KR20150039372A - Low saturation magnetization in Pt/(Co,Cu) multilyers with perpendicular magnetic anisotropy - Google Patents
Low saturation magnetization in Pt/(Co,Cu) multilyers with perpendicular magnetic anisotropy Download PDFInfo
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Abstract
The present invention relates to a perpendicular magnetic anisotropic multilayer thin film for a magnetic random access memory comprising a platinum thin film layer and a cobalt-copper thin film layer, and more particularly to a magnetic thin film comprising a magnetic layer constituted by substituting a part of cobalt, To a multi-layered thin film in which the perpendicular magnetic anisotropy is maintained and the saturation magnetization is reduced to reduce the influence of the leakage magnetic field. Since the multilayer thin film according to the present invention maintains the perpendicular magnetic anisotropy even after the subsequent heat treatment process, the multilayer thin film can be effectively utilized in high performance and high density magnetic random access memory.
Description
The present invention relates to a multilayer thin film based on platinum and cobalt-copper having a low saturation magnetization exhibiting perpendicular magnetic anisotropy, a method for manufacturing the same, and a magnetic random access memory (MRAM) application using the same.
As an effort to overcome the volatility of a dynamic random access memory (DRAM), which is a semiconductor memory device widely used in electronic devices such as a personal computer, a mobile phone, and the like, a magnetic random access memory Memory) has been actively studied. A nonvolatile memory is a characteristic in which a predetermined power is required only for writing and reading information, and the recorded information is maintained even when the power is turned off, so that no additional power is required. Particularly, recently, in integrating the dynamic random access memory, the limit is exposed, and the magnetic random access memory is considered as a substitute technology of the dynamic random access memory, and research and development in the related industry is actively performed.
The research on magnetic random access memory has been done in earnest since the early 2000s. In the early research, a method of changing the resistance of Tunneling Magneto-Resistance device by reversing the magnetization using a magnetic field generated by current application Mainstream. However, such a magnetic random access memory device has a disadvantage in that the amount of write current is greatly increased due to a reduction in the size of the device, so that it is difficult to implement a large-scale highly integrated memory.
High density magnetic random access The key to memory materials is the development of materials and structures with strong perpendicular magnetic anisotropy, which must be achieved with very thin films of less than 3 nm above all. Causes of perpendicular magnetic anisotropy can be classified by interface and bulk intrinsic properties, and perpendicular magnetic anisotropic materials include rare earth-3d transition metal amorphous alloys [N. Nishimura et al ., J. Appl. Phys. 91, 5246 (2002)], intermetallic compounds such as FePt and CoPt having an L1 0 structure [T. Shima et al ., Appl. Phys. Lett. 80, 288 (2002)], Co / Pd and Co / Pt multilayer thin films [WB Zeper et al ., J. Appl. Phys. 70, 2264 (1991)] and the CoFeB / MgO interface [S. Ikeda et al ., Nature Mater. 9, 721 (2010)], and so on. The former two materials are attributed to bulk intrinsic properties and the latter two materials are understood to be due to the perpendicular magnetic anisotropy at the interface.
The perpendicular magnetic anisotropy energy density of the rare earth-3d transition metal amorphous alloy is not sufficient, and crystallization occurs at a relatively low temperature of about 300 DEG C, and the perpendicular magnetic anisotropy property is rapidly reduced. The Co / Pd and Co / Pt Has sufficient vertical magnetic anisotropic energy density but the multilayer thin film structure is not maintained at a temperature (350 to 500 DEG C) accompanying the magnetic random access memory fabrication process, and thus the perpendicular magnetic anisotropy is reduced or eliminated. The CoFeB / MgO interface is obtained only at a CoFeB thickness with a very small vertical magnetic anisotropy (usually 1.5 nm or less), and the anisotropic distribution characteristics are also poor. On the other hand, intermetallic compounds such as FePt and CoPt having the L1 0 structure are known to have the most excellent properties as far as the perpendicular magnetic anisotropy energy density is sufficiently large and the temperature characteristic is good. However, since such an intermetallic compound having an L1 0 structure requires a high temperature of 600 ° C or higher in order to form an intermetallic compound having a long-range regularity, which is known to be the most important cause of perpendicular magnetic anisotropy, There is a problem in that it is not suitable for the temperature condition accompanying the memory element process. Also, it is difficult to design a seed layer and a buffer layer necessary for forming a (001) texture, which is a prerequisite of perpendicular magnetic anisotropy.
