Magnetic tunnel junction element and memory device including the same

Abstract

To provide a magnetic tunnel junction element having a high-tunneling magnetic resistance and an exchange coupling strength, and provide a memory device including the same.SOLUTION: A magnetic tunnel junction element comprises: a fixed layer and a free layer that face each other; a buffer layer that is positioned on the fixed layer; an auxiliary layer that is positioned on the buffer layer; a polarization improvement layer that is positioned between the auxiliary layer and the free layer; and a tunnel barrier layer that is positioned between the polarization improvement layer and the free layer. The buffer layer is amorphous, and contains CoFeBX, X being W, Mo, Re, or Ta, and the auxiliary layer contains W, Mo, Re, or Ta.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a magnetic tunnel junction element and a memory device including the same.

Background Art

[0002] A magnetic memory device such as MRAM (Magnetic Random Access Memory) is a memory device that stores data by utilizing a resistance change of a magnetic tunnel junction element. The resistance of the magnetic tunnel junction element changes depending on the magnetization direction of a free layer. For example, when the magnetization direction of the free layer is the same as that of a pinned layer, the magnetic tunnel junction element has a low resistance value, and when they are opposite to each other, the magnetic tunnel junction element has a high resistance value. When such a characteristic is utilized in a memory device, for example, the magnetic tunnel junction element indicates data "0" when it has a low resistance value and indicates data "1" when it has a high resistance value.

Summary of the Invention

Problems to be Solved by the Invention

[0003] The present invention has been made in view of the above prior art, and an object of the present invention is to provide a magnetic tunnel junction element having a high tunneling magnetoresistance and exchange coupling strength and a memory device including the same.

Means for Solving the Problems

[0004] A magnetic tunnel junction element according to an aspect of the present invention made to achieve the above object includes a pinned layer and a free layer facing each other, a buffer layer located on the pinned layer, an auxiliary layer located on the buffer layer, a polarization improvement layer located between the auxiliary layer and the free layer, and a tunnel barrier layer located between the polarization improvement layer and the free layer. The buffer layer is amorphous and contains CoFeBX, where X is W, Mo, Re, or Ta, and the auxiliary layer contains W, Mo, or Ta.

[0005] The magnetic tunnel junction device according to another aspect of the present invention made to achieve the above object includes a fixed layer and a free layer facing each other, a buffer layer located on one surface of the fixed layer, a polarization improvement layer located between the buffer layer and the free layer, and a tunnel barrier layer located between the polarization improvement layer and the free layer. The buffer layer is amorphous and contains CoFeBX, where X is W, Mo, Re, or Ta. The polarization improvement layer includes a first polarization improvement layer and a second polarization improvement layer. The second polarization improvement layer is located between the first polarization improvement layer and the free layer, and the concentration of boron contained in the second polarization improvement layer is lower than the concentration of boron contained in the first polarization improvement layer.

[0006] A memory device according to one aspect of the present invention made to achieve the above object includes a plurality of memory cells each including a magnetic tunnel junction device and a switching device connected to the magnetic tunnel junction device. The magnetic tunnel junction device includes a fixed layer and a free layer facing each other, a buffer layer located on the fixed layer, an auxiliary layer located on the buffer layer, a polarization improvement layer located between the auxiliary layer and the free layer, and a tunnel barrier layer located between the polarization improvement layer and the free layer. The buffer layer is amorphous and contains CoFeBX, where X is W, Mo, Re, or Ta, and the auxiliary layer contains W, Mo, or Ta.

Advantages of the Invention

[0007] According to the present invention, it is possible to provide a magnetic tunnel junction device having a high tunneling magnetoresistance and an exchange coupling strength, and a memory device including the same.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Embodiments for Carrying Out the Invention

[0009] Hereinafter, specific examples of embodiments for carrying out the present invention will be described in detail with reference to the drawings. The present invention can be implemented in various different forms and is not limited to the embodiments described herein.

[0010] To clearly explain the present invention, parts not related to the explanation are omitted, and the same reference numerals are given to the same or similar components throughout the specification.

[0011] Also, the sizes and thicknesses of the respective configurations shown in the drawings are arbitrarily shown for convenience of explanation, and the present invention is not necessarily limited to those shown. In the drawings, the thickness is enlarged to clearly represent a plurality of layers and regions. And, in the drawings, for convenience of explanation, the thicknesses of some layers and regions are exaggerated.

[0012] Also, when a part such as a layer, film, region, plate, etc. is “on” or “above” another part, this includes not only the case where it is “directly above” the other part, but also the case where there is another part in the middle. Conversely, when it is said that a part is “directly above” another part, it means that there is no other part in the middle. Also, being “on” or “above” a reference part means being located above or below the reference part, and does not necessarily mean being located “on” or “above” in the direction opposite to gravity.

