JPH11339414A - Projection detecting sensor and projection detecting method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain a good and high quality projection detecting signal for detection of projection existing on the surface of a disk type recording medium by a thermal resistance method. SOLUTION: An almost rectangular shape resistor 3 is mounted on a floating slider 2 and a first conductor 4 is connected to one end of long axis direction of a resistor 3, while a second conductor 5 is also connected to the other end thereof. Under the condition that the floating slider 2 is floated on a disk type recording medium 1, a sense current I is supplied to the resistor 3 via the first and second conductors 4, 5. Resistance change of the resistor 3 which is generated when the resistor 3 collides with a projection existing on the surface of the disk type recording medium 1 is detected by detecting a voltage change of the sense current I, thereby detects projection existing on the surface of disk type recording medium 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a projection detection sensor and a projection detection method for detecting a projection existing on the surface of a disk-shaped recording medium such as a magnetic disk or an optical disk.

[0002]

2. Description of the Related Art An abnormal projection on the surface of a disk-shaped recording medium such as a magnetic disk or an optical disk may cause an error in recording and reproduction,
Further, it may cause damage to a head used for recording and reproduction. Therefore, in a disk-shaped recording medium, the presence or absence of a protrusion is detected before shipment as a product, and if there is an abnormal protrusion that exceeds an allowable range, the disk-shaped recording medium is determined as a non-conforming product. It is desired to do so.

Conventionally, a method using a piezoelectric element has been mainly used as a method for detecting protrusions present on the surface of a disk-shaped recording medium. However, in recent years, a method using a piezoelectric element has been adopted. A thermal resistor method capable of detecting protrusions with sensitivity has been devised.

FIG. 7 shows a state in which protrusions present on the surface of a disk-shaped recording medium are detected by the thermal resistor method. As shown in FIG. 7, when detecting protrusions by the thermal resistance method, a protrusion detection sensor in which a resistor 102 whose resistance value increases when the temperature rises is mounted on the flying slider 101 is used. Then, the disk-shaped recording medium 103 is driven to rotate, and the flying slider 101 is floated on the disk-shaped recording medium 103. At this time, if the protrusion 104 exists on the surface of the disk-shaped recording medium 103, the protrusion 104 collides with the resistor 102, and the collision raises the temperature of the resistor 102. Then, the amount of heat generated when the resistor 102 collides with the protrusion 104 is detected as an increase in the resistance of the resistor 102, thereby detecting the protrusion 104 present on the surface of the disk-shaped recording medium 103.

[0005]

In the thermal resistor method, a signal indicating a change in the resistance of the resistor of the protrusion detection sensor (hereinafter, referred to as a protrusion detection signal) and noise included in the protrusion detection signal. The ratio (S / N) of the
The presence or absence of a protrusion is evaluated based on N. Conventionally, noise (hereinafter referred to as amplifier noise) of a measuring device that detects a change in resistance of a resistor is removed from a protrusion detection signal in order to improve signal quality. Above, the presence / absence of a protrusion is evaluated by obtaining the S / N of the protrusion detection signal. In particular,
The projection detection signal is expanded on the frequency axis using a spectrum analyzer, and the presence or absence of the projection is evaluated after subtracting the amplifier noise.

FIG. 8 shows an example of a profile obtained by expanding noise included in the protrusion detection signal on the frequency axis using a spectrum analyzer. The solid line A in FIG. 8 is the amplifier noise, and the solid line B in FIG. 8 is the total noise. The noise obtained by subtracting the amplifier noise from the total noise is the noise (hereinafter, referred to as sensor noise) from the protrusion detection sensor itself in which the flying slider is provided with the resistor.

When evaluating the presence or absence of a protrusion, a noise profile as shown in FIG. 8 is taken into a signal processing device such as a personal computer. Then, the signal processing device performs an arithmetic process of subtracting the amplifier noise from the protrusion detection signal, and then performs a ratio (S / S) between the protrusion detection signal and the sensor noise included in the protrusion detection signal.
N), and the presence / absence of a protrusion is evaluated based on the S / N.

The method of evaluating by subtracting the amplifier noise in this way is considered to be a very useful method on an experimental level because the signal quality is good and minute projections can be detected.

However, considering that the thermal resistor method is actually incorporated into a production line of a disk-shaped recording medium such as a magnetic disk or an optical disk, instead of an experimental level, the amplifier noise is subtracted as described above. The method of evaluation is not always preferred. This is because it is desirable in a manufacturing line to immediately judge the quality of a product, but it is difficult to develop a projection detection signal on a frequency axis using a spectrum analyzer in real time. That is, in the production line, the time cost must be taken into consideration, and the above-described method of performing the evaluation by subtracting the amplifier noise is not preferable because the processing takes time.

Therefore, when detecting protrusions by the thermal resistor method, it is desired to obtain a high-quality signal without performing a process of expanding a protrusion detection signal on a frequency axis using a spectrum analyzer. ing. If a sufficiently high-quality signal can be obtained and there is no need to use a spectrum analyzer to perform processing to expand the protrusion detection signal on the frequency axis, the thermal resistance method will enable instantaneous determination of the quality of the product. In addition, the thermal resistor method can be incorporated into a production line without increasing the time cost.

The present invention has been proposed in view of the above-mentioned conventional circumstances. A spectrum analyzer is provided as a protrusion detection sensor for detecting protrusions present on the surface of a disk-shaped recording medium by a thermal resistor method. Without using the process to expand the protrusion detection signal on the frequency axis using
It is an object of the present invention to provide a protrusion detection sensor capable of obtaining a high quality signal.