It is therefore an object of the present invention to provide a magnetic memory device capable of manufacturing a high density magnetic random access memory having a new material / structure that meets the subsequent heat treatment temperature of the current memory manufacturing process while maintaining a sufficient vertical magnetic anisotropic energy density, The need for The present invention relates to the fabrication of multilayer thin films made of platinum-cobalt-copper with perpendicular magnetic anisotropy and low saturation magnetization in conformity with process temperatures (350-500 ° C) suitable for magnetic random access memory and magnetic random access memory applications using them. Specifically, the effect of stray fields in high density magnetic random access memory cells is greatly reduced by replacing a portion of cobalt with copper in the platinum-cobalt multilayer thin film by significantly reducing saturation magnetization while maintaining vertical magnetic anisotropy. These magnetic multi-layered films have characteristics suitable for a high density magnetic random access memory cell, particularly a pinned structure of a cell.
The first problem to be solved by the present invention is a multi-layer thin film having low saturation magnetization and exhibiting perpendicular anisotropy, which exhibits a stable structure even after a subsequent heat treatment process, maintains vertical magnetic anisotropy, An object of the present invention is to provide a perpendicularly magnetically anisotropic multilayer thin film comprising a platinum thin film layer and a cobalt-copper thin film layer suitable for a magnetic random access memory cell or a fixed structure of a cell.
A second problem to be solved by the present invention is to provide a method for producing the platinum and cobalt-copper-based multilayer thin films.
In order to achieve the first object of the present invention,
A multilayer thin film having perpendicular magnetic anisotropy, comprising: a platinum thin film layer alternately stacked on a substrate; And a cobalt-copper thin film layer. The perpendicular magnetic anisotropic multilayer thin film for magnetic random access memory is provided.
According to an embodiment of the present invention, the content ratio of cobalt: copper in the cobalt-copper thin film layer may be 50:50 to 90:10 atomic ratio.
According to an embodiment of the present invention, the multilayer thin film may be deposited one to ten times each, in which the platinum thin film layer and the cobalt-copper thin film layer are alternately laminated.
According to another embodiment of the present invention, the total thickness of the alternately stacked platinum thin film layer and the cobalt-copper thin film layer may be 0.24 to 12.5 nm.
According to another embodiment of the present invention, the platinum thin film layer and the cobalt-copper thin film layer alternately stacked on each other may have a structure in which the thickness of the cobalt-copper thin film layer is thinner than or equal to the thickness of the platinum thin film layer The thickness of the cobalt-copper thin film layer is greater than the thickness of the platinum thin film layer (when the thickness of the platinum thin film layer is 1, the thickness of the cobalt- 4 or less).
According to another embodiment of the present invention, the substrate may be any one selected from the group consisting of a silicon substrate, a glass substrate, a sapphire substrate, and a magnesium oxide substrate.
According to another embodiment of the present invention, the multilayer thin film further comprises a buffer layer and a seed layer between the substrate and the alternately laminated platinum thin film layer and the cobalt-copper thin film layer, and the alternately laminated platinum thin layer and A protective layer may be further laminated on the cobalt-copper thin film layer,
Wherein the buffer layer, the seed layer and the protective layer are the same or different and each independently comprise at least one selected from the group consisting of Au, Pd, Cu, Pl, Tantanum, Ru, And at least one metal selected from the group consisting of metals.
According to another aspect of the present invention,
(1) mixing cobalt and copper to produce a mixed metal;
(2) alternately depositing platinum on the substrate and the mixed metal prepared in the step (1) to deposit a platinum thin film layer and a cobalt-copper thin film layer-based multilayer thin film; And
And (3) heat treating the multilayer thin film. The present invention also provides a method of manufacturing a perpendicular magnetic anisotropic multilayer thin film for magnetic random access memory.
According to an embodiment of the present invention, the heat treatment temperature may be 150 ° C to 550 ° C.
According to an embodiment of the present invention, the method may further include depositing a buffer layer and a seed layer before depositing the platinum thin film layer and the cobalt-copper thin film layer on the substrate, wherein the platinum thin film layer and the cobalt- And then laminating the protective layer.
According to another embodiment of the present invention, the platinum thin film layer and the cobalt-copper thin film layer may be alternately stacked one to ten times each.