[0013] Also, throughout the specification, when a part "includes" a certain component, it means that, unless otherwise stated to the contrary, it does not exclude other components but can further include other components.

[0014] Also, throughout this specification, "on a plane" means when looking at the target part from above, and "in a cross-section" means when looking at the cross-section obtained by vertically cutting the target part from the side.

[0015] FIG. 1 is a cross-sectional view showing a schematic structure of a magnetic tunnel junction element according to an embodiment.

[0016] Referring to FIG. 1, the magnetic tunnel junction element according to this embodiment includes an electrode 101, a seed layer 110 located on the electrode 101, a pinned layer 120 located on the seed layer 110, a buffer layer 151 located on the pinned layer 120, an auxiliary layer 152 located on the buffer layer 151, a polarization improvement layer 160 located on the auxiliary layer, a tunnel barrier layer 130 located on the polarization improvement layer 160, and a free layer 140 located on the tunnel barrier layer 130. Also, although not shown, a capping metal can be further disposed on the free layer 140. Here, the expression "located on" is for convenience of explanation and does not necessarily mean a vertical relationship.

[0017] The electrode 101 includes a conductive material for applying a current to the magnetic tunnel junction element. The electrode 101 includes a low-resistance metal or a metal nitrate. For example, the electrode 101 includes TiN or TaN. The electrode 101 can be regarded as a part of the magnetic tunnel junction element, but can also be regarded as a part of a memory device including the magnetic tunnel junction element.

[0018] The seed layer 110 is located on the electrode 101. The seed layer 110 contains Ru, Pt, Pd, or a combination thereof. In one embodiment, an intermediate layer (not shown) is located between the electrode 101 and the seed layer 110. The intermediate layer serves to match the crystal structure of the electrode 101 and the crystal structure of the seed layer 110 between the electrode 101 and the seed layer 110. As an example, the intermediate layer contains Ta.

[0019] The fixed layer 120 and the free layer 140 are composed of a ferromagnetic metal material having magnetism. For example, the fixed layer 120 and the free layer 140 include iron (Fe), cobalt (Co), nickel (Ni), manganese (Mn), ruthenium (Ru), Fe-containing alloys, Co-containing alloys, Ni-containing alloys, Mn-containing alloys, Ru-containing alloys, Heusler alloys, or combinations thereof. The fixed layer 120 has a fixed magnetization direction, and the free layer 140 has a variable magnetization direction. The magnetic tunnel junction element has a low resistance when the magnetization directions of the fixed layer 120 and the free layer 140 are the same (for example, parallel), and a high resistance when the magnetization directions are opposite (for example, antiparallel). Such a phenomenon is called tunneling magnetoresistance (TMR). By applying this TMR phenomenon, the magnetic tunnel junction element 100 can be used in a memory device.

[0020] Subsequently, although it will be described in detail separately, the magnetic tunnel junction element according to this embodiment can improve the problem that the exchange coupling strength (exchange field, Hex) of the magnetic tunnel junction element deteriorates and the tunneling magnetoresistance (TMR) deteriorates due to the diffusion and crystalline collision of each layer constituting the magnetic tunnel junction element.

[0021] The fixed layer 120 and the free layer 140 have high perpendicular magnetic anisotropy (PMA), particularly interface perpendicular magnetic anisotropy (IPMA). That is, the perpendicular magnetic anisotropy energy of the fixed layer 120 and the free layer 140 exceeds the out-of-plane demagnetization energy. In this case, the magnetic moments of the fixed layer 120 and the free layer 140 are stabilized in a direction perpendicular to the layer direction. Such a magnetic tunnel junction element 100 is applied to STT-MRAM (Spin Transfer Torque-Magnetic RAM) or SOT (spin-orbit coupling torque) MRAM.

[0022] To improve the operating speed of the memory device using the magnetic tunnel junction element 100, the free layer 140 has a low saturation magnetization (Ms). To lower the saturation magnetization of the free layer 140, the free layer 140 is further doped with a non-magnetic metal element. For example, the free layer 140 is doped with a metal such as calcium (Ca), scandium (Sc), yttrium (Y), magnesium (Mg), strontium (Sr), barium (Ba), zirconium (Zr), beryllium (Be), titanium (Ti), hafnium (Hf), vanadium (V), zinc (Zn), niobium (Nb), manganese (Mn), aluminum (Al), chromium (Cr), lithium (Li), cadmium (Cd), lead (Pb), indium (In), gallium (Ga), tantalum (Ta), or a combination thereof. The non-magnetic metal doped into the free layer 140 has an oxygen affinity higher than that of the ferromagnetic metal material of the free layer 140.

[0023] Alternatively, if necessary, the free layer 140 has two or more multilayer structures including a layer containing only a ferromagnetic metal material and a layer doped with a nonmagnetic metal. Such a material and structure of the free layer 140 can reduce or prevent the diffusion of oxygen or metal elements at the interface with the tunnel barrier layer 130 described later.

