Magnetic tunnel junction devices and magnetoresistive memory devices

Magnetic tunnel junction devices are provided. A magnetic tunnel junction device includes a pinned layer. The magnetic tunnel junction device includes a free layer on the pinned layer. The free layer includes a first layer, a second layer that is on the first layer, and a third layer that is between the first layer and the second layer. A Curie temperature of the third layer is lower than a Curie temperature of the first layer and lower than a Curie temperature of the second layer. Moreover, the magnetic tunnel junction device includes an insulating layer that is between the pinned layer and the free layer. Related magnetoresistive memory devices are also provided.

CROSS-REFERENCE TO RELATED APPLICATION

This U.S. non-provisional patent application claims priority under 35 U.S.C. § 119 to Japanese Patent Application No. 2017-226830, filed on Nov. 27, 2017, in the Japan Patent Office, the disclosure of which is hereby incorporated herein by reference in its entirety.

BACKGROUND

The present disclosure herein relates to magnetic tunnel junction (MTJ) devices and magnetoresistive devices including the same. A magnetoresistive device that has a perpendicular magnetization and performs a read operation by a magnetoresistive effect may have a high resistance to thermal disturbance caused by fine patterns and may be expected as a next generation memory. This next generation memory may include an MTJ device including an MTJ layer that has a free layer having a variable magnetization direction, a reference layer maintaining a predetermined magnetization direction, and a barrier layer provided between the free layer and the reference layer.

A ferromagnetic material having a high perpendicular magnetic anisotropy and a high spin polarizability may be beneficial as a basic constituent material of the next generation memory. However, it may be difficult to obtain a material having a perpendicular magnetic anisotropy and a high spin polarizability. Practically, the material having the perpendicular magnetic anisotropy and the high spin polarizability may include only a cobalt-iron-boron (CoFeB) metal ferromagnetic material using interfacial magnetic anisotropy, and a selection range of the material may be very narrow. Thus, it may be difficult to use the material having the high perpendicular magnetic anisotropy and the high spin polarizability as the basic constituent material of the next generation memory.

Meanwhile, a composite layer-type recording layer has been suggested to solve these limitations. This recording layer may be obtained by coupling a ferromagnetic material layer having a high spin polarizability and a perpendicular magnetization maintaining layer having a high perpendicular magnetic anisotropy.

For example, Japanese Patent Publication No. 2014-116474 (“patent document 1”) and Japanese Patent Publication No. 2016-092066 (“patent document 2”) disclose the composite layer structure.

SUMMARY

A composite layer-type recording layer disclosed in the patent documents 1 and 2 normally operates in a constant temperature environment, but a write current of the composite layer-type recording layer is changed by a change in temperature. Therefore, it may be difficult to guarantee whether a write operation by magnetization reversal is normally performed at other temperatures. Thus, the composite layer-type recording layer of the patent documents 1 and 2 may need to reduce the dispersion (change) of the write current in a wide temperature range from −40° C. to +150° C.

The present disclosure may provide a magnetic tunnel junction device and a magnetoresistive memory device which are capable of reducing the dispersion (change) of a write current in a wide temperature range from −40° C. to +150° C.

A magnetic tunnel junction device, according to some embodiments, may include a free layer having a changeable magnetization direction. The magnetic tunnel junction device may include a pinned layer configured to maintain a predetermined magnetization direction. Moreover, the magnetic tunnel junction device may include an insulating layer between the free layer and the pinned layer. The free layer may include a perpendicularity maintaining layer configured to maintain a magnetization direction in a direction parallel to an easy axis of magnetization. The free layer may include a polarizable magnetic layer. Moreover, the free layer may include a magnetic coupling control layer between the perpendicularity maintaining layer and the polarizable magnetic layer. A Curie temperature of the magnetic coupling control layer may be lower than a Curie temperature of the perpendicularity maintaining layer and a Curie temperature of the polarizable magnetic layer. Moreover, the magnetic coupling control layer may be configured to reduce magnetic coupling of the perpendicularity maintaining layer and the polarizable magnetic layer as a temperature rises.

Because the Curie temperature of the magnetic coupling control layer may, in some embodiments, be lower than the Curie temperatures of the perpendicularity maintaining layer and the high polarizability magnetic layer, and because the magnetic coupling control layer may reduce the magnetic coupling of the perpendicularity maintaining layer and the high polarizability magnetic layer as the temperature rises, a write current necessary for magnetization reversal of the perpendicularity maintaining layer may be reduced. In addition, a distribution of the write current may be reduced in the wide temperature range from −40° C. to +150° C.