According to another embodiment of the present invention, the content ratio of cobalt to copper in the cobalt-copper thin film layer may be 50:50 to 90:10 atomic ratio.
According to another embodiment of the present invention, the heat treatment may cause the interface formed between the platinum thin film layer and the cobalt-copper thin film layer to disappear and form a new bulk structure platinum-cobalt-copper intermetallic compound exhibiting perpendicular magnetic anisotropy have..
The perpendicular magnetic anisotropic multilayer thin film layer according to the present invention is manufactured by alternately stacking the platinum thin film layer and the cobalt-copper thin film layer on the substrate, and unlike the conventional multilayer thin film constituting the magnetic layer only of the magnetic material, By replacing a part with a non-magnetic material such as copper, a magnetic layer can be manufactured to reduce the influence of stray fields by lowering saturation magnetization while maintaining vertical magnetic anisotropy. The perpendicular magnetic anisotropic multilayer thin film according to the present invention exhibits vertical magnetic anisotropy as well as saturation magnetization even after a subsequent heat treatment process at 150 to 550 ° C to provide a high density magnetic random access memory cell, And thus can be usefully used in a high-performance, high-density magnetic random access memory.
1 is a cross-sectional view of a multilayer thin film according to an embodiment of the present invention.
Figure 2 is a multi-layer thin film of [Pt (0.2 nm) / CoCu (t CoCu nm)] The thickness of the platinum thin film layer (t pt) with respect to 6 is fixed at 0.2 nm and cobalt in accordance with one embodiment of the present invention of the copper thin-film layer The magnetic moment ( m ) - the applied magnetic field ( H ), obtained by measuring the state before the heat treatment of the multilayer thin film produced by changing the thickness ( t CoCu ) Hysteresis curve. (a) is t CoCu (0.4 nm), ( b) is t CoCu (0.5 nm), ( c) is t CoCu (0.6 nm).
FIG. 3 is a schematic diagram of a multi-layered thin film of [Pt (0.2 nm) / CoCu ( t CoCu nm)] The thickness of the platinum thin-film layer with respect to the 6 (t pt), after fixing and the subsequent heat treatment of the multilayer films produced thickness of the cobalt, copper thin film layer (t CoCu) is varied from 500 ℃ to 0.2 nm measured (m) - The applied magnetic field ( H ) is the hysteresis curve. (a) shows t CoCu (0.4 nm), (b) t CoCu (0.5 nm), (c) shows t CoCu (0.6 nm).
4 is a Scanning Transmission Electron Microscopy image of a multilayer thin film according to an embodiment of the present invention.
FIG. 5 is a graph of an energy dispersive X-ray spectroscopy (EDS) analysis of a multilayer thin film according to an embodiment of the present invention. (a) is an elemental analysis graph for the multilayer thin film after the subsequent heat treatment at 500 ° C before the heat treatment (b).
FIG. 6 is a graph showing the relationship between the Pt (0.2 nm) / CoCu ( t ) and the Co ( t ) produced by changing the thickness ( t pt ) of the platinum thin film layer to 0.2 nm and changing the thickness ( t CoCu ) of the cobalt- CoCu nm)] 6 multilayer thin film, which is a graph that analyzes the saturation magnetization ( M s ) and the perpendicular magnetic anisotropy energy density ( K eff ) according to the copper content change and the heat treatment temperature. (a) shows t CoCu (0.4 nm), (b) t CoCu (0.5 nm), (c) shows t CoCu (0.6 nm).
Hereinafter, the present invention will be described in more detail.
The present invention relates to a multilayer thin film having perpendicular magnetic anisotropy,
A platinum thin film layer alternately stacked on a substrate; And a cobalt-copper thin film layer. The perpendicular magnetic anisotropic multilayer thin film for a magnetic random access memory is provided.
