Patent Application
20080296711
The present invention relates generally to magnetoelectronic devices. More specifically, the present invention relates to low power magnetoelectronic devices that utilize enhanced permeability materials.
Magnetoelectronics, spin electronics and spintronics are synonymous terms for the use of effects predominantly caused by electron spin. Magnetoelectronics is used in numerous information devices, and provides non-volatile, reliable, radiation resistant, and high-density data storage and retrieval. The numerous magnetoelectronic information devices include, but are not limited to, Magnetoresistive Random Access Memory (MRAM), magnetic sensors, and read/write heads and hard disks for disk drives.
A magnetoelectronic information device, such as an MRAM, typically includes an array of magnetoresistive memory elements. Each magnetoresistive memory element typically has a structure that includes multiple magnetic layers separated by various non-magnetic layers. Information is stored as directions of magnetization vectors in the magnetic layers. Magnetic vectors in one magnetic layer are magnetically fixed or pinned, while the magnetization direction of another 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 magnetoresistive memory element represents two different resistances. The measured resistance of the magnetoresistive memory element 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 the measured resistance allows a magnetoelectronic information device, such as an MRAM device, to provide information stored in the magnetoresistive memory element.
Typically, a magnetoresistive memory element is programmed by a magnetic field created by current flowing through one or more conductors, or programming lines, disposed proximate the memory element. To program the magnetoresistive memory element, the magnetic field applied by the programming line is of sufficient magnitude to switch the direction of the magnetic vectors of one or more magnetic layers of the memory element.
There is an ever-increasing demand for smaller and lower power memory devices. Accordingly, it is desirable to provide a magnetoelectronic device structure that requires low power for programming. In addition, it is desirable to provide an magnetoelectronic device structure in which the current required to program a magnetoresistive memory element of the magnetoelectronic device structure is reduced. It also is desirable to provide a method for fabricating an magnetoelectronic device structure that is cost effective and is readily manufactured.
A more complete understanding of the present invention may be derived by referring to the detailed description and claims when considered in connection with the Figures, wherein like reference numbers refer to similar items throughout the Figures, and:
In one embodiment of the invention, a magnetoelectronic device structure includes multiple layers of a colloidal dispersion, deposited one layer at a time. The colloidal dispersion includes an electrically insulating material, such as a liquid spin-on dielectric material, with dispersed magnetic particles. In another embodiment of the invention, a method of making a magnetoelectronic device structure includes dispensing a colloidal dispersion of an electrically insulating material and magnetic particles using a spin coating technique. Magnetic material in the colloidal dispersion increases the magnetic permeability of the electrically insulating material. In the case of a magnetoelectronic memory element such as a Magnetoresistive Random Access Memory (MRAM), the increased magnetic permeability can reduce the required write current, thus lowering the power required for operation. In the case of other magnetoelectronic devices such as inductors, transformers, and magnetic sensors, the increased magnetic permeability can improve device performance by increasing magnetic coupling. The following description of the invention is exemplary in nature and is not intended to limit the invention.
Magnetoelectronic device 22 includes a magnetoresistive memory element 24, which may comprise, for example, a magnetic tunnel junction (MTJ) device or a giant magnetoresistive (GMR) device. Magnetoelectronic device 22 further includes a conductive programming line, referred to herein as a digit line 26, disposed below magnetoresistive memory element 24 and another conductive programming line, referred to herein as a bit line 28. Bit line 28 is disposed above magnetoresistive memory element 24 and is arranged orthogonal to digit line 26. While for discussion purposes digit line 26 is illustrated in
Magnetoelectronic device 22 further includes a top electrode 30, a bottom electrode 32, and vias 34 and 36. Top electrode 30 may be disposed overlying magnetoresistive memory element 24, and bottom electrode 32 may be disposed underlying magnetoresistive memory element 24. In addition, magnetoelectronic device structure 20 includes material layers 38, 40, and 42. Layer 38 is disposed between digit line 26 and bottom electrode 32. Layer 40 is disposed between bottom electrode 32 and top electrode 30, and layer 42 is disposed between top electrode 30 and bit line 28. Those skilled in the art will recognize that bit line 28 may function as top electrode 30. If such is the case, layer 42 may not be required. Layers 38, 40, and 42 are formed from a colloidal dispersion of an electrically insulating material and magnetic particles. Thus, layers 38, 40, and 42 yield an interlayer dielectric with enhanced magnetic permeability.
The term “colloidal dispersion” refers to a mixture containing particles larger than those found in a solution but small enough to remain suspended for a very long time. Typically, the size of dispersed phase particles in a colloidal dispersion ranges from approximately one nanometer to approximately one micrometer.
The electrically insulating material within the colloidal dispersion of material layers 38, 40, and 42 is a dielectric material, and more particularly, a flowable dielectric. In one embodiment, the flowable dielectric may be a spin-on material or spin-on glass formulation. A spin-on glass formulation is typically a liquid, silicon-based composition that can be applied to the surface of a substrate, such as in the various layers of magnetoelectronic device structure 20, and spun with structure 20 to provide a coating, preferably with a level top surface. With this technique, the spin-on glass formulation can fill in any valleys or recessed areas in the surface of structure 20 that result from the various insulating and conductive regions. The spin-on glass flowable liquid source is then dried to form a solid layer which can be cured at an appropriate temperature to form a dielectric film, or layer. Although spin-on glass is discussed herein, in an alternate embodiment, the spin-on dielectric may be a polyimide formulation or another material that can be applied by a spin-on process to become a dielectric film.
