JP4331383B2 - Interval measurement method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a distance measuring how, in particular, the height and minute of the flying amount of the unevenness of the surface of the rotating disk such as a magnetic disk used as a recording medium of HDD (hard disk drive) device those related to the distance measuring how characterized by the method and arrangement for measuring with high accuracy.
[0002]
[Prior art]
In recent years, in a magnetic recording apparatus such as an HDD apparatus used as an external storage device of an information processing apparatus, an improvement in recording density is required year by year as the amount of information increases.
[0003]
A magnetic recording medium such as a magnetic tape or a magnetic disk used in such a magnetic recording apparatus is generally used as a protective lubricating layer on the magnetic layer in order to protect the magnetic layer constituting the magnetic recording medium. Using a PVD method or a CVD method, a silicon oxide or silicon nitride film having a thickness of about 5 to 50 nm or a DLC (diamond-like carbon) film in an amorphous state is formed as a protective layer, and then on the protective layer 5 to 100 cm of an extremely thin lubricant layer is formed.
[0004]
As the recording density increases, the flying height of the magnetic head decreases and is about 10 nm or less. On the other hand, the surface of the magnetic disk has irregularities of about several nm. As the flying height decreases, the need for a technique for more accurately measuring the irregularities on the surface of the magnetic disk has increased.
[0005]
Conventionally, the flying height of the magnetic head is optically measured by irradiating a laser beam from the back side of the magnetic disk while the magnetic disk is rotated and measuring the reflected light.
[0006]
Further, as described above, since the surface of the magnetic disk is uneven, by controlling the flying height of the measuring head and causing the measuring head to collide with the unevenness on the surface of the magnetic disk, the unevenness of the magnetic disk is mechanically increased. Although the height of the portion was measured, sufficient accuracy was not always obtained.
[0007]
On the other hand, as an alternative to such a mechanical measurement method, a measurement conductive pattern is provided in a region facing the surface of the magnetic disk at the tip of the measurement head having exactly the same flying characteristics as the magnetic head. Attempts have been made to determine the height of the irregularities and the flying height of the surface of the magnetic disk by measuring the capacitance between the conductive pattern and the magnetic disk.
[0008]
That is, assuming a parallel plate type capacitor, the capacitance C is defined as S for the area of the conductive pattern for measurement provided on the measurement head, d for the distance between the measurement head and the magnetic disk, and the measurement head and magnetic field. When the relative dielectric constant of the medium (usually air) intervening with the disk is ε,
C = εS / d
Since ε and S are known, the distance d between the measuring head and the magnetic disk, that is, the flying height of the measuring head is obtained by electrically measuring the capacitance C.
[0009]
[Problems to be solved by the invention]
However, if the surface has irregularities, the capacitance C increases in inverse proportion to the distance d. Therefore, the smaller the flying height, the greater the contribution to the capacitance C is due to the influence of the convex portion. When the flying height is measured, the distance to the convex portion is measured instead of the reference surface of the magnetic disk, that is, the center height of the concave and convex portions. This situation will be described with reference to FIG. .
[0010]
Reference to FIG. 8A FIG. 8A shows a case where the unevenness of the surface of the conductive protective film 42 provided on the surface of the magnetic disk is approximated by a sine wave. ΔC (x) is
ΔC (x) ∝1 / d (x)
Thus, the capacitance per unit area corresponds to a value obtained by integrating x from 0 to 1.
In this case, the depth shape is assumed to be a corrugated shape in which a sine wave is kept constant.
[0011]
In such an approximate sine wave model, for example, the distance d between the reference surface of the magnetic disk and the measurement conductive pattern 41 is d, where b is the height b of the concavo-convex convex portion and b is 1.5 nm and y = 0. = A = 3 nm, the distance d ′ obtained by converting the capacitor into a parallel plate type based on the capacitance C obtained by calculation is d′ ≈2.6 nm, and the flying height measurement error is That is, the difference between the flying height from the reference surface and the flying height from the conversion surface 43 is about 13%.
[0012]
Reference to FIG. 8B FIG. 8B is a diagram showing the result of simulating the flying height dependence of the above-mentioned flying height measurement error. In this case, the height b of the convex portion is b = 1. .
As is apparent from the figure, it is understood that the measurement error increases rapidly as the flying height from the reference surface decreases. Therefore, the measurement error increases as the flying height decreases as the recording density increases. There is.