The multilayer thin film having perpendicular magnetic anisotropy according to the present invention has a magnetic layer formed by replacing a part of magnetic material such as cobalt with a non-magnetic material such as copper, unlike a conventional multi-layer thin film in which a magnetic layer is formed only of magnetic material. And a magnetic layer made of a non-magnetic layer made of a thin film layer and a cobalt-copper thin film layer alternately stacked on a substrate. The multilayered thin film according to the present invention can reduce the saturation magnetization of the multilayer thin film while maintaining the perpendicular magnetic anisotropy, thereby reducing the static magnetic interaction and reducing the influence of the stray fields. Even though the interface formed between the platinum thin film layer and the cobalt-copper thin film layer disappears when the subsequent heat treatment is performed at a temperature (350 to 500 ° C) suitable for the magnetic random access memory fabrication process after the formation of the multilayer thin film due to the above- , A new bulk structure of platinum-cobalt-copper intermetallic compound is formed to exhibit perpendicular magnetic anisotropy. The saturation magnetization value is reduced before the heat treatment and the saturation magnetic field is increased in the horizontal direction, It is suitable for random access memory cells, especially for pinned structures of cells.
In the present invention, the content ratio of cobalt to copper in the cobalt-copper thin film layer may be in the range of 50:50 to 90:10 atomic ratio, and preferably the content ratio of cobalt: copper is 85:15 to 70:30 It may be rain.
According to the present invention, the ratio of cobalt to copper in the cobalt-copper thin film layer during the production of the multilayered thin film can be controlled within the above range, so that the perpendicular magnetic anisotropic multilayer thin film for magnetic random access memory with controlled saturation magnetization can be manufactured.
In the multilayered thin film according to the present invention, when the content of cobalt in the cobalt-copper content ratio of the cobalt-copper thin film layer exceeds the above range and the content of copper is less than the above range, the content of copper contained in the magnetic layer is too small, Anisotropic multilayered thin film having a lower magnetic saturation magnetization than that of the conventional perpendicular magnetic anisotropic multilayered thin film, the leakage magnetic field is less likely to be reduced, so that it is difficult to apply to a pinned structure of a magnetic random access memory cell, The content of cobalt in the cobalt: copper content is less than the above range, and when the content of copper exceeds the above range, the content of copper as the nonmagnetic material is higher than the content of cobalt, which is a magnetic material, When magnetic anisotropy energy density is greatly reduced and applied to magnetic random access memory It is not desirable based hard disadvantages.
In the multilayer thin film according to the present invention, the thickness of the single platinum thin film layer may be 0.15 nm to 0.25 nm, and the thickness of the cobalt-copper thin film layer alternately stacked with the platinum thin film layer may be adjusted to control the magnitude of the perpendicular magnetic anisotropy energy . According to the present invention, the thickness of the single cobalt-copper thin film layer may range from 0.1 nm to 1.00 nm with respect to the thickness of the single platinum thin film layer. When the thickness of the cobalt-copper thin film layer is out of the above range, Density may be reduced, or a new bulk structure based on platinum-cobalt-copper may not be produced in a subsequent heat treatment process.
In the multilayer thin film according to the present invention, the thickness ratio of the platinum thin film layer to the cobalt-copper thin film layer may be 0.6 to 4 when the platinum thin film layer is 1, and the cobalt-copper thin film layer is 0.6 to 4 times. When the thickness ratio of the cobalt-copper thin film layer to the platinum thin film layer is less than 0.6, the thickness of the cobalt-copper thin film layer is too thin compared to the platinum thin film layer, so that the perpendicular magnetic anisotropy is not formed or the perpendicular magnetic anisotropy energy density Copper thin film layer is too low to be applied to the magnetic random access memory. When the thickness ratio of the cobalt-copper thin film layer to the thickness 1 of the platinum thin film layer is more than 4, the thickness of the cobalt-copper thin film layer is too thick to decrease the perpendicular magnetic anisotropic energy density I do not.
The multilayer thin film according to the present invention may have a structure in which the thickness of the cobalt-copper thin film layer is thinner than or equal to the thickness of the platinum thin film layer (the thickness of the cobalt-copper thin film layer ranges from 0.6 to 1.0 when the thickness of the platinum thin film layer is 1) The thickness of the cobalt-copper thin film layer may be thicker than the thickness of the platinum thin film layer (when the thickness of the platinum thin film layer is 1, the thickness of the cobalt-copper thin film layer is larger than 1 and not larger than 4). According to the present invention, the perpendicular magnetic anisotropy can be improved as the thickness ratio of the cobalt-copper thin film layer to the platinum thin film layer is increased within the above range. Further, the structure in which the thickness of the cobalt-copper thin film layer is thicker than the thickness of the platinum thin film layer is preferable because it exhibits a low saturation magnetization while retaining vertical magnetic anisotropy even after the subsequent heat treatment is performed.