[0024] The tunnel barrier layer 130 serves to provide a magnetic tunneling junction between the fixed layer 120 and the free layer 140. The tunnel barrier layer 130 includes a crystalline metal oxide. For example, the tunnel barrier layer 130 includes MgO, MgAl 2 O 4 , MgTiOx, or a combination thereof. In one embodiment, the tunnel barrier layer 130 includes MgO.

[0025] The fixed layer 120 is a synthetic antiferromagnet (SAF). The fixed layer 120 includes a first ferromagnetic layer 120a, a second ferromagnetic layer 120c, and an antiferromagnetic coupling layer (SAF coupling layer) 120b located between the first ferromagnetic layer 120a and the second ferromagnetic layer 120c.

[0026] The antiferromagnetic coupling layer 120b includes a conductive metal. For example, the antiferromagnetic coupling layer 120b includes at least one of iridium (Ir), ruthenium (Ru), aluminum (Al), copper (Cu), silver (Ag), and alloys containing these.

[0027] Each of the first ferromagnetic layer 120a and the second ferromagnetic layer 120c has a single-layer structure composed of a ferromagnetic metal or an alloy of a ferromagnetic metal and a transition metal, or has a multilayer structure including a plurality of layers containing a ferromagnetic metal or an alloy of a ferromagnetic metal and a transition metal. For example, each of the first ferromagnetic layer 120a and the second ferromagnetic layer 120c includes a single-layer or multilayer structure including Co, Fe, CoPt, CoPtCr, FePt, CoFe, etc. In one embodiment, the first ferromagnetic layer 120a includes CoPt and the second ferromagnetic layer 120c includes Co.

[0028] In such a structure of the fixed layer 120, the first ferromagnetic layer 120a and the second ferromagnetic layer 120c form an antiferromagnet through the antiferromagnetic coupling layer 120b by the RKKY interaction (Ruderman - Kittel - Kasuya - Yosida interaction). That is, the fixed layer 120 has a stable state when the magnetization directions of the first ferromagnetic layer 120a and the second ferromagnetic layer 120c are opposite to each other. For example, the first ferromagnetic layer 120a is magnetized toward the lower surface, and the second ferromagnetic layer 120c is magnetized toward the upper surface, or the first ferromagnetic layer 120a is magnetized toward the upper surface, and the second ferromagnetic layer 120c is magnetized toward the lower surface. The first ferromagnetic layer 120a and the second ferromagnetic layer 120c magnetized in opposite directions (e.g., antiparallel to each other) cancel each other's stray magnetic fields. Therefore, by using the first ferromagnetic layer 120a and the second ferromagnetic layer 120c magnetized in opposite directions, it is possible to reduce or prevent the stray magnetic field generated in the fixed layer 120 from affecting the free layer 140.

[0029] Referring to FIG. 1, a buffer layer 151 is located on the second ferromagnetic layer 120c. The buffer layer 151 is amorphous and relaxes the crystalline collision between the layer located below and the layer located above.

[0030] The buffer layer 151 contains CoFeBX. Here, X is W, Mo, Re, or Ta. The thickness of the buffer layer 151 is 1 Å to 4 Å. If the thickness of the buffer layer 151 is less than 1 Å, it may not have a sufficient crystalline collision relaxation effect, and if the thickness exceeds 4 Å, it may cause decoupling. Since the buffer layer 151 is amorphous, it can relax the crystalline collision due to the difference in crystal structure between the second ferromagnetic layer 120c located below and the polarization improvement layer 160 located above. Specific effects will be described later.

[0031] An auxiliary layer 152 is located on the buffer layer 151. The auxiliary layer 152 contains W, Mo, or Ta. Such an auxiliary layer 152 contains substances with high-temperature heat resistance and prevents the diffusion of cobalt and boron in the magnetic tunnel junction element. Table 1 below shows the structures and melting points of various substances.

[0032]

Table 1

[0033] Referring to Table 1 above, W, Mo, and Ta contained in the auxiliary layer 152 have higher melting points than Co. Therefore, when an auxiliary layer 152 containing such substances is located between the second ferromagnetic layer 120c and the polarization improvement layer 160, the diffusion of cobalt and boron can be prevented. However, as confirmed in Table 1 above, the crystal structures of Co and W, Mo, and Ta are different. That is, Co has a hexagonal close packing (HCP) structure, and W, Mo, and Ta have a body-centered cubic (BCC) structure. Therefore, when W, Mo, or Ta is directly formed on the Co layer, crystalline collisions may occur at the interface. However, in the case of the magnetic tunnel junction element according to the present embodiment, an amorphous buffer layer 151 is located between the second ferromagnetic layer 120c containing Co and the auxiliary layer 152 containing W, Mo, or Ta, and crystalline collisions can be prevented.

