Slider With Transverse Ridge Sections Supporting Air-Bearing Pads and Disk Drive Incorporating the Slider

This invention relates to data recording disk drives, and more particularly to a disk drive having an improved transducer carrier at the head-disk interface.

Disk drives, also called disk files, are information storage devices that use a rotatable disk with concentric data tracks containing the information, a head or transducer for reading and/or writing data onto the various tracks, and an actuator connected to a carrier for the head for moving the head to the desired track and maintaining it over the track centerline during read or write operations. There are typically a plurality of disks separated by spacer rings and stacked on a hub that is rotated by a disk drive motor. A housing supports the drive motor and head actuator and surrounds the head and disk to provide a substantially sealed environment for the head-disk interface.

In conventional magnetic recording disk drives, the head carrier is an air-bearing slider that rides on a bearing of air above the disk surface when the disk is rotating at its operational speed. The slider is maintained next to the disk surface by a relatively fragile suspension that connects the slider to the actuator. The slider is either biased toward the disk surface by a small spring force from the suspension, or is "self-loaded" to the disk surface by means of a "negative-pressure" air-bearing surface on the slider. Contact start/stop (CSS) disk drives operate with the slider in contact with the disk surface during start and stop operations when there is insufficient disk rotational speed to maintain the air bearing. In contrast to CSS disk drives, "load/unload" disk drives mechanically unload the slider from the disk when the power is turned off, typically by means of a ramp which contacts the suspension when the actuator is moved, and then load the slider back to the disk when the disk has reached a speed sufficient to generate the air bearing. Both types of disk drives maintain a relatively thin lubricant film on the disk surface to prevent damage to the head and disk caused by any contact between the head and disk.

It has been known since the early days of magnetic recording that minimizing the head-disk spacing is desirable because the amplitude of the read signal from the disk increases with decreasing head-disk spacing. Higher recording densities can thus be achieved. In conventional, commercially available air-bearing disk drives the minimum achievable head-disk spacing is typically between 1000-2000 Angstroms. In addition, this spacing is not maintained constant, but varies with disk radius because the air velocity beneath the air-bearing slider is directly proportional to the relative velocity of the disk beneath the slider. To both minimize the head-disk spacing and to maintain it constant with disk radius, liquid bearings have been proposed as possible alternatives to the conventional air bearing at the head-disk interface in magnetic recording disk drives. For example, in assignee's pending application, U.S. Ser. No. 264,604, filed Oct. 31, 1988, and published May 9, 1990, as European published application EP 367510, a disk drive is described which uses a continuously recirculating, low-viscosity liquid lubricant which is maintained as a relatively thick layer on the disk, and a transducer carrier that has triangular-shaped feet to plow through the low-viscosity liquid layer. The EP 367510 reference suggests that a head-disk spacing of approximately 500 Angstroms can be obtained with a liquid film having a thickness of approximately 10,000 Angstroms. Similarly, in U.S. Pat. No. 5,097,368 assigned to Conner Peripherals, filed Dec. 20, 1989, and issued Mar. 17, 1992, a recirculating liquid-bearing disk drive is described in which a head-disk spacing of approximately 300-700 Angstroms can be achieved at the operating speed of a conventional air-bearing disk drive if a load of approximately 45 grams is applied to force the head carrier against the liquid bearing (see FIG. 6 of the '368 patent).

In U.S. Pat. No. 4,901,185 assigned to Toshiba, filed in the U.S. on Jul. 10, 1986, and issued Feb. 13, 1990, the problems of minimizing and maintaining constant the head-disk spacing are addressed by a disk drive which uses a combined air and liquid bearing to support the transducer carrier. An air-bearing slider provides support for the forward portion of the carrier while the rear portion, which includes the magnetic head, contacts and is supported by a conventional liquid lubricant film. The '185 patent suggests that a head-disk spacing of less than approximately 800 Angstroms can be achieved using a lubricant film of greater than approximately 200 Angstroms thickness.

More recently, in assignee's U.S. Pat. No. 5,202,803, filed Jul. 2, 1991, and issued Apr. 13, 1993, a disk drive is described in which a conventional nonrecirculating, high-viscosity lubricant film is maintained on the disk and the transducer carrier is a modified three-rail air-bearing slider that has a rear "ski" pad. When the disk drive reaches operating speed, the air-bearing effect of the slider rails provides the primary support for the carrier, while the rear ski pad, which supports the magnetic head, contacts the lubricant film. The thickness of the lubricant film on the disk is approximately 20-100 Angstroms, which would also be the approximate head-disk spacing between the rear pad and the disk surface, assuming a perfectly smooth disk surface.

