JP2001176003A - Magnetic defect inspecting method for magnetic disk - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic defect inspecting method for magnetic disk, capable of carrying out highly accurate defect inspection by correcting the positional shifting of a magnetic head recording/reproducing element for inspecting a defect so as to make a reproducing signal high in S/N. SOLUTION: This inspecting method comprises the steps of obtaining the effective positional shifting of the recording/reproducing element of a defect inspection magnetic head by pre-measuring the off-track profile of a reproducing output signal, correcting positional shifting and reproducing all the tracks by the same track pitch as recording time such that the center of the reproducing element coincides with the center of a recording position after signals are recorded in all the tracks of the data area of an inspection magnetic disk, and judging a magnetic defect of a bit part reduced with respect to the one round average reading voltage of each track.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for inspecting magnetic defects on the surface of a magnetic disk.

[0002]

2. Description of the Related Art A magnetic disk device is a device for recording / reproducing data by a magnetic change with a magnetic head floating on the surface of a magnetic disk. The magnetic head has a function of moving relative to the magnetic disk, recording magnetic information at an arbitrary position on a recording medium, and reproducing the recorded magnetic information as necessary. In recent years, a magneto-resistive head (hereinafter, MR head) that reproduces information recorded on a magnetic recording medium with high sensitivity has become mainstream due to the increase in recording density of a magnetic disk device. The principle of this reproduction is that a change in the magnetic field from the magnetic recording medium changes the magnetoresistance, and this change in resistance
By passing a constant current through the MR element, it is converted into a DC voltage signal and the data is reproduced.

[0003] With the increase in recording density, even for magnetic disks, defect inspection using an MR head is performed in order to make magnetic defect inspection that cannot be tolerated by a magnetic disk device closer to practical use.

[0004] The inspection method is to perform recording / reproducing at a specified frequency while flying above the surface of the magnetic disk by using the same head mounted on the magnetic disk device or a head having a similar structure and electrical characteristics. It is determined whether the signal characteristic is other than the specified value, and an inspection for a magnetic defect is performed.

In general, as a method for inspecting this magnetic defect, first, a burst pattern having a prescribed frequency is written on one track, an average track reproduction signal voltage is measured without moving its position, and the average voltage value is measured. , A signal deviating from a specified slice level is converted into a pulse signal, detected as a defect, the magnetic head is moved to the next track, and the surface of the magnetic disk is similarly inspected in the order of recording, reproduction, and defect inspection.

[0006]

A magnetic head for inspecting a magnetic defect of a magnetic disk is required to have a capability of detecting a magnetic defect corresponding to a 1-bit size of a magnetic disk device for the purpose. For this reason, it is desirable to use a magnetic head used in an actual machine or a magnetic head having similar characteristics, but the width of the recording / reproducing element has been narrowing due to the recent increase in recording density. Due to the narrowing of the element width, the ratio of the positional deviation of the recording / reproducing element in the radial direction of the magnetic disk is increased, and the voltage level of the reproduced signal is lowered. The ability to detect stably decreases. This will be described with reference to FIGS. FIG. 1 shows an offset profile obtained by moving (offset) the magnetic head in the radial direction of the magnetic disk at the time of reproduction between the recording / reproducing elements of the magnetic head and measuring the head output signal. FIG. 7 shows a reproduced head output signal and an output signal waveform reproduced at a position shifted from a recording position. FIG. From this, it can be seen that the signal quality of the signal waveform reproduced in a state shifted from the recording position is degraded.

FIG. 2 shows the slice level dependence of a bit missing defect (missing error) with respect to a reproduction output due to a difference in offset between recording / reproducing positions of a magnetic head measured on the same magnetic disk. From this, it can be seen that the slice level rises higher as the recording / reproduction offset amount is smaller. The commonly used slice level is 65-70%, which indicates that magnetic defect inspection is becoming more difficult.

From the above, as the inspection conditions for detecting a magnetic defect of a magnetic disk, recording / recording of an MR magnetic head is performed.
It can be said that the smaller the magnetic displacement (offset) of the reproduction, the higher the detection accuracy. Furthermore, some magnetic disk devices are designed so that the recording / reproducing element position is shifted in the radial direction in advance due to the relative positional relationship between the magnetic disk and the magnetic head. There is a demand for an inspection method that eliminates such operations and can detect magnetic defects of a magnetic disk with high accuracy.

On the other hand, in the inspection apparatus, a fine adjustment function is added to the magnetic head feed mechanism with respect to the magnetic displacement amount of recording / reproducing. In this method, a positional deviation amount is learned in advance by a fine adjustment function, and recording / reproduction is performed with an offset amount learned for each track. In this method, since the offset operation is performed for each track, the measurement time is prolonged, which is a problem in mass productivity.

An object of the present invention is to provide an inspection method for detecting a magnetic defect on the surface of a high-density magnetic disk using an MR head with high accuracy and without impairing mass productivity.

[0011]

In order to achieve the above object, a disk magnetic defect inspection method according to the present invention makes it possible to inspect a minute magnetic defect at the time of high density by the following method.

According to the present invention, the data surface of a magnetic disk to be inspected must be larger than the width of the recording element so as not to lower the accuracy of detecting the magnetic defect caused by the radial displacement of the effective recording and reproducing elements of the magnetic head. After the burst signal is recorded on all tracks at the track pitch of, the reproduction is performed by correcting the positional deviation so that the center of the reproducing element is aligned with the recording center position, and reproduction is performed at the same track pitch.

Further, by dividing the magnetic disk in the radial direction to shorten the moving distance of the magnetic head, and by correcting the position by performing position correction for each divided area, the mechanical accuracy of the position correction can be further improved.

