KR101209328B1 - PERPENDICULAR MAGNETIC ANISOTROPY OF CoFeB/Pd MULTILAYER AND MAGNETIC RANDOM ACCESS MEMORY FABRICATED USING THE SAME - Google Patents

Abstract

The present invention relates to a CoFeB / Pd multilayer thin film having perpendicular magnetic anisotropy, and to a magnetic random access memory manufactured using the same, wherein the Pd layer formed on the substrate and the [CoFeB / Pd] N (N) formed on the Pd layer. A multi-layered thin film comprising a natural water of 3 or more), wherein the substrate is any one of a silicon substrate, a glass substrate, a sapphire substrate and a magnesium oxide substrate, and an Al or Ta seed layer formed between the substrate and the Pd layer. It further relates to the invention to exhibit excellent perpendicular magnetic anisotropy having a high coercive force (Hc) of 40 ~ 600 Oe.

Description

Cobalt-Iron-Boron / Palladium Multilayer Thin Film with Vertical Magnetic Anisotropy and Magnetic Random Access Memory Fabricated Using the Same

The present invention relates to a CoFeB / Pd multilayer thin film having perpendicular magnetic anisotropy, and to a magnetic random access memory manufactured using the same. Specifically, the vertical magnetic anisotropy of a multilayer thin film including multilayer CoFeB / Pd films is improved and used. A technique for manufacturing a magnetic random access memory is provided.

The operation of magnetic random access memory (MRAM) is based on magnetization inversion, and recently, current induced magnetization switching (CIMS) has proved to be suitable for high density MRAM implementation.

Spin-Transfer Torque (STT) occurs when a current is applied to the magnetic thin film, because CIMS can easily use such spin torque to reverse magnetization.

In addition, magnetization inversion using spin torque has several advantages, such as high integration, wide write window, and low power consumption, compared to magnetization inversion using a conventional magnetic field.

Until now, the main research has been conducted through In-plane Anisotropy Magnetic Tunnel Junctions (MTJs), and recently, the thermal stability in nanometer magnetic cells is relatively high. A low critical current density of several MA / cm 2 was obtained.

These results are usually obtained from MTJs structures based on MgO films using free and fixed layers of three-layer bonding structures, but lower critical current densities (less than 1MA / cm 2) are required for high-density MRAM for commercialization. Situation.

In this sense, the perpendicular magnetic tunnel junction (pMTJs) is an increase due to the anti-magnetic field (2πMs; where Ms is the saturation magnetization, which was inherently included in the critical current density of the conventional planar magnetization magnetic tunnel junction). It is attracting attention because it can be removed.

On the other hand, since the magnetization reversal (CIMS) using the current in the vertical magnetization magnetic tunnel junction (pMTJs) structure has been reported experimentally, a lot of researches on the implementation of the perpendicular magnetic anisotropy and the vertical magnetization magnetic tunnel junction using the same . Currently, the implementation of vertical magnetization magnetic tunnel junctions (pMTJs) requires not only an appropriate level of perpendicular magnetic anisotropy but also high tunneling magnetoresistance (TMR).

In addition, CoFeSiB / Pt multilayer thin films have been reported as thin films exhibiting perpendicular magnetic anisotropy. CoFeSiB / Pt multilayer thin films have high vertical magnetic anisotropy but try to minimize coercive force (Hc). Therefore, CoFeSiB alloy with small saturation magnetic flux density was used to achieve minimization of coercive force (Hc). At this time, CoFeSiB alloy has a problem that can not be applied to the MgO magnetic tunnel junction which is essential for manufacturing in high density magnetic random access memory having a high tunnel magnetoresistance (TMR). This is because CoFeSiB alloy was not able to form bcc Co or CoFe (001) due to the template effect of MgO during heat treatment. Therefore, CoFeSiB / Pt multilayer thin film can be applied to magnetization reversal by magnetic field and MRAM using the same, and is not suitable for application fields for manufacturing high density spin torque (STT) MRAM using CIMS technology by applying current. There was no problem.

Therefore, considering that the high tunnel magnetoresistance is obtained in the magnetic tunnel junction having the planar magnetization type CoFeB / MgO / CoFeB type, it is expected that the vertical magnetization type MTJs also exhibit suitable characteristics using CoFeB.

