CN1254914A - 光学信息记录介质 - Google Patents

光学信息记录介质 Download PDF

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Publication number
CN1254914A
CN1254914A CN99124895A CN99124895A CN1254914A CN 1254914 A CN1254914 A CN 1254914A CN 99124895 A CN99124895 A CN 99124895A CN 99124895 A CN99124895 A CN 99124895A CN 1254914 A CN1254914 A CN 1254914A
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China
Prior art keywords
medium
recording medium
layer
thermal diffusion
optical data
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CN99124895A
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CN1174399C (zh
Inventor
宇野真由美
山田升
长田宪一
草田英夫
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Panasonic Holdings Corp
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Matsushita Electric Industrial Co Ltd
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Publication of CN1254914A publication Critical patent/CN1254914A/zh
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Abstract

通过实现可以提高记录介质的冷却能力和降低重写标记畸变的高透过率的介质,提供更高速度、高记录密度的光学信息记录介质。在基板1上,顺序沉积保护层2、界面层3、利用激光照射使光学特性可逆变化的记录层4、界面层5、透过波长λ的所述激光的透光型反射层6和热扩散层7。在热扩散层7的折射率为n时,将热扩散层7的膜厚d设定在0< d≤(5/16)λ/n或(7/16)λ/n≤d≤(1/2)λ/n的范围内。

Description

光学信息记录介质
本发明涉及使用激光照射等光学装置可以进行高密度、高速度的信息记录重放和重写的光学信息记录介质。
光学信息记录介质是利用在记录材料上通过局部照射激光产生的不同光学特性作为记录状态的介质。在使用这种光学特性的变化是可逆的材料的情况下，可以进行信息记录的重写。作为重写型的介质，一般来说，众所周知有光磁型记录介质和相变型记录介质。这些光记录介质可以记录大容量的信息，同时可以进行高速的记录、重放和重写，并且由于携带性良好，所以在高度信息化的社会中，可以认为今后对它的需求将日益增加，并期望更加大容量化、高速化。
相变型记录介质是利用在结晶状态与非晶状态下相对于特定波长的光的不同反射光量的不同作为记录状态的记录介质，通过调制激光的输出功率，可以同时进行记录的删除和写上记录。因此，可以容易进行高速的信息信号的重写。
图9表示以往的相变型记录介质的层结构一例。如图9所示，以往的相变型记录介质由基板1、在基板1上顺序沉积的保护层2、记录层4、保护层8和反射层6构成。作为基板1，可使用聚碳酸酯、PMMA等树脂或玻璃等，在基板1上，形成用于引导激光的导入槽。记录层4有光学特性不同的状态，由可以使该状态之间可逆地改变而得到的物质构成。在重写型的相变型光记录材料的情况下，作为保护层4的材料，一般使用以Te、Se作为主要成分的硫族化合物材料，例如以Te-Sb-Ge、Te-Sn-Ge、Te-Sb-Ge-Se、Te-Sn-Ge-Au、Ag-In-Sb-Te、In-Sb-Se、In-Te-Se等作为主要成分的材料。反射层6一般由Au、Al、Cr等金属或这些金属的合金构成，以散热效果和保护层4的有效的光吸收为目的来设置。此外，在该图中虽然进行了省略，但以防止光学信息记录介质的氧化、腐蚀和尘埃等的附着为目的，在反射层6上设有外涂层，或使用紫外线固化树脂作为粘接剂，一般可采用粘结虚设基板的结构。保护层2、8具有防止记录层4的材料氧化、蒸发和变形的保护记录层4的功能。此外，由于通过调节保护层2、8的膜厚，可以调节记录介质的吸收率和记录部分与删除部分之间的反射率差，所以保护层2、8还具有调节记录介质的光学特性的功能。作为构成保护层2、8材料的条件，不仅要满足上述目的，而且记录层4的材料与基板1的粘接性也要良好。保护层2、8本身必须是不产生裂纹的耐久性良好的膜。此外，在连接这些保护层2、8与记录层4并使用的情况下，还必须是不损害记录层4材料的光学变化的材料。作为保护层2、8的材料，除了ZnS等硫化物、SiO2、Ta2O5、Al2O3等氧化物、Ge-N、Si3N4、Al3N4等氮化物、Ge-O-N、Si-O-N、Al-O-N等氮氧化物外，还建议使用碳化物、氟化物等介电体，或这些介电体的适当组合。一般来说，常采用ZnS-SiO2。