For example, referring to FIG. 2, when the thickness of the platinum thin film layer is equal to 0.2 nm, the thickness of the cobalt-copper thin film layer is 0.4 nm (FIG. 2A) When the ratio is decreased, the value of the magnetic moment ( m ) becomes smaller. As the content of copper in the magnetic layer increases, it can be confirmed that the magnetization value has a lower saturation magnetization value. 4 and 5, after the multilayer thin film is annealed at 500 ° C, the interface between the platinum thin film layer and the cobalt-copper thin film layer disappears and a new bulk structure of platinum-cobalt-copper intermetallic compound is formed Can be confirmed. On the other hand, Fig. 6, wherein the multilayer film is heat-treated before the 300 ℃ heat treatment there was no significant change in the value of saturation magnetization (M s), after performing a heat treatment at 500 ℃ a whole saturation magnetization (M s) It can be confirmed that it is lowered.
In the perpendicular magnetic anisotropic multilayer thin film for a magnetic random access memory according to the present invention, the platinum thin film layer and the cobalt-copper thin film layer may be laminated one time at a time. However, in order to secure a low saturation magnetization with superior perpendicular magnetic anisotropy, It is preferable that the platinum thin film layer and the cobalt-copper thin film layer are alternately stacked a plurality of times, each of which may be laminated one to ten times. However, when each layer is stacked more than 10 times, resistance increases when applied to a practical memory device, or critical current value required for magnetization inversion is increased due to volume increase of the magnetic thin film layer, which is disadvantageous for commercialization Which is undesirable.
Therefore, when alternately stacked on the substrate by the above-mentioned number of times in the above-mentioned thickness range, the total thickness of the laminated platinum thin film layer and the cobalt-copper thin film layer will have a value in the range of 0.24 to 12.5 nm.
More preferably, the platinum thin film layer and the cobalt-copper thin film layer alternate with each other four to eight times, respectively, to have a high perpendicular magnetic anisotropy and a low saturation magnetization. At this time, the total thickness of the laminated platinum thin film layer and the cobalt-copper thin film layer will have a value within the range of 0.96 to 10.0 nm.
Meanwhile, the multilayer thin film according to the present invention is laminated on the substrate. As the material of the substrate, any material selected from the group consisting of silicon, glass, sapphire, and magnesium oxide may be used, but the present invention is not limited thereto. A substrate commonly used in the field of the invention can be used.
The multilayer thin film according to the present invention may further include a buffer layer and a seed layer between the substrate and the alternately laminated platinum thin film layer and the cobalt-copper thin film layer, and the alternately laminated platinum thin film layer and the cobalt- And further comprising a protective layer on top of the thin film layer.
The materials used for the buffer layer, the seed layer, and the protective layer may be any materials that are commonly used in the art to which the present invention pertains. For example, they may be the same or different, The buffer layer, the seed layer and the protective layer may be formed of a single material selected from the group consisting of a single material selected from the group consisting of palladium (Pd), copper (Cu), platinum (Pt), tantalum (Ta) and ruthenium Layer to form a multilayer thin film, but it is also possible to laminate a plurality of layers.
1 is a cross-sectional view of a multilayer thin film according to an embodiment of the present invention. Referring to FIG. 1, a
For example, a Ta layer may be stacked as the
The thickness of the seed layer is preferably 5 to 40 nm, and the seed layer may participate in formation of a new bulk structure through a subsequent heat treatment. When the thickness of the seed layer is less than 5 nm, the multilayered thin film according to the present invention may not exhibit vertical magnetic anisotropy. If the thickness of the seed layer exceeds 40 nm, the efficiency relative to thickness may not be increased.
In order to accomplish the second object of the present invention, the present invention provides a method of manufacturing a composite metal comprising the steps of: (1) mixing cobalt and copper to prepare a mixed metal; (2) alternately depositing platinum on the substrate and the mixed metal prepared in the step (1) to deposit a platinum thin film layer and a cobalt-copper thin film layer-based multilayer thin film; And (3) heat treating the multi-layered thin film. The present invention also provides a method of manufacturing a perpendicular magnetic anisotropic multilayer thin film for a magnetic random access memory.