According to a recent report, a critical current density of 4.7 MA / cm 2 was observed at a current application time of 100 ns in a vertical magnetized magnetic tunnel junction with a TbFeCo / CoFeB / MgO / CoFeB / TbCoFe structure. However, the tunnel magnetoresistance was at a relatively low 15% level, which is likely due to the direct contact of TbCoFe and CoFeB, which did not result in the MgO template effect, which is known to be essential for high tunnel magnetoresistance.

Therefore, in order to realize vertical magnetization magnetic tunnel junction (pMTJs) and high magnetic tunnel resistance (TMR), it is important to isolate the CoFeB magnetic layer using a non-magnetic material, but to maintain perpendicular magnetic anisotropy. It is not enough.

In order to realize vertical magnetization type magnetic tunnel junction (pMTJs), the CoFeB magnetic layer is isolated by using a non-magnetic material, but by controlling the substrate and seed layer for forming the CoFeB / Pd multilayer, it is possible to maintain improved perpendicular magnetic anisotropy. An object of the present invention is to provide a cobalt-iron-boron / palladium multilayer thin film and a magnetic random access memory manufactured using the same.

In the perpendicular magnetic anisotropic multilayer thin film according to the present invention, an Al or Ta seed layer formed on a substrate, a Pd layer formed on the surface of the seed layer, and [CoFeB / Pd] formed on the Pd layer are repeated N times. It is characterized by including a laminated (N is a natural number of 3 or more) multilayer structure.

Here, the substrate is characterized in that the silicon substrate, glass substrate, sapphire substrate and magnesium oxide substrate, characterized in that the thickness of the seed layer is characterized in that 5 ~ 20nm, the thickness of the Pd layer is 5 ~ 20nm Characterized in that, the thickness of the CoFeB in the CoFeB / Pd: the thickness of the Pd is characterized in that the ratio of 1: 2.5, the N is characterized in that 3 to 20, the CoFeB is Co _x Fe _y B _z (atomic%, x + y + z = 100), but in one embodiment x = 45-60, y = 16-31, z = 24, and in another embodiment x = 43-58, It is characterized in that y = 15 ~ 30, z = 27, and the coercive force (Hc) of the multilayer thin film is characterized in that 40 ~ 600 Oe.

In addition, the magnetic random access memory according to the present invention is characterized by including the above-described vertical magnetic anisotropic multilayer thin film.

The critical current density of the vertical magnetization type magnetic tunnel junction (pMTJs) including the perpendicular magnetic anisotropic multilayer thin film according to the present invention is low threshold current density due to the characteristic that 2πMs corresponding to the half magnetic field of the planar magnetization type magnetic tunnel junction is not included. Magnetization reversal is possible even with a value. Accordingly, the present invention provides an effect of further improving the characteristics of the perpendicular magnetization magnetic tunnel junction by adjusting the substrate and the seed layer.

In addition, in the magnetic random access memory based on magnetization inversion, the magnetization inversion (CIMS) using the spin torque (STT) generated by the application of current is performed, but it is possible to reduce the current density required in the magnetization inversion. It provides the effect that a magnetic random access memory can be manufactured.

1 is a cross-sectional view showing an embodiment for testing the electromagnetic properties of each layer number of CoFeB / Pd multilayer thin film according to the present invention.
Figure 2 mH (magnetic moment-magnetic field) hysteresis curve for each layer number of CoFeB / Pd multilayer thin film according to the present invention.
Figure 3 is a graph showing the electromagnetic properties of each layer number of CoFeB / Pd multilayer thin film according to the present invention.
4 is a planar photograph showing an MFM image of a CoFeB / Pd multilayer thin film according to the present invention.
Figure 5 is a cross-sectional view showing an embodiment for testing the influence of the substrate and seed layer on the perpendicular magnetic anisotropy of the CoFeB / Pd multilayer thin film according to the present invention.
Figure 6 is a graph of the coercive force (Hc) function according to the type and the thickness (t _seed ) of the seed layer according to the present invention.
7 is a sectional view showing a magnetic random access memory according to an embodiment of the present invention.

Hereinafter, a cobalt-iron-boron / palladium multilayer thin film having perpendicular magnetic anisotropy and a magnetic random access memory manufactured by using the same will be described in detail based on the technique of the present invention described above.

Advantages and features of the present invention, and methods of accomplishing the same will be apparent with reference to the drawings and embodiments described below in detail. However, the present invention is not limited to the embodiments disclosed below, but may be implemented in various forms, and only the embodiments are intended to complete the disclosure of the present invention and to provide general knowledge in the technical field to which the present invention belongs. It is provided to fully convey the scope of the invention to those skilled in the art, and the present invention is defined only by the scope of the claims.