[0034] The thickness of the auxiliary layer 152 is 0.5 Å to 2 Å. The process of forming the thickness of the auxiliary layer 152 to be 0.5 Å or less is not easy, and when the thickness of the auxiliary layer 152 exceeds 2 Å, decoupling may be caused. Although it will be described in detail separately later, since the auxiliary layer 152 has the same crystal structure as the polarization improvement layer 160 formed later, it can function as a seed layer during the formation of the polarization improvement layer 160 and strengthen the crystallinity of the polarization improvement layer 160. As an example, the auxiliary layer 152 has a body-centered cubic (BCC) structure. The thickness of the auxiliary layer 152 is thinner than the thickness of the buffer layer 151.

[0035] The polarization improvement layer 160 is located on the auxiliary layer 152. The polarization improvement layer 160 aids in the growth of the tunnel barrier layer 130 and the free layer 140. Also, the polarization improvement layer 160 has a crystal structure similar to that of the tunnel barrier layer 130 or the free layer 140, and can further improve the crystal quality of the tunnel barrier layer 130 and the free layer 140. For this reason, the polarization improvement layer 160 includes a ferromagnetic material similar to that of the free layer 140.

[0036] The polarization improvement layer 160 includes a first polarization improvement layer 161 and a second polarization improvement layer 162. The second polarization improvement layer 162 is located between the first polarization improvement layer 161 and the tunnel barrier layer 130.

[0037] The first polarization improvement layer 161 and the second polarization improvement layer 162 contain the same material but have different composition ratios. The first polarization improvement layer 161 and the second polarization improvement layer 162 include, for example, CoFeB. The ratio of boron (B) in the second polarization improvement layer 162 is smaller than the ratio of boron (B) in the first polarization improvement layer 161. For example, the ratio of boron (B) in the first polarization improvement layer 161 is about 30 mol% to about 50 mol%, and the ratio of boron (B) in the second polarization improvement layer 162 is about 5 mol% to about 25 mol%.

[0038] Also, the thickness of the second polarization improvement layer 162 is smaller than the thickness of the first polarization improvement layer 161. For example, the thickness of the first polarization improvement layer 161 is about 5 Å to about 7 Å, and the thickness of the second polarization improvement layer 162 is about 1 Å to about 3 Å. Due to the gradual change in the composition ratio within the polarization improvement layer 160, the crystal structure easily changes from the fixed layer 120 to the free layer 140. Thus, the crystal quality of the tunnel barrier layer 130 and the free layer 140 is further improved.

[0039] Alternatively, the compositions of the first polarization improvement layer 161 and the second polarization improvement layer 162 are different. Specifically, the first polarization improvement layer 161 contains cobalt, and the second polarization improvement layer 162 does not contain cobalt. As an example, the first polarization improvement layer 161 includes CoFeB, and the second polarization improvement layer 162 includes FeB.

[0040] The second polarization enhancement layer 162 is located adjacent to the tunnel barrier layer 130. When the second polarization enhancement layer 162 adjacent to the tunnel barrier layer 130 in this way does not contain cobalt, the performance of the magnetic tunnel junction element can be improved. In the heat treatment process, cobalt diffuses to both sides in the directions of the fixed layer 120 and the free layer 140. Therefore, cobalt diffuses in the direction of the tunnel barrier layer 130, which may affect the performance of the magnetic tunnel junction element. However, when the second polarization enhancement layer 162 does not contain cobalt, the diffusion of cobalt in the direction of the tunnel barrier layer 130 can be reduced.

[0041] In the magnetic tunnel junction element according to this embodiment, with the antiferromagnetic coupling layer 120b interposed therebetween, the first ferromagnetic layer 120a constitutes the lower fixed layer, and the second ferromagnetic layer 120c, the buffer layer 151, the auxiliary layer 152, and the polarization enhancement layer 160 constitute the upper fixed layer. The first ferromagnetic layer 120a of the lower fixed layer contains CoPt. Also, for the upper fixed layer, Co is used as the second ferromagnetic layer 120c and CoFeB is used as the polarization enhancement layer 160. Such a combination of Co / CoFeB is preferable because it has a high tunneling magnetoresistance (TMR) value. However, since Co has an HCP structure and CoFeB has a BCC structure, when CoFeB is directly formed on Co, a crystalline collision occurs. Also, there is a problem that diffusion occurs at the boundary between Co and CoFeB in the high-temperature heat treatment process for manufacturing the magnetic tunnel junction element, and the tunneling magnetoresistance characteristics decrease. That is, the crystallinity of Co and CoFeB changes due to diffusion, which may lead to a decrease in the exchange field (Hex).