In the method of manufacturing a perpendicular magnetic anisotropic multilayer thin film for a magnetic random access memory according to the present invention, the atomic ratio of cobalt and copper constituting the cobalt-copper thin film layer, the thickness of the single platinum thin film layer and the single cobalt-copper thin film layer, The matters relating to the lamination recovery of the single cobalt-copper thin film layer, the material of the substrate, the buffer layer, the seed layer and the protective layer are all as described above. The method of manufacturing a multilayer thin film according to the present invention is different from the conventional platinum-cobalt-based multilayer thin film in which a magnetic layer is formed only of a magnetic material such as cobalt, and a magnetic layer is formed by replacing a part of cobalt, , It is possible to manufacture a multilayer thin film suitable for a magnetic random access memory cell, particularly a pinned structure of a cell, while maintaining vertical magnetic anisotropy and greatly reducing saturation magnetization unlike the prior art. Further, by controlling the thickness ratio of the cobalt-copper thin film layer and the copper content in the magnetic layer with respect to the thickness of the platinum thin film layer, a multilayer thin film having saturation magnetization of a desired size can be manufactured.
The temperature range of the heat treatment process performed after the deposition of each layer in the method according to the present invention may be from 150 ° C to 550 ° C due to the thermal stability problems of the thin film structure, To 300 < 0 > C, it should be understood that the subsequent heat treatment process can be carried out in a much wider temperature range, thus making it convenient and economical to carry out the present memory device process, Possibility, and selection of various materials. On the other hand, when the temperature range of the heat treatment is less than 150 ° C, there is no serious problem. However, when the temperature exceeds 550 ° C, the vertical magnetic anisotropy characteristic may be deteriorated.
FIG. 2 and FIG. 3 were prepared by varying the copper content in the multilayered thin film according to the present invention. The outer magnetic field was applied to the prepared multilayered thin film in the direction perpendicular to the plane and in plane ) And the vibrating sample magnetometer (VSM). Fig. 2 shows the results before the heat treatment, and Fig. 3 shows the result of the vibration sample magnetometer of the multilayered thin film subjected to the subsequent heat treatment at 500 deg.
As shown in FIG. 2 and FIG. 3, it was confirmed in FIG. 3 that the perpendicular magnetic anisotropy shown in FIG. 2 was a multilayer thin film which was subjected to a subsequent heat treatment at 500 ° C. The saturation magnetization was decreased and the saturation magnetic field was increased . This can be attributed to the fact that part of the cobalt was replaced with copper.
BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail with reference to preferred embodiments for better understanding of the present invention. However, the following examples are provided only for the purpose of easier understanding of the present invention, and the present invention is not limited thereto.
< Example >
Example 1.1
end. As a substrate, a high-quality (prime grade) wet-oxidation Si / SiO 2 substrate was used and a Ta (5 nm thick) buffer layer was formed thereon. Then, Pt (10 nm thick) and Ru ) Seed layers were formed in the direction of the maximum density. The thickness of the platinum thin film layer as the non-magnetic layer was fixed to 0.2 nm on the thus formed buffer layer and seed layer, and the non-magnetic copper material was mixed with the magnetic material cobalt to deposit the cobalt-copper thin film layer. - copper thin film layers were alternately deposited six times. Here, a Ru (3 nm thick) protective layer was formed on top of the finally prepared multilayer thin film to prepare a multilayer thin film.
Each layer was deposited by a magnetron sputter deposition method. The base pressure of the chamber was 7 × 10 -8 Torr. The deposition was performed at 2 × 10 -3 Torr through Ar gas injection. All layers during the deposition process were vacuum unbreakable and were deposited using each single target or alloy target. The overall structure is illustrated in Figure 1.
At this time, the thickness of the cobalt-copper thin film layer was 0.4 nm, and the mixing ratio of cobalt to copper was 80 to 20 atomic ratios (or 80 atomic% of cobalt and 20 atomic% of copper relative to 100 atomic% of total) (t CoCu = 0.4 nm; Co 80 Cu 20 ).
I. The prepared multilayer thin film was heat-treated at 500 ° C. The annealing temperature after annealing was 1 × 10 -6 Torr or less, and the annealing temperature and time were 300 ° C. to 500 ° C. for 1 hour, respectively.
Example 1.2
( T CoCu = 0.5 nm; Co 80 Cu 20 ) was prepared in the same manner as in Example 1.1, except that the thickness of the cobalt-copper thin film layer was 0.5 nm.