以往，在进行记录的重写情况下，已知重写后的标记位置被微妙地偏移，产生所谓的重写畸变的现象。产生该畸变的原因在于，由于重写前的记录层4的状态为非晶或结晶状态，所以激光照射时的温度上升方式不同，重写后的标记会偏离预定长度。就是说，如果标记为非晶状态，那么在重写前的状态为结晶状态的部分中，必然存在相变化成非晶状态造成的潜热，但由于在重写前的状态为非晶状态的部分中不需要这种潜热，所以多余的热量会使预定长度以上的记录层4非晶化。为了解决这个问题，在记录层4为非晶状态时的记录层4的光吸收率为Aa，记录层4为结晶状态时的记录层4的光吸收率为Ac时，使Ac/Aa保持在比1大的某个范围内，采用称为可吸收修正的结构。由此，由于可以有助于结晶部分的温度上升，所以重写后的标记区域内的温度上升变得均匀，难以产生标记应力。
作为实现Ac/Aa＞1的方法，提出了几种方法。例如，提出了非晶状态的反射率Ra比结晶状态的反射率Rc大的结构(Rc＜Ra)。在这种情况下，即使非晶状态与结晶状态之间的反射率差Ra-Rc增大，也可以增大Ac/Aa值。具体地说，例如在图7中，通过在基板1和保护层2之间设置其它层，使该层的光学常数处于某个一定的范围内，就可以实现Rc＜Ra。
此外，即使在Rc＞Ra的情况下，也可以实现Ac/Aa＞1。作为该方法，已知主要有透光型和光吸收型。透光型是在介质上产生透过率，当记录层处于非晶状态时的介质透过率为Ta，记录层处于结晶状态时的介质透过率为Tc时，采用具有0＜Tc＜Ta结构的方法。光吸收型是在介质中设置产生吸收的层，当该层的光吸收在记录层处于非晶状态时为Aa2，在记录层处于结晶状态时为Ac2时，采用具有0＜Ac2＜Aa2结构的方法。具体地说，在透光型的情况下，例如在图9中，反射层6薄，可以通过产生透光来实现。而在光吸收型的情况下，例如在图9中，在反射层6和保护层8之间通过插入吸收光的层来实现。
在有Rc＜Ra的反射率结构的介质的情况下，如上所述，具有容易设计Ac/Aa＞1结构的优点，但与有Rc＞Ra的反射率结构的介质相比，由于非晶部分与结晶部分的反射率之和已经增大，所以有信号重放时的噪音容易增加的缺点。在有Rc＞Ra的反射率结构的介质情况下，不容易产生这样的缺点，但不利于使Ac/Aa的值更大。因此，根据必要的介质，期望分别使用这些方法。
有关满足Rc＞Ra并且满足0＜Tc＜Ta的透光型的结构，在以往提出过几个改进建议。
例如，在特开平8-050739号公报中披露了有记录层和透光型的反射层，将有助于透光型反射层的热扩散的热扩散辅助层连接设置在反射层上的技术。但是，在该公报中，未记述使热扩散辅助层具有积极的光学效果的有关技术，其膜厚处于不妨碍光学设计的范围。此外，在特开平9-91755号公报中披露了在透光型反射层上设置电介质层的技术。但是，在这种情况下，电介质层是为了减小相位差而设置的层，在该公报中，未记述通过设置电介质层产生的有关热效果，此外，也未记述通过调节其膜厚来获得光学上的效果的情况。
此外，作为应用透光型介质的实例，已知所谓的多层记录介质的技术。为了实现介质的大容量化，这种技术通过透明的隔离层设置两组以上的记录介质，利用仅从单侧入射激光，可以进行对整个记录介质的存取。如果采用该技术，那么可以增大激光入射方向上的记录密度，可以增大作为整个多层记录介质的容量。
由于透光型的结构在介质中不流通的多余的热比较少，所以在重复特性和相邻删除特性方面有利。但是，由于反射层薄，所以记录层难以急速地进行变热后的冷却，存在难以形成标记的问题。而且，特别在满足Rc＞Ra的结构的情况下，而在根本上使Ac/Aa的值非常大是困难的。此外，为了构成多层记录介质，在设计配置在激光入射侧的透光型介质时，在以往，为了使透过率充分大，就必须使记录层的膜厚薄。但是，在记录层非常薄的情况下，由于结晶化变得困难，所以难以使高透过率和高删除率兼容。此外，没有对进一步提高透光型介质的重复记录特性的技术进行过考虑的实例，而且需要提高重复记录特性的新技术。
为了解决以往技术中的上述课题，本发明的目的在于提供可以使记录介质的冷却能力提高和重写标记畸变下降，并且还可以进一步高速度、高密度记录的光学信息记录介质，和提供可以使高透过率和高删除率兼容的多层记录介质用的透光型记录介质。
为了实现上述目的，本发明的光学信息记录介质的结构包括通过激光照射其光学特性可逆变化的记录层，透过波长为λ的所述激光的反射层和与所述反射层连接设置的热扩散层，其特征在于，在所述热扩散层的折射率为n时，所述热扩散层的膜厚d在0＜d≤(5/16)λ/n或(7/16)λ/n≤d≤(1/2)λ/n的范围内。按照该光学信息记录介质的结构，可以进一步提高记录层的冷却能力，同时由于通过Ac/Aa值的提高，可以降低重写畸变，所以可以使记录进一步高速化、高密度化。
此外，在上述本发明的光学信息记录介质的结构中，构成热扩散层材料在500K的热传导系数最好在0.05W/m·K以上。按照该优选例，可以使热扩散层的冷却效果更大。
此外，在上述本发明的光学信息记录介质的结构中，在信息的记录重放中使用的激光波长中，热扩散层的折射率最好在1.6以上。按照该优选例，可以使热扩散层的Ac/Aa提高效果更有效。
此外，在上述本发明的光学信息记录介质的结构中，对于用于信息记录重放中的激光的波长，热扩散层的吸收系数最好在1.5以下。按照该优选例，由于可以将热扩散层的发热抑制得更小，所以可以使热扩散层的冷却效果更有效。
此外，在上述本发明的光学信息记录介质的结构中，热扩散层最好包括从Al-N、Al-O-N、Al-C、Si、Si-N、SiO2、Si-O-N、Si-C、Ti-N、TiO2、Ti-C、Ta-N、Ta2O5、Ta-O-N、Ta-C、Zn-O、ZnS、ZnSe、Zr-N、Zr-O-N、Zr-C和W-C组成的组中选择的至少一种。
此外，在上述本发明的光学信息记录介质的结构中，反射层最好包括从Au、Ag和Cu组成的组中选择的至少一种。按照该优选例，可以增大Ac/Aa的值，同时由于热传导系数大，所以即使膜厚薄也可以获得大的冷却能力。
