Abstract:
Embodiments of the invention provide a read head which is implemented in a magnetic disk drive that supports a high recording density and a high transfer rate and is excellent in static electricity durability. In one embodiment, a magnetic head wherein a charge diffuses from a read element to a slider at a time constant of about 100 ms or less.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application claims priority from Japanese Patent Application No. JP2004-366052, filed Dec. 17, 2004, the entire disclosure of which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to a magnetic head having improved durability against static electricity and higher reliability. 
     A spin valve element using the giant magnetoresistive effect has come into practical use as a read element of a magnetic disk drive. Read sensitivity has been improved along with improvements in recording density, with the result that damage caused by static electricity in the manufacture process gives rise to a problem. Waveform fluctuation and an increase in noise are generated by such damage in addition to electric breakdown and fusion of devices. This presents a major challenge from the standpoint of yields and reliability of magnetic heads. Hence, the following countermeasures have been taken against the damage by static electricity.
     (1) A method for short-circuiting terminals is disclosed in Japanese Patent Laid-open No. 10-055511. In this disclosure, an MR lead is shunt by an MR head suspension, and means for opening a circuit before completion of assembly is used to take a measure for protection against the static electricity.   (2) A method for inserting a resistance between terminals is disclosed in Japanese Patent Laid-open No. 7-169005. In this disclosure, a discharge protection circuit is provided with a path for shunting a current to be applied to an MR head element.   (3) A method for inserting a diode between terminals is disclosed in Japanese Patent Laid-open No. 10-269534, in which a shot key diode is connected to a protection circuit.   

     BRIEF SUMMARY OF THE INVENTION 
     Although it is important to control an amount of a charge and a discharge time in a device susceptive to the static electricity, such as the GMR head (read element), any disclosure relating to such control has not been made. In order to further enhance durability against static electricity in the manufacture process, it is necessary also to improve control on the time the electric charge diffuses in addition to shunting between terminals and inserting a resistance or diode between terminals. When the charge diffuses in a short period of time, a large current is generated to damage the read element. In turn, when the charge diffuses for a long period of time, the charge is retained in a subsequent process to cause static electricity destruction. Hence, the present invention provides a read head which is implemented in a magnetic disk drive that supports a high recording density and a high transfer rate and is excellent in static electricity durability. 
     A magnetic head according to an embodiment of the present invention is characterized in that a charge diffuses from a read element to a slider at a time constant of about 100 ms or less. Further, the magnetic head is characterized in that a resistance value between an electrode and the slider is in the range of about 10 6  Ω to 10 11  Ω. 
     A head suspension assembly according to an embodiment of the present invention is characterized in that a charge diffuses from a read element to a suspension at a time constant of about 100 ms or less. Further, the head suspension assembly is characterized in that a resistance value between an electrode and the suspension is in the range of about 10 6  Ω to 10 11  Ω. The inventors have determined these ranges for the present invention. Some examples falling within the ranges are described hereinbelow. 
     According to the present invention, it is possible to improve static electricity durability and to realize a magnetic head which is high in yield and reliability. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a top view and a side view showing a disk drive according to an embodiment of the present invention. 
         FIG. 2  is an external view of a magnetic head of the present invention. 
         FIG. 3  is a diagram showing a magnetic head of the longitudinal magnetic recording method as viewed from a sectional direction of a magnetic disk. 
         FIG. 4  is a diagram showing a magnetic head of the vertical magnetic recording method as viewed from a sectional direction of a magnetic disk. 
         FIG. 5  is a diagram showing a relationship between a time it takes for a charge charged on a read element to diffuse and a resistance value between a read element and a slider. 
         FIG. 6  is a diagram showing a method for measuring the resistance value of  FIG. 5 . 
         FIG. 7  is a diagram showing a method for measuring the diffusion time of  FIG. 5 . 
         FIG. 8  is a diagram showing a relationship between a base alumina film thickness and the resistance value. 
         FIG. 9  is a diagram showing a relationship between a protection film thickness and the resistance value. 
         FIG. 10  is a diagram showing a relationship between a method for forming a protection film and the resistance value. 
         FIG. 11  is a diagram showing a relation ship between protection film processing and the resistance value. 
         FIG. 12  is a magnetic head according to a first embodiment of the present invention. 
         FIG. 13  is a magnetic head according to a second embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Hereinafter, embodiments of the present invention will be described with reference to the drawings. 
       FIGS. 1(   a ) and  1 ( b ) are conceptual diagrams showing a disk drive according to an embodiment of the present invention.  FIG. 1(   a ) is a top view of the disk drive, and  FIG. 1(   b ) is a side view of the disk drive. A magnetic head mounted on a slider  13  fixed to the tip of a suspension arm  12  writes and reads magnetized signals at a predetermined position on a magnetic disk rotated by a motor  4 . It is possible to select a position (track) of the magnetic head on the magnetic disk in a radial direction of the magnetic disk by driving a rotary actuator  15 . A write signal to the magnetic head and a read signal from the magnetic head are processed by signal processing circuits  35   a  and  35   b.    
       FIG. 2  shows an external view of a head suspension assembly of the present invention. The head suspension assembly has a suspension arm  12 , the slider  13  fixed to the tip of the suspension arm  12 , and a read element formed on a trailing edge side of the slider. 
