Abstract:
A merged MR head is formed by sequentially stacking a lower shield, a lower shield gap, a magnetoresistive (MR) element, an upper shield gap, a lower magnetic pole/upper shield, a recording gap layer, a coil, a coil insulating layer, and an upper magnetic pole on a side surface of a trailing edge of a floating slider having an air bearing surface. This merged MR head includes a pedestal which is formed on a portion on the lower magnetic pole/upper shield, including the air bearing surface, to have a width larger than that of the upper magnetic pole. The upper magnetic pole is stacked on the pedestal through the recording gap layer. A sidewall of the pedestal in the vicinity of the air bearing surface has a notch which is obtained by forming a plane where a sidewall of the upper magnetic pole is present. A method of manufacturing this merged MR head is also disclosed.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a division of application Ser. No. 09/111,931, filed Jul. 8, 1998 U.S. Pat. No. 6,141,821. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to a merged MR (magnetoresistive) head having aligned magnetic pole tips, and a method of manufacturing the same. 
     In a magnetic disk drive, data is read and written by using a magnetic disk medium serving as a storage medium, and a magnetic head having a electromagnetic transducing element mounted on a floating slider floating and supported by the air bearing effect caused by high-speed rotation of the magnetic disk medium. 
     Recent demands for an internal storage unit or external storage unit of a personal computer and the like increase remarkably, and downsizing, a higher operation speed, and a higher recording density are strongly demanded in a magnetic disk drive. 
     For this reason, improvements for high performance have been made in the magnetic head serving as the major portion of the magnetic disk drive, the magnetic disk medium, positioning servo, signal processing, and the like. In particular, whereas the magnetic head conventionally performs write (recording) and read (play) with one electromagnetic transducing element, recently, use of a so-called write/read separation type merged MR head is becoming the main stream. The merged MR head uses a conventional inductive element for data write, and an MR element, the output of which does not depend on the speed relative to the magnetic disk medium and which utilizes the magnetoresistive effect, for data read. These two elements are integrated and mounted on one floating slider. 
     This merged MR head is manufactured by utilizing photolithography technique, and micropatterning technique similar to a semiconductor manufacturing process. For example, Japanese Patent Laid-Open No. 7-262519 (U.S. Pat. No. 5,438,747) discloses a merged MR head and a technique concerning a method of manufacturing the same. 
     FIGS. 5A to  5 C show an example of a method of manufacturing a conventional merged MR head. 
     In order to decrease the side fringe magnetic field generated during recording, the conventional merged MR head has a recording gap layer having the same width as that of an upper magnetic pole and a sidewall aligned with the same plane where the side surface of the upper magnetic pole is present, and the pedestal of a lower magnetic pole/upper shield. 
     In the method of manufacturing a conventional merged MR head, the recording gap layer and the pedestal of the lower magnetic pole/upper shield are formed to have the same width as that of the upper magnetic pole. For this purpose, the recording gap layer is defined to have the same width as that of the upper magnetic pole by using ion milling and chemical etching. Subsequently, in accordance with ion milling, the pedestal of the lower magnetic pole/upper shield, having the same width as that of the upper magnetic pole and a side surface aligned with the same vertical plane where the side surface of the upper magnetic pole is present, is formed on the lower magnetic pole/upper shield by using the upper magnetic pole as the mask. 
     FIGS. 5A to  5 C show the manufacturing method which uses ion milling when defining the recording gap layer to have the same width as that of the upper magnetic pole. A recording gap layer  23  is deposited on a lower magnetic pole/upper shield  22 , and thereafter an upper magnetic pole  24  is formed on the recording gap layer  23  by electroplating using photoresist frame. A portion of the resultant structure other than the vicinity of the upper magnetic pole  24  is covered with a photoresist  26 , and the recording gap layer  23  is defined by ion milling to have the same width as that of the upper magnetic pole  24 . 
