Magnetoresistive element and magnetic memory

A magnetoresistive element according to an embodiment includes: a first layer containing nitrogen; a reference layer opposed to the first layer, the reference layer having a magnetization perpendicular to a face thereof opposed to the first layer, the magnetization of the reference layer being fixed; a storage layer disposed between the first layer and the reference layer, the storage layer having a magnetization perpendicular to a face thereof opposed to the first layer, the magnetization of the storage layer being changeable, and the storage layer including a second layer containing boron, and a third layer disposed between the second layer and the reference layer and containing boron, a boron concentration of the third layer being lower than a boron concentration of the second layer; and an intermediate layer disposed between the third layer and the reference.

FIELD

Embodiments described herein relate generally to magnetoresistive elements and magnetic memories.

BACKGROUND

Spin transfer torque magnetic random access memories (STT-MRAMs) serving as nonvolatile memories that do not lose information when used in high-speed reading and writing have received attention. STT-MRAMs may replace volatile memories in electronic devices. This may reduce the power consumption since the STT-MRAMs do not require standby power. In order to further reduce the power consumption, however, the write current used to perform a write operation on magnetic tunnel junction (MTJ) elements serving as storage elements of the STT-MRAMs should be lowered. An MTJ element has a multilayer structure in which a tunnel barrier layer is disposed between two magnetic layers. In order to reduce the write current, perpendicular magnetization MTJ elements, in which the magnetization direction in the magnetic layers of each MTJ element is perpendicular to the film plane, are employed. The “film plane” herein means a plane perpendicular to the stacking direction of layers constituting the MTJ elements.

DETAILED DESCRIPTION

A magnetoresistive element according to an embodiment includes: a first layer containing nitrogen; a reference layer opposed to the first layer, the reference layer having a magnetization perpendicular to a face thereof opposed to the first layer, the magnetization of the reference layer being fixed; a storage layer disposed between the first layer and the reference layer, the storage layer having a magnetization perpendicular to a face thereof opposed to the first layer, the magnetization of the storage layer being changeable, and the storage layer including a second layer containing boron, and a third layer disposed between the second layer and the reference layer and containing boron, a boron concentration of the third layer being lower than a boron concentration of the second layer; and an intermediate layer disposed between the third layer and the reference.

FIG. 1shows a magnetoresistive element according to a first embodiment. The magnetoresistive element according to the first embodiment has a multilayer structure in which a base layer10, a storage layer12including a magnetic layer of which the direction of magnetization is changeable, an intermediate layer14, a reference layer16including a magnetic layer of which the direction of magnetization is fixed, and an electrode18are stacked in this order. The “changeable” direction of magnetization herein means that a write current caused to flow in a direction perpendicular to the film plane of the magnetoresistive element may change the direction of magnetization. The “fixed” direction of magnetization herein means that the write current caused to flow in a direction perpendicular to the film plane of the magnetoresistive element may not change the direction of magnetization. The magnetic layers of the storage layer12and the reference layer16each have a magnetization perpendicular to the film plane. Thus, the magnetic layers of the storage layer12and the reference layer16each have a magnetic anisotropy perpendicular to the film plane.

The electric resistance between the base layer10and the electrode18varies depending on whether the magnetization direction of the storage layer12is parallel to or antiparallel (opposite) to the magnetization direction of the reference layer16. A number “0” is assigned to data to be stored in the magnetoresistive element in one of the parallel case and the antiparallel case, and a number “1” is assigned to data to be stored in the magnetoresistive element in the other.

A write operation to change the magnetization direction of the storage layer12from antiparallel to parallel to the magnetization direction of the reference layer16will be described below. In this case, a write current is caused to flow from the storage layer12to the reference layer16, i.e., from the base layer10to the electrode18. An electron current flows in a direction opposite to the direction of the write current. Therefore, the electron current flows from the reference layer16to the storage layer12via the intermediate layer14. The electrons passing through the reference layer16are spin-polarized by the reference layer16, and flows to the storage layer12via the intermediate layer14. The magnetization direction of the storage layer12is caused to be in parallel to the magnetization direction of the reference layer16by spin transfer torque switching. Then, the write operation ends.

