Abstract:
The present invention generally relates to a magnetic head and a magnetic storage device using a recording medium. More particularly, the present invention relates to a magnetic head for expanding the track width of the recording medium, a control circuit for controlling the magnetic head, and a storage device that uses the magnetic head and the control circuit. The magnetic head includes a slider, a read element disposed on the slider, and a heater element disposed closer to the leading edge side of the magnetic head than the read element in a position opposite to a recording medium.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention generally relates to a magnetic head and a magnetic storage device using a recording medium. More particularly, the present invention relates to a magnetic head for expanding the track width of the recording medium, a control circuit for controlling the magnetic head, and a storage device that uses the magnetic head and the control circuit. 
   2. Description of the Related Art 
   The development of magnetic storage devices, including a hard disk drive (HDD), is being advanced to achieve higher recording densities, and their recording density is increasing at an annual rate of 30 to 100%. In HDDs being mass-produced, there has already been realized an areal recording density of 100 Gb/in 2 . 
   Note here that the areal recording density of a magnetic storage device is determined by the product of bits per inch (BPI) and tracks per inch (TPI). In other words, the areal recording density is determined by the product of BPI denoting bit density in the track direction of a recording medium and TPI denoting bit density in the cross-track direction thereof. BPI is mainly dominated by the amount of noise in the magnetization reversal region of a recording medium. Accordingly, development efforts are being made to reduce the noise of the recording media, so as to be able to increase the density of BPI. Specifically, the development efforts are being made to reduce a residual magnetization-thickness product and increase coercivity since it is well known that the amount of noise in a recording medium is proportional to the residual magnetization-thickness product and is inversely proportional to the coercivity. Note here that although the amount of noise decreases as the residual magnetization-thickness product is reduced, there arises the problem that read signal output becomes smaller. In connection with this problem, the techniques called CPP-GMR (Current Perpendicular to Plane Giant Magneto Resistance) and TuMR (Tunneling Magneto Resistance) that overwhelmingly surpass the magneto-resistive effect rate of GMR (Giant Magneto Resistance), which is the related art, have already been employed in magnetic heads for mass-production since it is effective to increase the magneto-resistive effect rate of a read element of the magnetic head. 
   In addition, with regard to the increase of coercivity, there is the constraint that it is only possible to increase coercivity to the extent of causing magnetization reversal at the write magnetic field of a write element of the magnetic head. With regard to the write magnetic field intensity of a write element portion, a magnetic material having a magnetic flux density of 2.45 T, which is considered as a physical limit, has already been employed in magnetic heads for mass-production and, therefore, it is difficult to further increase the write magnetic field intensity. Note that failure to fully reverse magnetization at the write magnetic field of the write element is undesirable since magnetic crystal grains, the magnetization of which has not been reversed, serve as a noise source. In connection with this problem, there has been proposed a method wherein a heat source, such as a laser, is disposed in a magnetic head or in a head slider whereon the magnetic head is mounted, in order to radiate laser light at a recording medium when writing (recording) thereto, thereby temporarily decreasing the coercivity of the recording medium. Use of this mechanism makes it possible to attain large coercivity without being obliged to adhere to the write magnetic field intensity of the write head element portion. In this way, the densification of BPI has been achieved by a variety of technical approaches. 
   On the other hand, it is difficult to control TPI for reasons of the characteristics of the recording media and, therefore, the densification has been attempted by reducing the widths of the read and write elements of the magnetic head in the cross-track direction thereof, i.e., so-called core widths. The core width of the write element is designed to be larger than that of the read element so that the read head element does not sense the track edge noise of the recording medium. For this reason, the machining accuracy of the read element is required to be higher than that of the write element. Note here that the core width of the read element was as extremely large as approximately 2 μm for an areal recording density of 2 Gb/in 2 , whereas it is now as extremely small as approximately 100 nm for an areal recording density of 100 Gb/in 2 . A decrease in the core width means that tolerances for the dimensions of core width become even more stringent. Whereas the core width and tolerance of write elements for an areal recording density of approximately 100 Gb/in 2  currently in mass-production is approximately 185±50 nm, the core width and tolerance of the read element is required to satisfy machining accuracy as extremely stringent as approximately 100±10 nm. The read and write elements of the magnetic head are fabricated after being subjected to a series of complex processes wherein a process based on a photolithography technique for machining the elements into desired shapes, a plating process for depositing metal films, a sputtering process, and a polish process based on chemical mechanical polish (CMP) are repeated over and over again. For this reason, it becomes more difficult to make the magnetic head fall within the specified tolerances thereof in a manufacturing process as the core width becomes narrower. Although the degradation of read signal output is caused if the read element core width is narrower than the tolerable limit thereof, there is no major problem as long as CPP-GMR or TuMR elements having extremely high magneto-resistive effect rates are used. If the core width is wider than the tolerable limit thereof, however, there arises the problem that the read element senses track edge noise. It is therefore an object of the present invention to solve the problem of preventing track edge noise from being sensed even if the core width of the read element of the magnetic head is wider than the tolerable limit thereof. It is another object of the present invention to provide a control circuit for controlling the magnetic head. 
