Dynamic magnetic information storage or retrieval – Head – Magnetoresistive reproducing head
Reexamination Certificate
2001-02-28
2003-09-16
Evans, Jefferson (Department: 2652)
Dynamic magnetic information storage or retrieval
Head
Magnetoresistive reproducing head
C360S313000, C360S314000
Reexamination Certificate
active
06621664
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to integrated read/write perpendicular recording heads. More specifically, the invention relates to locating a read element between the main pole and the flux return pole portions of the writer.
2. Description of the Related Art
Recording heads for use with magnetic storage media have typically been of the longitudinal type, utilizing a pair of opposing write poles with their tips in close proximity to each other at the bottom surface of the recording head. The two poles are connected typically at the top by a yoke, typically made of the same ferromagnetic material as the poles. A coil is located in close proximity to one of the two opposing poles. When current passes through the coil, magnetic flux is induced in the yoke which produces a magnetic field with a bubble-like contour, across a gap separating the two poles. A portion of the magnetic flux across the write gap will pass through the magnetic storage medium, thereby causing a change in the magnetic state within the magnetic storage medium where the head field is higher than the media coercive force. The media coercive force is chosen high enough so that only the head fields across a narrow gap of a thin film inductive head, flowing with a slider on a air bearing between the surfaces of the disk and the slider, modify the bits of information on the storage media.
The bits of information are recorded on the disk along concentric tracks that are separated by guard bands. The width of the track plus that of the guard-band in which no information is stored defines the track density. The length of the bit along the track defines the linear density. The total storage capacity is directly proportional to the product of track density and linear density. The increase in linear density also enhances the data transfer rate. The demand for higher storage capacity and higher data rates led to the redesign of various components of disk drives.
The recording densities possible with longitudinal recording are limited to approximately 50 to 100 G bit/inch
2
, because at higher recording densities, superparamagnetic effects result in magnetic instabilities within the magnetic storage medium.
Perpendicular recording has been proposed to overcome the recording density limitations of longitudinal recording. Perpendicular recording heads for use with magnetic storage media typically include a pair of magnetically coupled poles, consisting of a main write pole having a small bottom surface area, and a flux return pole having a large bottom surface area. A coil is located adjacent to the main write pole, for inducing a magnetic field between that pole and a soft underlayer. The soft underlayer is located below the recording layer of the magnetic storage medium and enhances the amplitude of the field produced by the main pole. This in turn allows the use of media with higher coercive force, consequently, more stable bits can be stored in the media. In the recording process, an electrical current in the coil energizes the main pole, which produces a magnetic flux density field. The image of this field is produced in the soft underlayer, such that about double the field strength is produced in the magnetic media. The flux density that diverges from the tip into the soft underlayer returns to the main pole through the return flux pole. The return pole is located sufficiently far apart from the main pole, such that the soft material of the return pole does not affect the magnetic flux of the main pole, which is directed vertically into the hard layer and soft underlayer. Significantly higher recording densities may therefore be used before magnetic instabilities become an issue.
Originally, retrieval of the information stored in magnetic disks was accomplished with an inductive head. The rate of change of magnetic field passing through the gap between the poles of the recording head would induce a voltage across the coils. The voltage signal was directly proportional to the rate of change of the field across the gap. Since the 80's, magnetoresistive heads replaced thin film inductive heads for the reading process because they produce considerably higher change of voltage while sensing magnetic flux incoming from magnetic patterns of the media.
To overcome the limitations of inductive reading, various magnetoresistive (MR) read elements have been proposed. Such read elements are typically located between a pair of shields made from soft magnetic material similar to that used in the inductive heads. The shields define the linear resolution of the read head, as they prevent that the sensor from being affected by magnetic fields other than that from the bit being read.
For a decade, the magnetoresistive elements consisted of Permalloy thin films and exhibited an anisotropic magnetoresistive (AMR) effect. As the areal density requirement in disk drives approached 10 Gbit/in
2
, the AMR heads could not provide enough sensitivity for adequate signal to noise ratio even if they used extremely high electrical current. A new magnetoresistive effect, discovered in the early 80's needed to be applied. The magnetoresistive (MR) read element that has been adopted by most of the industry for magnetic disk drives is the spin valve sensor. The spin valve provides a spin dependent giant magnetoresistance effect with a very thin sensor layer. Hence, it exhibits enough sensitivity for current disk drives. The spin valve is generally composed of a pair of ferromagnetic layers having a nonmagnetic layer therebetween. One of the ferromagnetic layers is adjacent and in direct contact with an antiferromagnetic layer. The antiferromagnetic layer produces a unidirectional anisotropic field in the ferromagnetic layer. The unidirectional field is strong enough to remain constant during the head operation. The combination of the ferromagnetic layer and adjacent antiferromagnetic layer is commonly known as the pinned layer, with the opposite ferromagnetic layer known as the free layer. When the spin valve is exposed to a magnetic field, the orientation of the magnetization of the free layer will change accordingly. The change in the orientation of the magnetization of the free layer relative to the pinned layer will alter the spin dependent scattering of conduction electrons, thereby increasing or decreasing the resistance of the spin valve element. The change in resistance produces a corresponding change in the voltage signal for an applied electrical current. A constant voltage level indicates a binary “0” and a changing voltage level indicates a binary “1.”
Despite the fact that the spin valve provided enough sensitivity for 10 Gbit/in
2
areal density, the rapid pace of storage capacity increase required for current applications could not be overlooked. A dual spin valve was then proposed, wherein a second pinned layer and electroconductive layer are placed on the opposite side of the free layer. The dual spin valve (DSV) could provide higher signal output than the spin valve. The drawback of the DSV consisted in the need for a synthetic antiferromagnet (SAF) to overcome the fields of the two reference layers. This requirement resulted in a structure considerably thicker than the spin valve itself, which led to a large increase in minimum shield-to-shield spacing. The shield-to-shield spacing of the SV or the DSV, corresponding approximately to twice the read-back gap length, ultimately defines the read head linear resolution. Hence, the DSV was not pursued, because it exhibited lower signal output at higher linear densities.
The need for increasing the speed of the read and write operations, combined with the increasing storage density within the magnetic storage media, make it desirable to integrate a read head with very high linear resolution and sensitivity in very close proximity to the write head. The spatial distance between the write and read head require complex arm operations to correct it and increase seek time. For these reasons, some recording heads use a shared pole i
Batra Sharat
Parker Gregory John
Rottmayer Robert
Trindade Isabel Goncalves
Evans Jefferson
Lenart, Esq. Robert P.
Pietragallo Bosick & Gordon
Seagate Technology LLC
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