While liquid-bearing disk drives present the opportunity for closer head-disk spacing than air-bearing disk drives, they also present several difficulties. The carrier must provide a low-static friction ("stiction") interface when the carrier is at rest on the disk because liquid-bearing disk drives have thicker lubricant films and smoother disks than air-bearing disk drives. The carrier must also be designed to create small drag through the liquid film and to minimize liquid depletion from the disk. In addition, the carrier must be able to perform adequately over a wide range of relative carrier-disk velocities which occur at different disk radii.

What is needed is a disk drive with an improved head-disk interface that takes advantage of an air bearing to avoid the problems associated with liquid bearings, yet provides a head-disk spacing that is significantly less than even that achievable by a liquid bearing, and is less sensitive to variation with disk radius and to variations in head-carrier manufacturing parameters.

The invention is a disk drive having an improved head-disk interface provided by a transducer carrier that is essentially a low-flying, air-bearing slider designed to also function in contact and near contact with the lubricant film on the disk. The slider has a front air-bearing surface in the form of a pair of air-bearing pads, a rear centrally-located air-bearing pad, and a central nonair-bearing surface that separates the front and rear air-bearing pads. The two front pads have a surface area greater than that of the rear pad and thus provide a positive pitch up of the slider. This causes the rear pad to also be pitched up. This pitch, coupled with a step taper at the rear pad, permits air to flow beneath the rear pad to generate an air bearing in the rear portion of the slider. The presence of the central nonair-bearing region eliminates any lift in the central part of the slider, which allows for tight tolerances at the low-flying height. The flying height of the rear pad of the slider above the disk is controlled by the width of the rear air-bearing pad. The rear pad has its leading edge wider than its trailing edge so that it can withstand contact with the lubricant film on the disk, typically at the lower disk velocities near the disk inside diameter, without generating unacceptable drag forces or depleting the lubricant. The rear pad also has a skewed leading edge that compensates for skew of the slider to minimize the flying height variation from the disk inside diameter to outside diameter. In the preferred embodiment, the disk drive is a load/unload disk drive so that, under normal conditions, the slider does not contact the disk when the disk is not rotating.

For a fuller understanding of the nature and advantages of the present invention, reference should be made to the following detailed description taken together with the accompanying drawings.

FIG. 1 is a view in section of a schematic of the disk drive of the present invention.

FIG. 2 is an open top view of the disk drive depicted schematically in FIG. 1.

FIG. 3 is a plan view of the bottom or disk side of the preferred embodiment of the air-bearing slider of the present invention.

FIG. 4 is a sectional view of the slider-disk interface of the present invention illustrating the front and rear air-bearing pads and the intermediate nonair-bearing surface.

FIGS. 5A-5E are sectional views of the slider illustrating sequential steps in its fabrication.

FIGS. 6, 7, and 8 are plan views of the disk sides of alternative embodiments of the slider according to the present invention.

Referring first to FIG. 1, there is illustrated in sectional view a schematic of the disk drive according to the present invention. The disk drive comprises a base 10 to which are secured a disk drive motor 12 and an actuator 14, and a cover 11. The base 10 and cover 11 provide a substantially sealed housing for the disk drive. Typically, there is a gasket 13 located between base 10 and cover 11 and a small breather port (not shown) for equalizing pressure between the interior of the disk drive and the outside environment. This type of disk drive is described as being substantially sealed since the drive motor 12 is located entirely within the housing and there is no external forced air supply for cooling the interior components. A magnetic recording disk 16 is connected to drive motor 12 by means of hub 18 to which it is attached for rotation by the drive motor 12. A thin continuous film 50 of a relatively high-viscosity lubricant is maintained on the surface of disk 16. In the preferred embodiment, the lubricant is a conventional perfluoro-polyether (PFPE) disk lubricant, such as Demnum SP brand from Daikin, and is formed to a thickness of approximately 40 Angstroms. A read/write head or transducer 42 is formed on the trailing end of an air-bearing slider 20. Transducer 42 may be an inductive read and write transducer or an inductive write transducer with a magnetoresistive (MR) read transducer formed by thin film deposition techniques as is known in the art. The slider 20 is connected to the actuator 14 by means of a rigid arm 22 and a suspension 24, the suspension 24 providing a biasing force which urges the slider 20 onto the surface of the recording disk 16. During operation of the disk drive, the drive motor 12 rotates the disk 16 at a constant speed, and the actuator 14, which is typically a linear or rotary voice coil motor (VCM), moves the slider 20 generally radially across the surface of the disk 16 so that the read/write head may access different data tracks on disk 16.