Vertically anisotropic multilayer thin film according to the present invention is basically a substrate 10 / Pd layer 20 / [CoFeB (30) / Pd (40)] × N (N = 3 ~ 20) as shown in FIG. It has a multilayer thin film structure of.

Here, as another embodiment of the vertical magnetic anisotropic multilayer thin film according to the present invention, as shown in FIG. 5, the vertical magnetic field of [CoFeB 130 / Pd 140] between the substrate 100 and the Pd layer 120. It may have a multilayer thin film structure further includes a seed layer 110 for anisotropic reinforcement. At this time, the thickness of the seed layer 110 is preferably 5 ~ 20nm. Here, the [CoFeB / Pd] double layer structure refers to a structure in which Pd is formed on CoFeB, and may be expressed as CoFeB / Pd.

In addition, when the thickness of the seed layer 110 is less than 5 nm, the perpendicular magnetic anisotropy may not appear. When the thickness of the seed layer 110 exceeds 20 nm, there may be a problem in that efficiency is not increased compared to the thickness.

Hereinafter, as an embodiment for determining the influence of the substrate and the seed layer on the perpendicular magnetic anisotropy of the present invention described above, the influence of the CoFeB / Pd multilayer thin film (N) will be described first in detail.

1 is a cross-sectional view showing an embodiment for testing the electromagnetic properties of each layer number of CoFeB / Pd multilayer thin film according to the present invention.

Referring to FIG. 1, a 5 nm-thick Pd layer is formed on a 500 μm-thick silicon substrate (Si sub, 10), and a plurality of [CoFeB (0.3 nm) / Pd (0.8 nm)] layers are formed on the Pd layer. (N) It laminated | stacked. At this time, N was applied to the number of repetitions of the CoFeB / Pd bilayer structure 3 times, 9 times, 15 times, 20 times the experiment was carried out.

Here, the substrate was used a thermally oxidized Si (001) substrate, the deposition was carried out through a sputter having a vacuum of 1 ~ 5 × 10 ^-8 torr. The deposition holder is equipped with a Nd-Fe-B permanent magnet, which has a magnetic field of about 100 Oe applied to the thin film plane during deposition.

At this time, CoFeB was deposited through an alloy target of Co ₅₆ Fe ₂₄ B ₂₀ (atomic%), and Co ₅₁ Fe ₂₂ B ₂₇ (atomic%) in the analysis of CoFeB composition through ICP AES (Inductively Coupled Plasma Atomic Emission Spectroscopy) The composition of was confirmed. As another example, when depositing CoFeB through an alloy target of Co ₄₀ Fe ₄₀ B ₂₀ (atomic%), Co ₃₈ Fe ₃₈ B ₂₄ (atomic%) was analyzed by CoFeB composition analysis by Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP AES). ), And the composition of Co ₁₉ Fe ₅₇ B ₂₄ (atomic%) was confirmed when using an alloy target of Co ₂₀ Fe ₆₀ B ₂₀ (atomic%). From the results of the composition analysis, Co / Fe atomic ratio is the same in the target and the thin film, it can be seen that the B content is higher than the target thin film.

In addition, CoFeB according to the present invention can be configured in the composition range of Co _x Fe _y B _z (atomic%, x + y + z = 100), as an embodiment x = 45 ~ 60, y = 16 ~ 31, z = 24, and it is preferable that x = 43-58, y = 15-30, z = 27 as another embodiment. If it is out of the x, y, z range, the perpendicular magnetic anisotropy may be degraded or a crystal structure necessary for high tunnel magnetoresistance may not be formed.

In order to explain the specific critical significance of the composition range, a single CoFeB thin film having a thickness of 2 nm was formed, and by increasing the Co content, the saturation magnetization was lowered, and thus strong perpendicular magnetic anisotropy was obtained.

In this regard, in the conventional MgO-based magnetic tunnel junction layers (MTJs), many targets having a composition range of Co ₄₀ Fe ₄₀ B ₂₀ have been used. This is because the bcc CoFe phase, which is essential for achieving a high tunnel magnetoresistance ratio (TMR) in this composition range, is advantageously formed during heat treatment. However, the composition range of Co ₄₀ Fe ₄₀ B ₂₀ is high in saturation magnetization compared to the composition range of Co ₅₆ Fe ₂₄ B ₂₀ according to the present invention, which is disadvantageous in forming vertical magnetic anisotropy.