A magnetoresistive memory device, according to some embodiments, may include a magnetic tunnel junction device. The magnetoresistive memory device may include an electrode configured to apply a voltage to the magnetic tunnel junction device. The magnetic tunnel junction device may include a free layer having a changeable magnetization direction. The magnetic tunnel junction device may include a pinned layer configured to maintain a predetermined magnetization direction. The magnetic tunnel junction device may include an insulating layer between the free layer and the pinned layer. The free layer may include: a perpendicularity maintaining layer configured to maintain a magnetization direction in a direction parallel to an easy axis of magnetization; a polarizable magnetic layer; and a magnetic coupling control layer between the perpendicularity maintaining layer and the polarizable magnetic layer. A Curie temperature of the magnetic coupling control layer may be lower than a Curie temperature of the perpendicularity maintaining layer and a Curie temperature of the polarizable magnetic layer. Moreover, the magnetic coupling control layer may be configured to reduce magnetic coupling of the perpendicularity maintaining layer and the polarizable magnetic layer as a temperature rises.

According to the magnetoresistive memory device of some embodiments, because the Curie temperature of the magnetic coupling control layer is lower than the Curie temperatures of the perpendicularity maintaining layer and the high polarizability magnetic layer and the magnetic coupling control layer reduces the magnetic coupling of the perpendicularity maintaining layer and the high polarizability magnetic layer as the temperature rises, a write current necessary for magnetization reversal of the perpendicularity maintaining layer may be reduced. In addition, a distribution of the write current may be reduced in the wide temperature range from −40° C. to +150° C.

A magnetic tunnel junction device, according to some embodiments, may include a pinned layer. The magnetic tunnel junction device may include a free layer on the pinned layer. The free layer may include a first layer, a second layer on the first layer, and a third layer that is between the first layer and the second layer. A Curie temperature of the third layer may be lower than a Curie temperature of the first layer and lower than a Curie temperature of the second layer. Moreover, the magnetic tunnel junction device may include an insulating layer that is between the pinned layer and the free layer.

DETAILED DESCRIPTION

Embodiments of the inventive concepts will be described in detail with reference to the accompanying drawings.FIG. 1is a cross-sectional view illustrating a magnetic tunnel junction device according to some embodiments of the inventive concepts. Referring toFIG. 1, a magnetic tunnel junction device10may include a substrate11, a buffer layer12, a pinned layer13, an insulating (e.g., insulation) layer14, a free layer15, and a cap layer16.

The substrate11may be a silicon (Si) substrate. For example, the substrate11may be a silicon substrate having a thermal oxide layer, or a single-crystalline silicon substrate.

The buffer layer12may be a stabilization layer formed on the substrate11. For example, the buffer layer12may include chromium (Cr), tantalum (Ta), gold (Au), tungsten (W), platinum (Pt), or titanium (Ti).

The pinned layer13may be a layer maintaining its magnetization direction in a predetermined (e.g., fixed) direction. The pinned layer13may include at least one selected from materials of which magnetization directions are not easily changed as compared with that of the free layer15. In other words, the pinned layer13may include at least one selected from materials, each of which has a great (i.e., relatively high) effective magnetic anisotropy (Kueff), a great saturation magnetization (Ms), and a great magnetic relaxation constant (a). However, the material of the pinned layer13is not limited thereto. In some embodiments, the material of the pinned layer13may be selected from other various materials under various conditions. For example, the pinned layer13may include a layer13A including a Heusler alloy as a main ingredient, and a Co/Pt multi-layer13B. In some embodiments, the layer13A including the Heusler alloy as the main ingredient may be a layer including a Co-based full-Heusler alloy as a main ingredient. For example, the Co-based full-Heusler alloy may be Co2FeSi, Co2MnSi, Co2FeMnSi, Co2FeAl, or Co2CrAl, where Mn is manganese and Al is aluminum. In addition, the Co/Pt multi-layer13B may have a great perpendicular magnetic anisotropy. As illustrated inFIG. 1, the layer13A including the Heusler alloy as the main ingredient may be in contact with the insulating layer14, and the Co/Pt multi-layer13B may be in contact with the buffer layer12. The pinned layer13may be referred to as a reference layer.

