Abstract:
A magnetic head slider includes a magnetic head for recording/reproducing information from/into a magnetic disk and a slider on which the magnetic head is mounted. The slider has a first positive pressure generating portion provided at an air-inflow side and a positive pressure generating portion surface provided at an air-outflow side, projections being provided at the air-inflow side at positions with respect to the first positive pressure generating portion on a first surface which faces the magnetic disk upon read/write operation of the magnetic head slider, and a step surface provided at the air-inflow side with respect to said first positive pressure generating portion.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
   This is a continuation of U.S. application Ser. No. 10/618,760, filed Jul. 15, 2003, which is a continuation of U.S. application Ser. No. 10/217,439, filed Aug. 14, 2002, now U.S. Pat. No. 6,597,537, which is a continuation of U.S. application Ser. No. 10/102,679, filed Mar. 22, 2002, now U.S. Pat. No. 6,452,751,which is a continuation of U.S. application Ser. No. 09/299,909, filed Apr. 28, 1999, now U.S. Pat. No. 6,373,661, the subject matter of which is incorporated by reference herein. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a magnetic head slider for a magnetic disk device and also to a magnetic disk device, and more particularly to a magnetic head slider of a low flying height-type for achieving high reliability and high-density recording and also to a magnetic disk device having such a magnetic head slider. 
   2. Description of the Related Art 
   In magnetic disk devices, attempts have now been made to achieve a low flying height design of a slider and also to stabilize a flying height. 
   For example, as disclosed in JP-A-6-325530, there has been proposed a slider in which a surface (step surface) structured by a step extending in a recessing direction from a flat surface portion of a rail for flying (air bearing rail) is formed at an inflow-side portion of the rail of the slider, and the depth of this step surface (that is, the height of the step) is made microscopic so that a predetermined flying height of the slider can be achieved without depending on the peripheral speed of a disk. In this known example, the rail for flying has the step surface provided at the inflow-side portion, the step, and the flat surface portion extending from this step portion, and the depth of the step surface (that is, the height difference between the step surface and the flat surface portion) is not more than 700 nm, and by doing so, there can be provided the slider which can fly with a predetermined flying height without depending on the peripheral speed of the disk. A slider, having a step of such a microscopic depth (height), will be hereinafter referred to as “microscopic step slider”. 
   JP-A-7-21717 discloses a slider in which two inflow pads and one outflow pad are provided on the slider, and side edges of the pads are inclined to an angle generally equal to a predicted maximum inclination so that even on a smooth magnetic disk, the slider can be disposed in linear contact with the magnetic disk, thereby preventing the sticking of the slider to the disk. 
   Further, in order to achieve the above-mentioned low flying height design of the slider, the disk surface is made flat and smooth. The mean surface roughness Ra of a currently-used disk is reduced to not more than 10 nm. There has been adopted a contact start stop system (hereinafter referred to as “CSS system”) in which when the rotation of a magnetic disk is stopped, a slider is held in contact with a disk surface, and when the disk is rotated, the slider flies off the disk surface. In a device using this CSS system, a so-called sticking problem arises from a smooth disk surface, and more specifically, when the rotation of the disk is stopped, the slider sticks to the disk surface. When the slider sticks to the disk, there are encountered troubles such as the failure of the disk to rotate. In order to solve this problem, a slider, in which microscopic projections are formed, on the slider to reduce the area of contact between the slider and the disk, is disclosed in JP-A-4-28070 and JP-A-9-245451. 
   In a microscopic step slider as disclosed in the above JP-A-6-325530, a sticking problems arises from a smooth disk surface. In order to avoid this sticking problem, even if microscopic projections as disclosed in JP-A-4-28070 and JP-A-9-245451 are provided on a rear portion or front and rear portions of the flying rail, or a negative-pressure pocket thereof, the following problems are encountered: 
   (1) If the flying rail of the slider or the microscopic projection is brought into contact with the disk surface for some reason at the time of CSS or during the flying of the slider over the rotating disk, the flying surface (surface facing the disk) of the slider is pulled by a frictional force, so that the slider is turned or angularly moved about a pivot (load-acting point) of a suspension to lean forward, and as a result the front edge of the step surface of the slider is brought into contact with the disk surface. The front edge of the step surface is sharp, and when this front edge is brought into contact with the disk surface, there arises a problem that the disk is damaged by this front edge. Particularly in a magnetic disk device of the type in which the flying height of the slider is small, and the smooth disk is used for the purpose of achieving a low flying height, this problem is serious because of the large frictional force. Therefore, to prevent the slider from leaning forward so that the front edge will not brought into contact with the disk surface is an important subject matter for preventing damage to the disk and for securing the reliability, One method of overcoming this problem is to chamfer the front edge of the step surface (to provide a curvature) to increase the contact area, thereby reducing a contact stress (load pressure). With this method, however, an opening of the step surface (that is, the distance of the step surface from the disk surface) is large, and an increased amount of dust and dirt enter this opening, which leads to a possibility that the flying height is varied. When the flying height is thus varied, an error in the data reading and writing operation occurs. Therefore, this method is not effective in preventing the damage of the disk by the front edge (sharp edge portion) of the step surface. 