According to the present invention, as a projection detecting method for detecting projections present on the surface of a disk-shaped recording medium by a thermal resistance method, a process of expanding a projection detection signal on a frequency axis using a spectrum analyzer is provided. It is another object of the present invention to provide a projection detection method capable of obtaining a high-quality signal without performing the method.

[0013]

According to the present invention, there is provided a projection detection sensor comprising a flying slider which floats on a disk-shaped recording medium when the disk-shaped recording medium is rotated, and a substantially rectangular shape mounted on the flying slider. , A first conductor connected to one end of the resistor in the long axis direction, and a second conductor connected to the other end of the resistor in the long axis direction. Then, a current is supplied to the resistor via the first and second conductors while the flying slider is flying above the disk-shaped recording medium, and the resistor collides with a protrusion existing on the surface of the disk-shaped recording medium. The protrusion is detected by detecting a change in the resistance of the resistor that occurs when this occurs.

In this projection detecting sensor, the first and second conductors are connected to both ends of the resistor in the major axis direction. Therefore, the current supplied to detect the resistance change of the resistor flows substantially parallel to the longitudinal direction of the resistor. Then, the current supplied for detecting the resistance change of the resistor is made to flow substantially parallel to the longitudinal direction of the resistor, so that the signal quality of the protrusion detection signal is improved.

In the projection detecting method according to the present invention, a substantially rectangular resistor is mounted on a floating slider that floats on the disk-shaped recording medium when the disk-shaped recording medium is rotated, and the resistance is adjusted. A first conductor is connected to one end in the major axis direction of the body, and a second conductor is connected to the other end. Then, a current is supplied to the resistor via the first and second conductors while the flying slider is flying above the disk-shaped recording medium, and the resistor collides with a protrusion existing on the surface of the disk-shaped recording medium. The protrusion is detected by detecting a change in the resistance of the resistor that occurs when this occurs.

In this projection detecting method, a current for detecting a resistance change of the resistor is supplied to the resistor via the first and second conductors respectively connected to both ends of the resistor in the longitudinal direction. I am trying to do it. Therefore, the current supplied to detect the resistance change of the resistor flows substantially parallel to the longitudinal direction of the resistor. Then, the current supplied for detecting the resistance change of the resistor is made to flow substantially parallel to the longitudinal direction of the resistor, so that the signal quality of the protrusion detection signal is improved.

[0017]

Embodiments of the present invention will be described below in detail with reference to the drawings.

[0018] 1. Protrusion detection sensor In order to be able to instantly judge the quality of the product by the thermal resistance method, the signal of the protrusion detection signal on the time axis without expanding the protrusion detection signal from the protrusion detection sensor on the frequency axis It is necessary to be able to detect the presence or absence of a protrusion present on the surface of the disk-shaped recording medium by performing a simple comparison of whether the amplitude is large or small.

As a method of accurately determining the magnitude of the signal amplitude of the protrusion detection signal, the simplest method is to set a threshold value and determine whether the protrusion detection signal is larger or smaller than the threshold value. It can be determined in real time and is suitable for application to a production line.

In order to detect the presence or absence of a projection on the surface of the disk-shaped recording medium by judging whether the projection detection signal is larger or smaller than the threshold value, it is necessary to use the S of the projection detection signal. / N must be good.

Here, the noise included in the protrusion detection signal includes a sensor noise that is a noise from the protrusion detection sensor itself and an amplifier noise that is a noise of a measuring device that detects a change in resistance of the resistor.

As described above, it is possible to remove the amplifier noise by performing processing for expanding the protrusion detection signal from the protrusion detection sensor on the frequency axis, but it is necessary to realize real-time processing. In such a case, it is not preferable to perform processing for expanding the protrusion detection signal from the protrusion detection sensor on the frequency axis. Therefore, in order to realize real-time processing, it is desired that the S / N of the protrusion detection signal be good even if both sensor noise and amplifier noise are included.

In the projection detection sensor according to the present invention, in consideration of the above points, even if both the sensor noise and the amplifier noise are included in the projection detection signal, the S of the projection detection signal is not changed.
/ N is set to be good.

The above-described protrusion detection sensor according to the present invention will be described below with reference to specific examples. In addition,
In the following description, a type of projection detection sensor in which the direction of the current flowing through the resistor is substantially parallel to the surface of the disk-shaped recording medium (hereinafter referred to as a horizontal type projection detection sensor), and a current flowing through the resistor. A type of protrusion detection sensor in which the direction of current is substantially perpendicular to the surface of the disk-shaped recording medium (hereinafter referred to as a vertical type protrusion detection sensor) will be described as an example.

1-1 Horizontal Type Projection Detection Sensor FIGS. 1 and 2 show an example of a horizontal type projection detection sensor to which the present invention is applied.

This protrusion detection sensor is a sensor for detecting protrusions present on the surface of a disk-shaped recording medium by a thermal resistance method, and as shown in FIG. A flying slider 2 that floats on a disk-shaped recording medium 1 is provided. And
As shown in FIG. 2, a resistor 3 is mounted on the rear end surface of the flying slider 2.

The resistor 3 is formed in a thin film shape, and has a rectangular planar shape. The long axis direction of the resistor 3 formed in a rectangular shape is substantially parallel to the surface of the disk-shaped recording medium 1, and the short axis direction is substantially parallel to the surface of the disk-shaped recording medium 1. It is vertical. A first conductor 4 is connected to one end of the resistor 3 in the long axis direction, and a second conductor 5 is connected to the other end of the resistor 3 in the long axis direction.

