JP5387908B2 - Magnetic device and magnetic random access memory - Google Patents

Description

  This application claims the priority on the basis of the Japan patent application 2007-036441 for which it applied on February 23, 2007, and takes in those the indications of all here.

  The present invention relates to a magnetic device and a magnetic random access memory. In particular, the present invention relates to a magnetic device and a magnetic random access memory having a magnetic layer whose magnetization direction is fixed by an antiferromagnetic layer.

  Magnetic random access memories (MRAM), magnetic sensors, magnetic heads, and the like are known as magnetic devices that use a magnetic layer to realize a predetermined function. Among these, the MRAM is a nonvolatile memory using a magnetoresistive element as a memory cell. Known magnetoresistive elements include GMR (Giant Magneto-Resistive) elements and TMR (Tunnel Magneto-Resistive) elements.

FIG. 1 shows non-patent literature (Roy Scheuerlein et al., “A 10ns Read and Write Non-Volatile Memory Array Using a Magnetic Tunnel Junction and FET Switch in each Cell”, 2000 IEEE International Solid-State Circuits Conference, DIGEST OF TECHNICAL. PAPERS, pp. 128-129) shows the structure of the TMR element 100. In FIG. 1, a TMR element 100 includes an antiferromagnetic layer 101 (FeMn: 10 nm), a pinned layer 102 (CoFe: 2.4 nm) that is a ferromagnetic layer, a tunnel insulating layer 103 (Al ₂ O ₃ ), and A free layer 104 (NiFe: 5 nm) which is a ferromagnetic layer is provided. The thin tunnel insulating layer 103 is sandwiched between the pinned layer 102 and the free layer 104.

  The pinned layer 102 is formed on the antiferromagnetic material layer 101, and the magnetization direction is fixed in a certain direction by the antiferromagnetic material layer 101. On the other hand, the magnetization direction of the free layer 104 is stabilized in a state parallel or antiparallel to the magnetization direction of the pinned layer 102. Specifically, the free layer 104 is formed so that the easy axis of magnetization is substantially parallel to the magnetization direction of the pinned layer 102, and the magnetization direction of the free layer 104 is reversed by applying an external magnetic field. Is possible.

  Such a resistance value of the TMR element 100 depends on the relationship between the magnetization directions of the pinned layer 102 and the free layer 104. That is, the resistance value (R + ΔR) when the magnetization direction of the pinned layer 102 and the magnetization direction of the free layer 104 are antiparallel is larger than the resistance value (R) when they are parallel. The TMR element 100 stores data by utilizing the change in the resistance value. At the time of data writing, an external magnetic field is applied so that the magnetization of the free layer 104 is oriented in a desired direction. On the other hand, at the time of data reading, a voltage is applied between the pinned layer 102 and the free layer 104, and a read current flows through the tunnel insulating layer 103. Based on the magnitude of the read current, the resistance value of the TMR element 100, that is, the data stored in the TMR element 100 is sensed.

  FIG. 2 is described in non-patent literature (M. Durlam et al., “Nonvolatile RAM based on Magnetic Tunnel Junction Elements”, 2000 IEEE International Solid-State Circuits Conference, DIGEST OF TECHNICAL PAPERS, pp. 130-131). The wiring structure of the MRAM is shown. In FIG. 2, TMR elements 100 are arranged in an array. Upper wirings (B1, B2) and lower wirings (D1, D2, D3) intersecting with each other are provided above and below each TMR element 100. The free layer of the TMR element 100 is connected to the upper wiring, and the antiferromagnetic material layer is connected to the ground via the selection transistor TR. The read word lines (W1, W2, W3) are connected to the gate terminal of the selection transistor TR. At the time of data writing, a write current is passed through one intersecting upper wiring and one lower wiring. As a result, a synthetic magnetic field generated by the write current is applied to the TMR element 100 disposed at the intersection. At the time of data reading, the selection transistor TR connected to the target TMR element 100 is turned on, and a read current flows from the upper wiring to the ground through the TMR element 100.

  When a single-layer pinned layer is used as shown in FIG. 1, the “leakage magnetic field” that leaks from the end of the pinned layer affects the device characteristics. In order to suppress the leakage magnetic field from the pinned layer, a technique is known in which the pinned layer is formed of two ferromagnetic layers that are antiferromagnetically coupled with a nonmagnetic layer interposed therebetween. FIG. 3 shows a structural example of a TMR element having such a pinned layer. In FIG. 3, a pinned layer 202 is formed on the antiferromagnetic material layer 201, and a free layer 204 is formed on the pinned layer 202 via a tunnel insulating layer 203. The pinned layer 202 includes ferromagnetic layers 211 and 212 and a nonmagnetic layer 213 sandwiched between them. The ferromagnetic layers 211 and 212 are antiferromagnetically coupled to each other with the nonmagnetic layer 213 interposed therebetween, and their magnetization directions are opposite to each other. Thereby, the leakage magnetic fields of the ferromagnetic layers 211 and 212 are canceled to some extent.

