1. Field of the Invention
The present invention relates to a contoured pole tip structure for minimizing side track erasure and more particularly to an "I" shaped pole tip structure of a write head wherein side edges of the top portion of the "I" structure are rounded or beveled immediately adjacent an air bearing surface so that flux leakage from bottom corners of the top portion of the "I" structure to a bottom portion of the "I" structure is minimized.
2. Description of the Related Art
An inductive write head includes a coil layer embedded in first, second and third insulation layers (insulation stack), the insulation stack being sandwiched between first and second pole piece layers. A gap is formed between the first and second pole piece layers by a gap layer at an air bearing surface (ABS) of the write head. The pole piece layers are connected at a back gap. Currents are conducted through the coil layer, which produce magnetic fields in the pole pieces. The magnetic fields fringe across the gap at the ABS for the purpose of writing information in tracks on moving media, such as in circular tracks on a rotating magnetic disk or longitudinal tracks on a moving magnetic tape.
The second pole piece layer has a pole tip portion which extends from the ABS to a flare point and a yoke portion which extends from the flare point to the back gap. The flare point is where the second pole piece begins to widen (flare) to form the yoke. The placement of the flare point directly affects the magnitude of the magnetic field produced to write information on the recording medium. Since magnetic flux decays as it travels down the length of the second pole tip, shortening the second pole tip will increase the flux reaching the recording media. Therefore, performance can be optimized by aggressively placing the flare point close to the ABS.
Another parameter important in the design of a write head is the location of the zero throat height (ZTH). The zero throat height is the location where the first and second pole pieces first separate from one another after the ABS. ZTH separation is imposed by an insulation layer, typically the first insulation layer in the insulation stack. Flux leakage between the first and second pole pieces is minimized by locating the ZTH as close as possible to the ABS.
Unfortunately, the aforementioned design parameters require a tradeoff in the fabrication of the second pole tip. The second pole tip should be well-defined in order to produce well-defined written tracks on the rotating disk. Poor definition of the second pole tip may result in overwriting of adjacent tracks. A well-defined second pole tip should have parallel planar side walls which are perpendicular to the ABS. In most write heads the second pole tip is formed along with the yoke after the formation of the first insulation layer, the coil layer and the second and third insulation layers. Each insulation layer includes a hard-baked photoresist having a sloping front surface.
After construction, the first, second and third insulation layers present front sloping surfaces which face the ABS. The ZTH defining insulation layer rises from a plane normal to the ABS at an angle (apex angle) to the plane. The sloping surfaces of the hard-baked resist of the insulation layers exhibit a high optical reflectivity. When the second pole tip and yoke are constructed, a thick layer of photoresist is spun on top of the insulation layers and photo patterned to shape the second pole tip, using the conventional photo-lithography technique. In the photo-lithography step, ultraviolet light is directed vertically through slits in an opaque mask, exposing areas of the photoresist which are to be removed by a subsequent development step. One of the areas to be removed is the area where the second pole piece (pole tip and yoke) are to be formed by plating. Unfortunately, when the location of the flare point is placed on the sloping surfaces of the insulation layers, ultraviolet light is reflected forward, toward the ABS, into photoresist areas at the sides of the second pole tip region. After development, the side walls of the photoresist extend outwardly from the ultraviolet pattern, causing the pole tip to be poorly formed after plating. This is called "reflective notching". As stated hereinabove this causes overwriting of adjacent tracks on a rotating disk. It should be evident that, if the flare point is recessed far enough into the head, the effect of reflective notching would be reduced or eliminated since it would occur behind the sloping surfaces. However, this solution produces a long second pole tip which quickly reduces the amount of flux reaching the recording medium.
The high profile of the insulation stack causes another problem when the photoresist is spun on a wafer. The thickness of the resist in the pole tip region is excessively high. During the light exposure step the light progressively scatters like light in a body of water causing poor resolution during the light exposure step.
A scheme for minimizing the reflective notching and poor resolution problems is to employ a write head with an "I" shaped pole tip structure. In an exemplary prior art "I" shaped pole tip structure the first pole tip comprises the bottom horizontal component of the "I" and the second pole tip, which is "T" shaped, comprises the vertical component and the top horizontal component of the "I". The vertical component is constructed before the insulation layers to eliminate the reflective notching problem. After forming the first pole piece layer (bottom horizontal component) and the write gap layer, a photoresist layer is spun on the partially completed head for constructing the vertical component. The photoresist layer is very flat so that ultraviolet light from the photo-patterning step is not reflected forward. After plating the vertical component of the second pole tip the photoresist layer is removed and the first insulation layer, the coil layer and the second and third insulation layers are formed. The horizontal component of the second pole tip is then stitched (connected) to the vertical component. Since the second pole tip is well-formed, well-formed notches can be made in the first pole piece.
With the prior art "T" shaped second pole tip the ZTH is dependent upon the location of the recessed end of the vertical component. Since the vertical component has to be long enough to provide a sufficient stitching area for the horizontal component, this length may result in undesirable flux leakage between the first and second pole pieces. Another problem that has been observed with all "I" shaped pole tip structures is that flux fringes between the bottom corners of the top horizontal component and the bottom horizontal component, causing adjacent tracks to be overwritten.