JP2010061706A - Method and device for measuring distance, and storage device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and a device for accurately measuring distance between a head and a recording medium in a relatively simple structure. <P>SOLUTION: The method for measuring distance includes: applying two inverse AC voltages in inverse proportion to the area of an air-bearing surface 133 of a magnetic head, to two electrodes of a read element 132, the magnetic head being structured so that first and second shields 134 and 135 sandwiching the read element 132 are connected to the two electrodes of the read element 132; calculating, for complex impedance between the two electrodes of the read element 132, values of parallel capacitance of a parallel circuit composed of a resistor and a capacity by use of a calculation circuit, when the magnetic head 13 is separated from a reference surface and when the magnetic head 13 approaches the reference surface; and calculating the distance between the air-bearing surface 133 of the magnetic head and the reference surface based on the values of the two parallel capacitances calculated by the calculation circuit. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an interval measurement method and apparatus, and a storage device, and more particularly, to an interval measurement method and apparatus for measuring an interval between a head and a recording medium, and a storage device including such an interval measurement device. The present invention also relates to a head test apparatus provided with a distance measuring device and a shape inspection apparatus for a head flying surface.

  In the magnetic disk apparatus, information recording and reproduction operations are performed in a state where the magnetic head rotating on the magnetic disk is floated at a slight interval. The recording magnetic field generated by the write magnetic pole of the magnetic head and the medium magnetic field from the magnetic disk rapidly spread and attenuate according to the distance. For this reason, in order to achieve a high recording density, it is necessary to keep the flying height of the magnetic head from the magnetic disk small. Recently, the flying height is about 10 nm. In order to obtain high reliability, it is necessary to keep the flying height stable so as not to decrease too much, and to prevent damage to the magnetic head and magnetic disk due to contact between the magnetic head and the magnetic disk.

  The flat part of the air bearing surface of the magnetic head is formed by polishing or the like, but the ceramic used as the magnetic head substrate, the magnetic metal forming the write magnetic pole and the shield magnetic pole around the read element, and the magnetic metal Since the non-magnetic material such as alumina, which is separated from each other, is a material having different hardness, a step is likely to occur on the polished surface. In order to keep a small flying height stable, it is necessary for the flatness and level difference of the polished surface to be within the designed allowable range, and therefore it is necessary to measure and inspect the processing shape of the flying surface of the magnetic head.

  The flying height of the magnetic head varies not only due to manufacturing variations such as the shape of the air bearing surface of the magnetic head, but also due to suspension mounting conditions and variations in assembly to the magnetic disk device. When a write current is passed through the magnetic head, the flying height changes due to a shape change caused by thermal expansion of the head element due to heat generation, which changes according to the write current pattern. Further, the flying height varies depending on the change over time of the magnetic disk device, the use temperature environment, the atmospheric pressure environment, and the like. Therefore, in order to stably realize a low flying height, not only a test of a magnetic head element alone but also a head test performed in a state of being mounted on a suspension, a flying height measurement and a flying height control in a magnetic disk device are required. .

  As a method for inspecting the shape of the air bearing surface of a magnetic head, a method using an interference microscope or an atomic force microscope (AFM) is known. As a method of measuring the flying height of the magnetic head, a method of observing optical interference between the head flying surface and the magnetic disk from the back surface of the magnetic disk is known. Further, a method of measuring the flying height by analyzing the read signal waveform of a measurement pattern or servo pattern recorded at a specific rotational position of a magnetic disk is known (Patent Document 1). A method of measuring the flying height by measuring a change in impedance of a write element of a magnetic head is also known (Patent Document 2). There is also known a method for measuring the capacitance between the electrode on the head flying surface and the magnetic disk (Patent Documents 3, 4, and 5). A method is also known in which a current is passed through a thin film resistor provided in a magnetic head element to generate heat, and the tip of a magnetic pole is protruded by thermal expansion to control the flying height (Patent Document 6).

  As a method of inspecting the shape of the air bearing surface of the magnetic head, in the method using an interference microscope, even if the measurement resolution in the height direction is obtained by interference measurement, the spatial resolution in the in-observation direction is the resolution of the optical microscope. It is limited to the light wavelength which is the limit, and it is difficult to measure the height of the miniaturized magnetic part of the recent magnetic head.

  As a method of inspecting the shape of the air bearing surface of a magnetic head, the method using an atomic force microscope provides very high spatial resolution in both the height direction and the in-plane direction, but the horizontal movement accuracy and position drift of the piezo stage Therefore, it is difficult to keep the accuracy of height measurement constant between positions on the air bearing surface of the magnetic head. In addition, it takes time to search for a measurement position and to scan a large area.

  In the method of observing the optical interference between the head floating surface and the disk from the back of the disk, it is necessary to use a transparent dedicated disk, and measurement cannot be performed with an actual magnetic disk.

  As a method of measuring the flying height of a magnetic head, a method of analyzing a read signal waveform of a measurement pattern or servo pattern recorded at a specific position on a magnetic disk can use a normal magnetic head and a magnetic disk as they are. In addition, measurement is possible even when the magnetic head is incorporated in the magnetic disk device. However, such measurement is easily affected by characteristic variations and characteristic deterioration of the read element and the write element, and the flying height may be erroneously read. Furthermore, since it is difficult to simultaneously perform the write operation and the read operation, it is difficult to measure the flying height during the write operation.

