Dynamic magnetic information storage or retrieval – Head – Magnetoresistive reproducing head
Reexamination Certificate
1999-07-09
2004-04-13
Letscher, George J. (Department: 2653)
Dynamic magnetic information storage or retrieval
Head
Magnetoresistive reproducing head
Reexamination Certificate
active
06721141
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the structure and fabrication of magnetic devices having a spin-valve structure.
STATE OF THE ART
The giant magnetoresistance (GMR) effect is known in the art. It is of large interest for applications in magnetoresistive read and write heads and for magnetic sensors. GMR magnetic multilayers exhibit strong coupling characteristics and thus high saturation fields. A multilayer or superlattice is a multitude of ferromagnetic and antiferromagnetic layers. The ferromagnetic layers can be coupled or uncoupled.
Recently several research groups have shown that the single bath electrodeposition or electrodeposition technique, is an attractive technique for the production of GMR multilayers (W. Schwarzacher and D. S. Lashmore, Giant magnetoresistance in electrodeposited films, IEEE-Trans. Magn., 32 (1996) 3133-53). Due to the above mentioned high saturation fields, these electrodeposited/electroplated multilayers are unattractive for low field sensing. The largest sensitivity so far obtained in electrodeposited multilayers has been 0.1% per Oe (R. Hart, M. Alper, K. Attenborough and W. Schwarzacher, Giant magnetoresistance in Ni—Co—Cu/Cu superlattices electrodeposited on n-type (100) GaAs substrates, Proc. 3rd International Symposium on Magnetic Materials, Processes and Devices, Electrochem. Soc. Proc., 94 (1994) 215-221). If electrodeposition is to be considered as a suitable production technique for future magnetic field sensing devices, higher sensitivity at lower switching fields must therefore be achieved.
Electrodeposition or electroplating in the art usually takes place on a conductive seed layer, typically Cu. If this seed layer cannot be removed, problems of current shunting and signal loss occur when measuring the magnetoresistive properties of the electrodeposited or electroplated materials.
New magnetic field sensors having a spin-valve structure have been disclosed. These structures have the advantage of high magnetoresistance (MR) signals and high sensitivities at lower fields (J. C. S. Kools, Exchange-Biased Spin-Values for Magnetic Storage, IEEE Trans. Magn., 32 (1996) 3165-3184). Such combination of features is of importance for many sensing applications. The production of films, showing these effects, is usually achieved by sputtering techniques.
A spin-valve is a structure with a thin non-magnetic spacer layer sandwiched between two ferromagnetic (FM) layers, which have different coercivities. The coercivity of a magnetic material reflects the resistance to a change of the orientation of the magnetic field when a magnetic (or electric) field is externally applied. In sputtered spin-valves this can be achieved by having different layer thickness, different materials or by pinning one of the layers to an antiferromagnetic (AF) layer, leaving the other magnetic layer free to rotate. The magnetisation alignment of the ferromagnetic layers can be changed from antiparallel (high resistance state) to parallel (low resistance state) depending on the externally applied magnetic field.
A recent advance in spin-valve design used to replace the typical AF materials, e.g. FeMn or NiO, has been the implementation of an artificial or synthetic antiferromagnetic subsystem (AAF or SyAF)(H. A. M van den Berg, W. Clemens, G. Gieres, G. Rupp, W. Schelter and M. Vieth, GMR sensor scheme with artificial antiferromagnetic subsystem, IEEE Trans. Magn., 32 (1996) 4624-4626)) (J. L. Leal and M. H. Kryder, Spin-valves exchange biased by Co/Ru/Co synthetic antiferromagnets, J.Appl.Phys. 83, 3720 (1997)). These new spin-valve structures are comprised of a FM layer separated by a Cu spacer the AAF subsystem which itself consists of a few strongly coupled bilayers or multilayers such as Co/Cu bilayers or Co/Ru/Co respectively. They have an added advantage over the AF layers of improved resistance against corrosion and higher processing temperatures.