When detecting the protrusions present on the surface of the disk-shaped recording medium 1 using this protrusion detection sensor, the first conductor 4 is placed on the disk-shaped recording medium 1 with the flying slider 2 floating. A sense current I is supplied to the resistor 3 via the second conductor 5 and the disk-shaped recording medium 1.
The resistance change of the resistor 3 which occurs when the resistor 3 collides with the protrusion existing on the surface of the resistor 3 is detected.

More specifically, as shown in FIG. 3, the first conductor 4 and the second conductor 5 are connected to a constant current source 6, and the first conductor 4 and the second Resistor 3 via conductor 5
Is supplied with a constant sense current I. Then, the terminal 4a derived from the first conductor 4 and the terminal 5b derived from the second conductor 5 are used as voltage detection terminals, and the voltage fluctuation between the terminals 4a and 5b (that is, the resistor 3 Of the sense current I flowing through the resistor 3
Detect the change in resistance. That is, in the protrusion detection sensor, a signal corresponding to the voltage fluctuation of the sense current I supplied to the resistor 3 is output as a protrusion detection signal.

In this projection detection sensor, the first and second conductors 4 and 5 are connected to both ends of the resistor 3 in the major axis direction. Therefore, the sense current I supplied for detecting the resistance change of the resistor 3
Flows substantially parallel to the long axis direction. As described above, in this protrusion detection sensor, the sense current I supplied to detect the resistance change of the resistor 3 is caused to flow substantially parallel to the long axis direction of the resistor 3. The signal quality of the detection signal is good.

In the horizontal type projection detection sensor, the major axis direction of the resistor 3 is substantially parallel to the surface of the disk-shaped recording medium 1, and the major axis direction is substantially parallel to the major axis direction of the resistor 3 The reason why the signal quality of the protrusion detection signal is improved by flowing the sense current I substantially parallel to the surface of the shape recording medium 1 will be described later.

By the way, in the above-mentioned projection detecting sensor,
It is preferable that the medium facing surface of the resistor 3 facing the disk-shaped recording medium 1 to be inspected is exposed to the outside. When the resistor 3 is exposed in this way, when the protrusion existing on the surface of the disk-shaped recording medium 1 collides with the resistor 3, the collision energy is converted into thermal energy without any intervention. The light is directly propagated to the resistor 3.
As a result, even a minute projection can be detected.

In order to protect the resistor 3, a protective film may be formed on the surface of the medium facing surface. However, in that case, it is preferable that the protective film be an extremely thin film of about 10 nm or less. Even if a protective film is present on the medium facing surface, if the protective film is an extremely thin film, a collision energy between the protrusion existing on the surface of the disk-shaped recording medium 1 and the resistor 3 is almost the same. The heat energy is transmitted to the resistor 3 without attenuation. As a result, even a minute projection can be detected.

In the above-mentioned projection detecting sensor, the thickness t of the resistor 3 is preferably as thin as possible, and more specifically, is preferably on the order of nanometers. Since the smaller the thickness t of the resistor 3 is, the smaller the heat capacity of the resistor 3 is, a large change in resistance can be detected even when the resistor 3 collides with a minute projection having a small collision energy. Further, the thinner the thickness t of the resistor 3 is, the higher the thermal diffusivity of the resistor 3 is, so that the response to heat is faster and the time from the detection of the protrusion to the stabilization is reduced.

1-2 Vertical Projection Detecting Sensor FIGS. 4 and 5 show an example of a vertical projection detecting sensor to which the present invention is applied.

This protrusion detection sensor is a sensor for detecting protrusions present on the surface of the disk-shaped recording medium by a thermal resistance method, and as shown in FIG. Disk-shaped recording medium 11
It has a flying slider 12 that floats above. Then, as shown in FIG. 5, a resistor 13 is mounted on the rear end surface of the flying slider 12.

The resistor 13 is formed in a thin film shape, and has a rectangular planar shape. The long-axis direction of the resistor 13 formed in a rectangular shape is substantially perpendicular to the surface of the disk-shaped recording medium 11, and the short-axis direction is substantially perpendicular to the surface of the disk-shaped recording medium 11. It is parallel. The first conductor 14 is connected to one end of the resistor 13 in the long axis direction, and the second conductor 15 is connected to the other end of the resistor 13 in the long axis direction.

When detecting the protrusions on the surface of the disk-shaped recording medium 11 using this protrusion detection sensor, the first conductor 14 and the first conductor 14 and the floating slider 12 are floated on the disk-shaped recording medium 11. A sense current I is supplied to the resistor 13 via the second conductor 15 to detect a change in resistance of the resistor 13 that occurs when the resistor 13 collides with a protrusion on the surface of the disk-shaped recording medium 11. .

Specifically, as shown in FIG. 6, the first conductor 14 and the second conductor 15 are connected to a constant current source 16 and the first conductor 14 and the second A constant sense current I is supplied to the resistor 13 via the conductor 15. Then, the terminal 14a derived from the first conductor 14 and the second
The terminal 15a derived from the conductor 15 is used as a voltage detection terminal to detect a voltage change between the terminal 14a and the terminal 15a (that is, a voltage change of the sense current I flowing through the resistor 13). 13 is detected. That is, in this protrusion detection sensor, a signal corresponding to the voltage fluctuation of the sense current I supplied to the resistor 13 is
It is output as a protrusion detection signal.

