Patent Application
20100265618
The present application is directed to a read-write head for a disk drive with a protruding feature on the air bearing surface adapted to penetrate into the lubricant while reliably performing read-write operations, thereby reducing head-media spacing (HMS).
The realization of a data density of 1 Terabyte/inch2 (1 Tbit/in2) depends, in part, on designing a head-disk interface (HDI) with the smallest possible head-media spacing HMS. As used herein, “head-media spacing” or “HMS” refer to the distance between a read or write sensor and a surface of a magnetic media.
As illustrated in
The head 42 contributes head carbon overcoat (HOC) 52, sensor recession (SR), slider waviness and roughness, and the thickness and roughness of the lubricant attached to the carbon overcoat 52. The media 32 contributes media carbon overcoat (MOC) 56, media waviness and roughness, the lubricant layer 50 and the roughness of the lubricant 58.
The carbon overcoat is constructed from a film of hard carbon called diamond-like carbon. As used herein, the phrases “diamond-like carbon” and “carbon overcoat” refer to a material that is chiefly made of carbon, has a tetrahedral and/or amorphous structure, and exhibits a hardness of the order of about 2×109 to about 8×1010 Pa in Vickers hardness measurement. Further discussion of DLC can be found in U.S. Pat. No. 7,488,429, which is incorporated herein by reference. The lubricating layer is made of a variety of materials, such as for example PFPE (perfluoropolyether).
Conventional heads, such as illustrated in
As illustrated in
The shape of the actuated portion 44 depends on a number of variables, such as for example the relative size and placement of the heaters 60, 62, the thickness and material from which the air bearing surface 46 is constructed, and the like. “Actuated portion” refers to a section or subset of the air bearing surface that is adapted to be expanded by actuators used during a contact detection process and/or during read-write sequences. For many embodiments, the actuated portion is in proximity to heaters used to thermally expand the air bearing surface. Since the actuated portion is a subset of the air bearing surface, reference to the air bearing surface by implication includes both the actuated portion and the un-actuated portion of the air bearing surface.
As illustrated in
During read-write operations the actuated portion 44 typically remains thermally expanded above the primary portion of the air bearing surface. As illustrated in
Contact detection between the head and the media can be performed with a variety of methods including, position signal disturbance stemming from air bearing modulation, amplitude ratio and harmonic ratio calculations based on Wallace equations, and piezoelectric based acoustic emission sensors, such as disclosed in U.S. Pat. Publication 2009/0015962 (Daugela et al.). U.S. Pat. No. 7,440,220 (Kang et al.) takes advantage of a plateau in transducer spacing reached by actuating the expanding heater at the disk avalanche based on a read back signal. The plateau is interpreted as the point at which contact between the head and disk occurs, thus leveling of sensed magnetic signal improvement.
Manufacturing variability of the heads 42 creates the need to increase the active clearance 41 to reduce the chance of the head 42 impacting the carbon overcoat 56 and the lubricant 50. If this buffer or safety factor is reduced to decrease HMS, a larger percentage of the heads 42 will fail during manufacturing due to head modulation leading to signal degradation. A larger buffer increases HMS 30 so as to reduce data density. As the disk drive industry attempts to achieve a data density of 1 Tb/in2 manufacturing yield of heads 42 has dropped to commercially unsustainable levels. Many in the industry believe that current disk drive designs have reached the limits of physics.
Total HMS can be calculated using the following equation:
HMS=HOC+MOC+Lubricant thickness+SR+Clearance+GA
A discussion of head and media roughness, also referred to as glide avalanche (GA), can be found in Mate et al., Will the Numbers Add Up for Sub-7-nm Magnetic Spacing?, Vol. 41, No. 2 IEEE Transactions on Magnetics 626 (2005). Glide avalanche accounts for the topographical contributions of the head and media including the lubricant roughness. Media waviness is discussed in Weimin et al., Disk Shape and Its Effect on Flyability, Vol. 39, No. 2 IEEE Transactions on Magnetics 735-739 (2003). Thickness and roughness of lubricant attached to head and media is discussed in Mate et al., Roughness of Thin Perfluoropolyether Lubricant Films: Influence on Disk Drive Technology, Vol. 37, No. 4 IEEE Transactions on Magnetics 1821-1823 (July 2001).
The current practice is to apply a relatively thick carbon overcoat 52, 56 to both the read-write sensors 36, 38 and the magnetic media 32 that offers both corrosion protection and wear durability. The read-write sensors 36, 38 are typically protected by a carbon overcoat 52 about 20-30 Angstroms thick (1 Angstrom=1×10−10 meters). The head 42 is typically maintained in the active clearance 41 (see
For data densities in the 1 Tb/in2 range the HMS 30 will need to be reduced to about 60 Angstroms to about 65 Angstroms (see, R. Wood, The Feasibility Of Magnetic Recording At 1 Terabit Per Square Inch, Vol. 36 IEEE Transactions on Magnetics 716-721 (2000)). At this HMS level, however, head-lubricant interaction will have an increasingly stronger impact on read-write performance (see, X. Ma et al., Contribution Of Lubricant Thickness To Head-Media Spacing, Vol. 37, No. 4 IEEE Transactions on Magnetics 1824-1826, (2001)). The head-lubricant interaction creates large interfacial and shear forces that displaces the lubricant and causes lubricant moguls and washboard effects that lead to vibration of the head. Such a lubricant displacement becomes more pronounced with reduction of head media spacing.
