JP3476366B2 - Method for determining sense current of disk device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for determining a sense current of a disk device in which an MR head or a spin valve head, which produces an output by passing a sense current, is used as a read head. The present invention relates to a sense current determination method for a disk device that determines a sense current so as to satisfy both.

[0002]

2. Description of the Related Art With the recent demand for higher recording density of magnetic disk devices, read heads are required to have high output and high S / N ratio. MR elements and spin valve elements are used as read heads satisfying these requirements. Those using (GMR elements) have been put to practical use.

A read head using an MR element or a spin valve element passes a sense current during reproduction, and there is a demand to pass a higher sense current in order to obtain a high output and a high S / N ratio.

However, the MR element and the spin valve element are a laminated structure of thin films, and if an excessive sense current flows through the element, the element deterioration due to temperature rise such as migration is promoted and the life is shortened. Further, it causes deterioration of reproduction characteristics due to heat generation.

Therefore, under the present circumstances, the resistance value of the MR element or the spin valve element is measured to estimate the cross-sectional area of the element through which the sense current flows, and the sense current is determined from the current density satisfying the required life of the element.

For example, if the measured resistance of the MR element is R, then R = ρ (L / S) (1) where ρ is the resistivity (Ω · m) L is the length of the MR element (m) S is MR There is a relation of the cross-sectional area (m ² ) of the device. Therefore, the cross-sectional area S of the MR element through which the sense current flows can be estimated as S = ρ (L / R) (2). Then, the sense current I can be determined as I = J × S (3) from the current density J that satisfies the required life of the element. This also applies to the spin valve element.

[0007]

However, in such a conventional method for determining the sense current of the MR element or the spin valve element, the resistance value measured for the element is
In addition to the resistivity ρ of the element, variations in terminal resistance and the like due to a pair of electrode leads provided in the element are included, and the cross-sectional area obtained from the measured resistance value does not accurately represent the cross-sectional area of the element.

Therefore, the sense current calculated based on the measurement of the resistance value of the element is not used as it is, but a lower sense current value is determined and set in the magnetic disk device in consideration of the variation in the element cross-sectional area.

For this reason, the sense current flowing through the MR element or the spin valve element during reproduction is set to a low value, and there is no problem in terms of migration and heat generation, but the lower the sense current, the smaller the reproduction output and the S / N ratio. There was a problem of decline.

The present invention has been made in view of the above problems, and achieves a high output and a high S / N ratio while satisfying the required life in consideration of migration and heat generation of the MR element and the spin valve element. An object of the present invention is to provide a method for determining the sense current of the disk device.

[0011]

FIG. 1 is a diagram for explaining the principle of the present invention. Referring to FIG. 1A, the present invention is a method for determining a sense current of a disk device having a plurality of MR heads and a sense current supply source, for example, a magnetic disk device, and has the following first to fifth steps.

As shown in FIG. 1B, based on the element temperature and life characteristics of one or a plurality of sample heads selected as standard samples from the MR head, the element temperature satisfying a predetermined required life time h1. The first step of obtaining T1; the second step of calculating the sense current I1 flowing to heat the sample head to the element temperature T1 of the required life; the reproduction output of the sample head is maximized as shown in FIG. 1 (C). A third step of measuring the maximum output sense current I2 at the point 66; a current setting ratio α calculated by dividing the element life temperature sense current I1 obtained in the second step by the maximum output sense current I2 measured in the third step. 4 steps: Before assembling the apparatus, the maximum output sense current I3i (i is head number 1, 2, 3, ... N) at the point 66 that maximizes the reproduction output of a plurality of MR heads used in the magnetic disk apparatus Similarly measured 1 (C),
A fifth step of multiplying each of the measured maximum output sense currents I3i by the current setting ratio α calculated in the fourth step and setting the same as the sense current I4i to be flown to a plurality of MR heads during reproduction in the device; According to the sense current determination method of
The current setting ratio α between the sense current that satisfies the required life obtained from the sample head selected as the standard sample from the MR head and the optimum sense current that maximizes the reproduction output is
Since the reproduction sense current is determined by multiplying the maximum output sense current that maximizes the reproduction output actually measured for the MR head used in the apparatus, high output and high S / N ratio are achieved with reduced influence of variations in element shape. It is possible to set the optimum sense current, and it is possible to secure reliability against temperature deterioration factors such as migration.

