JPH11328670A - Apparatus and method for inspecting magnetic disk - Google Patents

Abstract

PROBLEM TO BE SOLVED: To inspect projections and defects concurrently by recording an inspection signal to a magnetic disk by an inductive type magnetic head, reproducing the signal by a magnetoresistance effect type magnetic (MR) head, separating the signal by a filter to a first, a second signal components of a lower, a higher frequencies than a predetermined frequency. SOLUTION: An inspecting apparatus 1 has a vanish head 3 for removing dust, etc., adhering to a surface of a magnetic disk 2 and an inspection sensor 4 as a combination of an inductive type magnetic head and an MR head. The inspection sensor 4 records an inspection signal to the magnetic disk 2 by the inductive type magnetic head and reproduces the recorded signal by the MR head. A reproduction signal 18 from the MR head is separated by a filter 6 with a predetermined frequency to a projection detection signal 18a of a relatively low frequency and a defect detection signal 18b of a relatively high frequency which are then processed by a projection detection circuit 5 and a defect detection circuit 8.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a magnetic disk inspection apparatus and method.

[0002]

2. Description of the Related Art A magnetic disk is manufactured by forming a magnetic layer on a disk-shaped non-magnetic substrate. Then, various inspections are performed on the manufactured magnetic disk, and a magnetic disk as a product is completed by removing a disk that does not meet the standard or a defective disk as a defective product.

[0003] Inspections performed on a magnetic disk include, for example, an inspection (certification) for an error generated in a reproduced signal due to a defect such as a minute scratch on the disk,
Inspection of protrusions (glide check) on the surface of the magnetic disk can be mentioned.

In certification, a signal for inspection is actually recorded on a magnetic disk, and the signal is reproduced,
A method of finding a defect in a magnetic disk from the occurrence of an error is used.

[0005] In the glide check, it is checked whether a protrusion having a predetermined size or more exists on the surface of the magnetic disk. When a magnetic disk is used in a magnetic disk device equipped with a floating magnetic head, if there are large protrusions on the surface of the magnetic disk, not only does the magnetic head not stably float above the magnetic disk, but also the magnetic head collides with the protrusion. As a result, the durability of the magnetic disk device is deteriorated.
Therefore, it is necessary to ensure that the height of the protrusion on the surface of the magnetic disk is less than a predetermined value.

Conventionally, a flying head on which a piezoelectric element is mounted is floated on a magnetic disk, and a projection is detected by detecting an electric signal generated by a collision between the piezoelectric element and the projection.

[0007] However, due to a mounting error when the piezoelectric element is mounted on the flying head, the flying height of the flying head becomes unstable and the measurement accuracy may be reduced. In addition, the piezoelectric element has a large variation in sensitivity when colliding with the projection,
For this reason, there is a disadvantage that highly reliable inspection cannot be performed.

The flying height of the magnetic head has been decreasing year by year due to the recent increase in recording density. Also, high-precision surface processing is required for magnetic disks, and the number of protrusions on the surface of the magnetic disk is reduced, and the size thereof is also reduced. For this reason, it is becoming difficult to perform high-accuracy detection using detection using a piezoelectric element.

To cope with this, the thermal asperity of a magnetoresistive effect type magnetic head (hereinafter referred to as MR head) equipped with a magnetoresistive effect element (hereinafter referred to as MR element) is called. Investigation of a technique for detecting protrusions using phenomena is in progress. This is because the heat generated when the MR head collides with the projection is M
This is based on the fact that the output of the MR head changes by changing the electrical resistance of the R element.

[0010]

However, in order to use a thermal phenomenon such as thermal asperity of an MR head, a thermal change must appear as a change in head output with high sensitivity. Usually, in order to increase the sensitivity of the head serving as a sensor, it is necessary to reduce the size of the head, that is, the area of the surface facing the magnetic disk. As the size of the head becomes smaller, the time required for the projection inspection becomes longer correspondingly.

The inspection performed on the magnetic disk is as follows.
Since multiple inspection items were performed separately using dedicated inspection equipment, the cost and time required for inspection,
This has been a factor in increasing the space for installing the device.