When the slider comes within about 10 Angstroms of the disk surface, a substantial attractive or adhesive force pulls down on the part of the slider closest to the disk surface, collapsing the air bearing. This adhesive force can arise from a combination of sources, including Van der Waals interactions between the slider and disk, chemical bonding across the contacting interface, electrostatic forces from a bias voltage on either the slider or disk, such as caused by disk drive spindle motor charging or intentional application, electrostatic forces from the slider-disk contact potential, electrostatic forces from charges generated by rubbing the slider against the disk (tribocharging), and meniscus forces from lubricant or contaminant wicking up around the contact points.
Dynamic effects of lubricant displacement from shear effect of low flying sliders have been observed (See, Q. Dai et al., Washboard Effect at Head-Disk Interface, Vol. 40, No. 4 IEEE Transactions on Magnetics 3159-3161 and successfully modeled (B. Marchon et al., The Physics of Disk Lubricant in the Continuum Picture, Vol. 41, No. 2 IEEE Transactions on Magnetics (2005). These dynamic effects are responsible for loss of necessary slider/disk clearance, tracking errors, and reduced reliability.
The head-lubricant interfacial meniscus force have been quantified by K. Ono, Dynamic Instability of Flying Head Slider and Stabilizing Design for Near Contact Magnetic Recording, No. 320 Journal of Magnetism and Magnetic Materials 3174-3182, (2008) according to the following formula:
F=2gA/h
where g is the surface tension of the lubricant, h is the clearance, and A is the total surface area of engagement with the lubricant. A typical interface with the following characteristics: g is about 22 microNewton meters; h is about 25 Angstroms; A is about 1,000 microns2 (10 microns×100 microns) creates an interfacial force of about 1760 mN. As the spacing (h) is reduced toward zero, even more lubricant is displaced and the force F quickly increaseS, causing head vibration and off-track movement degrade read-write performance to an unacceptable level.
If the interfacial lubricant forces exceed the air bearing forces, the slider body may be pulled further into the lubricant leading to contact modulation with the media and inhibiting the read and write operations. Care must be taken to ensure that the interfacial forces never exceed the lift forces provided by the air bearing under all environmental and operating conditions. K. Ono, Dynamic Instability of Flying Head Slider and Stabilizing Design for Near-Contact Magnetic Recording, 320 Journal of Magnetic Materials and Magnetism 3174-3182 (2008) warns that lubricant-head contact leading to instantaneous lubricant interfacial forces collapsing the air bearing performance and should be avoided.
With this background in the physics of HMS, the limitations in the existing solutions will become evident.
U.S. Pat. No. 6,320,725 (Payne) discloses a contact recording system with a wear-in contact pad. During a burn-in phase, the wear-in contact pad is burnished until it reaches an equilibrium and the wear rate converges to zero. Mechanical tolerances cause the contact pad to not sit flat with respect to the disk. The critical read-write sensors may be tilted impeding the read-write performance. Mechanical vibrations and bouncing is experienced due to disk run-out and waviness, causing the contact pad to bounce and leading to impractically large head media spacing fluctuations. The burn-in phase causes the protective overcoat to burnish, potentially exposing the read-write sensors to corrosion and causing mechanical and magnetic degradation. The strategy of Payne is not viable for modern head disk interfaces requiring sub-nanometer modulations and corrosion protection.
U.S. Pat. No. 7,029,590 (Alexopoulos et al.) reasons that as disk drive fly heights are getting closer to the disk to increase areal density, the ultimate fly height goal will be to put the element in contact with the disk media, thus reducing the fly height to zero. However in practice, a reliable contact interface is very difficult to achieve due to the wear of the head and disk, resulting in early failure when compared to higher fly heights with a cushion of air between them. The reliability problem is exacerbated by manufacturing tolerances which results in significant variation in the amount of interference in the contact interface.
Alexopoulos' approaches the above-described problems by fabricating a wearable pad surrounding the transducer so that the protruding element has a height that is greater than or equal to the designed fly height of the aerodynamic lift surface minus the disk roughness. See
U.S. Pat. Publication No. 2008/0080094 (Tani et al.) discloses a magnetic head slider with an element pad containing the read-write sensors. Tani teaches that the element pad requires a height in ranges from 50 Angstroms to 300 Angstroms. As with Alexopoulos, the height of the element pad in Tani is greater than the thickness of the lubricant layer on current magnetic disks. Consequently, it is not possible to bring the air bearing surface into contact with the lubricant layer to perform contact detection. Hence, the solution of Tani is unable to accurately determine sensor location and HMS. U.S. Pat. Publication No. 2005/0213250 (Kurita et al.) suffers from the same shortcomings as Tani et al.
U.S. Pat. No. 6,914,752 (Albrecht et al.) proposed continuous contact recording with a head-suspension assembly that compensates for the moment generated from an adhesive force between the head carrier or slider and the disk. The lubricant interaction with the contact pad can cause large off-track motions. Uncontrolled wear and interference between the contact pad and the disk lead to variations in read-write sensor height. Removal of the protective overcoat leads to generation of oxide layers that is susceptible to further degradation at high temperatures and high humidity.