此外，在上述本发明的光学信息记录介质的结构中，反射层的厚度可以在1nm以上20nm以下。在反射层的厚度不足1nm的情况下，难以使膜达到均匀的层状，热的、光学的反射层的效果下降，而在反射层厚度大于20nm的情况下，由于介质的光透过变小，所以难以实现光吸收补偿(Ac/Aa＞1)。
此外，在上述本发明的光学信息记录介质的结构中，记录层的厚度可以在3nm以上20nm以下。在记录层的厚度不足3nm的情况下，记录材料难以达到均匀的层状，在非晶和结晶之间难以产生有效的相变化，而在记录层的厚度在20nm以上的情况下，由于记录层膜面内的热扩散增大，所以在按高密度进行记录时容易发生相邻删除。
此外，在上述本发明的光学信息记录介质的结构中，记录层可以由包括从Te、Se和Sb组成的组中选择的至少一种的相变化材料构成。
此外，在上述本发明的光学信息记录介质的结构中，相对于激光的光学信息记录介质的平均透光率可以在40％以上80％以下，而且在50％以上70％以下更好。其中，将平均透光率定义为介质中信号处于记录状态下的透过率(以下，将平均透光率简单地记为‘透光率’)。按照该优选例，从介质观察，在与激光入射侧相反的一侧上设有其它记录介质的情况下，只要有来自一侧的激光照射，就能够使双方的介质记录重放。在采用这种所谓的多层记录介质结构的情况下，由于可以有效地增大介质的记录容量，所以非常好。
此外，在这种情况下，在与激光入射侧相反的一侧上，可以设置至少一个其它的光学信息记录介质。按照该优选例，可以实现更大的高密度介质。
此外，在上述本发明的光学信息记录介质的结构中，可以设有至少与记录层的一侧连接，具有促进记录层结晶化效果的界面层。
特别在透光型介质中按增大透光率来进行设计的情况下，由于记录层的膜厚变得非常薄，所以难以进行记录层的结晶化。但是，在连接记录层设置界面层的情况下，可以缩短记录层材料结晶化需要的时间，可以使记录进一步高速化。
此外，在这种情况下，界面层最好是至少包含N的材料。由于包含N的材料致密性优良，所以可以大幅度地缩短记录层材料结晶化需要的时间。
图1表示本发明一实施例中的光学信息记录介质的层结构剖面图。
图2表示在本发明一实施例的光学信息记录介质的制造中使用的成膜装置一例的示意图。
图3表示本发明一实施例的光学信息记录介质的热扩散层膜厚与光学特性关系的计算结果的图。
图4表示本发明一实施例的光学信息记录介质的热扩散层膜厚与Ac/Aa关系的计算结果的图。
图5表示本发明一实施例的另一光学信息记录介质的热扩散层膜厚与光学特性关系的计算结果的图。
图6表示本发明一实施例的另一光学信息记录介质的热扩散层膜厚与Ac/Aa关系的计算结果的图。
图7表示本发明一实施例的多层记录介质的层结构剖面图。
图8表示由本发明一实施例的两组介质构成的多层记录介质的层结构剖面图。
图9表示以往的相变型记录介质的层结构一例的剖面图。
以下，用实施例更具体地说明本发明。
<第一实施例>
图1是表示本发明第一实施例的光学信息记录介质的层结构的剖面图。
如图1所示，本实施例的光学信息记录介质由基板1、在基板1上顺序沉积的保护层2、界面层3、记录层4、界面层5、透光型反射层6和热扩散层7构成。其中，记录层4由通过激光照射使光学特性可逆变化的材料构成。
再有，本发明不限于上述结构，也可以是配备记录层4、透光型反射层6和与透光型反射层6连接的热扩散层7的结构。例如，可以如下构成：在图1中，在界面层5和透光型反射层6之间可设置保护层等其它层；用整个界面层3替换保护层2；或不设置界面层3；等等，在各种结构中都可采用本发明。
作为基板1的材料，可以使用聚碳酸酯、PMMA等树脂或玻璃等。此外，在基板1中可以形成用于导入激光的引导槽。
设置保护层2的主要目的在于调节记录层4的可有效光吸收的光学特性。作为保护层2的材料，可使用ZnS等硫化物，SiO2、Ta2O5、Al2O3等氧化物，Ge-N、Si3N4、Al3N4等氮化物，Ge-O-N、Si-O-N、Al-O-N等氮氧化物，碳化物、氟化物等电介质，或这些物质的适当组合(ZnS-SiO2等)等，以及可实现上述目的的材料。
界面层3、5承担着防止记录层4的氧化、腐蚀、变形等的保护记录层4的作用，同时，如以下所述，通过与记录层4连接设置，还具有两个重要的作用。
界面层的第一个重要作用在于，在记录层4和保护层2的原子扩散，特别是在保护层2中含有硫磺或硫化物的情况下，具有防止这些成分向记录层4扩散的作用。通过防止这种原子扩散，使介质的重复特性飞跃性地提高。设置界面层的位置可以在记录层4的其中一侧，也可以在其两侧，但为了更有效地防止原子扩散，最好设置在两侧。仅在记录层4的其中一侧的界面上设置界面层的情况下，通过设置在热负荷大的侧，即设置在记录、删除时温度上升高的侧(多数情况下为激光入射侧)，可以提高抑制原子扩散的效果。再有，在界面层中含有的成分还有在信息重复记录后扩散到记录层4中的情况，但即使有这种情况，作为界面层的构成材料，可以使用不易妨碍记录层4光学变化的材料。
界面层的第二个重要作用在于，在与记录层4连接设置的情况下，不损害记录标记(非晶部分)的热稳定性，起到促进记录材料结晶化的作用。由于界面层具有这样的重要作用，所以可以进行更快的高速删除。尤其在将界面层设置在因激光照射记录层后冷却时所产生的冷却快速推进侧的界面上或结晶核容易形成侧的界面上的情况下，即在大多数情况下，设置在与激光入射侧相反的一侧的记录层界面上的情况下，该效果变得显著。
以上，根据界面层的两个作用，为了兼容高速下的良好重写特性和良好的重复特性这两个方面，可以将界面层设置在记录层4的两侧。但是，也有在介质的记录条件可以松的情况下，例如在低线速度、低密度条件的情况下和不特别要求良好的重复特性等情况下，不特别设置界面层的情况。
