Source: http://www.google.com/patents/US6560077?dq=6101531
Timestamp: 2014-10-02 10:33:48
Document Index: 32757201

Matched Legal Cases: ['art 11', 'art 12', 'art 13', 'art 15', 'art 11', 'art 12', 'art 31', 'art 32', 'art 35', 'art 31', 'art 32']

Patent US6560077 - CPP spin-valve device - Google PatentsSearch Images Maps Play YouTube News Gmail Drive More »Sign in<nobr>Advanced Patent Search</nobr>PatentsA spin-valve device of a CPP structure which has a high resistance, and which generates a high output signal with low current. The CPP spin-valve device including a spin-valve element having a substrate and a layered structure formed on the substrate. The layered structure includes a first thin film...http://www.google.com/patents/US6560077?utm_source=gb-gplus-sharePatent US6560077 - CPP spin-valve deviceAdvanced Patent SearchPublication numberUS6560077 B2Publication typeGrantApplication numberUS 09/480,132Publication dateMay 6, 2003Filing dateJan 10, 2000Priority dateJan 10, 2000Fee statusPaidAlso published asUS20020054461Publication number09480132, 480132, US 6560077 B2, US 6560077B2, US-B2-6560077, US6560077 B2, US6560077B2InventorsHideo Fujiwara, Gary J. MankeyOriginal AssigneeThe University Of AlabamaExport CitationBiBTeX, EndNote, RefManPatent Citations (15), Non-Patent Citations (13), Referenced by (53), Classifications (20), Legal Events (3) External Links: USPTO, USPTO Assignment, EspacenetCPP spin-valve deviceUS 6560077 B2Abstract A spin-valve device of a CPP structure which has a high resistance, and which generates a high output signal with low current. The CPP spin-valve device including a spin-valve element having a substrate and a layered structure formed on the substrate. The layered structure includes a first thin film layer of ferromagnetic material, a second thin film layer of ferromagnetic material, and a thin non-magnetic layer structure separating the first and second layers. One of the first and second thin film layers is defined as a free layer and the other layer is defined as a pinned layer, where the free layer has a direction of magnetization that is easier to change than a direction of magnetization of the pinned layer by application of a magnetic field. The non-magnetic layer structure includes a conducting part and insulating part, with the conduction part having an area that is smaller than an area of the free layer. The device further includes a device for producing a current flow through the spin-valve element and a field sensor configured to sense variations in resistance of the spin-valve element due to a difference in rotation of the magnetizations in the free layer and the pinned layer caused by an applied magnetic field.
What is new and desired to be secured by Letters Patent of the United States is: 1. A CPP spin-valve device comprising;
a spin-valve element including a substrate and a layered structure formed on the substrate, the layered structure having a first thin film layer of ferromagnetic material and a second thin film layer of ferromagnetic material, the first thin film layer and the second thin film layer being separated by a thin non-magnetic layer structure, one of the first and second thin film layers being a free layer and the other of the first and second thin film layers being a pinned layer, the free layer having a direction of magnetization that is easier to change than a direction of magnetization of the pinned layer by application of a magnetic field, the nonmagnetic layer structure including a conducting part and insulating part, the conducting part having an area that is smaller than an area of the free layer; means for producing a current flow through the spin-valve element between the free layer and the pinned layer through the conducting part of the non-magnetic layer structure; and a field sensor connected to the spin-valve element configured to sense variations in resistance of the spin-valve element due to a difference in rotation of the magnetizations in the free layer and the pinned layer caused by an applied magnetic field; wherein the non-magnetic layer structure comprises a mosaic structure of a plurality of conducting parts and a plurality of insulating parts and a distance between adjacent conducting parts is less than an exchange length of the free layer. 2. The CPP spin-valve device of claim 1, wherein:
the mosaic structure is formed of metal and oxide; the metal is selected from the group consisting of Ag, Al, Au, Cr, Cu, Mg, Mn, Pd and their alloys; and the oxide is selected from the group consisting of the oxides of Al, Cr, Cu, Mg, Mn, Nb, Pd, Si, Ta, Ti, V and Zr. 3. The CPP spin-valve device of claim 1, wherein the conducting part is formed of metal and the insulating part is formed of oxide.