[0042] Therefore, in the magnetic tunnel junction element according to this embodiment, an amorphous buffer layer 151 containing CoFeBX (X = W, Mo, Re, or Ta) is positioned between the second ferromagnetic layer 120c containing Co and the polarization enhancement layer 160 containing CoFeB so as to maintain the crystallinity specific to each substance even in high-temperature heat treatment.

[0043] Since such a buffer layer 151 is amorphous, it can mitigate the crystallinity collision between the HCP structure of Co and the BCC structure of CoFeB. That is, when the BCC structure is directly formed on the HCP structure, due to the difference in crystal structures, crystallinity collision may occur at the interface. However, when an amorphous buffer layer is positioned between HCP and BCC as in this embodiment, such crystallinity collision can be prevented.

[0044] Also, in the case of this embodiment, an auxiliary layer 152 is positioned on the buffer layer 151. The auxiliary layer 152 contains W, Mo, or Ta. Such an auxiliary layer 152 has a BCC structure and is applied as a seed layer for the growth of CoFeB having a BCC structure thereafter. Therefore, the crystallinity of CoFeB formed on the auxiliary layer 152 can be enhanced. Also, since the auxiliary layer 152 contains a substance having high-temperature heat resistance, diffusion of elements between the second ferromagnetic layer 120c and the polarization improvement layer 160 can be prevented.

[0045] Also, in the magnetic tunnel junction element according to this embodiment, the buffer layer 151 and the auxiliary layer 152 are positioned between Co and CoFeB. Therefore, the overall thickness of the junction between Co and CoFeB will increase, and the Ms value can be decreased due to the increase in thickness. Thereby, the exchange coupling strength can be increased.

[0046] Here, the thickness of the buffer layer 151 is greater than the thickness of the auxiliary layer 152. The thickness of the buffer layer 151 is 1 Å to 4 Å, and the thickness of the auxiliary layer 152 is 0.5 Å to 2 Å. If the thickness of the buffer layer 151 is less than 1 Å, a sufficient crystal misfit relaxation effect may not be obtained. Also, if the thickness of the buffer layer 151 exceeds 4 Å or the thickness of the auxiliary layer 152 is greater than 2 Å, decoupling may occur between Co and CoFeB, which is not preferable. That is, it is preferable that the total thickness of the buffer layer 151 and the auxiliary layer 152 located between the layer containing Co and the layer containing CoFeB does not exceed 5 Å. If the total thickness of the buffer layer 151 and the auxiliary layer 152 exceeds 5 Å, decoupling between Co and CoFeB may occur.

[0047] Hereinafter, through specific experimental forms, the effects of the magnetic tunnel junction element according to the present embodiment will be described.

[0048] FIG. 2 is a diagram showing the measurement of the magnetic history curve while changing the materials of the buffer layer 151 and the auxiliary layer 152 of the magnetic tunnel junction element according to an embodiment.

[0049] Also, the resistance per unit area (RA, Ωμm 2 ) and the tunneling magnetoresistance (TMR) of the materials of the buffer layer 151 and the auxiliary layer 152 experimented in FIG. 2 are shown in Table 2 below. In Experimental Example 1 and Experimental Example 2, the order of the auxiliary layer / buffer layer was changed for the same material, and the improvement ratio of Experimental Example 2 when the efficiency of Experimental Example 1 was set to 100 was shown. In the cases of Experimental Example 3 and Experimental Example 4 as well, the order of the auxiliary layer / buffer layer was changed for the same material, and the improvement ratio of Experimental Example 4 when the efficiency of Experimental Example 3 was set to 100 was shown. In the cases of Experimental Example 5 and Experimental Example 6 as well, the order of the auxiliary layer / buffer layer was changed for the same material, and the improvement ratio of Experimental Example 6 when the efficiency of Experimental Example 5 was set to 100 was shown.

[0050] In Table 2 below, Experimental Examples 2, 4, and 6 are included in the embodiments of the present invention.

[0051]

Table 2

[0052] First, referring to FIG. 2, in the case of the combination of Experimental Example 1 (auxiliary layer CFBMo / buffer layer W), an inflection point appeared near about 18 kOe from the magnetic history curve. The portion where such an inflection point appears corresponds to the exchange coupling strength (exchange field: Hex) value of the magnetic tunnel junction element. However, in the case of Experimental Examples 2, 4, and 6 included in the embodiment of the present invention, since no inflection point of the magnetic tunnel junction element appears in FIG. 2, it was confirmed that the exchange coupling strength (Hex) value is 18 kOe or more.

[0053] Also, referring to Table 2 above, it was confirmed that Experimental Example 2 included in the embodiment of the present invention has a higher tunneling magnetoresistance (TMR) value than Experimental Example 1, and Experimental Example 4 has a higher tunneling magnetoresistance (TMR) value than Experimental Example 3.