  In order to cancel the leakage magnetic field as much as possible, the magnetization amount M1 of the ferromagnetic layer 211 and the magnetization amount M2 of the ferromagnetic layer 212 are designed to be substantially the same. Here, the leakage magnetic field of the ferromagnetic layer 212 includes not only a component toward the ferromagnetic layer 211 but also a component toward the free layer 204. As the amount of magnetization M2 increases, the component toward the free layer 204 also increases, which has a strong effect on element characteristics. Therefore, it is desirable that the magnetization amounts M1 and M2 are designed to be small as long as a desired function is not lost. That is, from the viewpoint of reducing the leakage magnetic field, the ferromagnetic layers 211 and 212 of the pinned layer 202 are preferably as thin as possible.

  The following are known as other related techniques related to the magnetic device.

  Japanese Patent Application Laid-Open No. 2005-85951 discloses a magnetic memory element. The magnetic storage element has a storage layer that holds information according to the magnetization state of the magnetic material, and an auxiliary magnetic layer whose magnetization state changes due to an external magnetic field. The auxiliary magnetic layer is composed of a plurality of magnetic layers divided by a nonmagnetic layer. Adjacent magnetic layers of the auxiliary magnetic layer are coupled by magnetic interaction that magnetizes in antiparallel. The sum of the magnetization amounts of the even-numbered magnetic layers of the auxiliary magnetic layer is substantially equal to the sum of the magnetization amounts of the odd-numbered magnetic layers of the auxiliary magnetic layer.

  Japanese Patent Application Laid-Open No. 2005-223086 describes a magnetic memory element. The magnetic memory element has a memory layer that holds information according to the magnetization state of the magnetic material. The storage layer is composed of at least two magnetic layers and a nonmagnetic layer therebetween. One of the two magnetic layers has a larger product of the damping constant of magnetization, the amount of magnetization, and the magnetic anisotropy than the other magnetic layer, and the product of the amount of magnetization and the magnetic anisotropy. small.

  JP-T-2005-525665 discloses a perpendicular magnetic recording head. The perpendicular magnetic recording head includes a multilayer main write pole. The main write pole includes a first material layer, a second material layer, and an intermediate layer located between the first material layer and the second material layer. The second material layer has a saturation magnetic moment that is greater than the saturation magnetic moment of the first material layer.

  As described with reference to FIG. 3, it is preferable to make both the ferromagnetic layers 211 and 212 of the pinned layer 202 thin from the viewpoint of reducing the leakage magnetic field. Here, the inventor of the present application paid attention to the following points.

  In the manufacturing process of the magnetic device, it is necessary to frequently perform high-temperature heat treatment. For example, high-temperature heat treatment is performed to make transistor characteristics uniform. Further, high-temperature heat treatment is also performed after the wiring is formed. When such high temperature heat treatment is performed, the elements contained in the antiferromagnetic material layer 201 are diffused into the pinned layer 202. The antiferromagnetic material layer 201 is generally formed of FeMn, PtMn, or IrMn. In particular, Mn contained in the antiferromagnetic material layer 201 diffuses into the pinned layer 202. At this time, if the ferromagnetic layer 211 of the pinned layer 202 is thin, Mn from the antiferromagnetic layer 201 easily reaches the nonmagnetic layer 213. When Mn reaches the nonmagnetic layer 213, the antiferromagnetic coupling in the pinned layer 202 is weakened and the characteristics are deteriorated. In some cases, normal device operation may not be obtained. Thus, as the ferromagnetic layer in the pinned layer is made thinner, the yield may be reduced by Mn diffusion.

  One object of the present invention is to provide a technique capable of preventing characteristic deterioration due to high-temperature heat treatment while suppressing a leakage magnetic field from a pinned layer.

  In one embodiment of the present invention, a magnetic device includes an antiferromagnetic layer and a pinned layer formed on the antiferromagnetic layer. The pinned layer has a stacked structure in which a plurality of magnetic layers and at least one nonmagnetic layer are alternately stacked. Two magnetic layers adjacent to each other across a certain nonmagnetic layer among the plurality of magnetic layers are ferromagnetically coupled or antiferromagnetically coupled to each other. The sum total of the magnetization amounts of the plurality of magnetic layers is zero. The plurality of magnetic layers in the pinned layer include a first magnetic layer in contact with the antiferromagnetic layer and a second magnetic layer located farthest from the antiferromagnetic layer. The thickness of the second magnetic layer is smaller than the thickness of the first magnetic layer.

  In one embodiment of the present invention, a magnetic device includes an antiferromagnetic layer and a pinned layer formed on the antiferromagnetic layer. The pinned layer has a stacked structure in which a plurality of magnetic layers and at least one nonmagnetic layer are alternately stacked. Two magnetic layers adjacent to each other across a certain nonmagnetic layer among the plurality of magnetic layers are ferromagnetically coupled or antiferromagnetically coupled to each other. The sum total of the magnetization amounts of the plurality of magnetic layers is zero. The plurality of magnetic layers in the pinned layer include a first magnetic layer in contact with the antiferromagnetic layer and a second magnetic layer located farthest from the antiferromagnetic layer. The magnetization amount of the second magnetic layer is smaller than the magnetization amount of the first magnetic layer.