  The method of measuring the flying height by measuring the change in impedance of the write element of the magnetic head is affected by manufacturing variations in the write element characteristics of the magnetic head and the magnetic characteristics of the magnetic disk. Furthermore, since the magnetic characteristics and the like of the magnetic disk are not simple physical characteristics, quantitative measurement is difficult.

  Many of the above problems can be solved by the method of measuring the capacitance between the electrode on the air bearing surface of the magnetic head and the disk. However, in the method of measuring the flying height and the inclination by measuring the capacitance between each electrode and the magnetic disk by providing electrodes for measuring the capacity on the magnetic head (for example, see Patent Document 3), a dedicated electrode is provided. It is necessary to create a magnetic head. Further, an extra wiring connection from the capacitance measuring electrode is required.

  In a method of measuring the capacitance between a write element, a read element, and a magnetic disk by connecting one end of a capacitance detection circuit to a write element or a read element and electrically connecting the other end to a magnetic disk (for example, Patent Literature 4), it is not necessary to add a capacitance measuring electrode or a wiring on a suspension for connecting the capacitance measuring electrode. However, one end of the capacitance detector must be electrically connected to the magnetic disk, the motor rotating shaft of the magnetic disk, and the motor body, and these electrically connected parts must be insulated from the ground. Further, since the measurement current path is a loop with a large opening via the magnetic head and the motor rotation shaft, it is easy to pick up electromagnetic induction noise.

  In the method of obtaining the flying height from the capacitance measurement value obtained by providing two capacitance measuring electrodes on the air bearing surface of the magnetic head, applying an AC voltage from one electrode, and detecting the current at the other electrode, Is electrically connected to the ground, or the static capacitance between the magnetic disk and the magnetic disk cannot be ignored compared to the electrostatic capacitance between the electrode and the magnetic disk, When these conduction and capacity are unstable, these factors affect the flying height measurement result.

Two electrodes provided on the air bearing surface of the magnetic head and an inductance are connected in series to form a resonance circuit. An alternating voltage near the resonance frequency is applied to the DC voltage and the phase difference between the voltage and current is determined by the DC voltage. In the method of controlling the flying height in a controlled manner (see, for example, Patent Document 5), the voltage amplitude to be applied between the two electrodes is not defined. In addition, since the circuit for applying a voltage to the two electrodes is not symmetrical with respect to the two electrodes, an AC voltage having the same amplitude is not applied to the two electrodes, and the magnetic disk has a stray capacitance or a ground. The effect of the connection status remains.
JP 2000-195211 A JP 2006-202391 A JP-A-6-203510 JP 2001-344920 A JP 2001-84724 A JP-A-5-20635

  Conventionally, there has been a problem that the distance between the head and the recording medium cannot be accurately measured with a relatively simple configuration.

  Accordingly, an object of the present invention is to provide an interval measuring method and apparatus, and a storage device that can accurately measure the interval between a head and a recording medium with a relatively simple configuration.

  According to an aspect of the present invention, a magnetic head having a structure in which a read element is sandwiched between first and second shields and the first and second shields are connected to two electrodes of the read element. A distance measurement method for measuring a distance between the air bearing surface of the first and second reference surfaces, wherein the amplitude is equal by an AC voltage source, or is inversely proportional to the area of the air bearing surface of the first and second shields, An applying step of applying two alternating voltages having opposite signs to the two electrodes of the read element, and a measuring step of measuring a current generated in the read element and measuring a complex impedance between the two electrodes of the read element A value of a parallel capacitance when the complex impedance is regarded as a parallel circuit of a resistor and a capacitor by an arithmetic circuit, and a state in which the magnetic head is separated from the reference plane The floating of the magnetic head in a state where the magnetic head is brought close to the reference plane from the step of calculating the state close to the reference plane and two parallel capacitance values calculated by the arithmetic circuit A distance measurement method is provided for calculating a distance between a surface and the reference surface.

  According to an aspect of the present invention, a magnetic head having a structure in which a read element is sandwiched between first and second shields and the first and second shields are connected to two electrodes of the read element. A distance measuring device for measuring a distance between the air bearing surface and a reference surface of the first and second shields having the same amplitude or inversely proportional to the area of the air bearing surface of the first and second shields and having opposite signs to each other A differential impedance measurement comprising an AC voltage source for applying two AC voltages to the two electrodes of the read element, measuring a current generated in the read element, and measuring a complex impedance between the two electrodes of the read element And a value of a parallel capacitance when the complex impedance is regarded as a parallel circuit of a resistor and a capacitor, a state in which the magnetic head is separated from the reference plane, and the magnetic head An arithmetic circuit that calculates a state in which the magnetic head is in proximity to a surface, and the arithmetic circuit calculates the magnetic head in a state in which the magnetic head is in proximity to the reference surface from the calculated two parallel capacitance values. A distance measuring device for calculating a distance between the air bearing surface and the reference surface is provided.

  According to an aspect of the present invention, there is provided a storage device including the magnetic head, a magnetic disk having a recording surface that forms the reference surface, and the interval measuring device.

  According to the disclosed distance measuring method and apparatus, and the storage device, the distance between the head and the recording medium can be accurately measured with a relatively simple configuration.