The insulating layer14may include an insulating material as a main ingredient. The insulating layer14may be disposed between the pinned layer13and the free layer15which have ferromagnetism. The insulating layer14may be formed of an insulating material such as magnesium oxide (MgO). In addition, the material of the insulating layer14may be an oxide having a sodium chloride (NaCl) lattice structure. For another example, the insulating layer14may include calcium oxide (CaO), strontium oxide (SrO), titanium oxide (TiO), vanadium oxide (VO), or niobium monoxide (NbO). However, embodiments of the inventive concepts are not limited thereto. In some embodiments, the insulating layer14may include spinel-type MgAl2O4. When a voltage is applied in a direction substantially perpendicular to junction surfaces of the pinned layer13and the free layer15, a current may flow through the magnetic tunnel junction device10by a tunneling effect.

The free layer15may have an easy axis of magnetization which is parallel to a direction substantially perpendicular to a surface of the free layer15. A magnetization direction of the free layer15may be changeable by magnetization rotation. The free layer15may include a perpendicularity maintaining layer15A, a high polarizability magnetic layer15C, and a magnetic coupling control layer15B. As illustrated inFIG. 1, the high polarizability magnetic layer15C, the magnetic coupling control layer15B, and the perpendicularity maintaining layer15A may be sequentially stacked on the insulating layer14. The cap layer16may be stacked on the perpendicularity maintaining layer15A. The free layer15may be referred to as a recording layer, a magnetization free layer, or a magnetization changeable or variable layer.

The perpendicularity maintaining layer15A may be formed of a ferromagnetic substance having an easy axis of magnetization in a direction substantially perpendicular to a surface of the layer and may maintain a magnetization direction in such a way that the magnetization direction is parallel to the easy axis of magnetization. The ferromagnetic substance may have a L10 type iron-palladium (FePd), iron-platinum (FePt) or manganese-gallium (MnGa) alloy, a D022 type MnGa or manganese-germanium (MnGe) alloy, a Co/Pd multi-layer including Co and Pd alternately stacked, a Co/Pt multi-layer including Co and Pt alternately stacked, or a L11 type CoPd or CoPt alloy having a structure in which Co and Pd (or Pt) are alternately stacked with respect to an atom close-packed plane. In some embodiments, the perpendicularity maintaining layer15A may include a ferrimagnetic substance having a compensation temperature (Tn) at which a magnetization becomes 0 (zero). For example, the perpendicularity maintaining layer15A may include a rare earth-transition metal (RE-TM) alloy as a main ingredient. For example, the perpendicularity maintaining layer15A may include (Gd100-xTbx)z(Fe100-yCoy)100-z(0≤x≤100, 0≤y≤100, 20<z<35)(at %) as a main ingredient, where Gd is gadolinium and Tb is terbium.

A thickness of the perpendicularity maintaining layer15A may be at least 1 nanometer (nm) or more. For example, the thickness of the perpendicularity maintaining layer15A may range from 2 nm to 5 nm.

The high polarizability magnetic layer15C may have a high spin polarizability, and may be referred to herein as a “polarizable” magnetic layer. For example, the high polarizability magnetic layer15C may include a Heusler alloy layer having a L21 structure or a B2 structure as a main ingredient. In particular, the high polarizability magnetic layer15C may include a Co-based full-Heusler alloy as a main ingredient. Here, the Co-based full-Heusler alloy may be Co2FeMnSi, Co2FeSi, Co2MnSi, Co2FeAl, or Co2CrAl. Alternatively, the high polarizability magnetic layer15C may be a CoFeB magnetic layer having a great (i.e., relatively high) polarizability.

The magnetic coupling control layer15B may control magnetic coupling of the perpendicularity maintaining layer15A and the high polarizability magnetic layer15C. In detail, the magnetic coupling control layer15B may control the magnetic coupling of the perpendicularity maintaining layer15A and the high polarizability magnetic layer15C in such a way that the magnetic coupling thereof when a write current flows is less than the magnetic coupling thereof when the write current does not flow. In addition, the magnetic coupling control layer15B may control the magnetic coupling of the perpendicularity maintaining layer15A and the high polarizability magnetic layer15C in such a way that the magnetic coupling thereof when a read current flows is greater than the magnetic coupling thereof when the write current flows. A temperature of the magnetic tunnel junction device when the write current flows may be higher than a temperature of the magnetic tunnel junction device when the read current flows. Thus, the magnetic coupling control layer15B may reduce the magnetic coupling of the perpendicularity maintaining layer15A and the high polarizability magnetic layer15C as a temperature rises.