[0013]
Accordingly, an object of the present invention is to accurately obtain the distance from the reference surface and the height of the convex portion from the measured capacitance when the surface has irregularities.
[0014]
[Means for Solving the Problems]
FIG. 1 is an explanatory diagram of the principle configuration of the present invention. Means for solving the problems in the present invention will be described with reference to FIG.
Refer to FIG. 1 (1) The present invention relates to a distance measuring method for obtaining a distance a between a conductive substrate 1 having a concavo-convex 2 and a component 3 from a capacitance between the conductive substrate 1 and the component 3, Capacitance is measured at a number of intervals a equal to the number of variables used in the approximate expression modeled by changing the distance a by a known amount, and this measurement result is used to model the unevenness 2 on the surface of the conductive substrate 1. It is characterized in that the distance a is obtained by comparing with the calculation formula of the capacitance obtained by the approximated expression.
[0015]
In this way, the capacitance is measured at the number of intervals a equivalent to the number of variables used in the approximate expression modeled by changing the distance a between the conductive substrate 1 and the component 3 by a known amount, and the conductivity A multi-dimensional simultaneous equation can be obtained by comparing with the calculation formula of the electrostatic capacity obtained by an approximate expression modeling the surface irregularities 2 of the substrate 1. Therefore, by solving this multi-dimensional simultaneous equation for each variable, conductivity can be obtained. The distance a between the substrate 1 and the component 3 can be accurately obtained based on the measured capacitance.
[0016]
Further, the present invention is characterized in that, in the above (1), the unevenness 2 on the surface of the conductive substrate 1 is approximated by a sine wave.
In particular, when the unevenness 2 is approximated by a sine wave, that is, in FIG.
d (x) = a−b · sin (2πx)
In this case, the capacitance C is
C∝1 / (a ² -b ² ) ^1/2
Because it is obtained as
Therefore, since it is possible to obtain a simple binary simultaneous equation only by obtaining the capacitance at two kinds of intervals a, the interval a can be easily obtained, and the height of the convex portion is also obtained. b can also be obtained.
[0017]
In the present invention (1), the rotation amount of the conductive substrate 1 may be controlled in order to change the distance a by a known amount.
Thus, in order to control the space | interval a, the floating amount of the components 3 which generate | occur | produces with rotation by controlling the rotation amount of the conductive substrate 1 should just be controlled.
The correlation between the rotation amount and the flying height may be measured in advance using the substrate 1 having a smooth surface.
[0018]
In the present invention (1), the capacitance may be measured even when the conductive substrate 1 and the component 3 are in contact with each other.
In this way, by measuring the capacitance even when the conductive substrate 1 and the component 3 are in contact with each other, a nonconductive film such as a nonconductive protective film is provided on the surface of the conductive substrate 1. Even in such a case, it is possible to accurately measure the true distance a between the non-conductive protective film.
[0019]
Further, the present invention is characterized in that, in the above (1), the conductive substrate 1 is a magnetic recording medium, and the component 3 is a distance measuring head having the same flying characteristics as the magnetic head.
As described above, the above-described distance measuring method is particularly suitable for controlling the flying height of the magnetic head.
[0024]
DETAILED DESCRIPTION OF THE INVENTION
Here, the minute interval measurement method according to the embodiment of the present invention will be described with reference to FIGS. 2 to 7. First, with reference to FIG. 2, an approximation method by modeling the irregularities on the surface of the magnetic disk. A method for calculating the flying height a associated therewith will be described.
Reference to FIG. 2A FIG. 2A is a diagram for explaining the case where the unevenness of the surface of the conductive protective layer 12 provided on the surface of the magnetic disk is approximated by a sine wave. Assume a corrugated plate that keeps the waves constant.
[0025]
In this case, the distance between the conductive pattern for measurement 11 and the conductive protective film 12 is expressed as d (x) where x is the horizontal axis.
d (x) = a−b · sin (2πx)
In addition, considering the depth as a unit width, the capacitance ΔC in the minute region Δx is
ΔC = εΔx / d (x)
It is represented by
[0026]
Therefore, in order to obtain the capacitance C per unit area, the above εΔx / d (x), that is, εdx / [ab−sin (2πx)] is integrated in the range of 0 → 1. As a result,
C = 1 / (a ² −b ² ) ^1/2
The capacitance C is obtained as follows.
The capacitance C is obtained by calculation processing software (Mathematica 3.0 for Macintosh), and the relative dielectric constant is not shown.