Here, the characteristics of the element temperature and the life time of the sample head used in the first step are as shown in FIG.
In a practical test time, for example, a test time of about 1 to 2 months, a sense current corresponding to the element temperature at which the element is destroyed is passed to measure the life time at least at two points 40 and 42.
The element temperature at the point 64 of the required life time is obtained by interpolation processing based on the actual measurement value of the point.

The characteristic of the life time and the element temperature in the first process is as shown in FIG. 1B, the logarithm of the life time (log h).
Is the reciprocal of the element temperature (1 / T) with respect to, and the element temperature T1 at the point 64 that satisfies the required life time is obtained by linear interpolation based on the measured values of the two points 40 and 42 of the life time.

A sense current I1 flowing to heat the sample head to the element temperature T of the required life in the second process.
Is the current density J of the sample head that obtains the temperature rise ΔT1 required to reach the required life element temperature T1 from the predetermined room temperature Ta, and the predetermined cross-sectional area S of the portion where the sense current of the sample head flows to this current density J Multiply by.

That is, in the second step, a quadratic function formula ΔT = aJ ² + bJ + c based on the actual measurement of the temperature rise ΔT with respect to the current density J of the sample head, where a, b, and c are constants, the element temperature T1 of the required life is The current density J of the sample head required for the temperature rise ΔT1 up to is calculated.

Further, the present invention is a method for determining a sense current of a magnetic disk device having a plurality of spin valve heads and a sense current supply source, and has the following first to fifth steps.

First step of obtaining an element temperature T1 satisfying a predetermined required life time h1 based on the characteristics of the element temperature and the life of one or a plurality of sample heads selected as standard samples from the spin valve head; Sense current I flowing to heat the sample head to the element temperature T of the lifetime
Second step for calculating 1; Third step for measuring the optimum sense current I2 that maximizes the reproduction output of the sample head; Second step
A fourth step of calculating a current ratio α by dividing the sense current I1 obtained in the step by the optimum sense current I2 measured in the third step;
Before assembling the apparatus, the maximum output sense current I3i (i is head number 1, 2, 3, ...) Which maximizes the reproduction output for a plurality of spin valve heads used in the magnetic disk apparatus.
n) is measured, and for each of the measured optimum sense currents I3i,
A fifth step of multiplying the current ratio α calculated in the fourth step and setting it in the device as a sense current I4i flowing through a plurality of spin valve heads at the time of reproduction; therefore, the spin valve head also has the required life obtained from the sample head. The current setting ratio α between the satisfactory sense current and the optimum sense current that maximizes the playback output is multiplied by the actual value of the sense current that maximizes the playback output of the spin valve head used in the device, and the sense current that flows during playback is multiplied. Is set, it is possible to set the optimum sense current in which the influence of the variation in the element shape is reduced, and the reliability can be ensured against the factors of temperature deterioration such as migration. The details of the method of determining the sense current of this spin valve head are the same as those of the MR head.

[0019]

2 is an internal structure of a disk enclosure in a hard disk drive using an MR head to which the sense current determining method of the present invention is applied.

In FIG. 2, the disk enclosure 10 of the hard disk drive is a spindle motor 15
A plurality of magnetic disks 12 rotated by the above are arranged in a stacked manner, and a rotary head actuator 14 is provided for the magnetic disks 12.

Rotary type head actuator 14
Is provided with a VCM 16 on the outside, and a head assembly 18 is arranged offset on the tip side, and a composite head 20 is attached to the tip of the head assembly 18. A head IC 22 is mounted on the FPC at the bottom of the disk enclosure 10.
22 and the head actuator 14 are connected by an FPC band portion 24.

FIG. 3 shows the head actuator 14 of FIG.
The head assembly 18 provided at the tip of is taken out. The head assembly 18 has a mounting portion 18-1 to be mounted on the actuator body, and a spring plate 18-2 following the mounting portion 18-1. The composite head 20 is mounted to the tip of the spring plate 18-2.

FIG. 4 shows the composite head 20 of FIG. 3 taken out with the medium surface side facing up. On the medium surface side of the composite head 20, side sliders 21-1 and 21-2 on both sides are provided.
A center slider 30 is formed, and an inductive head 24 that operates as a write head and an MR head 26 that operates as a read head are mounted on the end surface on the head center side.