     Since the ion beam etching rate of the recording gap layer  23  is lower than the ion beam etching rate of the upper magnetic pole  24 , when defining the recording gap layer  23  to have the same width as that of the upper magnetic pole  24 , the thickness (height) of the upper magnetic pole  24  decreases largely. More specifically, FIG. 5A shows a state before the recording gap layer  23  is etched by ion milling, and FIG. 5B shows a state after the recording gap layer  23  is defined by ion milling by using the upper magnetic pole  24  as the mask (the broken line in FIG. 5B shows a portion to be etched by ion milling). In FIG. 5B, the thickness of the upper magnetic pole  24  is apparently smaller than that in FIG.  5 A. 
     Subsequently, as shown in FIG  5 C, a pedestal  21  for the lower magnetic pole/upper shield  22  is formed on the lower magnetic pole/upper shield  22  in accordance with ion milling by using the upper magnetic pole  24  as the mask. The pedestal  21  has the same width as that of the upper magnetic pole  24  and is aligned with the same vertical plane where a sidewall or surface  24   s  of the upper magnetic pole  24  is present. In this case, the thickness of the upper magnetic pole  24  further decreases. 
     In other words, FIG. 5B shows a state before the pedestal  21 , aligned with the same vertical plane where the side surface of the upper magnetic pole  24  is present, is defined on the lower magnetic pole/upper shield  22  in accordance with ion milling by using the upper magnetic pole  24  as the mask. FIG. 5C shows a state after the pedestal  21  is defined on the lower magnetic pole/upper shield  22  by using the upper magnetic pole  24  as the mask. 
     In FIG. 5C, the sidewall  24   s  of the upper magnetic pole  24 , a sidewall  23 s of the recording gap layer  23 , and a sidewall  21   s  of the pedestal  21  are aligned within the same plane  25 . Similarly, the respective sidewalls on the opposite side (the left-hand side in FIG. 5C) are aligned within the same plane. 
     FIGS. 6A to  6 C show another example of a conventional merged MR head and a method of manufacturing the same. 
     A recording gap layer  33  is formed on a lower magnetic pole/upper shield  32 , and thereafter an upper magnetic pole  34  is formed on the recording gap layer  33  by electroplating using photoresist frame. Subsequently, the recording gap layer  33  is defined to have the same width as that of the upper magnetic pole  34  by chemical etching. 
     In this case, since a chemical etching solution that etches not the upper magnetic pole  34  but the recording gap layer  33  can be selected, the thickness (height) of the upper magnetic pole  34  does not decrease. Subsequently, a pedestal  31  for the lower magnetic pole/upper shield  32  is formed on the lower magnetic pole/upper shield  32  in accordance with ion milling by using the upper magnetic pole  34  as the mask. The pedestal  31  has the same width as that of the upper magnetic pole  34  and is aligned with the same vertical plane as the side surface of the upper magnetic pole  34 . In this case, the thickness of the upper magnetic pole  34  decreases (the broken line in FIG. 6B shows a portion to be etched by ion milling). 
     In the conventional merged MR head manufacturing methods described above, the thickness of the upper magnetic pole becomes undesirably smaller than the thickness necessary to generate a sufficiently strong magnetic field when the merged MR head records a signal on the magnetic recording medium. 
     The reason for this is as follows. When forming the recording gap layer and the pedestal of the lower magnetic pole/upper shield by ion milling in order to decrease the side fringe magnetic field, the upper magnetic pole serving as the mask during ion milling must be formed thicker in advance by an amount corresponding to the thickness decreased by ion milling. For this purpose, the photoresist required for forming the upper magnetic pole by electroplating using photoresist frame must be formed to have a thickness larger than that of the necessary upper magnetic pole and to have a desired width of the upper magnetic pole. However, as the width of the upper magnetic pole decreases to meet a demand for a higher density, such a photoresist becomes difficult to form. 
     In the former case, since the ion beam etching rate of the recording gap layer  23  is lower than the ion beam etching rate of the upper magnetic pole  24 , when defining the recording gap layer  23  to have the same width as that of the upper magnetic pole  24 , the thickness of the upper magnetic pole  24  decreases largely. In other words, the thickness of the upper magnetic pole  24  decreases largely in accordance with the procedure from FIG. 5A to FIG.  5 B. 