   (2) Another main factor in the variation of the flying height of the slider is a reduction of the atmosphere pressure. More specifically, when the magnetic disk device is used at a place of a high altitude, the pressure of the atmosphere is low, so that the flying height is reduced. When the flying height is reduced, there arises a problem that the slider comes into contact with the disk to damage the same. To reduce the amount of reduction of the flying height of the slider due to the decrease of the atmospheric pressure is an important subject matter for achieving the low flying height design of the slider and also for preventing the contact of the slider with the disk so as to secure the reliability. 
   And besides, when the microscopic projection is provided on the rail of the slider, the reduction of the flying height is, in some cases, limited depending on the height of this projection, so that there is a case that the low flying height design can not be achieved. 
   OBJECT AND SUMMARY OF THE INVENTION 
   It is therefore an object of the present invention to provide a magnetic head slider in which even when the slider is leaned forward, a front edge of each step surface is prevented from being brought into contact with a disk surface, and besides the amount of reduction of the flying height of the slider due to a decrease of the atmospheric pressure is reduced, thereby enabling the reading and writing of data in a stable manner, and to provide a magnetic disk device of a high reliability. 
   In order to achieve the above object, and in order to prevent a step slider from leaning forward and a front edge of each step surface from coming into contact with the disk surface, rails for flying (stepped pads) each structured to have a step surface are provided on a slider, and microscopic projections are formed on the step surface disposed at an inflow-side portion of the slider. The height of the microscopic projections are substantially equal to or higher than the depth (height) of the step. And besides, because of the provision of the microscopic projections, a variation of the flying height due to the decrease of the atmospheric pressure can be reduced. 
   The microscopic projections are formed on the step surface of the rail of the slider of the invention. The front edge of the step surface is provided at a position substantially coincides with the inflow end of the slider. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view of a first embodiment of a slider of the invention, showing a flying surface thereof; 
       FIG. 2  is a view explanatory of the condition for the forward leaning of the slider by a frictional force; 
       FIG. 3  is a view explanatory of the function of microscopic projections; 
       FIG. 4  is a diagram showing the relation between the depth of a step surface and a flying force; 
       FIG. 5  is a view showing a pressure distribution of the slider; 
       FIG. 6  is an enlarged view of a portion A of  FIG. 2 ; 
       FIG. 7  is a perspective view of a second embodiment of a slider of the invention, showing a flying surface thereof; 
       FIG. 8  is a front view of the second embodiment of the slider; 
       FIG. 9  is a perspective view of a third embodiment of a slider of the invention, showing a flying surface thereof; 
       FIG. 10  is a perspective view of a fourth embodiment of a slider of the invention, showing a flying surface thereof; 
       FIG. 11  is a perspective view of a fifth embodiment of a slider of the invention, showing a flying surface thereof; 
       FIG. 12  is a perspective view of a sixth embodiment of a slider of the invention, showing a flying surface thereof; 
       FIG. 13  is a view showing a method of forming a pad for flying; and 
       FIG. 14  is a perspective view of a magnetic disk device incorporating a magnetic head slider of the invention. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   A first embodiment of the present invention will now be described with reference to  FIGS. 1 to 6  and  FIG. 14 . 
     FIG. 1  is a perspective view of one embodiment of a slider of the invention, showing a flying surface thereof. 
   Three pads for flying  10  for producing a flying force are formed on a bleed surface  11  of the slider  1 . Two of these pads  10  are provided respectively at opposite ends of an inflow-side portion (to which an air stream, produced in accordance with the rotation of a disk, flows) of the slider  1 , and the other pad  10  is provided at a central portion of an outflow-side portion of the slider  1 . Each flying pad  10  has a flat surface portion  13 , a step portion  14  (defined by a surface disposed generally perpendicular to the flat surface portion  13 ) facing the air stream inflow side, and a step surface  12 . The flat surface portions  13  of the three flying pads  10  lie generally in a common horizontal plane. The step surface  12  is disposed generally parallel to the flat surface portion  13 , and structured to have a microscopic depth (the step portion  14 ) in a direction generally perpendicular to the flat surface portion  13 . The step surfaces  12  of the three flying pads  10  lie generally in a common horizontal plane. A microscopic projection  17  is formed on the step surface  12  of each of the two inflow-side pads  10 . The microscopic projection  17  is disposed near an outer corner portion  16   a  of the step surface  12 . The slider  1  is provided with a thin-film magnetic head  20  provided rearward of the flat surface portion  13  of the outflow-side pad  10 . A gap portion  21  of the magnetic head  20  is disposed generally in a plane in which the flat surface portion  13  lies. A coil portion  22  and lead terminals  23  are provided at the outflow end surface of the slider  1 . 
   In this embodiment, the flying pads each having the step are used in order to achieve the same effect as attained with the conventional flying rail having an inclined portion at the air inflow side. Namely, the flying pads each with the step are used in order to obtain a large flying force. 
   One example of specific numerical values in this embodiment are as follows. The slider  1  has a length of 1.2 mm, a width of 1 mm and a thickness of 0.3 mm. The size of each of the step surface  12  and the flat surface portion  13  of the flying pad  10  is 0.4 mm×0.1 mm, and the height of the step portion  14  is 0.09 μm. The height from the flat surface portion  13  to the slider surface (that is, the depth (height) of the bleed  11 ) is 6 μm. The microscopic projection  17  has a cylindrical shape, and its diameter is 0.06 mm, and the height of this projection  17  from the step surface  12  is 0.13 μm. Therefore, the microscopic projection  17  projects 0.04 μm beyond the flat surface portion  13 . The slider  1  is not limited to the above dimensions, and there is a tendency for these dimensions to become more microscopic. 
   Effects of the present invention will now be described with reference to  FIGS. 2 and 3 .  FIG. 2  is a side view of the magnetic head slider of the present invention.  FIG. 3  shows the slider with the microscopic projections and the slider without the microscopic projections, showing a contact condition between the slider and a magnetic disk. 
   If the slider is brought into contact with a rotating magnetic disk  70  for some reason during the flying of the slider  1  or at the time of CSS, a force as shown in  FIG. 2  is exerted at a point of contact between the slider  1  and the magnetic disk  70 . Although not shown in the drawings, a pressing force, acting in a direction toward the magnetic disk, is exerted on the slider  1  from a pivot of a suspension. When a moment Mf due to a frictional force F between the slider  1  and the magnetic disk  70  becomes larger than a turning moment Mw due to the pressing load applied to the slider  1  by the suspension, the slider  1  is turned about the pivot to lean forward, so that the front edges of the step surfaces are brought into contact with the disk surface. 
   The condition for the forward leaning of the slider  1  is Mw&lt;Mf. Here, there are established formulas, Mw=W×1 and Mf=F×d where W represents the pressing force applied to the slider by the suspension,  1  represents the distance from the pivot (load acting point) to the point of contact (axis of the turning movement) between the slider  1  and the magnetic disk  70 , F represents the frictional force between the slider  1  and the magnetic disk  70 , and d represents the thickness of the slider  1 . 
   As will be appreciated from the above formulas, in order to prevent the forward leaning of the slider, it is effective to increase the pressing load W, or to increase the distance  1  from the pivot to the point of contact between the slider and the disk, or to reduce the thickness d of the slider. However, the increase of W increases the amount of wear between the slider and the disk at the time of CSS, and this is not desirable. For reducing the thickness d of the slider  1 , the size of the magnetic head also need to be reduced, and this is difficult. Therefore, it is effective to increase the value of 1. 
   If the microscopic projection  17  is formed on the step surface of each of the flying pads provided at the inflow-side portion of the slider as shown in  FIG. 2 , Mw increases so that the slider  1  is less liable to be turned to lean forward. More specifically, assuming that the overall length of the slider is represented by L, the length of the step surface is represented by Is, the pivot is disposed generally at the center of the slider, and the microscopic projection  17  is provided at the center of the step surface, the following is obtained: 
   If the turning moment of the conventional microscopic step slider is represented by Mw1, the following formula is established:
 
 Mw 1= W ×( L/ 2−1s)  (1)
 
   If the turning moment of the microscopic step slider of the present invention is represented by Mw2, the following formula is established:
 
 Mw 2= W ×( L/ 2)  (2)
 
   In the present invention, the microscopic projection  17  is provided on each step surface  12  at the inflow side. Therefore, the axis of turning (angular movement) of the forwardly-leaning slider  1  is the point of contact between each microscopic projection  17  and the magnetic disk  70 . The condition for the turning of the slider  1  is represented by formula (2) as described above. On the other hand, the conventional slider has no microscopic projection  17 , and therefore the boundary between the step surface  12  and the flat surface portion  13 , that is, the inflow end of the flat surface portion  13 , serves as the axis of turning of the slider (that is, the point of contact with the magnetic disk). Therefore, the value of 1 is reduced by an amount corresponding to the length is of the step surface  12 , so that the slider is liable to lean forward. In other words, if the microscopic projection  17  is formed on the step surface  12  as in the present invention, the value of 1 is increased, so that the slider  1  is less liable to lean forward. 