However, the experimental results according to the present invention obtained the best perpendicular magnetic anisotropy when using the Co ₅₆ Fe ₂₄ B ₂₀ alloy target (Hc = 1050 Oe; Mr / Ms = 100%, where Hc is the coercivity, Mr is the residual magnetization, Ms is saturation magnetization, Mr / Ms represents square ratio), Co ₄₅ Fe ₃₁ B ₂₄ , Co ₆₀ Fe ₁₆ B ₂₄ , Co ₄₃ Fe ₃₀ B ₂₇ And perpendicular magnetic anisotropy close to the maximum were obtained in the Co ₅₈ Fe ₁₅ B ₂₇ thin film composition.

On the other hand, when the Co ₂₀ Fe ₆₀ B ₂₀ alloy target having the largest saturation magnetization was used, the most deteriorated perpendicular magnetic anisotropy such as Hc = 0 Oe and Mr / Ms = 0 was obtained, and the intermediate saturation magnetization was obtained. Medium size perpendicular magnetic anisotropy (Hc = 125 Oe; Mr / Ms = 15%) was obtained when using Co ₄₀ Fe ₄₀ B ₂₀ alloy target, and vertical magnetic anisotropy was sustained with low saturation magnetization of x = 62 or more. As a result it was reduced.

Thus, the CoFeB layer according to the present invention is Co _x Fe _y B _z (atomic%, x + y + z = 100) x = 45 ~ 60, y = 16 ~ 31, z = 24, or x = 43 ~ 58 , y = 15-30, z = 27 It can be seen that the reliability of the perpendicular magnetic anisotropy increases in the composition range.

Table 1 and Table 2 summarize the above experimental results. Table 1 summarizes the results for the case of z = 24 and Table 2 summarizes the results for case of z = 27.

[Table 1]

[Table 2]

Table 1 and Table 2 divided the Examples and Comparative Examples on the basis of the square ratio (Mr / Ms) = 100%, it takes the optimum composition ratio based on the coercive force (Hc) value.

In addition, if the surface / interface effect on the perpendicular magnetic anisotropy is ignored according to the above results, it means that the vertical magnetic anisotropy as large as 4πMs can be obtained compared to the prior art because the saturation magnetization is low when using the composition range according to the present invention do. This shows that saturation magnetization contributes to the formation of perpendicular magnetic anisotropy.

Next, the thickness of each layer, in particular the thickness of CoFeB and Pd, has a great influence on the properties of the entire film.Therefore, there are two experimental methods: Surface Profiler and Scanning Electron Microscope (SEM). It was measured accurately through.

Next, the hysteresis curve of M (or m) -H ((magnetic flux density or magnetic moment) -magnetic field) for characterization was measured at room temperature using a Vibrating Sample Magnetometer (VSM). Measured by magnetic force microscopy (MFM), the surface state of the thin film was measured by a non-contacting 3D Optical Profiler, chemical composition analysis was measured by ICP AES. The microstructure of the thin film was measured by X-ray diffractometer (XRD).

2 is a m-H (magnetic moment-magnetic field) hysteresis curve for each layer of CoFeB / Pd multilayer thin films according to the present invention.

FIG. 2 is a measurement in which the magnetic field is applied in the vertical direction of the thin film. As the N value increases, the saturation magnetic moment tends to increase, and the reversible or irreversible magnetization reversal is performed with vertical anisotropy. I could confirm that. More details on this will be described with reference to FIG. 3.

3 is a graph showing the electromagnetic properties of each layer of the CoFeB / Pd multilayer thin film according to the present invention.

FIG. 3 shows the coercive force (Hc) of the CoFeB / Pd multilayer thin film not including the seed layer of FIG. 1, showing a nearly constant value until N = 12, and having the highest value at N = 15. Afterwards, N = 20 showed a significant decrease.

The saturation magnetic field (Hs) (the magnetic field at the time when the m value changes and is saturated while being constant in FIG. 2) and the reverse magnetic field generating field (Hn) (nucleation field); The behavior of magnetization changes from reversible to irreversible) .Saturation magnetic field (Hs) increases from 114 Oe to 1360 Oe as N changes from 3 to 20. There was little change from N value 3 to 9 area.