     When forming the pedestal  21  for the lower magnetic pole/upper shield  22  by ion milling using the upper magnetic pole  24  as the mask, the thickness of the upper magnetic pole  24  further decreases. As a result, the thickness of the upper magnetic pole, which is necessary to generate a sufficiently strong magnetic field when recording a signal on the magnetic recording medium, may not be ensured. 
     In particular, when the width of the upper magnetic pole  24  becomes equal to or less than 2 μm, the thickness of the upper magnetic pole  24  that can be formed by electroplating using photoresist frame is about 5 μm at maximum. Therefore, when ion milling is performed for the recording gap layer  23  and the pedestal  21  portion for the lower magnetic pole/upper shield  22  by using the upper magnetic pole  24  as the mask, the thickness of the upper magnetic pole  24  becomes equal to or less than 3 μm, which is smaller than the required thickness, 4 μm. 
     In the latter case, the sidewall of the recording gap layer and the sidewall for the pedestal of the lower magnetic pole/upper shield cannot be formed on the same plane where the sidewall of the upper magnetic pole is present. 
     The reason for this is as follows. Assume that in order to avoid the problems of the former case, the recording gap layer is to be formed by chemical etching to have the same width as that of the upper magnetic pole and to have a sidewall within the same vertical plane where the sidewall of the upper magnetic pole is present. In this case, due to variations in chemical etching rate, it is difficult to stop etching as soon as the sidewall of the recording gap layer becomes located on the same plane where the sidewall of the upper magnetic pole is present. 
     More specifically, due to variations in etching rate of the recording gap layer  33  etched with a chemical etching solution, it is difficult to stop chemical etching as soon as the side surface of the recording gap layer  33  reaches the same plane  37   a  or  37   b  where a side surface or wall  34   s  of the upper magnetic pole  34  is present. As a result, as shown in FIG. 6B, the side surface of the recording gap layer  33  undesirably extends to the outer side of the same plane  37   a  where the sidewall  34   s  of the upper magnetic pole  34  is present, thus forming an etch residue  35 , or the side surface of the recording gap layer  33  undesirably retreats backward to the inner side of the same plane  37   b  where the sidewall  34   s  of the upper magnetic pole  34  is present, thus causing an over-etching  36 . 
     In the etch residue  35  portion, the over-extending recording gap layer  33  forms a mask. As shown in FIG. 6C, a sidewall  31   s  (on the left in FIG.  6 C), on the opposite side, of the pedestal  31  for the lower magnetic pole/upper shield  32  is formed on a plane  38  on the outer side of the same plane  37   a  where the sidewall  34   s  of the upper magnetic pole  34  is present. Accordingly, the side fringe magnetic field is not decreased. 
     Furthermore, in a portion of the recording gap layer  33  where the over-etching  36  has occurred, the sidewall  31   s  of the pedestal  31  for the lower magnetic pole/upper shield  32  can be formed on the same planes  37   a  and  37   b  where the sidewall  34   s  of the upper magnetic pole  34  is present. However, the over-etching  36  portion of the recording gap layer  33  is not filled even in the later steps but is left as a hole. A foreign matter may enter through this hole to reach an element portion covered with a protection film, to corrode the element. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a merged MR head in which the upper magnetic pole is formed to have a width equal to or less than 2 μm to perform high-density magnetic recording, and a method of manufacturing the same. 
     It is another object of the present invention to provide a merged MR head in which the sidewall of the upper magnetic pole and the sidewall of the pedestal for the lower magnetic pole/upper shield are aligned on the same plane, and a method of manufacturing the same. 