构成界面层3、5的材料可以是具有上述作用的材料，但也可以是以氮化物、氮氧化物、氧化物、碳化物或氟化物为主要成分的材料。根据情况，也可以混合硫化物或硒化物。例如，作为氮化物可使用Ge-N、Cr-N、Si-N、Al-N、Nb-N、Mo-N、Ti-N、Zr-N、Ta-N等，作为氮氧化物可使用Ge-O-N、Cr-O-N、Si-O-N、Al-O-N、Nb-O-N、Mo-O-N、Ti-O-N、Zr-O-N、Ta-O-N等，作为氧化物可使用SiO2、Al2O3、TiO2、Ta2O5、Zr-O等，作为碳化物可使用Ge-C、Cr-C、Si-C、Al-C、Ti-C、Zr-C、Ta-C等，作为氟化物可使用LiF、CaF等。或者，也可以使用它们的适当混合物。此外，在混合适量的硫化物和硒化物的情况下，可以使用ZnS、ZnSe等。总之，作为界面层3、5的材料，可以使用不易引起对记录层4扩散的材料，或即使在扩散进记录层4中的情况下也不会妨碍记录层4的光学变化的材料，并且，在与记录层4连接设置的情况下，可以使用促进记录层4结晶化的材料。
界面层3、5的膜厚可以在1nm以上。在界面层3、5的膜厚为1nm以下的情况下，原子扩散的防止效果会下降。
作为记录层4的材料，可以使用光学特性可逆变化的材料。在相变型记录介质的情况下，可以使用以Te、Se作为主要成分的硫族化合物材料。例如，可列举出以Te-Sb-Ge、Te-Sb、Te-Sb-Zn、Te-Sb-Ag、Te-Bi-Ge、Te-Sb-Ge-Se、Te-Sn-Ge-Au、Te-Sb-Ag-In、Se-In-Sb、Te-Se-In为主要成分的材料等。
在记录层4中，虽可包含Ar、Kr等溅射气体成分和H、C、H2O等杂质，但其含有率最好被抑制到不妨碍信号的记录重放的程度。此外，为了各种目的，虽有在记录层4的主要成分中添加微量(约10at％以下)的其它物质的情况，但在该情况下，其含有量最好被抑制到不妨碍信号的记录重放的程度。
记录层4的膜厚可以在3nm以上20nm以下。在记录层4的膜厚不足3nm的情况下，记录材料难以达到均匀的层状，在非晶和结晶之间难以产生有效的相变化，而在记录层4的膜厚在20nm以上的情况下，由于记录层膜面内的热扩散变大，在按高密度进行记录时，容易产生相邻删除。
作为反射层6的材料，可使用包含Au、Ag、Cu中至少一种的材料。使用这些材料的原因在于其光学常数有利于增大Ac/Aa值，此外，其原因还在于，为了增大热传导系数，即使膜厚薄也可以获得大的冷却能力。此外，作为反射层6的材料，也可以使用Au、Ag、Cu中的至少一种、与其它材料的混合物、或合金。使用这些其它材料的目的在于防止腐蚀和进行更有效的光学设计。具体地说，可列举出Cr、Pt、Pd、Al、Mg、W、Ni、Mo、Si、Ge等，但根据用途，也可以使用适当选择的材料。
反射层6的膜厚可以在1nm以上20nm以下。在反射层6的膜厚不足1nm的情况下，难以使膜达到均匀的层状，使热的、光学的反射层效果下降，而在反射层6的膜厚比20nm厚的情况下，由于介质的光透过变小，所以难以实现上述的光吸收补偿(Ac/Aa＞1)。
下面，说明构成本发明特征的主要部分的热扩散层7。热扩散层7具有两个重要的作用。
热扩散层7的第一个作用是冷却在记录层4中产生的热。作为反射层6，在使用透光型的薄层情况下，反射层6的冷却效果会下降。为了补偿冷却效果，不损失介质的光学特性，即保持原来的介质透过率，在热扩散层7中进行有效的热扩散。因此，在热扩散层7的记录重放激光波长区域的吸收必须低至某种程度。在热扩散层7的记录重放激光波长的复合折射率为n-ik时，吸收系数k最好满足k≤1.5的关系。此外，为了使热扩散层7的冷却效果更大，构成热扩散层7的材料的热传导系数最好尽量大。作为标准，可以使用500K时的热传导系数在0.05W/m·K以上的材料。利用该热扩散层7的冷却效果，可以提高记录信号的C/N比。此外，由于可以降低对介质的热负荷，所以还可以提高重复记录特性。
热扩散层7的第二个作用在于，通过调节其膜厚d，与未设置热扩散层7的情况相比，介质反射率相同时的Ac/Aa值更大。这是由于热扩散层7的膜厚d可以处于0＜d≤(5/16)λ/n或(7/16)λ/n≤d≤(1/2)λ/n的范围内的情况。在热扩散层7的膜厚d为所述范围内的某个值的情况下，Ta、Tc(Ta是记录层4处于非晶状态时的介质透过率，Tc是记录层4处于结晶状态时的介质透过率)可以增大。在除记录层4、反射层6以外的层的吸收为0的情况下，理论上说，表现该Ac/Aa提高效果的情况是膜厚d满足0＜d≤(1/4)λ/n的情况。但是，例如在界面层的吸收不为0情况下等，通过介质的层结构，会有些偏离该最佳范围。热扩散层7的膜厚d的上述范围考虑估计该偏差约为(1/16)λ/n左右。此外，在除记录层4、反射层6以外的层的吸收不为0的情况下，例如在界面层3、5和热扩散层7中的吸收不为0的情况下，有按比上述范围更小的范围(例如，0＜d＜λ/4等)获得Ac/Aa提高效果的情况。但是，与Ac/Aa提高效果相比，在重视上述冷却效果的情况下，即使热扩散层7的膜厚d与光学的最佳范围有若干偏离，膜厚d大的一方也可获得良好的光盘特性。因此，如果综合考虑这些情况，膜厚d的最佳范围认为是上述范围。
为了使在热扩散层7的第二个作用中说明的Ac/Aa提高效果更有效，热扩散层7的折射率n最好满足n＞1.60的关系。这是因为热扩散层7的折射率n越大，增大Ta、Tc的效果就越显著。其中，1.60是不设置热扩散层7的结构时设置在与反射层6连接的与激光入射侧相反的一侧上的层(涂敷层和UV树脂层或虚设基板等)的折射率的大致值。
对具有上述两个重要作用的热扩散层7的要求条件归纳如下。期望膜厚d在0＜d≤(5/16)λ/n或(7/16)λ/n≤d≤(1/2)λ/n中的任何一个范围内。此外，在复合折射率为n-ik的情况下，最好满足n＞1.60、k≤1.5的关系。热传导系数最好尽量大，在500K时最好在0.05W/m·K以上。此外，除此而外，不言而喻，热扩散层7应该为不产生裂纹、腐蚀和剥离等的良好膜。