U.S. Pat. No. 7,218,478 (Mate et al.) proposes a negative-pitch slider in near-contact or continuous-contact with the disk during reading and writing of data. In near contact recording the slider will be in contact with the rotating disk during a significant portion of the time the disk is at its operating speed. For continuous-contact recording the contact pad is wear-resistant and remains in substantially continuous contact with the disk during reading and writing of data. Direct contact at the head disk interface with the media can burnish and corrode the read-write sensors, leading to the same shortcomings found in Albrecht et al. (U.S. Pat. No. 6,914,752).
U.S. Pat. Publication 2007/0253111 (Shimizu et al.) discloses a read element and a write element of a magnetic head slider arranged on a spherical or ellipsoidal projection formed in the alumina. Manufacturing processes, however, are presently not able to easily fabricate three dimensional shapes, such as the proposed spherical pad. The spherical shape also creates a point contact that causes large stresses at the read-write sensors, increasing wear on the relatively soft alumina. Once the spherical pad starts wearing, a flat surface forms with the potential of increasing interfacial meniscus forces with the lubricant, especially in close proximity with media where the lubricant bridges to the head via the burnished surface. Controlling the attitude of the flying head is critical to assure that the transducers are located at the center of the contacting spherical pad. Geometrical tolerances impact the attitude of the flying slider, thus changing the location of the transducers relative to the media, translating to higher HMS.
As summarized above, the generalized wear-in pad and contact recording concepts suffer from the fundamental limitation of uncontrolled burnishing, protective overcoat burnish, and loss of mechanical and magnetic performance.
U.S. Pat. No. 5,991,113 (Meyer et al.) and U.S. Publication No. 2006/0285248 (Pust et al.) disclose a thermally expansive electric coil embedded in the trailing edge of the slider used to perform a contact detection process. During thermally induced expansion of the trailing edge, the transducer spacing with respect to the disk decreases until the slider penetrates the lubricant and contacts the media. The heat is then reduced to increase the flying height above the lubricant to the desired active clearance.
Mate M. et al., Roughness of Thin Perfluoropoyether Lubricant Films: Influence on Disk Drive Technology, Vol. 37 IEEE Transactions on Magnetics, No. 4 (July 2001) discloses that the head-lubricant interaction during contact detection causes head modulation and head-off track motion, leading to wear and burnish of the head and media overcoats. Contact between heads and media has two distinct consequences. First, the lubricant is displaced and forms ripples under the flying head. This washboard effect can cause increased fly height modulation as summarized in Dai Qing, et al., Washboard Effect at Head-Disk Interface, Vol. 40, No. 4 IEEE Transactions on Magnetics 3159-3161, (July 2004). Second, the carbon overcoat is burnished from the head disk interface, causing loss of magnetic performance at either the read or write sensors.
Bo et al., Towards Fly- and Lubricant-Contact Recording, Vol. 320, Journal of Magnetism and Magnetic Materials 3128-3133 (November 2008), proposes shaping a center pad on the slider to ski over the lubricant layer. It is proposed that fabrication of a rounded surface to promote hydrodynamic lift at the lubricant layer will reduce HMS. The fact that the lubricant thickness is not uniform increases the required peak pressure at the skiing pad. Waviness of the media in both short and long wavelengths challenges the flying ability of the skiing pad.
Song et al U.S. Pat. Nos. 7,428,124 and 7,430,098 (Song, et al.) disclose various arrangements of single and multiple heaters and thermal insulation layers to generate a relatively flat protruding profile on the trailing edge of the slider. Uniform deformation of the trailing edge leads to constant HMS for both read and write operations. The methodology presented is desirable for enhancing the contact area, but at the expense of modulation due to lubricant interactions with the large, albeit relatively flat, contact area.
U.S. Pat. No. 7,388,726 (McKenzie et al.) discloses control schemes for controlling the heater to dynamically adjust HMS. In one embodiment, a controller directs electrical current through the conductor to heat the write element without writing data to a storage disk. Heating the write element causes a deformation of the slider assembly to decrease the head-to-disk spacing. In another embodiment, the slider assembly includes a separate slider deformer.
U.S. Pat. Publication No. 2007/0035881 (Burbank et al.) discloses the use of a dual heater design, illustrated in
The present invention relates to systems and methods for reducing head media spacing (HMS) from about 100 Angstroms to about 65 Angstroms or less, without substantial reductions in the carbon overcoat or lubricant thickness. A HMS of about 65 Angstroms will enable to disk drive industry to achieve a data density of 1 Terabyte/inch2 (1 Tbit/in2) with minor engineering design changes to the current air bearing and heater implementations.
The present system makes it possible to reduce HMS through the use of a protruding feature on an actuated portion of the air bearing surface. The protruding feature preferably covers the entire read-write sensors. A distal end of the protruding feature extends above the actuated portion of the air bearing surface during read-write operations. The protruding feature can either be static or thermally actuated. The protruding feature is preferably constructed from the same material as the protective overcoat, such as diamond-like carbon.
During the contact detection process, the protruding feature preferably has a height above the actuated portion of the air bearing surface of less than or equal to the thickness of the lubricant layer. Consequently, the protruding feature does not prevent the actuated portion of the air bearing surface from interacting with the lubricant layer. In another embodiment, the protruding feature has a height above the air bearing surface during read-write operations of less than the active clearance, typically less than about 50 Angstroms, and preferably about 30 Angstroms to about 20 Angstroms.
