The reading and writing of magnetic information and, more generally, the generation and sensing of discrete magnetic fields, is an art applicable to the recording and retrieving of digital information. In such applications, the increasing demands for higher information density on the recording media and for faster and more reliable transfer of information between read or write heads and magnetic storage media increase the need for devices that will provide high reading sensitivity, high information density, low noise and high speed switching. Such needs result in the imposition of requirements on the properties of magnetic materials used in the processes of information transfer between circuits and storage media. Generally, in such processes, it is better to use products that sense magnetic fields while interfering as little as possible with the magnetic field that is being sensed.
In magnetic read-write heads that are used in the recording and retrieval of digital information from magnetic discs or other such storage devices, the material used in the manufacture of the magnetic head provides a magnetically sensitive path through which magnetic flux must easily pass. Increased demands of industry for higher storage capacity and smaller devices, and thus higher storage information density and higher transfer rates, require better and more efficient magnetic materials for use in the reading and writing heads.
For example, with Giant Magneto-Resistive (GMR) devices such as those used as read heads for digital magnetic discs, sputter coated thin films of soft magnetic material are used for the sensing elements. In such elements, the size, shape, composition and magnetic orientation of the magnetic domains of this magnetic material affect the performance of the heads in facilitating high speed, high sensitivity switching through the creation and annihilation of domain walls. In such uses, alignment of the domains of the magnetic material with the magnetic fields being sensed increases the high speed, high sensitivity reading of information of the heads by, for example, reducing a phenomenon referred to as Barkhausen noise. One way to reduce this Barkhausen noise and to otherwise increase the sensitivity of the magnetic material film has been to provide a bias magnetic field to align the domains of the thin film of magnetic material on the head.
Demands for improved material films have resulted in demands to increase the degree of parallelism in the alignment of the magnetic domains, increasing the requirements for the parallelism of the fields used in aligning the domains to, for example, within one angular degree. In response to such demands, the domain alignment property has been typically controlled by placing a strong magnetic field in the vicinity of the manufactured substrate of which the devices are to be formed that have thereon the magnetic alloy layer, and then subjecting the substrate to post-processing in the form of heat treating or annealing in the presence of the magnetic field. Such treatment in the magnetic field causes the magnetic material domains to realign to achieve the desired magnetic orientation.
Magnetic structures used to generate the parallel magnetic fields for processing of the magnetic devices to align the domains generally produce a region in space at which the fields are sufficiently parallel. However, as distance increases from the center of the region, the magnetic field lines tend to diverge, resulting in insufficient parallelism of the field beyond a certain distance from the center. As a result, only a small substrate, or a small area on a substrate is exposed to a sufficiently parallel field to produce high quality devices. Such an area may be a two to four inch diameter area on a 6.times.6 inch wafer. Where, under present economic circumstances, the ultimate devices being manufactured from a single substrate may have a retail value of upward of one million U.S. dollars, and where, up to the time of the deposition of the magnetic film, the cost already incurred in processing the wafer may be several hundred thousand U.S. dollars, the ability to commercially use only a small wafer or small portion of a wafer, for example less than 30%, results in a substantial loss in potential product value. The size of the useful area of such a wafer can be increased by increasing the size of the portion of the field that is acceptably parallel. Increasing the size of the portion of the field that is acceptably parallel can be achieved by increasing the size of the biasing magnet structure. However, as the magnet is increased in size, the overall strength of the field diminishes since the saturation of the field in the magnet cannot be increased in proportion to magnet size.
Furthermore, providing the domain alignment in a post-processing step after the deposition of the magnetic film onto the substrate increases the cost of the devices and the time of the device production process. It accordingly would be desirable to subject the wafer to the bias magnetic field during the process by which the thin magnetic film is being deposited. However, in such deposition processes which are performed in vacuum processing machines which, for many reasons, are preferably limited in size, large magnets and magnetic field orienting devices are unacceptable and cannot be practically placed within or in operative relationship with the processing chambers of such machines.
Accordingly, there is an increasing need for a method and apparatus that will provide a sufficiently strong magnetic field having a high degree of parallelism, for example to within one angular degree, over a large substrate area, and that occupies a small space, preferably to fit within the confines of a thin film deposition apparatus.
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