A write operation to change the magnetization direction of the storage layer12from parallel to antiparallel to the magnetization direction of the reference layer16will next be described below. In this case, a write current is caused to flow from the reference layer16to the storage layer12, i.e., from the electrode18to the base layer10. As a result, an electron current flows from the storage layer12to the reference layer via the intermediate layer14. The electrons passing through the storage layer12are spin-polarized. The electrons that are spin-polarized in a direction parallel to the magnetization direction of the reference layer16pass through the reference layer16, but electrons that are spin-polarized in an antiparallel direction are reflected at the interface between the intermediate layer14and the reference layer16, and flow into the storage layer12via the intermediate layer14. The electrons that are spin-polarized in the direction antiparallel to the magnetization direction of the reference layer16flowing into the storage layer12switch the magnetization direction of the storage layer12from parallel to antiparallel by spin transfer torque switching. Then, the write operation ends.

A read operation to read data from the magnetoresistive element1is performed by causing a read current to flow between the base layer10and the electrode18, for example, and measuring the voltage between the base layer10and the electrode18.

In the first embodiment, the storage layer12has a multilayer structure including layers with different boron concentrations. For example, the storage layer12includes a first layer121disposed between the base layer10and the intermediate layer14, and a second layer122disposed between the first layer121and the intermediate layer14. The boron concentration (atomic %) in the first layer121is higher than the boron concentration (atomic %) in the second layer122. For example, the first layer121is formed of Co20Fe20Hf25B35with the boron concentration of 35 atomic %, and the second layer122is formed of Co16Fe64B20with the boron concentration of 20 atomic %.

A magnetoresistive element1A according to a first modification of the first embodiment shown inFIG. 2may also be employed. The magnetoresistive element1A according to the first modification is obtained by replacing the storage layer12of the magnetoresistive element1according to the first embodiment shown inFIG. 1with a storage layer12a. The storage layer12ahas a multilayer structure including layers with different boron concentrations. Specifically, the storage layer12aincludes a first layer12a1disposed between the base layer10and the intermediate layer14, a second layer12a2disposed between the first layer12a1and the intermediate layer14, and a third layer12a3disposed between the second layer12a2and the intermediate layer14. The boron concentration (atomic %) of the first layer12a1is lower than the boron concentration (atomic %) of the second layer12a2, and the boron concentration (atomic %) of the third layer12a3is lower than the boron concentration (atomic %) of the second layer12a2. For example, the first and third layers12a1and12a3are formed of Co16Fe64B20with the boron concentration of 20 atomic %, and the second layer12a2is formed of Hf50B50with the boron concentration of 50 atomic %.

The base layer10may be a single film containing nitrogen and at least one element other than nitrogen.

A magnetoresistive element1B according to a second modification of the first embodiment shown inFIG. 3may also be employed. The magnetoresistive element1B according to the second modification is obtained by replacing the base layer10of the magnetoresistive element1according to the first embodiment shown inFIG. 1with a base layer10a. The base layer10aincludes a first base layer101and a second base layer102disposed between the first base layer101and the storage layer12. The base layer101contains at least one of Hf, Zr, Al, Be, Mg, Ca, Sr, Ba, Sc, Y, and La, and the second base layer102contains nitrogen and at least one element other than nitrogen. The first base layer101preferably contains less nitrogen than the second base layer102, or no nitrogen. This makes it easy to flatten the first base layer101.

A magnetoresistive element1C according to a third modification of the first embodiment shown inFIG. 4may also be employed. The magnetoresistive element1C according to the third modification may be obtained by replacing the base layer10of the magnetoresistive element1A according to the first modification shown inFIG. 2with a base layer10a. The base layer10ahas the same structure as the base layer10aof the second modification shown inFIG. 3.

The storage layer12is a magnetic layer containing Fe, and the base layer10contains nitrogen and easily forms a nitride in each of the first embodiment and its modifications. As a result, the interdiffusion of elements constituting the storage layer12and the base layer10may be prevented since the coupling energy of Fe with nitrogen is weak, and nitrogen may be selectively coupled with an element in the base layer10.

