This invention relates to a Hard Disk Drive (HDD). More particularly, this invention relates to a slider that includes a read/write head that is positioned over a disk to read and write data. Still more particularly, this invention relates to a slider that includes a piezoelectric actuator and a thermo actuator for controlling the flying height of the slider over a disk in a HDD.
Many electronic devices include a HDD to store the large amount of data needed to perform the functions of the device. As these electronic devices become smaller in size, the size of the HDD must also be reduced. The reduction in size of the HDD requires that a slider that includes the read/write heads of the HDD also be reduced in size. The reduced size of the head makes the head more susceptible to shear forces caused by an air flow in the HDD that is caused by the rotating disk.
One desire of designers of HDDs is to reduce the flying height of a read/write head over the disk. Designers want to reduce the flying height to reduce alignment problems with heads and the tracks to provide more accurate reading and writing of the data. However, the reduction in flying height must be balanced with the need to reduce the amount of sheer forces acting on the slider as the sheer forces acting on the slider may cause various alignment problems that the reduction in flying height is attempting to reduce. Thus, those skilled in the art are constantly looking at ways to reduce the flying height of the slider head while minimizing the effects of sheer forces on the slider head.
Those skilled in the art have proposed using actuators to reduce the flying height of a portion of the slider body or head while an operation is being performed and then having the slider body or head move back to an original configuration during movement. One type of actuator proposed is a thermo actuator. A thermo actuator is a material formed into a slider body that heats the surrounding material in the head in response to a current applied to the actuator. The heated material then expands causing a deformation in the body that reduces the flying height of the head over the disk below. These actuators are very effective. However, the amount of time needed for a thermo actuator to heat the surrounding material is often too long to be effective during disk operations.
A second proposed actuator is piezoelectric actuator. A piezoelectric actuator is a layer of piezoelectric material formed in the slider body between two electrodes. A current is applied to the piezoelectric material that causes the material to expand. The expansion of the material causes a portion of the slider body to deform reducing the flying height of the head within the deformed portion of the body. Piezoelectric actuators have a better response time than thermo actuators. However, the deformation caused by conventional PZTs is often unacceptably large and causes the airflow between the slider and the disk to be compressed, limiting the reduction of flying height. Furthermore, the deformation varies the shear force on the slider, altering the flying altitude of the slider.
To overcome these problems, those skilled in the art have foreseen a combination of piezoelectric and thermo actuators to overcome the problems with each type of actuator individually.
For example, US Patent Publication Number 2008/0074797, titled “Storage Medium Drive Capable of Reducing Wiring Related to Head Slider” in the name Ika et al. published Mar. 27, 2008; US Patent Publication Number US 2008/017919, titled “Disc Drive Actuator” in the name of White et al. published on Jul. 24, 2008; US Patent Publication Number 2001/0033546, titled “Flying Optical Recording/Playback Head and Method for Controlling the Flying Height” in the name Katayama published Oct. 25, 2001; European Patent Application Publication Number 0242597 on behalf of IBM published Oct. 28, 1987; U.S. Pat. No. 7,388,726 titled “Dynamically Adjustable Head Disk Spacing slider Using Thermo Expansion” issued to McKenzie et al. issued Jun. 17, 2008; and U.S. Pat. No. 6,950,266 titled “Active Fly Height Control Crown Actuator” issued to McCaslin et al. issued Sep. 27, 2005, all discuss the possibility of the use of a combination of thermo and piezoelectric actuators. However, these documents are all silent on a configuration in the slider body that will allow the combination to effectively reduce the flying height of the head while having the response time desired to perform read and/or write operations.
Thus, those skilled in the art are constantly striving to design for a configuration of a slider body that incorporates thermo and piezoelectric actuators in manner that allows the flying height of the head to be controlled within the time needed for the operation that is of an acceptable size for use in current HDDs.
The above and other problems are solved and an advance in the art is made by a slider and actuator system in accordance with this invention. A first advantage of this invention is that the use of two actuators reduces the flying height of a head over a rotating disk while read and/or write operations are being performed. A second advantage of this invention is that response time for the actuators is reduced through the use of a combination of actuators. A third advantage of this invention is the increased rigidity and stiffness of the flying head.
