Abstract:
Embodiments of the invention provide Femto and below form factor magnetic head slider designs both capable of minimizing reduction of its flying height at high altitude and lower flying height sensitivity on manufacturing process tolerance. In one embodiment, the air bearing surface of a magnetic head slider includes a plurality of inlet rails respectively having inlet rail surfaces, a step bearing surface extending at a predetermined first depth from a reference plane including the inlet and the outlet rail surfaces, a negative surface extending in a plane at a predetermined second depth greater than the first depth from the reference plane, longitudinal carbon islands of a predetermined height formed on the inlet rails, and an outlet rail having an outlet rail surface flush with the inlet rail surfaces and holding a magnetic R/W head. The step bearing surface extends at a predetermined first depth from a reference plane. The air bearing surface further includes two or more stepped leading air flow surfaces and three or more rising wall profiles.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The present invention relates to a magnetic disk drive and, more particularly, to a magnetic head slider capable of both suppressing the decrease of its flying height when used at high altitude or low pressure environments and reducing its flying height sensitivity on manufacturing process tolerance.  
         [0002]     Achieving higher areal magnetic recording density of magnetic disk drive requires an extremely small and constant spacing between the air bearing slider, which carries the recording element, and the magnetic disk. At the same time, physical contact between the slider and disk must be minimized under a growing demanding variety of operational and environmental conditions. The move to smaller and smaller disk drives has placed increasing demands on power consumption, shock performance, and disk storage capacity. One of the key contributors to achieving these demanding requirements has been the reduction of slider form factor. The reduction of slider form factor can significantly improve the slider&#39;s mechanical performances and greatly reduce manufacturing cost. It is very necessary to suppress the reduction of flying height as effectively as possible when the magnetic disk drive is used at high altitude and to decrease flying height sensitivity on manufacturing process tolerances of the smaller and smaller slider.  
         [0003]     Generally, the flying height of the slider decreases at high altitude because the mean free path of the air serving as a working fluid for the slider increases at high altitude. The reduction of the flying height is undesirable from the viewpoint of the reliability of the magnetic disk drive because the reduction of the flying height increases the possibility of the slider coming into contact with the magnetic disk. It is particularly desirable for a magnetic disk drive using a 2.5 in and 1.8 in and micro-drive and built in a portable information processing device that is often used at high altitude to prevent the change of the flying height of the slider with the increase of altitude, i.e., with the drop of the atmospheric pressure.  
         [0004]     The miniaturization of the slider and the reduction of the diameter of the disk have progressively advanced with the miniaturization of the magnetic disk drive. Since a miniaturized slider has a small area and the circumferential speed of a small-diameter magnetic disk is low, negative pressure produced by the miniaturized slider is low; consequently, suppression of the reduction of the flying height at high altitude by those known prior art techniques has become progressively difficult.  
         [0005]     A technique for suppressing the reduction of the flying height of the slider with the increase of the altitude is disclosed in U.S. patent application Ser. No. 11/104,998, filed Apr. 12, 2005 (Patent Document 1). According to patent document 1, the reduction of the flying height at high altitude can be effectively suppressed by the slider design with two longitudinal, separate carbon islands of a predetermined height h formed on the inlet rails.  
         [0006]     Another technique for suppressing the reduction of the flying height of the slider with the increase of the altitude is disclosed in JP-A No. 2000-57724 (Patent Document 2). According to Patent document 2, the reduction of the flying height at high altitude can be effectively suppressed by optimizing the ratio between the depth of a step bearing surface and the depth of a negative-pressure groove.  
         [0007]     Known magnetic head sliders similar in construction to a magnetic head slider according to the present invention are disclosed in JP-A Nos. 6-203514, 8-102164, 11-25629, 2003-151233, 2001-250215 and 2000-260015, and PCT patent Publication No. WO2003/515869. All those magnetic head sliders used a rail having a stepped surface or provided with a pad on air inlet side to reduce adhesion and friction between the slider and magnetic disk when the slider comes into contact with the magnetic disk.  
       BRIEF SUMMARY OF THE INVENTION  
       [0008]     A way to increase recording density in which a magnetic disk drive records data without losing the reliability of the magnetic disk drive is to reduce flying height across the entire surface of a magnetic disk and to suppress the reduction of the flying height at high altitude.  