FIG. 5 shows the inductive head 24 of FIG.
The MR head 26 is taken out and enlarged. The inductive head 24 has a coil 38 arranged between the magnetic poles 24-1 and 24-2, and writes the magnetic recording pattern 36 on a track on the surface of the magnetic disk medium. The MR head 36 is formed integrally with the inductive head 24,
The MR element 32 is supported by the lead terminals 34 located on both sides of the MR element 32.
The sense current I flows through 2.

As the MR element 34, a carbon film such as a Ni--Fe film exhibiting an anisotropic magnetoresistive effect is used. According to the present invention, the sense current supplied to the MR head 26 during reproduction is determined to be an optimum value.

FIG. 6 is a flow chart of the procedure of the sense current determination process according to the present invention for the MR head 26 of FIG. The procedure of the sense current determination process in FIG. 6 is divided into five steps, first to fifth. The first of these
The process to the fourth process, that is, the processes of steps S1 to S5 is a process of performing one or a plurality of sample heads selected from a plurality of MR heads prepared as parts prior to the assembly of the hard disk as a standard sample, MR to be used for an actual hard disk using the results obtained from the sample head in the processing of steps S6 and S7 of the fifth step
This is how to determine the sense current for the head.

First, in the first step, as in step S1, M
Targeting the sample head selected from the R heads,
A characteristic graph of the life time h with respect to the element temperature T is generated based on actual measurement.

FIG. 7 is a characteristic graph of the life time h with respect to the element temperature T generated in step S1 of FIG. That is, in FIG. 7, the horizontal axis has the temperature as a parameter, and specifically, the inverse number (1 / T) of the temperature T is taken. The temperature T is Fahrenheit (° F), 500 ° F and 400 ° F, respectively.
Corresponds to ° F and 330 ° F. This is 226 ° C., 126 ° C., and 59 ° C. in Celsius.

The vertical axis represents the life time h in logarithm.
The characteristic of the life time with respect to such element temperature is generally given by the following equation.

[0030]

[Equation 1] However, since a variation is expected between this theoretical formula and the actual characteristic, in the present invention, measurement point 4
0,42, the life time is 1000 hours. Element temperature not exceeding the interval (1 / T) = 2.2 × 10 ⁻³ and 2.
The life time is measured in the state where the sense current of 3 × 10 ⁻³ is kept flowing.

The standard of life is when the resistance value of the MR element changes by, for example, ± 0.5% or more. Further, the sample head is prepared for each temperature, and when a plurality of sample heads are used in measuring the life time at a certain temperature, the life time of the sample head having the shortest life time is defined as the life time at that temperature.

When the two measurement points 40 and 42 are obtained in this way, the temperature (1 /
The characteristic by linear interpolation of the life time log h for T) is obtained.

When the characteristic graph of the life time h with respect to the element temperature T of the MR element selected as the sample head is obtained as shown in FIG. 7, step S2 of FIG.
The element temperature T1 that satisfies the predetermined required time h1 is derived from the characteristic graph of 1. For example, when the energization life of the MR head is 2 years, the life time h = 17250 hours in FIG. 7, and the corresponding element temperature (1/1) from the intersection point 64 with the characteristic straight line obtained by the linear interpolation of the measurement points 40 and 42. T1) 1 / T1 = 2.701 × 10 ⁻³ [1 / ° F] can be obtained. In this case, the element temperature T1 is 370 ° K in Fahrenheit and 97 ° C in Celsius.

Next, step S3, which is the second step in FIG.
Then, based on the element temperature T1 = 97 ° C. obtained from the intersection point 64 of the life straight line where the life time h1 = 17250 hours in FIG. 7, the sample M is adjusted so that the element temperature T1 = 97 ° C.
A life element temperature sense current I1 flowing to heat the R head from a predetermined room temperature Ta is derived.

The flow chart of FIG. 8 shows the procedure of the calculation process of the life element temperature sense current I1 in step S3 of FIG. First, in step S1, the required life time h = h
The required life temperature T1 of the element obtained from
When a is set to Ta = 25 °, for example, the temperature rise ΔT with respect to the required life element temperature T1 = 97 ° with respect to the room temperature Ta is obtained. In this case, T = Ta + ΔT 97 ° C. = 25 ° C. + ΔT, so the temperature rise ΔT = 72 ° C. Next, in step S2, the current density J and the temperature rise ΔT in the MR element are
The relation of is set by the following formula.