A Curie temperature of the magnetic coupling control layer15B may be lower than a Curie temperature of the perpendicularity maintaining layer15A and a Curie temperature of the high polarizability magnetic layer15C. The magnetic coupling control layer15B may reduce the magnetic coupling of the perpendicularity maintaining layer15A and the high polarizability magnetic layer15C by the combination of the perpendicularity maintaining layer15A, the high polarizability magnetic layer15C and the magnetic coupling control layer15B as the temperature rises.

In detail, a temperature of the magnetic coupling control layer15B may rise by the write current. The Curie temperature (e.g., 140° C.) of the magnetic coupling control layer15B may be lower than those of the perpendicularity maintaining layer15A and the high polarizability magnetic layer15C. A perpendicular magnetic anisotropy of the magnetic coupling control layer15B may be reduced by the write current, and heat disturbance of the magnetic coupling control layer15B may be increased by the write current. Thus, the magnetic coupling control layer15B may behave like a paramagnetic substance. As a result, coupling of magnetization of the high polarizability magnetic layer15C and magnetization of the perpendicularity maintaining layer15A may be reduced, and thus the magnetization direction of the high polarizability magnetic layer15C may be inclined in an in-plane direction to easily perform magnetization reversal by a spin current.

In addition, the layers15A,15B and15C may be controlled in such a way that in-plane magnetization may not affect or disturb a reversal of perpendicular magnetization of the high polarizability magnetic layer15C when the perpendicular magnetization of the high polarizability magnetic layer15C is reversed. Furthermore, after the perpendicular magnetization of the high polarizability magnetic layer15C is reversed, a magnetization direction of the perpendicularity maintaining layer15A may be the same as the magnetization direction of the high polarizability magnetic layer15C.

Thus, the magnetic coupling control layer15B may have a thickness capable of magnetically coupling the perpendicularity maintaining layer15A and the high polarizability magnetic layer15C. For example, the thickness of the magnetic coupling control layer15B may be a non-zero thickness of 2 nm or less.

The cap layer16may be a stabilization layer formed on the free layer15. In some embodiments, the cap layer16may include ruthenium (Ru) and Ta.

The magnetic tunnel junction device10may be configured as described above. Next, a principle in which a magnetization reversal current of the free layer15is reduced will be described.FIGS. 2, 3 and 4are cross-sectional views illustrating a rewrite process of the magnetic tunnel junction device according to some embodiments of the inventive concepts. InFIGS. 2, 3 and 4, arrows indicate magnetization directions.

As illustrated inFIG. 2, first, the perpendicularity maintaining layer15A and the high polarizability magnetic layer15C may have perpendicular magnetization directions in a downward direction of the figure (i.e., a direction toward the insulating layer14).

Thereafter, a write current may flow through the magnetic tunnel junction device10to increase a temperature of the magnetic tunnel junction device10, and thus a change in state of the free layer15may occur inFIG. 3. The perpendicular magnetic anisotropy of the magnetic coupling control layer15B of which the Curie temperature (e.g., 140° C.) is lower than those of the perpendicularity maintaining layer15A and the high polarizability magnetic layer15C may be reduced as the temperature rises. In addition, the heat disturbance of the magnetic coupling control layer15B may be increased, and thus the magnetic coupling control layer15B may behave like a paramagnetic substance. As a result, the coupling of the magnetization of the high polarizability magnetic layer15C and the magnetization of the perpendicularity maintaining layer15A may be reduced, and thus the magnetization direction of the high polarizability magnetic layer15C may be inclined in the in-plane direction to easily perform the magnetization reversal by the spin current. InFIG. 3, the magnetization direction of the high polarizability magnetic layer15C may be changed from the downward direction into an upward direction. A current value at this time may be significantly reduced as compared with that of a typical composite MTJ.

After a write operation is finished, the free layer15may be in a state illustrated inFIG. 4. A read operation may be performed in the state ofFIG. 4. Since a read current is less than the write current, a temperature when the read current flows through the magnetic tunnel junction device10may be lower than a temperature when the write current flows through the magnetic tunnel junction device10.

As described above, the write current of the write operation may be reduced by the temperature and differences in state between the layers of the free layer15in each of the operations ofFIGS. 2 to 4, and thus thermal stability may be maintained in the read operation.

Next, the state illustrated inFIG. 3will be described in more detail. Since the temperature of the magnetic tunnel junction device10rises by the write current in the write operation as described above, the coupling of the magnetization of the high polarizability magnetic layer15C and the magnetization of the perpendicularity maintaining layer15A may be reduced, and thus the magnetization direction of the high polarizability magnetic layer15C may be easily reversed.