A specific spin-valve structure is disclosed in document WO98/14793.
AIMS OF THE INVENTION
A first aim of the present invention is to provide novel magnetic devices capable of high magnetoresistive signals and high sensitivities at low fields.
Another aim of the present invention is to provide a novel magnetic device of which the properties can be determined by varying its construction parameters, preferably by appropriate choice of a carrier substrate, and to provide a novel magnetic device that can be used for several purposes by varying its mode of operation.
Another aim of the present invention is to provide new magnetic memory devices that can show multi-value memory capacity.
A further aim of the present invention is to provide a novel method for producing a magnetic sensor capable of sensing high magnetoresistive signals and having high sensitivities at low fields.
Another aim of the present invention is to provide a novel low-cost fabrication method for spin-valve structures.
SUMMARY OF THE INVENTION
The present invention concerns in a first aspect a spin-valve structure comprising a first and a second free ferromagnetic layer and a spacer layer positioned between said first and second free ferromagnetic layers, and wherein said first free ferromagnetic layer is positioned on a substrate. In a preferred embodiment of the invention, said first free ferromagnetic layer is in direct contact with the surface of said substrate.
Advantageously, said spacer layer is an antiferromagnetic or metal or semimetal or conductive semiconductor layer or any combination thereof or any multiple layer structure of any of these layers.
In the free ferromagnetic layers, the orientation of the magnetic fields can be changed, preferably independently one of the other, with an externally applied electrical or magnetic field. The first and second free ferromagnetic layers, in a preferred embodiment of the present invention, can be switched at different externally applied electrical or magnetic fields. One of the free layers can have a parallel behaviour and one of the free layers can have an antiparallel behaviour.
Preferably, the spacer layer can be an artificial antiferromagnetic layer or a synthetic antiferromagnetic layer.
The artificial antiferromagnetic layer can comprise Cu layers and Co layers positioned therebetween, said Cu layers being thin enough as to increase magnetic coupling between said Co layers. These layers or any Co
x
Ni
y
Fe
1−x−y
alloy or any Co
x
Fe
y
X
1−x−y
alloy (X being Cr, V, Ni, Cu) can act as a single hard layer.
Said first and/or second free ferromagnetic layer can comprise Co, but can also comprise NiFe or CoFe. Preferably, the first free ferromagnetic layer that is positioned on said semiconductor substrate has a higher coercivity than the other free ferromagnetic layer.
Preferably, the substrate is a semiconductor substrate. Said semiconductor substrate can be a GaAs or Ge or Si or a polymer or any other semiconducting substrate.
Said substrate can be either a semiconductor (including GaAs and Si) or any substrate that is conductive enough to allow plating but some barrier is to be formed so that in the sensing operation the sensing current does not enter the substrate. The substrate choice can also include a semiconducting polymer, or a polymer that makes a Schottky or other Barrier contact with a metal deposited thereon. In an alternative, a highly ohmic layer should be deposited first on the substrate. Thus, the ferromagnetic layer can be separated from the substrate by an insulating tunnelling barrier.
The magnetic and structural properties of said first free ferromagnetic layer can be influenced by the structure of the surface and/or the lattice structure of the semiconductor substrate on which it is positioned. Foregoing the deposition of the first free ferromagnetic layer on the substrate, a change of the semiconductor surface structure by ion bombardment or any other method may change the magnetic and structural properties of the first free ferromagnetic layer that is grown thereon.
In a preferred embodiment, there is an electrical barrier between the
Attenborough Karen
Boeck Jo De
Boeve Hans
Celis Jean-Pierre
Interuniversitair Microelektronica Centrum (IMECVZW)
Letscher George J.
McDonnell & Boehnen Hulbert & Berghoff
LandOfFree
Spin-valve structure and method for making spin-valve... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Spin-valve structure and method for making spin-valve..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Spin-valve structure and method for making spin-valve... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3255889