Patent Application
20080273267
The present invention relates generally to magnetic data storage drives. In particular, this invention relates to structures for adjusting flying height of slider over magnetic storage media, and more specifically, the present invention relates to structures for flying height control as well as protecting read sensor and write pole of the slider from noise interference and electrostatic discharge.
Disk drives are widely used in computers, consumer electronics and data processing systems for storing information in digital form. The disk drive typically includes a series of rotatable storage disks, or other magnetic storage mediums and head stack assemblies. Each head stack assembly includes a slider having a read/write head that transfers information to and from the storage disk. The read/write head, commonly known as transducer, is typically carried by and embedded in the slider, and the slider is held in a closer relative position over discrete data tracks formed on the disk to permit a read or write operation to be carried out. In order to properly position the transducer with respect to the disk surface, an air bearing surface (ABS) formed on the slider experiences a fluid air flow that provides sufficient lift force to fly the slider with the transducer above the disk data tracks. The air flow is generated by high speed rotation of the magnetic disk which accordingly drives the air flow along its surface in a direction substantially parallel to the tangential velocity of the disk. The air flow cooperates with the ABS of the slider which enables the slider to fly above the spinning storage disk. That is, the rotation of the storage disk causes the slider to ride a distance “h” from the storage disk relative to the ABS of the slider. The distance “h” is referred to as the flying height or separation gap between the ABS and the spinning storage disk and represents the position that the slider assembly occupies when the storage disk is rotating during normal operation of the disk drive.
At present, each storage disk includes one or two disk surfaces that are divided into a plurality of narrow, annular regions of different radii, commonly referred to as data tracks. The number of tracks per radial inch (TPI) on the storage disk is known as track density. Digital information is recorded on the data tracks in the form of magnetic transitions or bits using the read/write head. The number of bits per inch (BPI) along the track is known as linear density. Areal density is necessarily increasing in an effort to raise the storage capacity of the disk drive, while maintaining a fixed or lower manufacturing cost of the drive.
For a given linear density, a target head-to-disk spacing is required to ensure accurate data transfer. Unfortunately, consistent head-to-disk spacing during data transfer is difficult to achieve due to the constant changing environment. Further, the flying height of the slider is viewed as one of the most critical parameters affecting the reading and recording capabilities of a mounted read/write head. A large variation in flying height from slider to disk can cause significant issues in reliability of the disk drives. In other words, an invariable flying height allows the transducer to achieve greater resolution between different data bit locations on the disk surface, thus improving data density and storage capacity. If the flying height deviates positively and significantly from the target flying height, the head-to-disk spacing may become too large and may cause unreliable reading from and writing to the storage disk. Conversely, if the flying height deviates negatively and significantly from the target flying height, the head may contact the surface of the storage disk.
In addition, with the increasing popularity of lightweight and compact notebook type computers that utilize relatively small yet powerful disk drives, the need for progressively lower flying height has continually grown. Some of the major objectives are to fly the slider and its accompanying transducer as close as possible to the surface of the rotating disk, and to uniformly maintain that constant close distance regardless of variable flying conditions. Hence, some mechanism to control the flying height of the slider has raised.
One approach that has been effectively used by disk drive manufacturers to proceed the positional control of slider is dynamic flying height (DFH) control, which employs a thermal actuator or heater to adjust the height between the slider and the disk through thermal expansion of the slider. With such mechanism, the flying height has well controlled. However, in fact, such mechanism is not effective because its response time is slow.
At present, some manufacturers utilize another mechanism called electrical flying height (EFH) control. This mechanism applies an electrostatic actuator between the disk and the slider to actively adjust the flying height by electrical attraction with low cost, low mass and low power consumption as well as 50% faster actuation efficiency than the conventional DFH control. Specially, referring to
In light of the above, the need exists to provide an improved EFH control structures that allow for precise adjustment for the slider's flying height as well as protecting read sensor and write pole of the slider from noise interference and electrostatic discharge.
Accordingly, an object of the present invention is to provide a slider with a slider substrate being applied a control voltage thereto for realizing EFH control while shields of the slider being simultaneously grounded thereby pits do not appear on the shields and ESD is eliminated.
A further object of the present invention is to provide a hard disk drive for adjusting flying height of a slider which applies a control voltage to a slider substrate of the slider for realizing EFH control while simultaneously grounds shields of the slider thereby pits do not appear on the shields and ESD is eliminated.
To achieve the above-mentioned objects, the present invention provides a slider adapted for controlling flying height thereof with respect to an electrically conductive storage medium. The slider comprises a slider substrate having an ABS configured to face the storage medium, a top shield and a bottom shield sandwiching a read sensor, and a write shield. The slider substrate is electrically connected to a substrate electrical connection which is adapted to provide a flying height control voltage to the slider substrate. Thus the slider substrate and the storage medium form two plates of a capacitor separated by a dielectric layer of air supporting the slider. The bottom shield and the write shield both are electrically connected to a ground electrical connection.
As an embodiment of the present invention, the slider further comprises a heater. An end of the heater electrically connects to the substrate electrical connection which is adapted to provide a flying height control voltage to the heater, and the other end of the heater electrically connects to the ground electrical connection.
As another embodiment of the present invention, the slider further comprises a bottom plate which is electrically connected to the ground electrical connection, and the top shield is electrically connected to the ground electrical connection.
As still another embodiment of the present invention, a shunting resistance is connected between the ground electrical connection and each of the write shield, the top shield and the bottom shield.
Preferably, the value of the shunting resistance between the ground electrical connection and either of the bottom shield and the top shield is selected from 10 k Ohm to 10M Ohm. Also preferably, the value of the shunting resistance between the ground electrical connection and the write shield is less than 10 Ohm.