[0054] That is, it was confirmed that the magnetic tunnel junction element including the same buffer layer and auxiliary layer as in the present embodiment has a high exchange coupling strength (Hex) and a high tunneling magnetoresistance (TMR). As described above, this is because the crystalline collision between cobalt and CoFeB is alleviated by the buffer layer, the auxiliary layer prevents the diffusion of cobalt and boron, and then the CoFeB in the BCC structure functions as a seed layer for growth.

[0055] In Table 2 and FIG. 2 above, since it was confirmed that the combination of the buffer layer (CFBMo) and the auxiliary layer (W) of Experimental Example 2 was the most excellent in effect, for such a combination of the buffer layer (CFBMo) and the auxiliary layer (W), while changing the material of the polarization improvement layer 160, the resistance per unit area (RA, Ωμm 2 ) and the tunneling magnetoresistance (TMR) were measured and shown in Table 3.

[0056]

Table 3

[0057] In Table 3 above, the numbers listed horizontally for B represent the boron content. That is, CoFeB30 means it contains 30 mol% of Boron, and FeB20 means it contains 20 mol% of Boron. In Experimental Example 7, the polarization improvement layer was experimented with as a single layer. In Experimental Example 8, the boron content of the second polarization improvement layer was lower than that of the first polarization improvement layer, and the experiment was conducted such that the second polarization improvement layer did not contain cobalt. In Experimental Example 9, the boron concentrations of the first polarization improvement layer and the second polarization improvement layer were the same, and the experiment was conducted such that the first polarization improvement layer did not contain cobalt. In Experimental Example 10, the experiment was conducted such that the first polarization improvement layer did not contain cobalt and the second polarization improvement layer did not contain boron.

[0058] Referring to Table 3 above, it was confirmed that Experimental Example 8 corresponding to this embodiment has the highest tunneling magnetoresistance (TMR) value.

[0059] That is, when the first polarization improvement layer 161 contains CoFeB and the second polarization improvement layer 162 contains FeB and does not contain cobalt, the diffusion of cobalt in the direction of the tunnel barrier layer 130 can be reduced, and the tunneling magnetoresistance (TMR) can be improved.

[0060] Such a magnetic tunnel junction element according to this embodiment has a buffer layer 151 and an auxiliary layer 152 positioned between the second ferromagnetic layer 120c and the polarization improvement layer 160, for example, between Co and CoFeB in the stacked structure of the magnetic tunnel junction element. The buffer layer 151 relaxes the crystalline collision between the HCP structure of cobalt and the BCC structure of CoFeB, and the auxiliary layer 152 having a BCC structure acts as a seed layer for the growth of CoFeB, so that the crystallinity of the CoFeB layer can be strengthened. In addition, the auxiliary layer 152 can prevent the diffusion of cobalt and boron during a high-temperature process of 400 °C or higher. In addition, since the polarization improvement layer 160 has a multilayer structure and the boron concentration in the upper layer is lower than that in the lower layer, the diffusion of boron into the tunnel barrier layer can be reduced. According to the embodiment, when the polarization improvement layer 160 has a multilayer structure, the upper layer does not contain cobalt. In this case, the diffusion of cobalt in the direction of the tunnel barrier layer 130 can be reduced, and the tunneling magnetoresistance (TMR) can be improved.

[0061] Hereinafter, other embodiments will be described. For the magnetic tunnel junction element according to this embodiment, after forming the auxiliary layer 152, heat treatment of the auxiliary layer 152 is performed. That is, after forming the auxiliary layer 152, the auxiliary layer 152 is heat-treated to strengthen the crystallinity of the auxiliary layer 152. When the crystallinity of the auxiliary layer 152 is strengthened by the heat treatment of the auxiliary layer 152 in this way, the crystallinity of the polarization improvement layer 160 formed thereafter can also be improved. This is because when the crystallinity of the auxiliary layer 152 as the seed layer is improved, the crystallinity of the polarization improvement layer 160 formed thereon is also improved.

[0062] In the previous FIG. 1, a configuration including all of the buffer layer 151, the auxiliary layer 152, the first polarization improvement layer 161, and the second polarization improvement layer 162 was shown, but in other embodiments, only a part of the above configuration is included.

[0063] FIG. 3 is a diagram showing the same cross section as FIG. 1 for other embodiments.

[0064] Referring to FIG. 3, the display device according to this embodiment is the same as the embodiment of FIG. 1, except that the polarization improvement layer 160 is a single layer. That is, in the embodiment of FIG. 3, the polarization improvement layer 160 is composed of a single layer. As an example, the polarization improvement layer 160 is a single layer containing CoFeB. For the descriptions of other layers, since they are the same as those in FIG. 1, they are omitted.

