JP4594694B2 - Magnetoresistive effect element - Google Patents

Description

  The present invention relates to the shape of a magnetoresistive effect element, and is particularly used for a magnetic random access memory.

  In recent years, with the development of a magnetic memory element exhibiting a giant magnetoresistive (GMR) effect, an element having a ferromagnetic tunnel junction has been used as a memory element of a magnetic memory.

  The ferromagnetic tunnel junction has a laminated structure of a ferromagnetic layer / insulating layer / ferromagnetic layer, and a tunnel current flows through the insulating layer by applying a voltage between the two ferromagnetic layers. In this case, the junction resistance value changes in proportion to the cosine of the relative angle of the magnetization directions of the two ferromagnetic layers.

  Therefore, the junction resistance value is the smallest when the magnetization directions of the two ferromagnetic layers are the same (parallel state), and conversely, the magnetization directions of the two ferromagnetic layers are opposite (anti-parallel state). ) Is the largest value.

  Such a phenomenon that the junction resistance value changes depending on the magnetization patterns of the two ferromagnetic layers is called a tunneling magnetoresistive (TMR) effect. Recently, it has been reported that the rate of change (MR ratio) in the resistance value of an MTJ (Magnetic Tunnel Junction) element due to the TMR effect is 49.7% at room temperature.

  In a magnetoresistive effect element having a ferromagnetic tunnel junction, one of two ferromagnetic layers is used as a reference layer (pinned layer) having a fixed magnetization pattern, and the other is changed in magnetization pattern according to data. A storage layer (free layer) is used. For example, “0” is set when the magnetizations of the reference layer and the storage layer are in a parallel state, and “1” is set when the magnetization is in an antiparallel state.

  Data is written, for example, by applying a magnetic field generated by a write current flowing through the write line to the magnetoresistive effect element and reversing the magnetization direction of the storage layer of the magnetoresistive effect element. Data is read by passing a read current through the ferromagnetic tunnel junction of the magnetoresistive effect element and detecting a resistance change of the ferromagnetic tunnel junction due to the TMR effect.

  A magnetic memory is configured by arranging such magnetoresistive elements in an array. As for the actual configuration, one switching transistor is connected to one magnetoresistive element, for example, like a dynamic random access memory (DRAM), so that the magnetoresistive element can be randomly accessed.

  In addition, a technique has been proposed in which a magnetoresistive effect element in which a diode and a ferromagnetic tunnel junction are combined is arranged at a position where a word line and a bit line intersect.

  Now, considering high integration of magnetoresistive effect elements having ferromagnetic tunnel junctions, the cell size must be reduced, and therefore the size of the ferromagnetic layer of the magnetoresistive effect element is inevitably reduced.

  Here, as a property of the ferromagnetic layer, the magnetic structure (magnetization pattern) of the ferromagnetic layer is composed of a plurality of magnetic domains. In the case of a rectangular ferromagnetic layer, the magnetic structure in the central part in the major axis direction forms a magnetic domain in which the magnetization is directed along the long side. A magnetic domain that faces in a direction along the short side, that is, a so-called edge domain is formed.

  The edge domain causes a decrease in the MR ratio due to the TMR effect, and the rate of decrease in the MR ratio due to the edge domain increases as the size of the ferromagnetic layer decreases. Further, when switching the magnetization pattern of the ferromagnetic layer (magnetization reversal), the change in the magnetic structure becomes complicated, which not only causes noise, but also increases the coercive force and increases the switching magnetic field.

  In order to solve this problem, there has been proposed a magnetoresistive element in which the shape of the storage layer (ferromagnetic layer) is asymmetric with respect to the easy magnetization axis, for example, a parallelogram (for example, a patent) Reference 1).

  According to this technique, since the edge domain becomes small, a single magnetic domain can be formed over almost the entire storage layer.

  On the other hand, as a method for preventing a complicated change in the magnetic structure of the ferromagnetic layer at the time of switching, a technique has been proposed in which the edge domain is always fixed by applying a hard bias to the end of the storage layer (ferromagnetic layer). (For example, refer to Patent Document 2).

  Further, there is a technique in which a part protruding in a direction perpendicular to the easy magnetization axis direction is newly added to the rectangular storage layer (ferromagnetic layer), and the shape of the storage layer is changed to an H type or an I type. It has been proposed (see, for example, Patent Document 3).

  Thus, by making the shape of the memory layer H type or I type, a complicated change in the magnetic structure of the ferromagnetic layer at the time of switching can be prevented and the switching magnetic field can be lowered.

  By the way, as the size of the ferromagnetic layer decreases, the coercive force increases. Since the magnitude of the coercive force is a measure of the magnitude of the switching magnetic field necessary for reversing the magnetization, an increase in the coercive force means an increase in the switching magnetic field of the magnetoresistive element.

  Therefore, if the size of the ferromagnetic layer is reduced due to the miniaturization of the magnetoresistive effect element, a large write current is required at the time of data writing, resulting in undesirable results such as an increase in power consumption and a shortened wiring life.

