Abstract:
An optical recording slider includes a slider body having a leading slider edge, a trailing slider edge and a center line extending from the leading slider edge to the trailing slider edge. The slider body carries an optical head along the center line. First and second longitudinal rails are positioned on the slider body. A third longitudinal rail is positioned on the slider body, between the first and second longitudinal rails and forward of the optical head. The third rail has a leading section, a waist section and a trailing rail edge. The leading section is rectangular and extends from the leading slider edge to the waist section. The waist section widens from a first width at the rectangular leading section to a maximum width of the third rail and then narrows from the maximum width toward the trailing rail edge. A recessed area extends from the leading slider edge to the trailing slider edge, between the first, second and third rails.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based on Provisional Application Ser. No. 60/049,658, filed Jun. 16, 1997. 
     Cross-reference is hereby made to U.S. Ser. No. 08/931,431, filed Sep. 16, 1997 and entitled SLIDER FOR OPTICAL DISC DATA STORAGE SYSTEM, which is based on Provisional Application Ser. No. 60/053,485, filed Jul. 23, 1997. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to disc drive storage systems and, more particularly, to a positive pressure slider having a wide center rail for slow disc speed and high flying height applications, such as optical disc drive storage systems. 
     In optical disc drive storage systems, data is accessed by focusing a laser beam onto the data surface of a rigid disc and detecting light reflected from or transmitted through the data surface. In general, data is stored in the form of physical or magnetic marks carried on the surface of the disc which are detected using the reflected laser light. There are a number of different optical disc technologies which are known in the industry. For example, CD-ROMs are currently used to store digital data such as computer programs or digitized music. Typically, CD-ROMs are permanently recorded during manufacture. Another type of optical system is write-once read-many (WORM) systems in which a user may permanently write information onto a blank disc. It is also desirable to provide a system which is erasable, such as phase change and magneto-optic (M-O) systems. Phase change systems detect data by sensing a change in reflectivity. M-O systems detect data by measuring the rotation of the incident light polarization due to the magnetic orientation of the storage medium. 
     High density optical recording, particularly near-field recording (i.e., M-O or phase change systems), typically requires an optical head gimbal assembly (OHGA) having a slider for carrying an optical element over the data surface of the optical media. U.S. Pat. No. 5,497,359, issued Mar. 5, 1996, entitled &#34;OPTICAL DISC DATA STORAGE SYSTEM WITH RADIATION-TRANSPARENT AIR-BEARING SLIDER&#34; shows an example of a slider for use with an optical disc drive storage system. 
     In order to write a magnetic bit of information onto the disc surface, the disc surface is optically heated. With M-O media, for example, the laser beam is directed through an optical aperture in the slider, which heats the disc surface to a point above the Curie temperature of the medium. A magnetic coil carried on the slider is energized and the laser is turned off. As the medium cools below the Curie temperature, the heated spot is left with a desired magnetic orientation. 
     An actuator mechanism moves the slider from track to track across the surface of the disc under the control of electronic circuitry. The actuator mechanism includes a track accessing arm and a suspension for each optical head gimbal assembly. The suspension includes a load beam and a gimbal. The load beam provides a preload force which forces the slider toward the disc surface. The gimbal is positioned between the slider and the load beam to provide a resilient connection that allows the slider to pitch and roll while following the topography of the disc. The slider has an air bearing surface which faces the disc surface. 
     There are generally two types of sliders used in the disc drive industry, positive pressure air bearing (PPAB) sliders and self-loading or &#34;negative pressure&#34; air bearing (NPAB) sliders. An NPAB slider typically has a pair of rails extending along the sides of the bearing, with a cavity dam or cross bar extending between the rails near the leading end of the slider. As the disc rotates, the surface of the disc drags air under the cavity dam by viscous friction. As the air passes over the cavity dam, the air expands into a &#34;cavity&#34; between the rails, which forms a partial vacuum in the cavity. The partial vacuum draws the slider closer to the disc surface and counteracts positive pressure developed along the rails. The cavity is open to atmospheric pressure at the trailing end of the slider, and may also include a center rail or an island at the trailing end of the slider to mount a single recording head. NPAB surfaces have many advantages, such as reduced take off and landing velocity during spindle start up and shut down, high bearing stiffness and lower sensitivity of flying height to changes in altitude and velocity, as compared to PPAB sliders having no cavity dam. 