If the nitride of the base layer10is a compound of nitrogen and at least one of Al, Sc, Y, La, Ti, Zr, Hf, and In, a stable base layer with a high melting point may be obtained. This may prevent the interdiffusion of the elements constituting the storage layer12and the base layer10. The first base layer and/or the second base layer may be formed of AlN, for example. Since AlN has an insulating property, such materials as AlTiN, AlScN, ScN, and AlInN are more preferable since these materials may a have lower resistance. Therefore, the base layer10preferably contains nitrogen and at least one of Al, Sc, Y, and La. Since the base layer10preferably has a satisfactorily lower resistance than the intermediate layer14, the thickness of the base layer10is preferably 0.2 nm or more and 2 nm or less. The AlInN, AlScN, or AlTiN film may be a continuous film, or may be separated by another material. Mixing AlN, which has the hexagonal close-packed structure, with TiN or ScN, which has the tetragonal structure, makes amorphous nitride. As a result, a flat base layer10may be formed. The storage layer12may have a lower Gilbert damping constant if the exchange of electrons and the interdiffusion of elements between the storage layer12and the base layer10are suppressed to reduce the spin pumping effect. As a result, the write current may be reduced.

FIG. 16shows values of the Gilbert damping constant of a AlN layer and a ScN layer in relation to the thicknesses thereof, the AlN layer and the ScN layer serving as the base layer10for a 13 Å storage layer12of Co8Fe72B20. The Gilbert damping constant may be satisfactorily reduced if the thickness of the AlN layer and the ScN layer is 2 Å (0.2 nm) or more. In consideration of the resistance of the nitride base layer, it is preferable that the thickness of the AlN layer and the ScN layer be 0.2 nm or more and 2 nm or less.

If the storage layer12on the base layer10of nitride contains iron and boron, the wettability of the storage layer12for the base layer10is not good, which makes the surface of the storage layer12irregular. Furthermore, boron in the storage layer12and nitrogen in the base layer10may have strong coupling properties. As a result, a heat treatment performed after the magnetoresistive element1is formed may prevent the storage layer12from changing from an amorphous state to a crystalline state, thereby lowering the MR ratio. The low MR ratio may lead to a decrease in spin torque applied to the storage layer12to increase the write current.

If, for example, the first layer121shown inFIG. 1of the storage layer12contains highly concentrated boron, the wettability of the storage layer12degraded by nitrogen of the base layer10is improved by the highly concentrated boron. The lack of boron caused by the coupling of boron and nitrogen is compensated by the highly concentrated boron. As a result, crystallization between the intermediate layer14and the storage layer12is advanced. If the storage layer12or the storage layer12ais formed on the base layer10or the top surface of the multilayer structure of the base layer10a, the amorphous state of the storage layer12or12ais improved by the highly concentrated boron. As a result, the smoothness and the MR ratio of the storage layer12or12amay be improved.

The material of the first base layer101is preferably conductive, and may be oxidized to become an insulating material. This allows the material of the first base layer101to become an insulating material if it is oxidized during the re-deposition as an accretion caused by etching on the side portions of the intermediate layer14when the magnetoresistive element is processed. Therefore, the first base layer101is formed of a material containing at least one of Hf, Zr, Al, Be, Mg, Ca, Sr, Ba, Sc, Y, and La. If a material that is easy to be oxidized to form an insulator with good quality during re-deposition is used to form the first base layer101, and if MgO is used to form the intermediate layer14, the element contained in the first base layer101attached to the sidewall of the intermediate layer14may be changed to an insulating material by natural oxidation during the separation of the magnetoresistive elements. This may prevent short-circuit of the magnetoresistive elements caused by the separation processing. If the thickness of the re-deposition including the element of the first base layer101is adjusted to be in a range of about 0.5 nm to 5 nm, the damage to the magnetoresistive elements caused by oxidation due to the exposure to the atmosphere after the magnetoresistive elements are separated may be prevented. This may suppress an increase in the write current and a decrease in the thermal stability.

The intermediate layer14may be formed of an insulating material such as MgO. If MgO is used, the intermediate layer14serves as a tunnel barrier layer.

The reference layer16may be a multilayer film including, for example, a TbCoFe layer and a CoFeB layer. A high MR ratio may be obtained by disposing a CoFeB layer between a TbCoFe layer and a tunnel barrier layer of MgO. If a shift adjustment layer of CoPt is disposed between the reference layer16and the electrode18, the magnetic field applied from the reference layer16to the storage layer12or12amay be cancelled. This would stably makes the magnetization of the storage layer12or12aoriented to be parallel or antiparallel to the magnetization of the reference layer16. If a nonmagnetic layer of Ru is disposed between the reference layer16and the shift adjustment layer, the magnetization of the reference layer and the magnetization of the shift adjustment layer may be coupled to be antiparallel to each other. This may stably cancel the stray magnetic field from the reference layer.