  In one embodiment of the present invention, a magnetic random access memory in which a plurality of magnetoresistive elements are arranged in an array is provided. Each of the plurality of magnetoresistive elements is formed on an antiferromagnetic layer, a pinned layer formed on the antiferromagnetic layer, a nonmagnetic spacer layer formed on the pinned layer, and a nonmagnetic spacer layer A free layer including a ferromagnetic layer formed. The pinned layer has a stacked structure in which a plurality of magnetic layers and at least one nonmagnetic layer are alternately stacked. Two magnetic layers adjacent to each other across a nonmagnetic layer among the plurality of magnetic layers are ferromagnetically coupled or antiferromagnetically coupled to each other. The sum total of the magnetization amounts of the plurality of magnetic layers is zero. The plurality of magnetic layers in the pinned layer include a first magnetic layer in contact with the antiferromagnetic layer and a second magnetic layer in contact with the nonmagnetic spacer layer. The thickness of the second magnetic layer is smaller than the thickness of the first magnetic layer. The magnetization directions of the plurality of magnetic layers of the pinned layer are fixed, and the magnetization direction of the ferromagnetic layer of the free layer is parallel or antiparallel to the magnetization direction of the second magnetic layer. It is allowed.

  According to the present invention, it is possible to achieve both suppression of the leakage magnetic field and maintenance of antiferromagnetic coupling in the pinned layer. That is, it is possible to avoid characteristic deterioration due to high-temperature heat treatment while suppressing the leakage magnetic field from the pinned layer.

  The above and other objects, advantages, and features will become apparent from the embodiments of the present invention described in conjunction with the following drawings.

FIG. 1 is a side view schematically showing the structure of a TMR element in the related art. FIG. 2 is a perspective view schematically showing a configuration of the MRAM using the TMR element shown in FIG. FIG. 3 is a side view schematically showing a structure of a TMR element in another related technology. FIG. 4 is a side view schematically showing the structure of the magnetic device according to the first embodiment of the present invention. FIG. 5 is a plan view showing the structure shown in FIG. FIG. 6 is a side view showing an example of the magnetoresistive element according to the first exemplary embodiment of the present invention. FIG. 7 is a circuit block diagram showing an example of the configuration of the MRAM according to the present invention. FIG. 8 is a diagram for explaining reading and writing of data to the magnetoresistive element. FIG. 9 is a side view showing another example of the magnetoresistive element according to the first exemplary embodiment of the present invention. FIG. 10 is a side view schematically showing the structure of the magnetic device according to the second embodiment of the present invention. FIG. 11 is a side view showing an example of the magnetoresistance element according to the second exemplary embodiment of the present invention.

  A magnetic device, a magnetoresistive element, and an MRAM according to an embodiment of the present invention will be described with reference to the accompanying drawings.

1. 1. First embodiment 1-1. Basic Structure FIG. 4 is a side view schematically showing the structure of the magnetic device according to the first embodiment of the present invention. FIG. 5 is a plan view showing the structure shown in FIG. The magnetic device includes an antiferromagnetic material layer 1, a pinned layer 2 including a magnetic material layer, and a functional layer 5. The pinned layer 2 is formed on the antiferromagnetic layer 1, and the magnetization direction is fixed by the antiferromagnetic layer 1. The functional layer 5 is formed on the pinned layer 2 and realizes a predetermined function together with the pinned layer 2.

  In the present embodiment, the pinned layer 2 has a stacked structure in which a plurality of magnetic layers 3 and at least one nonmagnetic layer 4 are alternately stacked. The stacking direction is the Z direction, and each layer is formed in parallel to the XY plane perpendicular to the Z direction. The plurality of magnetic layers 3 include a first magnetic layer 3-1 in contact with the antiferromagnetic layer 1 and a second magnetic layer 3-2 in contact with the functional layer 5. That is, of the plurality of magnetic layers 3, the second magnetic layer 3-2 is the magnetic layer that is located farthest from the antiferromagnetic layer 1 in the Z direction and is closest to the functional layer 5.

  In such a laminated structure, two magnetic layers 3 adjacent to each other with a nonmagnetic layer 4 interposed therebetween are ferromagnetically coupled or antiferromagnetically coupled to each other. For example, in FIG. 4, a magnetic layer 3-3 is formed on the first magnetic layer 3-1 via a non-magnetic layer 4-1, and the first magnetic layer 3-1 and the magnetic layer 3-1 are magnetic. The body layer 3-3 is antiferromagnetically coupled through the nonmagnetic body layer 4-1. The magnetization direction of the first magnetic layer 3-1 is the + X direction, and the magnetization direction of the magnetic layer 3-3 is the -X direction. Further, the second magnetic layer 3-2 is formed on the magnetic layer 3-4 via the nonmagnetic layer 4-2, and the second magnetic layer 3-2 and the magnetic layer 3- 4 is ferromagnetically coupled through the nonmagnetic layer 4-2. The magnetization direction of the second magnetic layer 3-2 and the magnetic layer 3-4 is the -X direction.

  In the present embodiment, the total sum of the magnetization amounts of all the magnetic layers 3 included in the pinned layer 2 is zero. Accordingly, the pinned layer 2 always includes at least one set of magnetic layers 3 that are antiferromagnetically coupled to each other via a certain nonmagnetic layer 4. For example, the magnetic layers 3-5 and 3-6 in FIG. 4 are antiferromagnetically coupled to each other via the nonmagnetic layer 4-3. As described above, the first magnetic layer 3-1 and the magnetic layer 3-3 are antiferromagnetically coupled via the nonmagnetic layer 4-1. Thus, the magnetization of each magnetic layer 3 is fixed in the + X direction or the −X direction, and the total amount of magnetization is zero. In other words, the total amount of magnetization fixed in the + X direction is equal to the total amount of magnetization fixed in the −X direction.

