# US 8,785,010 B2 · Glass substrate for a magnetic disk and magnetic disk

> Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt

- Number: US 8,785,010 B2
- Document ID: US8785010B2
- Status: Granted
- Kind: B2
- Application number: 13/120,320
- Filed: 2009-09-29
- Published: 2011-07-14
- Granted: 2014-07-22
- Earliest claimed: 2008-09-30
- Assignees: Hoya Corporation
- Applicants: Shinji Eda; Hideki Isono; Takashi Maeda; Hiroshi Tsuchiya; Yoshinori Marumo
- Inventors: Shinji Eda; Hideki Isono; Takashi Maeda; Hiroshi Tsuchiya; Yoshinori Marumo
- Web page: https://patentgrep.com/patent/US8785010B2

## CPC

- G11B 5/73921: {Glass or ceramic substrates}
- C03C 19/00: Surface treatment of glass, not in the form of fibres or filaments, by mechanical means (sand-blasting, grinding, or polishing glass B24)
- C03C 21/008: {in solid phase, e.g. using pastes, powders}
- C03C 23/0075: {Cleaning of glass (specially adapted to plate glass B08B11/00)}
- C03C 23/009: {Poling glass}
- C09G 1/02: containing abrasives or grinding agents {(abrasives as such C09K3/14; polishing of semi-conductors H10P52/40)}
- G11B 5/8404: {manufacturing base layers}
- C03C 2204/08: Glass having a rough surface
- G11B 5/8408: {protecting the magnetic layer}
- G11B: INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER (recording measured values in a way that does not require playback through a transducer G01D9/00; recording or playback apparatus using mechanically marked tape, e.g. punched paper tape, or using unit records, e.g. punched or magnetically marked cards G06K; transferring data from one type of record carrier to another G06K1/18; circuits for coupling output of reproducer to radio receiver H04B1/20; gramophone pick-ups or like acoustic electromechanical transducers or circuits therefor H04R)
- C03C: CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
- C09G: POLISHING COMPOSITIONS (French polish C09F11/00); SKI WAXES

## Abstract

Provided are a magnetic disk substrate and a method of manufacturing the same, wherein the magnetic disk substrate has very few defects present on its surface with an arithmetic mean roughness (Ra) at a level in the vicinity of 0.1 nm and thus is suitable as a substrate for a magnetic disk with high recording density. The magnetic disk glass substrate is such that the arithmetic mean roughness (Ra) of the main surface of the glass substrate measured using an atomic force microscope with a resolution of 256×256 pixels in a 2 μm×2 μm square is 0.12 nm or less and the number of defects detected to have a size of 0.1 μm to 0.6 μm in plan view and a depth of 0.5 nm to 2 nm is less than 10 per 24 cm2, wherein the defects are each detected using a shift in wavelength between incident light and reflected light upon irradiating and scanning helium neon laser light with a wavelength of 632 nm on the main surface of the glass substrate.

## Claims

### Claim 1

A magnetic disk glass substrate, wherein an arithmetic mean roughness (Ra) of a polished main surface of the glass substrate measured using an atomic force microscope with a resolution of 256×256 pixels in a 2 μm×2 μm square is 0.12 nm or less and, among defects detected to have a size of 0.1 μm or more and 0.3 μm or less upon irradiating light with a wavelength of 405 nm onto the glass substrate with a spot size of 5 μm and detecting scattered light from the glass substrate, the number of the defects fixed to the glass substrate, whose position on the glass substrate is not changed before and after the glass substrate is immersed for 200 seconds in the dilute sulfuric acid solution adjusted to pH4, is 1 or less per 24 cm2,
wherein the glass substrate is an amorphous aluminosilicate glass, and
wherein a ratio (Ra/Rp) of the arithmetic mean roughness (Ra) to a maximum peak height (Rp) on the main surface of the glass substrate is 0.15 or more.

### Claim 2

A magnetic disk glass substrate, wherein an arithmetic mean roughness (Ra) of a polished main surface of the glass substrate measured using an atomic force microscope with a resolution of 256×256 pixels in a 2 μm×2 μm square is 0.12 nm or less and the number of concave defects detected to have a size of 0.1 μm or more and 0.6 μm or less in plan view and a depth of 0.5 nm or more and 2 nm or less is less than 10 per 24 cm2, the defects each being detected using a shift in wavelength between incident light and reflected light upon irradiating and scanning helium neon laser light with a wavelength of 632 nm on the main surface of the glass substrate,
wherein the glass substrate is an amorphous aluminosilicate glass, and
wherein a ratio (Ra/Rv) of the arithmetic mean roughness (Ra) to a maximum valley depth (Rv) on the main surface of the glass substrate is 0.15 or more.

### Claim 3 (depends on 1, 2)

The magnetic disk glass substrate according to claim 1 or 2, wherein the glass substrate has a disk shape with a hole at a center thereof and, assuming that a distance from the center to an outermost periphery is 100%, a difference (RaO−RaI) between an arithmetic mean roughness (RaO) of the main surface in a range of 80% or more and 90% or less from the center and an arithmetic mean roughness (RaI) of the main surface in a range of 10% or more and 20% or less from the center is 0.01 nm or less.

### Claim 4 (depends on 1)

The magnetic disk glass substrate according to claim 1, wherein the glass substrate has the main surface and an end face,
the main surface and the end face each have a compressive stress layer, and
the compressive stress layer of the main surface has a depth which is shallower than that of the compressive stress layer of the end face.

### Claim 5 (depends on 1)

A magnetic disk, wherein at least a magnetic layer is formed on the magnetic disk glass substrate according to claim 1.

### Claim 6 (depends on 5)

The magnetic disk according to claim 5, wherein the magnetic disk is a patterned medium in which at least adjacent recording tracks are magnetically isolated from each other.

### Claim 7 (depends on 1)

The magnetic disk glass substrate according to claim 1, wherein the magnetic disk glass substrate is an isotropic substrate in which the surface roughness (arithmetic mean roughness (Ra)) of the glass substrate in its circumferential direction and the surface roughness thereof in its radial direction are equal to each other.

### Claim 8 (depends on 2)

The magnetic disk glass substrate according to claim 2, wherein the magnetic disk glass substrate is an isotropic substrate in which the surface roughness (arithmetic mean roughness (Ra)) of the glass substrate in its circumferential direction and the surface roughness thereof in its radial direction are equal to each other.