The electrode18may be a multilayer film including a 10-nm-thick Ru layer and a 100-nm-thick Ta layer, disposed on the reference layer16.

As described above, the first embodiment may reduce the write current.

FIG. 5shows a magnetoresistive element according to a second embodiment. The magnetoresistive element1D according to the second embodiment has a multilayer structure in which a base layer10b, a storage layer12including a magnetic layer containing boron, an intermediate layer14, a reference layer16including a magnetic layer, and an electrode18are stacked in this order. The magnetization direction of the magnetic layer of the storage layer12is changeable, and the magnetization direction of the magnetic layer of the reference layer16is fixed.

The storage layer12of the second embodiment contains, for example, Co16Fe64B20. A high perpendicular magnetic anisotropy may be obtained for this material since the content of Fe is set to be higher than the content of Co. A high perpendicular magnetic anisotropy would improve the nonvolatile performance of devices, thereby contributing to a decrease in power consumption.

The base layer10bhas a multilayer structure in which a first base layer10b1containing nitrogen and a second base layer10b2containing boron, disposed between the first base layer10b1and the storage layer12are stacked as shown inFIG. 5. The boron concentration (atomic %) of the second base layer10b2is higher than the boron concentration (atomic %) of the storage layer12.

The second base layer10b2is formed of, for example, Hf50B50with a thickness of 1 nm or less. The boron concentration of the second base layer10b2is higher than the boron concentration (20 atomic %) of the storage layer12of Co16Fe64B20. The first base layer10b1is formed of AlN with a thickness of about 1 nm, or nitride as used in the first embodiment. For example, AlInN, AlScN, AlYN, AlLaN, and ScN may be used to form the first base layer10b1. Thus, the first base layer10b1preferably contains nitrogen and at least one of Al, Sc, Y, and La. The thickness of the AlInN, AlScN, AlYN, AlLaN, or ScN layer is preferably 0.2 nm or more and 2 nm or less as in the case of the first embodiment. As will be described in the descriptions of the third embodiment, if AlInN is used, the ratio of In is preferably lower than the ratio of Al, and if AlScN, AlYN, or AlLaN is used, the ratio of Al is preferably lower than the ratio of Sc, V, or La. The same applies to the first embodiment. The AlInN, AlScN, AlYN, AlLaN, or ScN layer may be continuous, or separated by another material.

The use of the second base layer10b2with a higher boron concentration than the storage layer12as in the second embodiment may improve the wettability between the base layer10containing a nitride and the storage layer12containing Fe as a main constituent. As the thickness of the second base layer10b2increases, the magnetization of the storage layer12decreases as shown inFIG. 6. The lateral axis ofFIG. 6indicates the thickness of the storage layer12(Co16Fe64B20), and the longitudinal axis indicates the magnetization (saturation magnetization density (M)×thickness (t)) of the storage layer12. InFIG. 6, the black diamond marks represent the base layer10bincluding only the first base layer10b1of AlN, the cross marks represent the base layer10bincluding the first base layer10b1of AlN and the second base layer10b2of Hf50B50(1) (where (1) indicates that the thickness of the Hf50B50layer is 1 Å (=0.1 nm)), white square marks represent the base layer10bincluding the first base layer10b1of AlN and the second base layer10b2of Hf50B50(10) (where (10) indicates that the thickness of the Hf53B50layer is 10 Å (=1 nm)), and white circle marks represent the base layer10bincluding only a Hf50B50(50) layer (where (50) indicates that the thickness of the Hf50B50layer is 50 Å (=5 nm)). As can be understood fromFIG. 6, the magnetization may be reduced by disposing a base layer containing boron between the storage layer and a base layer containing nitride, or by directly disposing a base layer containing boron on the storage layer. The decrease in magnetization occurring between the base layer and the storage layer leads to an increase in damping constant (Gilbert damping constant) due to the spin pumping effect, which further leads to an increase in the write current. Therefore, the thickness of the second base layer10b2is preferably 1 nm or less, at which the amount of the decrease in magnetization of the storage layer12is less than the amount in the case where a base layer of boride is used.