For example, a projection inspection is first performed on a magnetic disk, and a defect inspection is performed on a magnetic disk that has passed the projection inspection. For this reason, even though the projection inspection passes, there is a case where the defect is determined to be defective in the defect inspection, and the inspection is troublesome twice. In such a case, the time and labor required for the projection inspection are wasted.

SUMMARY OF THE INVENTION The present invention has been proposed in view of the above-mentioned conventional circumstances, and provides a magnetic disk inspection apparatus and method capable of performing a projection inspection and a defect inspection of a magnetic disk in parallel. The purpose is to provide.

[0014]

A magnetic disk inspection apparatus according to the present invention comprises an inductive magnetic head for recording an inspection signal on a magnetic disk, and a magnetic head for reproducing the inspection signal recorded on the magnetic disk. A resistance effect type magnetic head; and a filter for separating a signal reproduced by the magnetoresistive effect type magnetic head into a signal component in a higher frequency range than a predetermined frequency and a signal component in a lower frequency range. The magnetic disk inspection apparatus records an inspection signal on the magnetic disk with the inductive magnetic head, and reproduces the inspection signal recorded on the magnetic disk with the magnetoresistive magnetic head. The signal reproduced by the magnetoresistive magnetic head is separated into a first signal component having a frequency lower than a predetermined frequency and a second signal component having a frequency higher than the predetermined frequency by the filter. Then, of the signal components separated by the filter, one of the signal components detects a protrusion on the surface of the magnetic disk, and the other signal component detects an error occurring in a reproduced signal from the magnetic disk. Features.

In the magnetic disk inspection apparatus according to the present invention as described above, the signal reproduced by the magnetoresistive head is filtered by the filter into the first signal component having a frequency lower than a predetermined frequency and the predetermined signal component. Since the signal is separated into the second signal component having a frequency higher than that of the second signal component, it is possible to separately detect each signal component. Further, in the magnetic disk inspection device, among the signal components separated by the filter, one of the signal components detects a protrusion on the surface of the magnetic disk, and the other signal component detects a defect of the magnetic disk. In addition, the detection of the protrusion on the magnetic disk and the detection of the signal error are performed in parallel, and the inspection time is shortened.

According to the method of inspecting a magnetic disk of the present invention, a signal recording step of recording an inspection signal on a magnetic disk by an inductive magnetic head, and the inspection signal recorded on the magnetic disk in the signal recording step are performed. A signal reproducing step of reproducing with a magnetoresistive magnetic head;
A signal separation step of separating the signal reproduced in the signal reproduction step into a first signal component having a lower frequency than a predetermined frequency and a second signal component having a frequency higher than the predetermined frequency by a filter; A detecting step of detecting a projection on the surface of the magnetic disk from one of the signal components separated in the signal separating step and detecting an error occurring in a reproduced signal from the magnetic disk from the other signal component; And characterized in that:

In the method for inspecting a magnetic disk according to the present invention as described above, in the signal separating step, the signal is divided by the filter into a first signal component having a lower frequency than a predetermined frequency and a first signal component having a higher frequency than the predetermined frequency. Since it is separated into the second signal component of the area, it is possible to separately detect each signal component. In the inspection method for a magnetic disk, in the inspection step, a protrusion on the surface of the magnetic disk is detected by one signal component, and an error generated in a reproduction signal from the magnetic disk is detected by the other signal component. Therefore, the detection of the protrusion on the magnetic disk and the detection of the signal error are performed in parallel,
Inspection time is reduced.

[0018]

Embodiments of the present invention will be described below.

FIG. 1 is a diagram conceptually showing a configuration example of a magnetic disk inspection apparatus (hereinafter, simply referred to as an inspection apparatus) of the present invention. The inspection device 1 includes a magnetic disk 2
The inspection is performed for the burnishing head 3
, An inspection sensor 4, an amplifier 5, a filter 6, a protrusion detection circuit 7, and a defect detection circuit 8.

The magnetic disk 2 has a magnetic layer formed on a disk-shaped non-magnetic substrate. The magnetic disk 2 may have a lubricant applied to the surface. Also,
The surface of the magnetic disk 2 is so smooth that the head can fly.

The burnishing head 3 is a head for removing dust and the like adhering to the surface of the magnetic disk 2.
If the inspection is performed with dust attached to the surface of the magnetic disk 2, the dust is detected as a defect of the magnetic disk 2,
The inspection may not be performed accurately. In addition, the dust causes the inspection sensor 4 to be clogged, thereby deteriorating the durability of the inspection device 1.