In this protrusion detection sensor, the first and second conductors 14 and 15 are connected to both ends of the resistor 13 in the major axis direction. Therefore, the sense current I supplied for detecting the resistance change of the resistor 13 is
The resistor 13 flows substantially parallel to the long axis direction. Thus, in this protrusion detection sensor, the resistor 13
Current I supplied to detect a resistance change of
Is caused to flow substantially parallel to the long axis direction of the resistor 13, so that the signal quality of the protrusion detection signal is good.

In the projection sensor of the vertical type, the major axis direction of the resistor 13 is substantially perpendicular to the surface of the disk-shaped recording medium 11, and is substantially parallel to the major axis direction of the resistor 13 (ie, The reason why the signal quality of the protrusion detection signal is improved by flowing the sense current I in a direction substantially perpendicular to the surface of the disk-shaped recording medium 11 will be described later in detail.

By the way, in the above-mentioned projection detecting sensor,
The resistor 13 is a disk-shaped recording medium 1 to be inspected.
It is preferable that the medium facing surface facing 1 is exposed to the outside. When the resistor 13 is thus exposed,
When a protrusion existing on the surface of the disk-shaped recording medium 11 collides with the resistor 13, the collision energy is directly transmitted to the resistor 13 as thermal energy without any intervention. As a result, even a minute projection can be detected.

In order to protect the resistor 13, a protective film may be formed on the surface of the medium facing surface.
However, in that case, it is preferable that the protective film be an extremely thin film of about 10 nm or less. Even if a protective film is present on the medium facing surface, if the protective film is an extremely thin film, the protrusions on the surface of the disk-shaped recording medium 11 and the resistor 1
3, the collision energy is transmitted to the resistor 13 as thermal energy with almost no attenuation. As a result, even a minute projection can be detected.

Further, in the above-mentioned projection detecting sensor, the thickness of the resistor 13 is preferably as thin as possible, and specifically, is preferably on the order of nanometers. Since the smaller the thickness of the resistor 13 is, the smaller the heat capacity of the resistor 13 is, a large change in resistance can be detected even when the resistor 13 collides with a minute projection having a small collision energy. Further, the thinner the film thickness of the resistor 13 is, the higher the thermal diffusivity of the resistor 13 is, so that the response to heat becomes faster, and the time from the detection of the protrusion to the stabilization becomes shorter.

[0045] 2. Next, the signal quality of the protrusion detection signal output from the protrusion detection sensor will be described in detail.

In the following description, the signal quality of the protrusion detection signal will be described in detail using mathematical expressions, but the symbols used in those mathematical expressions are as follows. The width L of the resistor, the height h of the resistor, and the thickness t of the resistor are also shown in FIGS.

I: current value of the sense current flowing through the resistor R: resistance value of the resistor U: energy generated when the resistor collides with the protrusion Q: energy required for the resistor to rise by 1 ° C. ε : The ratio of the resistance value that changes when the resistor rises by 1 ° C. (temperature resistance change rate) ρ: The resistivity of the resistor η: The specific heat of the resistor ν: The specific gravity of the resistor W: The resistor collides with the protrusion V: relative speed between the resistor and the projection when the resistor collides with the projection μ: friction coefficient between the resistor and the projection when the resistor collides with the projection L: width of the resistor (first conductor) H: height of the resistor t: film thickness of the resistor

2-1 Horizontal Type First, the signal quality of a projection detection signal obtained from the horizontal type projection detection sensor shown in FIGS. 1 to 3 will be described.

The resistor of the horizontal type projection detection sensor is
Assuming that the signal amplitude of the projection detection signal detected when the projection collides with the projection existing on the surface of the disk-shaped recording medium is ΔV, the signal amplitude ΔV is represented by the following equation (1-1).

ΔV = (IRUε) / Q (1-1) Here, the energy Q required for the resistor to rise by 1 ° C.
Is represented by the following equation (1-2), the energy U generated when the resistor collides with the protrusion is represented by the following equation (1-3), and the resistance value R of the resistor is represented by the following equation (1-4) ), And the current value I of the sense current flowing through the resistor is expressed by the following equation (1-5).
It is represented by

Q = L ht η ν (1-2) U = W μV (1-3) R = ρ L / (ht) (1-4) Therefore, the signal amplitude ΔV is calculated by the following equation (1) -6).

[0052] ΔV = (I R U ε) / Q = (I W μ V ρ ε) / (η ν h 2 t 2) (1-6) By the way, the noise contained in the projection detection signal, the projection detection There is sensor noise, which is noise from the sensor itself, and amplifier noise, which is noise of a measuring device that detects a change in resistance of a resistor.

In the projection detection sensor, since a resistor is used as a detection element, sensor noise should be dominated by thermal disturbance noise generated in the resistor. Therefore, _assuming that the sensor noise is N _s , the sensor noise N _s is Boltzmann's constant, B is the measurement bandwidth,
The temperature is represented by T, and is represented by the following equation (1-7).

N _s = (4 kBTR) ^1/2 (1-7) Here, the temperature T is represented by the following equation (1-8).

T = I ² R / (L ht η ν) (1-8) Accordingly, the sensor noise N _s is represented by the following equation (1-9).

N _s = 2 IR {k B / (L ht η ν)} ^1/2 (1-9) On the other hand, the amplifier noise cannot be formulated because it depends on the measuring device. However, if the amplifier noise and N _a, sensor noise N _s and amplifier noise N _a and the total noise N _t of the combined can be expressed by the following formula (1-10).

[0057] ^{_{N t = (N a 2 +}} N s 2) 1/2 (1-10) Then, S / N of the projection detection signal, and the signal amplitude [Delta] V, since the ratio of the total noise N _t, the following Equation (1-1)
It is represented by 1).