[0065] Also in this case, the buffer layer 151 relaxes the crystalline collision between the HCP structure of Co and the BCC structure of CoFeB, and the auxiliary layer 152 having the BCC structure acts as a seed layer for the growth of CoFeB, thus strengthening the crystallinity of CoFeB. Since the diffusion of cobalt and boron is prevented by the auxiliary layer 152, the tunneling magnetoresistance (TMR) and the exchange coupling strength (Hex) are improved.

[0066] FIG. 4 is a diagram showing the same cross-section as FIG. 1 for still another embodiment.

[0067] Referring to FIG. 4, the display device according to this embodiment is the same as the embodiment of FIG. 1, except that the auxiliary layer 152 is not included. Specific descriptions of the same components are omitted. That is, even when the auxiliary layer 152 is not included as in the embodiment of FIG. 4, the buffer layer 151 relaxes the crystalline collision between the HCP structure of cobalt and the BCC structure of CoFeB, so that the tunneling magnetoresistance (TMR) and the exchange coupling strength (Hex) are improved.

[0068] Hereinafter, the memory cell and the memory device including the magnetic tunnel junction element according to this embodiment will be described with reference to the drawings. However, such descriptions are merely examples, and the present invention is not limited thereto.

[0069] FIG. 5 is a diagram schematically showing one memory cell including a magnetic tunnel junction element according to an embodiment.

[0070] Referring to FIG. 5, the memory cell MC includes the magnetic tunnel junction element 100 described above and the switching element TR connected thereto. The switching element TR is a transistor such as a thin film transistor, for example, a field effect transistor. The memory cell MC is connected between the bit line BL and the word line WL. The bit line BL and the word line WL are arranged so as to cross each other, and the memory cell MC is arranged at the intersection thereof. The bit line BL is electrically connected to the free layer 140 of the magnetic tunnel junction element 100, and the word line WL is connected to the gate of the switching element TR. Further, the first source / drain electrode of the switching element TR is electrically connected to the electrode 101 of the magnetic tunnel junction element 100, and the second source / drain electrode is electrically connected to the selection line SL. The selection line SL extends, for example, in parallel with the word line WL. In such a structure, a write current, a read current, an erase current, etc. are applied to the memory cell M) via the word line WL and the bit line BL. In FIG. 5, the memory cell MC is illustrated as including the magnetic tunnel junction element 100 shown in FIG. 1, but the memory cell MC can also include a magnetic tunnel junction element according to other embodiments.

[0071] FIG. 6 is a circuit diagram schematically showing the configuration of a memory device including a plurality of memory cells shown in FIG. 5.

[0072] Referring to FIG. 6, the memory device 600 includes a plurality of bit lines B, a plurality of word lines WL, a plurality of selection lines SL, a plurality of memory cells MC respectively arranged at the intersections of the plurality of bit lines BL and the plurality of word lines WL, a bit line driver 601 that applies a current to the plurality of bit lines BL, a word line driver 602 that applies a current to the plurality of word lines WL, and a selection line driver 603 that applies a current to the plurality of selection lines SL. Each memory cell MC has the configuration shown in FIG. 6.

[0073] The memory device 600 shown in FIG. 6 is, for example, a 1T1MTJ element including one transistor and one magnetic tunnel junction element.

[0074] The memory device 600 shown in FIG. 6 is an MRAM (magnetic random access memory) and is used in an electronic device that uses a non-volatile memory. For example, the memory device 600 shown in FIG. 6 is a STT-MRAM in which the magnetization direction of the free layer changes due to a spin current directly applied to the free layer of the magnetic tunnel junction element. Since STT-MRAM does not require a separate conducting wire for generating an external magnetic field, it is advantageous for high integration and has a simple operation method. Further, the memory device 600 shown in FIG. 6 is also applicable to SOT-MRAM.

[0075] As described above, the magnetic tunnel junction element and the memory device including the same according to the present embodiment include a buffer layer 151 and a auxiliary layer 152, prevent a crystalline collision between the upper layer and the lower layer by the buffer layer 151, prevent the diffusion of elements in the magnetic tunnel junction element through the auxiliary layer 152, and can strengthen the crystallinity of the upper layer. Further, the polarization improvement layer 160 is formed in multiple layers, the boron content of the upper layer is smaller than that of the lower layer, and the upper layer does not contain cobalt, so that diffusion can be prevented. The magnetic tunnel junction element according to such an embodiment of the present invention can have a high tunneling magnetoresistance (TMR) and an exchange coupling strength (Hex).

[0076] As described above, the embodiments of the present invention have been described in detail with reference to the drawings. However, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the technical idea of the present invention.

