JP4753079B2 - Magnetic disk evaluation method - Google Patents

Description

  The present invention relates to a magnetic disk evaluation method, and more particularly, to a magnetic disk evaluation method for relatively evaluating a meniscus force of a lubricating layer formed on a magnetic disk surface.

  As the recording density of magnetic recording devices in recent years has increased, the flying height (FH) of the magnetic head slider has fallen below 10 nm, and intermittent contact between the head slider and the magnetic disk becomes inevitable. Yes. For this reason, in order to prevent solid contact between the head slider and the disk, a fluorine-based lubricant called PFPE (perfluoropolyether) is generally about 1.0 to 2.0 nm thick on the surface of the magnetic disk. Is applied to form a lubricating layer. However, when the lubricating layer is placed in an intermittent contact state, it tends to move (transfer) from the disk surface to the head slider surface, and when the transfer amount increases, the lubricating layer bridges between the head slider and the disk. Is formed, and an adsorption force called a meniscus force is generated. This meniscus force is a factor that hinders stable flying of the head slider. Therefore, the development of a lubrication method that suppresses the generation of meniscus force and the establishment of a method for evaluating the meniscus force in carrying out the development are problems.

Japanese Patent Laid-Open No. 6-147841

  However, there has been no method for evaluating the meniscus force of the lubricating layer acting on the head slider running on the magnetic disk, and this has been a major problem in considering a new lubricating layer.

  The present invention has been made in view of such problems, and an object of the present invention is to provide a magnetic material capable of evaluating the magnitude of the meniscus force of the lubricating layer acting on the head slider running on the magnetic disk. It is to provide a disk evaluation method.

  In order to achieve such an object, the invention described in claim 1 is a magnetic disk evaluation method, wherein the pitch angle rising peripheral speed value at the time of slider flying derived from the transition of the head slider flying posture at the time of take-off operation. And the difference between the circumferential speed value at which the head slider actually moves away from the disk, and the difference between the circumferential speed value at which the pitch angle rises away from the disk and the circumferential speed value at which the head slider moves away from the disk, It is characterized in that the magnitude of the meniscus force generated between the applied lubricating layer and the traveling head slider is evaluated.

  The invention according to claim 2 is a magnetic disk evaluation method, comprising: a first step of preparing a disk on which a lubricating layer is formed; contacting the lubricating layer of the disk with a head slider; and The lubricating layer for each of the second step of rotating the disk at a predetermined peripheral speed capable of maintaining contact with the head slider and a plurality of peripheral speeds that are higher than the predetermined peripheral speed. And measuring the angle formed between the surface of the head slider and the head slider to obtain a first peripheral speed at which the angle formed between the surface of the lubricating layer and the head slider increases rapidly, and each of the plurality of peripheral speeds On the other hand, it is determined whether or not the lubricating layer and the head slider are in contact with each other, and a third step of acquiring a second peripheral speed at which the head slider separates from the lubricating layer; Peripheral speed and the second And having a fourth step of obtaining a difference between the speed.

  A third aspect of the present invention is the magnetic disk evaluation method according to the second aspect, wherein, in the step 3, the angle formed by the surface of the lubricating layer and the head slider with respect to the plurality of peripheral speeds is determined. A first profile which is a profile is created, and the first peripheral speed is acquired based on the first profile.

  A fourth aspect of the present invention is the magnetic disk evaluation method according to the second or third aspect, wherein, in the third step, the lubricating layer of the head slider is applied to each of the plurality of peripheral speeds. A second profile, which is a profile of the flying height of the head slider from the lubricating layer with respect to the plurality of peripheral speeds, is created based on the second profile. It is characterized by acquiring the peripheral speed of.

  According to a fifth aspect of the present invention, there is provided a magnetic disk evaluation apparatus comprising a plurality of peripheral speeds having a peripheral speed greater than a predetermined peripheral speed capable of maintaining contact between the head slider, a disk having a lubricating layer, and the head slider. For each of the speeds, an angle formed between the surface of the lubricating layer and the head slider is measured to obtain a first peripheral speed at which the angle formed between the surface of the lubricating layer and the head slider increases rapidly. And determining whether the lubricating layer and the head slider are in contact with each of the plurality of peripheral speeds, and setting a second peripheral speed at which the head slider separates from the lubricating layer. Means for obtaining.

  As described above, according to the present invention, it is possible to provide a method for relatively evaluating the magnitude of the meniscus force of the lubricating layer acting on the head slider running on the magnetic disk.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a vertical cross-sectional view of the head slider and the disk, and FIG. 2 is a graph showing the relationship between the peripheral speed when the head slider re-lifts, the head slider flying height, and the pitch angle.

  First, the protective layer 4 made of carbon or the like is formed on the glass disk 5, and a lubricant is applied to the outermost surface to form the lubricating layer 2. In this manner, a disk for measuring the flying height of the head slider by a flying height tester described later is manufactured. The disk on which the lubricating layer 2 is formed is rotated, the head slider 1 is floated on the disk, and the flying height of the head slider can be measured using a head flying height measuring device called a flying height tester. A head flying height measuring device called a flying height tester is a device that measures the flying posture of the head slider, and can measure not only the flying height of the head slider but also the pitch angle of the head slider described later. . The principle of the flying height tester is detailed in Patent Document 1.

  Next, the number of disk revolutions is decreased to reduce the head slider flying height, and the head slider 1 and the disk are brought into contact with each other. In this way, the head slider 1 and the lubricating layer 2 are brought into contact with each other. Whether the head slider and the disk are in contact with each other is determined by an AE (Acoustic Emission) sensor installed near the head slider mounting portion. The flying height of the head slider from the lubricating layer can also be measured by the output value of the AE sensor.

  In the present embodiment, whether the head slider and the disk are in contact with each other is determined using the AE sensor, but is not limited to this. For example, in addition to the AE sensor, a laser is applied from the back of the head slider, the vibration of the head slider is detected, and it can be determined whether the contact has occurred because the vibration is very large at the time of contact. Any means can be used as long as it can detect contact between the head slider and the disk.

  When the head slider comes into contact with the disk, the head slider is slid in a posture substantially parallel to the disk surface. Thereafter, when the disk rotational speed is gradually increased and the head slider flying height is increased, the pitch angle 6 of the head slider 1 rapidly increases as shown in FIG. The pitch angle 6 is an angle formed by the surface of the disk (the surface of the lubricating layer) and the head slider. When the meniscus force by the lubricating layer formed on the disk surface between the head slider and the disk is sufficiently small, the head slider separates from the disk surface and re-floats. However, when the meniscus force is large, the head slider may be separated from the disk surface by the meniscus (bridging of the lubricant) 3 formed by the lubricating layer 2 as shown in FIG. It cannot be re-levitated unless the disk rotation speed is further increased. For example, as shown in FIG. 2, even if the pitch angle suddenly increases at a peripheral speed of the disk of 7.5 m / sec, the head slider does not re-lift, but re-levitates when the peripheral speed reaches 7.8 m / sec. To do.

  FIG. 2 is a diagram showing the relationship between the pitch angle of the head slider, the flying height of the head slider, and the peripheral speed of the disk according to an embodiment of the present invention. In FIG. 2, reference numeral 23 is a plot of the pitch angle with respect to the peripheral speed of the disk, and reference numeral 24 is a plot of the head slider flying height with respect to the peripheral speed of the disk. Reference numeral 21 denotes a region in the plot 23 where the pitch angle suddenly increases, and corresponds to a pitch angle -TOV described later. Reference numeral 22 denotes an area in the plot 24 where the flying height of the head slider increases rapidly, and corresponds to FH-TOV described later.

  As described above, the pitch angle increasing peripheral speed value (also referred to as “pitch angle−TOV” in this specification) in FIG. 2 and the peripheral speed value (“FH-TOV” in this specification) at which the head slider moves away from the disk. Is caused by the meniscus force by the lubricating layer existing between the disk and the slider.

  When there is almost no meniscus force, when the peripheral speed of the disk reaches the pitch angle -TOV, the pitch angle rapidly increases, and with the increase, the head slider 1 moves away from the lubricating layer 2, that is, the head slider flying height also increases rapidly. . However, if there is a meniscus force, even if the peripheral speed of the disk reaches the pitch angle -TOV and the pitch angle rapidly increases, the head slider 1 is not separated from the lubricating layer 2 by the meniscus 3, that is, by the meniscus force. In this case, the head slider 1 cannot be separated from the lubricating layer 2 unless the peripheral speed is increased to a peripheral speed larger than the pitch angle −TOV. The peripheral speed at which the head slider 1 is separated from the lubricating layer 2 that is larger than the pitch angle -TOV is FH-TOV. The difference between the pitch angle -TOV and FH-TOV increases as the meniscus force increases. When the head slider surface is actually observed, the larger the difference between the pitch angle -TOV and FH-TOV (the harder the head slider is away from the disk surface (lubricating layer surface)), the more the head slider end (the area in contact with the disk) It is observed that the lubricating layer gradually adheres to the surface. This observation result indicates that the larger the difference, the greater the meniscus force.

  As described above, the difference between the pitch angle -TOV and the FH-TOV is caused by the meniscus force. Therefore, if the difference between the pitch angle -TOV and the FH-TOV is obtained, the magnitude of the meniscus force is relative. It becomes possible to evaluate. 2 indicates that the smaller the difference between the pitch angle -TOV and FH-TOV, the smaller the meniscus force acting on the slider, and the slider is more likely to re-levitate.

  In one embodiment of the present invention, in order to perform the relative evaluation of the meniscus force described above, it is important to obtain the difference between the pitch angle -TOV and the FH-TOV. For this reason, the pitch angle -TOV and the FH- Each TOV is measured.

  Further, in one embodiment of the present invention, in order to obtain the pitch angle -TOV and FH-TOV, the peripheral speed (or the rotational speed) of the disk is measured before the measurement, and the head slider and the disk surface (lubricant layer surface). Set to the peripheral speed (or rotation speed) at which Next, the pitch angle -TOV and FH-TOV are gradually increased while increasing the peripheral speed (or rotational speed), for example, by increasing the peripheral speed (or rotational speed) by a predetermined peripheral speed (or rotational speed) every predetermined time. And are measured respectively.

Next, the evaluation method according to the present invention will be described.
First, a small AE sensor (manufactured by NF Circuit Block) is installed on the head arm to which a 30% size (1.2mm x 1.0mm) negative pressure head slider is attached. The head slider thus pressed is pressed against the disk on which the lubricating layer is formed with a load of 2.5 gf. Here, the signal output waveform of the AE sensor is measured with a digital oscilloscope via a preamplifier (NF circuit block / band 100 Hz to 20 MHz) and a disk eliminator (NF circuit block / 1 kHz to 2 MHz).

  Also, eight disks with different lubricating layer thicknesses are prepared as disk samples. These lubrication layers are formed using PFPE (perfluoropolyether) generally used for magnetic disks, and are 0.5 nm, 0.7 nm, 0.8 nm, 0.9 nm, 1.0 nm, 1 nm, respectively. The thickness is set to 2 nm, 1.5 nm, and 2.0 nm.

  Using these devices and each disk, the relative evaluation of the meniscus force acting on the head slider is performed according to the following procedure.

Measuring method
Step 1: The disk is rotated at a rotational speed of 7200 rpm (circumferential speed 18.8 m / sec), the head slider is floated at a radial position of 25 mm of the disk, and the flying height of the head slider is measured by a flying height tester. This is for confirming whether the head slider used for measurement floats normally and there is no abnormality in the head slider.

    Step 2: The disk rotational speed is reduced to 1910 rpm (circumferential speed 5.0 m / sec), and the head slider and the disk surface are continuously slid, that is, the head slider and the disk surface are in contact with each other. By rotating the disk at the rotation speed (circumferential speed) of the disk, the head slider and the disk surface (lubricating layer) are kept in contact with each other.

    Step 3: The head slider is lifted again by increasing the disk rotational speed by 38.4 rpm steps (peripheral speed 0.1 m / sec step). At this time, when the rotational speed (circumferential speed) is increased during one step, the peripheral speed value when a pitch angle increase of 50 [μrad] or more is measured by a flying height tester that performs measurement by optical interferometry is expressed as pitch angle− Let it be TOV.

The measurement of pitch angles -TOV and FH-TOV by this flying height tester will be specifically described.
Light is incident from a surface of the disk facing the surface in contact with the head slider at every predetermined number of rotations (circumferential speed). Interference caused by the difference in optical distance between the reflected light on the head slider surface and the reflected light on the head slider surface of the disk due to the incident light is detected by a sensor or the like. The distance from the surface is calculated to obtain the head slider flying height. Note that the rotation speed (circumferential speed) is constant during the flying height measurement. On the head slider, the above measurement is performed at a plurality of points. From the flying height values at two points on the front surface of the head slider (the area of the head slider near the disk) and the rear surface of the head slider (the area of the head slider far from the disk), The tilt angle (pitch angle) of the slider can be calculated.

  Further, the minimum value among the plurality of flying height measurement values described above is set as the head slider flying height at the peripheral speed. Usually, the measured value on the front surface of the head slider corresponds to the flying height of the head slider at the peripheral speed.

  In this way, the pitch angle and the head slider flotation are measured at each rotation speed (circumferential speed) measurement point (38.4 rpm step (peripheral speed 0.1 m / sec step)). The quantity is obtained to obtain a rotation speed (peripheral speed) -pitch angle profile. That is, the flying height tester performs the above measurement every 38.4 rpm steps (peripheral speed 0.1 m / sec step) from 1910 rpm (peripheral speed 5.0 m / sec) to determine the pitch angle and the head slider flying height. Get the quantity. Based on the obtained measurement points corresponding to the pitch angle and the head slider flying height, the control unit of the flying height tester obtains the profile of the pitch angle and the head slider flying height with respect to the measurement points. In this way, the plots 22 and 23 shown in FIG. 2 can be obtained. The profile may be displayed on a display unit such as a display included in the flying height tester, or a job including the profile data may be transmitted to an image forming apparatus such as a printer and output. In this way, the measurer can obtain a profile of the pitch angle and head slider flying height with respect to the measurement point of the rotation speed (circumferential speed).

  In one embodiment of the present invention, the profile need not be created by the flying height tester. In this case, for example, the pitch angle and the head slider flying height may be displayed on the display unit of the flying height tester for each measurement point of the rotation speed (circumferential speed). The measured person may record the displayed pitch angle and head slider flying height to create the profile.

  As described above, what is important in one embodiment of the present invention is to obtain the pitch angle and the head slider flying height for each rotation speed (circumferential speed) of the disk in order to create the profile.

  On the other hand, in order to calculate FH-TOV more easily, the peripheral speed value at which the signal output value from the AE sensor is 5% or less of the signal output value generated when the head slider and the disk are in contact is expressed as FH -TOV may be used.

  Note that the above-described determination value 50 [μrad] for pitch angle rise and 5% of the determination value for FH-TOV are merely examples, and it goes without saying that other determination values may be used as desired.

    Step 4: The difference between the pitch angle -TOV and FH-TOV is calculated. The measurer determines the pitch angle -TOV and FH-TOV from the obtained pitch angle -TOV and FH-TOV profiles, and obtains the difference between the pitch angle -TOV and FH-TOV.

    Step 5: Steps 1 to 4 are performed on each sample in the same procedure.

  FIG. 3 is a graph showing the results of measuring the difference between the pitch angle -TOV and FH-TOV for each sample by the above method. The horizontal axis represents the film thickness [nm] of the lubricating layer applied on the disk, and the vertical axis represents the difference [m / sec] between the pitch angle -TOV and FH-TOV. As shown in FIG. 3, the difference between the pitch angle -TOV and the FH-TOV varies depending on the film thickness of the lubrication layer. When the film thickness of the lubrication layer is 0.8 nm or less, the pitch angle -TOV and FH It can be seen that the difference from −TOV, that is, the meniscus force becomes almost zero. This is because the thinner the lubricant layer, the smaller the amount of lubricant that contributes to the formation of meniscus force.