  Furthermore, according to the present embodiment, the thickness T2 of the second magnetic layer 3-2 is smaller than the thickness T1 of the first magnetic layer 3-1. Preferably, the effective thickness of the second magnetic layer 3-2 (thickness that functions as a magnetic material) is smaller than the effective thickness of the first magnetic layer 3-1.

  Further, according to the present embodiment, the magnetization amount M2 of the second magnetic layer 3-2 is smaller than the magnetization amount M1 of the first magnetic layer 3-1. That is, unlike the structure shown in FIG. 3, the magnetization amount M1 of the first magnetic layer 3-1 and the magnetization amount M2 of the second magnetic layer 3-2 are not the same. Since the pinned layer 2 includes the magnetic layer 3 other than the first magnetic layer 3-1 and the second magnetic layer 3-2, the amount of magnetization M2 while making the total amount of magnetization of the pinned layer 2 zero. Can be made smaller than the amount of magnetization M1.

  As described above, according to the present embodiment, the thickness T2 and the magnetization M2 of the second magnetic layer 3-2 are made as small as possible, while the thickness of the first magnetic layer 3-1 is reduced. It becomes possible to design T1 and the amount of magnetization M1 large. The effects obtained by the magnetic device configured as described above are as follows.

  First, it becomes possible to prevent deterioration of characteristics due to high-temperature heat treatment. That is, the thickness T1 of the first magnetic layer 3-1 in contact with the antiferromagnetic layer 1 can be designed to be relatively large without depending on the thickness T2 of the second magnetic layer 3-2. Because. In that case, the element diffusing from the antiferromagnetic material layer 1 by the high-temperature heat treatment becomes difficult to reach the nonmagnetic material layer 4 in the pinned layer 2. As a result, weakening of the antiferromagnetic coupling in the pinned layer 2 is prevented. That is, characteristic deterioration due to high-temperature heat treatment is prevented, and yield is improved.

  Further, since the total sum of the magnetization amounts of all the magnetic layers 3 included in the pinned layer 2 is zero, the leakage magnetic field from the pinned layer 2 is suppressed. Furthermore, the thickness T2 of the second magnetic layer 3-2 does not depend on the thickness T1 of the first magnetic layer 3-1, and is designed to be relatively small. That is, the magnetization amount M2 of the second magnetic layer 3-2 closest to the functional layer 5 is designed to be small regardless of the magnetization amount M1 of the first magnetic layer 3-1. Thereby, the leakage magnetic field applied to the functional layer 5 is sufficiently reduced. That is, it is possible to sufficiently reduce the influence of the leakage magnetic field from the pinned layer 2 on the element characteristics and to reduce the variation in the operation characteristics. From this viewpoint, it is preferable that the thickness T2 of the second magnetic layer 3-2 is the smallest among the magnetic layers 3 of the pinned layer 2. Further, it is preferable that the magnetization M2 of the second magnetic layer 3-2 is the smallest among the magnetic layers 3 of the pinned layer 2.

  As described above, according to the present embodiment, it is possible to achieve both suppression of the leakage magnetic field and maintenance of antiferromagnetic coupling in the pinned layer 2. That is, it is possible to avoid characteristic deterioration due to high-temperature heat treatment while suppressing the leakage magnetic field from the pinned layer 2.

  The present embodiment is applied to, for example, a magnetoresistive element such as a GMR (Giant Magneto-Resistive) element or a TMR (Tunnel Magneto-Resistive) element, and an MRAM using the magnetoresistive element as a memory cell. Hereinafter, application examples of the present embodiment will be described in detail.

1-2. Application example: GMR element (Structure)
FIG. 6 is a side view showing an example of the magnetoresistive element (GMR element) 10 to which the present exemplary embodiment is applied. The magnetoresistive element 10 includes a lower electrode 11 (Ta: 20 nm), a seed layer 12 (NiFe: 1 nm), an antiferromagnetic layer 13 (PtMn: 20 nm), a pinned layer 2, and the like stacked in order on a semiconductor substrate. The functional layer 5 and the upper electrode 14 (Ta: 30 nm) are included. The antiferromagnetic material layer 13 corresponds to the antiferromagnetic material layer 1 in FIG.

  The pinned layer 2 is laminated in order on the antiferromagnetic material layer 13. The CoFe film 21 (2 nm), the Ru film 22 (0.8 nm), the CoFe film 23 (2 nm), and the Ru film 24 (0.8 nm). CoFe film 25 (1 nm), Ru film 26 (0.8 nm), and CoFe film 27 (1 nm). The CoFe film 21 and the CoFe film 23 are antiferromagnetically coupled via the Ru film 22. The CoFe film 23 and the CoFe film 25 are antiferromagnetically coupled via the Ru film 24. The CoFe film 25 and the CoFe film 27 are antiferromagnetically coupled via the Ru film 26. The total amount of magnetization of the CoFe films 21, 23, 25, and 27 is zero.

  Of the pinned layer 2, the CoFe film 21 (2 nm) and the CoFe film 27 (1 nm) correspond to the first magnetic layer 3-1 and the second magnetic layer 3-2 in FIG. The thickness of the CoFe film 27 is smaller than the thickness of the CoFe film 21. The CoFe film 27 and the CoFe film 21 are formed of the same material, and the magnetization amount M2 of the CoFe film 27 is smaller than the magnetization amount M1 of the CoFe film 21. As a result, the above-described effect can be obtained.