     In order to achieve the above objects, according to the present invention, there is provided a merged MR head formed by sequentially stacking a lower shield, a lower shield gap, a magnetoresistive (MR) element, an upper shield gap, a lower magnetic pole/upper shield, a recording gap layer, a coil, a coil insulating layer, and an upper magnetic pole on a side surface of a trailing edge of a floating slider having an air bearing surface, wherein the merged MR head comprises a pedestal which is formed on a portion on the lower magnetic pole/upper shield, including the air bearing surface, to have a width larger than that of the upper magnetic pole, the upper magnetic pole being stacked on the pedestal through the recording gap layer, and a sidewall of the pedestal in the vicinity of the air bearing surface has a notch which is obtained by forming a plane where a sidewall of the upper magnetic pole is present. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIGS. 1A to  1 F are views showing the steps in manufacturing a merged MR head according to the first embodiment of the present invention, in which the shape of a magnetic pole tip seen from a side corresponding to the air bearing surface of a merged MR head element is shown in the order of manufacturing steps; 
     FIGS. 2A to  2 E are views showing the steps in manufacturing a merged MR head according to the second embodiment of the present invention, in which the shape of a magnetic pole tip seen from a side corresponding to the air bearing surface of the merged MR head element is shown in the order of manufacturing steps; 
     FIGS. 3A to  3 E are views showing the steps in manufacturing a merged MR head according to the third embodiment of the present invention, in which the shape of a magnetic pole tip seen from a side corresponding to the air bearing surface of the merged MR head element is shown in the order of manufacturing steps; 
     FIGS. 4A and 4B are views showing a method of manufacturing a merged MR head according to the fourth embodiment of the present invention; 
     FIGS. 5A to  5 C are views showing the steps in an example of a method of manufacturing a conventional merged MR head; and 
     FIGS. 6A to  6 C are views showing the steps in another example of a method of manufacturing a conventional merged MR head. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention will be described in detail with reference to the accompanying drawings. 
     FIGS. 1A to  1 F show the steps in a method of manufacturing a merged MR head according to an embodiment of the present invention. In FIGS. 1A to  1 E, the shape of a portion above a lower magnetic pole/upper shield  2  is shown in the order of manufacturing steps. FIG. 1F shows the shape of a magnetic pole tip seen from a surface corresponding to the air bearing surface of a completed merged MR head. 
     To obtain this merged MR head, as shown in FIG. 1F, a lower shield  7  is formed, an MR element  6  is formed, and thereafter the lower magnetic pole/upper shield (to be referred to as the upper shield hereinafter)  2  is formed. After formation of the upper shield  2 , a pedestal for the lower magnetic pole/upper shield (to be referred to as a pedestal hereinafter)  1 , having a width  1   w  slightly larger than the width ( 5   w ) of an upper magnetic pole  5  and a height  1   h  equal to or larger than the recording gap layer thickness ( 3   t ), is selectively formed on the upper shield  2  (FIG.  1 A). 
     A recording gap layer  3  having a thickness  3   t  is formed on the upper shield  2  and pedestal  1 . Since the upper shield  2  has the pedestal  1 , the thickness of the recording gap layer  3  on the corner of the pedestal  1 , i.e., the thickness of a corner  4 , becomes smaller than the recording gap layer thickness  3   t  (FIG.  1 B). 
     A lower insulating layer, a coil, and an upper insulating layer (latter two are not shown) that constitute the merged MR head are formed. In this formation, the thickness of the recording gap layer corner  4  is further decreased. Subsequently, the upper magnetic pole  5  having a thickness  5   t  and the width  5   w  is formed on the recording gap layer  3  in the pedestal  1  region by electroplating using photoresist frame (FIG.  1 C). 
     By using the upper magnetic pole  5  as the mask, the recording gap layer  3  and the pedestal  1  are notched (removed) by ion milling to have the same width as the width  5   w  the upper magnetic pole  5  (FIG.  1 D). In FIG. 1D, the broken line indicates a portion to be etched by ion milling. As a result, a sidewall  5   s  of the upper magnetic pole  5 , a sidewall  3   s  of the recording gap layer  3 , and a sidewall  1   s  of the pedestal  1  are formed within the same plane  10  (FIG.  1 E). 
     The structure of a merged MR head having a floating slider with an air bearing surface, and a coil and a coil insulating layer stacked on the floating slider is described in Japanese Patent Laid-Open No. 7-262519 (U.S. Pat. No. 5,438,747), and a description thereof will be omitted accordingly. The structure of the merged MR head described in this reference is incorporated in this embodiment. 
