JP3366172B2 - Magnetic disk drive - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic resistance effect element (hereinafter abbreviated as MR element) for recording magnetic information recorded on a recording medium.
More specifically, the present invention relates to a magnetic disk device or an array system using the magnetic disk device, and more specifically, a sense current is supplied to reproduce information by an MR element, but when the sense current is supplied in a certain direction, electromigration occurs, Deteriorates. Therefore, the present invention relates to a preventive diagnosis device for a device failure that detects a state in which an element starts to deteriorate, and performs an abnormal process in the device or system based on the detection result, and a countermeasure based on the diagnosis result.

[0002]

2. Description of the Related Art An MR element is an element whose electric resistance has a value corresponding to a vector amount of a magnetic field input thereto. To reproduce the magnetic information of the recording medium using this element,
The resistance value of the MR element is changed by applying a bias magnetic field to the MR element and causing the magnetic flux from the recording medium to flow into the element. Information is reproduced by changing the change in the resistance value to a voltage across the element by the sense current and amplifying the terminal voltage in the reproducing circuit thereafter.

The problem is that a sense current must be passed in order to activate the MR head. However, if a high density current is kept flowing in a certain direction, a phenomenon called electromigration occurs and the MR element deteriorates. Fig. 2 shows MR by electromigration
The change in the resistance value of the device was shown.

An outline of electromigration will be given. When an electric field is applied to metal, electrons flow in a certain direction. At the same time, the free electrons held by the metal are drawn to the electric field and gradually disappear. Therefore, the corrosion of the element progresses,
Transformation begins from conductor to nonconductor. Then, the resistance value increases and the reproducing function deteriorates rapidly.

Therefore, as described in Japanese Patent Application Laid-Open No. 6-314405, it has been proposed that electromigration can be avoided by changing the direction of the sense current every certain period.

On the other hand, the MR element has a sensitivity distribution in the track width direction. The sensitivity distribution has a characteristic asymmetric with respect to the center of the track width. Therefore, even if the directions of the sense currents are switched, the same characteristics as the head cannot be maintained. Therefore, the method described in Japanese Patent Laid-Open No. 6-314405 has a problem in that electromigration can be prevented but is not practical.

[0007]

In order to make the MR head practical, it is not possible to switch the direction in which the sense current flows. Therefore, electromigration always occurs. Therefore, a problem to be solved by the present invention is to avoid the influence of electromigration and prevent a device failure.

[0008]

As a physical phenomenon due to electromigration, as shown in FIG.
The DC resistance value of the R element increases. Therefore, the DC resistance value Rmrdc at the normal time is stored, and the DC resistance value of the MR element is constantly detected and compared with the normal value. If the resistance value increases above a certain value, deterioration has started. Abnormality processing is performed as a thing. As an evaluation method of this resistance value,
There is a method of evaluating the voltage applied to the MR element. On this occasion,
In order to evaluate the voltage correctly, the signal pattern is constant.
Is desirable.

In the abnormal condition processing, after issuing a maintenance request, the data in the data area which the MR element whose deterioration has started is in charge is saved to another head area or another drive to maintain the sense current of the deteriorated element. Turn off until time.

According to the present invention, the elements other than the deteriorated elements can be operated in a normal state, and the saved data can be recorded / reproduced by the save destination head. it can.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment in the case of being applied to a magnetic disk device will be described. First, the configuration of the magnetic disk device will be described with reference to FIGS.

Here, 10 is a magnetic disk device,
Reference numeral 11 is a recording medium, 12 is an MR composite head, 13 is a recording / reproducing circuit system, 14 is an actuator, 15 is a voice coil motor, 16 is positioning control, 17 is a control unit, 18 is an interface circuit, 19 is a host machine, 20 is a Motor, 21
Is an inductive head (recording head), 22 is an MR head, 101 is an output from the preamplifier 104, 102 is a resistance abnormality detection unit, 103 is an output of the resistance abnormality detection unit, 10
4 is a preamplifier.

