Static information storage and retrieval – Systems using particular element – Magnetoresistive
Reexamination Certificate
2000-03-22
2002-10-22
Dinh, Son T. (Department: 2824)
Static information storage and retrieval
Systems using particular element
Magnetoresistive
C365S171000, C365S173000, C360S324110
Reexamination Certificate
active
06469926
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to magnetic elements for information storage and/or sensing and a fabricating method thereof, and more particularly, to a method of fabricating and thus defining the magnetic element to improve the magnetoresistance ratio.
BACKGROUND OF THE INVENTION
Typically, a magnetic element, such as a magnetic memory element, has a structure that includes ferromagnetic layers separated by a non-magnetic layer. Information is stored as directions of magnetization vectors in magnetic layers. Magnetic vectors in one magnetic layer, for instance, are magnetically fixed or pinned, while the magnetization direction of the other magnetic layer is free to switch between the same and opposite directions that are called “parallel” and “anti-parallel” states, respectively. In response to parallel and anti-parallel states, the magnetic memory element represents two different resistances. The resistance has minimum and maximum values when the magnetization vectors of the two magnetic layers point in substantially the same and opposite directions, respectively. Accordingly, a detection of change in resistance allows a device, such as an MRAM device, to provide information stored in the magnetic memory element. The difference between the minimum and maximum resistance values, divided by the minimum resistance is known as the magnetoresistance ratio (MR).
An MRAM device integrates magnetic elements, more particularly magnetic memory elements, and other circuits, for example, a control circuit for magnetic memory elements, comparators for detecting states in a magnetic memory element, input/output circuits, etc. These circuits are fabricated in the process of CMOS (complementary metal-oxide semiconductor) technology in order to lower the power consumption of the device.
Magnetic elements structurally include very thin layers, some of which are tens of angstroms thick. The manufacturability throughput and performance of the magnetic element is conditioned upon the magnetic structure utilized and its complexity. Accordingly, it is necessary to make a magnetic device in which a simple structure is sought. A magnetic element structure in which including are fewer layers than the standard magnetic element and less targets, is sought. In addition, it is sought to build a device in which a centered R-H(I) loop does not depend on the precise overly for each of the millions to billions of bits.
During typical magnetic element fabrication, such as MRAM element fabrication, metal films are grown by sputter deposition, evaporation, or epitaxy techniques. One such magnetic element structure includes a substrate, a base electrode multilayer stack, a synthetic antiferromagnetic (SAF) structure, an insulating tunnel barrier layer, and a top electrode stack. The base electrode layer stack is formed on the substrate and includes a first seed layer deposited on the substrate, a template ferromagnetic layer formed on the seed layer, a layer of an antiferromagnetic material on the template layer and a pinned ferromagnetic layer formed on and exchange coupled with the underlying antiferromagnetic layer. The ferromagnetic layer is called the pinned layer because its magnetic moment (magnetization direction) is prevented from rotation in the presence of an applied magnetic field. The SAF structure includes a pinned ferromagnetic layer, and a fixed ferromagnetic layer, separated by a layer of ruthenium, or the like. The top electrode stack includes a free ferromagnetic layer and a protective layer formed on the free layer. The magnetic moment of the free ferromagnetic layer is not pinned by exchange coupling, and is thus free to rotate in the presence of applied magnetic fields. As described, this type of magnetic element structure includes a very complex arrangement of layers and as such is not amenable to high throughput.
An alternative structure includes, a magnetic element material stack which includes three magnetic layers separated by one tunnel barrier and one conductive spacer, such as TaN
y
. The middle magnetic layer is formed so that it is free to rotate or change direction, while the top and bottom magnetic layers are locked in an antiparallel arrangement or direction due to lowered energy from flux closure at the ends. During operation, the structure will have different resistances depending on which of the two directions the middle magnetic layer points its magnetization. In order to achieve a magnetic element which includes a better signal, or an improved magnetoresistance ratio, it is desirable to includes dual tunnel barrier layers. Yet, it has been found that this structure will fail if a tunnel barrier is utilized in the place of the conductive spacer.
Accordingly, it is a purpose of the present invention to provide an improved magnetic element with an improved magnetoresistance ratio.
It is another purpose of the present invention to provide an improved magnetic element that includes a higher MR% or signal, and less voltage dependence.
It is a still further purpose of the present invention to provide a method of forming a magnetic element with an improved magnetoresistance ratio.
It is still a further purpose of the present invention to provide a method of forming a magnetic element with an improved magnetoresistance ratio which is amenable to high throughput manufacturing.
SUMMARY OF THE INVENTION
These needs and others are substantially met through provision of a magnetic element including a first magnetic layer, comprised of a pinned ferromagnetic material, a second magnetic layer, that is free to rotate, a third magnetic layer, comprised of a pinned ferromagnetic material, and two (2) tunnel barrier layers. The structure is defined as including two (2) tunnel barrier layers in which one tunnel barrier layer is normal and one is reversed, or a structure in which the two tunnel barrier layers are of the same type and the structure further includes a SAF structure to allow for same sign changing magnetoresistance ratios across both tunnel barriers. A spacer layer is generally included when the magnetic element includes the SAF structure. The magnetic element further includes a metal lead. The metal lead, the plurality of magnetic layers, the plurality of tunnel barrier layers, and the spacer layer being formed on a substrate material, such as a dielectric. Additionally disclosed is a method of fabricating the magnetic element with an improved magnetoresistance ratio.
REFERENCES:
patent: 6175475 (2001-01-01), Lin et al.
patent: 6259586 (2001-07-01), Gill
patent: 6295225 (2001-09-01), Oepts
patent: 09325746 (1999-06-01), None
Wang et al., “Spin Dependent Tunnel/Spin-Valve Devices with Different Pinning Structures made by Photolithography,” J.of Appl. Physics, vol. 85, No. 8 part 02A, Apr. 15, 1999, pp.5255-5257.
Dinh Son T.
Koch William E.
Motorola Inc.
LandOfFree
Magnetic element with an improved magnetoresistance ratio... 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 element with an improved magnetoresistance ratio..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Magnetic element with an improved magnetoresistance ratio... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2966112