     However, NPAB sliders are seldom used in ramp &#34;load-unload&#34; drive applications because of their high suction force. In these applications, the slider is unloaded from the disc surface by rotating the actuator mechanism until the suspension engages a ramp which lifts the suspension and thus the slider from the disc surface. The high suction force prevents an NPAB slider from following the suspension as the suspension rides up on the unloading ramp. The slider remains in close proximity to the spinning disc, and the ramp elastically deforms the suspension. The NPAB suction force breaks only when a significant elastic strain has accumulated in the suspension. The release of the suction force releases the elastic strain in the suspension and allows the slider to unload from the disc surface. This cycle of suction force and strain release occurs very rapidly relative to the time in which the suspension is in contact with the unloading ramp. The rapid release of elastic strain energy sets up vibratory oscillations in the slider position coordinate that is normal to the plane of the disc surface. These oscillations may be large enough to cause the slider to &#34;slap&#34; against the disc surface, thereby generating wear debris particles and possibly damaging the recording head. 
     Another problem observed with NPAB sliders during unloading occurs in the event that the unloading force exerted by the deformed suspension is too small to overcome the suction force. In this event, the suction force is broken when the slider is swung over the disc perimeter, allowing the atmosphere to flow into the cavity between the side rails with very little resistance. As the slider passes over the disc perimeter, pressurization between the side rails becomes unbalanced, causing the slider to roll to one side. As a result, the slider may contact the disc perimeter when unloading. Repetition of such contact causes wear on the slider and generates debris particles. 
     In contrast, PPAB sliders have a low suction force, making them more applicable for ramp load-unload drive applications than NPAB sliders. Although the side rails in a PPAB slider are not connected by a cavity dam, some air expansion typically occurs as the air is dragged under slider, if the slider has side rails with wide leading ends that transition to a narrow sections near the middle of the slider. The suction force due to these expansions is somewhat smaller than that obtained with the expansion over a cavity dam in an NPAB slider, which allows PPAB sliders to be used more effectively in ramp load-unload applications. A commonly encountered problem in PPAB sliders is that the flying height is much higher at the disc outer diameter (OD) than at the disc inner diameter (ID), particularly for applications having a low disc speed and a relatively high flying height, such as in optical disc drive storage systems. This can cause a reduction in the overall recording density achieved by the disc drive. 
     SUMMARY OF THE INVENTION 
     The optical recording slider of the present invention includes a slider body having a leading slider edge, a trailing slider edge and a center line extending from the leading slider edge to the trailing slider edge. The slider body carries an optical head along the center line. First and second longitudinal rails are positioned on the slider body. A third longitudinal rail is positioned on the slider body, between the first and second longitudinal rails and forward of the optical head. The third rail has a leading section, a waist section and a trailing rail edge. The leading section is rectangular and extends from the leading slider edge to the waist section. The waist section widens from a first width at the rectangular leading section to a maximum width of the third rail and then narrows from the maximum width toward the trailing rail edge. A recessed area extends from the leading slider edge to the trailing slider edge, between the first, second and third rails. 
     In one embodiment of the present invention, the first and second rails terminate prior to the trailing slider edge, and the third rail terminates prior to the trailing edges of the first and second rails. The maximum width of the third rail is preferably located at a position along the center line corresponding to a midpoint along the length of the first and second rails. The third rail further includes a rectangular trailing section extending and terminating prior to the optical head. 
     The narrow, rectangular leading section produces a relatively low suction force at the disc OD by providing a low air expansion ratio from the leading slider edge to the waist section, which improves the ramp unloading performance of the slider at the disc OD. In addition, the wide waist section increases the flying height at the disc ID while at the same time reduces the flying height at the disc OD. This results in a lower ID-to-OD rise. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a simplified illustration of an optical recording system employing a slider according to the present invention. 
     FIG. 2 is a plan view of the slider shown in FIG. 1 according to one embodiment of the present invention. 
     FIG. 3 is a computer-generated simulation of a pressure profile developed by the slider shown in FIG. 2 at the disc OD. 
     FIG. 4 is a plan view of a slider having a center rail with a narrow waist section as opposed to a wide waist section as in the slider shown in FIG. 2. 
     FIG. 5 is a graph comparing the flying height profiles of the sliders shown in FIGS. 2 and 4. 
     FIG. 6 is a plan view of a slider according to an alternative embodiment of the present invention. 