  As a read element of a magnetic head, an anisotropic magnetoresistive (AMR) element, a giant magnetoresistive (GMR) element, and in recent years a tunneling magnetoresistive effect (TMR: Tunneling Magneto-) Resistive) elements are used, but in the past, a DC bias current or DC bias voltage was applied between the two electrodes of these read elements to measure the voltage between the two electrodes and the current flowing between the two electrodes. Thus, the change in resistance between the two electrodes of the read element is measured to detect the medium magnetic field from the magnetic disk.

  Therefore, the inventors focused on the following three points.

  First, in a conventional read element such as an AMR element or a GMR element, a magnetic film is used to measure resistance by flowing a current in the in-plane direction of the magnetic film sensor (referred to as a CIP (Current In Plane) structure). In order to shield the read element from the peripheral magnetic field excluding the medium magnetic field from the magnetic disk directly under the read element, two magnetic shields sandwiched from above and below the read element film surface are provided on both ends of the read element. Basically insulated from the electrodes. However, in a read element such as a TMR element that has been put into practical use in recent years, a current is passed perpendicularly to the film surface of the TMR film to measure resistance (referred to as a CPP (Current Perpendicular to Plane) structure). The two magnetic shields sandwiched from above and below the surface also serve as two electrodes of the TMR element, and the two electrodes of the TMR element are electrically connected to the upper and lower shields with low resistance, respectively.

  Second, the capacitance connected in parallel to both ends of the TMR element can be used for magnetic field detection by measuring both the real part and the imaginary part of the complex impedance between the two electrodes of the TMR element. The parallel capacitance component can be separated from the resistance component of the element and measured.

  Third, when measuring the series capacitance of two capacitances formed between two electrodes and a magnetic disk, if the distance between the two electrodes and the magnetic disk can be regarded as the same, 2 By measuring the capacitance by applying alternating voltage components of opposite signs having an amplitude inversely proportional to the area of the two electrodes, the total current and charge flowing into the magnetic disk through capacitive coupling with the two electrodes are zero. Therefore, the stray capacitance of the magnetic disk, the presence / absence of conduction between the magnetic disk and the ground through the rotating shaft of the spindle motor, and the instability of conduction are not greatly affected by the series capacitance of the two capacitances. It becomes possible to measure stably.

  In the disclosed interval measuring method and apparatus, and the storage device, focusing on the above three points, the conventional technique is actively used by measuring the complex impedance between two electrodes of a read element such as a TMR element. The capacitance component between the two electrodes of the read element that did not occur is measured separately from the resistance component used as the magnetic field sensor, and the distance between the magnetic head and the magnetic disk is measured (or the magnetic disk of the magnetic head) Measurement of flying height from In addition, measurement that is not affected by the stray capacitance or grounding state of the magnetic disk is enabled.

  That is, the two magnetic shields sandwiching the read element are opposite to the two electrodes of the read element such as a TMR element that also serves as the two electrodes of the read element, and the sign whose amplitude is inversely proportional to the area of the air bearing surface of each magnetic shield is reversed. By measuring the current by applying an AC voltage, the complex impedance between the two electrodes of the read element is measured, and the value of the capacitance is calculated when the measured complex impedance is regarded as a parallel circuit of resistance and capacitance. To do. From this capacity value, the distance between the magnetic head and the magnetic disk is calculated. If there is no significant difference in the area of the air bearing surface of the two magnetic shields sandwiching the read element, the amplitude of the AC voltage applied to the two electrodes of the read element may be made equal.

  As a result, the flying height of the magnetic head levitated from the magnetic disk can be measured in the magnetic head test apparatus and the magnetic storage device. Further, the shape of the magnetic head air bearing surface can be inspected by measuring the distance while the air bearing surface of the magnetic head is pressed against a reference flat plate made of metal or having a metal layer on the surface. Here, a magnetic disk may be used as the reference plane plate. Furthermore, when a flying height control circuit is provided by controlling the shape of the air bearing surface by heating the heater element of the magnetic head element, the flying height of the magnetic head measured by the above method is within a predetermined range. In addition, a magnetic head test apparatus and a magnetic storage device that control the flying height can be realized.

  Embodiments of the interval measuring method and apparatus and the storage device of the present invention will be described below with reference to the drawings.

  FIG. 1 is a diagram showing a head test apparatus according to a first embodiment of the present invention. In this embodiment, the present invention is applied to a magnetic head testing apparatus.

  As shown in FIG. 1, the magnetic head test apparatus 1 includes an interval measuring device 11, a write current generating circuit 12, a magnetic head 13, a magnetic disk 21, a control circuit 14 for controlling these, and the like. In FIG. 1, the control circuit 14 is connected to the interval measuring device 11 and the write current generating circuit 12 via a control signal line 34. Usually, the magnetic head test apparatus includes an actuator for controlling the position of the magnetic head, a spindle motor for rotating the magnetic disk, etc., but these are omitted in FIG.

  The interval measuring device 11 includes a differential impedance measuring device 111 and an arithmetic circuit 112. Here, the arithmetic circuit 112 may be an arithmetic circuit controlled by a program, or may be included in the control circuit 14. The differential impedance measuring instrument 111 includes a voltmeter 113, an ammeter 114, an AC voltage source 115, and a control circuit 116. The voltmeter 113 includes first and second voltmeters 113-1 and 113-2. The ammeter 114 includes first and second ammeters 114-1 and 114-2. The AC voltage source 115 includes voltage amplifiers 117-1 and 117-2, phase adjustment circuits 118-1 and 118-2, and an oscillator 119.