After recording all tracks on the data surface of the magnetic disk, the center position of the reproduction position is made coincident, thereby increasing the S / N of the reproduction signal and detecting a minute magnetic defect. By dividing in the radial direction, the number of position corrections can be reduced, and inspection can be performed without impairing mass productivity.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 3 shows the configuration of the magnetic defect inspection apparatus for a magnetic disk used in the present invention. The defect inspection apparatus includes a rotary drive system including a 3.5-inch magnetic disk 1 to be inspected, a spindle 2, and a driving device 3, and a magnetic device that detects a magnetic defect by scanning the surface of the rotating magnetic disk 1. It comprises a head 4 and a magnetic defect detection signal processing unit 5 for amplifying and judging a signal detected by the magnetic head 4. The magnetic defect detection signal processing unit 5 includes a preamplifier 6 for amplifying a signal detected by the magnetic head 4, a buffer amplifier 7, and an error detection circuit 9 for determining whether the signal is a magnetic defect. In the present invention, the 3.5-inch magnetic disk 1 has a holding force of 197.5 KA / m (2.5 KOe) and a holding force squareness ratio of 0.85. The magnetic head 4 used had a flying height of 25 nm, a recording core width of 2.8 μm, a reproducing core width of 1.5 μm, and a magnetic displacement of 0.4 μm for recording and reproduction. The recording / reproducing conditions in the configuration of this inspection apparatus were set to a write current value of the magnetic head of 40 mA, a MR sense current value of 10 mA for reproduction, a burst pattern of a recording signal of 40 MHz, and the rotation speed of the magnetic disk was 6000 rpm.

(Embodiment 1) The measurement range of the magnetic defect of a 3.5-inch magnetic disk was set to the radial position R20 to 45 mm, the number of divisions in the radial direction was 1, 2, 5, 10, 20, 50, and the measurement stroke was 25 mm. Was divided equally by each division number. The following measurement was performed for each divided area.

At the inner peripheral position of the area, the off-track profile of the reproduction output shown in FIG. 1 is measured to measure the effective offset of the recording / reproducing element position of the magnetic head, which is 0.4 μm in this embodiment. Next, a signal is recorded in the divided area from the innermost portion to the outer portion at a pitch of 5 μm. Thereafter, the magnetic head is scanned to the inner circumferential position to correct the measured magnetic head position by 0.4 μm, and while reproducing all tracks at a pitch of 5 μm, a signal which is lower than the slice level 70% with respect to the average read voltage value of each track is generated. The number of pulsed signals of 5 bits or less was detected as the number of magnetic defects in order to confirm the detectability of fine defects. This measurement was repeated for each divided area to measure the magnetic disk radial position R20 to 45 mm. Further, in order to confirm the effect of the present invention, the main measurement was repeated five times under each of the division number conditions, and the reproducibility of the number of magnetic defects was confirmed.
The reproducibility was represented by the ratio of each measured value, with the average value of five measurements taken as 100%. FIG. 4 shows the results. When the number of divisions was 5 or less, no significant difference was observed in the reproducibility of the number of errors compared with the condition without off-track correction, but when the number of divisions was 10 or more, the result that the reproducibility was improved was obtained. This is because the influence of the accuracy of the mechanical system for scanning the magnetic head of the inspection apparatus is reduced by reducing the stroke of the divided area.

Example 2 The same measurement was performed under the same conditions as in Example 1 except that the recording core width of the magnetic head was 1.5 μm and the reproducing core width was 0.8 μm. Improved. As shown in FIG. 5 from the present embodiment and the first embodiment, it is more stable to detect magnetic defects by setting the number of divisions so that the ratio of the stroke of the division area to the recording core width is about 1: 1000 or less. it can.

[0020]

By using this method, it is possible to detect fine magnetic defects with good reproducibility regardless of the offset amount of the recording / reproducing element of the MR head and without impairing mass productivity.

[Brief description of the drawings]

FIG. 1 is an offset profile of a magnetic head, a head output signal obtained by reproducing data for one track at a recording center position, and an output signal waveform obtained by reproducing data at a position shifted from a recording position.

FIG. 2 is a diagram showing slice level dependence of an error caused by a difference in offset between recording and reproducing positions of a magnetic head.

FIG. 3 is a configuration diagram of a magnetic disk magnetic defect inspection apparatus according to an embodiment of the present invention.

FIG. 4 is a diagram showing an evaluation result 1.

FIG. 5 is a diagram showing an evaluation result 2.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Disk, 2 ... Spindle, 3 ... Drive device, 4 ... Magnetic head for defect detection, 5 ... Magnetic defect detection signal processing part,
6: Preamplifier, 7: Buffer amplifier, 8: Low Pass F
ilter, 9: error detection circuit section, 10: comparator,
11 ... Error flag.

Claims (2)

[Claims] A magnetic disk is rotated, and a recording / reproducing element is integrated into a composite thin film structure. The reproducing element uses a magnetic head of a magnetoresistive element, and the magnetic head is mounted on the magnetic disk. In the inspection method for detecting a magnetic defect by performing a recording / reproducing operation by floating the disk, a burst pattern having a specified frequency is recorded at a pitch of at least the recording element width over the entire surface of the magnetic disk in the radial direction, and then recording is performed. An inspection method characterized in that a positional deviation is corrected so that the center of the reproducing element is aligned with the center position, and magnetic defects are measured at the same pitch as during recording. 2. The inspection method according to claim 1, wherein the radial direction is divided and measured at the time of recording on the magnetic disk in the radial direction.