Preferably, the value of the shunting resistance between the ground electrical connection and either of the bottom shield and the top shield equals to 2M Ohm.
A hard disk drive for adjusting flying height of a slider of the present invention comprises a storage medium and the slider. The slider comprises a slider substrate having an ABS configured to face the storage medium, a top shield and a bottom shield sandwiching a read sensor, and a write shield. The slider substrate is electrically connected to a substrate electrical connection which is adapted to provide a flying height control voltage to the slider substrate. Thus the slider substrate and the storage medium form two plates of a capacitor separated by a dielectric layer of air supporting the slider. The bottom shield and the write shield both are electrically connected to a ground electrical connection.
In comparison with the prior art, the present invention imposes a flying height control voltage to the slider substrate, thus to realize EFH control. Therefore, shields of the slider are allowed to be grounded, and accordingly the slider can successfully eliminate pits on the shields and soundly suppress ESD in the slider.
Alternatively, the slider of the present invention also applies a bottom plate, a heater and a shunting circuit with shunting resistances to optimum reading and/or writing performance by further better preventing noise and cross-talk as well as ESD.
Other aspects, features, and advantages of this invention will become apparent from the following detailed description when taken in conjunction with the accompanying drawings, which are a part of this disclosure and which illustrate, by way of example, principles of this invention.
The accompanying drawings facilitate an understanding of the various embodiments of this invention. In such drawings:
Various preferred embodiments of the invention will now be described with reference to the figures, wherein like reference numerals designate similar parts throughout the various views. As indicated above, the invention is directed to a slider with a slider substrate being applied a flying height control voltage thereto and shields being grounded. Such design enables the slider of the present invention to realize EFH control and to eliminate pits on shields of the slider and ESD in the slider while simultaneously achieving noise immunity. Alternatively, the slider of the present invention can introduce a bottom plate, a heater or a shunting circuit with shunting resistances to optimum reading and/or writing performance by further better preventing noise and cross-talk and ESD.
Referring to
The slider 100 consists of a transducer 110 and a substrate 120. The transducer 110 has a read sensor 114 and a write coil 111. The read sensor 114 is typically protected from stray electromagnetic fields during operation by a top shield 113 and a bottom shield 115. The write coil 111 is typically an inductive coil with a write shield 112. The slider substrate 120 has an ABS 130 configured to face the electrically conductive surface of the disk 200. The structure of the top shield 113, the bottom shield 115 and the read sensor 114 are sequentially formed on the slider substrate 120.
The slider substrate 120 is electrically connected to a substrate electrical connection 400 which is adapted to provide a flying height control voltage to the slider substrate 120. The interface between the slider substrate 120 and the electrically conductive media surface of the disk 200, that is, the dielectric layer of the flying height spacing 140, enables the slider substrate 120 and the electrically conductive media surface to be modeled as a quasi-parallel capacitor 321. The slider substrate 120 and the electrically conductive media surface respectively form two opposing plates of the capacitor 321. More particularly, the slider substrate 120 acts as a first capacitor plate or first flying height control electrode 121 electrically separated from the transducer 110 by the bottom plate 116. The electrically conductive media surface of the disk 200 that faces the first capacitor plate functions as a second capacitor plate or a second flying height control electrode 221, which has an effective area equal to that of the first flying height control electrode 121. In this embodiment, the first capacitor plate 121 and the second capacitor plate 221 join together to realize EFH control.
The following paragraph explains principles of the EFH control of the subject slider 100 with respect to the disk 200 of this invention. When the flying height control voltage, which can be kept below certain levels to actively adjust the flying height spacing 140, is applied to the slider substrate 120 via the substrate electrical connection 400, a difference in electrical potential, which developed from a control voltage signal generated by the flying height control voltage, occurs between the first capacitor plate 121 and second capacitor plate 221, thus producing an electrostatic attractive force between the slider substrate 120 and the disk 200. The electrostatic attractive force will induce the first flying height control electrode 121 to be electrostatically attract to the second flying height control electrode 221 and accordingly shift the distance between the slider 100 and the disk 200, thus realizing adjusting the slider's flying height.
By acting as the quasi-parallel capacitor 321 during EFH operation, the amount of spacing in the head-disk interface (FIDI), that is the flying height spacing 140, may be increased or decreased based on the amount of control voltage applied. Specifically, the distance between the slider 100 and the disk 200 will decrease with increasing applied voltage, as the slider is driven by increased electrostatic attractive force between the first capacitor plate 121 and second capacitor plate 221 at high voltage. In other words, applying a control voltage may decrease the flying height spacing 140, thus achieve the purpose of electrostatically adjusting the flying height spacing 140 to maintain flying height of the slider 100 at a desired set point.
In the embodiment, the write shield 112 and the bottom shield 115 are both electrically connected to a ground electrical connection 300 which is grounded. In this case, charge only builds up on the slider substrate 120 because shield potential is the same as ground during EFH operation, thus pits will not appear at shields of the transducer 110. In addition, ESD potential hazard is eliminated and noise immunity is well achieved because of the grounded internal shunting circuit consisting of write shield grounding and the bottom shield grounding.
Alternatively, the slider of the present invention can be designed to possess some optimized structure. Such design will achieve optimal noise and cross-talk rejection and produce both the noise-rejection characteristics and the ESD protection while simultaneously achieving EFH control, which will be illustrated below.
Thus, the present invention provides, in various embodiments, an improved slider and associated hard disk drive for controlling flying height thereof with respect to an electrically conductive storage medium. The foregoing descriptions of specific embodiments have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed, and many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the invention and its practical application, and to enable others skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims appended hereto and their equivalents.