  The magnetic head 13 includes a write element 131, a TMR element 132 that is a read element, and an air bearing surface 133. The TMR element 132 is provided between first and second magnetic shields (hereinafter simply referred to as shields) 134 and 135. The ride element 131 is connected to the write current generation circuit 12 by the write differential wiring 31. The read differential wiring 32 connected to the two electrodes of the TMR element 132 is connected to the first and second shields 134 and 135. D indicates the distance between the air bearing surface 133 and the recording surface 211 of the magnetic disk 21.

  FIG. 2 is a view of the TMR element 132 of the magnetic head 13 as viewed from the air bearing surface 133 side. The TMR element 132 is sandwiched between the first and second shields 134 and 135 in order to shield the peripheral magnetic field in the same manner as a normal AMR element or GMR element. The TMR element 132 has a structure (CPP structure) in which a detection current flows perpendicularly to the TMR film surface, and the first and second shields 134 and 135 serve as two electrodes of the TMR element 132. ing. The area of the first shield 134 on the air bearing surface 133 is S1, and the area of the second shield 135 on the air bearing surface 133 is S2. The areas S1 and S2 are determined at the time of designing for each magnetic head 13, and can be easily measured with an optical microscope or an electron microscope if necessary.

  The magnetic disk 21 has a known configuration including, for example, a flat substrate coated with a metal film. However, it goes without saying that a measurement-dedicated disk may be used instead of the recording / reproducing magnetic disk 21. Since the positions of the first and second shields 134 and 135 on the air bearing surface 133 of the magnetic head 13 are close to each other, the magnetic head 13 is pressed against the magnetic disk 21 or floated from the recording surface 211 of the magnetic disk 21 Then, the distance D between the air bearing surface 133 and the recording surface 211 at the positions of the first and second shields 134 and 135 can be regarded as the same value. The distance D to be measured is about 10 nm. Thus, when the distance D is sufficiently smaller than the film thickness (about 1 μm) of the first and second shields 134 and 135, the first shield 134. A capacity C1 is formed between the magnetic disk 21 and the magnetic disk 21, and a capacity C2 is formed between the second shield 135 and the magnetic disk 21, and these capacity C1 and C2 are given by the following equations (1) and (2).

C1 = ε0 × S1 / D (Formula 1)
C2 = ε0 × S2 / D (Formula 2)
Here, ε0 is the dielectric constant of vacuum, and is used as an approximate value of the dielectric constant of air. When the magnetic head 13 is sufficiently separated from the magnetic disk 21, C1 = C2 = 0.

  In FIG. 1, C0 indicates a capacitance measured between two electrodes of the TMR element 132 when the interval D is sufficiently increased. Cd represents the capacity between the magnetic disk 21 and the ground GND.

  The differential impedance measuring device 111 is connected to the first and second shields 134 and 135 through the differential wiring for lead 32 and measures the complex impedance Z between the two electrodes of the TMR element 132. In the magnetic head 13 mounted on the suspension (not shown), the transmission line on the suspension that reads the read signal as a differential signal from the TMR element 132 is a differential wiring, and special wiring is added or modified. This transmission line can be used as the measurement differential wiring 32 without adding.

  In the differential impedance measuring instrument 111, the AC voltage source 115 adjusts the phase and amplitude from the sine wave output of the oscillator 119 using the phase adjustment circuits 118-1 and 118-2 and the voltage amplifiers 117-1 and 117-2. Two sine wave voltages generated are generated. These two sine wave voltages are output via the ammeters 114-1 and 114-2 and the voltmeters 113-1 and 113-2, and are applied to the TMR element 132 by the read differential wiring 32. The ammeters 114-1 and 114-2 can measure two output currents I1 and I2 of the differential impedance measuring instrument 111. The voltmeters 113-1 and 113-2 can measure the two output voltages V1 and V2 of the differential impedance measuring instrument 111. Here, the voltmeters 113-1 and 113-2 and the ammeters 114-1 and 114-2 are vector measuring instruments capable of measuring both the amplitude and the phase with respect to the sine wave, and the currents I 1 and I 2 and the voltage V1 and V2 are vector quantities, that is, complex display quantities including phases. Further, the actual voltage output of the AC voltage source 115 may be obtained by superimposing the DC bias voltage on the AC voltages V1 and V2, and the actual current in this case is the DC current generated by the DC bias voltage on I1 and I2. However, this does not affect the following explanation.

  The phases of the AC voltages V1 and V2 applied to the two electrodes of the TMR element 132 are opposite to each other, and the amplitude is a value inversely proportional to the areas S1 and S2 of the first and second shields 134 and 135. That is, the following expression 3 is established.

V1 / V2 = −S2 / S1 (Formula 3)
Here, if S1 and S2 are approximately equal, V1 may be set to −V2.

  By applying the voltages V1 and V2, the current and charge induced in the magnetic disk 21 through the first and second shields 134 and 135 are canceled out. Therefore, since the potential of the disk 21 is not changed regardless of the stray capacitance of the disk 21 or the connection state with the ground GND, the measurement can be performed without being influenced by these.