The protruding feature is small enough to engage with the lubricant without causing large head media disturbances and lubricant pickup and re-distribution. The protruding feature is also extremely small relative to the size of the air bearing surface. Consequently, a stable air bearing is maintained, even when the protruding feature penetrates into the lubricant.
For example, a typical actuated portion of the air bearing surface is about 100 microns by about 10 microns, or about 1,000 microns2. The protruding feature according to the present invention is preferably less than about 100 microns2, and more preferably less than about 50 microns2. In another embodiment, the protruding feature is less than about 10 microns2, more preferably about 1 microns2. The distal surface of the protruding feature is preferably less than about 5% of a surface area of the actuated portion of the air bearing surface, and more preferably less than about 1%, and still more preferably less than about 0.1%. The protruding feature can have a cross-sectional that is rectangular, elliptical, triangular, teardrop, or random. The size of the protruding feature minimizes the transfer of lubricant to the head, generates acceptably low off-track motion, and minimizes temperature increases at the head-disk interface.
Thick carbon overcoat tends to be denser and provide better wear protection than thin carbon overcoat layers when exposed to the same level of stress. To provide a more robust protruding feature it may be desirable to initially start with a thick carbon overcoat layer and allow it to burnish to its natural state. Note that care must be taken to allow the final carbon overcoat thickness after burnish to be capable of providing wear protection against media defects and interactions. Therefore, in some embodiments, it may be desirable for the protruding feature before the contact detection process to have a height slightly greater than the thickness of the lubricant layer. After completing the various test processes and the contact detection process, the height of the protruding feature will naturally converge to less than or equal to the lubricant thickness. In this embodiment, the height of the protruding feature is preferably less than about 25% greater than the thickness of the lubricant layer. Alternatively, the height of the protruding feature is preferably less than about five Angstroms more than the thickness of the lubricant layer.
The typical read-write sensors have a cross-section of about 0.1 microns by about 0.1 microns (0.01 microns2). Even in embodiments where the protruding feature has a cross section of about 1 micron2, the protruding feature still has a cross-sectional area 100 times larger than the read-write sensors. Consequently, the protruding feature provides adequate corrosion and wear protection, while still being small enough to penetrate the lubricant layer without generating unacceptable vibration.
In some embodiments, the protruding feature can be shaped to further reduce modulation due to interaction with the lubricant. For example, the protruding feature can have a rectangular cross-section, rather than square. In one embodiment, the narrower side of a rectangular protruding feature acts as a leading edge cutting through the lubricant. The shape of the protruding feature can be rectangular, elliptical, triangular, teardrop, or a random shape to further lower the interfacial forces with the lubricant and optimize the clearance of the heat activated shape. The shape of the protruding feature can also be designed to match the shape of the protruded trailing edge area due to heating. The most likely scenario is an elliptical shape.
During contact detection heat is applied to the head until contact is detected by the interactions of the actuated portion of the air bearing surface with the surface of the lubricant. The distal surfaces of the protruding features are very small, causing no practical interfacial lubricant interactions, even during lubricant penetration. To avoid burnishing of the protruding features, the air bearing must be capable of following the disk waviness of the magnetic media.
In embodiments where the height of the protruding features is equal or smaller than the thickness of the lubricant and the air bearing is adequate to follow the waviness of the magnetic media, burnishing of the protruding features is minimized. In this embodiment, the safety margin designed into the carbon overcoat thickness on the head and the magnetic media can be reduced, with a corresponding reduction in HMS.
One embodiment of the present invention is directed to a slider for use in a data storage system having a rotating magnetic media with a lubricant layer on a media surface. A slider body includes at least one read-write sensor and an air bearing surface that causes the slider to fly above a lubricant surface at a first distance. At least a first actuator induces thermal expansion in the slider body so an actuated portion of the air bearing surface contacts the lubricant surface during a contact detection process. The slider flies above the lubricant surface at a second distance less than the first distance after the contact detection process. At least one protruding feature generally covers the read-write sensors. The protruding feature includes a distal surface generally opposite the media surface with an area of less than about 100 microns2 and a height above the air bearing surface after the contact detection process less than or equal to a thickness of the lubricant layer.
In an alternate embodiment, the protruding feature has a height before the contact detection process greater than the lubricant thickness, but less than or equal to the lubricant thickness after the contact detection process. In one embodiment, the protruding feature has a height above the air bearing surface before the contact detection process less than about 25% greater than the thickness of the lubricant layer. The protruding feature typically has a height above the air bearing surface before the contact detection process of less than about 30 Angstroms to about 10 Angstroms.
In one embodiment, at least one secondary actuator is provided to induce thermal expansion of the protruding feature, without substantial thermal deformation of the air bearing surface adjacent to the protruding feature. Some embodiments provide a recessed actuated portion of the air bearing surface to minimize the impact of the secondary actuators on active clearance.
In another embodiment, a distal end of the read-write sensor is preferably located at or above the actuated portion of the air bearing surface before activation of the secondary actuator. In yet another embodiment, the distal end of the read-write sensor is located at or above the actuated portion after activation of the secondary actuator. The HMS is preferably less than about 65 Angstroms, and more preferably less than 55 Angstroms after activation of the secondary actuator.