     The steps of FIGS. 1A to  1 F described above will be individually described in detail. 
     Referring to FIG. 1A, the width  1   w  of the pedestal  1  is formed to be slightly larger than the width  5   w  of the upper magnetic pole  5  so that, even if the position of the photoresist frame used when forming the upper magnetic pole  5  by electroplating using photoresist frame may slightly vary, the end of the photoresist frame is formed on the pedestal  1 . When considering these variations, the width  1   w  of the pedestal  1  is preferably larger than the width  5   w  of the upper magnetic pole  5  by 0.1 μm to 2.0 μm, and is particularly most preferably larger by 1.0 μm. With this size, the corner  4  is exposed beside the lower portion of the upper magnetic pole  5 . 
     The height  1   h  of the pedestal  1  is preferably larger than the recording gap layer thickness  3   t . For example, when the recording gap layer thickness  3   t  falls within the range of 0.1  82  m to 0.5 μm, the height  1   h  of the pedestal  1  preferably falls within the range of 0.1 μm to 2 μm. In particular, the height  1   h  of the pedestal  1  is preferably equal to or larger than twice the recording gap layer thickness  3   t . For example, when the recording gap layer thickness  3   t  is 0.3 μm to 0.4 μm, the height  1   h  of the pedestal  1  is preferably equal to or larger than 1.0 μm. 
     This is because it facilitates formation of a notched portion height  8  of the pedestal  1 , having the sidewall  1   s  aligned within the same plane where the sidewall  5   s  of the upper magnetic pole  5  is present, to be equal to or larger than twice the recording gap layer thickness  3   t.    
     Referring to FIG. 1B, since a step formed by the pedestal  1  is present on the upper shield  2 , a thickness  4   t  of the recording gap layer corner  4  on the corner of the pedestal  1  becomes smaller than the recording gap layer thickness  3   t  on the pedestal  1 . For example, when the recording gap layer thickness  3   t  falls within the range of 0.3 μm to 0.4 μm, the thickness  4   t  of the recording gap layer corner  4  is decreased to 0.2 μm to 0.1 μm. 
     Referring to FIG. 1C, after the upper magnetic pole  5  is formed by electroplating using photoresist frame, the photoresist that has served as the frame is removed. When the width  5   w  of the upper magnetic pole  5  is equal to or smaller than 2 μm, the thickness  5   t  of the upper magnetic pole  5  can be formed to as small as 5 μm at maximum. This is because when the upper magnetic pole  5  is to be formed by electroplating using photoresist frame, the thickness of the photoresist, that serves as the frame when forming the width  5   w  of the upper magnetic pole  5  to be equal to or smaller than 2 μm, can be formed to as small as 5 μm at maximum. 
     In other words, if the thickness of the thinnest portion of the photoresist that serves as the frame is set to be equal to or larger than 5 μm, the thickness of a portion of the photoresist corresponding to a  5   w -width portion of the upper magnetic pole  5  becomes equal to or larger than 10 μm, and the width  5   w  of the upper magnetic pole  5  cannot be formed to be equal to or smaller than 2 μm accordingly. 
     In the steps of forming the lower insulating layer, the coil, and the upper insulating layer, the thickness  4   t  of the recording gap layer corner  4  is decreased to about ⅕ to ⅙ the recording gap layer thickness  3   t  due to ion milling which is practiced when forming the coil. For example, when the recording gap layer thickness  3   t  is 0.3 μm to 0.4 μm, the thickness  4   t  of the recording gap layer corner  4  is decreased to 0.08 μm to 0.05 μm. 
     This is due to the following reason. When performing ion milling to form the coil, in order to remove the film between the coils, an ion beam is made incident in a direction perpendicular, or close to perpendicular, to the upper shield  2 . Because of the presence of the pedestal  1 , the surface of the recording gap layer corner  4  is obliquely inclined, as shown in FIG. 1B, and the ion beam comes incident on the recording gap layer corner  4  obliquely. 
     When the recording gap layer  3  is made of, e.g., aluminum oxide, the ion milling rate for aluminum oxide is larger in oblique incidence of the ion beam than in perpendicular incidence. As a result, the recording gap layer corner  4  is etched in a larger amount than the recording gap layer  3  on the upper shield  2 . 