ΔT = aJ ² + bJ + c (5) where a, b, and c are constants. FIG. 9 is a characteristic diagram of the relational expression in step S2 of FIG.
The temperature rise ΔT of the element is given by a quadratic function with respect to the current density J of the sense current flowing in the MR element. The relationship between the temperature rise ΔT and the current density J in this MR element is previously obtained as a constant by experimentally obtaining the coefficients a, b, and c. Therefore, in step S3 of FIG. 8, the current density J is calculated by substituting the temperature increase ΔT = 72 ° C. obtained in step S1 into the equation (5).

Then, in step S4, the sense current I1 corresponding to the element temperature T1 = 97 ° C. corresponding to the required life is calculated as I1 = J × S (6). Here, S is a cross-sectional area of the Ni-Fe single layer film of the MR element, which is obtained from a predetermined shape as a design parameter through which the sense current flows. For example, by the sense current calculation process of FIG.
I1 = 9.3 milliamperes is calculated as the sense current I1 for heating the element temperature T1 = 97 ° C. for 17500 hours.

Next, in step S4 of the third step shown in FIG. 6, the sense current I2 that maximizes the reproduction output of the sample head is measured. When a plurality of sample heads are used, the average value of the sense current that maximizes the reproduction output in each is I2.

FIG. 10 is a flowchart of the current measuring process of the sense current I2 that maximizes the reproduction output in step S4 of FIG. The measurement process of the sense current that maximizes the reproduction output is performed using the head tester 40 as shown in FIG. 11, for example. In the head tester 40 of FIG. 11, for example, a single magnetic disk 12 is mounted on a spindle motor 42.

A head assembly 18 of FIG. 3 to be tested is removably attached to the tip of a test arm 45 provided on a head actuator 44 that is vertically movable with respect to the magnetic disk 12. Also head tester 4
0 is provided with a control board 46. The control board 46 is composed of, for example, the circuit block shown in FIG.

In FIG. 12, the control board 46
Is MPU48, HDC (hard disk controller)
50, write modulation circuit 46, read demodulation circuit 54, sense current setting circuit 56, head IC 22,
8 is a spindle motor 4 according to a predetermined test sequence
2 and the actuator 44 are driven, and the test pattern is further modulated by the write modulation circuit 46 via the HDC 50, and then written on the magnetic disk 12 by the inductive head 24 via the head IC 22.

The test pattern written on the magnetic disk 12 is read by the MR head 26, demodulated by the read demodulation circuit 54, and passed through the HDC 50 to the MPU 48.
The read data and further the output from the MR head 26 can be determined. Therefore, the process of measuring the sense current that maximizes the output of the MR head of FIG. 10 is executed by the function of the MPU 48 that has programmed this process procedure.

In the sense current measuring process of FIG. 10, first, in step S1, the initial current I of the sense current is set in the MR head 26, and in the next step S2, the reproduction output Vn of the MR head 26 is measured. Then, in step S3, the magnitude relationship between the current reproduction output Vn and the previous reproduction output Vn-1 is compared. If the reproduction output Vn is larger than the previous reproduction output Vn-1, the sense current I at that time is set to the sense current I2 that maximizes the reproduction output in step S4. If the current reproduction output Vn is less than or equal to the previous reproduction output Vn-1 in step S3, step S4 is skipped.

Then, in step S5, the current sense current I
Is increased by a predetermined value ΔI, and the processing from step S2 is repeated until the upper limit current determined in step S6 is reached. If the current sense current I reaches the upper limit current in step S6, the process proceeds to step S7, and the sense current set in step S4 at that time is determined as the sense current I2 that can obtain the reproduction output.

FIG. 12 is a characteristic diagram of the reproduction output of the MR head with respect to the sense current I obtained in the sense current measurement process of FIG. In this case, the sense current I is increased from the initial value of 2 mA to the upper limit value of 12 in ΔI = 1 mA unit.
The current is increased to milliamperes, and the sense current I2 at the peak point 66 at which the reproduction output is maximized is 11 milliamps.

Here, the element temperature of the MR element at the sense current I2 = 11 milliampere corresponding to the peak point 66 of the reproduction output can be experimentally obtained and is about 130.
It was ℃. This value is the temperature (1 / T) in FIG. 7 = 2.47.
Corresponding to × 10 ^-3 [1 / ° F], life time h in this case
Is about 1100 hours, and the required life time h = 1725
It is well under 0 hours.