  The functional layer 5 includes a Cu film 30 (2.5 nm) formed on the CoFe film 27 of the pinned layer 2 and a NiFe film 31 (4 nm) formed on the Cu film 30. The NiFe film 31 that is a ferromagnetic film serves as a free layer of the magnetoresistive element 10. Further, the Cu film 30 that is a non-magnetic material sandwiched between the free layer 31 and the pinned layer 2 serves as a spacer layer of the magnetoresistive element 10. The magnetization direction of the free layer 31 is allowed to be parallel or antiparallel to the magnetization direction of the CoFe film 27 (second magnetic layer) of the pinned layer 2. The resistance value of the magnetoresistive element 10 changes depending on the relationship between the magnetization directions of the free layer 31 and the CoFe film 27. Thus, the functional layer 5 implements the magnetoresistive element 10 together with the pinned layer 2.

(Production method)
The manufacturing method of the magnetoresistive element 10 shown in FIG. 6 is as follows. First, the above films 11 to 13, 21 to 27, 30 to 31, and 14 are sequentially formed on a semiconductor substrate by a sputtering method. The film thickness of each of the Ru films 22, 24, and 26 is set to a film thickness (for example, 0.8 nm) that realizes antiferromagnetic coupling. Thereafter, each of the lower electrode 11, the seed layer 12, the antiferromagnetic layer 13, the pinned layer 2, the nonmagnetic spacer layer 30, the free layer 31, and the upper electrode 14 is patterned by photolithography.

  Next, the magnetic field application step is performed at a temperature higher than the blocking temperature of the antiferromagnetic material layer 13. For example, a magnetic field of about 1000 to 10000 Oe is applied in a high temperature environment of 250 ° C. to 300 ° C. The direction of the applied magnetic field is the long side direction (easy magnetization direction) of the pattern of the free layer 31. As a result, the magnetizations of the CoFe films 21, 23, 25, and 27 in the pinned layer 2 are directed in the direction along the applied magnetic field. Next, after the temperature is lowered, the application of the magnetic field is stopped. At this time, since the CoFe film 21 is antiferromagnetically coupled to the antiferromagnetic layer 13, the magnetization of the CoFe film 21 is fixed in the direction of the applied magnetic field. Since the CoFe film 23 is antiferromagnetically coupled to the CoFe film 21, the magnetization of the CoFe film 23 is fixed in the opposite direction to the magnetization of the CoFe film 21. Similarly, the magnetization of the CoFe film 25 is fixed in the opposite direction to the magnetization of the CoFe film 23, and the magnetization of the CoFe film 27 is fixed in the opposite direction to the magnetization of the CoFe film 25. In this way, the magnetization direction of the magnetic layer of the pinned layer 2 is fixed in a desired direction.

(Circuit configuration)
FIG. 7 shows an example of the configuration of an MRAM 80 that uses the magnetoresistive element 10 described above as a memory cell. In the MRAM 80, a plurality of word lines WL1 to WL3 and a plurality of bit lines BL1 to BL3 are provided so as to intersect each other. The word lines WL1 to WL3 are connected to the word line control circuit 81 and the word line termination circuit 82. On the other hand, the bit lines BL1 to BL3 are connected to a bit line control circuit 83 and a bit line termination circuit 84.

  A plurality of magnetoresistive elements 10 are arranged in an array at each intersection of the word line WL and the bit line BL. For example, the upper electrode 14 of one magnetoresistive element 10 is connected to a certain bit line BL, and the lower electrode 11 is connected to the ground via a selection transistor 85. The gate terminal of the selection transistor 85 is connected to the read control circuit 86. The bit line control circuit 83 is connected to a sense amplifier 87 that compares the reference potential Vref and the bit line potential to perform data discrimination.

(Operation)
FIG. 8 shows one magnetoresistive element (magnetic memory cell) 10, one word line WL, and one bit line BL. The word line WL and the bit line BL cross each other and are formed so as to sandwich the magnetoresistive element 10 therebetween. One select transistor 85 is provided for one magnetoresistive element 10. Data writing and data reading with respect to the magnetic memory cell 10 will be described with reference to FIGS.

At the time of data writing, the word line control circuit 81 causes a write current _IWL to flow through one word line WL, and the bit line control circuit 83 causes a write current _IBL to flow through one bit line BL. A combined magnetic field generated by the write currents I _WL and I _BL is applied to the magnetoresistive element 10 disposed at the intersection. As a result, the magnetization direction of the free layer 31 of the magnetoresistive element 10 is oriented in a desired direction.

  When reading data, the read control circuit 86 turns on the selection transistor 85 connected to the magnetoresistive element 10 to be read. The bit line termination circuit 84 is set in an open state, and the bit line control circuit 83 applies a predetermined voltage to the bit line BL connected to the magnetoresistive element 10 to be read. As a result, the read current flows from the bit line control circuit 83 to the ground through the bit line BL, the magnetoresistive element 10, and the selection transistor 85. The magnitude of this read current depends on the resistance value of the magnetoresistive element 10. The bit line control circuit 83 converts this read current into a potential value (bit line potential) and outputs it to the sense amplifier 87. The sense amplifier 87 senses the resistance value of the magnetoresistive element 10, that is, data, by comparing the bit line potential with the reference potential Vref.