At this time, the inverse magnetically generated magnetic field (Hn) is expressed as a negative value, which means that the magnetization is reversed when the magnetic field in the opposite direction is taken by the general behavior of the general magnetic material. However, this value is close to 0 Oe when N = 12, and becomes a positive value at larger N. For example, when N = 20, it means that irreversible magnetization reversal starts even though an external magnetic field is applied in the same direction as the magnetization.

In the case of N = 20, the magnetic moment (m) value is rapidly decreased in the inverse magnetic field generating magnetic field (Hn), and in the state where the external magnetic field is zero, the value is almost zero. Such behavior can be explained by the formation of magnetic domains having perpendicular magnetic anisotropy and the movement of magnetic domain walls when they have a large N value. In addition, this behavior can be seen through the MFM image of the multilayer thin film. FIG. 4 shows an MFM image (scanned area of 5 μm × 5 μm) of a sample having N = 20 shown in FIG. 2, which is a typical strip. It shows the form of grammar. The width is about 125 nm, which is in good agreement with the value of 117 nm calculated using Kaplan's model. At this time, the parameters used in the calculation are Ms (effective saturation magnetization considering CoFeB and Pd) = 450 emu / cc, Ku (uniaxial anisotropy constant) = 5.6 × 10 ⁵ erg / cc and A (exchange stiffness) = 10 ^-6 erg / cm.

In addition, referring to FIG. 2, since it was confirmed that the perpendicular magnetic anisotropy was good even at the minimum value of N = 3, the conditions for optimizing the thickness of Pd acting as an underlayer under the condition of N = 3 were investigated. As a result, the dependence of the perpendicular magnetic anisotropy of the Pd thickness (t _Pd) is showed the appearance is increased with increasing Pd thickness (t _Pd), the substantial scope showed the pattern to be saturated at 5 ~ 20nm. If the Pd thickness t _Pd is less than 5 nm, the perpendicular magnetic anisotropy of the CoFeB / Pd multilayer thin film may not appear, and if the thickness exceeds 20 nm, there may be a problem that efficiency is not increased compared to the thickness of the laminate. Therefore, the optimum Pd thickness t _Pd is preferably fixed at 20 nm.

Next, in the structure of the CoFeB / Pd multilayer thin film of FIG. 1 formed so far, the type of substrate was changed, and the effect of the seed layer on the perpendicular magnetic anisotropy was investigated.

5 is a cross-sectional view showing an embodiment for testing the influence of the substrate and the seed layer on the perpendicular magnetic anisotropy of the CoFeB / Pd multilayer thin film according to the present invention.

Referring to FIG. 5, a seed layer 110 having a thickness of 5 to 20 nm (t _seed ) is formed on the substrate 100 having a thickness of about 500 μm.

Herein, the substrate may include a thermally oxidized Si (001) substrate, a glass (Pyrex 7740) substrate, a single crystal sapphire (0001) substrate, and a magnesium oxide (MgO (001)) substrate. Any one selected was used. And seed layer used Al or Ta.

Next, a Pd (120) layer having a thickness of 20 nm was formed, and a multilayer thin film having a [CoFeB (0.3 nm) / Pd (0.8 nm)] structure was formed through a deposition process.

Here, the deposition was carried out through a sputter having a vacuum of 1-5 × 10 ^-8 torr. In this case, the Nd-Fe-B permanent magnet is mounted on the deposition holder, and a magnetic field of about 100 Oe is applied in the thin film plane direction during the deposition process through the permanent magnet.

Next, the thickness of each layer, especially the thicknesses of CoFeB and Pd, have a great influence on the perpendicular magnetic anisotropy of the entire film, so that the deposition rate that determines the film thickness is determined by the surface roughness and the scanning profiler. (Scanning Electron Microscope; SEM) was confirmed through two experimental methods.

The mH hysteresis curve was measured by applying a magnetic field perpendicular to the thin film plane to the laminated structure of FIG. 5 thus formed. Next, the coercive force (Hc) was obtained through the measured mH hysteresis curve.

6 is a graph of the coercive force (Hc) function according to the type of seed layer and its thickness t _seed according to the present invention.

Referring to FIG. 6, the coercive force Hc is shown for four different substrates Si, Glass, Sapphire, and MgO.

Among them, Figure 6 (a) shows the results for the Al seed layer, Figure 6 (b) shows the results for the Ta seed layer.