  In particular, when V1 = −V2, etc., it may be expected that the following expression 4 is substantially satisfied.

I1 = −I2 (Formula 4)
The complex impedance Z between the two electrodes of the TMR element 132 is given by the following Equation 5.

Z = 2 (V1-V2) / (I1-I2) (Formula 5)
The complex impedance Z comprises a real component resistance R and an imaginary component reactance X, as shown in Equation 6 below.

Z = R + j × X (Formula 6)
Here, j is an imaginary unit.

  A circuit model of the TMR element 132 is expressed as a parallel connection of a resistor and a capacitor, and a capacitor between the first and second shields 134 and 135 and the magnetic disk 21 is connected in parallel to the TMR element 132 in the magnetic head 13. Capacitors other than the elements are also connected in parallel. Therefore, the entire circuit of the magnetic head 13 can be expressed by a parallel circuit of resistance and capacitance. Further, the capacitance of the lead differential wiring 32 is also connected in parallel. The complex impedance Z between the two electrodes of the TMR element 132 measured by the above method includes the impedance of the lead differential wiring 32 unless correction calculation is performed, but this is a fixed value. Therefore, for example, the correction calculation can be performed so as to remove the influence by measuring the impedance of the lead differential wiring 32 in advance. Assuming that the measured complex impedance Z is equal to the impedance of the parallel connection circuit of resistance and capacitance, the parallel capacitance Cp and the parallel resistance Rp can be obtained from the following equations 8 and 9 by the following equation 7.

1 / Z = 1 / (R + j × X) = 1 / Rp + j × 2πfsCp (Expression 7)
Cp = −X / (2πfs (R ² + X ² )) (Formula 8)
Rp = (R ² + X ² ) / R (Formula 9)
Here, fs is the frequency of the sine wave voltage output from the AC voltage source 115 used for this measurement. If the value of the parallel resistance Rp is not particularly used, the calculation of the parallel resistance Rp may be omitted.

FIG. 3 is a flowchart for explaining a procedure for measuring the parallel capacitance Cp as described above. In FIG. 3, in step S <b> 1, voltages V <b> 1 and V <b> 2 satisfying V1 / V2 = −S2 / S1 are applied to the two electrodes of the TMR element 132 for the AC voltage source 115. In step S2, currents I1 and I2 flowing through the two electrodes of the TMR element 132 are measured by the ammeters 114-1 and 114-2. In step S3, complex impedance Z = R + jX is calculated from Z = 2 (V1-V2) / (I1-I2). In step S4, the parallel capacitance Cp and the parallel resistance Rp are calculated from Cp = −X / (2πfs (R ² + X ² )) and Rp = (R ² + X ² ) / R, and the process ends.

  The parallel capacitance Cp measured as described above in a state where the magnetic head 13 is sufficiently separated from the magnetic disk 21 (unloaded state) is C0, and the air bearing surface 133 of the magnetic head 13 and the magnetic disk 21 are brought close to each other and the distance D therebetween. Is a state to be measured (load state), and the parallel capacitance Cp measured as described above is Cn, Cn−C0 is a series capacitance of the capacitance C1 and the capacitance C2, as shown in the following Expression 10.

Cn−C0 = 1 / ((1 / C1) + (1 / C2)) (Formula 10)
Accordingly, the distance D between the magnetic disk 21 and the flying surface 133 of the magnetic head 13 can be obtained by calculating the following Expression 11 by the arithmetic circuit 112.

D = ε0 / ((Cn−C0) ((1 / S1) + (1 / S2))) (Formula 11)
FIG. 4 is a flowchart for explaining an example of the procedure for measuring the interval D as described above. In FIG. 4, in step S11, the magnetic head 13 is put into an unload state, and in step S12, the measured parallel capacitance Cp is set to C0. In step S13, the magnetic head 13 is loaded, and in step S14, the measured parallel capacitance Cp is set to Cn. In step S15, D = ε0 / ((Cn−C0) ((1 / S1) + (1 / S2))) is calculated, and the process ends.

  If sufficient measurement accuracy of the interval D cannot be obtained by one measurement, the measurement result of FIG. 4 may be repeated N times as shown in the flowchart of FIG. 5 to obtain the average of the measurement results. In this case, the measurement accuracy of the interval D can be improved.

  FIG. 5 is a flowchart for explaining an example of the procedure for measuring the average of the intervals D as described above. In FIG. 5, in step S21, the number of repetitions i is set to i = 1. In step S22, the measured interval D is set to D (i). In step S23, it is determined whether i = N (N is a natural number of 2 or more). If the decision result in the step S23 is NO, in a step S24, i is incremented to i = i + 1, and the process returns to the step S22. On the other hand, if the decision result in the step S23 is YES, in a step S25, an addition average value of D (i) (i = 1 to N) is obtained by calculating D = ΣD (i) / N. finish.

  Note that the voltmeters 113-1 and 113-2 can be omitted if the outputs of the voltage amplifiers 117-1 and 117-2 of the AC voltage source 115 are adjusted in advance so that the above Equation 3 is established.

  As the ammeter 114, a differential ammeter that measures I1-I2 can also be used.