By the sense current measurement process of FIG. 10, for example, the sense current I2 that maximizes the reproduction output as shown in FIG.
= 11 milliamps can be actually measured for the sample head, in step S5 which is the fourth step of FIG.
The current setting ratio α for obtaining the optimum sense current is calculated by the following equation.

Α = I1 / I2 (7) Here, the sense current corresponding to the element temperature T = 97 ° C. of the required life obtained from the sense current calculation process of FIG. 8 is I1 =
It is 9.3 milliamperes, and the sense current I2 = 1 obtained from the sense current measurement process that maximizes the reproduction output of FIG.
Since it is 1 milliampere, the current setting ratio α for obtaining the optimum sense current is α = I1 / I2 = 9.3 ÷ 11.0 = about 0.85. Therefore, for example, the current setting ratio α for calculating the optimum sense current is set to α = 0.85 (= 85%).

The processing of the first to fourth steps S1 to S5 of FIG. 6 may be obtained by selecting a single head from the MR heads as the sample head of the standard sample. By obtaining the current setting ratio α using a plurality of sample heads and obtaining the average thereof, it is possible to reduce the influence of variations in MR elements.

In this case, the processing of steps S1 to S3 is 1
For each of the sample heads, the sense current I2 that maximizes the reproduction output in step S4 is measured for a plurality of sample heads, and the sense current I2 is calculated from the average value.
It is desirable to determine 2 and calculate the current setting ratio α in step S5.

In this way, if the current setting ratio α for determining the optimum sense current from the sample head is obtained in the first to fourth steps of FIG. 6, in the fifth step, steps S6 and S7, Prior to assembling the hard disk drive shown in FIG. 2, for the head assembly 18 shown in FIG. 3 for one device used for the assembly, the sense current I3i that maximizes the reproduction output is measured for each head in step S6, and in step S7. The measured sense current I3i for each head is multiplied by the current setting ratio α obtained in step S5 to determine the optimum sense current for each head and set it in the device.

In this case, the actual measurement of the sense current I3i for maximizing the reproduction output for each head used in the apparatus of FIG. 6 may be the same as the sense current measurement processing of FIG.
1, actual measurement is performed using a head tester 44 as shown in FIG.

Further, the device setting of the optimum current I3i for each head obtained by multiplying the measured value of the sense current that maximizes the reproduction output in step S7 of FIG.
The MPU 48 provided on the control board 46 of the head tester 44 supplies the calculated optimum sense current I3i to the input / output device such as a printer or a magnetic disk drive via the interface 58 and outputs the optimum sense current I3i. For example, the determined sense current for each head is set in the head IC 22 provided in the disk enclosure 10 of FIG.

FIG. 13 shows, together with the disk enclosure side, the circuit block of the control board provided under the disk enclosure 10 of FIG. 2 in which the sense current of each head determined in steps S6 and S7 of FIG. 6 is set. ing.

In FIG. 13, the disk enclosure 10 is provided with eight composite heads 20-1 to 20-8 for the head IC 22. Compound head 20-1
To 20-8 are respectively inductive heads 24-
1 to 24-8 and MR heads 26-1 to 26-8 are provided. Further, the disk enclosure 10 is provided with a spindle motor 15 and a boil coil motor 16.

On the control board 112 side, an MCU (micro control unit) 128 for controlling the entire hard disk drive, a hard disk controller (HDC) 130, a read channel circuit 132, a control logic circuit 134 having a servo demodulation circuit, and a VCM.
124 and the spindle motor 126 to the power amplifier 14
Servo controller 1 using DSP driven by 0
38, flash P-provided as non-volatile memory
Buffer RAM14 using ROM142 and DRAM
4. Further, a host interface 146 for exchanging data and signals with a host as a host device is provided.

FIG. 14 is a circuit block diagram of the head IC 22 provided on the disk enclosure 10 side of FIG. The head IC 22 has a mode selector 148,
A write operation or a read operation is selected by the chip select signal (CS signal) E1 from the control logic circuit 134 of FIG. When the read operation is selected, the write current source 54 is enabled, and the write current is determined by the write current setting signal (WIS signal) E3 supplied at that time.

When the write operation is selected, the write data signal (WD signal) E2 is input to the write FF 150 from the read channel circuit 32 of FIG.
2 in the inductive heads 24-1 to 24-1, which are switched by the write head switching circuit 156 at that time.
A write current is passed through any one of 24-8 to perform magnetic recording on the magnetic disk.