S / N = ΔV / N _t (1-11) Here, the signal quality of the protrusion detection signal is evaluated by the square of the reciprocal of S / N. That is, here, the signal quality of the protrusion detection signal is evaluated by the value of (N _t / ΔV) ² . Naturally, the better the signal quality, the more (N
_t / ΔV) ² becomes smaller.

The value (N _t / ΔV) ² indicating the signal quality of the protrusion detection signal can be modified as in the following equation (1-12).

[0060] ^{_{(N t / ΔV) 2 =}} (N a 2 + N s 2) / ΔV 2 = (N a 2 / ΔV 2) + (N s 2 / ΔV 2) (1-12) here, (N _a ² / ΔV ² ) = (N / S) _a ² and (N _s
² / ΔV ² ) = (N / S) _s ² , then (N _t / ΔV)
² is represented by the following formula (1-13).

(N _t / ΔV) ² = (N / S) _a ² + (N / S) _s ² (1-13) (N / S) _s is represented by the above equation (1-9). The sensor noise N _s and the signal amplitude ΔV represented by the above equation (1-6)
Corresponding to the ratio. Therefore, (N / S) _s ² is represented by the following formula (1-14).

[0062] ^{_{(N / S) s 2 =}} [{2 I R (k B / (L h t η ν)) 1/2} / {(I W μ V ρ ε) / (η ν h 2 t 2 ^{)}] 2 = (4 k} B η ν h t L) / (W μ V ε) 2 (1-14) On the other hand, (N / S) _a is an amplifier noise N _a, the equation (1
-6), which corresponds to the ratio to the signal amplitude ΔV. Therefore, (N / S) _a ² is represented by the following equation (1-15).

(N / S) _a ² = [N _a / {(I W μV ρ ε) / (η ν h ² t ² )}] ² = (N _a ² η ² ν ² h ⁴ t ⁴ ) / (I ² W ² μ ² V ² ρ ² ε ² ) (1-15) From the above equations (1-14) and (1-15), (N _t ) represented by the above equation (1-13) / ΔV) ² is given by the following equation (1)
-16) can be rewritten.

(N _t / ΔV) ² = (N / S) _a ² + (N / S) _s ² = {(4 kB ην ht L) / (W μV ε) ² } +} ( ^{_{N a 2 η 2 ν 2 h}} 4 t 4) / (I 2 W 2 μ 2 V 2 ρ 2 ε 2)} (1-16) i.e., the sensor noise N _s and amplifier noise N _a the projection detection signal If both are included, the above equation (1)
−16), the smaller the value of (N _t / ΔV) ² ,
This means that the signal quality of the protrusion detection signal is good.

2-2 Vertical Type Next, the signal quality of the protrusion detection signal obtained from the vertical type protrusion detection sensor shown in FIGS. 4 to 6 will be described.

The resistor of the vertical type protrusion detection sensor is
Assuming that the signal amplitude of the projection detection signal detected when the projection collides with the projection existing on the surface of the disk-shaped recording medium is ΔV, the signal amplitude ΔV is represented by the following equation (2-1).

ΔV = (IRUε) / Q (2-1) Here, the energy Q required for the resistor to rise by 1 ° C.
Is represented by the following equation (2-2), the energy U generated when the resistor collides with the protrusion is represented by the following equation (2-3), and the resistance value R of the resistor is represented by the following equation (2-4) ), And the current value I of the sense current flowing through the resistor is expressed by the following equation (2-5).
It is represented by

Q = L ht η ν (2-2) U = W μV (2-3) R = ρ h / (L t) (2-4) Therefore, the signal amplitude ΔV is calculated by the following equation (2) -6).

ΔV = (I RU ε) / Q = (I W μV ρ ε) / (η ν L ² t ² ) (2-6) By the way, noise included in the protrusion detection signal includes protrusion detection. There is sensor noise, which is noise from the sensor itself, and amplifier noise, which is noise of a measuring device that detects a change in resistance of a resistor.

In the projection detection sensor, since a resistor is used as a detection element, sensor noise should be dominated by thermal disturbance noise generated in the resistor. Therefore, _assuming that the sensor noise is N _s , the sensor noise N _s is Boltzmann's constant, B is the measurement bandwidth,
The temperature is represented by T, and is represented by the following equation (2-7).

N _s = (4 kBTR) ^1/2 (2-7) Here, the temperature T is represented by the following equation (2-8).

T = I ² R / (L ht η ν) (2-8) Accordingly, the sensor noise N _s is represented by the following equation (2-9).

N _s = 2 IR {k B / (L ht η ν)} ^1/2 (2-9) On the other hand, the amplifier noise cannot be formulated because it depends on the measuring device. However, if the amplifier noise and N _a, sensor noise N _s and amplifier noise N _a and the total noise N _t of the combined can be expressed by the following formula (2-10).

[0074] ^{_{N t = (N a 2 +}} N s 2) 1/2 (2-10) Then, S / N of the projection detection signal, and the signal amplitude [Delta] V, since the ratio of the total noise N _t, the following Equation (2-1)
It is represented by 1).

S / N = ΔV / N _t (2-11) Here, it is assumed that the signal quality of the protrusion detection signal is evaluated by the square of the reciprocal of S / N. That is, here, the signal quality of the protrusion detection signal is evaluated by the value of (N _t / ΔV) ² . Naturally, the better the signal quality, the more (N
_t / ΔV) ² becomes smaller.

The value (N _t / ΔV) ² indicating the signal quality of the protrusion detection signal can be modified as in the following equation (2-12).