  If the above equation 4 is expected to hold, one of the ammeters 114-1 and 114-2 can be omitted and 2I1 or -2I2 can be used instead of I1-I2.

  In addition, by connecting the intermediate tap of the output side coil to the lead differential wiring 32 via a balun transformer connected to the ground GND, a single output AC voltage source and a single ammeter can be used to read the lead element. The differential impedance of Equation 5 can also be measured by applying a differential voltage to and measuring the differential current flowing through the read element. At this time, the ratio of the two amplitudes of the differential voltage can be adjusted by adjusting the position of the intermediate tap of the output side coil.

  The magnetic head test apparatus 1 or the magnetic disk for testing the read / write characteristics of the magnetic head 13 by the distance measuring device 11 that measures the distance D between the air bearing surface 133 of the magnetic head 13 and the recording surface 211 of the magnetic disk 21. The flying height of the flying surface 133 of the magnetic head 13 from the magnetic disk 21 can be measured on the apparatus. The flying height of the magnetic head 13 is the distance between the flying surface 133 and the recording surface 211 as with the distance D, but indicates the distance when the magnetic disk 21 is rotated. The magnetic head test apparatus and the recent magnetic disk apparatus are equipped with a mechanism for loading and unloading the magnetic head to and from the magnetic disk medium. When the flying height is measured, the magnetic head 13 is loaded and unloaded. Can be used for loading and unloading.

  On the other hand, recorded information recorded on the magnetic disk 21 can be read from a change in resistance of the TMR element 132 due to the medium magnetic field of the magnetic disk 21.

  The first method for reading the recorded information on the magnetic disk 21 obtains the resistance of the TMR element 132 from Equation 9 using the measurement result of the complex impedance Z as described above. In this case, the recorded information on the magnetic disk 21 can be read simultaneously with the measurement of the flying height of the magnetic head 13. However, the impedance measurement frequency fs needs to be equal to or higher than the recording frequency.

  A second method for reading the recorded information on the magnetic disk 21 applies a DC bias voltage to the outputs of the voltage amplifiers 117-1 and 117-2, and reads the recorded information on the magnetic disk 21 from the output of the ammeter 114. In this case, by making the impedance measurement frequency fs lower than the lower limit of the recording frequency band, it is possible to simultaneously read the recorded information and measure the flying height. Note that when reading recorded information, the measurement of the flying height by impedance measurement may be stopped.

  As shown in FIG. 6, the third method of reading the recorded information on the magnetic disk 21 is provided with a read signal detection device 41 separately from the interval measurement device 11, and the read signal detection device 41 and the interval measurement device 11 are switched by the switching circuit 42. To be connected to the TMR element 132. FIG. 6 is a diagram showing a magnetic head test apparatus 201 in the second embodiment of the present invention. In FIG. 6, the same parts as those in FIG. The switching circuit 42 may be configured to be switchable by the control circuit 14.

  Further, as shown in FIG. 7, a flying height control circuit 45 for controlling the shape change of the flying surface 133 due to heating of the heater element 136 provided in the magnetic head 13 is provided, and the magnetic head 13 measured by the interval measuring device 11 is provided. The flying height may be controlled so that the interval D is within a predetermined range. FIG. 7 is a diagram showing a magnetic head test apparatus 301 in the third embodiment of the present invention. In FIG. 7, the same parts as those in FIG. In this case, the interval D measured by the interval measuring device 11 is supplied to the flying height control circuit 45 via the control signal line 34, and the flying height control circuit 45 controls the heat generation of the heater element 136 according to the space D. To control the flying height of the magnetic head 13.

  The magnetic head test apparatus and magnetic disk apparatus can be realized by adding an actuator for controlling the position of the magnetic head, a spindle motor for rotating the magnetic disk, etc., which is omitted in the figure, to the configuration of FIG. 6 or FIG. Needless to say.

  The resistance of the TMR element 132 is about several hundreds Ω, and a relatively small resistance is connected in parallel to a minute capacitance of about several tens of fF used for flying height measurement. In order to measure the flying height with high accuracy, it is desirable that the resistance connected in parallel to the measurement capacity is high. Therefore, if a head in which the resistance between two electrodes is made higher than that of a normal magnetic head by making the tunnel insulating layer of the TMR element 132 thicker than usual, the flying height can be measured with higher sensitivity. Although it becomes possible and the magnetic field detection capability is sacrificed, it can be used for design verification of the shape of the flying surface 133 as a dedicated head for flying height characteristic evaluation.

  The configuration of each of the above embodiments can be applied as long as the first and second shields 134 and 135 sandwiching the TMR element 132 serve as two electrodes of the TMR element 132, and the magnetic head having the TMR element 132 is applicable. It can be applied not only to the magnetic head 13 but also to a magnetic head having a read element such as a GMR element having a CPP structure.

  Further, instead of the magnetic disk 21, a reference flat plate made of metal or having a metal layer on the surface is used, and the distance D in a state where the air bearing surface 133 of the magnetic head 13 is pressed against the reference flat plate is measured. In addition, it is possible to inspect the shape of the air bearing surface 133 of the magnetic head 13 such as the flatness and the recess amount. The magnetic disk 21 may be used as the reference flat plate. For example, if the flatness of the air bearing surface 133 is poor or the portions of the first and second shields 134 and 135 are abnormally deeply polished due to a defect in the polishing process of the air bearing surface 133 when the magnetic head 13 is manufactured. Since the first and second shields 134 and 135 are not close to the reference flat plate, the distance D is measured to be an abnormal value compared to the case of a normal magnetic head, and polishing failure is found.