At least one pressure relief is optionally located proximate the protruding feature. In one embodiment, the pressure relief is located between the protruding feature and the actuated portion of the air bearing surface. The pressure relief is optionally a generally circular or generally elliptical cross-sectional recess. A separate pressure relief can be located around the read sensor and the write sensor, or a single pressure relief can extend around both. In one embodiment, the actuated portion of the air bearing surface is also recessed relative to the remainder of the air bearing surface.
The present invention is also directed to a slider for use in a data storage system having a rotating magnetic media with a lubricant layer on a media surface. A slider body includes at least one read-write sensor and an air bearing surface that causes the slider to fly above a lubricant surface at a first distance. At least a first actuator induces thermal expansion in the slider body so an actuated portion of the air bearing surface contacts the lubricant surface during a contact detection process. The slider flies above the lubricant surface at a second distance less than the first distance after the contact detection process. At least one protruding feature generally covers the read-write sensors. The protruding feature has a height above the air bearing surface after the contact detection process less than or equal to a thickness of the lubricant layer. The signal modulation from the read-write sensors is less than 20% after the contact detection process, even when the protruding feature engages with the lubricant layer on the rotating magnetic media.
The present invention is also directed to a slider for use in a data storage system having a rotating magnetic media with a lubricant layer on a media surface. A slider body includes at least one read-write sensor and an air bearing surface that causes the slider to fly above a lubricant surface at a first distance. At least a first actuator induces thermal expansion in the slider body so an actuated portion of the air bearing surface contacts the lubricant surface during a contact detection process. The slider flies above the lubricant surface at a second distance less than the first distance after the contact detection process. At least one protruding feature generally covers the read-write sensors. The protruding feature has a height above the air bearing surface after the contact detection process less than or equal to a thickness of the lubricant layer. Air provides a reliability buffer between the air bearing surface and the surface of the lubricant. Air and lubricant provide a reliability buffer between the protruding feature and the media surface.
The present invention is also directed to a data storage system including a rotating magnetic media with a lubricant layer on a media surface. A slider body with at least one read-write sensor and an air bearing surface flies above a lubricant surface at a first distance. At least a first actuator thermally induces expansion in the slider body so an actuated portion of the air bearing surface contacts the lubricant surface during a contact detection process. The slider flies above the lubricant surface at a second distance less than the first distance after the contact detection process. At least one protruding feature generally covers the read-write sensors. The protruding feature includes a distal surface generally opposite the media surface with an area of less than about 100 microns2 and a height above the air bearing surface after the contact detection process less than or equal to a thickness of the lubricant layer.
In one embodiment, at least one secondary actuator thermally induces expansion of the protruding feature, without substantial thermal deformation of the air bearing surface adjacent to the protruding feature. The resulting HMS is preferably less than about 65 Angstroms, and more preferably less than 55 Angstroms after activation of the secondary actuator.
The present invention is also directed to a method for use in a data storage system. The method includes locating a slider body having at least one read-write sensor above a rotating magnetic media. The slider body includes at least one protruding feature generally covering the read-write sensors. An air bearing is generated that causes the slider to fly above a lubricant surface at a first distance. The slider body is thermally expanded so a actuated portion on an air bearing surface contacts the lubricant surface during a contact detection process and the at least one protruding feature penetrates the lubricant layer. The thermal expansion of the slider body is reduced after the contact detection process so the slider flies above the lubricant surface at a second distance less than the first distance, and the protruding feature comprising height above the air bearing surface after the contact detection process less than or equal to a thickness of the lubricant layer. Data is then written to the magnetic media.
The present method optionally includes the step of activating at least one secondary actuator to induce thermal expansion of the protruding feature without substantial thermal deformation of the air bearing surface adjacent to the protruding feature. In one embodiment, thermal expansion of the slider body is reduced to compensate for a decrease in the second distance caused by activating the secondary heater.
The position of the read sensor and the write sensor relative to the plane of the air bearing surface typically varies from head to head. For example, due to differential lapping removal and etch removal rates during the manufacturing processes, the read sensor and writer sensor may have different recessions with respect to the air bearing surface. Also, increasing the air bearing pitch (i.e., the pitch of the slider relative to the magnetic media) will lead to a higher clearance for the read sensor than to the write sensor. Heater design can also lead to variability in the shape of the protruding feature, which leads to different clearance between the read and write sensors during the active clearance settings. Consequently, active clearance for the read sensor may be different than the active clearances for the write sensor, both in terms of mean and sigma. To maximize reliability it is possible to provide different carbon overcoat thickness for the read sensor and the write sensor. For purposes of simplicity, however, this disclosure presents the carbon overcoat thickness as constant for the read sensor and the write sensor.
By way of example only, the following tolerance illustrates the points noted above. For example, lubricant thickness is about 15 Angstrom, the sensor recession is about −3 Angstrom for reader and about −2 Angstrom for writer with respect to contact features, and sensor location with respect to the lubricant during contact detection is about 5 Angstrom above lubricant for reader and about 0 Angstrom above lubricant for writer. This simple example demonstrates that the required carbon overcoat on the protruding feature is about 23 Angstrom (15+3+5) and for the writer about 17 Angstrom (15+2+0). To maximize the reliability it is recommended to create a protruding feature about 23 Angstroms above the air bearing surface.