作为满足这些条件的具体材料，例如，可列举出Al-N、Al-O-N、Al-C、Si、Si-N、SiO2、Si-O-N、Si-C、Ti-N、TiO2、Ti-C、Ta-N、Ta2O5、Ta-O-N、Ta-C、Zn-O、ZnS、ZnSe、Zr-N、Zr-O-N、Zr-C、W-C。或者，也可以使用它们的混合物，也可以使用这些材料与适量的金属、半金属的混合物，也可以使用合金。
由于本发明的光学信息记录介质具有透光型结构，所以可以构成通过来自单面的激光照射可进行信息的记录重放的多层记录介质。由此，可以实现更高密度记录的光学信息记录介质。
图7表示本实施例的多层记录介质的结构例。如图7所示，本实施例的多层记录介质由基板23和在基板23上通过隔离层17、19、21等顺序沉积的n组(n为满足n≥2的自然数)介质16、18、…、20、22构成。其中，从激光入射侧计数至第(n-1)组的介质16、18…、20(以下，将从激光入射侧计数至第n组的介质称为‘第n介质’)由透光型介质构成。
隔离层17、19、21等由紫外线固化树脂和延效性树脂等树脂或电介质等构成，相对于使用的激光为透明层。在这种情况下，仅通过来自单侧的激光照射，通过第一～第(k-1)介质可记录重放第k介质(k为满足1＜k≤n的自然数)。实际上，期望通过n＝2即两组介质构成多层记录介质。
可以将从第一介质至第n介质的其中一个作为重放专用型介质(ROM(只读存储器))，或也可以作为仅可一次写入型的介质。
以下，以n＝2即由两组介质构成的多层记录介质为例进行详细说明。
图8表示由两组介质构成的多层记录介质的结构例。如图8所示，该多层记录介质由基板100、在基板100上顺序沉积的第一介质101、隔离层109、和第二介质201构成。第一介质101由从基板100侧顺序沉积的保护层102、界面层103、记录层104、界面层105、保护层106、反射层107和热扩散层108构成。此外，第二介质201由从隔离层109侧顺序沉积的保护层202、界面层203、记录层204、界面层205、保护层206和反射层207构成。在保护层102、106、202、206、界面层103、105、203、205、记录层104、204、反射层107、207、热扩散层108中，可以使用与图1所示介质中的说明相同的材料。
以光学隔离第一介质101和第二介质201作为主要目的来设计隔离层109，相对于记录重放中使用的激光，由光吸收尽量小的材料构成隔离层。例如，可以使用由紫外线固化树脂和迟效性树脂等有机材料构成的树脂、光盘使用的两面粘接片、SiO2、Al2O3、ZnS等无机电介质或玻璃材料等。
在使一个介质记录重放时，为了将来自其它介质的交扰抑制得小到可忽略的程度，隔离层109的厚度就必须达到激光焦点深度ΔZ以上的厚度。其中，在聚光点强度以无象差情况的80％的点作为基准的情况下，焦点深度ΔZ可近似地按下式来表示。
ΔZ＝λ/{2×(NA)2}
其中，NA是物镜的数值口径，λ是进行记录重放时的激光波长。例如，在λ＝400nm、NA＝0.60的情况下，焦点深度变为ΔZ＝0.56μm。因此，在这种情况下，为了使约±0.60μm的范围内都在焦点深度内，必须将隔离层109的厚度至少设定为比1.20μm大的值。
此外，为了使两个介质间的距离在物镜可聚光的范围内，期望隔离层109的厚度为物镜可允许公差内的厚度。
通过使激光透过第一介质101来进行第二介质201的记录重放。因此，在对于进行记录重放的激光波长第一介质101的透过率为T1，反射率为R1，仅在第二介质201下的反射率为R2时，通过第一介质101重放第二介质201时的反射率r2可按下式表示。
r2＝R2×T1×T1
此外，对于信号振幅来说，同样地，在第二介质201本身的反射率差为ΔR2，通过第一介质101重放第二介质201的情况下的第二介质201的反射率差为Δr2时，下述关系成立。
Δr2＝ΔR2×T1×T1
例如，在ΔR2＝24％，T1＝50％时，通过第一介质101重放第二介质201的情况下的第二介质201的反射率差Δr2变为Δr2＝24％×0.5×0.5＝6％。
由以上可知，为了从第二介质201中得到充分的信号，必须尽量提高第一介质101的透过率T1，尽量增大第二介质201的信号振幅。与此同时，必须按某个程度来提高第一介质101的反射率差，并且，必须极大地提高第二介质201的记录灵敏度。第一介质101、第二介质201的光学设计必须按使这些要素完全平衡来确定。
以下，示出具体的光学设计例。作为一例，第一介质101的记录层104结晶状态时的反射率R1c设计为7.5％，非晶状态时的反射率R1a设计为0.5％，将第二介质201的记录层204结晶状态时的反射率R2c设计为15％，非晶状态时的反射率R2a设计为43％，以便仅在第一介质101上进行记录情况下的第一介质101的透过率达到50％。光学设计值的调节主要是通过改变记录层104、保护层102、106、反射层107的膜厚来进行。
在以上例的情况下，通过第一介质101记录重放第二介质201情况下的反射率差为Δr2＝(43-15)×0.5×0.5＝7％，此外，第一介质101的反射率差也变为7.5-0.5＝7％。这样，期望这样设计第一介质101、第二介质201的反射率差，即信号振幅的大小大致相等。按照这样的设计，在第一介质101和第二介质201之间切换进行记录重放的介质时，通过信号振幅的极端变化，可以防止寻迹的不稳定。
此外，由于难以使第一介质的高透过率与第二介质的高反射率差两者兼容，所以进行设计后多数情况反射率差比较小，信号振幅会变得比较小。在这种情况下，按比以往稍大地设定重放光的功率等级P3，可以增大重放信号振幅。但是，如果过大地设定P3的等级，那么由于记录标记受到热的影响，重放信号会劣化，所以必须在不产生由该重放光产生的信号劣化的范围中设定P3的等级。此外，第一介质101和第二介质201的重放功率等级可以分别不同。此外，进行第一介质101和第二介质201重放的激光波长也可以不同，但一般使用同一波长的激光。