Switching of the write head switching circuit 156 is performed by
This is performed by the head selector 158. A head selector signal (HS signal) E4 is sent to the head selector 158.
Is given and any one of the head numbers HH = 00 to 08 is given.
One head is selected by specifying one.

On the other hand, when the read operation is selected by the mode selector 148, the booster 164 provided in the read circuit system is made effective so that the read signal (RD signal) E
7 is output to the read channel circuit 132 of FIG. A fixed gain read amplifier 162 is provided in front of the booster 164.
Are provided, and the eight MR heads 26-1 to 26-1 are connected to the read amplifier 162 via the read head switching circuit 160.
26-8 is connected.

The read head switching circuit 160 receives the head select signal E4 for the head selector 158,
Any one of them is switched and connected to the read amplifier 162 side. Further, a read head controller 166 is provided,
The head control signal E4 is input from the control logic circuit 134 of FIG. 13 through a plurality of signal lines.

The read head controller 166 controls the read heads, that is, the MR heads 26-1 to 26-8, by setting the current value of the sense current. That is,
The read head controller 166 is provided with a sense current switching circuit 70, and switches the sense current for the MR head selected in response to the head switching signal based on the head select signal E4 from the head selector 158.

The set sense current used for switching the sense current is stored in the EEPROM 172 in advance.
That is, the optimum sense currents I31 to I38 for each MR head 26-1 to 26-8 determined by the sense current determination process of the present invention in FIG. 6 are stored in the EEPROM 1 as table information.
It is stored in advance in 70. Therefore, at the time of reproduction, the sense current of the selected MR head is read from the EEPROM 170, and the sense current switching circuit 70 causes the sense current to flow to the corresponding MR head via the read head switching circuit 160.

Next, an embodiment of the present invention in which a spin valve head is used as the read head will be described. FIG. 16 shows a disk enclosure 10 of the hard disk drive of FIG.
5 is an explanatory diagram of a spin valve head used as a read head of the composite head 20 provided in FIG.

In FIG. 16, a spin valve head 70 is provided.
Has a pair of lead terminals 74 and 76, and a spin valve element 78 is arranged between them. Lead terminals 74, 7
For example, a sense current I in the disturbing direction is passed through 6 as indicated by an arrow. Therefore, in the spin valve element 78, the magnetic field M in the direction opposite to the pinned layer magnetic field is generated by the sense current I in the disturbing direction.
s is generated as an arrow.

FIG. 17 shows the spin valve element 78 of FIG.
To show its structure. The spin valve element 78 basically has a multi-layered film structure including four layers, and has a diamagnetic layer 80, a pinned layer 82, a non-magnetic layer 84 and a free layer 86 from above. Fe in the diamagnetic layer 80
-Mn, CoO, Ni-Fe-Tb, etc. are used.

Further, Ni--Fe, Co--Fe, etc. are used for the pin layer 82 and the free layer 86 which are magnetic layers. Cu is used for the nonmagnetic layer 84. Further, a protective layer 88 is formed on the antiferromagnetic layer 80, and a ferromagnetic underlayer 90 is provided below the free layer 86.

In the multilayer film structure of the spin valve element 78, the magnetization direction of the pinned layer 82 in contact with the antiferromagnetic layer 80 is fixed to the pinned layer magnetic field Mp indicated by the arrow. On the other hand, the free layer 86 separated by the non-magnetic layer 84 is in a state where it does not have a fixed magnetization direction. When an external magnetic field 94 due to the recording magnetic field of the magnetic disk is applied here, the direction of the external magnetic field 94 determines the direction of the magnetic field Mf of the free layer 86.

The resistance value of the film changes due to the difference between the free layer magnetic field Mf and the fixed pinned layer magnetic field Mp. This resistance value becomes maximum when the magnetization directions of the free layer 86 and the pinned layer 82 are opposite by 180 °, and becomes minimum when they are the same.

With respect to the spin valve head 70 shown in FIGS. 16 and 17, as shown in the flowchart of FIG. 6, the hard disk drive is processed by performing the processes of the first to fifth steps S1 to S7. The optimum sense current used for each of the spin valve heads used can be set.