  FIG. 8 is a view showing an air bearing surface shape inspection apparatus 401 in the fourth embodiment of the present invention. In FIG. 8, the same parts as those in FIG.

  In FIG. 8, the table 51 is provided with a position control device 52 and a reference plane plate 121. The position control device 52 controls the magnetic head 13 via the head fixing unit 53. The position controller 52 presses (loads) or pulls (unloads) the air bearing surface 133 of the magnetic head 13 against the surface 1211 of the reference flat plate 121. If the interval D measured by the interval measuring device 11 is within a predetermined range between the minimum value Dmin and the maximum value Dmax, it is determined that the magnetic head 13 is a normal product, otherwise it is an abnormal product. This determination can be made by the control circuit 14.

  FIG. 9 is a flowchart for explaining an example of the procedure for inspecting the air bearing surface shape. In FIG. 9, in step S <b> 41, the magnetic head 13 is pulled away from the reference flat plate 121 by the position control device 52 to be in an unloaded state. In step S42, the parallel capacitance Cp measured by the interval measuring device 11 is set to C0. In step S <b> 43, the magnetic head 13 is pressed against the surface 1211 of the reference flat plate 121 by the position control device 52 to be in a loaded state. In step S44, the parallel capacitance Cp measured by the interval measuring device 11 is set to Cn. In step S45, the distance measuring device 11 calculates D = ε0 / ((Cn−C0) ((1 / S1) + (1 / S2))). In step S46, it is determined whether or not the interval D measured by the interval measuring device 11 is within a predetermined range between the minimum value Dmin and the maximum value Dmax. If the decision result in the step S46 is NO, it is judged that the magnetic head 13 is abnormal in a step S47. On the other hand, if the decision result in the step S46 is YES, it is judged in a step S48 that the magnetic head 13 is normal.

  As described above, in each of the above embodiments, both the real part and the imaginary part of the complex impedance between the two electrodes of the read element are detected in the magnetic head having the read element having the CPP structure. As a result, it is possible to measure the capacitance component between the two electrodes of the read element, which has not been conventionally used, and to measure the distance between the magnetic head and the magnetic disk or the reference plane plate from this capacitance component. Further, without adding a special structure including wiring to the magnetic head element, the magnetic head suspension, the spindle motor, etc., and the presence or absence of electrical connection (conduction) with the ground of the magnetic disk, Regardless of the stray capacitance, the capacitance between the magnetic disk and the ground, and the instability of these capacities, the shape of the flying surface of the magnetic head, the measurement of the flying height of the magnetic head, and the magnetic head based on the measured flying height It is possible to control the flying height. Furthermore, since a differential measurement configuration using differential wiring is adopted, electromagnetic induction noise is not easily applied to the measurement result.

  The present invention is not limited to a head testing apparatus provided with a distance measuring device, but can also be applied to a storage device such as a magnetic disk device and a shape inspection device for a head flying surface.

The following additional notes are further disclosed with respect to the embodiment including the above examples.
(Appendix 1)
A floating surface of a magnetic head having a structure in which a read element is sandwiched between first and second shields, and the first and second shields are connected to two electrodes of the read element, and a reference plane An interval measurement method for measuring an interval between
An application step of applying two alternating voltages of opposite signs that are equal in amplitude to each other by an alternating voltage source or inversely proportional to the area of the air bearing surface of the first and second shields, to the two electrodes of the read element;
A measurement step of measuring a current generated in the read element to measure a complex impedance between two electrodes of the read element;
When the complex impedance is regarded as a parallel circuit of a resistor and a capacitor by an arithmetic circuit, the values of the parallel resistance and the parallel capacitance are set such that the magnetic head is separated from the reference plane and the magnetic head is brought close to the reference plane. A process of calculating with
A distance measurement for calculating a distance between the air bearing surface of the magnetic head and the reference surface in a state where the magnetic head is brought close to the reference surface from two parallel capacitance values calculated by the arithmetic circuit. Method.
(Appendix 2)
The interval measuring method according to appendix 1, wherein the two sine wave voltages are applied to two electrodes of the read element via a differential wiring.
(Appendix 3)
The distance measuring method according to any one of appendices 1 to 2, wherein the read element is a TMR element or a GMR element.
(Appendix 4)
The interval measuring method according to any one of appendices 1 to 3, wherein the reference surface is a recording surface of a magnetic disk.
(Appendix 5)
A floating surface of a magnetic head having a structure in which a read element is sandwiched between first and second shields, and the first and second shields are connected to two electrodes of the read element, and a reference plane An interval measuring device for measuring an interval between
An AC voltage source that applies two AC voltages having opposite amplitudes that are equal in amplitude or inversely proportional to the area of the air bearing surface of the first and second shields to the two electrodes of the read element; A differential impedance measuring instrument that measures a current generated in the element and measures a complex impedance between two electrodes of the lead element;
The values of parallel resistance and parallel capacitance when the complex impedance is regarded as a parallel circuit of resistance and capacitance, the state where the magnetic head is separated from the reference surface, and the state where the magnetic head is close to the reference surface With an arithmetic circuit to calculate
The arithmetic circuit calculates an interval between the air bearing surface of the magnetic head and the reference surface in a state in which the magnetic head is brought close to the reference surface from two calculated parallel capacitance values. measuring device.
(Appendix 6)
The distance measuring device according to appendix 5, further comprising a differential wiring that applies the two sine wave voltages from the AC voltage source to two electrodes of the read element.
(Appendix 7)
The distance measuring device according to any one of appendices 5 to 6, wherein the read element is a TMR element or a GMR element.
(Appendix 8)
The distance measuring device according to any one of appendices 5 to 7, wherein the reference surface is a recording surface of a magnetic disk.
(Appendix 9)
The magnetic head;
A magnetic disk having a recording surface forming the reference surface;
A storage device or a magnetic head testing device comprising the interval measuring device according to any one of appendices 5 to 8.
(Appendix 10)
A lead signal detection device;
The storage device or magnetic head test device according to appendix 9, further comprising a switching circuit that selectively connects the read signal detection device or the differential impedance measuring instrument to two electrodes of the read element.
(Appendix 11)
The magnetic head has a heater element,
The supplementary note 9 or 10, further comprising a flying height control circuit for controlling a flying height from the magnetic disk during rotation of the magnetic head by controlling heat generation of the heater element based on the measured interval. Storage device or magnetic head testing device.
(Appendix 12)
The magnetic head;
A reference plane plate forming a surface forming the reference plane;
A position control device that controls the magnetic head in a state separated from the reference surface, and a state in which the magnetic head is pressed and brought close to the reference surface;
Including the interval measuring device according to any one of appendices 5 to 8,
The air bearing surface shape inspection apparatus that determines whether the magnetic head is normal or abnormal based on the measured interval.