FIG. 2 is a top view of the interior of the disk drive with the cover 11 removed, and illustrates in better detail the suspension 24 which provides a force to the slider 20 to urge it toward the disk 16. The suspension may be a conventional type of suspension such as the well-known Watrous suspension, as described in U.S. Pat. No. 4,167,765 assigned to IBM. This type of suspension also provides a gimbaled attachment of the slider which allows the slider to pitch and roll as it rides on the air bearing. In the preferred embodiment of the disk drive, a load/unload ramp 30 is mounted to the base 10. Ramp 30 contacts suspension 24 and lifts the slider 20 away from the disk 16 when the actuator 14 rotates the slider 20 toward the disk outside diameter when the disk drive is powered down. Examples of conventional types of load/unload ramps are described in U.S. Pat. Nos. 3,984,873 assigned to Information Storage Systems, Inc. (see FIG. 5), and 5,027,241 assigned to Quantum Corporation. The data detected from disk 16 by the transducer 42 is processed into a data readback signal by signal amplification and processing circuitry in the integrated circuit chip 15 located on arm 22. The signals from transducer 42 travel via flex cable 17 to chip 15, which sends its output signals via cable 19.

The bottom or disk side of slider 20 is shown in FIG. 3, and the side view of slider 20 in its air-bearing relationship with disk 16 and lubricant film 50 is shown in FIG. 4. The front air-bearing surface is a pair of air-bearing pads 25, 27 which provide the air-bearing effect to support the front end of slider 20 above the disk 16 when the disk is at its operational speed. The pads 25, 27 extend from a front ridge section 23 that acts as a step taper for the pads. The pads 25, 27 are generally equally spaced about the slider longitudinal centerline 60. The front pads 25, 27 have convex curved leading edges to minimize the air drag and to brush aside any particulate debris that may be present on the disk. A rear air-bearing pad 29 extends from a rear ridge section 26 that also acts as a step taper. Ridge sections 23, 26 are oriented generally parallel with each other and perpendicular to longitudinal centerline 60. The ridge sections 23, 26 are separated by a central nonair-bearing surface 28 which extends across the entire width of slider 20. The nonair-bearing surface 28 removes any air lift in that region of the slider 20, thus minimizing the total air lift on slider 20 and assuring that the front end is pitched up to enable air to flow under pitched-up rear pad 29.

The rear pad 29 has a leading edge 31 which is wider than its trailing edge 33. The sides 35, 37 of rear pad 31 are thus slanted relative to the length of the slider. In the preferred embodiment, the sides 35, 37 are angled approximately 20 degrees relative to the longitudinal axis of the slider. By making the rear pad 29 wider in the front than in the back, the rear pad 29 is prevented from acting as a plow, thereby minimizing depletion of the lubricant in the wake of movement of the disk 16 under the rear pad 29 during any contact of the pad 29 with the lubricant film 50. This also maintains low drag and minimizes thinning of the lubricant under the pad 31.

In disk drives with rotary actuators, the longitudinal axis of the slider is tangent to the disk at only one track position. For example, in one commercially available 2.5 inch disk drive the slider is skewed at approximately minus 4 degrees at the inside diameter (ID) and positive 17 degrees at the outside diameter (OD). By making the angle of the sides 35, 37 of rear pad 31 greater than the maximum absolute value of skew, for example approximately 20 degrees, it is assured that the rear pad remains nonplowing over the complete angle range of operation of the disk drive as the slider moves from disk ID to disk OD.

The rear pad 29 is also asymmetric in that its leading edge 31 is nonparallel or slanted relative to the trailing edge 33. This skewed leading edge provides extra air-bearing lift at the disk ID where the local disk velocity is low and less lift at the disk OD where the air-bearing effect is greater due to the higher local disk velocity.

As shown in FIG. 3, the total surface area of front air-bearing pads 25, 27 is greater than the surface area of rear pad 29. This feature, and the presence of the nonair-bearing surface 28 separating the two ridge sections 23, 26, results in a positive pitch up of the slider 20 (see FIG. 4) which causes rear pad 29 to also have a positive pitch, thereby enabling the air-bearing effect beneath pad 29 to support the rear portion of slider 20.

The area of the front pads 25, 27 and the depth of the step taper surface of ridge section 23 relative to the pads affect the slider-to-disk stiction, the flying height of the front pads, and the lift on the rear pad 29. The stiction has been found to be directly proportional to the area of the slider wetted by the lubricant from film 50 and inversely proportional to the separation between the slider and the disk, where "separation" is the distance from the disk to the part of the slider which is just wetted.

