Dynamic magnetic information storage or retrieval – Head – Magnetoresistive reproducing head
Reexamination Certificate
2000-03-08
2003-10-07
Renner, Craig A. (Department: 2652)
Dynamic magnetic information storage or retrieval
Head
Magnetoresistive reproducing head
Reexamination Certificate
active
06631057
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Cross-Reference to Related Application
The present application claims priority to European Application Number 99105662.3, filed on Mar. 19, 1999 by R. Allenspach et al., assigned to the assignee of the present application.
2. Technical Field
The present invention relates to magnetic devices and generally to devices having a pinning layer. More particularly the invention relates to magnetic memories (MRAM) and magnetoresistive sensors based on the so-called “spin-value” or “giant magnetoresistive (GMR)” effect. Although the present invention is applicable in a variety of magnetic applications it will be described with the focus put on an application to magnetoresistive sensors as GMR sensors, for example.
3. Description of the Related Art
The change in electrical resistance of a material in response to a magnetic field is called magnetoresistance which has made it possible to read information on a magnetic medium, such as a computer hard disk. The prior art discloses a magnetic read tranducer referred to as a magnetoresistive (MR) sensor or head which has been shown to be capable of reading data from a magnetic surface at great linear densities. A MR sensor detects magnetic field signals through the resistance changes of a read element fabricated of a magnetic material as a function of the strength and direction of magnetic flux being sensed by the read element. These prior art MR sensors operate on the basis of the anisotropic magnetoresistive (AMR) effect in which a component of the read element resistance varies as the square of the cosine of the angle between the magnetization and the direction of sense current flow through the element. A more detailed description of the AMR effect can be found in “Memory, Storage, and Related Applications”, D. A. Thompson et al., IEEE Trans. Mag. MAG-11, p. 1039 (1975).
More recently, a different, more pronounced magnetoresistive effect has been described in which the change in resistance of a layered magnetic sensor is attributed to the spin-dependent transmission of the conduction electrons between the magnetic layers through a nonmagnetic layer and the accompanying spin-dependent scattering of electrons at the layer interfaces and within the ferromagnetic layers. This magnetoresistive effect is variously referred to as the “giant magnetoresistive” (GMR) or “spin valve” effect. A magnetoresistive sensor based on the before-mentioned effect provides improved sensitivity and greater change in resistance than observed in sensors utilizing the AMR effect. The electrical resistance read-out means that the signal is much stronger in such GMR sensors. The increased signal offered in the GMR sensor allows more information to be stored on a hard disk. For a bit that aligns the ferromagnetic layers parallel under the GMR sensor, the resistance goes down, the electrons do not scatter very much and the current flow increases. Such a sensor can also use a multifilm laminated pinned ferromagnetic layer in place of the conventional single-layer pinned layer.
U.S. Pat. No. 4,949,039 to Grunberg describes a layered magnetic structure which yields enhanced MR effects caused by a antiparallel alignment of the magnetizations in the magnetic layers. Grunberg describes the use of antiferromagnetic-type exchange coupling to obtain the antiparallel alignment of the magnetizations in the magnetic layers. Grunberg describes the use of antiferromagnetic-type exchange coupling to obtain the antiparallel alignment in which adjacent layers of ferromagnetic materials are separated by a thin interlayer of Cr or Y.
U.S. Pat. No. 5,206,590 to Dieny et al. discloses a MR sensor in which the resistance between two uncoupled ferromagnetic layers is observed to vary as the cosine of the angle between the magnetizations of the two layers. This mechanism produces a magnetoresistance that is based on the spin valve effect and, for selected combinations of materials, is greater in magnitude than the AMR.
The U.S. Pat. No. 5,159,513 to Dieny et al. discloses a MR sensor based on the above-described effect which includes two thin layers of ferromagnetic material separated by a thin film layer of a nonmagnetic metallic material wherein at least one of the ferromagnetic layers is of a cobalt or a cobalt alloy. The magnetization of the one ferromagnetic layer is maintained perpendicular to the magnetization of the other ferromagnetic layer at zero externally applied magnetic field by exchange coupling to an antiferromagnetic layer.
Published European Patent Application EP-A-0,585,009 discloses a spin valve effect sensor in which an antiferromagnetic and an adjacent magnetically soft layer cooperate to fix or pin the magnetization of a ferromagnetic layer. The magnetically soft layer enhances the exchange coupling provided by the antiferromagnetic layer.
The spin valve structures described in the above-cited U.S. patents and European patent application require that the direction of magnetization in one of the two ferromagnetic layers be fixed or “pinned” in a selected orientation such that under non-signal conditions the direction of magnetization in the other ferromagnetic layer, the “free” layer, is oriented either perpendicular to (i.e. at 90°) or antiparallel to (i.e. at 180°) the direction of magnetization of the pinned layer. When an external magnetic signal is applied to the sensor, the direction of magnetization in the non-fixed or “free” layer rotates with respect to the direction of magnetization in the pinned layer. The output of the sensor depends on the amount of this rotation. In order to maintain the magnetization orientation in the pinned layer, a means for fixing the direction of the magnetization is required. For example, as described in the above-cited prior art documents, an additional layer of antiferromagnetic material can be formed adjacent to the pinned ferromagnetic layer to provide an exchange coupled bias field and thus pinning. Alternatively, an adjacent magnetically hard layer can be utilized to provide hard bias for the pinned layer.
Another magnetic device is a magnetic random access memory (MRAM) which is a non-volatile memory. This memory basically includes a GMR cell, a sense line, and a word line. The MRAM employs the GMR effect to store memory states. Magnetic vectors in one or all of the layers of GMR material are switched very quickly from one direction to an opposite direction when a magnetic field is applied to the GMR cell over a certain threshold. According to the direction of the magnetic vectors in the GMR cell, states are stored, and the GMR cell maintains these states even without a magnetic field being applied. The states stored in the GMR cell can be read by passing a sense current through the cell in a sense line and sensing the difference between the resistances (GMR ration) when one or both of the magnetic vectors switch. The problem is that in most GMR cells the GMR ratio is relatively low (e.g. 10% or less) and, consequently, reading or sensing the state stored in the GMR cell can be relatively difficult.
In general, magnetic devices often use an antiferromagnetic layer to pin the magnetic moment of a subsequently deposited ferromagnetic layer. Typically used materials are FeMN, NiMn, CoO, NiO, and TbCoFe. The main advantage of using exchange bias is that the bias field cannot be reset or changed accidently during the lifetime of the device. To reset the antiferromagnet it is necessary to cool the antiferromagnet from above its Néel temperature in the presence of a magnetic field. A disadvantage of FeMn is that this material is a metal and allows a current flow. Therefore, FeMn is not ideally suited as pinning material. NiO is an insulator, thus having the disadvantage that the strength of the pinning, i.e. the exchange bias, is not as strong as desired.
Since the load of data which have to be stored increases dramatically, there is a need for faster operation in read and write processes with higher density. Thus, the operating temperature of the data storage systems is increasing. Today's sensor
Allenspach Rolf
Fompeyrine Jean
Fullerton Eric
Locquet Jean Pierre
Moran Timothy
Bracewell & Patterson L.L.P.
Feece Ronald
Knight G. Marlin
Renner Craig A.
LandOfFree
Magnetic device with ferromagnetic layer contacting... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Magnetic device with ferromagnetic layer contacting..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Magnetic device with ferromagnetic layer contacting... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3145715