In the case of a multilayer thin film using an Al seed layer, the coercive force (Hc) value has little dependence on the type of substrate, but is sensitively changed depending on the thickness (t _seed ) of the seed layer. That is, the coercive force (Hc) also increases as the thickness (t _seed ) of the seed layer increases. Although the increase is small in the early and late stages, the thickness of the seed layer in the middle region (t _seed ; 10-15 nm) is increased. In, the coercive force (Hc) change was large with increasing thickness. The coercive force (Hc) in the thickness (t _seed ) region of the irradiated seed layer was nearly doubled from 301 Oe (5nm) to 586 Oe (20nm).

However, when the Ta seed layer was used as shown in FIG. 6 (b), other forms of behavior were observed. In this case, the coercive force (Hc) showed a large difference depending on the type of substrate (except for Si and glass). When Si and glass substrates were used, the results were almost the same. The coercivity (Hc) increased from 322 Oe up to 469 Oe as the seed layer thickness (t _seed ) increased from 5 nm to 15 nm. Next, when the thickness (t _seed ) of the seed layer was increased to 20 nm, similar values of 465 Oe to 472 Oe levels were shown.

When the Ta seed layer was used as shown in FIG. 6 (b) and the sapphire substrate was used, the dependency on the seed layer thickness (t _seed ) was small, and the largest value was observed at 15 nm.

However, when the Ta seed layer is used as shown in FIG. 6 (b) and the MgO substrate is applied, the dependence of the coercive force (Hc) on the thickness (t _seed ) of the seed layer is significantly different. In this case, two characteristic behaviors are observed. First, the thickness dependence of the coercive force (Hc) decreases as the thickness (t _seed ) of the seed layer increases, as opposed to when the Al seed layer is used. Second, the change in coercive force (Hc) with respect to the thickness of the seed layer (t _seed ) was larger than in other cases. The coercive force change was remarkable in the thickness (t _seed ) range of 5 nm to 15 nm. .

In addition, the coercive force (Hc) of 576 Oe observed in the case of the Ta seed layer (t _seed = 5 nm) is a very large value. This is comparable to the coercive force (Hc) value of the highest 586 Oe observed when the Al seed layer was used.

As described above, in the case of the multilayer thin film according to the present invention, even though a thick Pd layer (20 nm) is deposited on the seed layer, the perpendicular magnetic anisotropy is greatly changed according to the change of the substrate and the seed layer. This implies that perpendicular magnetic anisotropy is not associated with the nature of the interface of Pd / CoFeB. In addition, this shows that the characteristics of the Co / Pd interface in the Co / Pd multilayer thin film is consistent with the results of conventional experiments, which are not directly related to the crystal direction of Pd.

Surface roughness was observed to explain the results obtained in the present invention. This is because the roughness of the seed layer and the substrate on which the multilayer thin film is deposited may affect the surface anisotropy generated at the Pd / CoFeB interface. In order to confirm this, the surface morphology of the multilayer thin film was measured in a wide range of 450 μm × 600 μm using a non-contacting 3D optical profiler.

In the result, there was no significant difference between the substrate and the seed layer. As an example of the surface roughness, when the Si substrate is used, the value of the range of 0.71 to 0.62 nm was measured as the thickness of the Ta seed layer varied from 0 to 10 nm.

In addition, since it is known that the perpendicular magnetic anisotropy value of the conventional Co / Pd multilayer thin film is proportional to the degree of texture of the underlying layer Pd (111), in the present invention, the multilayer thin film is formed by using an X-ray diffractometer (XRD). The Pd (111) texture of was measured.

In the case of Si substrate, the thickness of the Ta seed layer varied from 0 to 10 nm, resulting in a significant change depending on the thickness of the seed layer for the Pd (111) texture. 111) Almost no texture was developed, but Pd (111) texture was remarkable when the Ta seed layer was deposited over 3 nm.

As the thickness of the Ta seed layer was increased to 5 nm and 10 nm, the strength of the Pd (111) texture was observed to decrease. This result is not consistent with the tendency to increase the perpendicular magnetic anisotropy for the seed layer thickness in this range, it is determined that the Pd (111) texture did not affect the vertical magnetic anisotropy.

Next, an attempt was made to find the possibility of magnetoelastic interaction except surface roughness and Pd (111) texture. CoFeB is an amorphous material, which will not show the stress effect due to the difference in lattice constant, but the thermal stress due to the difference in the coefficient of thermal expansion during deposition may occur in the thin film, which may be combined with the magnetostriction of CoFeB. . In general, the magnetostriction of CoFeB is known to be about +10 ppm.