   SUMMARY 
   In accordance with an aspect of embodiment, a magnetic head includes a slider, a read element disposed on the slider, and a heater element disposed closer to the leading edge side of the magnetic head than the read element in a position opposite to a recording medium. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic view illustrating the inside of a common magnetic storage device for which the magnetic head of an embodiment of the present invention is used. 
       FIG. 2  is a schematic view illustrating a cross-section of the magnetic head of the embodiment. 
       FIG. 3  is a schematic view illustrating another cross-section of the magnetic head of the embodiment. 
       FIG. 4  is a schematic view illustrating a lateral side of the magnetic head of the embodiment. 
       FIG. 5  is a graphical representation illustrating the relationship between the temperature of tracks raised by a heater element and the amount of track width expansion. 
       FIG. 6  is a block diagram illustrating a control circuit for controlling the magnetic head of the embodiment. 
   

   DETAILED DESCRIPTION OF THE EMBODIMENTS 
   Hereinafter, an embodiment of the present invention will be described with reference to  FIGS. 1 to 6 .  FIG. 1  is a schematic view illustrating the inside of a common magnetic storage device for which the magnetic head of an embodiment of the present invention is used. Inside a magnetic storage device  1 , there are equipped a magnetic disk  11  serving as a recording medium, a head slider  12  whereon a magnetic head is mounted, a head amplifier IC  13  responsible for controlling read/write signals, a read/write channel LSI  14 , and the like.  FIG. 2  is a schematic view illustrating a cross-section of the magnetic head of the present embodiment.  FIG. 3  is a schematic view illustrating the ABS surface, i.e., the air bearing surface of the magnetic head of the present embodiment. A low-thermal expansion layer  22  made of Ta or B is formed on an Al—Ti—C substrate  21  serving as the head slider and made of Al 2 O 3 —Ti—C, using, for example, a plating process to a thickness of approximately 5 μm. Next, a heater element  23  made of, for example, a Cu thin film is formed using a plating process to a thickness of approximately 3 μm. At this point, though not shown in the figure, a pair of electrodes is formed in the heater element  23 . Note that as the heater element, a semiconductor laser, such as a GaAlAs laser, may be used rather than the Cu thin film. Then, the low-thermal expansion layer  22  is once again formed using a plating process to a thickness of approximately 5 μm. As a result, it is possible to suppress the propagation of heat generated from the heater element  23 . In other words, it is possible to suppress the thermal damage of the read and write elements due to heat propagation from the heater element and the expansion of the head slider whereon the magnetic head is mounted. Note here that in  FIG. 2 , the widths of the low-thermal expansion layers  22  and  24  and the heater element  23  are defined as 0.7 mm, the same as the width  33  of the head slider. As described above, it is possible to heat the tracks of the recording medium even if a skew angle is given, by forming the low-thermal expansion layers  22  and  24  and the heater element  23  so as to extend in the cross-track direction. 
   Next, an alumina insulating layer made of Al 2 O 3 , though not shown in the figure, is formed to a thickness of approximately 0.3 μm. Then, on the alumina insulating layer, there is formed an approximately 2.0 μm-thick lower magnetic shield layer  25  made of, for example, an Ni—Fe alloy, intended to alleviate the effect of unnecessary read signals from the recording medium, using a common plating process. Then, a read element  26  having a GMR, CPP-GMR or TuMR magneto-resistive effect is formed using a common sputtering process so that the width (refers to a read core width) thereof equals 100 nm. Then, an approximately 1.5 μm-thick upper magnetic shield layer  27  made of, for example, an Ni—Fe alloy is formed. Note that an interspatial part between the lower magnetic shield layer  25  and the upper magnetic shield layer  27  is assumed to be covered with alumina, though not shown in the figure. 
   Next, an insulating layer made of alumina is formed on the upper magnetic shield layer  27  to a thickness of 0.26 μm. Then, a write element is formed. The write element is formed by forming an approximately 1.0 μm-thick first lower magnetic pole layer  28 , an approximately 4.3 μm-thick second lower magnetic pole layer  30 , an approximately 5.0 μm-thick joint part  31 , approximately 1.8 μm-thick thin film coil portions  29 , and an approximately 5.0 μm-thick upper magnetic pole layer  32 , using a common plating process. Note that it is possible to use a common photolithography or CMP technique to machine the write element into a desired shape. In addition, it should be assumed that spatial parts, such as gaps between the thin film coil portions  29 , between the second lower magnetic pole layer  30  and the upper magnetic pole layer  32  are covered with alumina, though not shown in the figure. In other words, it should be assumed that spatial parts in the entirety of  FIG. 2  are covered with alumina. 
