Static information storage and retrieval – Systems using particular element – Magnetic thin film
Reexamination Certificate
1999-10-21
2001-03-20
Le, Vu A. (Department: 2824)
Static information storage and retrieval
Systems using particular element
Magnetic thin film
C365S171000, C365S158000
Reexamination Certificate
active
06205052
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 magnetic field response.
BACKGROUND OF THE INVENTION
This application is related to a co-pending application that bears Motorola docket number CR 99-001, and U.S. Ser. No. 09/356,864, entitled “MAGNETIC ELEMENT WITH IMPROVED FIELD RESPONSE AND FABRICATING METHOD THEREOF”, filed on Jul. 19, 1999, assigned to the same assignee and incorporated herein by this reference, issued U.S. Pat. No. 5,940,319, entitled “MAGNETIC RANDOM ACCESS MEMORY AND FABRICATING METHOD THEREOF,” filed on Aug. 31, 1998, assigned to the same assignee and incorporated herein by this reference, co-pending application that bears Motorola docket number CR 97-158 and U.S. Ser. No. 08/986,764, entitled “PROCESS OF PATTERNING MAGNETIC FILMS” filed on Dec. 8, 1997, assigned to the same assignee and incorporated herein by this reference and issued U.S. Pat. No. 5,768,181, entitled “MAGNETIC DEVICE HAVING MULTI-LAYER WITH INSULATING AND CONDUCTIVE LAYERS”, issued Jun. 16, 1998, assigned to the same assignee and incorporated herein by this reference.
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 the 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 “antiparallel” states, respectively. In response to parallel and antiparallel 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.
In addition, magnetic elements structurally include very thin layers, some of which are tens of angstroms thick. The performance of the magnetic element is sensitive to the surface conditions on which the magnetic layers are deposited. Accordingly, it is necessary to make a flat surface to prevent the characteristics of a magnetic element from degrading.
During typical magnetic element fabrication, such as MRAM element fabrication, which includes metal films grown by sputter deposition, evaporation, or epitaxy techniques, the film surfaces are not absolutely flat but instead exhibit surface or interface roughness. This roughness of the surfaces and/or interfaces of the ferromagnetic layers is the cause of magnetic coupling between the free ferromagnetic layer and the other ferromagnetic layers, such as the fixed layer or pinned layer, which is known as topological coupling or Néel's orange peel coupling. Such coupling is typically undesirable in magnetic elements because it creates an offset in the response of the free layer to an external magnetic field.
A magnetic structure is known as bottom pinned when the fixed layer is formed before the spacer layer, and the free layer is formed after the spacer layer. In such a bottom-pinned structure the antiferromagnetic (AF) pinning layer is contained in the bottom magnetic electrode. Conventional bottom-pinned magnetic tunnel junctions (MTJ) and spin valve structures use seed and template layers to produce an oriented, crystalline AF layer for strong pinning. The bottom electrode of a typical bottom-pinned MTJ structure includes stacked layers of Ta/NiFe/FeMn/NiFe, which is followed by the AlO
x
tunnel barrier, and a top electrode that includes a free layer of NiFe, where the Ta/NiFe seed/template layers induce growth of a highly oriented FeMn(
111
) layer. This highly oriented FeMn layer provides for strong pinning of the NiFe layer below the AlO
x
tunnel barrier. The FeMn layer, or other oriented polycrystalline AF layer produces roughness which causes an increase in undesirable Néel coupling between the pinned NiFe layer and the top free NiFe layer.
In practical MTJ elements the bottom electrode is formed upon a base metal layer which provides a low resistance contact to the junction. The base metal layer is typically polycrystalline and produces roughness which propagates into the bottom electrode and produces roughness at the spacer layer interfaces resulting in an increase in undesirable Néel coupling between the pinned NiFe layer and the top free NiFe layer. The roughness propagated from the base metal layer and the bottom electrode is additionally disadvantageous because it limits the minimum tunnel barrier thickness that can be achieved while retaining high MR and device resistance that scales inversely with junction area.
The topological coupling strength, or Néel coupling, is proportional to surface magnetic charge density and varies as the inverse of an exponential of the interlayer thickness. As disclosed in U.S. Pat. No. 5,764,567, issued Jun. 9, 1998, and entitled “MAGNETIC TUNNEL JUNCTION DEVICE WITH NONFERROMAGNETIC INTERFACE LAYER FOR IMPROVED MAGNETIC FIELD RESPONSE”, by adding a non-magnetic copper layer next to the aluminum oxide tunnel barrier in a magnetic tunnel junction structure, hence increasing the separation between the magnetic layers, reduced ferromagnetic orange peel coupling, or topological coupling, is achieved. However, the addition of the copper layer will lower the MR of the tunnel junction, and thus degrade device performance. In addition, the inclusion of the copper layer will increase the complexity for etching the material.
Accordingly, it is a purpose of the present invention to provide an improved magnetic element with improved field response whereby a reduction in Néel coupling is achieved, thereby resulting in improved switching characteristics for MRAM bits and more ideal response in sensor applications.
It is another purpose of the present invention to provide an improved magnetic element that includes reduced ferromagnetic coupling, more particularly ferromagnetic coupling of topological origin.
It is still another purpose of the present invention to provide an improved magnetic element that includes a flatter tunneling barrier, thus lower tunneling barrier thickness and enabling lower resistance.
It is a still further purpose of the present invention to provide a method of forming a magnetic element with improved field response.
It is still a further purpose of the present invention to provide a method of forming a magnetic element with improved field response that 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 base metal layer, a first electrode, a second electrode and a spacer layer. The base metal layer is positioned on an uppermost surface of a substrate element. One of the two electrodes includes a fixed ferromagnetic layer whose magnetization remains fixed in a preferred direction in the presence of an applied magnetic field that is large enough to switch the free layer, and the other electrode includes a free ferromagnetic layer whose magnetization is free to rotate or switch between magnetization states in
Chen Eugene
Shi Jing
Slaughter Jon
Tehrani Saied
Koch William E.
Le Vu A.
Motorola Inc.
Nguyen Tuan T.
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