Electricity: measuring and testing – Magnetic – Magnetometers
Reexamination Certificate
1998-10-19
2001-04-10
Patidar, Jay (Department: 2862)
Electricity: measuring and testing
Magnetic
Magnetometers
C428S209000
Reexamination Certificate
active
06215301
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to an element comprising a layer structure bounded by two substantially parallel main faces, having at least two layers of mutually different magnetical behavior, the layer structure having a zone which, viewed in a direction parallel to the main faces, extends between spaced electric connection areas, in which zone a current
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directing means is present for producing, during current passage, a current component directed transversely to the layer structure.
Such an element is known as a magnetoresistive detector from U.S. Pat. No. 5,474,833. The known element comprises a stack of layers of different magnetical properties. The layer structure thus formed is present on a substrate and has two electrodes which are localized on two facing ends of the layer structure, The stack of layers is provided with one or more interruptions of electric conductance. These interruptions are obtained by locally performed etching operations in order to form a square-shaped structure in the zone between the electrodes. In this structure, the electric current is forced, during current passage, to pass the layers more or less perpendicularly.
A drawback of the known element is the method of its manufacture, notably because the formation of the square-shaped structure requires complicated etching processes.
OBJECTS AND SUMMARY OF THE INVENTION
It is an object of the invention to improve the element described in the opening paragraph in such a way that it is easily obtainable.
To this end, the element according to the invention is characterized in that the current-directing means on at least one of the main faces comprises at least one electric conductor.
This measure, in which the current-directing means is present outside the layer structure, provides the possibility of passing an electric current perpendicularly or at least with a perpendicular component through the layers of the layer structure without having to adapt the structure of the layers themselves for this purpose. The current-directing means forces the electric current from the exterior into a desired direction. In principle, the layer structure, which is generally provided on a substrate, may be any type of GMR system, such as spin valve, hard/soft multilayer, AF-coupled multilayer. In such a system, the angle between the directions of magnetization as a function of a magnetic field changes as a result of mutually different magnetical behavior of layers present in the layer structure.
It is known per se that the giant magnetoresistance effect (GMR effect) of a layer structure as used in the element is greater in the presence of an electric current passing perpendicularly through the layers than in the presence of an electric current passing in the plane of the layers. The article Appl. Phys. Lett. 66 (14), Apr. 3, 1995, pp. 1839-1841 “Perpendicular giant magnetoresistance of Co/Cu multilayers deposited under an angle on grooved substrates”, M. A. M. Gijs et al. further describes the advantages of a CPP geometry, with CPP standing for “current perpendicular to layer plane” as compared with a CIP geometry, with CIP standing for “current in-plane”. This publication proposes to provide a multilayer on a grooved substrate so as to realize a perpendicular current passage through the layers. Although a greater GMR effect is indeed achievable in this way, the known proposal has a number of drawbacks. First, the manufacture of the necessary micro-structured substrates requires specific techniques, which renders the substrates expensive. Moreover, it is not easy to realize a good multilayer without shunting, and since deposition under a well-defined angle is often required, the customary sputter deposition processes are not possible or not possible without any further measures. Said article proposes vapor deposition for the formation of the multilayer. Apart therefrom, the grooved substrate leads to a complicated micro-structure and texture of the multilayer materials.
Unlike the known CPP geometries, the CPP geometry realized in the element according to the invention has the advantage that the novel concept is independent of the type of layer structure and the deposition method used. A further advantage is that the concept does not require any new materials or processes. Moreover, the electric connection areas may be present at locations which are customary in CIP geometries.
in that the current directing means on both main faces include at least an electric conductor, the electric conductor or conductors on one main face being offset with respect to the electric conductor or conductors on the other main face in a direction towards one of the electric connection areas. Due to the presence of one or more electric conductors on both sides of the layer structure, the electric current passes the layer structure at least once completely during operation. In the presence of different conductors on both sides, a zigzag-shaped passage pattern is produced, with the electric current repeatedly crossing the interfaces between the layers which are present.
It is to be noted that a read/write head with a GMR element is known from EP-A 0 712 117, in which the GMR element is placed between two electric contact elements which are positioned directly opposite each other and sandwich the GMR element. The system constituted by the GMR element and both contact elements is present between two electrically conducting, magnetic layers. During scanning, an electric current flows perpendicularly through the GMR element. This read/write head entirely deviates from the customary CIP geometries due to the contact elements which are positioned directly opposite each other and opposite the GMR element. Moreover, the known system has the drawback that the total resistance to which a read current is subjected is relatively small, which is unfavorable for the output signal and hence for the signal-to-noise ratio of the read signal obtained.
in that the conductor or conductors on the one main face and the conductor or conductors on the other main face are located opposite each other in a non-overlapping position. It has been found that the most favorable effect on the output signal is obtained if the conductor or conductors on one main face are not present in the area or areas exactly opposite the conductor or conductors on the other main face. This effect is achieved by the relatively large resistance to which the current is subjected.
in that the conductor or conductors on the on the one main face and the conductor or conductors on the other main face at least substantially bound the same plane or planes, respectively, oriented transversely to the main faces. In this embodiment, the distance between the electric conductor present on the one or the other main face or, in the presence of more electric conductors, between the conductors alternately present on the one and the other main face is minimal, which results in an optimal CPP geometry.
An embodiment of the element according to the invention is characterized in that the conductor or conductors is, or are, strip-shaped. The strip-shaped conductor or conductors is, or are, preferably formed from a satisfactorily conducting metallic material or metal such as Au. Due to the great difference in resistance which is achievable between a strip-shaped conductor and the layer structure, the electric current flows within a relatively small area near the edges of the conductor during current passage, which results in a relatively large CPP resistance. Moreover, an automatic series connection of contiguous current paths takes place, which leads to a relatively large total resistance and hence to a relatively large GMR effect.
in that the conductor substantially extends in a direction transverse to a connection axis through the electric connection areas. Unlike the electrically conducting strips which, as presumed to be known, are used on an AMR element (anisotropic magnetoresistive element) for linearization of the magnetoresistive element and are arranged at an angle of 45° to the lo
Biren Steven R.
Patidar Jay
U.S. Philips Corporation
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