Example 1.3
( T CoCu = 0.6 nm; Co 80 Cu 20 ) was prepared by the method of Example 1.1 except that the thickness of the cobalt-copper thin film layer was 0.6 nm.
Example 2.1
The mixing ratio of the cobalt-copper thin-film layer was changed from 60 to 40 atomic ratio (or 60 atomic% of cobalt and 40 atomic% of copper relative to 100 atomic% of total) to the ratio of cobalt to copper. ( T CoCu = 0.4 nm; Co 60 Cu 40 ).
Example 2.2
The mixing ratio of the cobalt-copper thin film layer was changed from 60 to 40 atomic ratio (or 60 atomic% of cobalt and 40 atomic% of copper to 100 atomic% of total) in the ratio of cobalt to copper. ( T CoCu = 0.5 nm; Co 60 Cu 40 ).
Example 2.3
Except that the mixing ratio of the cobalt copper thin film layer to the cobalt to copper ratio was 60 to 40 atomic weight ratio (or 60 atomic% cobalt and 40 atomic% copper based on 100 total atomic%). ( T CoCu = 0.6 nm; Co 60 Cu 40 ).
Example 3.1
Except that the mixing ratio of the cobalt-copper thin film layer to the cobalt-copper ratio was 50 to 50 atomic ratio (or 50 atomic% of cobalt and 50 atomic% of copper relative to 100 atomic% of total) (T CoCu = 0.4 nm; Co 50 Cu 50 ).
Example 3.2
The mixing ratio of the cobalt-copper thin film layer was changed from 50 to 50 atomic ratio (or 50 atomic% of cobalt and 50 atomic% of copper to 100 atomic% of total) in the ratio of cobalt to copper. ( T CoCu = 0.5 nm; Co 50 Cu 50 ).
Example 3.3
Except that the mixing ratio of the cobalt-copper thin film layer to the cobalt-copper ratio was 50 to 50 atomic ratio (or 50 atomic% of cobalt and 50 atomic% of copper relative to 100 atomic% of total) (T CoCu = 0.6 nm; Co 50 Cu 50 ).
Comparative Example 1.1
A multilayer thin film was prepared by the method of Example 1 except that a cobalt thin film layer was used instead of the cobalt-copper thin film layer ( t Co = 0.4 nm)
Comparative Example 1.2
( T Co = 0.5 nm) was prepared in the same manner as in Example 1 except that a cobalt thin film layer was used instead of the cobalt-copper thin film layer.
Comparative Example 1.3
A multilayer thin film was prepared by the method of Example 1 except that a cobalt thin film layer was used instead of the cobalt-copper thin film layer ( t Co = 0.6 nm)
Test Example 1. Magnetic Characteristic Analysis
In order to analyze the magnetic characteristics of the multilayer thin films produced according to Examples 1-3 and Comparative Examples of the present invention, a vibrating sample magnetometer (VSM) was used to measure the external magnetic field in a direction perpendicular to the plane out-of-plane and m - H hysteresis curve measured while going in plane to the plane are shown in FIGS. 2 and 3. FIG. 2 is a graph showing the magnetic characteristics before the heat treatment of the multilayer thin film, and FIG. 3 is a graph showing the magnetic characteristics after the multilayer thin film is heat-treated at 500 ° C. FIG.
2 and 3, the perpendicular magnetic anisotropy observed in the state prior to the heat treatment was observed even after the heat treatment at 500 ° C., and the saturation magnetic field ( H s , hard) in the horizontal direction with the decrease of the magnetic moment ( m ) Is increased. Also, it can be seen that the magnetic moment ( m ) value is lowered as the content of copper is increased, while the multilayer thin film having the magnetic layer of cobalt alone has a higher magnetic moment ( m ) value.
Test Example 2. Multilayer Thin Film Formation Analysis
The thickness of the thin film was controlled by controlling the time accurately from the deposition rate to prepare the multilayer thin film according to Example 3.3. In order to accurately measure the thin film speed, the thickness of the deposited thin film was measured with a surface roughness tester (Surface Profiler) It was measured by transmission electron microscopy (TEM), which is shown in FIG. In addition, an energy analyzer (Energy Dispersive X-ray Spectroscopy, hereinafter referred to as EDS) was used for profiling an accurate elemental analysis of the prepared multilayer thin film, and the deposition rate for a single thin film layer is shown in Table 1 below Respectively.