The contact detection process will naturally burnish the protruding feature on the write sensor from about 23 Angstrom to about 17 Angstrom, while not burnishing the protruding feature deposited on the read sensor. Another possibility would be to deposit about 23 Angstroms on the read sensor and about 17 Angstroms on the write sensor, without the need for burnish during contact detection. For purposes of illustration and simplicity this disclosure presents the read sensor and the write sensor in the same reference plane during contact detection with the lubricant.
The systems and methods disclosed herein reduces the current HMS of about 100 Angstroms to about 65 Angstroms or less, without substantial carbon overcoat reductions or lubricant reduction. This reduction in HMS will enable the industry to achieve 1 Tbit/in2 with minor engineering design changes to the current air bearing and heater implementations.
While the prior art typically relied on the indiscriminate application of carbon overcoat to protect both sensitive and non-critical area, the embodiments disclosed herein selectively retain carbon overcoat in critical areas to protect the transducer areas against corrosion and wear.
The protruding feature 106 is fabricated at the trailing edge of the read-write head 100. The protruding feature 106 is typically formed from portions of the read-write sensors 110, 112, the alumina, and/or the diamond-like carbon overcoat 102. In one embodiment, the entire protruding feature 106 is constructed entirely from diamond-like carbon, with or without portions of the read-write sensors 110, 112.
In one embodiment, the protruding feature 106 has a height 108 above the air bearing surface 104 before completing the contact detection process of about the same as lubricant 118 thickness. In another embodiment, the protruding feature 106 has a height 108 before the contact detection process greater than the thickness of the lubricant 118. During the contact detection process the height 108 of the protruding feature 106 is burnished to less than or equal to the thickness of the lubricant 118. Consequently, the protruding feature 106 does not prevent or interfere with the contact detection process. In this embodiment, the protruding feature 106 has a height 108 above the air bearing surface 104 before the contact detection process less than about 25% greater than the thickness of the lubricant layer 118. The protruding feature 106 typically has a height above the air bearing surface 104 before the contact detection process of less than about 30 Angstroms to about 10 Angstroms.
The read-write sensors 110, 112 typically have surface areas 130, 132 opposite the magnetic media 114 typically less than about 0.1 micron×about 0.1 micron. Distal surfaces 124 of the protruding feature 106 is preferably less than about 100 microns2. Consequently, the distal surface 124 of the protruding feature 106 is about 5,000 times larger than the combined surfaces 130, 132 of the read-write sensors 110, 112 (100 microns/0.02 microns=5,000). An oxygen molecule must travel through both the carbon overcoat 102 and the thickness of the protruding feature 106 to reach the read-write sensors 110, 112. The distal surface 124 is referred to as “above” or “located above” the air bearing surface 104 or actuated portion 138, without regard to the spatial orientation of the head 100. The “thickness” or “height” of the protruding feature 106 is the perpendicular distance from the actuated portion 138 of the air bearing surface 104 to the distal surface 124.
As illustrated in
After completing the contact detection process the protruding feature 106 has a height 108 above the actuated portion 138 of the air bearing surface 104 about the same as lubricant 118 thickness. The present embodiment contrasts with the prior art practice of using the active clearance 152 as the only reliability buffer. The illustrated embodiment uses both the clearance 152 and feature clearance 154 as the reliability buffer, with minimal lubricant induced modulation. Feature clearance 154 is the distance between distal end 124 of the protruding feature 106 and surface of carbon overcoat 116 on magnetic media 114. Since the read-write sensors 110, 112 can be located in a variety of locations within the protruding feature 106, the active clearance 152 is effectively decoupled from HMS 155. The HMS 155 is thus reduced while the same or similar active clearance 152 is maintained.
In essence, the protruding feature 106 permits the locations of the read-write sensors 110, 112 to be decoupled from the location of the air bearing surface 104. In order to do so, however, the protruding feature 106 preferably does not prevent the contact detection process. Otherwise, the locations of the read-write sensors 110, 112 will be in doubt and read-write operations compromised.
The reduction in HMS 128 arises from the fact that in the prior art the active clearance 120 was equal to the feature clearance 122. That is, the distal end 124 of the protruding feature 106 was maintained 25 Angstroms above the surface 126 of the lubricant 118. As illustrated in
By way of example only, the carbon overcoat thickness 102 is about 15 Angstroms and the protruding feature 106 has a height of about 15 Angstroms. The lubricant layer 118 and carbon overcoat 116 on the magnetic media 114 are maintained at 15 and 25 Angstroms, respectively, as discussed above. If the active clearance 152 is maintained at about 25 Angstroms, the overall HMS 128 is reduced by about 15 Angstroms relative to the prior art embodiment of
Since the active clearance 152 is maintained at about 20 Angstroms to about 25 Angstroms, the air bearing is very stable. It is likely, however, that the distal end 124 will penetrate into the lubricant layer 118. In order to minimize the transfer of lubricant 118 to the read-write heads 110, 112 and off-track motion, the area of distal surface 124 is preferably extremely small relative to the area of the actuated portion 138 of the air bearing surface 104. For example, a typical actuated portion is about 100 microns by about 10 microns, or 1,000 microns2. The exposed surface 124 of the protruding feature 106, by comparison, is preferably less than about 100 microns2 for the distal surface 124. Consequently, the exposed surface 124 is preferably less than 10% of the surface area of the actuated portion 138 of the air bearing surface 104.