Since low stiction is desired, the area of the pads 25, 27 must be kept low in combination with a large depth of the surface of ridge section 23. However, the area of pads 25, 27 must also be sufficient to provide the positive pitch of the slider in operation. With the same pad area, different combinations of length-to-width ratio (L/W) of each of the pads 25, 27 can be used. ("Length" of the pads 25, 27 is the direction parallel to centerline 60.) It has been determined that as L/W increases for a given pad area, the total lift begins to decrease and thus L/W should not exceed approximately 2. If L/W is made too small, however, the slider loses roll stiffness, and the tolerances due to manufacturing variances become unacceptable. Thus, L/W should not be less than approximately 0.25.

The depth of the step taper surface of ridge section 23 must also be chosen with regard to flyability. For example, if this depth is too low, the lift will be too small and the pad area will have to be increased. It is also desirable to select a depth such that any change in the depth due to manufacturing tolerances will cause only a very small resulting change in the flying height of the front pads 25, 27. Taking these considerations into account, it has been determined that the depth must be greater than the flying height of the slider in the rear, and less than approximately 3 times the flying height of the slider in the front. For cases where the slider is designed to be in contact, the "flying height" becomes essentially the waviness and effective roughness of the disk.

In one experimental example the slider 20 was designed, by appropriate selection of suspension preload and air-bearing pad size and shape, to fly at the disk ID on a theoretically smooth disk with a spacing between the front pads 25, 27 and disk 16 of approximately 1000 Angstroms and a spacing between the rear pad 29 and disk 16 of approximately 100 Angstroms. The leading edge 31 of rear pad 29 was slanted or skewed at an angle of approximately 20 degrees relative to trailing edge 33. This slider was tested on a disk having a conventional amorphous carbon overcoat and a lubricant film of approximately 40 Angstroms of Demnum SP. The ID velocity was 4.4 m/sec with a skew of -6.7 degrees, and the OD velocity was 9.5 m/sec with a +14 degree skew angle. The suspension preload was 5 gm. Under these conditions, the slider-disk spacing (the spacing between the top of the disk carbon overcoat and the bottom of rear pad 29) was approximately 100 Angstroms at the ID and 150 Angstroms at the OD. Measurements of the drag force on the slider indicated that it dropped from a relatively high value to an essentially constant relatively low value at a velocity of approximately 3.5 m/sec, which is the approximate velocity at which the rear pad 29 is making minimal contact with the lubricant film. Because the disk 16 is not perfectly smooth but has a peak-to-peak waviness within the range of the designed flying height, it is believed that the rear pad 29 is at least partially contacting the lubricant film 50 up until approximately 7 m/sec, at which point the air bearing is fully supporting the rear pad 29. Based on correlations of drag force with flying height, it is estimated that during the period the rear pad 29 is in contact with the lubricant film 50, the air bearing generated beneath pad 29 due to its positive pitch and ion-milled step taper provides approximately 90% of the support for the rear half of slider 20. The designed flying height is controlled by the width of the rear pad 29. For example, decreasing this width by 60 microns, while maintaining all other parameters the same, caused the drag profile to flatten out at approximately 5.5 m/sec rather than 3.5 m/sec. The fact that lift is concentrated over small areas of the slider, compared to conventional sliders where it is distributed over essentially the whole slider surface, makes the slider substantially insensitive to manufacturing tolerances, especially tolerances for crown and camber.

The slider design of the present invention enables the slider to function in both the air-bearing and contact head-disk interface regimes. While the slider provides an extremely low-flying height air-bearing support over a substantial part of the disk, the unique design, particularly the design of the rear pad, enables the slider to also be in contact and near contact with the lubricant film on the disk without deleterious effects. The result is a low-flying height disk drive which can also operate in the contact and near-contact regimes, yet without the disadvantages presented by conventional liquid bearings.

The preferred method of manufacturing the slider will be described with reference to FIGS. 5A-5E, which illustrate the steps of manufacturing the slider depicted in FIGS. 3 and 4. FIGS. 5A-5E are sectional views of the slider taken through a section intersecting the front air-bearing pad 27.