         [0009]     The miniaturization of the slider and the reduction of the diameter of the disk have progressively advanced with the miniaturization of the magnetic disk drive. Since a miniaturization of the slider has a small area and the circumferential speed of a small-diameter magnetic disk is low, negative pressure that can be produced by the miniaturized slider is low. Therefore, suppression of the reduction of the flying height at high altitude by those known techniques has become progressively difficult. Suppression of the reduction of the flying height of a small slider with 0.85 mm in overall length and 0.7 mm in overall width generally called Femto and below form factor slider at high altitude is difficult and further improvement of a small slider is desired.  
         [0010]     The present invention has been made in view of such circumstances and it is a feature of the present invention to provide a magnetic head slider capable of minimizing the reduction of its flying height at high altitude and the lower sensitivity on manufacturing process tolerance.  
         [0011]     According to one aspect of the present invention, there is provided a magnetic head slider comprising: a length less than or equal to 0.85 mm, a width less than or equal to 0.7 mm, and a thickness less than or equal to 0.23 mm, an air inlet end, an air outlet end and an air bearing surface wherein the air bearing surface includes a plurality of inlet rails respectively having inlet rail surface, a step bearing surface extending at a predetermined first depth from a reference plane including the inlet and the outlet rail surfaces, a negative surface extending in a plane at a predetermined second depth greater than the first depth from the reference plane, and longitudinal carbon islands of a predetermined height formed on the inlet rails, and an outlet rail having an outlet rail surface flush with the inlet rail surfaces and holding a magnetic R/W head wherein the step bearing surface extends at a predetermined first depth from a reference plane, and wherein the air bearing surface further includes two or more stepped leading air flow surfaces and rising wall profiles.  
         [0012]     According to another aspect of the present invention, there is provided a magnetic head slider comprising: a length less than or equal to 0.85 mm, a width less than or equal to 0.7 mm, and a thickness less than or equal to 0.23 mm, an air inlet end, an air outlet end and an air bearing surface wherein the air bearing surface includes a plurality of inlet rails respectively having inlet rail surface, a step bearing surface extending at a predetermined first depth from a reference plane including the inlet and the outlet rail surfaces, a negative surface extending in a plane at a predetermined second depth greater than the first depth from the reference plane, and longitudinal carbon islands of a predetermined height formed on the inlet rails, and an outlet rail having an outlet rail surface flush with the inlet rail surfaces and holding a magnetic R/W head wherein the step bearing surface extends at a predetermined first depth from a reference plane; and wherein the air bearing surface further includes two or more stepped leading air flow surfaces and rising wall profiles; and wherein a load point is located to the point between the air inlet and the center of the magnetic head slider.  
         [0013]     According to the present invention, the reduction of the flying height of the magnetic head slider at high altitude can be prevented, and the sensitivity of the flying height on the manufacturing process tolerance can be reduced and thereby the reliability of a magnetic disk drive can be improved. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]      FIG. 1  is a perspective view of a magnetic head slider in a first embodiment according to present invention.  
         [0015]      FIG. 2  is a plan view of a magnetic head slider in the first embodiment.  
         [0016]      FIG. 3  is a three-dimensional diagram showing a pressure distribution on the magnetic head slider in the first embodiment.  
         [0017]      FIG. 4  is a perspective view of a magnetic head slider in the first embodiment flying over a magnetic disk.  
         [0018]      FIG. 5  is a plan view of a magnetic head slider in Comparative example 1.  
         [0019]      FIG. 6  is a graph showing simulated flying height profiles of a magnetic head slider in the first embodiment and the magnetic head slider in comparative examples for 0 and 3000 m altitudes.  
         [0020]      FIG. 7  is a graph showing simulated flying height 3 Sigma of a magnetic head slider in the first embodiment and magnetic head slider in Comparative example 1.  
         [0021]      FIG. 8  is a graph showing simulated flying height profiles of a magnetic head slider in the first embodiment for the sub-deep depth tolerance.  
         [0022]      FIG. 9  is a plan view of a magnetic head slider in a second embodiment according to the present invention.  
         [0023]      FIG. 10  is a plan view of a magnetic head slider in a third embodiment according to the present invention.  
         [0024]      FIG. 11  is a plan view of a magnetic head slider in a fourth embodiment according to the present invention.  
         [0025]      FIG. 12  is a perspective view of a magnetic head drive provided with a magnetic head slider according to the present invention, and a load/unload mechanism.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
     First Embodiment  
       [0026]     A magnetic head slider in a first embodiment according to the present invention and a magnetic disk drive provided with this magnetic head slider will described with reference to the accompanying drawings.  FIG. 1  is a perspective view of the magnetic head slider in the first embodiment;  FIG. 2  is a plan view of the slider shown in  FIG. 1 .  FIG. 3  is a three-dimensional diagram showing a pressure distribution on the slider in  FIG. 1 , and  FIG. 4  is a perspective view of the slider flying over a disk.  