In addition, a magnetic anisotropy constant Ku1 of the perpendicularity maintaining layer15A, a magnetic anisotropy constant Ku2 of the magnetic coupling control layer15B, and a magnetic anisotropy constant Ku3 of the high polarizability magnetic layer15C may satisfy a relation of Ku1≥Ku2>Ku3 at a temperature when the read current flows.

Moreover, since the Curie temperature (Tc) of the magnetic coupling control layer15B is lowered when the temperature rises by the write current, a reduction in the magnetic anisotropy constant Ku2 of the magnetic coupling control layer15B may be greater than a reduction in the magnetic anisotropy constant Ku1 of the perpendicularity maintaining layer15A, and thus the magnetic anisotropy constants Ku1, Ku2 and Ku3 of the layers15A,15B and15C may satisfy a relation of Ku1>Ku2≥Ku3. In other words, the free layer15may have a three-layer structure (e.g., a graded-Ku structure) in which the magnetic anisotropy constant Ku is changed in three steps in a thickness direction of the free layer15. The magnetization of the three-layer structure of the free layer15may be easily reversed as compared with that of a typical two-layer structure (e.g., an exchange spring-like structure). A difference in the magnetic anisotropy constant Ku between adjacent layers in the three-layer structure may be less than a difference in magnetic anisotropy constant between adjacent layers in the two-layer structure, and thus it is possible to reduce the write current necessary for the magnetization reversal of the perpendicularity maintaining layer15A.

FIG. 5is a view illustrating an example (exchange spring-like) of a structure and a magnetic anisotropy constant Ku of a free layer15having a two-layer structure. As illustrated inFIG. 5, since a difference in magnetic anisotropy constant Ku between the perpendicularity maintaining layer15A and the high polarizability magnetic layer15C is great, a write current necessary for magnetization reversal of the perpendicularity maintaining layer15A may be great.

On the other hand,FIG. 6is a view illustrating an example (graded-like) of a structure and a magnetic anisotropy constant Ku of the free layer15having a multi-layer structure. As illustrated inFIG. 6, the free layer15may have three or more layers and may be configured such that the magnetic anisotropy constant Ku is gently changed in the perpendicular magnetization direction. InFIG. 6, since a difference in magnetic anisotropy constant Ku between adjacent layers to each other is small, the write current necessary for magnetization reversal may be small. In addition, in some embodiments, the free layer15includes the perpendicularity maintaining layer15A, the high polarizability magnetic layer15C, and the magnetic coupling control layer15B. However, embodiments of the inventive concepts are not limited thereto. In some embodiments, the free layer15may include four or more layers, and thus the magnetic anisotropy constant Ku may be gently changed as illustrated inFIG. 6.

An experiment for verifying the principle described above was performed. Magnetization curves at the room temperature and 172° C. were obtained from a [Co(0.4)/Pd(1.2)]3/[CoPd(0.3)/Pd(1.2)]3/[Co(0.4)/Pt(1.2)]6multi-layer. The [CoPd(0.3)/Pd(1.2)]3multi-layer has the function of the magnetic coupling control layer15B.

FIG. 7is a graph showing the magnetization curve at the room temperature. InFIG. 7, a horizontal axis shows a magnetic field axis (kOe), and a vertical axis shows a Kerr rotation angle (θk). Since the perpendicularity maintaining layer15A is strongly magnetically coupled to the high polarizability magnetic layer15C at the room temperature, a hysteresis loop without a step difference is obtained as shown inFIG. 7. This may mean that the magnetization directions of the perpendicularity maintaining layer15A and the high polarizability magnetic layer15C are reversed together.

FIG. 8is a graph of the magnetization curve showing behavior of the free layer15of which the temperature rises to 172° C. in the write operation. InFIG. 8, a horizontal axis shows a magnetic field axis (kOe), and a vertical axis shows a Kerr rotation angle (θk). Since the magnetic coupling of the perpendicularity maintaining layer15A and the high polarizability magnetic layer15C is weakened when the write current flows, a shape of a hysteresis loop with a step difference is obtained as shown inFIG. 8. This may mean that the magnetization directions of the perpendicularity maintaining layer15A and the high polarizability magnetic layer15C are individually reversed.