   As will be appreciated from the above formulas, by providing the microscopic projection on the step surface of each inflow-side pad, the moment can be increased, so that the slider is less liable to lean forward. 
   In the present invention, there is achieved an advantage (effect) that even when the slider leans forward, the slider is less liable to damage the surface of the magnetic disk. If any microscopic projection  17  is not formed on the step surface  12  as shown in  FIG. 3( 1), the slider is liable to be leaned forward by the frictional force F as described above. When the slider thus leans forward, the front edge  16  of the step surface  12  is brought into contact with the surface of the magnetic disk  70  to damage the same. In order to  10  prevent the intrusion of dust and dirt and also to reduce the depth Ds of the step surface  12 , the front edge  16  of the step surface  12  is formed into a sharp edge. Therefore, when the slider  1  is brought into contact with the surface of the magnetic disk, a contact stress can easily exceed a stress limit of the magnetic disk surface, thereby damaging the magnetic disk. If the magnetic disk is thus damaged, an error in the information reading and writing operation occurs, thus adversely affecting the reliability of the device. 
   On the other hand, in the case where the microscopic projection  17  is formed on the step surface of each inflow-side pad, the microscopic projection  17  is brought into contact with the magnetic disk  70  when the slider  1  leans forward as shown in  FIG. 3( 2), and the front edge  16  of the step surface  12  will not be brought into contact with the surface of the magnetic disk  70 . The contact area of the microscopic projection  17  is so small that the microscopic projection  17  hardly damages the magnetic disk surface. As shown in the drawings, the height of the microscopic projection  17  need only to be so determined that the corner portion of the flat surface portion  13  will not be brought into contact with the disk surface, and this height may be smaller than the height of the flat surface portion  13 . 
   When the slider without any microscopic projection is leaned forward while turned in the direction of the width (transverse direction), the corner portion  16   a  of the front edge  16  of the step surface  12  is brought into contact with the disk surface. The contact of the corner portion  16   a  with the disk surface is more liable to damage the disk surface than the contact of the front edge  16  with the disk surface is. On the other hand, in the case where the microscopic projection  17  is formed on the outer end portion of the step  10  surface  12 , the microscopic projection  17  is brought into contact with the surface of the magnetic disk  70 , and the corner portion  16   a  will not be brought into contact with the surface of the magnetic disk  70 . Therefore, in the present invention, even when the slider  1  is leaned forward upon contact with the magnetic disk  70 , damage to the magnetic disk  70  can be prevented. 
   The relation between the depth Ds of the step surface (which is the height difference between the flat surface portion  13  and the step surface  12 ) and the flying force Q was obtained by calculation, and results thereof are shown in  FIG. 4 . With respect to conditions of the calculation, the length of the slider was 1.25 mm, its width was 1.0 mm, the size of the step surface  12  of the flying pad was 0.3 mm×0.25 mm, the size of the flat surface portion  13  was 0.3 mm×0.05 mm, and the height from the flat surface portion to the bleed  11  was 6 μm. The flying height of the air inflow end of the slider was 30 nm, and the flying height of the air outflow end thereof was 90 nm, and the height Ds of the step portion was used as a parameter, and the calculation was made. 
   As will be appreciated from  FIG. 4 , the smaller Ds becomes, the smaller the difference between the flying force at the disk speed of 6 m/s and the flying force at the disk speed of 12 m/s becomes. As Ds decreases from 0.3 μm to 0.2 μm, the difference of the flying force due to the difference of the speed abruptly decreases. When Ds becomes not more than 0.2 μm, the difference of the flying force Q becomes not more than 10%. This value is sufficiently smaller as compared with a variation of the flying force Q due to processing and assembling errors and so on. Therefore, if Ds is not more than 0.2 μm, the stable flying can be achieved. In this embodiment, the value of Ds is 0.2 μm, and therefore there can be obtained the slider in which the predetermined flying force Q is obtained without depending on the peripheral speed of the disk, and a variation in the flying height is small, and the flying height is constant over the entire circumference of the disk. 