[0027]
The equation for the capacitance C is as follows:
C ² (a ² −b ² ) = 1
Therefore, if there are two measured values for the capacitance C, the flying height a and the height b of the convex portion can be easily obtained by a binary simultaneous equation.
First, the measured value of the capacitance C when measured in a first state and C _1, the floating amount at that time is a.
[0028]
See FIG. 2B. Next, as shown in FIG. 2B, the measured value of the capacitance C when measured in the second state where the flying height is higher by A than the first state is C ₂ . To do.
The flying height at that time is naturally a + A.
[0029]
Therefore, based on these measurement results,
C ₁ ² (a ² −b ² ) = 1
C ₂ ² [(a + A) ² −b ² ] = 1
The following two simultaneous equations are obtained, and these are easily solved. As a result, the flying height a is
a = (C ₁ ² -C ₂ ² -A ² C ₁ ² C ₂ ² ) / (2AC ₁ ² C ₂ ² )
Thus, C ₁ and C ₂ are actually measured values, and A is a set value, so that the flying height a is obtained based on the actually measured capacitance values C ₁ and C ₂ .
[0030]
Further, the height b of the convex portion is also obtained at the same time,
_{^{b = (C 1 4 -2C 1}} 2 C 2 2 -2A 2 C 1 4 C 2 2 + C 2 4 -2A 2 C 1 2 C 2 4 + A 4 C 1 4 C 2 4) 1/2 / (2AC 1 ² C ₂ ² )
Thus, like the flying height a, it is a function of C ₁ , C ₂ , and A, so that the height b of the convex portion can also be obtained based on the actually measured value.
[0031]
Next, with reference to FIG. 3, the structure of the measuring apparatus for calculating | requiring an electrostatic capacitance is demonstrated.
3 is a conceptual configuration diagram of the capacitance measuring device used in the embodiment of the present invention. The magnetic disk 21 is rotated by a spindle motor 22 at a predetermined number of revolutions, and a cantilever 24 provided on an arm 23 is shown. A measurement conductive pattern (on the surface of the flying head 25 facing the magnetic disk 21 in a state where the flying head 25 for measurement attached to the tip of the magnetic head 21 is floated with a flying height corresponding to the rotation amount of the magnetic disk 21). The capacitance C between the magnetic disk 21 and the magnetic disk 21 is measured by a capacitance measuring device 26.
[0032]
Next, a first measurement method according to the embodiment of the present invention will be described with reference to FIG.
4A. First, the capacitance C ₁ is obtained by measuring the capacitance in the first state in which the magnetic disk 21 is rotated at the first rotation speed by the spindle motor.
The flying height a in this case is unknown because it is a measurement target.
[0033]
Next, referring to FIG. 4B, the electrostatic capacity C ₂ is obtained by measuring the electrostatic capacity in the second state where the rotational speed of the spindle motor is increased and rotated at the second rotational speed.
The difference A between the first state and the second state in this case is known based on the difference in the flying height measured in advance using a rotating disk having a smooth surface.
Therefore, the flying height a can be obtained based on the measured values of C ₁ and C ₂ for the reasons described above.
[0034]
Next, with reference to FIG. 5, a minute interval measurement sensor used in the second measurement method of the embodiment of the present invention will be described.
FIG. 5 is a schematic configuration diagram of the flying head at the tip of the minute distance measuring sensor used in the second measuring method according to the embodiment of the present invention, and the surface of the flying head 25 facing the magnetic disk. The main part is provided with two step portions, and separate conductive patterns 27 and 28 for measurement are provided on the respective step portions.
Note that the protrusions provided on both sides are levitation rails for controlling the levitation characteristics.
[0035]
In this case, the capacitance may be measured independently by the measurement conductive pattern 27 and the measurement conductive pattern 28 while the magnetic disk is rotated by the spindle motor at a predetermined rotational speed. Since the step A is a known value determined by the processing accuracy of the flying head 25, the measurement value of the capacitance by the measurement conductive pattern 27 is C ₁ , and the measurement of the capacitance by the measurement conductive pattern 28. If the value is C ₂ , the same state as the first measurement method is realized.
[0036]
In this second measurement method, it is possible to measure two states without changing the flying height of the flying head 25, and the accuracy of the step A is better than the difference due to the control of the rotation amount. In addition, highly accurate measurement is possible.
[0037]
Next, with reference to FIG. 6, a minute interval measuring sensor used in the third measuring method of the embodiment of the present invention will be described.