     FIG. 7 is a plan view of a slider according to another alternative embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 is a simplified illustration of an optical recording system 10 employing a slider in accordance with the present invention. System 10 includes optical disc 12 having a data surface which carries optically encoded information. Disc 12 rotates about spindle 14 and is driven by a spindle motor 16 which is mounted on base 18. A slider 20 is positioned proximate disc 12 and is coupled to an actuator 22. Actuator 22 includes armature 24 and actuator motor 26. Actuator motor is coupled to base 18. Slider 20 includes an optical aperture 30 which is spaced from an optical source/sensor apparatus 32. A controller 34 is electrically coupled to apparatus 32, actuator 26 and data bus 36 and is used for controlling operation of system 10. 
     During operation, spindle motor 16 rotates disc 12, and actuator 22 positions slider 20 radially over the data surface of disc 12. Controller 34 controls the position of slider 20, whereby information may be read from or written to disc 12 using optical source/sensor apparatus 32. This information may be received or transmitted on data bus 36. 
     FIG. 2 is a plan view of slider 20 according to one embodiment of the present invention. Slider 20 includes leading slider edge 40, trailing slider edge 42, side edges 44 and 46, center line 48, length 49 and width 51. Length 49 is measured from leading slider edge 40 to trailing slider edge 42, and width 51 is measured from side edge 44 to side edge 46. In one embodiment, slider 20 is a &#34;70-series&#34; slider, in which length 49 is about 4.00 mm and width 51 is about 2.20 mm. However, in other embodiments, slider 20 can have other sizes, such as the size of a &#34;50-series&#34; slider in which length 49 is about 2.00 mm and width 51 is about 1.60 mm or a &#34;30-series&#34; slider in which length 49 is about 1.25 mm and width 51 is about 1.0 mm. 
     Slider 20 further includes side rails 50 and 52, center rail 54 and optical head 56. Side rails 50 and 52 are positioned along side edges 44 and 46, respectively. Side rails 50 and 52 extend from leading slider edge 40 and terminate prior to trailing slider edge 42. In the embodiment shown in FIG. 2, side rails 50 and 52 terminate at a position along length 49 that substantially corresponds to the position of optical head 56. Center rail 54 is positioned along center line 48, between side rails 50 and 52. Center rail 54 extends from leading slider edge 40 and terminates prior to optical head 56 and the trailing edges of side rails 50 and 52. Side rails 50 and 52 and center rail 54 form air bearing surfaces 60, 62 and 63, respectively. Optical head 56 is aligned with center line 48 and is positioned between center rail 54 and trailing slider edge 42. 
     Slider 20 further includes recessed areas 66 and 68 which extend from leading slider edge 40 to trailing slider edge 42 and are positioned between center rail 54 and side rails 60 and 62, respectively. In one embodiment, recessed areas 66 and 68 are recessed from air bearing surfaces 60 and 62 by approximately 11.5 microns. Other depths can also be used. 
     Side rails 50 and 52 each include a leading section 70, a leg section 72, a waist section 74, a trailing section 76, an outside rail edge 90, an inside rail edge 92 and a trailing rail edge 94. Outside and inside rail edges 90 and 92 extend parallel to center line 48 along leading section 70, from leading slider edge 40 to leg section 72. Outside and inside rail edges 90 and 92 diverge from center line 48 along leg section 72, from leading section 70 to waist section 74. Outside and inside rail edges 90 and 92 extend parallel to center line 48 along waist section 74. Outside rail edge 90 extends parallel to center line 48 along trailing section 76, while inside rail edge 92 diverges from center line 48 along trailing section 76. Side rails 50 and 52 have a minimum rail width 100 at trailing rail edge 94. The divergence of inside rail edges 92 along trailing sections 76 forms a notch 98 at the trailing edge of each side rail. 
     With this geometry, leg sections 72 of side rails 50 and 52 angle toward center line 48 as they extend forward from waist section 74 to leading section 70. This causes leading sections 70 to have an offset 102 toward center line 48. By offsetting leading sections 70, the disc tangential velocity intersects the outside edges of leg sections 72 at an angle when slider 20 is positioned at the middle diameter (MD) of the disc. This &#34;angled leading rail&#34; configuration results in a reduction of the flying height at the disc MD, which improves the recording density on the middle data tracks. The middle diameter flying height (MDFH) is commonly quantified relative to the inner diameter flying height (IDFH) and the outer diameter flying height (ODFH) by an &#34;MD hump&#34; parameter, where: 
     
         MD hump=MDFH-[(IDFH+ODFH)/2] 
    
     The MD hump reflects a deviation of the middle diameter flying height from an ideal straight-line flying height profile between the inner diameter flying height and the outer diameter flying height. Reduction of the MD flying height therefore reduces the MD hump. 