In other words, in the free layer15which has the three-layer structure including the magnetic coupling control layer15B having the low Curie temperature (Tc), it may be easy to individually reverse the magnetization directions of the perpendicularity maintaining layer15A and the high polarizability magnetic layer15C in the write operation, and thus the write current for the magnetization reversal may be reduced.

In addition, in the read operation, the temperature of the magnetic tunnel junction device10may be relatively low, and thus the magnetic tunnel junction device10may thermally stably behave. Since a magnitude of energy for thermal stability is proportional to an equation of Ku1h1+Ku2h2+Ku3h3 (where ‘h1’, ‘h2’, and ‘h3’ are a thickness of the perpendicularity maintaining layer, a thickness of the magnetic coupling control layer, and a thickness of the high polarizability magnetic layer, respectively), the magnetic tunnel junction device10may be thermally very stable. In the read operation, the magnetization of the perpendicularity maintaining layer15A may be strongly coupled to the magnetization of the high polarizability magnetic layer15C, and thus the magnetization direction of the free layer15may not be reversed. The Curie temperature (Tc) of the perpendicularity maintaining layer15A may be equal to the Curie temperature (Tc) of the high polarizability magnetic layer15C and may be greater (i.e., higher) than the Curie temperature (Tc) of the magnetic coupling control layer15B.

In addition to the verifying experiment, a write current characteristic was calculated by a simulation using a Landau-Lifshitz-Bloch (LLB) equation. For example, a consumption current in the write operation was evaluated by a current density when the magnetization direction of the free layer15was reversed or switched.

Details and set parameters of the perpendicularity maintaining layer15A, the magnetic coupling control layer15B and the high polarizability magnetic layer15C will be described hereinafter.

Material: two kinds of FePt-based materials for the room temperature and a high temperature were introduced. Parameters (CGS Gauss) are shown in the following table 1.

Perpendicular magnetic anisotropy constant (Ku1): 7.8×105J/m3or 8.58×105J/m3(7.8 Merg/cc or 8.58 Merg/cc) at the room temperature

Material: a MnCrGaGe-based material and a MnFeGa-based material were introduced. Parameters (CGS Gauss) are shown in the following table 1.

In addition, the cases in which the perpendicular magnetic anisotropy constants (Ku1 and Ku2) of the perpendicularity maintaining layer15A and the magnetic coupling control layer15B are great (i.e., relatively high) are referred to as ‘high A’.

Material: CoFe, CoFeB and CFMS(Co2FeMnSi) materials were introduced. Parameters (CGS Gauss) are shown in the following table 1.

Here, the parameters represented in CGS units in parentheses were used in the LLB simulation described above. In addition, the parameters represented in SI units and described together therewith are converted into the parameters represented in the CGS units in the parentheses by the following conversion formulas (A) and (B).
10 erg/cc=1 J/m3(A)
1 G=1 emu/cc=1×103A/m  (B)

A height (a thickness) of the perpendicularity maintaining layer15A was 2 nm (h1=2 nm), a height of the magnetic coupling control layer15B was 1.0 nm (h2=1 nm), and a height of the high polarizability magnetic layer15C was 1 nm (h3=1 nm).

A diameter (D, a width) of the free layer15was 20 nm. Here, it was assumed that the free layer15had a cylindrical shape, and a diameter of a cross section of the free layer15was used as a value representing a size of the free layer15. When the cross section of the free layer15is a circle, the size of the free layer15may use the diameter of the free layer15. Alternatively, when the cross section of the free layer15is an ellipse, the size of the free layer15may use a long diameter (e.g., the longest diameter in an ellipse) of the free layer15. When the cross section of the free layer15has another shape, the size of the free layer15may use a diameter of a circle circumscribed about the free layer15.

A rise in temperature (ΔT) was used as a parameter, and a change in temperature corresponding to a write current value was set from 2.1° C. to 123° C. The temperature in a write operation was changed as shown inFIG. 9.FIG. 9is a graph showing a change in a write current value according to a rise in temperature. It was assumed that a temperature change amount was the same in the free layer15.

It was assumed that the following temperature change occurred in the free layer15in the write operation.

(1) After the write current was applied, the temperature of the free layer15rose, and thus the free layer15reached a saturation state within 1 nanosecond (ns).

(2) Thereafter, the write current was applied for 10 nanoseconds. At this time, a temperature of the device was in a normal state.

(3) After the write operation, the temperature of the free layer15was reduced to 300K within 5 nanoseconds.