The magnetic disk device 10 includes one or a plurality of magnetic recording media 11, and at least one MR composite head 12 and MR composite head 1 on each surface of the magnetic recording medium 11.
2, a recording / reproducing circuit system 13 for recording / reproducing, an interface circuit 18 for inputting / outputting data to / from the host computer 19, and an MR composite head 12 are mechanically supported at a predetermined radial position on the magnetic recording medium 11. An actuator 14 for sending, a voice coil motor (VCM) 15 for driving the actuator, a positioning control 16 for performing control to take servo information by the MR composite head 12 and move it to a predetermined radial position of a magnetic disk, magnetic recording. The control unit 17 controls the motor 20 for rotating the medium 11.

The MR composite head 12 comprises an inductive head 21 for recording and an MR head 22 for reproduction only.

The MR head 22 is a reproducing magnetic head utilizing the magnetoresistive effect in which the magnetoresistive effect element is magnetized by the magnetic field from the medium and the electric resistance of the magnetoresistive effect element changes according to the inclination of the magnetization vector. .

The reproducing circuit system of the MR head 22 uses a sense current M to detect a change in the resistance of the MR head 22.
A reproduced signal is obtained by detecting a change in the voltage generated at both ends of the MR head 22 at that time, or a change in the sense current when a constant voltage is applied between the terminals. The recording / reproducing circuit system 13 obtains digital data "0" and "1" from the reproduced signal, and the information is transferred to the host device 19 via the interface circuit 18.

An embodiment of the present invention will be described with reference to FIGS. 1, 2 and 8.

When reproducing with the MR head, it is necessary to flow the sense current as described above. When the sense current is kept flowing, the DC resistance value of the MR element increases due to electromigration, as shown in FIG. When the resistance value becomes higher than the normal resistance value Rmrdc by 5%, the resistance value rapidly increases thereafter. Therefore, it is defined that the deterioration has started at this time, and the abnormal resistance value is issued.

A signal corresponding to the resistance value of the MR head is input to the resistance abnormality detecting unit 102 via the output 101 from the preamplifier 104 shown in FIG. Resistance abnormality detection unit 102
Then, a value corresponding to the resistance value Rmrdc in the normal state and 10
The values input from 1 are compared, and if the resistance value increases by 5% or more, a resistance abnormality signal is sent to the control unit 17 via 103. When the control unit 17 receives the resistance abnormality signal, the control unit 17 controls each unit according to the procedure of the abnormality process shown in FIG.

Next, a first embodiment of the preamplifier 104 that produces a signal corresponding to the resistance value of the MR head will be described with reference to FIG.

FIG. 3 shows a preamplifier similar to the conventionally used current bias current sense system. In the present embodiment, the base potential of Q2 corresponds to the terminal voltage of the DC resistance of the MR head 22, as described later. Therefore, the signal corresponding to the resistance value of the MR head is output via 101. The operation of the preamplifier 104 will be briefly described.

Since the current source current J has a differential amplification structure in Q1 and Q2, the amount of current to Q1, that is, the MR element is determined depending on the base voltage of Q2. Therefore, J is set to a current twice the sense current, and Q1, Q
The base potential of Q2 is determined so that 2 shunts equally.
However, since the MR head 22 is connected to the emitter of Q1, it is necessary to set the base potential of Q2 to a potential that reduces the voltage drop of the MR head 22.

Therefore, the resistors R1 and R2 connected to the collectors of Q1 and Q2 are used as load resistors of Q1 and Q2, and their respective potentials are input to the amplifier G as differential signals. The output of the amplifier G is input to the DC level extraction circuit 201, and at 201, a DC offset voltage is extracted. By applying that voltage to the base of Q2, it operates so that there is no DC offset. Therefore, a potential corresponding to the resistance of the MR head 22 is output via 101.

Next, a second embodiment of the preamplifier 104 that produces a signal corresponding to the resistance value of the MR head will be described with reference to FIG.

In this embodiment, the DC level detection circuit 202 detects the voltage across the MR head 22 before the signal is input to the preamplifier, and outputs it to 101.

DC level detection circuit 2 shown in FIGS. 3 and 4.
Reference numerals 01 and 202 are low-frequency filters that pass only the DC component.

Next, an embodiment of the resistance abnormality detecting unit 102 of FIG. 1 will be described with reference to FIG.

The signal input from 101 is converted into a digital value by the sampling ADC 203. In the next selector 204, by a select signal 211 from the outside,
Choose between initial set or normal resistance evaluation.
For example, in the inspection before shipment, when the initial state is set, the select signal 211 is operated to set the voltage value corresponding to the resistance value of the MR head in the normal state to the storage unit 20 in the normal state.
Register at 6. After registration in 206, the select signal 211 is fixed and the normal evaluation system is selected. As a result, the output of the selector 204 is output to the storage unit 205.

As shown in FIG. 5, the signal 101 from the detection monitor in the DC resistance detector is sampled 203, converted into a digital value, and stored in the storage means 207. A plurality of times of data are fetched from the detection monitor, input to the storage means 205, and the average output is calculated by the average 27. This calculated output is used as one input of the comparator 209. The coefficient unit 208 multiplies the output of the storage unit 206, which stores the voltage value corresponding to the normal resistance value of the MR head, by a constant coefficient (example 1.05), and outputs the output of this coefficient unit to the other of the comparator 209. Input it.

The output from the average 207 is the coefficient unit 20.
When it becomes larger than the output from 8, it is judged that the DC resistance value of the MR head is abnormal, and the process at the time of abnormality is performed next.

Next, when evaluating the potential difference of the MR head, if a dedicated signal is recorded and evaluated by reproducing it, the storage area of user data becomes small.
Therefore, the servo area shown in FIG. 6 is proposed as a place where the potential difference of the MR head can be correctly evaluated without being affected by the reproduction signal. In the servo area, as a place where the signal amplitude does not change even if a position shift in the track width direction occurs,
For example, a burst part having a constant amplitude at a constant cycle, an A burst part in the case of track #N, a track # N +
When it is 1, it is the B burst portion, and when it is track # N + 2, it is the C burst portion. Since the track number can be known by the address marker, the phase of the burst signal for evaluation can be determined.

By using the servo signal area, it is possible to store data for evaluating the resistance abnormality of the MR head for each round. Further, by using the burst portion, the frequency spectrum becomes substantially constant, and it becomes easy to extract only this signal component.

The flow shown in FIG. 7 shows the above-described operation of the resistance abnormality detecting unit shown in FIG. 5 and the mode of use of the signal pattern suitable for detecting the DC resistance of the MR head shown in FIG. 6 in time series. This is the procedure shown.

Finally, the items and procedures of the abnormal process shown in FIG. 8 will be described. The purpose of the abnormal time processing is to protect the data in the data area in which the MR head showing the abnormal resistance plays the data. That is, when the MR head cannot reproduce, the data on that side cannot be read out unless a special method is used. Therefore, it is necessary to move all the data to a place in charge of the MR head capable of reproducing all the data before the reproduction becomes impossible.

Before describing the abnormal time processing method, there are four types of drive systems shown in FIG.

1.1 HDA (Head Disk Assembly)
One head drive is composed of one drive.

2.1 A drive in which two or more heads in HDA are composed of one drive.

3.1 HDA has 1 head drive and 2 drives
A drive system consisting of multiple units.

A drive system in which a drive having two or more heads in one HDA is composed of two or more heads.

Here, in a system in which the drive of one head / HDA is composed of one drive, after a resistance abnormality of the MR element is detected, a maintenance request is issued, all the data on the medium surface are moved to the cache memory, and the drive is performed. Set to the stop mode and wait for maintenance.

Also, two or more heads / HDA drive
In a system consisting of 1 drive,
After a resistance abnormality is detected, a maintenance request is issued and
The data on the medium surface handled by the head
Stop the system by moving to the area where the head is in charge
Instead, perform anomaly processing that waits for maintenance.

In addition, one head / two HDA drives are used.
In a system consisting of multiple drives or more, MR
After the resistance abnormality of the element is detected, a maintenance request is issued,
All data on the medium surface handled by the head that caused element deterioration is
Move to another drive, without stopping the system,
Abnormal processing that waits for maintenance is performed.

In a system having two or more heads / two or more HDA drives,
After the MR element resistance abnormality is detected, a maintenance request is issued, and all the data on the medium surface that the head that has caused element deterioration is in charge of is moved to the part in which another head is in charge or another drive, without stopping the system. , Abnormal process waiting for maintenance.

Of the above four types, 3 and 4 are M
If the abnormal resistance value of the R head is detected, the data can be moved to at least another drive, so that the system stop for maintenance can be prevented.

With respect to No. 2, when an abnormal resistance value of the MR head is detected, data transfer is performed to another head in the drive. After that, it is only necessary to stop the system when performing maintenance.

With respect to No. 1, even if the abnormal resistance value of the MR head is detected, the evacuation work can hardly be performed. Therefore,
A cache memory for storing data on one side is mounted, and when an abnormal resistance value of the MR head is detected, transfer to the cache memory is started. After the transfer is completed, the drive function is stopped until maintenance is performed.

[0047]

According to the present invention, the phenomenon in which the MR head is deteriorated by electromigration can be constantly monitored in a normal reproducing state. As a result, the deterioration can be detected promptly and the abnormal-time process can be carried out promptly, so that it is possible to achieve the function of promptly saving the data that would otherwise be unreproducible. Also, the signal pattern
The state of the device is evaluated using the area where
Therefore, the deterioration of the MR element can be correctly detected.

With such a function, a fault tolerant system can be constructed in some drive systems.

[Brief description of drawings]

FIG. 1 is a main block diagram of a magnetic disk device including a portion of the present invention.

FIG. 2 is a diagram showing a change in DC resistance value of an MR element due to electromigration.

FIG. 3 is a diagram showing a first embodiment of a DC resistance value detection unit.

FIG. 4 is a diagram showing a second embodiment of a DC resistance value detection unit.

FIG. 5 is a diagram showing an embodiment of a resistance abnormality detection unit.

FIG. 6 is a reproduction signal pattern suitable for DC resistance detection.

FIG. 7 is a process flow of resistance abnormality detection and abnormality detection.

FIG. 8 shows items and procedures of abnormal time processing.

FIG. 9 is a configuration diagram of a magnetic disk device.

[Explanation of symbols] 10 Magnetic disk unit 11 recording media 12 MR composite head 13 Recording / reproducing circuit system 14 Actuator 15 Voice coil motor 16 Positioning control 17 Control unit 18 Interface circuit 19 High-end machine 20 motor 21 Inductive head (recording head) 22 MR head 101 Output from preamplifier 104 102 Resistance abnormality detector 103 Output of resistance abnormality detector 104 preamplifier 201 DC level extraction circuit 202 DC level extraction circuit 203 Sampling ADC 204 selector 205 storage means 206 Normal storage means 207 Average 208 coefficient unit 209 Comparison means 210 control output 211 Select signal J current source Is sense current source

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Claims (10)