As shown schematically in FIG. 2, the inspection sensor 4 has an inductive magnetic head 9 and an MR head 10 integrally formed. FIG. 2 shows the inspection sensor 4 as viewed from the surface facing the magnetic disk 2.

The inductive magnetic head 9 is a recording magnetic head in which a pair of magnetic cores 11 are formed to face each other with a magnetic gap 12 therebetween, and records an inspection signal on the magnetic disk 2. Also, MR head 1
Numeral 0 denotes a reproducing magnetic head in which the MR element 13 is sandwiched between a pair of magnetic substances 15 via a non-magnetic substance 14, and outputs a signal for inspection recorded on the magnetic disk 2 by the inductive magnetic head 9. Reproduce. These magnetic heads may be determined according to the required track pitch,
For example, the head track width is set to 2.5 μm.

As shown in FIG. 3, the inspection sensor 4 is attached to a slider 16 and floats on the magnetic disk 2 by a predetermined flying height t ₁ to record or reproduce an inspection signal. The flying height t ₁ of the inspection sensor 4 is set to a value allowed as the size t ₂ of the projection 17 present on the surface of the magnetic disk 2. Specifically, the flying height t ₁ of the inspection sensor 4 is, for example, about 38 nm.

Here, when a signal for inspection is reproduced by the MR head 10, a projection 17 larger than the flying height t ₁ of the MR head 10, that is, the flying height t ₁ of the inspection sensor 4 is formed on the surface of the magnetic disk 2. Is present, this projection 17
And the MR head 10 collide. When the MR head 10 and the projection 17 collide, heat is generated by the collision. The temperature of the MR head 10 (hereinafter, referred to as head temperature) fluctuates due to the influence of heat at the time of the collision. Generally, the MR element 13 mounted on the MR head 10 has temperature dependency, and when the head temperature fluctuates, noise appears in the reproduction output. The noise depending on the fluctuation of the head temperature is called thermal asperity.

The inspection apparatus 1 inspects the magnetic disk 2 for a defect based on an error in a signal reproduced by the MR head 10 and detects the thermal asperity of the MR head 10 from the signal to thereby detect the surface of the magnetic disk 2. It is inspected whether there is a protrusion having a predetermined size or more.

The amplifier 5 amplifies the signal 18 reproduced by the MR head 10 to a predetermined level.

The filter 6 separates the signal 18 reproduced by the MR head 10 and amplified by the amplifier 5 into two components, a signal component having a frequency higher than a predetermined frequency and a signal component having a lower frequency. .

The band of the signal caused by the thermal asperity due to the collision between the MR head 10 and the projection is narrow and low. This is because the fluctuation of the head temperature is a fluctuation of the low frequency. On the other hand, signals used for defect detection include a linear recording density of 10
A signal of 0 Kfci or more is used. At this time, although the signal frequency varies depending on the disk rotation speed, the signal frequency is as high as several tens MHz or more.

Therefore, the reproduction signal 1 from the MR head 10
8 is separated at a predetermined frequency by the filter 6, thereby separating the reproduction signal from the MR head 10 into a projection detection signal 18a having a relatively low frequency and a defect detection signal 18b having a relatively high frequency. Can be led to different circuit systems for processing. Therefore, the cut-off frequency of the filter 6 needs to be about the upper limit frequency of the thermal asperity and lower than the lower limit frequency of the signal band for inspection.

FIGS. 4 and 5 show a signal due to the collision between the MR head and the projection and its spectrum. here,
FIG. 4 shows a signal due to the collision between the MR head and the projection,
FIG. 5 shows a spectrum of a signal due to a collision between the MR head and the protrusion shown in FIG. From FIG. 5, it can be seen that the signal band caused by thermal asperity due to the collision between the MR head and the projection is narrow and low, and is concentrated in a frequency band of about 100 kHz to 300 kHz or less.

On the other hand, in the detection of a defect of the magnetic disk 2, when an error of about 100 bit length (25 μm) is detected using a signal of a linear density of about 100 Kfci, for example, if the linear velocity is 15 m / sec, the frequency is Is 3
0 MHz. Since the 100-bit length is equivalent to 50 wavelengths, the frequency is 1/50, which is a signal frequency of about 600 kHz.