  In this embodiment, the same lubricant is used for each sample, but it goes without saying that the magnitude of the meniscus force can be compared and evaluated using different lubricants.

  As described above, according to the present invention, the pitch angle rising peripheral speed value (pitch angle -TOV) at the time of flying the head slider derived from the transition of the head slider flying posture during the take-off operation and the circumferential distance at which the head slider moves away from the disk. From the difference from the speed value (FH-TOV), it is possible to relatively evaluate the magnitude of the meniscus force generated in the traveling head slider by the lubricating layer applied on the magnetic disk.

1 is a schematic vertical sectional view of a head slider and a disk according to an embodiment of the present invention. 6 is a graph showing a relationship between a peripheral speed at the time of re-levitation of the head slider, a flying height of the head slider, and a pitch angle according to an embodiment of the present invention. It is a graph which shows the result of having measured the difference of pitch angle -TOV and FH-TOV based on one Embodiment of this invention.

Explanation of symbols

1 Head slider 2 Lubrication layer 3 Meniscus (cross-linking of lubricant)
4 Protective layer 5 Glass disk 6 Pitch angle 21 Pitch angle rising peripheral speed value (Pitch angle-TOV)
22 Peripheral speed at which the head slider moves away from the disk (FH-TOV)
23 Plot of pitch angle against peripheral speed of disk 24 Plot of head slider flying height against peripheral speed of disk

Claims (5)

  The pitch angle rising peripheral speed value at the time of slider flying derived from the head slider flying posture transition during take-off operation and the peripheral speed value at which the head slider actually moves away from the disk are measured. And the difference between the peripheral speed value at which the head slider moves away from the disk, and the magnitude of the meniscus force generated between the lubricating layer applied to the disk surface and the traveling head slider is evaluated. To evaluate magnetic disk. A first step of preparing a disk on which a lubricating layer is formed;
A second step of bringing the lubricating layer of the disk into contact with the head slider and rotating the disk at a predetermined peripheral speed capable of maintaining contact between the disk and the head slider;
For each of a plurality of peripheral speeds that are higher than the predetermined peripheral speed, an angle formed between the surface of the lubricant layer and the head slider is measured, and the surface of the lubricant layer and the head slider are measured. A first peripheral speed at which an angle formed suddenly rises, and whether or not the lubricating layer and the head slider are in contact with each of the plurality of peripheral speeds; A third step of obtaining a second peripheral speed at which the slider moves away from the lubricating layer;
A magnetic disk evaluation method comprising: a fourth step of obtaining a difference between the first peripheral speed and the second peripheral speed.   In the third step, a first profile that is a profile of an angle formed by the surface of the lubricating layer and the head slider with respect to the plurality of peripheral speeds is created, and the first profile is generated based on the first profile. The magnetic disk evaluation method according to claim 2, wherein a peripheral speed is acquired. In the third step,
Measuring the flying height of the head slider from the lubricating layer for each of the plurality of peripheral speeds;
Generating a second profile that is a profile of the flying height of the head slider from the lubricating layer with respect to the plurality of peripheral speeds, and acquiring the second peripheral speed based on the second profiles; The magnetic disk evaluation method according to claim 2 or 3. A head slider;
An angle formed between the surface of the lubricant layer and the head slider with respect to each of a plurality of peripheral speeds that are higher than a predetermined peripheral speed capable of maintaining contact between the disk having the lubricant layer and the head slider. Means for obtaining a first peripheral speed at which an angle formed by the surface of the lubricating layer and the head slider abruptly increases;
Means for determining whether or not the lubricating layer and the head slider are in contact with each of the plurality of peripheral speeds, and obtaining a second peripheral speed at which the head slider separates from the lubricating layer; A magnetic disk evaluation apparatus comprising:

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