The magnetic particles within the colloidal dispersion of material layers 38, 40, and 42 may be magnetic nanoparticles of iron, cobalt, nickel, or alloys thereof. Other magnetic particles may include mu-metal, and nanoparticles of manganese, magnesium, or their alloys. The colloidal dispersion of electrically insulating material and magnetic particles may be formed by mixing, doping, or otherwise incorporating the magnetic particles into the flowable dielectric to yield a uniform distribution of the magnetic particles within the flowable dielectric. A concentration of magnetic particles within the flowable dielectric may be between approximately twenty-five and approximately thirty percent of the magnetic particles relative to the flowable dielectric. This concentration can produce an enhanced permeability property for the flowable dielectric in a range from approximately two to approximately one hundred. In one embodiment, each of layers 38, 40, and 42 have an equivalent concentration of magnetic particles. However, in alternate embodiments, layers 38, 40, and 42 may have different concentrations of magnetic particles in accordance with a desired permeability property for each of layers 38, 40, and 42.
Typical non-ferromagnetic materials, including flowable dielectrics, have a magnetic permeability that is approximately equal to one. The magnetic permeability of the flowable dielectric is increased above one within layers 38, 40, and 42, through the addition of magnetic particles within the flowable dielectric. By increasing the permeability of layers 38, 40, and 42, the magnetic field generated at electromagnetic device 22 may be increased without a commensurate increase in the write current through bit line 28. Accordingly, by using layers 38, 40, and 42 having an “enhanced permeability,” that is, a permeability greater than about one, a lower current may be required to produce the magnetic field. In this manner, a low power magnetoresistive memory element 24 may be fabricated. For other magnetic devices, the increased permeability of the interlayer dielectric improves device performance in increasing magnetic coupling.
Colloidal particles, such as the magnetic particles that may be used to form the colloidal dispersion, often carry an electrical charge and therefore can attract or repel each other. Unstable colloidal dispersions can form floc, or clumps of particles, as the particles aggregate due to interparticle attractions. Such a situation is undesirable in layers 38, 40, and 42 because excessive clumping of magnetic particles within the dielectric layers 38, 40, and 42 can cause localized areas of conductivity which can compromise the function and reliability of magnetoelectronic device 22. Accordingly, the magnetic particles of the colloidal dispersion may be passivated or otherwise stabilized so that the magnetic particles are made “passive” in relation to one another. Passivation entails the formation of a thin adherent film or layer on the surface of a metal or mineral, such as magnetic particles, that acts as a protective coating to protect the underlying surface from further chemical reaction. The passive film is often, though not always, an oxide. If the magnetic particles are passivated or otherwise stabilized prior to forming the colloidal dispersion, the magnetic particles will be less likely to aggregate, or clump, within the colloidal dispersion thereby preventing the formation of localized areas of conductivity within dielectric layers 38, 40, and 42.
Both digit line 26 and bit line 28 may be surrounded at all surfaces except surfaces 44 most proximate magnetoresistive memory element 24 by ferromagnetic cladding layers (not shown), as is known in the art. As such, it is not necessary to have materials with enhanced permeability disposed about the cladded surfaces of digit line 26 and bit line 28. However, it should be appreciated that in the absence of cladding layers, a material layer 46 disposed about digit line 26 and another material layer 48 disposed about bit line 28 may exhibit enhanced permeability.
Fabrication process 50 is described in terms of the fabrication of magnetoelectronic device structure 20 (
Fabrication process 50 commences with ellipses 52. Ellipses 52 refer to an omission of operations in the fabrication of the underlying elements of magnetoelectronic device structure 20, which are fabricated in accordance with known methodologies. Accordingly, only that portion of fabrication process 50 for fabricating magnetoelectronic device structure 20 is discussed below.
Fabrication process 50 continues with a task 54. At task 54, digit line 26 (
At task 56, digit line 26 and any underlying materials and structures, such as material layer 46 (
Following task 56, a task 58 is performed. At task 58, via 34 (
Next, a task 60 is performed. At task 60, bottom electrode 32 (
Fabrication process 50 continues with a task 62. At task 62, magnetoresistive memory element 24 (
Following task 62, a task 64 is performed. At task 64, magnetoresistive memory element 24 and any exposed portion of lower electrode 32 are spin coated with colloidal dispersion of flowable dielectric and magnetic materials to form layer 40 (
Next, a task 66 is performed. At task 66, via 36 (
Following task 66, a task 68 is performed. At task 68, top electrode 30 (
Next, a task 72 is performed to produce another conductive programming line, in this embodiment, bit line 28 (
A magnetoelectronic device structure that utilizes enhanced permeability dielectric material disposed between a magnetoresistive memory element and programming lines has been described. The enhanced dielectric material is a colloidal dispersion of a flowable dielectric material and magnetic particles. The colloidal dispersion is dispensed using a spin coating technique. Magnetic material in the colloidal dispersion increases the magnetic permeability of the dielectric material. In the case of a magnetoelectronic memory element such as a Magnetoresistive Random Access Memory (MRAM), the increased magnetic permeability can reduce the required write current, thus lower the power required for operation. In the case of other magnetoelectronic devices such as inductors, transformers, and magnetic sensors, the increased magnetic permeability can improve device performance by increasing magnetic coupling. The application of an increased permeability spin-on material, using a known spin coating technique and existing spin-on tooling, increases manufacturing efficiencies and commensurately decreases manufacturing costs.
Although an embodiment of the invention has illustrated and described in detail, it will be readily apparent to those skilled in the art that various modifications may be made therein without departing from the spirit of the invention or from the scope of the appended claims.