Therefore, the cut-off frequency of the filter 6 depends on the relative speed between the MR head 10 and the magnetic disk 2 and the like, but in many cases, 300 kHz to 600 kHz.
It is preferable to be about z. By setting the cutoff frequency of the filter 6 to about 300 kHz to 600 kHz,
The projection detection signal 18a and the defect detection signal 18b can be separated without damaging their waveforms. Specifically, the cutoff frequency is, for example, 500 kHz.

As such a filter 6, for example,
Examples include a combination of a low-pass filter that passes a signal having a frequency equal to or lower than a predetermined frequency and a high-pass filter that passes a signal having a frequency equal to or higher than a predetermined frequency.

The protrusion detection circuit 7 determines the presence or absence of a protrusion of a predetermined size or more on the surface of the magnetic disk 2 by performing a level determination on the protrusion detection signal 18 a separated by the filter 6. To detect.

If the surface of the magnetic disk 2 is not magnetized, only the output voltage resulting from the heat generated when the magnetic head 2 collides with the projection is obtained from the MR head 10, as shown in FIG. An inspection can be performed by assuming that a projection exists when an output voltage caused by such a thermal fluctuation is detected. When a signal is recorded on the magnetic disk 2, the signal waveform is superimposed on the waveform shown in FIG.

The defect detection circuit 8 detects an error in the defect detection signal 18b separated by the filter 6 and judges the level thereof, thereby detecting a defect in the magnetic disk 2. As such an error, for example, a missing error in which the output decreases in a bit unit is cited.

In order to inspect the magnetic disk 2 using the inspection apparatus 1 as described above, first, the magnetic disk 2 is supplied to the inspection apparatus 1 by a handling device (not shown) or the like. Next, a burnishing operation is performed using the burnishing head 3 to remove dust and the like attached to the surface of the magnetic disk 2.

Next, the inspection sensor 4 is connected to the magnetic disk 2.
Inspection is started by loading at a predetermined radius position of. In order to inspect the magnetic disk 2, first, an inductive magnetic head 9 records an inspection signal on the magnetic disk 2. For example, a signal having a linear recording density of 100 Kfci or more is used as the inspection signal. When a signal having a linear recording density of 100 Kfci or more is used as a signal for inspection, it varies depending on the number of rotations of the disk.
The above signal frequency is obtained.

Next, the inspection signal recorded by the inductive magnetic head 9 is reproduced by the MR head 10. At this time, as shown in FIG. 3, the inspection sensor 4 having the MR head 10 is mounted on the slider 16 and floats on the magnetic disk 2 with a predetermined flying height t ₁ . The flying height t ₁ of the inspection sensor 4 is set to the allowable height t _{2 of the} projection 17. Specifically, the flying height t ₁ of the inspection sensor 4 is, for example, 38 nm.
Degree. The signal 18 reproduced by the MR head 10 is
After being amplified by the amplifier 5 to a predetermined signal level, it is input to the filter 6.

The signal input to the filter 6 is separated by the filter 6 into a projection detection signal 18a in a frequency range lower than a predetermined frequency and a defect detection signal 18b in a frequency range higher than the predetermined frequency. . At this time, filter 6
Is about 300 kHz to 600 kHz. 300 kHz cut-off frequency of filter 6
By setting the frequency to about 600 kHz, the protrusion detection signal 18
a and the defect detection signal 18b can be separated without damaging their waveforms. Specifically, the cutoff frequency of the filter 6 is set to, for example, about 500 kHz.

FIG. 7 shows an example of the signal 18 reproduced by the MR head 10. By separating this signal 18 by the filter 6, the projection detecting signal 18 as shown in FIG.
a and a defect detection signal 18b as shown in FIG. In this way, by performing frequency discrimination, it is possible to separate the protrusion detection signal 18a and the defect detection signal 18b and to lead them to different circuit systems for processing.

The protrusion detection signal 18a discriminated by the filter 6 is sent to the protrusion detection circuit 7, and the defect detection signal 18b is sent to the defect detection circuit 8, respectively. The protrusion detection circuit 7 and the defect detection circuit 8 constitute independent circuits. Thereby, two types of inspections, that is, the projection detection and the defect detection, can be performed in parallel.