     Since the width  1   w  of the pedestal  1  is slightly larger than the width  5   w  of the upper magnetic pole  5 , the recording gap layer corner  4  is exposed under the right and left sidewalls of the upper magnetic pole  5 . 
     Referring to FIGS. 1D and 1E, the recording gap layer  3  and the pedestal  1  are defined to have the same width as that of the upper magnetic pole  5  by ion milling using the upper magnetic pole  5  as the mask. In this case, of the recording gap layer  3  which is etched by ion milling, a portion corresponding to the corner of the pedestal  1  formed to have the width  1   w  slightly larger than the width  5   w  of the upper magnetic pole  5  slightly extends horizontally from the upper magnetic pole  5 , so that the recording gap layer corner  4  is exposed laterally at the lower portion of the sidewall  5   s  of the upper magnetic pole  5 . Accordingly, the width of the recording gap layer  3  can be defined to the thickness  5   t  of the upper magnetic pole  5  by only etching the recording gap layer corner  4  which has a thickness ⅕ to ⅙ the recording gap layer thickness  3   t  on the pedestal  1 . 
     In particular, when the width  1   w  of the pedestal  1  is formed to be larger than the width  5   w  of the upper magnetic pole  5  by 0.1 μm to 2.0 μm, the recording gap layer corner  4  can be exposed laterally at the lower portion of the sidewall  5   s  of the upper magnetic pole  5 . When the width  1   w  of the pedestal  1  is formed to be larger than the width  5   w  of the upper magnetic pole  5  by 1.0 μm, the recording gap layer corner  4  can be exposed laterally at the lower portion of the sidewall  5   s  of the upper magnetic pole  5  most reliably. 
     More specifically, before deposition of the recording gap layer  3 , the pedestal  1  is formed to have a width slightly larger than the width  5   w  of the upper magnetic pole  5 , so that the recording gap layer corner  4  having a thickness ⅕ to ⅙ the recording gap layer thickness  3   t  on the pedestal  1  can be exposed laterally at the lower portion of the sidewall  5   s  of the upper magnetic pole  5 . Accordingly, the ion milling time required for defining the recording gap layer  3  to have the width  5   w  of the upper magnetic pole  5  by ion milling using the upper magnetic pole  5  as the mask can be decreased to ⅕ to ⅙ the conventionally required time. As a result, the amount of decrease in thickness  5   t  of the upper magnetic pole  5 , obtained when defining the recording gap layer  3  to have the width  5   w  of the upper magnetic pole  5  by ion milling, can be decreased to ⅕ to ⅙ the conventionally required amount. 
     Referring to FIG. 1E, after the recording gap layer  3  is defined to have the width  5   w  of the upper magnetic pole  5  by ion milling, the pedestal  1  is sequentially defined to have the width  5   w  of the upper magnetic pole  5  by ion milling using the upper magnetic pole  5  as the mask. 
     In this manner, when the recording gap layer  3  and the pedestal  1  are defined in accordance with ion milling by using the upper magnetic pole  5  as the mask, the sidewall  5   s  of the upper magnetic pole  5 , the sidewall  3   s  of the recording gap layer  3 , and the sidewall  1   s  of the notched portion of the pedestal  1  can be formed within the same plane  10 . 
     When defining the pedestal  1  and recording gap layer  3  to have the width  5   w  of the upper magnetic pole  5  by using the upper magnetic pole  5  as the mask, the height  8  of the notched portion of the pedestal  1  is preferably formed to be equal to or larger than twice the recording gap layer thickness  3   t . This is because it can decrease widening of the fringe magnetic field during recording. 