   This effect is not changed even if the depth of the bleed (the height from the slider surface to the flat surface portion  13  of the pad) relative to the flying pad is changed. The smaller the depth Ds of the step portion  14  is made than 0.2 μm, the smaller the difference of the flying force due to the difference of the peripheral speed becomes. With the compact design of the slider, the flying force Q tends to be small. However, if the height Ds of the step portion  14  is 0, this pad has no step, so that the flying force is not produced. Therefore, in view of variations in the processing of the slider, the minimum value of Ds should be so determined that it will not become 0. 
     FIG. 5  shows a pressure distribution on the flying surface of the slider with the microscopic projections, which pressure distribution was obtained by calculation. 
   By providing the microscopic projection  17  on the step surface  12 , the amount of reduction of the flying height can be reduced even if the ambient atmospheric pressure decreases. More specifically, in the case where the magnetic disk device is used at a place with an altitude of 3,000 m, the ambient atmospheric pressure is smaller than the ordinary atmospheric pressure (1 atmospheric pressure), so that the flying height of the slider is reduced. Therefore, conventional sliders need to have a separate negative pressure-producing mechanism in order to prevent the reduction of the flying height. In the slider of the present invention, having the microscopic projection  17  formed on the step surface  12  of each inflow-side pad, a negative pressure-producing region is formed rearward of each microscopic projection  17 , as shown in  FIG. 5 . Therefore, any separate negative pressure-producing portion as in the conventional sliders is not needed. Therefore, the amount of reduction of the flying height due to the altitude difference (between 0 m and 3,000 m) can be made smaller as compared with the sliders having no microscopic projection  17 . 
   It has been confirmed through calculation that the amount of reduction of the flying height in the construction of this embodiment is not more than about ½ of that obtained in the slider having no microscopic projection  17 . 
   Although explanation of the detailed mechanism is omitted here, the following relation is established among the flying height Fs of the slider, the load W and the negative pressure Fn. The slider flies with the flying height satisfying this relation.
 
 Fs=W+Fn   (3)
 
   In this embodiment, as the atmospheric pressure decreases, the flying force Fs decreases as in the conventional sliders, and at the same time the negative pressure Fn decreases. Therefore, the flying height of the slider will not be changed in accordance with the decrease of the atmospheric pressure. This effect is achieved by forming the microscopic projection on the step surface of a microscopic depth (height) as described above. And besides, there is achieved an advantage that a variation of the flying force due to a change in the peripheral speed of the disk can be reduced as in the conventional slider utilizing a negative pressure. 
     FIG. 6  shows a portion A of  FIG. 2  on an enlarged scale. In  FIG. 6 , however, the microscopic projection  17  projects beyond the flat surface portion  13  of each inflow-side pad. As shown in  FIG. 6 , the microscopic projection  17  is formed on the step surface  12 , and the height Dp of the microscopic projection  17  is higher than the height Ds (the depth Ds from the flat surface portion  13  to the step surface  12 ) from the step surface  12  to the flat surface portion  13 , and therefore the microscopic projection  17  is held in contact with the surface of the magnetic disk  70 . Therefore, the flat surface portion  13  of each flying pad  10 , having the microscopic projection  17 , is held out of contact with the magnetic disk  70 . The area of contact between the flat surface portion  13  and the magnetic disk  70  can be arbitrarily changed by adjusting the height Dp of the microscopic projection  17 . 
   In this embodiment, the microscopic projection  17  is higher than the flat surface portion  13 , and therefore the flat surface portion  13  of each air inflow-side flying pad  10  will not be brought into contact with the surface of the magnetic disk  70 . The flying pad  10 , provided at the air outflow-side of the slider, does not come into contact with the magnetic disk  70  at its flat surface portion  13  over the entire area thereof, but come into contact with the magnetic disk at its flat surface portion  13  at a predetermined inclination angle. Therefore, the area of contact between the slider  1  and the disk  70  is greatly reduced. It is known that a sticking force, by which the slider sticks to the disk, is proportional to the area of contact between the two. In this embodiment, the area of contact is further reduced by the provision of the microscopic projections  17 , the sticking force is reduced. 
