  608 , a reflective layer  610  and a material layer  612 . The transparent substrate  602  is a polycarbonate (PC) substrate having a thickness of about 0.6 mm. The transparent layer  604  is a silicon thin layer. The thickness of the transparent layer  604  is between about 10 nm and 100 nm. The semi-reflective layer  606  is a gold thin layer. The thickness of the semi-reflective layer  606  is between about 7 nm and 30 nm. The dielectric layer  608  is a ZnS—SiO2 complex thin layer. The dielectric layer  608  also could be an organic dielectric material. The thickness of the dielectric layer  608  is between about 10 nm and 150 nm. The reflective layer  610  is gold thin layer. The thickness of the reflective layer  610  is between about 10 nm and 100 nm. The material layer  612  is also a polycarbonate (PC) substrate having a thickness of about 0.6 mm.  
     [0059] The material of the transparent layer  607  is same as the material of the transparent layer  604  but the thickness is between about 5 nm and 50 nm. The purpose of the transparent layer  607  is to improve the thermal conductingcharacter of the recording layer and to decrease the misjudgment of the recorded marks on the recording layer.  
     [0060] The optical recordable medium is tested with a 1× writing speed on a dynamic tester Pulsetech DDU-1000 with a 650 nm read/write wavelength. The optimum writing power is between about 11 milliwatts and 20 milliwatts. The test result is that the reflectivity of the recording layer is between about 0.2 and 0.65, and the largest variation of the reflectivity between before writing and after writing is about sixty percent. Compared with the character of the optical recordable medium described in embodiment 2, the jitter of the recorded position decreases by about 0.5-2%.  
     [0061] It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention cover modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents.