JP2001195704A - Method for applying magnetic head using magneto- resistive effect element to magnetic recorder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem that a sense current suited to the magnetic head having a large elemental resistance value is set from the limit of current density and the regenerative output of the magnetic head of a small elemental resistance is lowered because of the dispersion of the height of magneto-resistive effect element and to provide a magnetic recorder attaining the full performance of a magnetic head using a magneto-resistive effect element independent of dispersion. SOLUTION: An output reference voltage 17 of a reproducing circuit 11 for magneto-resistive effect element is made the inter-terminal voltage of a magneto-resistive effect reproducing head, the reference voltage is evaluated and a sense current switching circuit 12 is controlled so that the reference voltage nearly coincides with a prescribed value. Further, as another means, tracking information containing at least a reference amplitude signal is recorded beforehand on the recording medium of the magnetic recorder, and the sense current switching circuit 12 is controlled so that the amplitude or the effective value of the reference amplitude signal nearly coincides with the prescribed value.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to magnetic recording and, more particularly, to a magnetic recording apparatus for reproducing information using a magnetoresistance effect type electromagnetic transducer.

[0002]

2. Description of the Related Art In a magnetic tape device and a magnetic disk device, a magnetoresistive element is being adopted as an information reproducing element. The magnetoresistive element utilizes a change in resistivity (magnetoresistive effect) corresponding to a leakage magnetic field from a recording medium. The magnetoresistive element has higher reproduction sensitivity than the conventional inductive element, and has no dependency (peripheral speed dependency) on the running speed of the magnetic tape or the rotation speed of the magnetic disk medium. Such characteristics are extremely effective in reducing the size of a magnetic tape device, increasing the capacity of a magnetic disk device, increasing the recording density of a tape medium, or reducing the diameter of a disk medium. Magnetic heads are rapidly spreading.

FIG. 2 schematically shows a recording medium (magnetic tape or magnetic disk) generally used and a configuration of a magnetoresistive element portion of a magnetic head. The region sandwiched between the electrodes 2 of the magnetoresistive element 1 forms a substantially single magnetic domain, and when there is no leakage magnetic field from the recording medium 4, the bias magnetic field is magnetized in a predetermined direction. Has been applied. This region is called a magnetic sensing portion, and magnetization is easily rotated from a bias state due to superposition of a leakage magnetic field 6 generated from the recording medium 4, and the resistivity of the magnetoresistive element 1 changes according to the rotation angle. I do.

Therefore, this area works effectively for information reproduction, and the width of this area corresponds to the reproduction track width of the magnetic head. Shield films 3 on both sides of magnetoresistive element 1
Improves the spatial resolution so that even when information is recorded at a high density on the recording medium 4, the leakage magnetic field 6 corresponding to each information is improved.
This is for preventing interference between the information and distinguishing each information.

The change in resistivity of the magnetoresistive element 1 corresponding to the leakage magnetic field 6 from the recording medium 4 is caused by a voltage drop across the element when a constant current called a sense current 5 is applied to the magnetoresistive element 1. Alternatively, a change in the sense current 5 flowing when a constant voltage is applied to the magnetoresistive element 1 can be converted into an electric signal.

FIG. 3 shows an example of a circuit configuration generally used as a reproducing circuit for a magnetoresistive element.
In this configuration, the voltage applied across the element is feedback-controlled so that a current having a value determined by the external resistance element 7 for setting the sense current flows through the magnetoresistive element 1. The low-pass filter LPF8 performs feedback only for a low frequency response. As a result, a constant sense current 5 flows through the magnetoresistive element 1 irrespective of its resistance value. Also, with respect to the resistance change of the magnetoresistive element 1 due to the leakage magnetic field, the sense current is changed corresponding to the resistance change by driving the magnetoresistive element 1 at a constant voltage. This change in sense current is converted into a change in voltage by the load resistor 9 and extracted as a reproduction signal.

For this reason, for example, a reproducing channel of a magnetic disk drive using a magnetoresistive element as a reproducing element generally has a configuration as shown in the block diagram of FIG. As a characteristic of the reproducing channel due to the fact that the reproducing element is a magnetoresistive element, the R / W amplifier 10 is connected to the sense element 7 for setting the sense current. By supplying the sense current 5 set by the resistance element 7 to the magnetoresistive element 1, a reproduction signal is obtained according to the above principle. The rest of the reproduction channel configuration is the same as when an inductive element other than the magnetoresistive element is used.

[0008]

In the prior art, a change in resistivity of a magnetoresistive element is detected as a change in voltage drop with respect to a constant current or a change in element current with respect to a constant voltage. If there is a variation in the element resistance value due to the dimensional variation (dispersion), the reproduced signal amplitude is greatly dispersed. For example, JP-A-5-3
No. 25110 discloses a technique of a magnetic disk drive, in which a sense current is controlled so that a reproduction level of an MR head is maximized. Then, as shown in FIG.
The sense current giving the maximum reproduction output differs depending on the individual difference of the R head. If the sense current is increased, the life of the magnetoresistive element is shortened, so that the sense current cannot be increased more than necessary. For this reason, it is necessary to set a predetermined upper limit of the sense current, and to use the sense current below the upper limit.

For the following description, dimensions of the magnetoresistive element are defined as shown in FIG.

The lower part of the figure shows the recording medium side, and the depth direction shows the recording track width direction. Here, since the element height (h) of the magnetoresistive element is usually determined by mechanical processing of the element, the element is easily dispersed due to the processing accuracy. Other element width
(w) and the element thickness (t) are usually determined by a thin film process. For this reason, the variation ratio of the element height (h) is larger than the variation ratio of the other element widths (w) and the element thicknesses (t), and the influence tends to appear.

When the element height is lower than usual, the element resistance becomes large. Therefore, when a constant current flows, the amplitude of the reproduced signal appearing at the terminal voltage of the element becomes larger than usual. Further, since the current density is higher than usual, destruction due to migration or heat generation is likely to occur, and the reliability deteriorates from the viewpoint of life.

This relationship will be described with reference to FIG. FIG.
Shows a case where resistance variation occurs due to variation in element height of the magnetoresistive element. With respect to the inter-terminal resistance of the magnetoresistive read head, the upper part of FIG. 6 shows a change in read output, and the lower part of FIG. 6 shows a change in current density of the magnetoresistive element.

The inter-terminal resistance of the magnetoresistive read head is composed of the resistance of the magnetoresistive element itself and the resistance of electrodes and wiring. As a result, characteristics as shown in FIG. 6 are exhibited. In a conventional reproduction channel for a magnetic disk device as shown in FIG. 4, the sense current is set to be constant regardless of the resistance value of the magnetoresistive element. Therefore, if the resistance of the magnetoresistive element varies, the current density in the magnetoresistive element also varies. From the viewpoint of reproduction performance, it is desirable to set the sense current to be large so that the reproduction output is as large as possible. However, as shown in the lower part of FIG.
It is necessary to set the sense current within a range not exceeding the upper limit of the current density from the viewpoint of the conduction life of the magnetoresistive element. As a result, the reproduction output varies within the range shown in the upper part of FIG. Here, since the resistance of the element having the high element height is small (FIG. 5), the amplitude of the reproduction signal is low.

As described above, an element having a high element height has a low resistance value of the element itself, so that the reproduced output is small, and it appears as if the performance is low. However, since the current density of an element having a high element height is small, if the sense current is increased within a range not exceeding the upper limit of the current density, it is possible to increase the reproduction output while ensuring reliability. That is, the inventors of the present application have found that the performance of the device having a high device height cannot be sufficiently utilized in the conventional technology.

Although the above description has been made with respect to variations in element height, the same can be said for element thickness.

An object of the present invention is to provide an element height as described above,
It is an object of the present invention to provide a magnetic recording apparatus that compensates for an apparent lack of performance due to a variation in element thickness and sufficiently exploits the inherent performance of a magnetoresistive element.

[0017]

An object of the present invention is to provide a reproducing circuit for a magneto-resistive element of a magnetic tape device, a magnetic disk device, and other magnetic recording devices by providing at least a monitor output means for a voltage between terminals of the magneto-resistive element. This is achieved by having means for changing the current flowing through the magnetoresistive element so that the terminal voltage substantially matches a predetermined value.

As another means, the above-mentioned object is to provide a magnetic recording apparatus in which tracking information including at least a reference amplitude signal is recorded in advance on a recording medium, and the amplitude of the reference amplitude signal reproduced by a magnetoresistive element, Alternatively, it is achieved by having a means for changing the current flowing through the magnetoresistive element so that the effective value substantially matches the predetermined value.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A magnetic tape device to which the present invention is applied will be briefly described with reference to FIG. The magnetic tape records or reproduces information by running while keeping contact or a slight gap with a magnetic head installed in a tape running system. In this apparatus, a plurality of magnetic heads using a magnetoresistive element are provided along the width direction c of the tape. The magnetic tape can run in the forward direction or the reverse direction (direction a or direction b), and can record or reproduce information in any case. The magnetic head is connected to the R / W amplifier 11, and has a function of amplifying a small signal detected from the magnetic tape, amplifying an information signal at the time of writing, and a predetermined selection function when implementing the present invention.

Next, a magnetic disk drive to which the present invention is applied will be described with reference to FIGS. The magnetic disk device includes a closed container 40, a disk 41 as a magnetic medium, a spindle motor 42 for supporting and rotating the disk 41, a magnetic head for reading information from the disk 41, and a head assembly 43 having a suspension arm and a head assembly. A swing arm including a pivot shaft 44 for supporting and swinging on the disk, a voice coil motor 45 for driving the swing arm, and a circuit 51 for writing to and reading from the disk 41 by the magnetic head And a printed wiring board 46 for making an electrical connection to a controller for controlling the operations of the spindle motor 42 and the voice coil motor 45. The disk 41, the spindle motor 42, the head assembly 43, the printed wiring board 46, and the voice coil motor 45 are inside the container 40 and are sealed by the container 40.

The spindle motor 42 is an in-hub type motor having a hub for fixing the disk 41 on the outer circumference and a rotor and a stator arranged inside the hub.
Is installed on the base member. However, it is not limited to the in-hub type motor. Disk 41
Is an important component that determines the data storage capacity of the magnetic disk drive. Normally, for example, it is composed of one to several sheets according to the capacity. In this magnetic disk drive, the disk 41
Are alternately inserted into the hub of the spindle motor 42 with the disk spacer 48a (FIG. 14). The disk clamp 48b fixes the disk 41 to the spindle motor 42 by pressing the disk stack in the axial direction of the spindle motor 42.

The swing arm has a plurality of swing arms according to the number of disks 42, and includes a plurality of sliders 49 on which magnetic heads are mounted and a suspension arm 50 (FIG. 13). The swing arm is rotatably fixed to the base member by a pivot shaft 44. The magnetic head is equipped with a dual head in which a thin film head for writing and a magnetoresistive head for reading are integrated, and is attached to each of the sliders 49.

Next, the block of the reproduction channel of the magnetic recording apparatus according to the present embodiment will be described with reference to FIG. This read channel is connected to at least the magnetoresistive element 1 to supply the sense current 5 and to the read output terminal 17 to supply the differential read signal and the terminal voltage of the magnetoresistive read head thereto. R / W amplifier 1 for superimposed output
1, an automatic gain control amplifier (AGC amplifier) for inputting the differential reproduction signal, and a reproduction channel connected thereto (low-pass filter LPF, adaptive equalizer, decoding circuit)
LPF 13 for extracting a DC component of the differential reproduction signal
An analog / digital converter 14 for inputting the DC component extracted by the LPF 13 and converting it into a digital signal; a memory 16 in which a correspondence table between the digital signal and the sense current setting signal is stored in advance; The controller 15 outputs the sense current setting signal 18 with reference to the correspondence table in the memory 16 and the sense current setting signal 18.
The sense current setting circuit 12 switches the sense current 5.

The correspondence table in the memory 16 may be described in a program for controlling the controller 15. In this case, the memory 16 becomes unnecessary.

FIG. 7 shows an example of the configuration of the R / W amplifier. The inter-terminal voltage of the magnetoresistive read head is the inter-terminal voltage from which the high frequency has been removed by the LPF after being input to the LPF via the buffer. An output differential signal is output based on the inter-terminal voltage from which the high frequency has been removed. Here, the resistance between the terminals of the magnetoresistive read head, except for the resistance of the magnetoresistive element itself, is generally constant and can be measured and evaluated in advance. A conversion table of the resistance values other than the elements and the sense current setting signal corresponding to the sense current is stored in the memory 16 (FIG. 1).
Therefore, the potential difference between both ends of the magnetoresistive element can be calculated from the set sense current value and the resistance between the terminals of the magnetoresistive read head. After calculating a sense current value for setting the potential difference between both ends of the element itself to a predetermined value, a setting signal value to be sent to the sense current setting circuit 12 can be obtained.
As described above, the potential difference between both ends of the magnetoresistive element can be set to a substantially constant value.

Next, the effect of this embodiment will be described. FIG. 8 shows the reproduction output of the magnetoresistive read head 600 when the sense current is set to a constant value by the conventional reproduction channel. The horizontal axis represents the resistance between terminals (not the resistance between the terminals of the element itself) of each magnetoresistive read head, which is distributed up to 27Ω. Here, the sense current is fixed at 11 MA (megaampere). This current value is the maximum current density (approximately 20 MA /
Square cm) or less.

As a result, the reproduction output is in the range of 400 μVpp to 700 μVpp (more expressed in accordance with FIG. 8,
(In the range of 350 μVpp to 750 μVpp),
The voltage between the terminals of the magnetoresistive read head at this time is
It reaches up to 297 mV. The characteristics in FIG. 8 do not show a linear correlation as shown in FIG. 6, but include variations in head flying height, variations in element width, variations in element sensitivity, and the like. However, it shows that there is a roughly upward-sloping correlation, which indicates that the influence of the variation in the element height and the element thickness as described above is large.

On the other hand, FIG. 9 shows a reproduction output in which the sense current is controlled according to the present invention. Here, as in the example of FIG. 8, the maximum current density was limited to 20 MA (megaampere) / cm 2, and the sense current was switched in eight stages.

A method of setting a sense current value as a control target will be described with reference to FIG. First, among the inter-terminal resistances of the magnetoresistive read head, the resistance other than the resistance of the magnetoresistive element itself is found to be approximately 5Ω from the measurement and evaluation of the head alone. For this reason,
In the above conventional example in which the sense current is fixed to 11 MA, the potential difference between both ends of the magnetoresistive element itself is 242 m at the maximum.
Reaches V.

Therefore, even if the potential difference between both ends of the magnetoresistive element itself does not exceed 242 mV, the current density of the magnetoresistive element is suppressed to the same level as that of the conventional example. The reliability such as the service life can be secured to the same degree as the conventional example.

The crosses shown in FIG. 10 plot the sense current values at which the potential difference between both ends of the magnetoresistive element itself in each magnetoresistive reproducing head is estimated to substantially coincide with the aforementioned 242 mV. The horizontal axis represents a value (V / Is) obtained by normalizing the terminal voltage V of the magnetoresistive read head with the sense current Is at the time of measuring the terminal voltage.
It is. The horizontal axis is the analog / digital converter 14
It corresponds to a value that can be evaluated by the disk controller 15 from the digital signal output from FIG. 1 and the sense current set value.

The sense current value to be controlled is determined as shown by a solid line so as not to exceed the mark x in FIG. As a result, the reproduction sensitivity can be improved while maintaining the reliability such as the current-carrying life of the magnetoresistive element. The conversion table shown in Table 1 is created from FIG. 10, and the corresponding data is stored in the memory 16 (FIG. 1). The disk controller 15 sends a sense current setting signal 18 to the sense current setting circuit 12 to achieve switching of the sense current in the relationship shown in FIG.

In the present invention, as shown in FIG. 9, the reproduction output is in the range of 480 μVpp to 800 μVpp (from FIG. 9).
Expressed in accordance with the formula, 420 μVpp to 800 μVp
(range of p). Compared with the conventional example of FIG. 8, in the present invention, the lower limit output of the dispersion can be increased by about 20%, and the entire dispersion of the reproduction output can be reduced. As a result, the ratio of producing finished products of magnetic disk devices, magnetic tape devices, and other magnetic recording devices could be improved.

As described above, according to the present embodiment, the sense current of the magnetoresistive element can be maintained at the same level as the maximum current density of the conventional sense current, and the reliability of the element such as the conduction life can be maintained. Playback output of about 2
Can be increased by 0%. As a result, the S / N ratio of the magnetic recording / reproducing signal can be improved, so that the overall performance of the magnetic recording device can be improved.

In the present embodiment, it is essential to switch the sense current based on the result of evaluating the difference between the voltages of the terminals of the magnetoresistive read head to reduce the variation in read sensitivity, and it is essential that the maximum current is not changed. It is not necessary to switch the sense current so that the densities are at the same level.

The sense current setting circuit 12 of the present embodiment
May be built in the R / W amplifier 11. Also,
LPF13 and ADC14 together with other functional blocks
/ W channel IC or may be built in the controller 15.

The R / W amplifier 11 according to the present embodiment
Alternatively, instead of superimposing the inter-terminal voltage of the magnetoresistive read head on the read output terminal 17, another terminal may be provided and output, and directly input to the ADC. In this case LPF
13 becomes unnecessary.

It is not necessary to constantly monitor the voltage between the terminals of the magnetoresistive read head. The evaluation for each head or each cylinder position may be performed when the apparatus is started, and may be stored in the memory 16. Further, an evaluation before shipment of the magnetic disk device may be performed, recorded on the magnetic disk medium, read out at the time of starting the device, and stored in the memory 16.

Next, a second embodiment of the present invention will be described. As shown in FIG. 8, when the sense current is constant, the reproduction output is correlated with the inter-terminal resistance of the magnetoresistive head. Since there is such a correlation, the reproduced output can be used as a monitor of the resistance value between the head terminals. A second embodiment in which the sense current is controlled based on the reproduction output will be described with reference to FIG. The reproduction channel is connected to at least the magnetoresistive element 1 to supply the sense current 5 and output a differential reproduction signal to the reproduction output terminal 17. The R / W amplifier 10 receives the differential reproduction signal. AGC amplifier and a normal reproduction channel (low-pass filter, adaptive equivalent circuit, and decoding circuit) connected thereto, the differential reproduction signal 17, the servo gate signal, and the servo AGC hold signal 21 are input.
An amplitude evaluation circuit 19 for outputting an evaluation value of the amplitude or the effective value of the servo reference amplitude signal, and an analog / digital converter for inputting the servo signal reference amplitude evaluation value extracted by the amplitude evaluation circuit 19 and converting it into a digital signal. Converter AD
C14, a memory 16 in which a correspondence table between the digital signal and the sense current setting signal is stored in advance, and a disk controller 20 which receives the digital signal and outputs a sense current setting signal 18 by referring to the correspondence table. And a sense current setting circuit 12 which receives the sense current setting signal 18 and switches the sense current.

As in the first embodiment, the memory 1
The correspondence table in 6 may be described in a program that controls the controller 20. In this case,
The memory 16 becomes unnecessary.

Tracking information such as a servo track is recorded on the magnetic recording medium in advance, and the tracking information includes at least a reference amplitude signal. With the configuration of FIG. 11, the amplitude or the effective value of the reference amplitude signal is evaluated by the amplitude evaluation circuit 19. Here, if the amplitude evaluation circuit 19 is constituted by a peak hold circuit, the amplitude evaluation circuit 19 can evaluate the amplitude of the reference amplitude signal. Further, if the amplitude evaluation circuit 19 is configured by full-wave rectification and an integration circuit, an effective value can be evaluated by comparing the effective value thereof with a predetermined reference value.

FIG. 12 shows an example of the configuration and timing of the amplitude evaluation circuit 19 composed of a peak hold circuit. The reproduced signal of the servo section (FIG. 12- (a)) includes a reference amplitude signal, which is input to a full-wave rectifier circuit 22 included in the amplitude evaluation circuit 19, and receives a full-wave rectified waveform (FIG. 1).
2- (b)) and sent to the peak hold circuit 23. The peak hold circuit 23 generates and outputs a peak hold waveform (FIG. 12- (d)) of the reference amplitude signal section using the timing of the servo gate signal and the servo AGC hold signal 21 (FIG. 12- (c)). I do. This peak hold waveform is supplied to the servo A via the ADC 14.
It is sampled at the rising timing of the GC hold signal and is taken into the disk controller 20 (FIG. 11). Subsequent processing is the same as in the first embodiment.