期望重放第二介质201情况下的第一介质101的透光率在40％以上80％以下，而且最好在50％以上70％以下。如上所述，由于通过第一介质101记录重放第二介质201时的信号振幅变为乘以第一介质101的透过率T1平方的值，所以在第一介质101的透光率比40％小的情况下，变为0.16倍以下，会变得相当小。此外，在第一介质101的透光率非常小的情况下，由于透过第二介质201的光量极大地减少，所以第二介质201的记录灵敏度会下降。因此，第一介质101的透光率应在40％以上，最好在50％以上。但是，如果第一介质101的透光率过大，那么由于难以增大第一介质101的反射率差，所以第一介质101的透光率应在80％以下，最好在70％以下。
下面，以配有图1结构的光学信息记录介质为例，说明以上说明的光学信息记录介质的制造方法。作为制作构成上述光学信息记录介质的多层膜的方法，有溅射法、真空镀敷、CVD等方法。其中，以采用溅射法的情况为例进行说明。图2是表示成膜装置一例的示意图。
如图2所示，真空容器9通过排气口15连接真空泵(图中未示出)，由此可以使真空容器9内保持高真空。此外，在真空容器9上设有气体供给口14，从该气体供给口14可以供给固定流量的稀有气体、氮气、氧气或它们的混合气体。在图2中，10是配置在真空容器9内的基板，该基板10被安装在可使基板10自转和公转的驱动装置11上。12是真空容器9内与基板10对置配置的多个溅射靶，这些溅射靶12分别与阴极13连接。其中，阴极13通过图中未示出的开关与直流电源或高频电源(图中未示出)连接。此外，通过将真空容器9接地，真空容器9和基板10具有阳极作用。
作为成膜气体，可使用稀有气体或根据情况使用在稀有气体中混有微量氮或氧等的气体。作为稀有气体，可以使用Ar、Kr等可成膜的气体。一般来说，已知在成膜记录层4和保护层2时，如果使用稀有气体与微量的氮或微量的氧混合的气体，那么可以抑制介质重复记录时的物质移动，提高重复特性。
作为界面层3、5或热扩散层7，在使用氮化物和氧化物的情况下，如果按照反应性溅射法进行溅射，那么可得到品质良好的膜。例如，作为界面层3、5，在使用Ge-Cr-N的情况下，以Ge-Cr或包含Ge、Cr和O的材料当靶，作为成膜气体使用稀有气体与氮的混合气体。或者，也可以使用包含N2O、NO2、NO、N2等氮原子的气体和适当组合这些气体与稀有气体的混合气体。此外，在膜为硬质的情况下和膜应力大的情况下等，根据需要，通过将微量的氧混合在成膜气体中，有可以获得良好膜品质层的情况。
下面说明如以上那样形成的光学信息记录介质的记录重放方法、删除方法。在信号的记录重放、删除中，使用装载激光光源和物镜的光头、将照射激光的位置向预定位置导入的驱动装置、控制径迹方向和与膜面垂直的方向的位置的寻迹控制装置和聚焦控制装置、调制激光功率的激光驱动装置和旋转介质的旋转控制装置。
首先，使用旋转控制装置使介质旋转，使用光学系统将激光缩小成微小的点，通过向介质照射进行信号的记录、删除。通过激光的照射，记录层4内的局部向非晶状态可逆地变化得到的非晶状态生成功率等级为P1，通过相同的激光照射，向结晶状态可逆变化得到的结晶状态生成功率等级为P2，利用调制激光功率使在P1和P2之间，形成记录标记或删除部分。由此，进行信息的记录、删除和写入记录。照射P1功率的部分由脉冲串形成，一般为所谓的多脉冲。
此外，通过比上述P1、P2中的任何一个的功率等级低的该功率等级下的激光照射，记录标记的光学状态不受影响，并且，使为了记录标记重放通过该照射从介质得到充分反射率的功率等级为P3，通过用检测器读出利用P3功率的激光照射得到的来自介质的信号，进行信息信号的重放。
【实施例】
下面，说明本发明的优选实施例。
在本实施例中，作为基板1使用厚度为0.6mm、直径120mm的圆盘状聚碳酸酯树脂，作为保护层2采用在ZnS中混合20mol％的SiO2的材料，作为记录层4采用Ge21Sb25Te54，作为界面层3、5采用Ge-Cr-O-N，作为反射层6采用Au，作为热扩散层7采用Al-O-N，制作图1所示结构的光学信息记录介质。
图3表示此时的光学特性模拟结果。其中，各层的膜厚是记录层4为10nm，界面层3、5分别为20nm、30nm，反射层6为10nm。而且，使保护层2和热扩散层7的膜厚从0至λ/2n(λ为激光波长，n为各个膜的波长λ时的折射率)变化，对于记录层4分别为非晶状态、结晶状态时的记录层4中的吸收率Aa、Ac、反射率Ra、Rc和反射层6中的吸收率Aa-RL、Ac-RL、介质的透过率Ta、Tc，进行光学计算。横轴表示作为热扩散层7的膜厚(单位：xλ/64n)，在满足Ra≤5％并且Rc≥15％的结构中Ac/Aa值达到最大时的值。此时的保护层2的膜厚为(26～30)λ/64n左右。作为比较例，在图中横轴为0的地方表示未设置热扩散层7时的计算结果。此外，图4表示由上述光学计算得到的Ac/Aa值的变化。由图3、图4可知，在热扩散层7(Al-O-N)的膜厚d满足0＜d≤λ/4n的情况下，与未设置热扩散层7(Al-O-N)的情况相比，大致相同的Rc、Ra时的Ac/Aa值增加。
使用上述材料，制作实际上如图1所示的光盘。各层的膜厚是保护层2为100nm，记录层4为10nm，界面层3、5分别为10nm、30nm，反射层6为10nm，热扩散层7分别为40nm(8λ/64n)、60nm(12λ/64n)、80nm(16λ/64n)。这些介质分别为(1)、(2)、(3)。
作为比较例，在介质(1)中，除了未设置热扩散层7外，制作与(1)有相同结构的介质(0)。