FIG. 6 is a schematic configuration diagram of the flying head at the tip of the minute distance measuring sensor used in the third measuring method according to the embodiment of the present invention, and the surface of the flying head 25 facing the magnetic disk. Are provided with a measurement conductive pattern 27 and a measurement conductive pattern 28, and a dielectric layer 29 having a known relative permittivity is partially provided on one measurement conductive pattern 27. is there.
[0038]
In this case as well, it is sufficient to measure the capacitance independently with the measurement conductive pattern 27 and the measurement conductive pattern 28 in a state where the magnetic disk is rotated at a predetermined rotational speed by the spindle motor. Since the measured capacitance value by the conductive pattern 27 and the measurement conductive pattern 28 differs by a value determined by the film thickness and relative dielectric constant of the dielectric layer 29, the electrostatic capacitance by the measurement conductive pattern 27 is different. If the measured value of C ₁ is C ₁ and the measured capacitance value of the measurement conductive pattern 28 is C ₂ , the same state as that of the first measuring method is effectively realized.
[0039]
Also in this third measurement method, it is possible to measure two states without changing the flying height of the flying head 25, and the difference between the measured values of the capacitance is the film thickness and ratio of the dielectric layer 29. Although it depends on the dielectric constant, the accuracy of the film thickness by film formation is sufficiently high and the relative dielectric constant is known, so that it is possible to obtain a highly accurate flying height a without performing step processing.
[0040]
Next, referring to FIG. 7, the reliability of the flying height “a” and the height “b” of the convex portion obtained by the above measurement method is evaluated.
7 FIG. 7 is an approximation of the unevenness on the surface of the conductive protective film 32 provided on the surface of the magnetic disk modeled by a corrugated plate made of sawtooth waves. In this case, the measurement conductive pattern 31 and The distance from the conductive protective film 32 is expressed by d (x) where x is the horizontal axis.
d (x) = ab (2x-1)
In addition, considering the depth as a unit width, the capacitance ΔC in the minute region Δx is
ΔC = εΔx / d (x)
= ΕΔx / [ab (2x-1)]
It is represented by
[0041]
Therefore, in order to obtain the capacitance C per unit area, the above-mentioned εΔx / d (x) = εΔx / [ab (2x−1)], that is, εdx / [ab (2x−1). )] May be integrated in the range of x from 0 to 1, and as a result, by simple integration,
C = ln (a + b) / 2b-ln (ab) / 2b
The capacitance C is obtained as follows.
In this case, [ln] means log _e .
[0042]
Next, substituting into the above-mentioned electrostatic capacity C as a = 2 and b = 1, and obtaining the electrostatic capacity C ₁ in the first state,
C ₁ = ln [3] / 2
It becomes.
Next, by substituting as a = 4 (that is, a = 2, A = 2) and b = 1 into the capacitance C, the capacitance C ₂ in the second state is obtained.
C ₂ = ln [5] / 2-ln [3] / 2
It becomes.
[0043]
Substituting the numerical values of C ₁ and C ₂ obtained in this way into the expression of the capacitance C obtained by the sinusoidal approximation described with reference to FIG. 2, and solving the binary simultaneous equations again,
a≈2.000372
b≈0.837144
It becomes.
[0044]
Therefore, when the capacitances C ₁ and C ₂ obtained by assuming that a = 2, b = 1, and A = 2 in the sawtooth wave approximation are substituted for the measured value of the sine wave approximation, the flying height a Is approximately 0.2% between the two, and it can be evaluated that the reliability of the flying height a when the unevenness is modeled and approximated is quite high.
On the other hand, the height b of the convex portion is evaluated as being less reliable than the flying height a because there is a difference of about 20% between the two.
[0045]
Although the embodiments of the present invention have been described above, the present invention is not limited to the solutions described in the embodiments, and various modifications can be made.
For example, in the above embodiment, the flying heights in the two measurement states are calculated as a and a + A, but may be calculated as a and αa. In this case, the above-described sawtooth wave is used. In the approximation, a and b obtained by substituting the capacitance values C ₁ and C ₂ obtained by assuming that a = 2, b = 1, and α = ₂ into the sinusoidal approximation formulas, respectively. ,
a≈2.000124
b≈0.831156
Thus, almost the same result as that obtained when a and a + A are calculated is obtained.