FIG. 14shows the relationship between the thickness and the Gilbert damping constant of the base layer10b2containing boron disposed between the storage layer12and the first base layer10b1containing nitride. The Gilbert damping constant in a case where the base layer10bcontaining Hf50B50is directly disposed on the storage layer is 0.0074, and the Gilbert damping constant in a case where a base layer containing AlN is directly disposed on the storage layer is 0.0037. It can be understood fromFIG. 14that the Gilbert damping constant may be reduced by disposing a base layer of Hf50B50having a thickness of 1 Å, which contains boron, between the nitride base layer10b1of AlN and the storage layer12as compared to the case where the AlN layer is directly bonded to the storage layer. The wettability between the nitride base layer10b1and the storage layer12may be improved by disposing a very thin base layer10b2containing boron between the storage layer12and base layer10b. As a result, a uniform storage layer may be formed. A uniform storage layer may lead to an improvement in Curie temperature (Tc) of the storage layer. The improvement in Tcmay prevent spin information from being lost, and may allow the Gilbert damping constant and the write current to be decreased.

FIG. 15shows values of a current (magnetization switching current) required for switching magnetization of the storage layer12from parallel to antiparallel relative to the magnetization of the reference layer16in cases where the base layer10bis a 6 Å AlN layer, a multilayer including a 1 Å Hf50B50layer and a 6 Å AlN layer, and a multilayer including a 10 Å Hf50B50layer and a 6 Å AlN layer. The lateral axis ofFIG. 15indicates the area of the MTJ element. If the area of the MTJ element is the same, the magnetization switching current in the case where the base layer10bhas the multilayer structure including a 1 Å Hf50B50layer and a 6 Å AlN layer is less than the magnetization switching current in the case where the base layer10bis simply a AlN layer. The decrease in switching current leads to the decrease in write current. Therefore, MTJ elements with lower power consumption may be manufactured. In order to obtain a high MR ratio, the thickness of the base layer10b2of Hf50B50, which contains boron, is preferably thick. However, a thick Hf50B50layer disposed between the storage layer12and the nitride base layer10b1may increase the Gilbert damping constant as shown inFIG. 14, and may increase the magnetization switching current as shown inFIG. 15. Thus, a too thick layer is not preferable. Therefore, the thickness of the base layer10b2containing boron is preferably set to be 1 nm or less.

FIG. 7shows a magnetoresistive element according to a first modification of the second embodiment. The magnetoresistive element1E according to the first modification is obtained by replacing the base layer10bof the magnetoresistive element1D according to the second embodiment shown inFIG. 5with a base layer10c. The base layer10cincludes a first base layer10c1containing at least one of Hf, Zr, Al, Be, Mg, Ca, Sr, Ba, Sc, Y, and La, a second base layer10c2containing nitrogen and disposed between the first base layer10c1and the storage layer12, and a third base layer10c3containing boron and disposed between the second base layer10c2and the storage layer12. The boron concentration (atomic %) of the third base layer10c3is higher than the boron concentration (atomic %) of the storage layer12. For example, the storage layer12is formed of Co16Fe64B20, and the third base layer10c3is formed of Hf50B50having a thickness of 1 nm or less. The first base layer10c1preferably contains less nitrogen than the second base layer10c2, or no nitrogen so that the first base layer10c1may be flattened easily.

An MTJ element including a base layer of a single layer containing nitrogen (for example, AlN), and MTJ elements each including a base layer having a multilayer structure with a first base layer containing nitrogen and a second base layer containing boron are prepared.FIG. 8shows a result of the comparison in MR ratio among these MTJ elements. The lateral axis inFIG. 8indicate the area resistance, and the longitudinal axis indicates the MR ratio. The first base layer is a AlN layer having a thickness of about 6 Å, and the second base layer is a Hf50B50layer. It can be understood fromFIG. 8that the base layers each having a multilayer structure obtain higher MR ratios. Thus, a base layer with a multilayer structure provides a higher MR ratio, which may improve the spin torque, thereby reducing the write current. The thickness of the base layer that is a single layer containing nitrogen, and the thickness of the first base layer containing nitrogen are preferably 0.2 nm or more and 2 nm or less as in the first embodiment. The material of the first base layer10c1is preferably conductive, and may be oxidized to become an insulating material during the re-deposition on the side portions of the tunnel barrier layer (intermediate layer) when the MTJ element is processed. For example, the first base layer10c1is formed of a material containing at least one of Hf, Zr, Al, Be, Mg, Ca, Sr, Ba, Sc, Y, and La.