[0077] ^{_{(N t / ΔV) 2 =}} (N a 2 + N s 2) / ΔV 2 = (N a 2 / ΔV 2) + (N s 2 / ΔV 2) (2-12) here, (N _a ² / ΔV ² ) = (N / S) _a ² and (N _s
² / ΔV ² ) = (N / S) _s ² , then (N _t / ΔV)
² is represented by the following formula (2-13).

(N _t / ΔV) ² = (N / S) _a ² + (N / S) _s ² (2-13) (N / S) _s is represented by the above formula (2-9) and sensor noise N _s, the signal amplitude ΔV represented by the above formula (2-6)
Corresponding to the ratio. Therefore, (N / S) _s ² is represented by the following formula (2-14).

[0079] ^{_{(N / S) s 2 =}} [{2 I R (k B / (L h t η ν)) 1/2} / {(I W μ V ρ ε) / (η ν L 2 t 2 ^{)}] 2 = (4 k} B η ν h t L) / (W μ V ε) 2 (2-14) On the other hand, (N / S) _a is an amplifier noise N _a, the equation (2
-6), which corresponds to the ratio to the signal amplitude ΔV. Therefore, (N / S) _a ² is represented by the following equation (2-15).

(N / S) _a ² = [Na / {(I W μ V ρ ε) / (η ν L ² t ² )}] ² = (N _a ² η ² ν ² L ⁴ t ⁴ ) / (I ² W ² μ ² V ² ρ ² ε ² ) (2-15) From the above formulas (2-14) and (2-15), (N _t / ΔV) ² is given by the following equation (2)
-16) can be rewritten.

(N _t / ΔV) ² = (N / S) _a ² + (N / S) _s ² = {(4 kB ην ht L) / (W μV ε) ² } +} ( ^{_{N a 2 η 2 ν 2 L}} 4 t 4) / (I 2 W 2 μ 2 V 2 ρ 2 ε 2)} (2-16) i.e., the sensor noise N _s and amplifier noise N _a the projection detection signal If both are included, the above equation (2)
−16), the smaller the value of (N _t / ΔV) ² ,
This means that the signal quality of the protrusion detection signal is good.

2-3 Comparison between Horizontal Type and Vertical Type Next, which of the vertical type projection detection sensor and the horizontal type projection detection sensor is more advantageous in terms of S / N will be described.

The value of (N _t / ΔV) ² in the horizontal type represented by the above equation (1-16) is set to (N _t / ΔV) _v ² . Further, the formula (2-16), in a vertical type the value of (N _t / [Delta] V) ^2, is denoted by ^{_{(N t / ΔV) h 2}} . Then, as represented by the following equation (3-1),
Let G be the difference between (N _t / ΔV) _h ² and (N _t / ΔV) _v ² .

G = (N _t / ΔV) _h ² − (N _t / ΔV) _v ² (3-1) At this time, the S / N of the horizontal type projection detection sensor is longer than the vertical type projection detection sensor. G> 0 if the S / N is larger than S / N. Conversely, the S / N of the vertical type projection detection sensor is better than the S / N of the horizontal type projection detection sensor.
If it is larger than / N, G <0.

Then, in the above (3-1), the above formula (1-
16) and the above equation (2-16), G becomes the following equation (3-2).

[0086] _{^{G = N a 2 η 2 ν}} 2 t 4 (L 4 -h 4) / (I 2 W 2 μ 2 V 2 ρ 2 ε 2) (3-2) where, N _a ² η ² ν ² / (I ² W ² μ ² V ² ρ ² ε ² )
If = P, G can be expressed as the following equation (3-3).

G = P t ⁴ (L ⁴ −h ⁴ ) = P t ⁴ (L ² + h ² ) (L + h) (L−h) (3-3) Then, P> 0, t> 0, L> 0, h> 0, so
G> 0 when L> h, and G <0 when L <h. That is, when L> h, the horizontal type protrusion detection sensor has a higher S / N than the vertical type protrusion detection sensor, and the signal quality of the protrusion detection signal is better. Conversely, when L <h, the vertical type projection detection sensor has a higher S / N than the horizontal type projection detection sensor, and the signal quality of the projection detection signal is better.

From the above, it can be seen that when the resistor has a rectangular shape, the S / N becomes better when the sense current is passed in a direction parallel to the longitudinal direction of the resistor. . That is, in a horizontal type protrusion detection sensor that allows a sense current to flow substantially parallel to the surface of a disk-shaped recording medium, as shown in FIGS. And the sense current is made to flow substantially parallel to the long axis direction of the resistor, thereby improving the signal quality of the protrusion detection signal. On the other hand, in a vertical-type projection detection sensor in which a sense current flows substantially perpendicularly to the surface of the disk-shaped recording medium, the longitudinal direction of the resistor is set to the direction of the disk-shaped recording medium as shown in FIGS. By making the sense current substantially perpendicular to the surface and flowing the sense current substantially parallel to the long axis direction of the resistor, the signal quality of the protrusion detection signal is improved.

[0089] 3. In order to verify the relationship between the resistor shape and the sense current supply direction and the S / N of the protrusion detection signal, Table 6 shown in Table 1 was used.
Prototypes of various types of protrusion detection sensors were prototyped and the S / S
N was measured. In addition, as the disk-shaped recording medium to be inspected, a magnetic disk having a magnetic layer formed on a substrate was used.