     Notches 98 formed in side rails 50 and 52 counteract an increase in flying height at the disc OD caused by a higher disc tangential velocity at the disc OD. Notches 98 narrow the width of rails 50 and 52 to the minimum width 100 along trailing edge 94. The lift force on trailing sections 76 is equal to the pressure along the trailing sections times the area of the trailing sections. By cutting trailing sections 76 along notches 98, the lift force on trailing sections 76 decreases, resulting in a lower flying height at the disc OD. 
     Center rail 54 has lateral rail edges 110 and 112, a trailing rail edge 114, a narrow leading section 116, a wide waist section 118 and a narrow trailing section 120. Waist section 118 has transition sections 130 and 132 and a mid portion 133. Lateral rail edges 110 and 112 extend parallel to center line 48 along leading section 116 and then diverge from center line 48 along transition section 130 to a maximum rail width 134 at mid portion 133 of waist section 118. Lateral rail edges 110 and 112 extend parallel to center line 48 along mid portion 133 and then converge toward center line 48 along transition section 132. Lateral rail edges 110 and 112 extend parallel to center line 48 along trailing section 120. 
     In one embodiment, the maximum width 134 of center rail 54 is greater than the maximum rail width of side rails 50 and 52. Maximum width 134 is preferably located at a position along center line 48 corresponding to a midpoint along a length 136 of side rails 50 and 52. This provides increased lift at the center of the air bearing surfaces. Also, maximum rail width 134 is preferably confined to a range along center line 48 that corresponds to 1/5 and 2/3 of the length 136, as measured from leading slider edge 40. 
     The narrow, rectangular leading section 116 produces a relatively low suction force at the disc OD by providing a low air expansion ratio from leading edge 40 to waist section 118, which further improves the ramp unloading performance of slider 20 at the disc OD. In addition, the wide waist section 118 increases the flying height at the disc ID while at the same time reduces the flying height at the disc OD, which results in a lower ID-to-OD rise. The wide waist section 118 increases the flying height at the disc ID by increasing the lift force developed on the waist section. The lift force equals the positive pressure per unit area developed on the bearing surface times the area of the air bearing surface. Since the area of the air bearing surface is increased at the waist section, the total positive pressure developed on the waist section increases which increases the lift force. A higher lift force results in a higher flying height at the disc ID. 
     At the disc OD, the wide waist section 118 of center rail 54 generates higher positive pressure toward the front of center rail 54, as discussed above. However, narrowing center rail 54 along transition section 132 and trailing section 120 creates air expansion or subambient pressure regions 140 and 142 adjacent optical head 56 within recessed areas 66 and 68. Air expansion within regions 140 and 142 is further increased by notches 98 in side rails 50 and 52. This results in a higher suction force behind center rail 54 at the disc OD. A high lift force at the front end of center rail 54 lifts the leading portion of slider 20 while a high suction force at the trailing end of center rail 54 sucks the trailing portion of slider 20 down toward the disc surface, which increases the pitch angle of slider 20 at the disc OD. Since optical head 56 is located behind center rail 54, the flying height at the disc OD of optical head 56 decreases. 
     A relatively shallow leading step surface 150 is formed at the leading edge of side rails 50 and 52 and center rail 54. Each leading step surface 150 extends along the leading section of the rail, from leading slider edge 40 to a substantially vertical face 152. Face 152 extends from leading step surface 150 to the respective air bearing surface of the rail. Each leading step surface 150 is recessed from and parallel to the air bearing surfaces for easing pressurization of air bearing surfaces 60, 62 and 63. 
     The air bearing surface features of slider 20 can be formed by ion milling, chemical etching or Reactive Ion Etching (RIE), for example, with one or more masking and etching iterations. Forming leading step surfaces 150 by ion milling, chemical etching or Reactive Ion Etching reduces the sensitivity of the slider&#39;s flying characteristics to manufacturing tolerances as compared to similar tapered surfaces which are typically formed by less accurate lapping processes. 