The materials of the intermediate layer (tunnel barrier layer), the reference layer16, and the electrode18of the second embodiment and its modifications are the same as the materials of these elements in the first embodiment.

As in the case of the first embodiment, the second embodiment and its modification may reduce the write current.

FIG. 9shows a magnetoresistive element according to a third embodiment. The magnetoresistive element1F according to the third embodiment has a multilayer structure in which a base layer10, a storage layer12, an intermediate layer (tunnel barrier layer)14, a reference layer16, and an electrode18are stacked in this order.

The storage layer12is formed of, for example, Co16Fe64B20. A high perpendicular magnetic anisotropy may be obtained by setting the Fe concentration (atomic %) of the storage layer12to be higher than the Co concentration (atomic %). A high perpendicular magnetic anisotropy would improve the nonvolatile performance of devices, thereby contributing to a decrease in power consumption.

The base layer10is formed of a compound containing nitrogen. For example, the base layer10is formed of a nitride containing at least one of Al, Sc, Y, La, and In. The base layer10of a compound containing nitrogen would suppress the magnetic interaction with a material containing a transition metal such as Fe and Co as a main constituent. Therefore, the storage layer12may have a low Gilbert damping constant.

However, there is a problem in that a storage layer on a nitride layer may have a concave-convex surface. As a result, the Gilbert damping constant of the storage layer on the nitride layer may increase, thereby increasing the write current.FIG. 10shows the result of the magnetic characteristic measurements and the ferromagnetic resonance (FMR) measurements of storage layers, one being on a base layer of AlN, and the other being on a base layer of AlInN. As can be understood fromFIG. 10, the base layer of AlInN results in a better perpendicular magnetic anisotropy than the base layer of AlN, and the width between the peaks of resonant magnetic fields in the FMR measurement is narrower for the base layer of AlInN than for the base layer of AlInN. The width between peaks is dependent on the magnitude of the Gilbert damping constant. Accordingly, the Gilbert damping constant is smaller, and therefore the write current is lower for the base layer of AlInN. The same effect may be obtained for AlScN, AlYN, AlLaN, and ScN. Therefore, the base layer10is preferably formed of AlInN AlScN, AlYN, AlLaN, or ScN. In other words, the base layer10is preferably formed of nitrogen and at least one of Al, Sc, Y, and La. The thickness of the AlInN, AlScN, AlYN, AlLaN, or ScN film is preferably 0.2 nm or more and 2 nm or less as in the first embodiment. As can be understood fromFIG. 10, the ratio of In is preferably lower than the ratio of Al in AlInN, and the ratio of Al is preferably lower than the ratio of Sc, Y, or La in AlScN, AlYN, or AlLaN. This also applies to the first embodiment. The AlInN, AlScN, AlYN, AlLaN, or ScN film may be continuous, or separated by another material.

FIG. 11shows a magnetoresistive element according to a modification of the third embodiment. The magnetoresistive element1G according to the modification is obtained by replacing the base layer10of the magnetoresistive element1F according to the third embodiment shown inFIG. 9with a base layer10d. The base layer10dincludes a first base layer10d1and a second base layer10d2disposed between the first base layer10d1and the storage layer12.

The material of the first base layer10d1is preferably conductive, and may be oxidized to become an insulating material during the re-deposition on the side portions of the tunnel barrier layer (intermediate layer) when the MTJ element is processed. For example, the first base layer10d1is formed of a material containing at least one of Hf, Zr, Al, Be, Mg, Ca, Sr, Ba, Sc, Y, and La.