In FIG. 5A the body of the slider 20, which is typically formed of a conventional ceramic mixture of titanium carbide (TIC) and alumina (Al.sub.2 O.sub.3), has been saw cut to remove its central portion and thereby define the center nonair-bearing surface 28, which separates front ridge section 23 from rear ridge section 26. The depth of the cut can be in the range of 10-100 microns. (As is known in the art, the sliders are processed in rows and then cut into individual sliders, so that FIG. 5A is actually the end view of a row of sliders.) Next, as shown in FIG. 5B, the ends of the ridge sections 23, 26 are rough lapped and polished to the correct height for the transducer 42 (FIG. 4) to be formed later. A layer of photoresist 63, such as Riston brand of poly methylmethacralate (PMMA), is then deposited on top of the ridge sections 23, 26 to a thickness of approximately 0.1 millimeters. The photoresist is then exposed through a suitable mask which defines a pattern corresponding to the air-bearing pads, including pad 27, as shown in FIG. 5C. (Front pad 25 and rear pad 29 are also formed at this time but are not shown in FIG. 5C because it is a sectional view only through front pad 27.) The row of sliders is then ion milled or otherwise etched to the desired depth, e.g., 0.2 microns, to build the air-bearing pads, as shown in FIG. 5D. The photoresist is then removed (FIG. 5E) and the row of sliders cut into the individual sliders.

The design of the slider according to the present invention enables a manufacturing process which is simplified over the process for manufacturing conventional air-bearing sliders of the type having air-bearing rails. Because there are no rails with their typically complex geometries, it is not necessary to use reactive ion etching or other complex steps to remove material from the center of the slider body. Instead, a single and much simpler saw cut is used to define the parallel ridge sections 23, 26. Also, as can best be seen in FIG. 4, all of the air-bearing pads are coplanar and are thus formed by a single photoresist process step.

An alternative embodiment of the slider is illustrated in FIG. 6. The alternative slider 70 is similar to slider 20 (FIG. 3) except that the front ridge section comprises two laterally spaced-apart ridge areas 72, 74, and the rear ridge section 76 does not extend across the entire width of the slider 70. The slider 70 is used when the desired material removal step for the central part of the slider is by reactive ion etching (RIE), rather than the saw cut for the embodiment of FIG. 3. The whole area, including the area between ridge areas 72, 74 and the areas on the sides of ridge section 76, can be removed in a single RIE step, resulting in the central nonair-bearing region 77 separating ridge areas 72, 74 from ridge section 76.

The embodiment of slider 80 shown in FIG. 7 is identical to that of slider 20 of FIG. 3, with the exception that a taper 82 is added to the front of ridge section 84 to improve the pitch and to better direct the air beneath front pads 86, 88. The taper 82 is lapped at an angle relative to the flat surface of ridge section 84, and requires an additional processing step during manufacture.

The embodiment of slider 90 in FIG. 8 has front struts 91, 92 that extend from front air-bearing pads 93, 94, respectively, and a rear strut 95 that extends from rear air-bearing pad 96. The struts 91, 92, 95 extend out from their respective pads a distance of approximately 500 to 1500 Angstroms, which is sufficient to support the pads out of contact with the lubricant film, thereby minimizing the static friction and low-velocity drag of the slider 90 during start up of the disk drive when the slider 90 is in contact with the disk. In the manufacture of the slider 90, a first ion-milling step is required to form the struts 91, 92, 95, followed by a second ion-milling step to form the air-bearing pads 93, 94, 96 around their respective struts. The front struts 91, 92 can be formed to have a greater thickness, by deposition of material, than the rear strut 95 so that the slider 90 has a positive pitch up when at rest on the disk. The struts, as well as the air-bearing pads around them, provide lift in the front and rear.

The slider embodiments shown in FIGS. 4, 6, 7, and 8 can also include an amorphous carbon film, as is known in the art for use on slider air-bearing surfaces, which is deposited on the entire front portion of the slider to a suitable thickness, e.g., 2000 Angstroms. The carbon film has the effect of jacking up the front part of the slider when the slider is at rest on the disk to thereby minimize the amount of pad surface area that is in contact with the disk and/or the lubricant. Since the carbon film is only on the front portion of the slider, it results in a reduction in stiction without otherwise affecting the performance of the slider. In this embodiment, the front pads are not coplanar with the rear pad.

The struts in FIG. 8 and the carbon film on the front portion of the carrier improve the performance of the drive in both CSS disk drives and in L/UL disk drives in the event of a failure of the L/UL system. In both cases, the struts and the carbon film raise up the carrier above the lubricant film when the carrier is on the disk and the disk drive is not operating.

While the preferred embodiments of the present invention have been illustrated in detail, it should be apparent that modifications and improvements may be made to the invention without departing from the spirit and scope of the invention as described in the following claims.