As shown in FIG. 4, the multi-layered thin film according to the present invention had a precise lamination of the respective layers, and confirmed the perpendicular magnetic anisotropy characteristic of the multi-layered thin film formed on the new bulk after heat treatment at 500 ° C.
Further, as shown in FIG. 5, the multilayer thin film according to the present invention firstly detected platinum and ruthenium in the order of deposition, followed by platinum, cobalt and copper simultaneously, and finally ruthenium was detected again Respectively. From the above results, it can be confirmed that the multilayer thin film according to the present invention is accurately formed. In addition, comparing the positions indicated by boxes before and after the heat treatment in FIG. 5, it can be seen that the structure of platinum-cobalt-copper was affected by the ruthenium seed layer through heat treatment.
The above results support the fact that the properties of the multilayer thin film produced according to the present invention with perpendicular magnetic anisotropy and low saturation magnetization directly depend on the structure of the platinum thin film layer and the cobalt-copper thin film layer.
Test Example 3. Depending on the change of copper content Saturation magnetization Change measurement
For the [Pt / Co 100-x Cu x ] 6 multi-layer thin film, which is a novel structure according to the present invention, the thickness of the platinum thin film layer which is a nonmagnetic layer is fixed to 0.2 nm and the thickness of the cobalt- The effect of copper addition was measured while increasing the thickness of the thin film layer and varying the copper content in the cobalt - copper thin film layer. The saturation magnetization was measured by heat treatment at 300 ° C and 500 ° C, which is shown in FIG.
6 (a) is a graph showing the thickness of a single cobalt-copper thin film layer deposited to 0.4 nm, FIG. 6 (b) is a graph showing a thickness of a single cobalt-copper thin film layer deposited to 0.5 nm, And the thickness of the single cobalt-copper thin film layer was 0.6 nm.
When the thickness of the platinum thin layer was fixed to 0.2 nm and the magnetic layer was formed only of pure cobalt, the thickness of the layer was 790 emu / cc when the layer was deposited to a thickness of 0.4 nm, 1060 emu / cc and 0.6 nm (Co 80 Cu 20 ) in the case of the magnetic layer having a thickness of 0.4 nm, it was 644 emu / cc when the magnetic layer was composed of cobalt 80 and
On the other hand, the saturation magnetization of the multilayer thin film annealed at 300 ° C was not significantly different from that before the annealing, but it was confirmed that the saturation magnetization was reduced in the whole range of saturation magnetization when treated at a high temperature of 500 ° C. Thus, the structure according to the present invention can exhibit more effective characteristics in the temperature range that accompanies the magnetic random access memory process. In the case of the perpendicular magnetic anisotropy energy density ( K eff ) value, the abrupt decrease was observed in the multilayered film in which the content ratio of cobalt: copper was 80:20, and the content ratio of cobalt: copper was 85:15 to 70:30 It was confirmed that it was more desirable to contain the compound
That is, by substituting a part of cobalt with copper in the multilayer thin film according to the present invention, the saturation magnetization value can be largely lowered while maintaining perpendicular magnetic anisotropy, and the perpendicular magnetic anisotropy can be stably maintained even at a high heat treatment temperature of 150 to 550 ° C. . Further, the multilayered thin film having the vertical magnetic anisotropy energy density and the saturation magnetization value adjusted to the desired size can be manufactured by changing the substituted copper content.
The multilayer thin film according to the present invention can further be used to manufacture and utilize high density magnetic random access memory which can replace dynamic random access memory which is different from current limit.
100: substrate 110: buffer layer
120: seed layer 130: platinum thin layer
140: cobalt-copper thin film layer 150: protective layer
Claims (14)
A platinum thin film layer alternately stacked on a substrate; And a cobalt-copper thin film layer. The perpendicular magnetic anisotropic multilayer thin film for magnetic random access memory comprises:
(2) alternately depositing platinum on the substrate and the mixed metal prepared in the step (1) to deposit a platinum thin film layer and a cobalt-copper thin film layer-based multilayer thin film; And
(3) heat treating the multilayer thin film. The method of manufacturing a perpendicular magnetic anisotropic multilayer thin film for a magnetic random access memory according to claim 1,
And depositing a protective layer after depositing the platinum thin film layer and the cobalt-copper thin film layer on the protective layer. The method of manufacturing a perpendicular magnetic anisotropic multilayer thin film for magnetic random access memory according to claim 1,
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