The level of the protrusion detection signal 18a sent to the protrusion detection circuit 7 is determined by the protrusion detection circuit 7. From the projection detection signal 18a, an output voltage resulting from a thermal fluctuation generated when the projection 18 collides with the projection is obtained as shown in FIG. An inspection can be performed by assuming that a projection exists when an output voltage caused by such a thermal fluctuation is detected. Then, the presence or absence of the protrusion and the size of the protrusion are determined by comparing this voltage with a certain reference value.

In order to determine the level of the protrusion detection signal 18a, the protrusion detection signal is measured in advance for a disk having a protrusion with a known height, and the signal voltage of the obtained protrusion detection signal 18a is measured. By comparing the signal voltage of the protrusion detection signal with respect to the protrusion having a known height, the presence or absence of the protrusion and the size of the protrusion can be known.
Further, the protrusion detection circuit 7 outputs the input protrusion detection signal 1.
The filter 8a may be subjected to processing such as filtering or passing through an amplifier as necessary.

The level of the defect detection signal 18b sent to the defect detection circuit 8 is determined by the defect detection circuit 8 and the error is measured. As the error, a so-called missing error or the like in which the signal amplitude decreases in a bit unit is measured. To detect a missing error, for example, 100b
It detects errors up to an it length (about 25 μm in the case of 100 Kfci). Further, the defect detection circuit 8 may perform processing such as filtering or inputting the inputted defect detection signal 18b as necessary.

When a defect or a protrusion is detected on the magnetic disk 2, it is necessary to perform a similar inspection by changing the frequency of an inspection signal or the like, that is, to perform a so-called retry.

As described above, the inspection apparatus 1 including the MR head 10 and the inductive magnetic head 9 can perform the projection inspection and the defect inspection in parallel. Therefore, the inspection time can be reduced.

Conventionally, the projection inspection and the defect inspection have been performed separately. For example, a projection inspection is first performed on a magnetic disk, and a defect inspection is performed on a magnetic disk that has passed the projection inspection. Therefore, even if the projection inspection passes,
In some cases, the defect is determined to be defective in the defect inspection, and the inspection is troublesome twice.

In this inspection apparatus 1, the protrusion inspection and the defect inspection are performed in parallel, and the magnetic disk 2 is removed when it is determined to be defective in one of the inspections, so that the inspection can be performed more efficiently. It can be carried out.

Another advantage of performing the inspection at the same time is that the disk rotation time in the projection inspection and the defect inspection can be shared. Conventionally, a head is fixed at a certain radial position, where a projection inspection and a defect inspection are performed. After the inspection is completed, the sensor is moved to an adjacent position to inspect the adjacent position. Since the time required for moving to the adjacent position can be shared by the two inspections, the inspection time can be reduced.

In the above-described embodiment, a case has been described as an example where a head in which an inductive magnetic head and an MR head are integrally formed is used as an inspection sensor. , As shown in FIG.
The inductive magnetic head 20 and the MR head 21 may be separately arranged.

Similarly, when the magnetic disk 22 is inspected by using the inspection apparatus 1 in which the inductive magnetic head 20 and the MR head 21 are separately arranged, similarly, first,
After the dust on the surface of the magnetic disk 22 is removed by the burnishing head 23, an inspection signal is recorded on the magnetic disk 22 by the inductive magnetic head 20. Then, the signal recorded on the magnetic disk 22 is reproduced by the MR head 21, and the reproduced signal 24 is amplified to a predetermined level by the amplifier 25.
And a defect inspection signal 24b. By processing the separated projection inspection signal 24a and the defect inspection signal 24b by the projection inspection circuit 27 and the defect inspection circuit 28, respectively, the projection and the defect of the magnetic disk 22 can be inspected.

[0054]

According to the magnetic disk inspection apparatus of the present invention,
Since the signal reproduced by the MR head is separated into two signals and one of the signals is used for the protrusion inspection and the other signal is used for the defect inspection, the protrusion inspection and the defect inspection are performed in parallel in the same apparatus. It can be carried out. Therefore, in the magnetic disk inspection apparatus of the present invention, the space occupied by the apparatus can be reduced and the inspection time can be shortened.