其中，按一定流量供给整个压力可分别达到1.0mTorr、0.5mTorr的在Ar中混合2.5％的氮的气体，在阴极上分别投入DC为1.27W/cm2、RF为5.10W/cm2的功率，进行记录层4和保护层2的成膜。按整个压力可达到3.0mTorr来供给Ar气体，投入DC4.45W/cm2的功率，进行反射层6的成膜。在成膜界面层3、5时，靶材料为Ge-Cr，溅射气体为Ar与氮的混合气体，溅射气体压力为1mTorr，溅射气体中的氮分压为40％，溅射功率密度为6.37W/cm2。
按反射率、C/N比和重写删除率进行光盘的特性评价。
记录的信号方式为(8-16)调制方式，使用波长650nm的激光和数值口径0.60的物镜进行记录。此外，最短位长度为0.28μm(即最短标记长度为0.41μm)，光盘的旋转速度为线速度8.2m/s。此外，作为基板1，使用信迹间距为1.20μm的基板，即使用交错形成每隔0.60μm的槽部分和纹间表面部分的基板。
通过在(8-16)调制方式中记录3T长度的标记，测定该C/N比，进行C/N比的评价。此外，通过在适当的激光功率下记录(8-16)调制方式下3T长度的标记后，测定11T长度标记中重写时的3T标记删除率(以下称为‘3T删除率’)和在11T标记上重写3T标记时的11T标记删除率(以下称为‘11T删除率’)，进行删除特性的评价。在下述(表1)中表示介质(0)～(3)的评价结果。
【表1】
介质序号        反射率(％)        透过率(％)   C/N比(db)  3T删除率(-db)  11T删除率(-db)
  Rc   Ra   Tc   Ta
(0)   16.1   4.7   20.0   40.0   52.0  30  33
(1)   16.2   4.5   24.5   48.0   54.5  33  36
(2)   16.8   4.4   23.8   48.0   55.0  33  35
(3)   17.1   4.2   21.0   45.0   55.0  32  34
由上述(表1)可知，与没有热扩散层的介质(0)相比，在有热扩散层的介质(1)～(3)中，使其中任何一个的C/N比都得到提高。可以认为这是由于实现了热扩散层7(Al-O-N)的冷却效果。此外，在介质(1)～(3)中，3T删除率、11T删除率中的任何一个都得到提高。这表示介质的Ac/Aa提高。再有，在上述(表1)中，Ta是记录层4处于非晶状态时的透过率，而Tc是记录层4处于结晶状态时的透过率。其中，通过在镜面基板上制作具有与介质(0)～(3)完全相同结构的光盘，使用分光器测定这些光盘的透过率来进行介质的透过率测定。由上述(表1)可知，与没有热扩散层的介质(0)相比，在有热扩散层的介质(1)～(3)中，其中任何一个的透过率都有提高。
下面，说明除了界面层3、5为Cr-A1-O-N、热扩散层7为Si以外，与介质(1)有相同结构的介质。图5、图6表示光学特性的模拟结果。此时的各层膜厚是记录层4为10nm，界面层3、5分别为20nm、35nm，反射层6为15nm。由图6、图7可知，在热扩散层7(Si)的膜厚d满足0＜d≤12λ/64n的情况下，与未设置热扩散层7(Si)的情况相比，大致相同的Rc、Ra时的Ac/Aa值增加。
接着，在介质(1)中，除了保护层2为120nm，界面层3、5分别为20nm、35nm的Cr-Al-O-N，反射层6为15nm的Au，热扩散层7为30nm(8λ/64n)的Si以外，制作与介质(1)有相同结构的介质(4)。
作为此时的比较例，除了未设置热扩散层7以外，制作与介质(4)有相同结构的介质(0)。在下列(表2)中，表示相对于介质(4)、(0)进行与介质(0)～(3)相同评价的结果。
【表2】
  介质序号     反射率(％)    C/N比(db)     3T删除率(-db)    11T删除率(-db)
    Rc     Ra
  (0)     15.1     1.2     52.4     30    32
  (4)     16.5     1.4     54.3     33    35
由上述(表2)可知，在该情况下，在设置热扩散层7时，与未设置热扩散层时相比，C/N比和删除率提高。
(第二实施例)
下面，采用其它实施例，进一步详细说明本发明。这里，仍参照在上述第一实施例中使用的图8。
在本实施例中，作为基板100使用厚度为0.6mm、直径120mm的圆盘状聚碳酸酯树脂，作为保护层102、106、202、206，采用在ZnS中混合20mol％的SiO2的材料，作为界面层103、105、203、205，采用Ge-Cr-N，作为反射层107、207，采用AgPdCu合金，作为热扩散层108，采用TiO2，而作为记录层104、204，采用Ge4Sb2Te7，制作图8所示结构的光学信息记录介质。各层的膜厚为记录层104、204分别为6nm、9nm，界面层103、105、203、205为2nm，反射层107、207分别为10nm、80nm，热扩散层108为40nm，保护层102、106分别为110nm、34nm，保护层202、206分别为90nm、40nm。
各层的成膜条件与上述第一实施例的情况相同。
通过测定对于第一介质101和第二介质201双方的C/N比、重写删除率和循环特性进行光盘的特性评价。
记录的信号方式为(8-16)调制方式，在第一介质101、第二介质201中都使用波长405nm的激光和数值口径0.65的物镜进行记录和重放。此外，最短的标记长度为0.26μm，光盘的旋转速度为线速度8.2m/s。此外，作为基板100，使用信迹间距为0.39μm的基板，即使用每隔0.195μm交错形成槽部分和纹间表面部分的基板。