Physical parameters such as coefficient of thermal expansion (α), Young's modulus (E), and Poisson's ratio (ν) required to calculate thermal stress are summarized as shown in Table 3 below. The specific method for calculating the thermal stress is as follows.

[Table 3]

First, thermal stress was calculated using a commercial program package (the multiphysics finite element method COMSOL). At this time, since the CoFeB / Pd multilayer thin film is much thinner than other layers, this multilayer thin film is regarded as one effective layer, so that the mesh formation is efficiently performed to increase the accuracy of the calculation.

Here, the calculation of the thermal stress assumes a situation where the multilayer thin film is cooled to room temperature (300K) after the deposition at 400K. In this case, in a simple two-layer film, a tensile stress is formed in a film having a relatively high coefficient of thermal expansion, and a compressive stress can be easily formed in a film having a relatively low coefficient of thermal expansion.

In the present invention, the thermal stress generated in CoFeB is mainly influenced by the coefficient of thermal expansion of the substrate, because the thickness of the substrate is relatively much thicker. For example, materials with a smaller coefficient of thermal expansion than other layers, such as silicon (Si) and glass, form compressive stress on the substrate and tensile stress on CoFeB / Pd multilayers. It is expected to be.

As a result, the results calculated in the present invention were observed to be the result of the tensile stress (Co) is formed in the CoFeB / Pd multilayer thin film for all samples, the size of the seed layer (Ta or Al) and the thickness (t _Seeds do not depend heavily on _seed ).

On the other hand, considering that the thermal expansion coefficient of the MgO substrate is relatively large compared to other layers (except Al), the tensile stress formed in the CoFeB / Pd multilayer thin film using the MgO substrate has an exceptional result. This can be understood as a phenomenon in which the influence of the type of the substrate is greatly reduced in that the effect of the thermal stress on the entire substrate in the state where the thermal stress is concentrated at the interface is small. However, the calculated value itself when MgO was used was much smaller than when other substrates were used. At this time, MgO formed a tensile stress of 6.4 MPa, sapphire substrate 129MPa, glass substrate 173MPa, silicon substrate 178MPa tensile stress was formed.

In the above situation, tensile stress plays a role of inhibiting perpendicular magnetic anisotropy formation from magnetic elastic interaction in that CoFeB has a positive value of the saturation magnetostriction coefficient.

From the above results, the description by combining the thermal stress and the saturation magnetostriction effect can be used as an auxiliary means for explaining the perpendicular magnetic anisotropy according to the substrate and the thickness (t _seed ) obtained in the present invention.

As described above, in the CoFeB / Pd multilayer thin film according to the present invention, it can be seen that the perpendicular magnetic anisotropy changes according to the type and thickness (t _seed ) of the substrate and the seed layer. The perpendicular magnetic anisotropy of the CoFeB / Pd multilayer thin film shows a result corresponding to that reported in the well-known Co / Pd multilayer.

The coercive force (Hc) of [Co (0.3nm) / Pd (1nm)] × 14 is 1300 Oe, and the coercive force (Hc) of [Co (0.3nm) / Pd (0.6nm)] × 4 is reported as 500 ~ 1000Oe. The CoFeB / Pd multilayer thin film of the present invention has a corresponding coercive force (Hc) of 40 to 600 Oe through the results of FIGS. 3 to 6.

Therefore, the CoFeB / Pd multilayer thin film of the present invention has a high possibility of achieving a high tunnel magnetoresistance ratio (TMR) and a low critical current density. pMTJs) can be applied more suitably. Hereinafter, the MRAM according to an embodiment of the present invention will be described in detail.

7 is a cross-sectional view illustrating a magnetic random access memory according to an embodiment of the present invention.

The magnetic random access memory according to the present invention of FIG. 7 includes a first impurity region 215D and a second impurity region 215S spaced apart from each other by doping impurities on the substrate 200. In this case, the substrate 200 may be a wafer substrate.

Next, a gate dielectric layer 220 formed on the substrate 200 between the first and second impurity regions 215D and 215S and a gate word line 230 formed on the gate dielectric layer 220 are provided.

Next, a first interlayer insulating film 235 including contacts 240 and 245 connected to the first and second impurity regions 215D and 215S, respectively, and filling a region between the gates is provided.