[0046]
In the above embodiment, the flying height is measured in two states. However, when three or more variables are set according to the approximate expression to be modeled, measurement is performed in three or more states. What is necessary is just to solve a multiple simultaneous equation based on it.
[0047]
In this case, the step provided in the sensor for measuring a minute interval shown in FIG. 5 may be provided with n steps when the set state is n. The step for measuring the minute interval shown in FIG. The dielectric layer patterns provided in the sensor for the sensor may be (n−1) pieces having different thicknesses, or the dielectric layer patterns having the same thickness using dielectrics having different relative dielectric constants (n−1). ) Just provide one.
[0048]
In the above embodiment, the protective film provided on the surface of the magnetic disk has been described as a conductive protective film. However, the protective film is also applied to a non-conductive protective film. In addition to the measurement of capacitance in the above two states, the measurement may be performed in a state where the measurement conductive pattern provided on the flying head and the protective film provided on the magnetic disk are in contact with each other. By using it, the distance between the reference surface of the non-conductive protective layer and the conductive pattern for measurement, that is, the true flying height can be measured.
[0049]
In the above embodiment, the method for measuring the flying height of the magnetic head and the height of the irregularities on the surface of the magnetic disk has been described. However, the present invention is not necessarily limited to the measurement of the flying height of such a magnetic head. However, the present invention is applied to measurement of a minute interval between a conductive substrate having minute irregularities on the surface and a minute part, and the application target is not limited.
[0050]
(Additional remark 1) About the space | interval measurement method which calculates | requires the space | interval of the electrically conductive board | substrate which has an unevenness | corrugation on the surface from the electrostatic capacitance between the said electrically conductive board | substrate and a component, the said space | interval was modeled by changing known amount Capacitance is measured at a number of intervals a equal to the number of variables used in the approximate expression, and the measurement result is obtained by using the approximate expression obtained by modeling the irregularities on the surface of the conductive substrate. An interval measuring method, wherein the interval is obtained by comparing with a calculation formula.
(Supplementary note 2) The interval measuring method according to supplementary note 1, wherein the rotation amount of the conductive substrate is controlled in order to change the interval by a known amount.
(Additional remark 3) Capacitance is measured also in the state which contacted the said electroconductive board | substrate and the said component, The space | interval measuring method of Additional remark 1 or 2 characterized by the above-mentioned.
[0051]
【The invention's effect】
According to the present invention, the surface unevenness is approximated and modeled by a sine wave or the like, the capacitance is measured in at least two states, and the minute interval and the height of the uneven protrusion are determined based on the measured values. Is calculated from the approximate expression, so even when the minute interval is small compared to the height of the irregularities, it is possible to measure and calculate with high accuracy and in a short time. There is a great contribution to the practical application of storage devices.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram of a basic configuration of the present invention.
FIG. 2 is an explanatory diagram of a flying height calculation method according to the embodiment of this invention.
FIG. 3 is a conceptual configuration diagram of a measuring apparatus used in an embodiment of the present invention.
FIG. 4 is an explanatory diagram of a first measurement method according to the embodiment of the present invention.
FIG. 5 is a schematic configuration diagram of a minute interval measurement sensor used in the second measurement method of the embodiment of the present invention.
FIG. 6 is a schematic configuration diagram of a minute interval measurement sensor used in a third measurement method according to the embodiment of the present invention.
FIG. 7 is an explanatory diagram of a calculation value evaluation method according to the embodiment of this invention.
FIG. 8 is an explanatory diagram of a capacitance measurement error on an uneven surface.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Conductive substrate 2 Concavity and convexity 3 Component 11 Conductive pattern 12 for measurement Conductive protective layer 21 Magnetic disk 22 Spindle motor 23 Arm 24 Cantilever 25 Flying head 26 Capacitance measuring instrument 27 Conductive pattern for measurement 28 Conductive pattern for measurement 29 Dielectric layer 31 Conductive pattern for measurement 32 Conductive protective film 41 Conductive pattern for measurement 42 Conductive protective film 43 Converted surface

Claims (1)

The present invention relates to a distance measuring method for obtaining a distance between a conductive substrate having irregularities on a surface and a component from a capacitance between the conductive substrate and the component, and uses an approximate expression modeled by changing the distance by a known amount. The capacitance is measured at intervals equal to the number of variables , and the measurement result is compared with the calculation formula of the capacitance obtained by the approximate expression obtained by modeling the unevenness of the surface of the conductive substrate. Thus, the interval measurement method is characterized in that the interval is obtained.

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