FIGS. 10 and 11are graphs showing write current characteristics.FIG. 10shows write current characteristics when an operating temperature of the device is the room temperature.FIG. 11shows write current characteristics when the operating temperature of the device is changed to −30° C., the room temperature, and 100° C. A horizontal axis represents a magnetization reversal current value, and a vertical axis represents reversal probability.FIGS. 10 and 11show write current characteristics of a magnetic tunnel junction device having a TcC structure, write current characteristics of a magnetic tunnel junction device having an EcC structure, write current characteristics of the magnetic tunnel junction device10(New, having a thermal stability index of about 57 to about 60 near the room temperature) according to some embodiments, and write current characteristics of a device (h_delta, using Ku of high A of the table 1 to have a thermal stability index of about 70 near the room temperature) obtained by improving the thermal stability index of the magnetic tunnel junction device10of some embodiments. In addition, the TcC structure is disclosed in IEEE Trans. Magn. DOI: TMAG. 2711247, Machida et al. (2017). The EcC structure is disclosed in Appl. Phys. Lett. 99, 132502, Yulaev, et al. (2011).

Referring toFIG. 10, the write current value of the magnetic tunnel junction device10of some embodiments is reduced by about 50%, compared to those of the magnetic tunnel junction device having the TcC structure and the magnetic tunnel junction device having the EcC structure.

As described above, according to the magnetic tunnel junction device10of some embodiments, the Curie temperature of the magnetic coupling control layer15B may be lower than the Curie temperature of the perpendicularity maintaining layer15A and the Curie temperature of the high polarizability magnetic layer15C, and the magnetic coupling control layer15B may reduce the magnetic coupling of the perpendicularity maintaining layer15A and the high polarizability magnetic layer15C as the temperature rises. Thus, the write current necessary for the magnetization reversal of the perpendicularity maintaining layer may be reduced.

As shown inFIG. 11, the write current necessary for the magnetization reversal of the perpendicularity maintaining layer15A may be reduced in a wide temperature range from −40° C. to +150° C.

FIG. 12is a graph showing a change in temperature of a thermal stability index. InFIG. 12, a horizontal axis represents an operating temperature in a read operation, and a vertical axis represents a thermal stability index (ΔKuV/Kt). Here, ‘K’ is the Boltzmann constant, and ‘t’ is a temperature.

As shown inFIG. 12, changes in the thermal stability index and the write current of the magnetic tunnel junction device10of some embodiments are inhibited in the wide temperature range from −40° C. to +150° C., as compared with those of the magnetic tunnel junction device having the TcC structure and the magnetic tunnel junction device having the EcC structure.

Thus, according to the magnetic tunnel junction device10of some embodiments, a distribution of the write current may be small in the wide temperature range from −40° C. to +150° C.

In some embodiments, the magnetic coupling control layer15B is a single layer. Alternatively, the magnetic coupling control layer15B may include a plurality of layers. In some embodiments, the magnetic coupling control layer15B including the plurality of layers will be described as an example.

FIG. 13is a cross-sectional view illustrating a magnetic tunnel junction device according to some embodiments of the inventive concepts. InFIG. 13, the same components or elements as inFIG. 1will be indicated by the same reference numerals or designators, and the descriptions thereto will be omitted.

Referring toFIG. 13, a magnetic tunnel junction device20may include the substrate11, the buffer layer12, the pinned layer13, the insulating layer14, a free layer15, and the cap layer16. The free layer15may include the perpendicularity maintaining layer15A, the high polarizability magnetic layer15C, and a magnetic coupling control layer15B.

The magnetic coupling control layer15B may include a first layer15D, a second layer15E, and a third layer15F.

The first layer15D may include CoPd or CoPt.

The second layer15E may include Ru or iridium (Ir).

The third layer15F may include CoPd or CoPt, like the first layer15D.

By these components, the magnetic coupling control layer15B may have a three-layer structure having a Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction. When Ru or Ir is used, total magnetization of the free layer15may be reduced and a speed of the magnetization reversal may be increased.

According to the magnetic tunnel junction device20of some embodiments described above, the magnetic coupling control layer15B between the perpendicularity maintaining layer15A and the high polarizability magnetic layer15C may reduce the distribution of the write current in the wide temperature range from −40° C. to +150° C. by the three-layer structure of low-Tc CoX/Ru (or Ir)/low-Tc CoX, which has the RKKY interaction.

A magnetoresistive memory device using the magnetic tunnel junction device10of some embodiments will be described.