1-3. Application example: TMR element (Structure)
FIG. 9 is a side view showing an example of a magnetoresistive element (TMR element) 10 to which the present exemplary embodiment is applied. The magnetoresistive element 10 includes a lower electrode 11 (Ta: 10 nm), a seed layer 12 (NiFe: 1 nm), an antiferromagnetic material layer 13 (PtMn: 20 nm), a pinned layer 2, and the like stacked in order on a semiconductor substrate. The functional layer 5 and the upper electrode 14 (Ta: 30 nm) are included. The antiferromagnetic material layer 13 corresponds to the antiferromagnetic material layer 1 in FIG.

  The pinned layer 2 is laminated on the antiferromagnetic layer 13 in order, the CoFe film 41 (1.4 nm), the Ru film 42 (0.9 nm), the CoFe film 43 (2.4 nm), and the Ru film 44 ( 0.9 nm) and a CoFe film 45 (1 nm). The CoFe film 41 and the CoFe film 43 are antiferromagnetically coupled via the Ru film 42. The CoFe film 43 and the CoFe film 45 are antiferromagnetically coupled via the Ru film 44. The total amount of magnetization of the CoFe films 41, 43, and 45 is zero.

  Of the pinned layer 2, the CoFe film 41 (1.4 nm) and the CoFe film 45 (1 nm) correspond to the first magnetic layer 3-1 and the second magnetic layer 3-2 in FIG. The thickness of the CoFe film 45 is smaller than the thickness of the CoFe film 41. The CoFe film 41 and the CoFe film 45 are formed of the same material, and the magnetization amount M2 of the CoFe film 45 is smaller than the magnetization amount M1 of the CoFe film 41. As a result, the above-described effect can be obtained.

  The functional layer 5 includes an AlO film 50 (0.86 nm) formed on the CoFe film 45 of the pinned layer 2. The AlO film 50 is a tunnel insulating layer of the TMR element 10 and plays a role as a nonmagnetic spacer layer.

  The functional layer 5 includes a NiFe film 51 (3.1 nm), a Ta film 52 (0.3 nm), a NiFe film 53 (3 nm), and a Ru film 54 (2.1 nm) that are sequentially formed on the tunnel insulating layer 50. ), A NiFe film 55 (3.1 nm), a Ta film 56 (0.3 nm), and a NiFe film 57 (3 nm). The NiFe film 51 and the NiFe film 53 are ferromagnetically coupled via the Ta film 52. The NiFe film 53 and the NiFe film 55 are antiferromagnetically coupled via the Ru film 54. The NiFe film 55 and the NiFe film 57 are ferromagnetically coupled via the Ta film 56. The laminated structure of the ferromagnetic film and the nonmagnetic film plays a role as a free layer of the TMR element 10.

  FIG. 9 shows the state of data “1” and the state of data “0”. Data “1” is associated with a state in which the magnetization direction is antiparallel in the NiFe film 51 of the free layer and the CoFe film 45 of the pinned layer 2 sandwiching the tunnel insulating layer 50. On the other hand, data “0” is associated with the NiFe film 51 and the CoFe film 45 in a state in which the magnetization directions are parallel. As shown in FIG. 9, the magnetizations of the ferromagnetic films 51, 53, 55, and 57 in the free layer are entirely reversed between data “1” and “0”. Thus, the functional layer 5 realizes the TMR element 10 together with the pinned layer 2. The TMR element 10 is used particularly in a toggle operation type MRAM.

  The manufacturing method of the magnetoresistive element 10 shown in FIG. 9 is the same as the method described in Section 1-2. However, in the case of the toggle operation type MRAM, the TMR element 10 is formed so that the easy axis of magnetization of the free layer is inclined 45 degrees from the extending direction of the word line.

(Circuit configuration and operation)
The circuit configuration of the MRAM is the same as the configuration shown in FIGS. The data reading method is the same as the method described in Section 1-2.

The data writing method in the case of the toggle operation type is as follows. First, supply of the write current I _BL (5 mA) to the bit line BL is started. Next, supply of the write current I _WL (5 mA) to the word line WL is started. Next, the supply of the write current _{I BL} to the bit line BL is stopped. Finally, the supply of the write current _{I WL} for the word line WL is stopped. By such a write current supply procedure, the magnetization of the free layer is reversed like a toggle switch. Since the magnetization of the free layer is inverted every time the write operation is performed, the read operation is performed before the write operation, and the write operation is performed only when the read data is different from the write data.

The inventor of the present application evaluated the variations in the write currents I _WL and I _BL with respect to the TMR element 10 having the above structure through experiments. In that experiment, a memory cell array of 2 cells × 4 cells was created. The planar shape of the free layer was an ellipse having a major axis of 0.80 μm and a minor axis of 0.32 μm. As a comparative example, a TMR element including a pinned layer having a CoFe (2.6 nm) / Ru (0.9 nm) / CoFe (2.8 nm) structure (hereinafter referred to as a comparative structure) instead of the present structure is also prepared. It was done. In the case of the comparative structure, the variations in the write currents I _BL and I _WL were 7.6% and 9.2%, respectively. On the other hand, in the case of this structure, the variations in the write currents I _BL and I _WL were 7.4% and 8.3%. That is, the variation in write current was improved. As described above, according to the present embodiment, the thickness T2 of the second magnetic layer 3-2 can be reduced as much as possible, so that the characteristic variation is reduced.