Next, the electrode pads 250 and 255 are electrically connected to the contacts 240 and 245, and the perpendicular magnetic anisotropic CoFeB / is connected to any one selected from the first and second impurity regions 215D and 215S. The Pd multilayer thin film 300 is provided. At this time, the vertical magnetic anisotropic CoFeB / Pd multilayer thin film 300 is composed of a seed layer 310, a Pd layer 320, CoFeB 340 / Pd (360), and a drain impurity region connected to the bit line and It is provided to be connected.

Next, a vertical magnetic anisotropic CoFeB / Pd multilayer thin film 300 and a second interlayer insulating film 260 filling the electrode pads 250 and 255 are provided.

Next, a bit line 270 is connected to the vertical magnetic anisotropic CoFeB / Pd multilayer thin film 300 on the second interlayer insulating layer 260, and is arranged in a direction perpendicular to the gate word line 230.

Next, the high-density spin torque MRAM according to the present invention is used to drive a memory device such as a current applying circuit unit and a sense amplifier capable of supplying current to the gate word line 230 and the bit line 270 in addition to the above main configuration. Various circuit devices may further be included.

In addition, since the process steps for forming the respective components are the same as the gate word line and bit line forming process of the general semiconductor manufacturing process, detailed description thereof will be omitted here.

In addition, since the above-described drawings are only described based on the basic structure of the high density spin torque MRAM, they do not represent all cases of the MRAM. Therefore, the present invention is not limited by the above-described FIG. 7, and any vertical magnetic anisotropic multilayer thin film used in MRAM should be regarded as the same applies.

Next, in the above-described high density spin torque (STT) MRAM, the CoFeB / Pd multilayer thin film has a coercive force (Hc) of 40 to 600 Oe, and has a high magnetoresistance ratio (TMR) and a low critical current density. In the form of magnetic tunnel junctions (pMTJs), they provide optimal conditions for the implementation of MRAM. In addition, compared to the conventional magnetization reversal MRAM using the magnetic field, high integration and write window margins (writes the current, reads the current is small) and improves the low power consumption, the optimum MRAM configuration has the advantage of working have.

Although the embodiments of the present invention have been described above with reference to the accompanying drawings, the present invention is not limited to the above embodiments, but may be modified in various forms, and having ordinary skill in the art to which the present invention pertains. It will be understood by those skilled in the art that the present invention may be embodied in other specific forms without changing the technical spirit or essential features of the present invention. It is therefore to be understood that the above-described embodiments are illustrative in all aspects and not restrictive.

10, 100, 200: substrate 20, 120, 320: Pd layer
30, 130, 340: CoFeB 40, 140, 360: Pd
110, 310: seed layer 215D: first impurity region
215S: second impurity region 220: gate dielectric film
230: gate word line 235: first interlayer insulating film
240, 245: contacts 250, 255: electrode pads
270: bit line 300: vertical magnetic anisotropic CoFeB / Pd multilayer thin film

Claims (11)

A seed layer of Al or Ta material formed on the substrate;
A Pd layer having a thickness of 5 to 20 nm on the seed layer; And
A multi-layered film formed over the Pd layer, in which [CoFeB / Pd] is repeatedly stacked N times (N is a natural number of 3 or more).
The Pd layer is formed in direct contact with the seed layer,
The CoFeB is formed of Co _x Fe _y B _z (atomic%, x + y + z = 100), wherein x = 43 to 58, y = 15 to 30, and z = 27. Vertical magnetic anisotropic multilayer thin film.
The method of claim 1,
The substrate is a perpendicular magnetic anisotropic multilayer thin film, characterized in that selected from the silicon substrate, glass substrate, sapphire substrate and magnesium oxide substrate.
delete The method of claim 1,
Vertically anisotropic multilayer thin film, characterized in that the thickness of the seed layer is 5 ~ 20nm.
delete The method of claim 1,
The thickness of CoFeB in the CoFeB / Pd: the thickness of the Pd is a vertical magnetic anisotropic multilayer thin film, characterized in that consisting of a ratio of 1: 2.5.
The method of claim 1,
N is 3 to 20, characterized in that the perpendicular magnetic anisotropic multilayer thin film.
delete delete delete A magnetic random access memory comprising the perpendicular magnetic anisotropic multilayer thin film of any one of claims 1, 2, 4, 6 and 7.

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