   Next, the dimensions of the various portions in this embodiment will be described. As described above, the depth (height) Ds from the flat surface portion  13  to the step surface  12  is set to 0.09 μm. The relation between this depth and the flying force will be described later. The depth Db from the flat surface portion  13  of the flying pad  10  to the bleed surface  11  is 6 μm. For the purpose of reducing the processing amount, the bleed depth Db is made as small as possible in such a range that the bleed surface will not produce a flying force, but the value of Db is not limited to 6 μm. The height Dp of the microscopic projection  17  is larger than Ds, and therefore Dp&gt;0.09 μm is provided. 
   The diameter of the microscopic projection  17  is 0.06 mm. If this diameter is too small (for example, not more than 0.01 mm), the microscopic projection  17  is worn upon contact with the magnetic disk. In contrast, if this diameter is too larger (for example, not less than 0.1 mm), the microscopic projection  17  sticks to the magnetic disk. Wear and the sticking vary depending on the surface roughness of the magnetic disk surface. 
   In this embodiment, the amount of projecting of the microscopic projection  17  beyond the flat surface portion  13  toward the magnetic disk surface is 40 nm (Dp−Ds=0.13 μm−0.09 μm). The height Dp of the microscopic projection  17  is so determined that the projecting amount (Dp−Ds) is smaller than the flying height of the flat surface portion  13 , and is larger than the roughness of the magnetic disk surface. If the mean surface roughness Ra of the magnetic disk surface is 2 nm, the maximum surface roughness Rmax is 6 nm which is about three times larger than Ra, and therefore the projecting amount should be not less than 6 nm. 
   The slider is inclined, and therefore with respect to the flying height ho of the air outflow-side flying pad and the flying height hi of each air inflow-side pad, the gap ratio (hi/ho) is usually 2 to 8. In this embodiment, hi/ho=3 is provided, and ho=20 nm and hi=60 nm are provided. Therefore, even though the projecting amount is 40 nm, the microscopic projection will not come into contact with the rotating magnetic disk. 
   For the above reasons, if the flying height is made microscopic, the projection height Dp need to be reduced so as to avoid the contact of the microscopic projection with the magnetic disk. Also, the projecting amount (Dp−Ds) need only to be larger than the maximum surface roughness Rmax (=3 Ra), and therefore Dp may be reduced if Rmax is small. 
   As described above, the microscopic projection  17  is formed on the step surface  12  of each inflow-side flying pad, and therefore the forward leaning of the slider is prevented, and besides even if the slider is leaned forward, damage to the disk is prevented. Furthermore, the reduction of the flying height due to the decrease of the ambient pressure is prevented, and also the sticking force is reduced. 
   A second embodiment of the present invention will be described with reference to  FIGS. 7 and 8 .  FIG. 7  is a perspective view of the second embodiment of a slider of the invention, showing a flying surface thereof.  FIG. 8  is a plan view showing the flying surface of the slider of  FIG. 7 . 
   This embodiment differs from the first embodiment in that two inflow-side flying pads  10  are offset inwardly from opposite sides of the slider  1 , respectively. As shown in  FIG. 8 , a front edge  16  of a step surface  12  of each inflow-side pad  10  is offset slightly rearward of a front edge  15  of the body of the slider  1 . The outer side edge of each inflow-side flying pad  10  is offset inwardly from the corresponding side edge of the slider  1 . With this arrangement, even if chipping occurs when sliders are cut one by one from a rectangular bar by machining, the configuration of the flying pads will not be changed by this chipping. Therefore, the efficiency of the production by machining can be enhanced. Similar effects as described above for the first embodiment are achieved also in this embodiment. 
   A third embodiment of the present invention will be described with reference to  FIG. 9 .  FIG. 9  is a perspective view of the third embodiment of a slider of the invention, showing a flying surface thereof. 
   This embodiment differs from the first embodiment in that a rear step surface  18  is formed at a rear side of each of two inflow-side flying pads  10 . The rear step surfaces  18  are disposed in a plane in which step surfaces  12  lie, that is, the rear step surfaces  18  and the step surfaces  12  have the same height, and are provided along outer sides  13   a  of the pads. Because of the provision of the rear step surface  18 , an air stream, flowing to a rear side of a flat surface portion  13 , is limited, and that region, disposed at the rear side of the flat surface portion  13 , forms a negative pressure-producing region  18 a for producing a negative pressure. The negative pressure decreases with the decrease of the ambient pressure, and therefore even when the ambient pressure decreases, the amount of reduction of the flying height of the slider is small similarly with the effect of the negative pressure due to the microscopic projection  17 . And besides, the amount of reduction of the flying height due to the decrease of the pressure is small when the negative pressure is large. Therefore, a variation of the flying height due to the decrease of the ambient pressure is smaller as compared with the first embodiment, and therefore there can be provided the slider of a higher reliability. And besides, similar effects as described above for the first embodiment can be expected. 