         [0027]     Referring to FIGS.  1  to  4 , the slider in the first embodiment has an air inlet end  1 , an air outlet end  2  and an air bearing surface  3 . The air bearing surface  3  includes an inlet step bearing surface  4 , inlet rails  5  and  6  respectively having an inlet rail surfaces, an outlet rail  7  having an outlet rail surface and holding a magnetic head  8 , two outlet step bearing surfaces  9  and  19 , three rising wall profiles  15   a ,  15   b  and  15   c , a negative-pressure groove  10 , and island  11  and  12  formed on the respective inlet rails  5  and  6 .  
         [0028]     The inlet rail surfaces of the inlet  5  and  6  and the outlet rail surface of the outlet rail  7  are substantially flush with each other and included in a reference plane. Air  20  that flows through a space between a slider and a magnetic disk  22  produces an aerodynamic pressure to cause the slider to fly over the magnetic disk  22 . Thus, the inlet rail surfaces  5  and  6  and the outlet rail surface of the outlet rail  7  serve as positive-pressure rail surfaces.  
         [0029]     The inlet step bearing surface  4  and the outlet step bearing surface  9  are substantially flush with each other and included in a plane including the inlet rail surface of the rails  5  and  6  and the outlet rail surface of the outlet rail  7 . Air  20  passes through the air inlet end  1  into the space between the slider and the magnetic disk  22 , then flows along the inlet step bearing surface  4  and the outlet step bearing surfaces  9  and  19 . The aerodynamic pressure of air  20  is increased by rising surface  13 ,  14 ,  15   a ,  15   b  and  15   c . Air  20  of an increased aerodynamic pressure flows along the inlet rail surfaces of the inlet rails  5  and  6  and the outlet rail surfaces of the outlet rail  7 .  
         [0030]     The aerodynamic pressure of air  20  flowing along the inlet rail surfaces of the inlet rails  5  and  6  and reaching the islands  11  and  12  is further increased to a high aerodynamic pressure sufficient to lift up the slider by the second rising surfaces  17  and  18 , i.e., the front surfaces of the island  11  and  12 . The height of the second rising surfaces  17  and  18  of the islands  11  and  12  from the inlet rail surfaces of the inlet rails  5  and  6  is on the order of 20 nm. The islands  11  and  12  need to have certain length in the flowing direction of air  20 , i.e., along the length of the slider, to produce a high aerodynamic pressure by the islands  11  and  12 . Such a high aerodynamic pressure, namely, an aerodynamic lift, can be produced by the island  11  and  12  having the second rising surfaces  17  and  18  of such a very low height.  
         [0031]     The stepped air flow surfaces  9  and  19  and rising wall profiles  15   a ,  15   b  and  15   c  are the foremost feature of the present embodiment. The first rising surfaces  13  and  14  of the inlet rails  5  and  6  produce aerodynamic pressure  30  and  31  to lift up the slider, and the second rising surfaces  17  and  18  of islands  11  and  12  increase the aerodynamic pressures to higher aerodynamic pressures  32  and  33 . The first rising profile  15   c  produces the aerodynamic pressure of the airflow, the aerodynamic pressure is increased while the air flows through the rising wall profiles  15   b  and  15   c , and produces the aerodynamic pressure  34   b  and  34   a  at outlet rail  7 .  
         [0032]     The length of the stepped surfaces  9  and  19  necessary for producing a high positive pressure is about 50 μm or longer, preferably about 100 μm or longer, and the stepped surface  19  is wider than stepped surface  9 . In this embodiment, the length of the island  11  and  12  is about 100 μm.  
         [0033]     Since the arrangement of the rising surfaces at two steps is effective in producing a high aerodynamic lift, the sizes of the inlet rails  5  and  6  and the outlet  7  can be reduced, therefore the negative pressure area is increased.  
         [0034]     The inlet rail surfaces of the inlet rails  5  and  6  and the outlet rail surfaces of the outlet rail  7  that serve in producing the aerodynamic pressure are positive-pressure rail surfaces. Since the area of the rail surfaces of the slider of the present embodiment necessary for producing a predetermined aerodynamic lift can be reduced, the reduction of the flying height at high altitude can be minimized, which will be described later.  