[0090]

[Table 1]

As shown in Table 1, the protrusion detection sensors 1 and 2
Has a resistor formed in a rectangular shape, and its major axis direction is substantially parallel to the surface of the magnetic disk. The protrusion detection sensor 1 is a vertical type protrusion detection sensor, and allows a sense current to flow substantially perpendicularly to the surface of the magnetic disk. On the other hand, the protrusion detection sensor 2 is a horizontal type protrusion detection sensor, and allows a sense current to flow substantially parallel to the surface of the magnetic disk.

The protrusion detection sensors 3 and 4 have a resistor formed in a rectangular shape, and the major axis direction is substantially perpendicular to the surface of the magnetic disk. The projection detection sensor 3 is a vertical type projection detection sensor, and is configured to allow a sense current to flow substantially perpendicularly to the surface of the magnetic disk. On the other hand, the protrusion detection sensor 4 is a horizontal type protrusion detection sensor, and allows a sense current to flow substantially parallel to the surface of the magnetic disk.

The projection detection sensors 5 and 6 are formed by forming the resistors in a square shape. Then, the protrusion detection sensor 5
Is a vertical type protrusion detection sensor, which allows a sense current to flow substantially perpendicular to the surface of the magnetic disk. On the other hand, the protrusion detection sensor 6 is a horizontal type protrusion detection sensor, and allows a sense current to flow substantially parallel to the surface of the magnetic disk.

In each of the protrusion detection sensors 1 to 6, the volume of the resistor was the same, and the sense current flowing through the resistor when detecting the protrusion detection signal was 13 mA, all of which were constant.

Then, the above-described protrusion detection sensors 1 to
6 with a flying height of 70 nm on a rotating magnetic disk.
In the state of floating, the protrusion detection signals were respectively detected, and the S / N of the protrusion detection signals was measured. More specifically, bumps having a height of 100 nm and a diameter of 30 μm are previously formed on the surface of the magnetic disk, and the bump detection sensors 1 to 6 are caused to collide with the bumps to detect the bump detection signals. The S / N of the detection signal was measured.

It should be noted that the projection detection signal can be evaluated in more detail by expanding the projection detection signal on the frequency axis using a spectrum analyzer. However, in this case, in order to simplify the evaluation, an oscilloscope was used. The evaluation was performed using. That is, here, the S / N of the protrusion detection signal was evaluated as the ratio of the amplitude of the protrusion detection signal measured by the oscilloscope to the effective amplitude of the noise.

As described above, the protrusion detection sensors 1 to 6
Table 2 shows the results of measuring the S / N of the protrusion detection signal for
Shown in

[0098]

[Table 2]

As shown in Table 2, the protrusion detection sensors 2 and 3 of the type in which the sense current flows in parallel to the long axis direction of the resistor are more parallel to the short axis direction of the resistor. The S / N of the protrusion detection signal was better than those of the flow-type protrusion detection sensors 1 and 4 and the protrusion detection sensors 5 and 6 having a square resistor. In addition, the protrusion detection sensor 2 and the protrusion detection sensor 3 use the S
/ N differed by 1 dB, but considering the measurement error,
This is almost the same.

From the above results, when the protrusion is detected by the thermal resistor method, the sense current is caused to flow substantially parallel to the long axis direction of the resistor to thereby improve the signal quality of the protrusion detection signal. Was confirmed to be good.

4. Application to Detection of Protrusion on PERM Disk Normally, on a magnetic disk, a servo signal is previously written on the surface of a magnetic disk before shipment so that a magnetic head can accurately trace a track on which data is recorded. Conventionally, writing of such a servo signal has been performed for each track by a magnetic head.

However, if the recording track width is reduced to increase the track density, there arises a problem that the time required for writing such a servo signal increases. That is, if the recording track width is narrowed and the track density is increased, the number of tracks arranged on the magnetic disk increases. Therefore, if the servo signal is written for each track by the magnetic head, the servo The time required for writing a signal becomes very long.

Further, as the recording density increases, a very fine servo signal pattern is required, and the servo signal must be written for each track by a magnetic head. It is becoming difficult to write servo signals on a magnetic disk with high accuracy.

Therefore, as described in JP-A-6-68444, a fine concave / convex pattern corresponding to the servo signal is formed in advance on the disk surface, and the convex upper surface and concave concave bottom of the concave / convex pattern are formed. A method has been devised in which the magnetization direction is reversed so that the servo signals are collectively written. As described above, a magnetic disk in which a concavo-convex pattern is formed in advance on the disk surface and servo signals are written at once is generally a PE disk.
It is called an RM disk (Pre-Embossed Rigid MagneticDisk).

When writing a servo signal in such a PERM disk, first, a sufficiently large magnetic field is applied by the magnetizing magnetic head so that the magnetization direction is constant from the top of the projection to the bottom of the recess. Then, the convex portions and the concave portions are collectively magnetized in a certain direction. Next, a magnetic field of an appropriate magnitude is applied by the magnetizing magnetic head, and the magnetization direction of the upper surface of the projection is directed to a direction different from the magnetization direction of the bottom surface of the depression. Thereby, magnetization reversal occurs between the convex portion and the concave portion,
The leakage magnetic field from the magnetization reversal part can be used as a servo signal.

In such a PERM disk, the time required for writing a servo signal does not depend on the number of tracks, and even when the number of tracks arranged on a magnetic disk is large, writing of a servo signal is extremely difficult. It can be done promptly. Also, with a PERM disk,
A fine concavo-convex pattern corresponding to the servo signal is formed on the disk surface in advance, but such a concavo-convex pattern can be easily formed with very high precision, as is clear from the results of disk substrate molding for optical disks and the like. It is. Therefore, a fine uneven pattern corresponding to the servo signal is formed on the disk surface in advance.
In an RM disk, it is possible to write a servo signal with much higher accuracy than when a servo signal is written for each track by a magnetic head.