In accordance with this invention, a slider for an HDD is configured in the following manner. The slider includes a slider body. Preferably, the slider body is substantially 1.25 millimeter by 1 millimeter by 0.3 millimeter in dimension. The slider body has a leading surface, a trailing surface, a bottom surface and a top surface. A head is formed in the slider body in a portion of the body proximate to the trailing surface. The head may include a shield, a pole, and write coils. Preferably the shield and poles are formed of a Ni—Fe compound while the write coils are formed of copper (Cu). The slider body also includes a first actuator that causes the portion of the body including the head to deform to reduce the flying height of the portion. A second actuator in the body then causes a protrusion from the bottom surface of the portion of the slider body that includes the head. The protrusion includes an end of the head to further reduce the flying height of the head over the disk.
In accordance with some embodiments of this invention, the first actuator is a piezoelectric actuator. Preferably, the piezoelectric actuator includes a first electrode formed in a substrate in the slider body proximate to the leading surface of the body, a layer of piezoelectric material formed on the first electrode in the substrate and second electrode formed between the layer of piezoelectric material and a base coat proximate to the portion of the body including the head. Preferably, the substrate is Al2O3—TiC, the piezoelectric material is Tokin N-21 and the base coat is Al2O3.
The electrodes apply a current to the layer of piezoelectric material. The current causes the piezoelectric material to expand. The expansion of the piezoelectric material causes the portion of the body including the head to deform. The deformation of the portion reduces the flying height of the portion over the disk.
In accordance with an embodiment of the invention in which the slider body is substantially 1.25 millimeter by 1 millimeter by 0.3 millimeter in dimension, the piezoelectric material is approximately 200 μm in thickness. In accordance with this embodiment, a drive voltage of 30 volts is applied across the layer of piezoelectric material to cause the portion of the slider body to deform towards the disk with a bottom edge of the trailing surface deformed approximately 27.34 nanometers towards the disk.
In accordance with some embodiments of this invention, the second actuator is a heat actuator element. In accordance with some of these embodiments, the heat actuator element includes a thermo actuator. The thermo actuator is formed in the portion of the body proximate to the head. Current is applied to the thermo actuator that causes the thermo actuator to heat the material around the actuator including the material in at least one end of the head proximate to the bottom surface of the body. The heating of the material causes the material to expand and form a protrusion in the bottom surface of the body. The protrusion includes the end of the read/write head to reduce the flying height of the head over the disk.
In accordance with some embodiments of this invention, the heat actuator element includes multiple thermo actuators formed in the portion of the slider body proximate to the head. In accordance with some particular embodiments, a first thermo actuator is formed at a first distance from the bottom surface of the slider body proximate to a first side of the head and a second thermo actuator is formed at a second distance from the bottom surface of the slider body proximate to a second side of the head. Preferably the first and second distances are not equal and the first and second actuators are positioned so as to heat the head along substantially the entire length of the head. Furthermore, the first and second actuators may each be formed to have a heating material proximate to the head and an insulating material distal from the head to prevent other components of the portion of the slider body from being heated to localize the protrusion proximate to the head. In the preferred embodiment, 10 milliwatts of power is applied to each of the first and second thermo actuators to cause a protrusion including an end of the head to form that protrudes substantially 9.70 nanometers from the bottom surface of the portion of the slider body.
The above and other features and advantages of this invention are described in the Detailed Description set forth below and the following drawings:
This invention relates to Hard Disk Drives (HDD). More particularly, this invention relates to a slider that includes a read/write head that is positioned over a disk to read and write data. Still more particularly, this invention relates to a slider that includes a piezoelectric actuator and a thermo actuator for controlling the flying height of the slider over a disk in a HDD.
Slider body 200 also includes portion 225 proximate to trailing surface 210 that includes read/write head 230 that is a structure formed within portion 225. One skilled in the art will note that only one read/write head 230 is included in portion 225 in this embodiment of the invention. However, more than one read/write head may be formed within section 225 without departing from this invention.