In one embodiment, the exposed surface 124 of the protruding feature 106 is less than about 50 microns2. Consequently, the exposed surface 124 is preferably less than about 5% of the surface area of the actuated portion 138 of the air bearing surface 104. In another embodiment, the exposed surface 124 of the protruding feature 106 is less than about 10 microns2 or less than about 1% of the surface area of the actuated portion 138. In yet another embodiment, the exposed surface 124 of the protruding feature 106 is less than about microns2 or less than about 0.1% of the surface area of the actuated portion 138.
Using the head-lubricant interfacial meniscus force equation discussed above (F=2 gA/h), where g is about 22 microNewton meters; h is about 25 Angstroms; A is the area of the exposed surface 124, in this example about 16 microns2 (e.g., 4 microns×4 microns) the interfacial force generated if the protruding feature 106 is immersed in the lubricant layer 114, is about 28.2 microNewtons meters, compared to an interfacial force of about 176 microNewton meters generated if the actuated portion 138 engages with the lubricant layer 118. In this example, the interfacial force created by the protruding feature 106 is about 16% of the interfacial force created by the actuated portion 138.
When the protruding feature 106 is engaged with the lubricant, the signal modulation is preferably less than about 20 percent, and more preferably less than about 10 percent, to avoid read and write signal modulation failures. Signal modulation is a standard measure of signal integrity in disk drives. As used herein, “signal modulation” refers to a variation in a periodic waveform generated by a read-write sensor in a magnetic disk drive indicative of vibration or off-track motion. These levels of signal modulation have been found to be acceptable for conventional read write operations.
As best illustrated in
The leading edge 168 of the protruding feature 106 also engages with the lubricant layer 118 during rotation of the magnetic media 114. The protruding feature 106 is preferably about 15 Angstroms (0.0015 microns) high. Assuming for example that the exposed surface 124 of the protruding feature 106 is about 10 microns×10 microns, the surface area of the leading edge 168 is only 0.015 microns2 (0.0015 microns×10 microns), which is a fraction of the surface area of exposed surface 124.
While the feature clearance 316 is generally the same as in the embodiment of
Assuming the clearance 330 is maintained at about 25 Angstroms, lubricant layer 332 about 15 Angstroms, and carbon overcoat 334 at about 25 Angstroms, the overall HMS 318 can be reduced to about 65 Angstroms. In the event that the 15 Angstroms thick protruding features 320, 322 provides inadequate protection against corrosion, the disk drive can optionally be located in an oxygen-free environment.
Further reduction in HMS can be achieved by increasing the lubricant thickness to offset a reduction in carbon thickness. For example, an increase of about 4-5 Angstroms in lubricant thickness can yield about 10 Angstroms reduction in carbon overcoat on the magnetic media.
In another embodiment, the thickness of the lubricant layer 332 is increased and the thickness of the carbon overcoat 334 on the magnetic media 302 is reduced. The reduction in carbon overcoat 334 can be greater than, less then, or equal to, the increase in lubricant layer 332. This configuration allows the protruding features 320, 322 to have a thickness greater than 15 Angstroms, without increasing HMS 318. For example, if the lubricant 322 is increased to 25 Angstroms and the carbon overcoat 334 is reduced to 15 Angstroms, the thickness of the protruding features 320, 322 can be increased to 25 Angstroms while maintaining the HMS 318 at about 65 Angstroms, without the use of secondary heaters.
A variety of manufacturing process can be used to create the protruding features disclosed herein, including additive and/or subtractive processes, such as for example etching. It is also possible to create a separate protruding feature to protect both the read sensor and the write sensor.
The introduction of one or more secondary thermal actuators to promote thermal actuation of a relatively small area becomes very challenging due to the thermal issues associated with the heater design and controlling the flow of heat across the entire air bearing surface. The prior art teaches using a relatively large secondary heater (see Burbank et al., 2007/0035881) thermal actuator to avoid the reliability issues associate with a micro heater. The large heaters of Burbank, however, cause material diffusion, melt down of the conductors, and reduced life of the read-write sensors. The practical and physical limitation of thermal diffusion dictates a relatively large protrusion area that will cause a significant interfacial force at the onset of lubricant interaction.
By way of example only, the carbon overcoat 356 and the protruding feature 358 are each about 15 Angstroms thick. Lubricant layer 370 and carbon overcoat 372 on the magnetic media 352, and active clearance 383 between the actuated portion 366 and the lubricant layer 370 (see
The protruding feature 358 and the relief 354 are rigidly attached to the air bearing surface 386 and experience generally the same amount of displacement toward the magnetic media 352 as the actuated portion 366. In the embodiment of
The relief 354 minimizes thermal expansion of the carbon overcoat 356 due to heat from the secondary heaters 368, 370. The relief 354 also allows for larger and more practical secondary heaters 368, 370, with minimal or no thermal expansion of the actuated portion 366 into the active clearance 383. The relief 354 reduces the effects of self compensation during the actuation of the secondary heaters 368, 370. Self compensation refers to a total change of active clearance 383 due to activation of one or more secondary heaters.