         [0035]     The depth  16  of the negative-pressure groove  10  from the plane including the inlet step bearing surface  4  is on the order of about 800 nm. The depth of the negative-pressure groove  10  from the reference plane including the inlet rail surfaces of the inlet rails  5  and  6  is on the order of about 1 μm.  
         [0036]     The depth of the stepped surface  19  from the plane including the outlet step bearing surface  9  is on the order of about 300 nm. The depth of stepped surface  9  from the reference plane including the inlet rail surfaces of the outlet rail  7  is on the order of about 200 nm.  
         [0037]     The slider in the first embodiment is the so-called Femto slider with 0.85 mm in length 0.7 mm in width and 0.23 mm in thickness. Generally, the area of the negative-pressure groove  10  decreases with the decrease of the area of the slider, negative pressure that can be produced by the slider decreases with the decrease of the area of the slider and, consequently, the reduction of the flying height at high altitude increases.  
         [0038]     At present, the magnetic disk drive has been progressively miniaturized and magnetic disks of smaller diameters that are rotated at low rotational speeds have been used. Consequently, negative pressure that can be produced by the slider has been progressively decreased. These matters are factors that increase the reduction of flying height at high altitude.  
         [0039]     As mentioned above, the present embodiment achieves the minimization of the reduction of the flying height at high altitude successively because the area of the rails of the slider in the first embodiment necessary for producing a predetermined aerodynamic lift can be reduced.  
         [0040]     The effect of the first embodiment will be concretely described. Air  20  causes the slider to fly over the disk  22  in an inclined position such that the flying height of the air inlet end  1  is higher than that of the air outlet end  2 . Consequently, the flying height  23  of the outlet rail surface of the outlet rail holding the magnetic head  8  is the lowest.  
         [0041]     If the flying height  24  of the back end of the island  11  and the flying height  25  of the back end of the island  12  is lower than the flying height  23  of the outlet rail surface of the outlet rail  7 , the islands  11  and  12  contact with the disk  22 . If the islands  11  and  12  contact with the disk  22 , the slider vibrates significantly and, in the worst case, the slider would crash. Therefore, the islands  11  and  12  of the slider must be designed such that the slider flies in a proper position and the flying heights  24  and  25  never decrease less than the flying height  23 .  
         [0042]      FIG. 5  is a plan view of a prior slider in Comparative example 1 disclosed in Patent document 1. This prior slider differs from the slider in the first embodiment in that the former does not include stepped surface  19  and rising wall profile  15   c  that have an effect of increasing the aerodynamic pressure. Therefore, the prior slider needs larger rail surfaces  7  than those of the first embodiment in order to make the slider fly at the same flying height, hence reducing the area of negative pressure and further decreasing the air bearing stiffness.  
         [0043]      FIG. 6  is a graph showing calculated flying height profiles, i.e., flying height distributions along the radius of a disk, of the slider in the first embodiment at altitudes of 0 m and 3000 m. The normal operation of the magnetic disk drive must be guaranteed for an altitude of 3000 m (about 0.7 atm.) and hence the reduction of the flying height at an altitude of 3000 m must be suppressed to the least possible extent. The disk was rotated at 5400 rpm.  
         [0044]     As illustrated in  FIG. 6 , the flying height reduction ratio, i.e., the ratio of a reduction of the flying height of the slider due to the increase of the altitude from 0 m to 3000 m, is in a range of about 6% to about 7%.  
         [0045]     Flying height profiles of the sliders in Comparative example 1 shown in  FIG. 5  at altitudes of 0 m and 3000 m are shown in  FIG. 6 . Flying height reduction ratio, i.e., the ratio of reductions of the flying heights of the sliders due to the increase in altitude from 0 m to 3000 m normalized by the flying height at the sea level. The flying height reduction ratio for the comparative example is in a range of about 13% to 20%. As illustrated in  FIG. 6 , the reduction of the flying height of the slider in the first embodiment due to the increase in altitude is very small.  
         [0046]     As mentioned above, the step surface  19 ,  9  and rising wall profiles  15   a ,  15   b  and  15   c  can increase the air bearing stiffness in translation and pitch direction in the trailing pad due to increasing the pressure gradient. The increase of air bearing stiffness also reduces its sensitivity on the manufacturing process tolerance.  FIG. 7  is a graph showing calculated flying height 3 Sigma of the magnetic head slider in a first embodiment and magnetic head slider in Comparative example 1. A 0.5˜0.6 nm reduction in flying height is achieved in the first embodiment compared to the Comparative example of a prior slider.  