   A fourth embodiment of the present invention will be described with reference to  FIG. 10 .  FIG. 10  is a perspective view of the fourth embodiment of a slider of the invention, showing a flying surface thereof. 
   This embodiment differs from the third embodiment in that step surfaces  12  of two inflow-side flying pads  10  are interconnected by a central step surface  19 . Because of the provision of the central step surface  19 , an air stream, flowing through a gap between the two flying pads, is limited, and a negative pressure is produced at a wide region disposed at the rear side of the flying pads. The depth from a flat surface  13  to a bleed surface  11  is set to 2 μm, thereby increasing the negative pressure. By adjusting this depth, the magnitude of the negative pressure can be adjusted. Therefore, the negative pressure can be more increased as compared with the third embodiment, and the amount of reduction of the flying height due to the decrease of the ambient pressure can be made smaller as compared with the third embodiment. With the increased negative pressure, a variation of the flying height due to the difference of the peripheral speed of the disk can be further reduced. And besides, similar effects as described above for the first embodiment can be expected. 
   A fifth embodiment of the present invention will be described with reference to  FIG. 11 .  FIG. 11  is a perspective view of the fifth embodiment of a slider of the invention, showing a flying surface thereof. 
   This embodiment differs from the first embodiment in that only one flying pad, which is generally equal in size to a slider body, is provided on a slider. A step surface  12  is provided around a flat surface portion  13 . In this embodiment, the step surface  12  is thus provided generally over the entire periphery of the flat surface portion  13 , and with this construction, even when an air stream flows obliquely into the slider  1  (in this case, the slider is arranged at an angle relative to the direction of the periphery of the disk), a predetermined flying height can be obtained over the entire circumference of the disk since the step surface  12  produces a flying force. And besides, since the only one flying pad is provided on the slider, the compact design of the slider can be easily achieved. Furthermore, microscopic projections  17  as described above for the first embodiment are provided at the inflow-side portion of the step surface  12 , and therefore similar effects as described above for the first embodiment can be expected. 
   A sixth embodiment of the present invention will be described with reference to  FIG. 12 .  FIG. 12  is a perspective view of the sixth embodiment of a slider of the invention, showing a flying surface thereof. 
   This embodiment differs from the fourth embodiment in that rear step surfaces  18  extend rearward from opposite side surfaces of a flat surface portion  13 , respectively, and that microscopic projections  17  are provided on the rear step surfaces  18 , respectively. In this embodiment, the step surface  12  is provided generally over the entire periphery except a magnetic head-mounting surface, and with this construction even when an air stream flows obliquely into the slider  1 , a predetermined flying height can be obtained over the entire circumference of the disk as in the fourth embodiment since the step surface  12  produces a flying force. And besides, by increasing the number of the microscopic projections  17 , the effect of the negative pressure is enhanced, thereby achieving the slider having a more stable flying height. Furthermore, the microscopic projections  17  as described above for the first embodiment are provided at the inflow-side portion of the step surface  12 , and therefore similar effects as described above for the first embodiment can be expected. 
   The number of the above-mentioned microscopic projections  17  is not limited to two, and an optimum number of microscopic projections  17  can be provided in so far as these projections do not adversely affect the flying force. The microscopic projections  17  are made of a material hard enough to withstand the contact and sliding contact between the magnetic disk  70  and the slider  1  and are formed by thin film process such as etching. 
   The microscopic projection  17  has a cylindrical shape, and with this configuration, the length of the edge of the microscopic projection for contact with the magnetic disk  70  is shorter as compared with the case where the microscopic projection has a rectangular shape. Therefore, the contact area is reduced, so that the sticking force is reduced. The distal end of the microscopic projection  17  is not limited to the flat surface, and in order to reduce the stress of contact with the magnetic disk, this distal end can be formed into a semi-spherical shape or a shape having a curvature. 
   The microscopic projections  17  can be easily formed by etching. 
     FIG. 13  shows a specific method of forming flying pads and microscopic projections  17 . 
   First, a first mask  21 , shown in  FIG. 13B , is placed on a slider substrate  20  shown in  FIG. 13A , and the first-stage etching is effected, thereby forming flying pads. Then, a second mask  22 , shown in  FIG. 13C , is placed on the slider substrate  20 , and the second-stage etching is effected as shown in  FIG. 13D , thereby forming step surfaces  12  and microscopic projections  17 . As a result, there is produced the slider in which the height Dp of the microscopic projections  17  is equal to the depth (height) Ds of the step surfaces  12 . Namely, at this time, there is produced the slider having the microscopic projections  17  whose height is equal to a flat surface portion  13 . 