FIG. 14is a perspective view illustrating main components of an example of a magnetoresistive memory device according to some embodiments of the inventive concepts. Referring toFIG. 14, the magnetoresistive memory device may include a memory cell30, a bit line31, contact plugs35and37, and a word line38.

The memory cell30may include a semiconductor substrate32, diffusion regions33and34, a source line36, a gate insulating layer39, and a magnetic tunnel junction device10. In some embodiments, the magnetic tunnel junction device20may be used in the memory cell30instead of the magnetic tunnel junction device10.

The magnetoresistive memory device may include a plurality of the memory cells30arranged in a matrix form. The plurality of memory cells30may be connected to each other by using a plurality of the bit lines31and a plurality of the word lines38. The magnetoresistive memory device (e.g., MRAM) may perform a write operation of data by a spin torque injection method (e.g., a spin torque transfer (STT) method). For example, a magnetic tunnel junction device10or20may be used in a perpendicular STT-MRAM device that has high integration density and uses a spin injection magnetization reversal effect.

The semiconductor substrate32may have the diffusion regions33and34at its surface, and the diffusion region33may be spaced apart from the diffusion region34by a predetermined distance. The diffusion region33may function as a drain region, and the diffusion region34may function as a source region. The diffusion region33may be connected to the magnetic tunnel junction device10with the contact plug37interposed therebetween.

The bit line31may be disposed over the semiconductor substrate32and may be connected to the magnetic tunnel junction device10. The bit line31may be connected to a write circuit and a read circuit.

The diffusion region34may be connected to the source line36with the contact plug35interposed therebetween. The source line36may be connected to the write circuit and the read circuit.

The word line38may be adjacent to the diffusion regions33and34and may be disposed on the semiconductor substrate32with the gate insulating layer39interposed therebetween. The word line38and the gate insulating layer39may function as a selection transistor. A current may be supplied from a circuit, and thus the word line38may be activated and the selection transistor may be turned on.

In the magnetoresistive memory device, a voltage may be applied to the magnetic tunnel junction device10by using the bit line31and the diffusion region33as electrodes, and thus a magnetization direction of a ferromagnetic layer (e.g., the free layer) may be changed by spin torque of electrons aligned in a certain direction. In addition, a data value written in the magnetoresistive memory device may be changed by changing a current direction.

According to the magnetoresistive memory device of some embodiments described above, the Curie temperature of the magnetic coupling control layer may be lower than the Curie temperature of the perpendicularity maintaining layer and the Curie temperature of the high polarizability magnetic layer, and the magnetic coupling control layer may reduce the magnetic coupling of the perpendicularity maintaining layer and the high polarizability magnetic layer as the temperature rises. Thus, the write current necessary for the magnetization reversal of the perpendicularity maintaining layer may be reduced. In addition, according to the magnetoresistive memory device of some embodiments, the distribution of the write current may be reduced in the wide temperature range from −40° C. to +150° C.

However, the inventive concepts are not limited to the aforementioned embodiments, and the embodiments may be variously changed or modified without departing from the scope of the inventive concepts. For example, since the magnetic anisotropy constant (Ku) of the perpendicularity maintaining layer is less than that of the magnetic coupling control layer at the room temperature, the same effects may be expected in a parameter in which the magnetic anisotropy of the perpendicularity maintaining layer becomes less than the magnetic anisotropy of the magnetic coupling control layer in the write operation.

In the magnetic tunnel junction device according to some embodiments, the magnetic anisotropy constant of the magnetic coupling control layer may be equal to or greater than the magnetic anisotropy constant of the high polarizability magnetic layer at the temperature when the write current flows through the magnetic tunnel junction device.

In the magnetic tunnel junction device according to some embodiments, the magnetic anisotropy constant of the high polarizability magnetic layer may be 0 (zero) at the temperature when the write current flows through the magnetic tunnel junction device.

In the magnetic tunnel junction device according to some embodiments, the magnetic anisotropy constants of the perpendicularity maintaining layer and the magnetic coupling control layer may be equal to each other at the temperature when the write current flows through the magnetic tunnel junction device, and the magnetic anisotropy constant of the perpendicularity maintaining layer may be greater than the magnetic anisotropy constant of the magnetic coupling control layer at a temperature higher than the room temperature. In some embodiments, the magnetic coupling control layer15B may have a structure which has two layers having other magnetic anisotropy constants (Ku2a and Ku2b).

According to some embodiments of the inventive concepts, the magnetic tunnel junction device may reduce the distribution of the write current in the wide temperature range from −40° C. to +150° C.