         [0047]     An additional step surface and relative rising wall profile is in the first embodiment compared to the prior sliders; consequently, an additional process is done in the process of manufacturing, so that this process tolerance effect on slider flying height should be evaluated.  FIG. 8  shows the simulated flying height profiles of the magnetic head slider in a first embodiment for a +/−4% sub-deep depth tolerances, the effect of the sub-deep depth tolerance is very small; that is, the new structure of the slider in the first embodiment has very small effect on the flying height 3 Sigma.  
         [0048]     A load point where a suspension load  21  is applied to the slider in the first embodiment is set to the point between the air inlet end  1  and the center of the slider, and corresponds to the opposite side of the islands  11  and  12 . When the aerodynamic pressures  32  and  33  acting on the islands  11  and  12  decrease at high altitude, a moment M p  tending to decrease the flying height of the air inlet end  1  acts on the slider to suppress the decrease of the flying height  23  of the air outlet end  2 .  
       Second Embodiment  
       [0049]      FIG. 9  is a plan view of a magnetic head slider in a second embodiment according to the present invention. The slider in second embodiment has outlet rail  7 , and stepped surfaces  9 ,  19  and rising wall profiles  15   a ,  15   b  and  15   c , where the depth of surface  9  is different from that of surface  4  from the reference plane. The difference provides more choices for air bearing design. In this embodiment, stepped air surface  9  may be higher or lower than stepped air surface  4 . Air flow comes through the air inlet end  1  into the space between the slider and magnetic disk  22 , then flows along the inlet step bearing surface  4  and the outlet step bearing surfaces  19  and  9 . The aerodynamic pressure of air  20  is increased by rising profiles  13 ,  14 ,  15   a ,  15   b  and  15   c . Air  20  of an increased aerodynamic pressure flows along the inlet rail surfaces of the inlet  5  and  6  and the outlet rail surface of the outlet rail  7 . The depth difference between surface  4  and  9  can result in the difference of air bearing stiffness in the inlet rail and outlet rail, and achieve a slider design with lower altitude sensitivity.  
       Third Embodiment  
       [0050]      FIG. 10  is a plan view of a magnetic head slider in third embodiment according to the present invention. The stepped surface  19  is formed by a double U shape. The first rising profile  15   a  produces the aerodynamic pressure at the outlet rail  7 , then second rising profile  15   b  and third profile  15   c  further increases the aerodynamic pressure  34   b  and  34   a . The double U shape surface  19  and U shape  9  can increase damping and reduce the flying height sensitivity of the velocity such that the dynamic performances of the slider are improved.  
       Fourth Embodiment  
       [0051]      FIG. 11  is a plan view of a magnetic head in a fourth embodiment according to the present invention. The slider is less than 0.85 mm in length, less than 0.7 mm in width and less than 0.23 mm in thickness. Generally, the area of the negative-pressure groove  10  decreases with the decrease of the area of the slider, negative pressure that can be produced by the slider decreases with the decrease of the area of the slider and, consequently, the reduction of the flying height at high altitude increases. For that, more step surfaces  19   a ,  19   b ,  19   c ,  19   d  and rising wall profiles are formed in the front of the outlet rail  7  in order to increase the air bearing stiffness, hence the flying height loss due to higher altitude is suppressed and the flying height sensitivity on manufacturing process tolerance is reduced.  
         [0052]      FIG. 12  is a perspective view of a magnetic disk drive  35  provide with one of the magnetic head sliders of the first to fourth embodiments according to the present invention. The magnetic disk drive  35  is provided with a load/unload mechanism. The load/unload mechanism holds the magnetic head slider on a ramp while the magnetic disk drive is stopped or holds the magnetic head slider at a working position for a recording or reproducing operation above a magnetic disk  22  while the magnetic disk drive is in operation.  
         [0053]     The slider of the foregoing embodiments capable of reducing the reduction of flying height at high altitude improves the reliability of the magnetic head drive. The effect of the slider of the present invention is particularly significant when the slider of the present invention is applied to a magnetic disk drive provided with small magnetic disks smaller than 2.5-inch magnetic disks.  
         [0054]     It is to be understood that the above description is intended to be illustrative and not restrictive. Many embodiments will be apparent to those of skill in the art upon reviewing the above description. The scope of the invention should, therefore, be determined not with reference to the above description, but instead should be determined with reference to the appended claims alone with their full scope of equivalents.