     FIG. 4  is a schematic view illustrating a lateral side of the magnetic head of the embodiment. On the lateral side of the magnetic head&#39;s head slider, there are formed trenches as heat sinks  45  using, for example, a focused ion beam (FIB) process or a damascene process, so that both the width and depth thereof are approximately 100 μm and the trenches are virtually parallel with the length direction of the head slider. By forming heat sinks  45  in this way, it is possible to cool down the head slider heated by the heater element by means of airflow when air flows from a leading edge  44  to a trailing edge  43  at the time of flying, without increasing air resistance. In addition, the head slider is provided with a front rail  41  and a rear rail  42 . By forming the low-thermal expansion layer  22  along with the heat sinks  45  as described above, the issue of heat propagation caused by the heater element  23  becomes ignorable. In other words, it is possible to prevent the magnetic head and the recording medium from coming into contact with each other due to the thermal expansion of the head slider and thus becoming damaged. 
     FIG. 5  is a graphical representation illustrating the relationship between the temperature of track of the recording medium  11  raised by the heater element  23  and the amount of track width expansion of the recording medium  11 . Simulations performed by the inventor of the present invention have revealed that the track width of the recording medium expands by 12.4 nm as the track temperature rises by 1° C. It is therefore only necessary to expand the track width of the recording medium  11  by the heater element  23  in accordance with the core width of the read element by taking advantage of this value. The core width of the read element can be measured using either an optical method wherein a scanning electron microscope (SEM) is used or a micro-track method wherein the core width is calculated from track profiles of the recording medium. Note that the measurement of the read element&#39;s core width based on the micro-track method may be performed using a head tester before assembling the magnetic head into the magnetic storage device  1 , or may be performed by calculation from track profiles of the recording medium  11  within the magnetic storage device  1  after assembling the magnetic head into the magnetic storage device  1 . If the measured core width is, for example, 130 nm for a standard core width value of 100 nm, it is only necessary to raise the track of the recording medium temperature by 2.4° C. by heating the track of the recording medium with the heater element at the time of read operation. Also note that it is necessary to previously quantify the relationship between the thermal dose of the heater element  23  and the rise of track temperature using a temperature sensor, such as a thermocouple. As described above, in the embodiment of the present invention, the track width of the recording medium is expanded by instantaneously heating the tracks of the recording medium using a pulse voltage at the time of read operation for detecting read signals. At this point, it is possible to save electric power by controlling the thermal dose according to the dimensions of the core width. 
     FIG. 6  is a block diagram illustrating a control circuit for controlling the magnetic head of the embodiment. First, a read power supply  71  for controlling the read element, a read data buffer  72 , a read amplifier  73 , a write power supply  74  for controlling the write element, a write data buffer  75 , and a write driver  76  are equipped in a head amplifier IC  13 , in order to perform normal read/write processing. Note that the read terminal portion  61  of the read element of a magnetic head  60  is connected to the read amplifier  73  and the write terminal portion  62  of the write element is connected to the write driver  76 . At this point, the head amplifier IC  13  is further equipped with a heater element power supply  77  and a heater element driver  79 . By connecting a pulse modulation circuit  78  to the heater element power supply  77 , it is possible to instantaneously heat the heater element  23 . Note that the heater element driver  79  is connected to a heater element terminal portion  63 . 
   The decoder unit  82  of the read/write channel LSI  14  has the function of decoding read data received from the read data buffer  72 . Read operation is performed by amplifying a read signal from the recording medium by the read amplifier  73  and transmitting data to the read/write channel LSI  14  via the read data buffer  72 . Note that power to the read terminal portion  61  is applied from a read voltage regulator  81  via the read power supply  71 . Write operation is performed in such a manner that an encoder unit  84  encodes write data and transmits the encoded write data to a write data buffer  75  so that a write magnetic field is applied from the write element through the write driver  76  and the write terminal portion  62  to the recording medium. Note that power to the write terminal portion  62  is applied from a write voltage regulator  83  through the write power supply  74 . Also note that the decoder unit  82  and the encoder unit  84  are connected to a waveform equalizing FIR filter, a Viterbi decoder, and the like, though not shown in the figure. In addition, a heater element voltage regulator  85  is disposed in the read/write channel LSI  14 . The heater element voltage regulator  85  has the same function as those of the aforementioned read voltage regulator  81  and the write voltage regulator  83 . 
   Note here that a heater element control circuit  86  is further disposed in the read/write channel LSI  14 . A memory is equipped in the heater element control circuit  86  to store the value of the read element&#39;s core width measured using the above-described methods and the relationship between the thermal dose of the heater element  23  and the amount of track temperature rise. The heater element control circuit  86  initiates read operation and puts the heater element driver  79  into operation to expand the track width. Note that the heater element control circuit  86  may be disposed within the head amplifier IC  13  or may be disposed independently so as to intermediate between the read/write channel LSI  14  and the head amplifier IC  13 . 
   According to the configurations of the magnetic head and the control circuit of the present embodiment, read element does not involve the detection of track edge noise. In addition, by using low-thermal expansion materials and heat sinks, it is possible to prevent thermal damage to the read element and the write element due to heat propagation caused by the heater element and the expansion of the head slider. Accordingly, it is possible to provide a magnetic storage device having high HDI reliability. 
   It should be noted that the magnetic head in accordance with the foregoing embodiment of the present invention is applicable to magnetic heads in a variety of forms, including magnetic heads for perpendicular magnetic recording and magneto-optical recording, in addition to a magnetic head for in-plane magnetic recording.