  While the present invention has been described with reference to the embodiments, it is needless to say that the present invention is not limited to the above-described embodiments, and various modifications and improvements can be made within the scope of the present invention.

It is a figure which shows the head test apparatus in the 1st Example of this invention. It is the figure which looked at the TMR element of the magnetic head from the air bearing surface side. It is a flowchart explaining an example of the measurement procedure of parallel capacity. It is a flowchart explaining an example of the measurement procedure of a space | interval. It is a flowchart explaining an example of the measurement procedure of the addition average of an interval. It is a figure which shows the head test apparatus in 2nd Example of this invention. It is a figure which shows the head test apparatus in 3rd Example of this invention. It is a figure which shows the air bearing surface shape test | inspection apparatus in 4th Example of this invention. It is a flowchart explaining an example of the test | inspection procedure of an air bearing surface shape.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Magnetic head test apparatus 11 Space | interval measuring apparatus 12 Write current generation circuit 13 Magnetic head 14 Control circuit 21 Magnetic disk 111 Differential impedance measuring device 112 Arithmetic circuit 131 Write element 132 TMR element D Interval

Claims (5)

A floating surface of a magnetic head having a structure in which a read element is sandwiched between first and second shields, and the first and second shields are connected to two electrodes of the read element, and a reference plane An interval measurement method for measuring an interval between
An application step of applying two AC voltages of opposite signs, which have the same amplitude or are inversely proportional to the area of the air bearing surface of the first and second shields, to the two electrodes of the read element by an AC voltage source; ,
A measurement step of measuring a current generated in the read element to measure a complex impedance between two electrodes of the read element;
The value of the parallel capacitance when the complex impedance is regarded as a parallel circuit of a resistor and a capacitor by an arithmetic circuit, a state where the magnetic head is separated from the reference plane and a state where the magnetic head is brought close to the reference plane The process of calculating in
A distance measurement for calculating a distance between the air bearing surface of the magnetic head and the reference surface in a state where the magnetic head is brought close to the reference surface from two parallel capacitance values calculated by the arithmetic circuit. Method. A floating surface of a magnetic head having a structure in which a read element is sandwiched between first and second shields, and the first and second shields are connected to two electrodes of the read element, and a reference plane An interval measuring device for measuring an interval between
An AC voltage source for applying two AC voltages of opposite signs, which are equal in amplitude or inversely proportional to the area of the air bearing surface of the first and second shields, to the two electrodes of the read element; A differential impedance measuring instrument that measures a current generated in the read element and measures a complex impedance between two electrodes of the read element;
A parallel capacitance value when the complex impedance is regarded as a parallel circuit of a resistor and a capacitance is calculated in a state where the magnetic head is separated from the reference plane and a state where the magnetic head is brought close to the reference plane. Arithmetic circuit,
The arithmetic circuit calculates an interval between the air bearing surface of the magnetic head and the reference surface in a state in which the magnetic head is brought close to the reference surface from two calculated parallel capacitance values. measuring device. The magnetic head;
A magnetic disk having a recording surface forming the reference surface;
A storage device comprising the interval measuring device according to claim 2. A lead signal detection device;
The storage device according to claim 3, further comprising a switching circuit that selectively connects the read signal detection device or the differential impedance measuring instrument to two electrodes of the read element. The magnetic head has a heater element,
5. A flying height control circuit for controlling a flying height from the magnetic disk during rotation of the magnetic head by controlling heat generation of the heater element based on the measured interval. The storage device described.

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