Not Applicable.
Not Applicable.
1. Field of Invention
The present invention relates generally to magnetically recorded data and, more particularly, to magnetoresistive read heads for reading magnetically recorded data.
2. Description of the Background
Magnetoresistive (MR) materials are materials whose electrical resistance changes when brought in contact with a magnetic field. Because of this property, MR materials are often used in the read element of a read/write head used to read data recorded on a high-density magnetic disk. Unlike inductive heads in which the data bit on the medium induces the current across a gap, the MR mechanism is an active element with current flowing through it. The magnetic orientation of the bit increases the resistance in a thin-film, nickel-iron layer of the MR read head, and the difference in current is detected by a read circuit coupled to the MR read head. Because MR heads are more sensitive to weaker fields than the earlier inductive read coils, MR read heads are widely used in magnetic data storage systems because as storage capacity increases, the bit gets smaller and its magnetic field becomes weaker.
A giant magnetoresistive (GMR) head is a MR head which includes additional thin films in the sensing element to enhance the change in resistance caused by a magnetic field. Consequently, GMR heads are more sensitive to weaker fields than conventional MR heads. Accordingly, as the storage density of magnetic data storage media continues to double approximately every sixteen months, GMR read heads are becoming increasingly prevalent.
A typical GMR read head includes a GMR sensing layer sandwiched between two shield layers. The GMR sensing layer is typically formed in a patterned multilayer structure including at least a non-magnetic metal layer sandwiched by two ferromagnetic layers. When the magnetic moments of the ferromagnetic layers are parallel, the GMR sensing layer has a low electrical resistance. Conversely, when the magnetic moments of the ferromagnetic layers are anti-parallel, the GMR sensing layer has a high electrical resistance. The resolution of the read element is inversely proportional to the distance (or gap) between the shield layers. Accordingly, the smaller the gap (or window), the greater the resolution of the read element, hence permitting the data to be recorded more densely on the recording medium.
One known type of high-density read head design including a GMR sensing layer is a spin valve read head. In this structure, at least one anti-ferromagnetic layer is formed adjacent to one of the ferromagnetic layers of the GMR sensing layer to pin the magnetization of that ferromagnetic layer such that the direction of the magnetic spin of the pinned ferromagnetic layer is fixed in the range of several tens to several hundreds Oersted (Oe) in magnetic field. On the other hand, the direction of the magnetic spin of the free ferromagnetic layer is freely varied by an external magnetic field. As a result, there can be achieved a magnetoresistance change ratio (MR ratio) of two to five percent in a small magnetic field range.
According to spin valve read head designs, the anti-ferromagnetic layer must be sufficiently sized to pin the magnetization of the pinned ferromagnetic layer. Accordingly, there is a practical limit to how thin the anti-ferromagnetic layer may be fabricated, preventing further reduction of the shield-to-shield spacing, hence limiting the linear recording density. For current spin valve and advanced spin valve head designs, the anti-ferromagnetic layer typically has a thickness greater than 15 nm. As a result, the width of the GMR element of current and advanced spin valve head designs is ordinarily 30 nm or greater, which is too wide for higher density applications, such as on the order of 100 Gbits/sq inch.
Accordingly, there exists a need for a magnetoresistive read head that has a high sensitivity to even weak magnetic fields as well as a reduced shield-to-shield spacing, thereby permitting a further increase in linear recording densities.
The present invention is directed to a magnetoresistive read head. According to one embodiment, the magnetoresistive read head includes a magnetoresistive element including a lower surface and an upper surface, wherein an electrical resistance of the magnetoresistive element varies in response to varying magnetic fields adjacent to the lower surface of the magnetoresistive element, and a magnetic element adjacent to the upper surface of the magnetoresistive element. The magnetoresistive element may be, for example, a giant magnetoresistive (GMR) element or a tunneling magnetoresistive (TMR) element.
The read head of the present invention eliminates the need for an anti-ferromagnetic film in the active region of the read sensor, which is required for the spin valve read head structure. Consequently, the read head of the present invention enables a much thinner read sensor to be utilized, leading to a much smaller shield to shield spacing in the active region, hence permitting data to be recorded more densely on a magnetic recording medium. According to one embodiment of the present invention, the read sensor may have an effective track width of less than 0.1 xcexcm, thus permitting recording densities of, for example, 100 Gbits/sq inch. These and other benefits of the present invention will be apparent from the detailed description hereinbelow.