Perpendicular recording has been developed in part to achieve higher recording density than is realized with longitudinal recording devices. A PMR writer typically has a main pole with a small surface area at an air bearing surface (ABS) and a return flux pole or opposing pole with a large surface area (at the ABS) which is magnetically coupled to the main pole. Critical dimensions of the main pole include a neck height (NH) and a pole width in a pole tip region adjacent to the ABS. After depositing and planarizing the main pole, an ion milling process is typically used to trim excess magnetic material at its edges. Since the pole tip region has small dimensions, the ion milling step generally produces a large variation in NH. Moreover, a small NH leads to a large variation in pole width which is also referred to as track width.
A conventional PMR head 1 with a merged read/write head structure is depicted in FIG. 1. The read head 19 is formed on a substrate 2 that has a top surface 2a. There is a first shield 3 formed on the substrate 2 and first and second gap layers 4a, 4b consecutively formed on the first shield. Between the first and second gap layers 4a, 4b at the ABS A-A′ is a sensor 5 with a stripe height SH. A second shield 6 forms the top of the read head. The read head is separated by a distance d from the write head 20 with a separation layer 7 such as Al2O3.
The bottom layer in the write head 20 is a bottom yoke 8 which can be recessed from the ABS A-A′ by a distance c which is typically about 1 micron. Adjacent to the bottom yoke 8 on the separation layer 7 is formed an insulator layer 9 that extends from the ABS toward the back side of the write head. A main pole layer 10 on the insulator layer 9 and bottom yoke 8 has a pole tip 10a in a pole tip region (FIG. 2) at the ABS. There is a write gap layer 11 on the main pole layer 10 and a second insulation layer 12 on the write gap layer. The write gap layer extends toward a back end of the write head but is interrupted by a back gap region (not shown). A plurality of coils 13 located within the second insulation layer 12 is wrapped around the back gap region where the main pole layer 10 joins a third write shield 17. An overcoat dielectric layer 14 such as alumina typically covers the coils 13 to separate the coils from the third write shield 17. There is a first write shield 15 on the main pole layer 10 along the ABS and a second write shield 16 between the first write shield and the third write shield 17.
Referring to FIG. 2, a top view of a portion of the main pole layer 10 is pictured with surrounding layers removed. The main pole layer 10 with a pole tip region 10b is formed in a write head on a slider that is part of an array of sliders on a wafer. An ion milling process is typically employed to reduce an initial pole width a1 in each main pole layer to a2 and also trim the edges of the main pole layer 10 by a similar dimension along the dashed lines. Thus, the length of the pole tip region along the x-axis is reduced by a distance of about 0.5×(a1-a2) and a pole tip 10c is formed after the ion milling step. Note that the corners where the pole tip region 10b meets the main pole layer 10 are shown as well defined points for the purpose of this discussion. Typically, the intersection of the pole tip region and main pole layer has a rounded shape before and after the ion milling process and the distances a1 and a2 may be difficult to measure. Once the write head is fabricated, the wafer is sliced to form rows of sliders along an initial lapping plane ABS1.
A subsequent lapping process forms a final ABS2 lapping plane that defines a pole tip 10a in the pole tip region 10b with a neck height NH. However, there are large variations in the NH dimension, largely due to variations in the ion milling process. For example, the distance 0.5×(a1-a2) can sometimes exceed the desired NH dimension and large variations in the location of the pole tip 10c can result. In some cases, the pole tip 10c may be closer to the main pole layer 10 than the desired NH distance and a subsequent lapping process cannot correct the overtrimmed condition. Therefore, a method of fabricating a PMR head is desirable in which the NH dimension is not determined by an ion milling step in order to improve process control. To our knowledge, the prior art does not teach a method for independently forming NH and pole width dimensions.
In U.S. Pat. No. 6,687,084, a yoke layer is formed on a main pole layer in order to improve the passing efficiency of magnetic flux from the main pole layer to a recording medium. The yoke layer is thicker than the main pole layer and both are formed above a coil layer while a return pole is below the coil layer.
A yoke layer with a low magnetic moment is formed on a main pole layer having a high magnetic moment in U.S. Pat. No. 6,693,768. The magnetic flux is channeled into the main pole tip before writing to the recording medium. Again, the yoke layer and main pole layer are above a coil layer and an auxiliary pole is formed below the coils.
An inductive write head including a thin high moment pedestal with a tapered edge is disclosed in U.S. Pat. No. 6,650,503 and a method for forming the same is provided in U.S. Pat. No. 6,430,806. A bilayer resist is patterned on a stack consisting of a high Bsat layer on a soft magnetic first pole layer. The high Bsat layer is etched to give a tapered edge that is determined by an overhang in the bilayer profile. The tapered edge promotes a smooth flux flow through the pole tip region of the first pole.