       FIG. 3  is a diagram showing a magnetic head of the longitudinal magnetic recording method as viewed from a sectional direction of a magnetic disk. A read head has a read element  25  disposed on a substrate  34  and sandwiched between an upper magnetic shield  29  and a lower magnetic shield  27 . A current is applied to the read element  25  by an electrode. A write head defines a magnetic gap on an air bearing surface facing a magnetic disk  33  by way of a lower pole  30 , an upper pole  31 , and a magnetic gap layer  32  positioned between the upper and lower poles  31 ,  32 . With the longitudinal recording method, a magnetic flux leaked from the lower pole  30  magnetizes an orbital track on the magnetic medium in the longitudinal direction as shown in  FIG. 3  in a writing operation. The read element  25  of the read head injects the magnetic flux into the magnetized region on the rotating magnetic medium to cause a change in resistance inside the read element  25  in a reading operation. 
     Shown in  FIG. 4  is a diagram illustrating a magnetic head of the vertical magnetic recording method as viewed from a sectional direction of a magnetic disk. A read head has a read element  25  disposed on a substrate  34  and sandwiched between an upper magnetic shield  29  and a lower magnetic shield  27 . A current is applied to the read element  25  by an electrode. A write head defines a magnetic gap on an air bearing surface facing to the magnetic disk  33  by way of a lower pole  30 , an upper pole  31 , and a magnetic gap layer  32  positioned between the upper and lower poles  31 ,  32 . In a writing operation, a signal current is guided through a coil layer C, and a magnetic flux leaks onto the air bearing surface. The leaked magnetic flux returns to the magnetic head via a lower soft magnetic film  34  of the recording medium. The magnetic flux magnetizes an orbital track on the magnetic medium in the vertical direction. In a reading operation, the read element  25  of the read head injects the magnetic flux into the magnetized region on the rotating magnetic medium to cause a change in resistance inside the read element  25 , which is detected as a change in voltage of the read element  25 . 
     Shown in  FIG. 5  is a relationship between the time it takes for a charge charged on the read element to diffuse and a resistance value between the read element and the slider. As is apparent from  FIG. 5 , the diffusion time is determined depending on the resistance value. The resistance value between the read element and the slider is a value determined by a resistance value Rr between the electrode and the shield, a resistance value R 1  between the shield and the slider, and the resistance value Rc of the protection film on the air bearing surface. When a diffusion constant is small, a large current flows to the read element to damage the read element. In turn, when a diffusion constant is large, the charge is retained for a long period of time to cause static electricity destruction during assembling. Therefore, the resistance between the electrode of the read element and the slider may preferably be in the range of about 10 6  Ω to 10 11  Ω. 
       FIG. 6  shows a method for measuring the resistance value of  FIG. 5 . A resistance value between a read element terminal  37  and the slider  13  is measured by a high resistance meter. 
       FIG. 7  shows a method for measuring the diffusion time in  FIG. 5 . A surface of the slider  13  is grounded to be charged by a power unit  16  (through a wire  22 , a plate  21 , and a contact probe  18 ) via a lead terminal  17  of the suspension  12 , and then a damping time is measured by a potential meter  20  and displayed on a digital oscilloscope  19 . 
       FIG. 12  shows a magnetic head according to a first embodiment of the present invention. In this embodiment, a 1 nm-thick Si underlayer is formed and then a 2 nm-thick CAC carbon film is formed on the Si underlayer to obtain an ABS protection film  38 . Further, a 0.7 nm-thick base alumina is formed, and a 3-μm thick lower magnetic shield  27  is formed. With the above constitution, a resistance value between a slider  13  and a read element terminal  37  becomes 10 10  Ω, wherein a diffusion time becomes 10 ms. 
       FIG. 13  shows a magnetic head according to a second embodiment of the present invention. In this embodiment, a dense film is formed under decreased gas pressure by changing a sputtering rate for a CAC carbon from 10 −4  Torr to 10 −5  Torr. A 1 nm-thick Si underlayer is formed and then a 2 nm-thick CAC carbon film is formed on the Si underlayer to obtain an ABS protection film  38 . Further, a 0.7 nm-thick base alumina is formed, and a 3 μm-thick lower magnetic shield  27  is formed. With the above constitution, a resistance value between a slider  13  and a read element terminal  37  becomes 10 8  Ω, wherein a diffusion time becomes 1 ms. 
       FIG. 8  is a diagram showing a relationship between the base alumina film thickness and the resistance value. As is apparent from  FIG. 8 , it is possible to reduce the resistance value when the base alumina  39  of the magnetic heads shown in  FIGS. 12 and 13  is decreased in thickness. 
       FIG. 9  is a diagram showing a relationship between the protection film thickness and the resistance value. As is apparent from  FIG. 9 , it is possible to reduce the resistance value when the protection film  32  of the magnetic heads shown in  FIGS. 12 and 13  is decreased in thickness. 
       FIG. 10  shows a dependency on the method for forming the protection film. As is apparent from  FIG. 10 , the CAC carbon used in the present invention reduces the resistance value relative to a conventional CVD carbon. 
       FIG. 11  is a diagram showing a relationship between protection film processing and the resistance value. As is apparent from  FIG. 11 , the resistance value is reduced by using about 10% of nitride in the CAC carbon method as in the second embodiment. 
     It is to be understood that the above description is intended to be illustrative and not restrictive. Many embodiments will be apparent to those of skill in the art upon reviewing the above description. The scope of the invention should, therefore, be determined not with reference to the above description, but instead should be determined with reference to the appended claims along with their full scope of equivalents.