The second base layer10d2is formed of a compound containing nitrogen, like the base layer10of the third embodiment. For example, the second base layer10d2is formed of a nitride containing at least one of Al, Sc, Y, La, and In. The material of the second base layer10d2is preferably AlInN, AlScN, AlYN, AlLaN, or ScN. The AlInN, AlScN, AlYN, AlLaN, or ScN layer preferably has a thickness of 0.2 nm or more and 2 nm or less as in the first embodiment. The ratio of In is preferably lower than the ratio of Al in the AlInN layer, and the ratio of Al is preferably lower than the ratio of Sc, Y, or La in the AlScN, AlYN, or AlLaN layer. The second base layer10d2of AlInN, AlScN, AlYN, AlLaN, or ScN may be continuous, or separated by another material.

The materials of the intermediate layer (tunnel barrier layer), the reference layer16, and the electrode18of the third embodiment and its modifications are the same as those for the first embodiment.

The third embodiment and its modifications may reduce the write current as in the case of the first embodiment.

A magnetic memory (MRAM) employing a spin transfer torque write method according to a fourth embodiment will be described below.

The MRAM according to the fourth embodiment includes a plurality of memory cells.FIG. 12is a cross-sectional view of a main part of one of the memory cells of the MRAM according to the fourth embodiment. The memory cell includes, as a storage element, a magnetoresistive element according to any of the first to third embodiments and their modifications. In the descriptions of the fourth embodiment, the storage element is the magnetoresistive element (MTJ element)1according to the first embodiment.

As shown inFIG. 12, the top surface of the MTJ element1is connected to a bit line32via an upper electrode31. The lower surface of the MTJ element1is connected to a drain region37aof source/drain regions37aand37bof a semiconductor substrate36via a lower electrode33, an extraction electrode34, and a plug35. The drain region37a, the source region37b, a gate insulating film38formed on the substrate36, and a gate electrode39formed on the gate insulating film38constitute a selection transistor Tr. The selection transistor Tr and the MTJ element1constitute one memory cell of the MRAM. The source region37bis connected to a bit line42via a plug41. The lower electrode33and the plug35may be directly connected to each other without using the extraction electrode34by disposing the plug35below the lower electrode33. Each of the bit lines32and42, the electrodes31and33, the extraction electrode34, and the plugs35and41is formed of such elements as W, Al, AICu, and Cu.

Memory cells each having the structure shown inFIG. 12are arranged in rows and columns to form a memory cell array in the MRAM according to the fourth embodiment.FIG. 13is a circuit diagram showing a main part of the MRAM according to the fourth embodiment.

As shown inFIG. 13, a plurality of memory cells53each including the MTJ element1and the selection transistor Tr are arranged in rows and columns. A first terminal of each of the memory cell53connected to the same column is connected to the same bit line32, and a second terminal is connected to the same bit line42. Gate electrodes (word line)39of the selection transistors Tr of the memory cells53connected to the same row are connected to one another, and are further connected to a row decoder51.

Each of the bit line32is connected to a current source/sink circuit55via a switching circuit54such as a transistor. Each of the bit line42is connected to a current source/sink circuit57via a switching circuit56such as a transistor. The current source/sink circuits55and57supply or extract a write current to or from the bit lines32and42.

Each of the bit line42is connected to a readout circuit52. The readout circuit52may be connected to each of the bit lines32. The readout circuit52includes such circuits as a read current circuit, a sense amplifier, etc.

In a write operation, one of the switching circuits54and one of the switching circuits56connected to the memory cell to be written, and the selection transistor Tr of the memory cell to be written are turned ON to form a current path passing through the memory cell to be written. One of the current source/sink circuits55and57serves as a current source circuit, and the other serves as a current sink circuit depending on the data to be written. As a result, a write current flows in a direction determined by the data to be written.

With respect to the writing speed, the spin transfer torque writing may be performed with a current having a pulse width of a few nanoseconds to a few microseconds.

In a read operation, a read current that is satisfactorily low not to cause magnetization switching in the designated MTJ element1is supplied from a read current circuit in the same manner as the write operation. The readout circuit52determines the resistance state of the MTJ element1by comparing, with a reference value, a current value or a voltage value of the MTJ element1resulting from a resistance value obtained from the magnetization state.

The current pulse width in the read operation is preferably narrower than the current pulse width in the write operation because this may reduce the possibility of erroneous writing caused by the read current. This is based on the fact that a narrower pulse width of a write current leads to a greater absolute value thereof.

As described above, a magnetic memory including a magnetoresistive element capable of reducing a write current may be obtained according to the fourth embodiment.