In the illustrated embodiment, layer of piezoelectric 310 is formed of Tokin N-21 and is approximately 200 μm in thickness at a distance of 92.8 μm from trailing surface 210. One skilled in the art will recognize that the exact piezoelectric material used and the thickness used will be design choices based upon the requirements of the system. Base coat 320 is then formed over layer of piezoelectric material 310. Preferably, base coat 320 is Al2O3.
In accordance with this described embodiment of the invention, base coat 320 and substrate 305 act as electrodes to apply a current to layer piezoelectric material 310. In response to the current being applied, layer of piezoelectric material 310 deforms. The resulting deformation from applying current is determined by the following equation:
Δx=d15*V
where:
In the embodiment described herein, including a layer 310 of Tokin N-21 that is approximately 200 μm thick, a drive voltage of 30 volts results in a deformation of a maximum of 27.34 nm towards disk 130. One skilled in the art will recognize that other configurations of a piezoelectric actuator may be used without departing from this invention.
Slider body 200 includes read/write head 230 formed within portion 225. Read/write head 230 includes structures formed in the layers of portion 225. The structures include shield 345, pole 346, and coils 347. Preferably, shield 345 and pole 346 are structures formed in portion 225 proximate to bottom surface 215. However, other configurations may be used without departing from this invention. Preferably shield 345 and pole 346 are Ni—Fe material as is common in the art. Coils 347 are also formed proximate to bottom surface 215 in portion 225 and are preferably made of Cu.
At least one second actuator is located proximate to read/write head 230. The second actuator causes a protrusion to form from bottom surface 215 that includes an end of read/write head 230. In the illustrated embodiment, the second actuator is thermo actuator 350 formed on one side of read/write head 230. Thermo actuator 350 includes a heat element 325 formed proximate to read/write head 230 and insulating element 330 formed distal read/write head 230. Current is applied to heat element 325 which causes heat element 325 to raise the temperature of material adjacent heat element 325. The rise in temperature causes the material to expand and form a protrusion from bottom surface 215. Since heat element 325 is proximate to read/write head 230, the protrusion includes an end of read/write head 230.
In some embodiments, the second actuator includes more than one actuator. In particular, the embodiment shown in
In the illustrated embodiment, first thermo actuator 350 is formed 1.22 μm from bottom surface 215 in portion 225 and second thermo actuator 351 is formed 9.72 μm from bottom surface 215 in portion 225. Each of the insulating elements 330, 340 has a thickness of 0.16 μm. In the illustrated embodiment, 10 milliwatts of power is applied to each thermo actuator 350, 351 to cause a protrusion of about 9.70 nanometers. The application of current causes a temperature increase of approximately 155 degrees Celsius around each thermo actuator and increase of 27.95 degrees Celsius of bottom surface 215 around read/write head 230. When first actuator 355 and second actuator 350, 351 are applied, the flying height of head 230 is reduced to 3.18 nm compared to 8.40 nm of a conventional slider. Furthermore, the pitch angle is significantly reduced from 97.66 μrad to 57.07 μrad.
In a preferred embodiment, the flying height is reduced without substantial variation to the pitch angle of the slider. Varying the pitch angle by too much causes turbulence in the air between the slider and the disk. The turbulence, in turn, causes the slider to oscillate. The variation in the pitch angle of the slider is reduced through the usage of a combination of PZT and thermal actuators.
Furthermore, it is known from experimentation that the maximum pressure exerted on a bottom or air bearing surface of a conventional slider is 1.65*106 Pa and is exerted near the trailing edge of a rear pad. However, the maximum pressure exerted on bottom surface 215 of slider body 200 in accordance with this invention is 4.47*106 Pa which is 2.7 time greater the convention slider. The difference arises because the trailing part of the slider body 200 is vertically deformed towards the disk owing to the deformation caused by layer of piezoelectric material 310 and thermal protrusion. However, the pressure profile of slider body 200 is significantly narrower and sharper due to the protrusion.