the mosaic structure is formed of metal and nitride; the metal is selected from the group consisting of Ag, Al, Au, Cr, Cu, Mg, Mn, Pd and their alloys; and the nitride is selected from the group consisting of the nitrides of Al, B, C, Si and Ta. 6. The CPP spin-valve device of claim 1, wherein the conducting part is formed of metal and the insulating part is formed of nitride.
the conducting part has a width that is smaller than a width of the insulating part; and the conducting part has a length that is smaller than a length of the free layer. 11. The CPP spin-valve device of claim 1, wherein the conducting part has an upper edge that is recessed from an upper surface of the free layer and an upper surface of the pinned layer which form an air bearing surface of a magnetic recording read head.
a spin-valve element comprising a substrate and a layered structure formed on said substrate, the layered structure comprising a first and a second thin film layer of ferromagnetic material separated by a thin non-magnetic layer structure, the magnetization of one of said layers of ferromagnetic material, called a free layer, being easier to change a direction thereof than a direction of the other of said layers of ferromagnetic material, called a pinned layer, by application of a magnetic field and said non-magnetic layer structure including a conducting part; means for producing a current flow through said spin-valve element between said free and pinned layers through said conducting part of said non-magnetic layer structure; and means for sensing variations in resistance of said spin-valve element due to a difference in rotation of magnetizations in said free and pinned layers caused by an applied magnetic field, wherein said non-magnetic layer structure comprises an insulator part and a conductor part, the width of said non-magnetic layer structure within which said conducting part of said non-magnetic layer structure exists is smaller than a width of the free layer which defines the track width of the spin-valve device at least by the exchange length in the free layer. 14. The CPP spin-valve device of claim 13, wherein said non-magnetic layer structure comprises a mosaic structure of conducting, low resistivity and insulating, high resistivity parts.
a spin-valve element including a substrate and a layered structure formed on the substrate, the layered structure having a first thin film layer of ferromagnetic material and a second thin film layer of ferromagnetic material, the first thin film layer and the second thin film layer being separated by a thin non-magnetic structure, one of the first and second thin film layers being a free layer and the other of the first and the second thin film layers being a pinned layer, the free layer having a direction of magnetization that is easier to change than the direction of magnetization of the pinned layer by application of a magnetic field, the nonmagnetic layer structure having at least one current-confining path; means for producing a current flow through the spin-valve element between the free and the pinned layer through the at least one current-confining path; means connected to the spin-valve element for sensing variations in resistance of the spin-valve element due to a difference in rotation of the magnetizations in the free layer and the pinned layer caused by an applied magnetic field; wherein the at least one current-confining path is formed within every flux path of a width of the exchange length of the free layer except at the edge of the free layer. 20. The CPP spin-valve device of claim 19, wherein the non-magnetic layer structure comprises a mosaic structure of a plurality of conducting parts and a plurality of insulating parts.
the mosaic structure is formed of metal and oxide; the metal is selected from the group consisting of Ag, Al, Au, Cr, Cu, Mg, Mn, Pd and their alloys; and the oxide is selected from the group consisting of the oxides of Al, Cr, Cu, Mg, Mn, Nb, Pd, Si, Ta, Ti, V and Zr. 23. The CPP spin-valve device of claim 19, wherein the conducting part is formed of metal and the insulating part is formed of oxide.
the mosaic structure is formed of metal and nitride; the metal is selected from the group consisting of Ag, Al, Au, Cr, Cu, Mg, Mn, Pd and their alloys; and the nitride is selected from the group consisting of the nitrides of Al, B, C, Si and Ta. 26. The CPP spin-valve device of claim 19, wherein the conducting part is formed of metal and the insulating part is formed of nitride.
the conducting part has a width that is smaller than a width of the insulating part; and the conducting part has a length that is smaller than a length of the free layer. 31. The CPP spin-valve device of claim 19, wherein the conducting part has an upper edge that is recessed from an upper surface of the free layer and an upper surface of the pinned layer which form an air bearing surface of a magnetic recording read head.
This invention relates, in general, to the field of magnetoresistive spin-valve (SV) devices. More particularly, the present invention relates to a current perpendicular-to-the-plane (CPP) spin-valve device configuration, applicable as a magnetic non-volatile mass-memory called �MRAM,� and/or as a magnetic transducer or �head� for reading information signals recorded on a magnetic medium.