2. Second embodiment 2-1. Basic Structure A device for making the thickness T1 of the first magnetic layer 3-1 relatively large while minimizing the thickness T2 of the second magnetic layer 3-2 will be described in the first embodiment. It is not limited to what was done. For example, it is conceivable to use a material having a small magnetic moment as at least a part of the material of the first magnetic layer 3-1. Thereby, even if it is the same magnetization amount M1, it becomes possible to make comparatively large thickness T1 of the 1st magnetic body layer 3-1.

  FIG. 10 is a side view schematically showing the structure of the magnetic device according to the second embodiment of the present invention. The same components as those in the first embodiment are denoted by the same reference numerals, and redundant descriptions are omitted as appropriate.

  In FIG. 10, the magnetic device includes an antiferromagnetic material layer 1, a pinned layer 2, and a functional layer 5. The pinned layer 2 has a stacked structure in which a plurality of magnetic layers 3 and at least one nonmagnetic layer 4 are alternately stacked. The plurality of magnetic layers 3 include a first magnetic layer 3-1 in contact with the antiferromagnetic layer 1 and a second magnetic layer 3-2 in contact with the functional layer 5. Two magnetic layers 3 adjacent to each other with a certain nonmagnetic layer 4 interposed therebetween are ferromagnetically coupled or antiferromagnetically coupled to each other. In addition, the total amount of magnetization of all the magnetic layers 3 included in the pinned layer 2 is zero.

  According to the present embodiment, at least a part of the first magnetic layer 3-1 is formed of a material whose magnetic moment is smaller than that of the second magnetic layer 3-2. For example, in FIG. 10, the first magnetic layer 3-1 includes a magnetic layer 3-1A and a magnetic layer 3-1B. The material of the magnetic layer 3-1A is the same as the material of the second magnetic layer 3-2. On the other hand, the magnetic moment of the material of the magnetic layer 3-1B is smaller than that of the material of the second magnetic layer 3-2. As a result, the thickness T1 of the first magnetic layer 3-1 is larger than the thickness T2 of the second magnetic layer 3-2. Preferably, the effective thickness of the first magnetic layer 3-1 is larger than the effective thickness of the second magnetic layer 3-2.

  As described above, according to the present embodiment, the thickness T2 and the magnetization amount M2 of the second magnetic layer 3-2 are made as small as possible, while the thickness T1 of the first magnetic layer 3-1 is relatively reduced. Large design is possible. As a result, the same effect as the first embodiment can be obtained. The magnetization amount M2 of the second magnetic layer 3-2 is preferably as small as possible, but the magnetization amount M1 of the first magnetic layer 3-1 does not necessarily need to be greater than the magnetization amount M2. It is only necessary that the total amount of magnetization of all the magnetic layers 3 included in the pinned layer 2 is zero.

2-2. Application Example: TMR Element FIG. 11 is a side view showing an example of a magnetoresistive element (TMR element) 10 to which the present exemplary embodiment is applied. The magnetoresistive element 10 includes a lower electrode 11 (Ta: 20 nm), a seed layer 12 (NiFe: 1 nm), an antiferromagnetic layer 13 (PtMn: 20 nm), a pinned layer 2, and the like stacked in order on a semiconductor substrate. The functional layer 5 and the upper electrode 14 (Ta: 30 nm) are included. The antiferromagnetic material layer 13 corresponds to the antiferromagnetic material layer 1 in FIG.

  The pinned layer 2 is sequentially stacked on the antiferromagnetic material layer 13 and includes a CoFe film 61 (0.5 nm), a NiFe film 62 (1.5 nm), a Ru film 63 (0.8 nm), and a CoFe film 64. (1.2 nm). Of these, the CoFe film 61 and the NiFe film 62 correspond to the magnetic layers 3-1A and 3-1B in FIG. 10, respectively. Therefore, the thickness T1 of the first magnetic layer 3-1 is 2.0 nm. On the other hand, the CoFe film 64 corresponds to the second magnetic layer 3-2 in FIG. The thickness T2 of the second magnetic layer 3-2 (CoFe film 64) is smaller than the thickness T1 of the first magnetic layer (CoFe film 61, NiFe film 62). The first magnetic layer 3-1 and the second magnetic layer 3-2 are antiferromagnetically coupled via the Ru film 63, and the magnetization amount M2 of the second magnetic layer 3-2 is the first magnetic layer. It is the same as the magnetization amount M1 of 3-1. Accordingly, the sum of the magnetization amounts of all the magnetic layers 3 included in the pinned layer 2 is zero. With such a structure, the above-described effects can be obtained.

  The functional layer 5 includes an MgO film 70 (1.5 nm) formed on the CoFe film 64 of the pinned layer 2 and a NiFe film 71 (4 nm) formed on the MgO film 70. The NiFe film 71 that is a ferromagnetic film serves as a free layer of the TMR element 10. The MgO film 70 sandwiched between the free layer 71 and the pinned layer 2 is a tunnel insulating layer of the TMR element 10 and plays a role as a nonmagnetic spacer layer. The magnetization direction of the free layer 71 is allowed to be parallel or antiparallel to the magnetization direction of the CoFe film 64 (second magnetic layer) of the pinned layer 2. The resistance value of the TMR element 10 changes depending on the relationship between the magnetization directions of the free layer 71 and the CoFe film 64. Thus, the functional layer 5 realizes the TMR element 10 together with the pinned layer 2.

