1. Field of the Invention
The present invention relates, in general, to a magnetoresistive (MR) read/write head and method for making a MR read/write head, and, more particularly, to a MR read/write head having decreased track width and method for making a MR read/write head with high control over track width definition.
2. Relevant Background
The desktop personal computer market continues to demand higher capacity and faster performance from hard disk and tape drives. With applications such as file downloading, increased file sizes, advanced operating systems, and multimedia applications, demand for hard disk drive capacity, for example, is doubling every year. Technologies for storing and retrieving data from magnetic media must also be cost effective. Because lower cost per megabyte (MB) is also desired, the prior practice of simply adding more disks and "heads" (i.e., structure in which read and write elements are provided) to a hard drive is less and less effective. Disk and tape drive suppliers continue to increase areal densities, or the number of data bits per square inch, to meet the increasing demand for storage at competitive pricing. Read and write head design are key technologies needed to achieve these capacity increases.
The write element that writes data on the disk is typically made up of two poles that are separated by a write gap, and which generate a magnetic field when they are excited by a coil magnetically coupled to the poles. When the write element is in proximity to the disk, a magnetic field generated by the poles sets the magnetic orientation in given locations on the disk. In this manner, data is written on the disk.
The read element that reads data from the disk is sandwiched between two shields. During a read operation the read element flies in proximity to the disk so that the read element senses the magnetic orientation of the given disk locations. To enable the read element to focus on a small disk location during reading at (i.e. the read element must not be affected by the magnetic orientation of adjoining disk locations), it is desirable to shield the read element. The two relatively large shields filter out the magnetic effects of adjoining disk locations, so that a specific disk location can be focused upon for reading.
Hard disk drives with lower areal densities typically use inductive read and write elements. Inductive heads offer low cost and mature processing technology suitable for high volume production. To increase the signal strength from an inductive head, designers have increased the number of turns in the read head as the read signal is directly proportional to the number of turns. Some inductive heads use fifty or more turns in the read/write head. However, increasing the number of turns increases the head's inductance. There is a limit to the amount of inductance a head can tolerate to effectively perform data write operations. Since thin-film inductive heads use the same inductive element for both reading and writing, the head cannot be optimized for either operation. Moreover, the increased inductance decreases the frequency at which data can be written to and read from the magnetic media.
Magnetoresistive (MR) head technology is used to provide higher areal density than possible with inductive heads in both disk and tape drives. MR head structures include an MR element as a magnetic field sensor. A coil is formed above the read head and magnetically coupled to the magnetic yoke that defines the poles of the write element. Although the coil and yoke are magnetically coupled, they are separated by an insulating material to prevent current flow between the coils and the yoke. To provide an area efficient structure, it is desirable to vertically stack the coils in two or more layers.
An MR head generally combines the read and write elements of the head into an integrated unit. It does so by eliminating one of the poles of the write element and substituting in its place one of the shields of the read element. In doing so an integrated pole/shield element is created.
Using an MR structure as a read element provides high signal output and low noise compared to inductive heads. This higher signal output allows the write element to write data in a much narrower track while still being reliably detected by the MR read element. Separate read and write heads allow each head to be optimized for one particular function (i.e., reading or writing data). With an MR head, the number of wire turns in the write element can be greatly reduced, resulting in a low inductance head enabling high frequency write operations.
The track width of an MR head is largely determined by the size of the area of the disk that is affected by the write head. Where the pole/shield structure is physically large, the pole/shield will tend to undesirably affect a larger part of the disk during a write operation, which is a phenomenon referred to as "fringing". Fringing has an adverse effect on the efficient storage of data on the disk given that it is usually desirable to pack data on the disk as densely as possible, thereby increasing the storage capacity of the disk.
The track width can be decreased by making the poles physically small at the write tip (i.e., the portion of the yoke that forms the poles), thereby concentrating the magnetic field into a smaller area. However, in conventional MR head processes, the yoke, including the write tip, are formed as an integrated structure over the coil structure. The coil structure is very thick, especially when vertically stacked coils are used. Hence, the write tip is typically patterned using thick photoresist (on the order of 10-15 microns thick) making it difficult to define the small structures that are required to decrease track width. Critical dimension control is poor when patterning thick layers of photoresist resulting in unacceptable variation in the size of the patterned feature.
What is needed therefore, is an MR head that combines the advantages of a small write tip structure, but that can be manufactured with a high degree of process control.