In the case of this spin valve head 70,
As the cross-sectional area S of step S4 in the calculation of the sense current I1 corresponding to the required life temperature T1 of FIG. 8, the pin layer 82 through which the sense current flows in the spin valve element 78 of FIG.
The cross-sectional areas of the nonmagnetic layer 84 and the free layer 86 are used. Of course, the characteristics of the life time with respect to the element temperature in FIG. 7 and the constants a, b, and c of the current density J given by a quadratic function with respect to the temperature rise ΔT in FIG. 9 are values unique to the spin valve head 70.

In the above embodiment, step S in FIG.
The processes from the first process to the fifth process of S1 to S7 are automatically performed as much as possible by using the head tester 40 as shown in FIGS. 11 and 12, for example. The optimum sense current value of each MR head or spin valve head used in the apparatus may be determined and set through manual labor using the measuring apparatus.

Further, the current setting ratio α obtained in step S5 of FIG. 6 and the sense current I which maximizes the reproduction output of each MR head or spin valve head of the apparatus measured in step S6.
3i may be stored in the hard disk drive side, and at the time of reproduction, the optimum sense current may be set by multiplying the current setting ratio α in step S7 by the sense current I3i that maximizes the reproduction output.

The present invention also includes appropriate modifications within the range not impairing the objects and advantages thereof. Furthermore, the present invention is not limited by the numerical values of the above embodiments.

[0075]

As described above, according to the present invention, the sense current and the reproduction output satisfying the required life obtained from the sample head selected as the standard sample from the MR head and the spin valve head are maximized. The current setting ratio to the sense current is multiplied by the value of the sense current that maximizes the reproduction output measured by the MR head or spin valve head used in the device to determine the sense current to flow during reproduction. It is possible to set the optimum sense current with high output and high S / N ratio while reducing the influence of variations in the element shape of the spin valve head, and to secure a sufficient required life against temperature deterioration factors such as migration. Therefore, the reliability of stable operation for a long period can be guaranteed.

[Brief description of drawings]

FIG. 1 is an explanatory view of the principle of the present invention.

FIG. 2 is an explanatory diagram of an internal structure of a hard disk drive in which a sense current determined by the present invention is set.

FIG. 3 is an explanatory diagram of a head assembly including an MR head.

FIG. 4 is an explanatory diagram of the head as seen from the medium surface side.

5 is an enlarged structural explanatory view of the inductive head and the MR head of FIG.

FIG. 6 is a flowchart showing the procedure of a sense current determination process of the present invention.

FIG. 7 is a characteristic diagram of element temperature and life time used for deriving the element temperature from the required life time in the first process of FIG.

8 is a flowchart of a procedure for calculating a sense current from an element temperature satisfying a required life in the second process of FIG.

9 is a characteristic diagram of the temperature rise ΔT of the element with respect to the current density J used in FIG.

10 is a flowchart of a sense current measurement process that maximizes the reproduction output in the third and fifth steps of FIG.

FIG. 11 is an explanatory diagram of a head tester used in the present invention for measuring the reproduction output with respect to the sense current of the MR head.

12 is a block diagram of a control board of the head tester of FIG.

13 is an explanatory diagram of the measurement result of FIG.

14 is a block diagram of a control board provided in the hard disk controller of FIG.

15 is a circuit block diagram of the head IC of FIG.

FIG. 16 is an explanatory diagram of a spin valve head.

17 is a structural explanatory view of the spin valve element of FIG.

[Explanation of symbols]

10: Disk enclosure 12: Magnetic disk 14: Head actuator 15: Spindle motor 16: VCM 18: Head assembly 20: Composite head 22: Head IC 24: Inductive head (light head) 26: MR head (read head) 28-1, 28-2: Side slider 30: Center slider 32: MR element 34: Lead terminal 36: Magnetic recording pattern 38: coil 40: Head tester 42: Spindle motor 44: Head actuator 45: Test arm 46: Control board 48: MPU 50: HDC (hard disk controller) 52: Light modulation circuit 54: Read demodulation circuit 56: Sense current setting circuit 58: Interface 70: Spin valve head 74, 76: Lead terminal 78: Spin valve element 80: Antiferromagnetic layer 82: Pin layer 84: Non-magnetic layer 86: Free layer 88: Protective layer 90: Ferromagnetic underlayer

─────────────────────────────────────────────────── --- Continuation of the front page (56) References JP-A-8-36713 (JP, A) JP-A-10-105909 (JP, A) JP-A-10-308001 (JP, A) JP-A-11- 238205 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) G11B 5/00-5/09 G11B 5/39

Claims (10)