As described above, by using the amplitude of the reference amplitude signal or the evaluation value of the effective value included in the tracking information, regardless of the data reproducing state or the operating state of the magnetic recording apparatus when moving the magnetic head. The same control as in the first embodiment can be performed.

[0044]

According to the magnetoresistive element used in the magnetic recording apparatus, apparent performance deterioration (reduction in reproduction output) caused by dispersion of the element height and other element shapes can be reduced. Since the inherent performance of the element can be brought out, the performance of the magnetic recording device can be improved.

[Brief description of the drawings]

FIG. 1 is a block diagram of a reproduction channel of a magnetic recording apparatus according to a first embodiment of the present invention.

FIG. 2 is a schematic diagram showing a configuration of a magnetoresistive element in a magnetic head.

FIG. 3 is a diagram showing a conventional reproducing circuit for a magnetoresistive element.

FIG. 4 is a diagram showing a block diagram of a reproduction channel of a conventional magnetic recording device (magnetic disk device).

FIG. 5 is a diagram for explaining the definition of dimensions of a magnetoresistive element.

FIG. 6 is a conceptual diagram showing the relationship between the read head terminal resistance, the read output, and the current density due to variations in the element height of the magnetoresistive element.

FIG. 7 is a diagram showing a configuration example of a reproducing circuit for a magnetoresistive element according to the present invention.

FIG. 8 is a diagram showing a reproduction output variation when the sense current is made constant according to the related art.

FIG. 9 is a diagram showing a reproduction output variation when the sense current is controlled according to the first embodiment of the present invention.

FIG. 10 is a diagram illustrating a method of determining a control value of a sense current according to the first embodiment of the present invention.

FIG. 11 is a diagram showing functional blocks of a reproduction channel of a magnetic recording device according to a second embodiment of the present invention.

FIG. 12 is a diagram for explaining amplitude evaluation according to the second embodiment of the present invention.

FIG. 13 is a plan view of a magnetic disk drive to which the present invention is applied.

FIG. 14 is a side view of the magnetic disk drive of FIG.

FIG. 15 is a diagram for explaining a conventional sense current control that maximizes the output of a magnetic head using a magnetoresistive element.

FIG. 16 is a perspective view of a magnetic tape device to which the present invention is applied.

FIG. 17 is a sense current setting table according to the first embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Magnetoresistance effect type element, 2 ... electrode, 3 ... Shield film,
4 recording medium, 5 sense current, 6 leakage magnetic field, 7 sense current setting resistance element, 8 LPF, 9 load resistance,
Reference numerals 10, 11: reproduction circuit for magnetoresistive effect element, 12: sense current setting circuit, 17: reproduction output terminal, 18: sense current setting signal, 21: timing signal of servo reference amplitude signal.

Claims (5)

[Claims] 1. A first step of determining one sense current in advance, and a second step of selecting one sense current value corresponding to the sense current determined in the first step from a plurality of sense current candidate values. And a third step of flowing the sense current value selected in the second step to the magnetic head, the method being applied to a magnetic recording device of a magnetic head using a magnetoresistive element. A first step of determining one sense current for each magnetic head in advance; and a plurality of sense current values corresponding to each sense current determined in the first step. A second step of selecting from the candidate values of the following; and, when one magnetic head is selected, a sense current value corresponding to the magnetic head selected in the second step,
A method for applying a plurality of magnetic heads using a magnetoresistive element to a magnetic recording device, comprising a third step of flowing the magnetic head to the magnetic head. 3. The method according to claim 1, wherein a correspondence between the sense current in the first step and a plurality of candidate values of the sense current in the second step is described in a program. A method for applying a magnetic head using a magnetoresistive element to a magnetic recording device. 4. The magnetic recording method according to claim 1, wherein the selection in the second step is based on a sense current setting signal. How to apply to the device. 5. The application method according to claim 1, wherein the magnetic recording device is a magnetic disk device.
A method of applying a magnetic head using a magnetoresistive element to a magnetic recording device.