(57) [Claims] 1. In a magnetic disk device for reproducing information recorded in a magnetic recording medium in the form of magnetization reversal by using a magnetoresistive effect element, in a normal reproducing mode in which a sense current is flowed, the servo pattern is constant at a constant cycle. A change in the direct current resistance value of the magnetoresistive effect element is monitored by using a burst signal of amplitude, and the magnetoresistive resistance is increased when the direct current resistance value increases more than a certain value from the normal direct current resistance value of the magnetoresistive effect element. When it is determined that the effect element is in an abnormal state, and when the effect element is determined to be in the abnormal state, the data on the surface of the magnetic recording medium that is in charge of the abnormal state magnetoresistive effect element is moved to the cache memory, or the abnormal state magnetoresistive effect element A magnetic disk device characterized by moving to the surface of a magnetic recording medium which is handled by a magnetoresistive element other than the above, and performing abnormal data processing. 2. The magnetic disk device according to claim 1, wherein the change in the DC resistance value of the magnetoresistive effect element is monitored by measuring the inter-terminal voltage of the magnetoresistive effect element or the current value flowing through the magnetoresistive effect element. A magnetic disk device characterized by being monitored. 3. The magnetic disk device according to claim 1 or 2, wherein the constant value is 5% of a normal DC resistance value. 4. A magnetic disk device for reproducing information recorded on a magnetic recording medium in the form of magnetization reversal by using a magnetoresistive effect element, wherein terminals of the magnetoresistive effect element by a burst signal having a constant cycle and a constant amplitude in a servo pattern. A sampling means for inputting an inter-voltage and sampling for digitization; a selecting means connected to the sampling means for selecting and outputting one of two outputs; and an output of one of the selecting means. First storage means for storing a signal corresponding to a normal DC resistance value of the magnetoresistive effect element, coefficient means for multiplying the output of the first storage means by a coefficient, and the other output of the selection means. A second memory for storing a signal corresponding to a DC resistance value of the magnetoresistive effect element to be monitored
Storage means, averaging means for averaging the outputs obtained by monitoring a plurality of times stored in the second storage means, comparing the output of the coefficient means and the output of the averaging means,
Comparing means for outputting a signal indicating that the DC resistance value of the magnetoresistive effect element is abnormal when the output of the averaging means becomes larger than the output of the coefficient means, and the DC resistance of the magnetoresistive effect element When the value is abnormal, the data on the surface of the magnetic recording medium that the magnetoresistive effect element in the abnormal state is in charge of is moved to the cache memory, or the magnetic resistance effect element other than the magnetoresistive effect element in the abnormal state is in charge. A magnetic disk drive, comprising: a processing unit that moves to a recording medium surface and performs abnormal data processing. 5. The magnetic disk device according to claim 4, wherein the coefficient of the coefficient means is 1.05. 6. The magnetic disk drive according to claim 1, wherein the change in the direct current resistance value of the magnetoresistive effect element is monitored by the emitter of the first amplifying element of the differential amplifying circuit Of the second amplifying element, the emitter of the second amplifying element is connected to the second terminal of the magnetoresistive element, and the emitter of the second amplifying element is further connected to the bias current source circuit of the differential amplifying circuit, For extracting an amplified output signal from the collectors of the first amplifying element and the second amplifying element and inputting the amplified output signal to the second differential amplifying circuit, and extracting a DC component from the output of the second differential amplifying circuit. A DC resistance detection unit having a function of supplying a potential corresponding to a voltage drop generated in the magnetoresistive effect element to the base of the second amplification element via a DC level extraction circuit and extracting the potential as a detection monitor. Magnetic disk apparatus characterized by being configured I. 7. The magnetic disk device according to claim 1, wherein the change in the DC resistance value of the magnetoresistive effect element is monitored by detecting the voltage across the magnetoresistive effect element with a DC level extraction circuit. A magnetic disk device comprising a DC resistance detection unit having a function of extracting the detected voltage as a detection monitor. 8. The magnetic disk device according to claim 6, wherein the DC level extraction circuit is a low-frequency pass filter that passes only a DC component. 9. A function of reproducing information recorded in a magnetic recording medium in the form of magnetization reversal by using a magnetoresistive effect element, and constant in a constant cycle in a servo pattern in a normal reproduction mode in which a sense current is passed. A change in the direct current resistance value of the magnetoresistive effect element is monitored by using a burst signal of amplitude, and the magnetoresistive resistance is increased when the direct current resistance value increases more than a certain value from the normal direct current resistance value of the magnetoresistive effect element. In a drive system in which it is determined that the effect element is in an abnormal state, and when abnormal data processing is performed when the abnormal state is determined, in the case of abnormal data processing, one head is formed in one HDA and one drive is configured. When the magnetic resistance effect element is determined to be in an abnormal state, a maintenance request is issued and all data on the magnetic recording medium is cached. Drive system, characterized in that the moved to the drive stop mode. 10. A magnetic recording medium has a function of reproducing information recorded in the form of magnetization reversal using a magnetoresistive effect element, and is constant at a constant cycle in a servo pattern in a normal reproduction mode in which a sense current is passed. A change in the direct current resistance value of the magnetoresistive effect element is monitored by using a burst signal of amplitude, and the magnetoresistive resistance is increased when the direct current resistance value increases more than a certain value from the normal direct current resistance value of the magnetoresistive effect element. In a drive system which determines that an effect element is in an abnormal state and performs abnormal data processing when it is determined that the abnormal state is present, a single HDA has a plurality of heads for one drive or a plurality of drives during the abnormal data processing. In the case of configuring the above, when the magnetoresistive effect element is judged to be in an abnormal state, a maintenance request is issued and the head in the abnormal state takes charge. Drive system data of the magnetic recording medium, to move to the partial or another drive another head is responsible, characterized in that it does not stop the system that.