  The manufacturing method of the TMR element 10 shown in FIG. 11 is the same as the method described in the first embodiment. Further, the circuit configuration of the MRAM using the TMR element 10 as a memory cell is the same as the configuration shown in the first embodiment (see FIGS. 7 and 8). Further, the data writing method and the data reading method are the same as those described in the first embodiment.

  The present invention can be applied to magnetoresistive elements such as GMR elements and TMR elements, and MRAMs using the magnetoresistive elements as memory cells. The MRAM may be an asteroid system or a toggle operation system. The present invention can also be applied to a spin injection MRAM. The present invention can be applied to any magnetic device having a magnetic layer whose magnetization direction is fixed by an antiferromagnetic material layer.

  The embodiments of the present invention have been described above with reference to the accompanying drawings. However, the present invention is not limited to the above-described embodiments, and can be appropriately changed by those skilled in the art without departing from the scope of the invention.

Claims (10)

An antiferromagnetic layer,
A pinned layer formed on the antiferromagnetic material layer,
The pinned layer has a stacked structure in which a plurality of magnetic layers and at least one nonmagnetic layer are alternately stacked, and two adjacent layers sandwiching a nonmagnetic layer among the plurality of magnetic layers. The two magnetic layers are antiferromagnetically coupled to each other,
The total amount of magnetization of the plurality of magnetic layers is zero,
The plurality of magnetic layers are
A first magnetic layer in contact with the antiferromagnetic layer;
A second magnetic layer that is located farthest from the antiferromagnetic layer and is one of the two adjacent magnetic layers; and
A thickness of the second magnetic layer is smaller than a thickness of the first magnetic layer. The magnetic device according to claim 1,
The effective thickness of the second magnetic layer is smaller than the effective thickness of the first magnetic layer. The magnetic device according to claim 1 or 2,
The thickness of the second magnetic layer is the smallest among the plurality of magnetic layers. A magnetic device according to any one of claims 1 to 3,
The amount of magnetization of the second magnetic layer is smaller than the amount of magnetization of the first magnetic layer. The magnetic device according to claim 4,
The amount of magnetization of the second magnetic layer is the smallest among the plurality of magnetic layers. A magnetic device according to any one of claims 1 to 3,
At least a part of the first magnetic layer is formed of a material having a magnetic moment smaller than that of the second magnetic layer. The magnetic device according to claim 6,
The first magnetic layer includes a magnetic layer formed of the same material as that of the second magnetic layer, and a magnetic layer formed of a material having a magnetic moment smaller than that of the second magnetic layer. Magnetic body device having a laminated structure of A magnetic device according to any one of claims 1 to 7,
Furthermore,
A nonmagnetic spacer layer formed on the second magnetic layer of the pinned layer;
A free layer including a ferromagnetic layer formed on the nonmagnetic spacer layer, and
The magnetization directions of the plurality of magnetic layers of the pinned layer are fixed, and the magnetization direction of the ferromagnetic layer of the free layer is parallel to the magnetization direction of the second magnetic layer. Or allowed to be antiparallel,
The pinned layer, the nonmagnetic spacer layer, and the free layer constitute a magnetoresistive element. An antiferromagnetic layer,
A pinned layer formed on the antiferromagnetic material layer,
The pinned layer has a stacked structure in which a plurality of magnetic layers and at least one nonmagnetic layer are alternately stacked, and two adjacent layers sandwiching a nonmagnetic layer among the plurality of magnetic layers. The two magnetic layers are antiferromagnetically coupled to each other,
The total amount of magnetization of the plurality of magnetic layers is zero,
The plurality of magnetic layers are
A first magnetic layer in contact with the antiferromagnetic layer;
A second magnetic layer that is located farthest from the antiferromagnetic layer and is one of the two adjacent magnetic layers; and
The amount of magnetization of the second magnetic layer is smaller than the amount of magnetization of the first magnetic layer. A magnetic random access memory in which a plurality of magnetoresistive elements are arranged in an array,
Each of the plurality of magnetoresistive elements is
An antiferromagnetic layer,
A pinned layer formed on the antiferromagnetic material layer;
A nonmagnetic spacer layer formed on the pinned layer;
A free layer including a ferromagnetic layer formed on the nonmagnetic spacer layer, and
The pinned layer has a stacked structure in which a plurality of magnetic layers and at least one nonmagnetic layer are alternately stacked, and two adjacent layers sandwiching a nonmagnetic layer among the plurality of magnetic layers. The two magnetic layers are antiferromagnetically coupled to each other,
The total amount of magnetization of the plurality of magnetic layers is zero,
The plurality of magnetic layers are
A first magnetic layer in contact with the antiferromagnetic layer;
A second magnetic layer that is one of the two adjacent magnetic layers and is in contact with the nonmagnetic spacer layer;
The thickness of the second magnetic layer is smaller than the thickness of the first magnetic layer,
The magnetization directions of the plurality of magnetic layers of the pinned layer are fixed, and the magnetization direction of the ferromagnetic layer of the free layer is parallel to the magnetization direction of the second magnetic layer. Or magnetic random access memory that is allowed to be antiparallel.

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