     FIG. 3 is a graph illustrating a computer-generated simulation of the pressure developed on slider 20 at the disc OD. The locations of the side rails and the center rail are represented by arrows 50, 52 and 54, respectively. The location of the optical head is represented by arrow 56. Lines indicating above ambient pressure are oriented out of the page while lines indicating below ambient pressure are oriented into the page. At the disc OD, air flow 160 is orientated at an angle 162 with respect to slider center line 48. As the air is dragged beneath slider 20, the air compresses along side rails 50 and 52 and center rail 54, which develops positive pressure on side rails 50 and 52 and center rail 54. Air expansion in regions 104, 106, 140 and 142 develops areas of subambient pressure. 
     FIG. 4 is a plan view of a slider having a thin, rectangular center rail, as opposed to a wide center rail. The same reference numerals are used in FIG. 4 as were used in FIG. 2 for the same or similar elements. Slider 160 has a leading edge 40, a trailing edge 42, side rails 50 and 52, center rail 162 and optical head 56. Center rail 162 has the same length as center rail 54 shown in FIG. 2 but does not have a wide waist section. Rather, the waist section of center rail 162 is relatively narrow. 
     FIG. 5 is a graph illustrating the results of flying height comparison of the sliders shown in FIGS. 2 and 4. The flying height in microinches is plotted as a function of the disc radius in inches. Line 170 represents the flying height of slider 20. Line 172 represents the flying height of slider 160. Application of the wide center rail on slider 20 reduced the ID-to-OD rise by 50 percent as compared to the ID-to-OD rise of slider 160. Also, the flying height of slider 20 is maintained significantly higher at the disc ID than slider 160. These characteristics are particularly useful in large disc drive applications having a relatively low disc rotational velocity and a high target flying height, such as in optical disc drive storage systems. 
     Referring back to FIG. 2, optical head 56 optically couples optical source/sensor apparatus 32 (shown in FIG. 1) to the surface of disc 12. In one embodiment, the optical aperture includes a solid immersion lens (SIL) which is formed by an objective lens, a cap lens and a MESA. A plurality of conductors (not shown) are coiled around the MESA for providing an electromagnetic field. Conductive traces 180 and 182 (shown in phantom) are applied to the floor of recessed areas 66 and 68 for providing current to the coils surrounding the MESA. 
     To write data on a magneto-optic (M-O) disc, optical source/sensor apparatus 32 directs a laser beam through the SIL-type lens in optical head 56 to heat a small spot on the disc surface to a temperature above the Curie temperature of the magnetic medium. The coil surrounding the MESA is energized and the laser is turned off. As the magnetic medium cools below the Curie point, the heated spot is left with the desired magnetic orientation. 
     Data is read from the M-O disc by reflecting the laser beam off of the disc surface and measuring the rotation of the polarization of the reflected beam. Optical head 56 and source/sensor apparatus 32 are described in greater detail in U.S. application Ser. No. 08/931,431, filed Sep. 16, 1997 and entitled SLIDER FOR OPTICAL DISC DATA STORAGE SYSTEM, which is hereby incorporated by reference. U.S. Ser. No. 08/931,431 is based on U.S. Provisional Application Ser. No. 60/053,485 which was filed on Jul. 23, 1997. 
     FIG. 6 is a plan view of an optical recording slider according to an alternative embodiment of the present invention. The same reference numerals are used in FIG. 6 as were used in FIG. 2 for the same or similar elements. Slider 200 includes leading slider edge 40, trailing slider edge 42, side edges 44 and 46, side rails 50 and 52, center rail 54 and optical head 56. In this embodiment, waist section 118 of center rail 54 is lengthened toward optical head 56, and the rectangular trailing section 120 (show in FIG. 2) is removed. Also, trailing sections 76 of side rails 50 and 52 extend beyond optical head 56 along the length of slider 200. In addition, a stepped trailing surface 202 has been added to trailing section 76 of each side rail 50 and 52 at trailing rail edge 94. Trailing step surface 202 is recessed from and parallel to air bearing surfaces 60 and 62 of side rails 50 and 52. Trailing step surfaces 202 increase pitch stiffness while keeping the lowest flying point of slider 200 as high as possible. 
     FIG. 7 is a top plan view of an optical recording slider according to another alternative embodiment of the present invention. Again, the same reference numerals are used in FIG. 7 as were used in FIG. 2 for the same or similar elements. In FIG. 7, side rails 50 and 52 extend all the way to trailing slider edge 42. 
     The optical recording slider of the present invention provides a low suction force at the disc OD for ramp load-unload drive applications and reduces the rise in flying height from the disc ID to the disc OD. These advantages are particularly useful for low disc speed and high flying height applications, such as optical disc drive storage systems. 
     Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.