The related art discloses a magnetic transducer referred to as a spin-valve (SV) magnetoresistive sensor, e.g., in U.S. Pat. No. 5,159,513, issued on Oct. 27, 1992. An SV element includes at least two ferromagnetic layers with different magnetic field sensitivity, the one of the higher sensitivity being called a �free layer� and the other a �pinned layer.� The resistance depends on the angle between the magnetizations of the two layers as cosine of the angle and is independent of the current direction with respect to the magnetization directions, which is traditionally called the giant magnetoresistive effect (GMR). In MRAM's, the information of �0� and �1� is stored either by the direction of the magnetization in the free layer or in the pinned layer. The stored information is read out by applying a field and sensing the sign of the change of the resistance of the SV element. See, for instance, �Characteristics of AP Bias in Spin Valve Memory Elements,� J. Zhu and Y. Zheng, IEEE Trans. Magn. Vol. 34, 1063-1065 (1998); �Pseudo Spin Valve MRAM Cells with Sub-Micrometer Critical Dimension,� B. A. Everitt et al, IEEE Trans. Magn. Vol. 34, 1060-1062 (1998). An SV element can also be applied to a magnetic field sensor, detecting a magnetic field through the resistance changes of the element. It has been shown that an SV head is capable of reading data from a magnetic surface at great linear densities.
The GMR effect is larger when measured with a current perpendicular to the layer structure than when measured with a current in plane direction. See, for example, �Perpendicular Giant Magnetoresistance of Microstructured Fe/Cr Magnetic multilayers from 4.2 to 300 K,� M. A, M. Gijs, S. K. J. Lenczovski and J. B. Giesbers, Physical Review Letters, Vol. 70, 3343-3346 (1993). The former is called CPP (current perpendicular-to-the-plane) and the latter, CIP (current-in-plane). Therefore, it is desirable to make use of CPP rather than CIP if the circumstances allow. However, the drawback in the CPP structure is the fact that only a very low resistance change is obtainable compared to the CIP structure making it necessary to apply a very large current to obtain a reasonable output signal level.
SUMMARY OF THE INVENTION An objective of the present invention is to provide a spin-valve (SV) device of a CPP structure which has a high resistance, and which generates a high output signal with a low current.
In accordance with the present invention, an SV device having a layered structure called an �SV element� formed on a substrate includes first and second thin film layers of ferromagnetic materials separated by a thin layer structure of non-magnetic material. In the present invention the magnetization of one of the layers of a ferromagnetic material, called a �free layer,� is easier to change its direction than that of the other of the layers of a ferromagnetic material, called a �pinned layer,� by application of a magnetic field and means to produce a current flow between the free and pinned layers through a conducting part of the non-magnetic layer structure. The area of the conducting part of the non-magnetic layer structure being smaller than the area of the free layer, thus making the resistance between the free and pinned layers much higher than otherwise. The resistance of the SV element changes as a function of the angle between the magnetizations in the free and pinned layers. For memory applications, the information of �0� and �1� is stored by the direction of the magnetization either in the free layer or in the pinned layer. The stored information is read out by applying a field and sensing the sign of the change of the resistance of the SV element. When applied to a field sensor such as a read head in magnetic recording devices, the resistance change of the SV element is sensed due to the difference in rotation of the magnetizations in the free and pinned layers as a function of the magnetic field being sensed. The present invention provides a way of obtaining substantially higher output by applying a lower current than that obtained by devices in the related art.
DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 depicts a conceptual structure of a CPP SV-device of the related art. An SV-element is composed of a free-layer part 11 and a pinned layer part 12 with a conducting layer part 13 in between. The device is also equipped with a device to apply a current from one lead to the other through the contacts provided by the window 14 opened in the insulator layer part 15 coated upon the free layer part 11 and by the conductor 16 underneath the pinned layer part 12. The whole structure is mounted on a substrate (not depicted) which may be either of a magnetic or of a nonmagnetic material with or without a magnetic shield part on top of it and with or without an insulating layer on top. The change of the resistance R, ΔR of the SV element is expressed as a function of the angle θ between the magnetizations of the free and pinned layers is expressed roughly as
ΔR=(Δρ/D)(2−cos θ)/2, where Δρ denotes the resistance change for the SV element of a unit area with the change of the angle θ from 0 to 180� by an application of a field and S denotes the area of the SV element. A typical value of Δρ is in the order of 1015 Ωm2. See, for instance, �Two-channel analysis of CPP-MR data for Ag/Co and AgSn/Co multilayers,� S. -F. Lee et al., Journal of Magnetism and Magnetic Materials, Vol. 118, L1-L5 (1993). Assuming that the necessary output voltage is in the order of 10 volts, it turns out that the current density i to be applied to the spin-valve element is to be in the order of 1011 A/m2. This means that for an SV-element with the area of 1 μm2 the current to be applied comes to be in the order of 100 mA. This is too high a current for ordinary applications, especially for MRAM or high density magnetic recording heads. Desirably the current to be applied is 2 to 3 orders of magnitude lower than these current levels.
In order to overcome the drawback described above, a CPP-GMR structure has been a proposed as is depicted in FIG. 2. See, for instance, �Perpendicular Giant Magnetoresistance of Microstructured Fe/Cr Magnetic Multilayers from 4.2 to 300 K,� M. A. M. Gijs, S. K. J. Lenczovski and J. B. Giesbers, Physical review Letters, Vol. 70, 3343-3346 (1993) and �Perpendicular giant magnetoresistance of multilayered Co/Cu nanowires,� K. Liu et al., Physical Review, Vol. 51, 7381-7384 (1995). The parts in FIG. 2 indicated using reference numbers with the same last digit as in FIG. 1 represent the same parts. The GMR-element is made into a narrow pillar structure or nanowires 27 of multilayers of magnetic and nonmagnetic metals embedded in an insulator 28. The number of layers is, typically, greater than 100.
Thus, the object of the present invention is to provide an SV device of a simple structure which allows a substantial reduction in the current to be applied to the CPP-SV element. An exemplary embodiment of the CPP-SV devices, according to the present invention, is depicted schematically in FIG. 3a. FIG. 3a depicts a conceptual structure of a CPP SV-device of the present invention. The SV-element is composed of a free-layer part 31 and a pinned layer part 32 with a non-magnetic layer structure 33 in between. The device is also equipped with a device to apply a current from one lead to the other through the contacts provided by the window 34 opened in the insulator layer part 35 coated upon the free layer part 31 and by the conductor 36 underneath the pinned layer part 32. The whole structure is mounted on a substrate (not depicted) which may be either of a magnetic or of a nonmagnetic material with or without a magnetic shield part on top of it and with or without an insulating layer on top.
The mosaic structure described above can include any inhomogeneous lateral distribution of at least two kinds of parts with a resistivity substantially different from each other, such as a structure with metallic pillars embedded in an insulator medium and a structure with a metal defused into the grain-boundaries of insulator grains. When applied to magnetic recording read heads it is especially beneficial for avoiding the additional magnetic noise if the distance between the adjacent conducting parts is made smaller than the, so called, �exchange length� of the free layer material, which is usually in the range of between several tens of nanometers to several hundred nanometers.
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confined pass layer for magnetic elements utilizing spin-transfer and an mram device using such magnetic elements* Cited by examinerClassifications U.S. Classification360/324.1, G9B/5.114International ClassificationH01F10/32, G01R33/09, G11C11/16, G11B5/39Cooperative ClassificationB82Y10/00, G11C2213/81, G11B2005/3996, G01R33/093, H01F10/324, G11C11/16, B82Y25/00, G11B5/3903European ClassificationB82Y10/00, B82Y25/00, G11B5/39C, G01R33/09B, H01F10/32N, G11C11/16Legal EventsDateCodeEventDescriptionOct 26, 2010FPAYFee paymentYear of fee payment: 8Sep 18, 2006FPAYFee paymentYear of fee payment: 4May 1, 2000ASAssignmentOwner name: UNIVERSITY OF ALABAMA, THE, ALABAMAFree format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:FUJIWARA, HIDEO;MANKEY, GARY J.;REEL/FRAME:010780/0697Effective date: 20000217Owner name: UNIVERSITY OF ALABAMA, THE G60 ROSE ADMINISTRATIONRotateOriginal ImageGoogle Home - Sitemap - USPTO Bulk Downloads - Privacy Policy - Terms of Service - About Google Patents - 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