Explanation of Reference Numerals

[0077] 100 Magnetic tunnel junction element 101 Electrode 110 Seed layer 120 Fixed layer (pinned layer) 120a First ferromagnetic layer 120b Antiferromagnetic coupling layer (SAF coupling layer) 120c Second ferromagnetic layer 130 Tunnel barrier layer 140 Free layer 151 Buffer layer 152 Auxiliary layer 160 Polarization improvement layer 161 First polarization improvement layer 162 Second polarization improvement layer 600 Memory device 601 Bit line driver 602 Word line driver 603 Selection line driver BL Bit line MC Memory cell SL Selection line TR Switching element WL Word line

Claims

1. A fixed layer and a free layer facing each other; a buffer layer located on the immobilizing layer; an auxiliary layer located on the buffer layer; a polarization enhancing layer located between the auxiliary layer and the free layer; a tunnel barrier layer located between the polarization enhancing layer and the free layer; the buffer layer is amorphous and comprises CoFeBX; X is W, Mo, Re, or Ta; The auxiliary layer comprises W, Mo, or Ta.

2. The magnetic tunnel junction element according to claim 1 , wherein the auxiliary layer is thinner than the buffer layer.

3. The magnetic tunnel junction device of claim 1, wherein the buffer layer has a thickness of 1 Å to 4 Å.

4. 2. The magnetic tunnel junction device of claim 1, wherein the auxiliary layer has a thickness of 0.5 Å to 2 Å.

5. The magnetic tunnel junction element of claim 1 , wherein the sum of the thickness of the buffer layer and the thickness of the auxiliary layer is less than 5 Å.

6. the polarization enhancing layer includes a first polarization enhancing layer and a second polarization enhancing layer, 2. The magnetic tunnel junction element of claim 1, wherein the second polarization enhancing layer is located between the first polarization enhancing layer and the free layer.

7. 7. The magnetic tunnel junction element of claim 6, wherein the concentration of boron contained in the second polarization enhancing layer is lower than the concentration of boron contained in the first polarization enhancing layer.

8. the first polarization enhancing layer comprises CoFeB; The magnetic tunnel junction element of claim 6 , wherein the second polarization enhancing layer does not contain Co.

9. the first polarization enhancing layer comprises CoFeB; The magnetic tunnel junction device of claim 6 , wherein the second polarization enhancing layer comprises FeB.

10. The fixing layer has a multi-layer structure, The magnetic tunnel junction element according to claim 1 , wherein the pinned layer in contact with the buffer layer contains Co.

11. 2. The magnetic tunnel junction element of claim 1, wherein the auxiliary layer and the polarization enhancing layer have a body-centered cubic (BCC) structure.

12. 2. The magnetic tunnel junction element according to claim 1, wherein the fixed layer and the polarization enhancing layer have different crystal structures.

13. A fixed layer and a free layer facing each other; a buffer layer located on one surface of the immobilizing layer; a polarization enhancing layer located between the buffer layer and the free layer; a tunnel barrier layer located between the polarization enhancing layer and the free layer; the buffer layer is amorphous and comprises CoFeBX; X is W, Mo, Re, or Ta; the polarization enhancing layer includes a first polarization enhancing layer and a second polarization enhancing layer, the second polarization enhancing layer is located between the first polarization enhancing layer and the free layer; A magnetic tunnel junction element, wherein the concentration of boron contained in said second polarization enhancing layer is lower than the concentration of boron contained in said first polarization enhancing layer.

14. the first polarization enhancing layer comprises CoFeB; The magnetic tunnel junction element of claim 13 , wherein the second polarization enhancing layer does not contain Co.

15. further comprising an auxiliary layer located between the buffer layer and the first polarization enhancing layer; The magnetic tunnel junction element of claim 14 , wherein the auxiliary layer comprises W, Mo, or Ta.

16. the first polarization enhancing layer comprises CoFeB; The magnetic tunnel junction element of claim 13 , wherein the second polarization enhancing layer comprises FeB.

17. The fixing layer has a multi-layer structure, The magnetic tunnel junction element according to claim 13 , wherein the pinned layer in contact with the buffer layer contains Co.

18. A plurality of memory cells each including a magnetic tunnel junction element and a switching element connected to the magnetic tunnel junction element; The magnetic tunnel junction element includes: A fixed layer and a free layer facing each other; a buffer layer located on the immobilizing layer; an auxiliary layer located on the buffer layer; a polarization enhancing layer located between the auxiliary layer and the free layer; a tunnel barrier layer located between the polarization enhancing layer and the free layer; the buffer layer is amorphous and comprises CoFeBX; X is W, Mo, Re, or Ta; The auxiliary layer comprises W, Mo, or Ta.

19. the polarization enhancing layer includes a first polarization enhancing layer and a second polarization enhancing layer, the second polarization enhancing layer is located between the first polarization enhancing layer and the free layer; 20. The memory device of claim 18, wherein the concentration of boron contained in the second polarization enhancing layer is lower than the concentration of boron contained in the first polarization enhancing layer.

20. the first polarization enhancing layer comprises CoFeB; 20. The memory device of claim 19, wherein the second polarization enhancing layer does not contain Co.

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