The present invention provides the above-described PERM
The present invention is also applicable when detecting abnormal protrusions present on the surface of a disk.

In the thermal resistor method, whether or not the resistor collides with the projection is detected based on a change in resistance of the resistor caused by thermal energy generated by the collision.
Therefore, even if a concavo-convex pattern is formed on the disk surface like a PERM disk, it is considered that a protrusion detection signal is not detected unless the resistor collides with the protrusion. However, actually, even when the resistor does not collide with the protrusion, when the resistor passes over a region (hereinafter, referred to as a servo zone) in which a concavo-convex pattern corresponding to the servo signal is formed. , A slight amplitude fluctuation appears in the protrusion detection signal. This is considered as follows.

The clearance between the resistor and the magnetic disk is equal to the flying height of the flying slider on which the resistor is mounted.
Although it is about 0 nm, the resistor always emits heat onto the magnetic disk through the minute gap. Usually, in a PERM disk, the ratio of the concave portion to the convex portion is different between the servo zone and an area other than the servo zone (hereinafter, referred to as a data zone), so that the thermal resistance between the resistor and the magnetic disk is different. Are different between the servo zone and the data zone. Therefore, even when the resistor passes over the servo zone, the resistor changes in temperature and the resistance value changes as in the case where the resistor collides with the protrusion.

However, the surface of the resistor facing the disk surface is the end face of the resistor. Considering that the thickness of the resistor is on the order of nanometers, the amount of heat released due to the difference in the unevenness ratio of the disk surface is considered. Is much smaller than the magnitude of the thermal energy generated when the resistor hits the protrusion. Therefore, the amount of change in resistance of the resistor when passing over the servo zone is much smaller than the amount of change in resistance of the resistor when it collides with the protrusion. Therefore, it is considered that the signal detected when the resistor passes over the servo zone does not cause any problem at the level for detecting the protrusion.

However, if the signal detected when the resistor passes over the servo zone becomes problematic,
The obtained signal may be subjected to signal processing to extract only the signal detected when the resistor collides with the protrusion. That is, since the signal detected when the resistance value passes over the servo zone and the signal detected when the resistor collides with the projection have different signal waveforms,
By passing these signals through a signal processing circuit such as a filter, the signal detected when the resistor passes over the servo zone is removed, and only the signal detected when the resistor collides with the protrusion is removed. You may take it out.

[0112]

As described above in detail, according to the present invention, when detecting the protrusions present on the surface of the disk-shaped recording medium by the thermal resistance method, a sufficiently high quality protrusion detection signal is detected. This eliminates the need to perform processing for expanding the protrusion detection signal on the frequency axis using a spectrum analyzer. That is, according to the present invention, the presence or absence of a protrusion on the surface of a disk-shaped recording medium is determined.
Direct determination can be made based on the magnitude of the signal amplitude of the protrusion detection signal, and the time required for determining the presence or absence of a protrusion can be greatly reduced. Therefore, according to the present invention, in performing the projection inspection of the disk-shaped recording medium, the number of processed sheets per time can be greatly increased, and the manufacturing cost of the disk-shaped recording medium can be significantly reduced.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a state in which a flying slider of a horizontal type projection detection sensor is flying above a disk-shaped recording medium.

FIG. 2 is a diagram illustrating a main part of a horizontal type protrusion detection sensor, and is an enlarged diagram illustrating a portion indicated by a circle A1 in FIG. 1;

FIG. 3 is a diagram illustrating a circuit configuration of a horizontal type protrusion detection sensor.

FIG. 4 is a schematic diagram showing a state in which a flying slider of a vertical type projection detection sensor is flying above a disk-shaped recording medium.

5 is a diagram illustrating a main part of a vertical type protrusion detection sensor, and is a diagram illustrating a portion indicated by a circle A2 in FIG. 4 in an enlarged manner.

FIG. 6 is a diagram showing a circuit configuration of a vertical type protrusion detection sensor.

FIG. 7 is a diagram showing a state when a protrusion present on the surface of a disk-shaped recording medium is detected by a thermal resistor method.

FIG. 8 is a diagram illustrating an example of a profile in which noise included in a protrusion detection signal is developed on a frequency axis using a spectrum analyzer.

[Explanation of symbols]

1,11 disk-shaped recording medium, 2,12 flying slider, 3,13 resistor, 4,14 first conductor,
5,15 second conductor, 6,16 constant current source

Claims (2)

[Claims] 1. A flying slider that floats on a disk-shaped recording medium when the disk-shaped recording medium is rotated, a substantially rectangular resistor mounted on the flying slider, and one end of the resistor in a major axis direction. And a second conductor connected to the other end of the resistor in the longitudinal direction of the resistor. Detecting the protrusion by supplying a current to the resistor through the conductor and detecting a change in resistance of the resistor that occurs when the resistor collides with a protrusion existing on the surface of the disk-shaped recording medium. A protrusion detection sensor characterized by the above-mentioned. 2. A slider having a substantially rectangular shape mounted on a flying slider which floats on the disk-shaped recording medium when the disk-shaped recording medium is rotated, and a first resistor is provided at one end of the resistor in the longitudinal direction of the resistor. A second conductor is connected to the first conductor and the other end, and a current is supplied to the resistor via the first and second conductors in a state where the flying slider floats on the disk-shaped recording medium. A projection detection method, wherein the projection is detected by detecting a resistance change of the resistor that occurs when the resistor collides with a projection existing on a surface of a recording medium.