     The amount of decrease in thickness of the upper magnetic pole  5 , obtained when defining the recording gap layer  3  and the pedestal  1  by ion milling using the upper magnetic pole  5  as the mask, is the sum of the amount of decrease obtained when removing the recording gap layer  3  and the amount of decrease obtained when notching the pedestal  1  for the lower magnetic pole/upper shield  2  to have the same width as that of the upper magnetic pole  5 . When the recording gap layer thickness  3   t  is 0.3 μm to 0.4 μm, the amount of decrease in thickness of the upper magnetic pole  5 , obtained when removing the recording gap layer  3 , is about 0.1 μm to 0.2 μm when calculated on the basis of the thickness of the remaining recording gap layer  3  (⅕ to ⅙ the initial value) and the rate ratio (about twice) in ion milling of the material of the recording gap layer to the material of the magnetic pole. 
     The amount of decrease in thickness of the upper magnetic pole  5 , obtained when notching the pedestal  1 , is 0.6 μm to 0.8 μm when the notched portion height  8  is set to equal or larger than twice that of the recording gap layer  3 . Accordingly, when the thickness of the initial upper magnetic pole  5  is 5 μm, the thickness of the upper magnetic pole  5 , after the recording gap layer  3  and pedestal  1  are defined by ion milling and the pedestal  1  is notched to have the same width as that of the upper magnetic pole  5 , is 4.0 μm to 4.3 μm. 
     When the method of manufacturing the merged MR head described above is employed, a merged MR head satisfying all the following conditions can be provided: 
     (1) the width  5   w  of the upper magnetic pole  5  is equal to or smaller than 2 μm and the thickness of the upper magnetic pole  5  is equal to or larger than 4.0  82  m; 
     (2) the recording gap layer thickness  3   t  falls within the range of 0.1 μm to 0.4 μm; 
     (3) the sidewall  3   s  of the recording gap layer  3  and the sidewall  1   s  of the notched portion of the pedestal  1  are aligned within the same plane where the sidewall  5   s  of the upper magnetic pole  5  is present; and 
     (4) the height of the sidewall  1   s  of the notched portion of the pedestal  1  falls within the range of 0.5 to 4 times the recording gap layer thickness  3   t  of the recording gap layer  3  having the same width as the width  5   w  of the upper magnetic pole  5 . 
     In particular, a merged MR head satisfying all the following preferable conditions can be provided: 
     (1) the width  5   w  of the upper magnetic pole  5  is equal to or smaller than 2 μm and the thickness of the upper magnetic pole  5  is equal to or larger than 4.0 μm; 
     (2) the recording gap layer thickness  3   t  falls within the range of 0.3 μm to 0.4 μm; 
     (3) the sidewall  3   s  of the recording gap layer  3  and the sidewall  1   s  of the notched portion of the pedestal  1  are aligned within the same plane where the sidewall  5   s  of the upper magnetic pole  5  is present; and 
     (4) the height  8  of the notched portion, which is formed by notching the sidewall is of the notched portion of the pedestal  1  to have the same width as the width  5   w  of the upper magnetic pole  5 , is 0.6 μm to 0.8 μm or is larger than 0.8 μm. 
     FIGS. 2A to  2 E show a method of manufacturing a merged MR head according to the second embodiment of the present invention. In FIGS. 2A to  2 E, portions that are identical to those of FIGS. 1A to  1 F are denoted by the same reference numerals as in FIGS. 1A to  1 F, and a description thereof will be omitted. 
     As shown in FIGS. 2C to  2 E, the upper magnetic pole of this embodiment is formed by stacking two members, i.e., upper magnetic poles  5   a  and  5   b . The upper magnetic pole  5   b  on the recording gap layer  3  side is made of, e.g., a material having a higher saturation magnetic flux density than that of a nickel-iron alloy. More specifically, a cobalt-nickel-iron alloy, a cobalt-tantalum-zirconium alloy, a cobalt-niobium-zirconium alloy, iron nitride, or an iron-aluminum-silicon alloy is used. 
     In this embodiment, after the recording gap layer  3  is formed on a pedestal  1  for an upper shield  2  in FIGS. 2A and 2B, the two upper magnetic poles  5   b  and  5   a  are sequentially stacked on the recording gap layer  3  in the pedestal  1  region by using a predetermined material. FIGS. 2D and 2E show steps identical to those shown in FIGS. 1E and 1D, and a detailed description thereof will thus be omitted. 