(57) [Claims] 1. A method for determining a sense current of a disk device comprising an MR head and a sense current supply source, which is based on characteristics of element temperature and life time of one or a plurality of sample heads selected from the MR heads. A first step of obtaining an element temperature satisfying a predetermined required life time, a second step of calculating a life element temperature sense current flowing through the sample head for heating to the element temperature of the required life, the sample head Third step of measuring the maximum output sense current that maximizes the reproduction output, and a current setting ratio α obtained by dividing the life element temperature sense current obtained in the second step by the maximum output sense current measured in the third step. And a fourth step of calculating the maximum output sense current that maximizes the reproduction output of the MR head used in the disk device before the device is assembled. And a fifth step of multiplying the current setting ratio α calculated in the step to set a sense current to be flown to each MR head at the time of reproduction in the apparatus. 2. A method for determining a sense current for a disk device according to claim 1, wherein the characteristics of the element temperature and the life time of the sample head used in the first step are measured by measuring the life time at two points. A method for determining a sense current of a disk device, wherein the element temperature of the required life time is obtained by interpolation processing based on two measured values. 3. The method for determining a sense current of a disk device according to claim 1, wherein the characteristics of the life time and the element temperature are:
The reciprocal of the device temperature (1) with respect to the logarithm of the lifetime (log h)
/ T), and the element current satisfying the required life time is obtained by linear interpolation based on the two actual measurement values of the life time. 4. The method for determining a sense current of a disk device according to claim 1, wherein a sense current flowing to heat the sample head to a required life element temperature in the second step is from a predetermined room temperature Ta to A disk characterized by obtaining a current density of the sample head that obtains a temperature rise necessary for heating up to a required life element temperature, and multiplying the current density by a cross-sectional area of a portion of the sample head where a sense current flows. Method for determining sense current of device. 5. The method for determining a sense current of a disk device according to claim 4, wherein the second step is a quadratic function formula ΔT = aJ2 + bJ + c based on an actual measurement of a temperature rise ΔT with respect to a current density J of the sample head. However, a, b, and c are constants, and a current density J of the sample head required for temperature rise up to the required life element temperature is obtained. 6. A method for determining a sense current of a disk device comprising a spin valve head and a sense current supply source, wherein the element temperature and life characteristics of one or a plurality of sample heads selected from the spin valve heads are determined. A first step of obtaining an element temperature satisfying a predetermined required life time, a second step of calculating a sense current flowing through the sample head for heating to the element temperature of the required life, and reproduction of the sample head. A third step of measuring the maximum output sense current that maximizes the output, and a current setting ratio obtained by dividing the life element temperature sense current obtained in the second step by the maximum output sense current measured in the third step. Fourth step, and before assembling the device, measure the maximum output sense current that maximizes the reproduction output of the spin valve head used in the disk device. A fifth step of multiplying the current setting ratio calculated in the fourth step to set the device as a sense current to be flown to the plurality of spin valve heads at the time of reproduction, and a sense current determination of the disk device. Method. 7. The method for determining a sense current of a disk device according to claim 6, wherein the characteristics of the element temperature and life time of the sample head used in the first step lead to element destruction within a practical test time. A sense current of a disk device characterized in that a sense current corresponding to an element temperature is flown to measure the life time at least at two points, and the element temperature of the required life time is obtained by interpolation processing based on the measured values at the two points. How to decide. 8. The method of determining the sense current of a disk device according to claim 6, wherein the characteristics of the life time and element temperature are:
The reciprocal of the device temperature (1) with respect to the logarithm of the lifetime (log h)
/ T), and the element current satisfying the required life time is obtained by linear interpolation based on the two actual measurement values of the life time. 9. The method for determining a sense current of a disk device according to claim 6, wherein the sense current flowing to heat the sample head to the element temperature of the required life in the second step is from a predetermined room temperature Ta. The current density of the sample head that obtains the temperature rise necessary for heating to the element temperature of the required life is obtained, and the current density is obtained by multiplying the cross-sectional area of the portion where the sense current of the sample head flows. Disk device sense current determination method. 10. The method for determining a sense current of a disk device according to claim 6, wherein the second step is a quadratic function formula ΔT = aJ ² + bJ + c, which is based on an actual measurement of a temperature rise with respect to a current density of the sample element. , A, b, and c are constants, the current density of the sample head required for temperature rise up to the element temperature of the required life is determined, and the method for determining the sense current of the disk device.