In the magnetic disk inspection method of the present invention, M
Since the signal reproduced by the R head is separated into two signals and one of the signals is used for the protrusion inspection and the other signal is used for the defect inspection, the protrusion inspection and the defect inspection can be performed in parallel. . Therefore, in the magnetic disk inspection method of the present invention,
Inspection time can be reduced.

Therefore, according to the present invention, the time and cost required for the inspection can be reduced, and the production efficiency of the magnetic disk can be improved.

[Brief description of the drawings]

FIG. 1 is a diagram conceptually showing a configuration example of a magnetic disk inspection apparatus according to the present invention.

FIG. 2 is a diagram schematically showing a configuration example of the inspection sensor of FIG. 1 on a surface facing a magnetic disk.

FIG. 3 is a cross-sectional view showing a state where the inspection sensor is flying above the magnetic disk.

FIG. 4 is a diagram showing a signal waveform when an MR head collides with a protrusion.

FIG. 5 is a spectrum of the signal shown in FIG. 4;

FIG. 6 is a diagram showing an example of a signal waveform when an MR head collides with a protrusion.

FIG. 7 is a diagram showing an example of a waveform of a reproduction signal from an MR head.

FIG. 8 is a diagram illustrating an example of a waveform of a protrusion detection signal.

FIG. 9 is a diagram illustrating an example of a waveform of a defect detection signal.

FIG. 10 is a diagram conceptually showing a configuration example of a magnetic disk inspection apparatus according to the present invention.

[Explanation of symbols]

1 inspection device, 2 magnetic disk, 3 burnish head, 4 inspection sensor, 5 amplifier, 6 filter, 7 protrusion detection circuit, 8 defect detection circuit

Claims (7)

[Claims] 1. An inductive magnetic head for recording a test signal on a magnetic disk, a magnetoresistive magnetic head for reproducing a test signal recorded on the magnetic disk, and a magnetoresistive magnetic head And a filter that separates the signal reproduced by the above into a first signal component having a lower frequency than a predetermined frequency and a second signal component having a higher frequency than the predetermined frequency. The inductive magnetic head includes: A signal for inspection is recorded on the magnetic disk, a signal for inspection recorded on the magnetic disk is reproduced by the magnetoresistive magnetic head, and a signal reproduced by the magnetoresistive magnetic head is The filter separates the signal component into a signal component in a higher frequency range than a predetermined frequency and a signal component in a lower frequency range, and one of the signal components separated by the filter is used. Detecting a projection of the surface of the magnetic disk by the signal component of the inspection apparatus of the magnetic disk and detects errors that occur in the reproduced signal from the magnetic disk by the other signal components. 2. The magnetic disk inspection apparatus according to claim 1, wherein the inductive magnetic head and the magnetoresistive magnetic head are integrally formed. 3. The predetermined frequency is 300 kHz to 6 kHz.
2. The magnetic disk inspection apparatus according to claim 1, wherein the frequency is within a range of 00 kHz. 4. A projection on a surface of the magnetic disk is detected by the first signal component among the signal components separated by the filter, and is generated in a reproduction signal from the magnetic disk by the second signal component. 2. The magnetic disk inspection apparatus according to claim 1, wherein an error is detected. 5. A signal recording step of recording an inspection signal on a magnetic disk by an inductive magnetic head, and the inspection signal recorded on the magnetic disk in the signal recording step is transmitted by a magnetoresistive magnetic head. A signal reproducing step of reproducing, a signal reproduced in the signal reproducing step, a first signal component having a frequency lower than a predetermined frequency by a filter, and a second signal component having a frequency higher than the predetermined frequency. And a signal separation step of separating the signal components in the signal separation step. One of the signal components detects a protrusion on the surface of the magnetic disk, and the other signal component converts the signal into a reproduction signal from the magnetic disk. A magnetic disk inspection method, comprising: a detection step of detecting an error that occurs. 6. The magnetic disk inspection method according to claim 5, wherein in the signal separation step, the predetermined frequency is in a range of 300 kHz to 600 kHz. 7. In the detecting step, a protrusion on the surface of the magnetic disk is detected by the first signal component,
6. The magnetic disk inspection method according to claim 5, wherein an error generated in a reproduction signal from the magnetic disk is detected by the second signal component.