     FIGS. 3A to  3 E show a method of manufacturing a merged MR head according to the third embodiment of the present invention. 
     The upper magnetic pole of this embodiment is constituted by two members, i.e., upper magnetic poles  5   a  and  5   b , in the same manner as in the second embodiment. The upper magnetic pole  5   b  on the recording gap layer  3  side is made of, e.g., a material having a higher saturation magnetic flux density than that of a nickel-iron alloy. More specifically, a cobalt-nickel-iron alloy, a cobalt-tantalum-zirconium alloy, a cobalt-niobium-zirconium alloy, iron nitride, or an iron-aluminum-silicon alloy is used. 
     In this embodiment, furthermore, a pedestal  1   a  is made of a material having a higher saturation magnetic flux density than that of a nickel-iron alloy, in the manner as the upper magnetic pole  5   b . For example, a cobalt-nickel-iron alloy, a cobalt-tantalum-zirconium alloy, a cobalt-niobium-zirconium alloy, iron nitride, or an iron-aluminum-silicon alloy is used. 
     According to this embodiment, in FIG. 3A, the pedestal  1   a  is formed on an upper shield  2  by using a specific material. FIGS. 3B to  3 E show steps identical to those of FIGS. 2B to  2 E, and a detailed description thereof will thus be omitted. 
     FIGS. 4A and 4B show a merged MR head according to the fourth embodiment of the present invention. 
     FIG. 4A shows the shape of the air bearing surface of the merged MR head manufactured in accordance with the same manufacturing method as in FIG. 1. A notched portion height  8  of a pedestal  1  which is notched to have the same width as that of an upper magnetic pole  5  is different from a height  11  of the pedestal  1 . Thus, the initial width of the pedestal  1  and the width of the pedestal  1  which is notched to have the same width as that of the upper magnetic pole  5  are different from each other, thus forming a corner  12 . Due to the shadow of the upper magnetic pole of an upper shield  2  which is formed when forming the pedestal  1  by ion milling, a tapered portion  13  is formed. 
     In this embodiment, the time required for ion milling, which is practiced by using the upper magnetic pole  5  in the steps of FIGS. 1D and 1E as the mask, is set long within such a range that the thickness of the upper magnetic pole  5  does not become smaller than a desired thickness. When the ion milling time is adjusted in this manner, a notched portion height  9  of the pedestal  1  which is formed to have the same width of the upper magnetic pole  5  is set close to the height  11  of the pedestal  1 . As a result, a shape can be obtained in which the corner  12  as shown in FIG. 4A is not formed in the tapered portion  13  formed due to the shadow of the upper magnetic pole  5  of the upper shield  2  which is formed when forming the pedestal  1  by ion milling. 
     As has been described above, according to the present invention, before forming a recording gap layer, a pedestal having a width slightly larger than that of an upper magnetic pole and a height equal to or larger than the thickness of the recording gap layer is formed. The thickness of the recording gap layer at the pedestal corner can be set thin to ⅕ to ⅙ the thickness of the recording gap layer on the pedestal, and the corner of the recording gap layer can be exposed laterally at the lower portion of the sidewall of the upper magnetic pole. 
     More specifically, the milling time, which is required for defining the recording gap layer so as to have the same width as that of the upper magnetic pole and a sidewall formed within the same plane where the sidewall of the upper magnetic pole is located by using the upper magnetic pole as the mask, is decreased to ⅕ to ⅙ the conventionally required time, and the amount of decrease in thickness of the upper magnetic pole which is obtained at this time is decreased to ⅕ to ⅙ the conventional amount. As a result, the amount of decrease in thickness of the upper magnetic pole, which is obtained when forming the recording gap layer and the pedestal by ion milling such that they have the same width as that of the upper magnetic pole and that their side surfaces are aligned within the same plane by using the upper magnetic pole as the mask, can be greatly decreased. 
     Since the upper magnetic pole can be formed thin in advance, the thickness of the photoresist used when forming the upper magnetic pole by electroplating using photoresist frame can be decreased, and variations in width of the upper magnetic pole can be decreased accordingly.