Glass-ceramics

Details Glass-ceramics Glass-ceramics

2000-09-15

2002-07-30

Group, Karl (Department: 1755)

Compositions: ceramic

Ceramic compositions

Devitrified glass-ceramics

C428S690000

Reexamination Certificate

active

06426311

ABSTRACT:

BACKGROUND OF THE INVENTION
This invention relates to novel glass-ceramics which are light but have sufficient mechanical strength and light transmittance and also have a thermal expansion characteristic which is compatible with other materials. Particularly, the invention relates to glass-ceramics which are suitable for use both as a substrate for an information storage medium which requires a thermal expansion characteristic which is compatible with materials of component parts of a magnetic information storage device and super flatness which is suitable for a high density recording and as glass-ceramics for a light filter (particularly for WDM or DWDM light filter or gain-flattening filter) which requires excellent adhesion to a multi-layer film, proper thermal expansion characteristic and excellent light transmittance.
Recent multi-media tendency of personal computers and development of digital video cameras and digital cameras necessitate handling of a large amount of data such as moving pictures and voice and there is an increasing demand for an information storage device capable of recording information at a high recording density. For coping with such tendency, an information storage device is required to reduce the size of its bit cell for increasing the recording density. As the bit cell is reduced in size, a magnetic head is caused to operate in close proximity to the surface of an information storage medium such as a magnetic disk. As the magnetic head operates in a low glide height (near contact) state or in a contact state on the information storage medium, super flatness of the surface of the information storage medium becomes an important factor. On the other hand, in contrast to the conventional landing zone system, there is development of the ramp loading system according to which the magnetic head is in complete contact with the surface of the magnetic disk except when the magnetic head is started or stopped when the magnetic head. is moved out of the magnetic disk. Thus, there is an increasing demand for smoother surface of an information storage medium.
Further, as the amount of information to be handled increases, a finer, more accurate and thinner magnetic film is required and this necessitates a lower amount of elution of alkali ingredients (Li, Na and K) from the substrate.
Furthermore, there are new applications of such information storage medium to mobiles including APS cameras, cellular phones, digital cameras, digital video cameras and card drive, hard disk drives of mobile and desk top personal computers, hard disk drives of servers and new high recording density media including perpendicular magnetic recording medium, island magnetic recording medium and storage medium for a semiconductor memory. For coping with such new applications, higher physical, chemical and electrical properties are required for a substrate of an information storage medium.
An aluminum alloy has conventionally been used for a magnetic disk substrate. In the aluminum alloy substrate, however, projections or spot-like projections and depressions are produced on the surface of the substrate in the polishing process due to defects in the material and, therefore, is not sufficient in its flatness for a substrate for an information storage medium as described above. The aluminum alloy is a soft material having low Young's modulus and surface hardness and therefore vibration takes place during a high speed rotation of the drive which causes deformation of the medium. The aluminum alloy has also difficulty in thinning the substrate. Moreover, the aluminum alloy substrate tends to be damaged upon contact with the magnetic head. Accordingly, the aluminum alloy cannot cope sufficiently with the current requirements for the high density recording.
As a material which eliminates the defects of the aluminum alloy, there are known chemically tempered glasses such as alumino-silicate glass (SiO
2
—Al
2
O
3
—Na
2
O). The chemically tempered glasses, however, have the disadvantages that (1) since polishing is made after the chemically tempering process, the reinforced layer becomes instable in thinning the disk and (2) since the glasses contain Li
2
O, Na
2
O or K
2
O ingredient as an essential ingredient, the film forming property is deteriorated and etching or all-surface barrier coating becomes necessary for preventing elution of such ingredient. Further, the chemically tempered glass substrate has slight undulation or the surface of the substrate and it is difficult to manufacture the product on a stable basis at a low cost.
For overcoming the defects of the chemically tempered glass substrates, some glass-ceramic substrates are known. The SiO
2
—Li
2
O—Mgo—P
2
O
5
glass-ceramics disclosed in Japanese Patent Application Laid-open Publication No. 6-329440 is an excellent material as an all-surface textured material which contains, as predominant crystal phases, lithium disilicate (Li
2
O·2SiO
2
) and &agr;-quartz (&agr;-SiO
2
) and in which the conventional mechanical or chemical texturing is obviated by controlling the size of the crystal grains of &agr;-quartz and a surface roughness Ra (arithmetic mean roughness) is controlled within a range from 15 Å to 50 Å. However, surface roughness Ra which is sought today is 5.0 Å or below, preferably 3.0 Å or below and, more preferably, 2.0 Å or below and the prior art glass-ceramics cannot cope sufficiently with the low-glide height tendency accompanying the high density recording. Further, the prior art glass-ceramics contain lithium disilicate (Li
2
·2SiO
2
) as a predominant crystal phase and no consideration has been given to the problems of elution of alkali ingredients and forming of small pits during polishing, though the amounts of alkali ingredients in the glass-ceramics is smaller than in the chemically tempered glasses.
The SiO
2
—Li
2
O—K
2
O)—MgO—ZnO—P
2
O
5
—Al
2
O
3
glass-ceramics or the SiO
2
—Li
2
—K
2
O—MgO—ZnO—P
2
O
5
—Al
2
O
3
—ZrO
2
glass-ceramics disclosed in Japanese Patent Application Laid-open Publication No. 10-45426 are glass-ceramics for laser texturing containing, as a predominant crystal phase or phases, at least one of lithium disilicate (Li
2
O·2SiO
2
), a mixture of lithium disilicate and &agr;-quartz, and a mixture of lithium disilicate and &agr;-cristobalite (&agr;-SiO
2
). These glass-ceramics are not sufficient for coping with the low-glide height tendency resulting from the rapidly increasing recording capacity which requires the surface roughness Ra of 5.0 Å or below, preferably 3.0 Å or below and, more preferably 2.0 Å or below. Further, the glass-ceramics contain lithium disilicate as a predominant crystal phase and no consideration has been given to the problems of elution of alkali ingredients and forming of small pits during polishing which are sought to be solved today.
Japanese Patent Application Laid-open Publication No. 9-35234 discloses a magnetic disk substrate of SiO
2
—Al
2
O
3
—Li
20
glass-ceramics containing lithium disilicate and &bgr;-spodumene (Li
2
O·Al
2
O
3
·4SiO
2
) as predominant crystal phases. In the glass-ceramics, the predominant crystal phase is &bgr;-spodumene which has a negative thermal expansion characteristic with resulting low thermal expansion characteristic of the substrate and growth of crystal phases having positive thermal expansion characteristic such as &agr;-quartz and &agr;-cristobalite is restricted. As a result, the glass-ceramics have a surface roughness Ra after polishing of 20 Å (12 Å to 17 Å in the examples) which is still too rough for coping with the current requirement and cannot sufficiently cope with the low glide height tendency of the magnetic head resulting from increasing recording capacity. Further, the material which grows the crystal having the negative thermal expansion characteristic as a predominant crystal phase is apparently disadvantageous because it produces difference in the average linear thermal expansion coefficient relative to the component parts of the infor

Affiliated with

Also associated with

Rating

Glass-ceramics does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Glass-ceramics, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Glass-ceramics will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2870135