   If it is desired that the height Dp of the microscopic projections  17  should be higher than the depth (height) Ds of the step surfaces  12  for the purpose of preventing the sticking, a third mask  23 , shown in  FIG. 13E , is placed on the slider, and the flat surface portions  13  are etched, and by doing so, this design can be obtained. In the type of magnetic disk device required to solve the sticking problem, such as one using a CSS system, the process up to the step of  FIG. 13E  must be performed. 
   Examples of this etching process includes a chemical etching process, such as laser inducing chemical etching and plasma etching, a physical etching process, such as reactive ion milling, and an electrochemical etching process such as electrolytic etching. By the use of these etching processes, the flying pads and microscopic projections of various shapes can be formed. And besides, the depth of the step surfaces and the height of the microscopic projections can be adjusted. 
   In this method, although the microscopic projections  17  are made of the same material as that of the slider substrate  20 , these projections can be formed by carbon, diamond-like carbon, or hydrogen- or nitrogen-added carbon, using a similar thin film process. The wear resistance of the microscopic projections  17  can be enhanced by the use of these materials. Further, protective films can be formed respectively on the flat surface portions  13  and microscopic projections  17  for contact with the disk  70 , and by doing so, the wear resistance can be enhanced. Because of the enhanced wear resistance, the lifetime of the flat surface portions  13  and microscopic projections  17  can be increased, and also the amount of production of dust can be reduced, so that the reliability of the device is enhanced. The above protective films are formed by vapor deposition, sputtering, CVD (chemical vapor deposition) and so on. 
     FIG. 14  shows a magnetic disk device including a magnetic head slider of the present invention. 
   The magnetic head slider (hereinafter referred to merely as “slider”)  1  is supported by a suspension  81 , and the suspension  81  is connected to a guide arm  82 . The guide arm  82  is pivotally moved about an axis of a pivot bearing  83  by a voice coil motor  84 , thereby moving the slider  1  to a desired radial position on a magnetic disk  70  rotated by a spindle motor  60 . In this manner, the magnetic head slider  1  reads and write data relative to the magnetic disk  70 . These mechanisms are sealed by a base  90  and a cover (not shown). 
   Although the magnetic disk device of this embodiment employs a CSS system, the slider of the present invention can be mounted on a magnetic disk device using a load-unload system in which when the rotation of the disk is stopped, the slider  1  is taken refuge from the disk  70 . 
   The magnetic head slider of the present invention is effective particularly for a smooth magnetic disk in which the surface roughness of the magnetic disk surface is small. More specifically, in order to achieve a surface recording density of not less than 10 Gb/inch 2 , it is necessary to reduce the flying height of the slider to not more than 20 nm, and in order to achieve this, it is necessary to reduce the mean surface roughness Ra of the magnetic disk to not more than 2 nm. 
   The mean surface roughness Ra is measured by using a surface roughness meter of the tracer type, and the surface is measured over a length of 1 mm, and the measurement is effected at a cut-off frequency of 25 Hz while ignoring 0.1 mm-long opposite end portions of this length. In the measurement using AFM (Atomic Force Microscope), the measurement is effected over a square area (10 μm×10 μm). 
   In the case of a smooth disk having Ra (≦2 nm), even when the flying slider is brought into contact with the magnetic disk surface for some reason, the friction coefficient is large, and therefore with the conventional slider, a large frictional force F is produced. When the value of F becomes large, the conventional slider can be easily turned and leaned forward to damage the magnetic disk surface. On the other hand, in the present invention, even if the mean surface roughness Ra of the magnetic disk is less than 2 nm (Ra&lt;2 nm) , only the microscopic projections, formed on the slider, are brought into contact with the magnetic disk surface, and the corner portion of the slider will not be brought into contact with the magnetic disk surface, and therefore the disk surface will not be damaged. Therefore, there can be provided the slider having the low flying height and high reliability, and also the magnetic disk of a large capacity can be achieved. 
   As described above, even if the magnetic head slider of the present invention is brought into contact with the rotating magnetic disk for some reason at the time of CSS or during the flying of the slider, the slider is less liable to lean forward, and even if the slider leans forward, the front edge of the step surface will not damage the magnetic disk surface. And besides, even if the ambient atmospheric pressure decreases, the predetermined flying height can be achieved. Furthermore, using this slider in combination with the smooth disk, the magnetic disk device of a large capacity and high reliability can be achieved.