Optics: measuring and testing – By dispersed light spectroscopy – Utilizing a spectrometer
Reexamination Certificate
1997-12-19
2001-06-12
Font, Frank G. (Department: 2877)
Optics: measuring and testing
By dispersed light spectroscopy
Utilizing a spectrometer
Reexamination Certificate
active
06246475
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an apparatus for measuring the flying height of a magnetic head used in a magnetic disk apparatus.
In a magnetic disk apparatus, a magnetic disk forming a magnetic film on a disk-shaped substrate is used as a recording medium, and a magnetic head for recording and reproducing is disposed on the magnetic disk. While being stopped, the magnetic head is contacting with the magnetic disk, but when the magnetic disk is rotated at high speed when driving, the magnetic head is lifted by a negative pressure generating groove provided in a slider of the magnetic head so as to be in a non-contact state, and recording or reading is done while keeping a small flying height. Recently, for high density recording, the flying height of the magnetic head is required to be as small as 100 nm or less.
When manufacturing such magnetic disk apparatus, it is necessary to measure preliminarily if the flying height of the magnetic head is a specified value or not, and a measuring apparatus of flying height of magnetic head is used for this purpose.
In this apparatus, as shown in
FIG. 1
, instead of the original magnetic disk, a transparent disk
10
made of glass or the like is used, a magnetic head
20
to be measured is disposed at one side of this transparent disk
10
, and light emitting means
11
and light detecting means
12
are provided at other side. Usually, the magnetic head
20
contacts with the transparent disk
10
, and is lifted when the transparent disk
10
is rotated at high speed, and in this state an exit light
13
is emitted from the light emitting means
11
toward the magnetic head
20
through the transparent disk
10
, this exit light
13
is reflected on a principal plane
10
a
of the magnetic head
20
side of the transparent disk
10
, and this reflected light
14
a
and reflected light
14
b
from the magnetic head
20
are received in the light detecting means
12
, and by making use of the interference by phase difference of both reflected lights
14
a
,
14
b
, the flying height h of the magnetic head
20
is measured.
In such magnetic head flying height measuring apparatus, although the magnetic head
20
is lifted during rotation, when starting or stopping rotation, the magnetic head
20
contacts and slides with the transparent disk
10
Accordingly, the glass-made transparent disk
10
is worn out excessively due to sliding with the magnetic head
20
, and by using for about a week, it is hard to read the reflected light
14
due to flaw, and hence it must be replaced. It is hence not only bothersome but is also inferior in reliability of measured value.
Yet, since the glass-made transparent disk
10
is low in stiffness, it is likely to be deformed when rotating at high speed, and hence it was hard to form thinly to reduced weight.
Still more, by using the glass-made transparent disk
10
, when the flying height h of the magnetic head
20
is reduced to scores of nm, the transparent disk
10
is charged with static electricity, and adverse effects are caused on the magnetic head
20
. In particular, as the magnetic head
20
is advanced in density, it is changed from the ID (inductive) head to the MR (magnetic resistance) head, and this MR head is weak in static electricity, and is damaged by static electricity when the flying height h is 20 to 40 nm.
SUMMARY OF THE PREFERRED EMBODIMENTS
It is hence a feature of the invention that the transparent disk made of a transparent material is formed of a monocrystalline sapphire in the apparatus for measuring the flying height of the magnetic head by make use of interference of light.
It is also feature of the invention that the principal plane of the transparent disk coincides with C-plan.
According to the invention, since the transparent disk is formed of monocrystalline sapphire of high hardness, it is resistant to scratches by sliding with the magnetic head, and it can be used for a long period. Besides, since the monocrystalline sapphire is high in stiffness, it is hardly deformed in high speed rotation, so that the transparent disk may be thin and lightweight. Morever, as the flying height of the magnetic head is smaller, light of shorter wavelength is needed, but the monocrystalline sapphire shows a sufficient permeability to the light of short wavelength.
Further, when the principal plane of the transparent disk coincides with C-plane of the monocrystalline sapphire, the flying height can be measured accurately by eliminating the effects of birefringence.
REFERENCES:
patent: 4862414 (1989-08-01), Kuchnle
patent: 5063538 (1991-11-01), Kuchnle
patent: 5619331 (1997-04-01), Li
patent: 5767964 (1998-06-01), Wahl et al.
patent: 5781299 (1998-07-01), Womack et al.
patent: 5818658 (1998-10-01), Balster et al.
patent: 5831733 (1998-11-01), De Groot
Sato Masaki
Umehara Motohiro
Font Frank G.
Hogan & Hartson LLP
Kyocera Corporation
Stafira Michael P.
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