Small changes in active clearance 383 due to activation of one or more secondary heaters 368, 370 can be neutralized by developing a transfer function between the change in active clearance 383 versus secondary heater actuation using Wallace's equations. For example, the power to one or more primary heaters 380, 382 can be reduced to reduce the active clearance 383 to compensate for the effects of one or more secondary heaters 368, 370.
In the illustrated embodiment, the application of one or more primary heaters 380, 382 and one or more secondary heaters 368, 370 causes the relief 354 and protruding feature 358 to expand an additional 15-30 Angstroms above the actuated portion 366. The read-write sensors 360, 362 are now 15-30 Angstroms closer to the magnetic media 352, reducing the HMS 390 (see
In the embodiment of
By way of example only, the base layer 468 is about 15 Angstroms thick, while the protruding feature 462 is about 30 Angstroms thick. The protruding feature 462 extends about 15 Angstroms above the actuated portion 466 before activation of primary heaters 470, 472. Lubricant layer 474 and carbon overcoat 476 over the magnetic media 458, and active clearance 488 (see
In one embodiment, secondary heaters 480, 482 are not required. Heat from the primary heaters 470, 472 thermally deforms both the actuated portion 466 and increases the height 463 of the protruding feature 462. The height 463 of the protruding feature 466 above the thermally deformed actuated portion 466 is preferably less than or equal to the thickness of the lubricant layer 474 so as to not interfere with the contact detection process. Alternatively, the height 463 is less than about 25% greater than the thickness of the lubricant layer 474.
In the illustrated embodiment, the application of one or more primary heaters 470, 472 and one or more secondary heaters 480, 482 cause the relief 460 and protruding feature 462 to deform about an additional 5-30 Angstroms above the actuated portion 466. The read-write sensors 454, 456 are now about 5-30 Angstroms closer to the magnetic media 458, reducing the HMS 452 by that amount, without reducing the active clearance 488 necessary for a stable air bearing. In the present embodiment, the HMS 452 is in the range of about 60 Angstroms to about 65 Angstroms.
Curve 492 shows a distribution of the active clearance of the protruding features 462 extending above the actuated portion 466 after activation of one or more secondary heaters 480, 482. Most of the protruding features 462 are located in the lubricant 474 (see also,
In the embodiment of
By way of example only, if the lubricant layer 534 is increased from about 15 Angstroms to about 25 Angstroms, the carbon overcoat 540 on the magnetic media 532 can be reduced from about 25 Angstroms to about 15 Angstroms, resulting in a HMS 502 of about 55 Angstroms, thus permitting a data density of about 2 Tbit/in2.
Further reductions in HMS can be realized by reducing the environmental losses in the disk drive due to temperature, humidity and altitude. Sensors can optionally be added to the disk drive to compensate for temperature changes, humidity changes and altitude changes, as done in commercially available disk drives.
Where a range of values is provided, it is understood that each intervening value, to the tenth of the unit of the lower limit unless the context clearly dictates otherwise, between the upper and lower limit of that range and any other stated or intervening value in that stated range is encompassed within the inventions. The upper and lower limits of these smaller ranges which may independently be included in the smaller ranges is also encompassed within the inventions, subject to any specifically excluded limit in the stated range. Where the stated range includes one or both of the limits, ranges excluding either both of those included limits are also included in the inventions.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which these inventions belong. Although any methods and materials similar or equivalent to those described herein can also be used in the practice or testing of the present inventions, the preferred methods and materials are now described. All patents and publications mentioned herein, including those cited in the Background of the application, are hereby incorporated by reference to disclose and described the methods and/or materials in connection with which the publications are cited.
The publications discussed herein are provided solely for their disclosure prior to the filing date of the present application. Nothing herein is to be construed as an admission that the present inventions are not entitled to antedate such publication by virtue of prior invention. Further, the dates of publication provided may be different from the actual publication dates which may need to be independently confirmed.
Other embodiments of the invention are possible. Although the description above contains much specificity, these should not be construed as limiting the scope of the invention, but as merely providing illustrations of some of the presently preferred embodiments of this invention. It is also contemplated that various combinations or sub-combinations of the specific features and aspects of the embodiments may be made and still fall within the scope of the inventions. It should be understood that various features and aspects of the disclosed embodiments can be combined with or substituted for one another in order to form varying modes of the disclosed inventions. Thus, it is intended that the scope of at least some of the present inventions herein disclosed should not be limited by the particular disclosed embodiments described above.
Thus the scope of this invention should be determined by the appended claims and their legal equivalents. Therefore, it will be appreciated that the scope of the present invention fully encompasses other embodiments which may become obvious to those skilled in the art, and that the scope of the present invention is accordingly to be limited by nothing other than the appended claims, in which reference to an element in the singular is not intended to mean “one and only one” unless explicitly so stated, but rather “one or more.” All structural, chemical, and functional equivalents to the elements of the above-described preferred embodiment that are known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by the present claims. Moreover, it is not necessary for a device or method to address each and every problem sought to be solved by the present invention, for it to be encompassed by the present claims. Furthermore, no element, component, or method step in the present disclosure is intended to be dedicated to the public regardless of whether the element, component, or method step is explicitly recited in the claims.