在(8-16)调制方式中，通过将3T长度的标记在适当的激光功率下记录10次，测定该C/N比来进行C/N比的评价。此外，通过将(8-16)调制方式下的3T长度的标记在适当的激光功率下记录9次后，在相同功率下将11T长度的标记重写1次，测定此时的3T标记的删除率(以下称为‘3T删除率’)来进行重写删除特性的评价。此外，通过评价记录随机信号时的抖动值在哪个记录次数上恶化来进行循环特性的评价。
进行信号重放的功率在第一介质101、第二介质201上都为1.0mW。第二介质201的重放容易在未在第一介质101上记录信号的状态下进行。
其中，以上述双层记录介质为介质(5)。为了比较，除未设置热扩散层108以外，制作与介质(5)有相同结构的双层记录介质，该介质为介质(6)。在下列表3中，表示对介质(5)和介质(6)进行评价的结果。
【表3】
 介质序号  热扩散层  C/NL1   L2  删除率L1    L2 周期特性L1    L2
 (5)  TiO2  ○   ○  ○    ○ ○    ○
 (6)  无  ×        ○  ×          ○ ×          ○
在上述(表3)中，将第一介质101简记为L1，第二介质201简记为L2。此外，对于C/N比来说，将50dB以上的情况用○表示，而不足50dB的情况用×表示。此外，对于删除特性来说，所得到的3T删除率为33dB以上的情况用○表示，而不足33dB的情况用×表示。此外，对于循环特性来说，在适当的激光功率下将随机信号重复记录1万次，将10次重复记录时的抖动值的劣化量在2％以下的情况用○表示，而劣化量比2％大的情况用×表示。
由上述(表3)可知，在有热扩散层108的介质(5)中，第一介质101(L1)、第二介质201(L2)同时获得大的C/N比和高删除率。与此相对，对于没有热扩散层的介质(6)的第一介质101(L1)来说，在C/N比、删除率都只能获得比介质(5)低的值。
这是由于在没有热扩散层的介质(6)中，由于难以增大上述结晶状态与非晶状态的光吸收补偿值(Ac/Aa的值)，所以删除率低，并且10次重写记录后的3T信号的C/N比也低。
在有热扩散层108的介质(5)中，由于对于第一介质101(L1)不仅获得大的C/N比和高删除率，而且对于第一介质101(L1)可以同时实现高透过率，所以也可以获得对于第二介质201(L2)的良好特性。
此外，如果比较介质(5)和介质(6)，那么显然热扩散层108具有使循环特性提高的效果。可以认为这是由于通过采用薄的反射层，热扩散层108补偿下降的冷却能量，在介质(5)中，可以降低重复记录时对介质的热负荷。
此外，作为其它例，用除Ti-N、Ta2O5、Si-N、Zr-N以外的材料作为热扩散层108的材料，分别制作与介质(5)有相同结构的双层记录介质，这些介质为介质(7)～(10)。在对介质(7)～(10)进行与前面相同的评价时，可得到与介质(5)同样的良好特性。而且，在这些介质(7)～(10)的情况下，通过设置热扩散层108，还可以兼容高透过率和高吸收补偿，并且也明显地提高循环特性。
如以上说明，按照本发明，配有利用激光照射使光学特性可逆地变化的记录层，透过波长λ的所述激光的反射层，和与所述反射层连接设置的热扩散层，在所述热扩散层的折射率为n时，通过将所述热扩散层的膜厚d设定在0＜d≤(5/16)λ/n或(7/16)λ/n≤d≤(1/2)λ/n的范围内，可以进一步提高记录层的冷却能力，同时由于通过Ac/Aa值的提高，可以降低重写畸变，所以可以使记录更高速化、高密度化。此外，利用热扩散层的冷却效果，可以使记录信号的C/N比提高。再有，由于可以降低对介质的热负荷，所以还可以提高重复记录特性。

Claims (13)

1.一种光学信息记录介质，包括利用激光照射可逆地改变光学特性的记录层，透过波长λ的所述激光的反射层和与所述反射层连接设置的热扩散层，其特征在于，在所述热扩散层的折射率为n时，所述热扩散层的膜厚d在0＜d≤(5/16)λ/n或(7/16)λ/n≤d≤(1/2)λ/n的范围内。
2.如权利要求1所述的光学信息记录介质，其特征在于，构成热扩散层的材料的500K时的热传导系数在0.5W/m·K以上。
3.如权利要求1所述的光学信息记录介质，其特征在于，对于用于信息记录重放中的激光波长，热扩散层的折射率在1.6以上。
4.如权利要求1所述的光学信息记录介质，其特征在于，对于用于信息记录重放中的激光波长，热扩散层的吸收系数在1.5以下。
5.如权利要求1所述的光学信息记录介质，其特征在于，热扩散层包含从Al-N、Al-O-N、Al-C、Si、Si-N、SiO2、Si-O-N、Si-C、Ti-N、TiO2、Ti-C、Ta-N、Ta2O5、Ta-O-N、Ta-C、Zn-O、ZnS、ZnSe、Zr-N、Zr-O-N、Zr-C和W-C组成的组中选择的至少一种。
6.如权利要求1所述的光学信息记录介质，其特征在于，反射层包含从Au、Ag和Cu组成的组中选择的至少一种材料。
7.如权利要求1所述的光学信息记录介质，其特征在于，反射层的厚度在1nm以上20nm以下。
8.如权利要求1所述的光学信息记录介质，其特征在于，记录层的厚度在3nm以上20nm以下。
9.如权利要求1所述的光学信息记录介质，其特征在于，记录层由包含从Te、Se和Sb组成的组中选择的至少一种的相变化材料构成。
10.如权利要求1所述的光学信息记录介质，其特征在于，相对于激光的光学信息记录介质的平均透光率在40％以上80％以下。
11.如权利要求10所述的光学信息记录介质，其特征在于，在与激光入射侧相反的一侧，设有至少一个其它的光学信息记录介质。
12.如权利要求1所述的光学信息记录介质，其特征在于，设有与记录层的至少一侧连接，具有促进记录层结晶化效果的界面层。
13.如权利要求12所述的光学信息记录介质，其特征在于，界面层为至少包含N的材料。
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