  For this reason, simultaneously miniaturizing the magnetoresistive effect element and reducing the coercive force of the ferromagnetic layer used for it are indispensable issues for practical use of a large-capacity magnetic memory.

  In order to solve this problem, there has been proposed a magnetoresistive effect element in which the storage layer is composed of at least two ferromagnetic layers and a nonmagnetic layer disposed between them (for example, Patent Documents). 4).

  In this case, the two ferromagnetic layers have different magnetic moments or thicknesses, and the magnetization directions are opposite to each other due to antiferromagnetic coupling. For this reason, in order to effectively cancel out the influences of magnetization, the entire storage layer can be considered as equivalent to a ferromagnetic material having a small magnetization in the easy axis direction.

  When a magnetic field is applied to the small magnetization direction in the easy axis direction, the magnetization of the ferromagnetic layer is reversed while maintaining antiferromagnetic coupling. At this time, the influence of the demagnetizing field is reduced because the magnetic lines of force are closed. In addition, since the switching magnetic field of the storage layer is determined by the coercive force of the ferromagnetic layer, the magnetization can be reversed with a small switching magnetic field.

  When there is no interlayer coupling between the two ferromagnetic layers, an interaction due to magnetostatic coupling occurs due to the leakage magnetic field from these ferromagnetic layers. Even in this case, the switching magnetic field can be reduced (for example, see Non-Patent Document 1).

However, when there is no interlayer coupling between the two ferromagnetic layers and only magnetostatic coupling exists, the magnetic structure of the ferromagnetic layer becomes unstable. Further, in this case, the squareness ratio in the hysteresis curve or the magnetoresistance curve becomes small, and it becomes difficult to obtain a large magnetoresistance ratio.
Thus, regarding the magnetic domain of the storage layer, it is indispensable to avoid the complication and stabilize it in order to obtain a large output signal with little noise.

  However, in general, in the parallelogram storage layer, the magnetic structure is simplified, and the coercive force and the switching magnetic field are increased while the magnetic layer is almost a single magnetic domain.

  Further, by adding a hard bias structure for fixing the edge domain to the end of the storage layer, the behavior at the time of magnetization reversal can be controlled, but in this case also the coercive force increases. Further, since it is necessary to add a hard bias structure for fixing the edge domain, it is not suitable for high density required for a large capacity memory or the like.

  Further, in the H-type or I-type storage layer, in order to maximize the effect of preventing a complicated change in the magnetic structure of the ferromagnetic layer at the time of switching, it protrudes in a direction perpendicular to the easy axis direction. It is necessary to enlarge the part. However, in this case, since the size of the magnetoresistive effect element is substantially increased, it is not suitable for high integration required for a large capacity memory or the like.

  In the data write operation in the magnetic random access memory, the switching curve of the MTJ element having the magnetic tunnel junction is important.

  The MTJ element is disposed at the intersection of two write lines that intersect each other. Data writing is performed by reversing the magnetization direction of the MTJ element by a magnetic field generated by currents flowing through these two write lines. Data writing to the MTJ element is not performed only with a magnetic field generated by a current flowing through one of the two write lines.

  Therefore, the switching curve shows the magnetic field in the easy axis direction necessary for switching (magnetization reversal) on the plane formed by the easy axis and hard axis of the memory layer of the MTJ element. It is defined by the magnitude and the magnitude of the magnetic field in the hard axis direction.

  It is known that the switching curve is expressed as an asteroid curve in the single domain model. Since the write characteristics are almost determined by the switching curve, the switching curve is deformed to increase the write window, or the half-selection in which only the magnetic field generated by the current flowing through one of the two write lines is applied. Attempts have been made to increase the stability of state MTJ elements.

  As a method for realizing such a switching curve, a proposal has been made to change the shape of the MTJ element.

  For example, there is a so-called (C-type) MTJ element (see, for example, Patent Document 5). The feature of the uniform MTJ element is that when the magnetic field in the hard axis direction is small, the magnetic structure (magnetization pattern) forms a C-type magnetic domain, and when the magnetic field in the hard axis direction is large, the magnetic structure forms an S-type magnetic domain. It is in the point to do.

  When the C-type magnetic domain is configured, the magnetization direction of the storage layer is difficult to reverse. When the S-type magnetic domain is configured, the magnetization direction of the storage layer is easily reversed. In addition to preventing erroneous writing, it is possible to reduce the coercive force during writing and to reduce the switching magnetic field (CS switching).

  Further, as a shape in which the magnetic structure when the magnetic field in the hard axis direction is small forms a C-type magnetic domain, there is a cross shape in addition to the flat shape. The cross-shaped MTJ element is characterized in that the magnetic structure when the magnetic field in the hard axis direction is small forms two C-type magnetic domains. In the cross-shaped MTJ element, the switching magnetic field in the direction of 45 ° with respect to the easy magnetization axis or the hard magnetization axis can be reduced.

However, in any case, a sufficiently satisfying write characteristic cannot be obtained with the current MTJ element having the uniform or cross shape. Furthermore, there is a demand for a shape having a wide writing window and capable of stabilizing the state of the half-selected MTJ element.
Japanese Patent Laid-Open No. 11-273337 US Pat. No. 5,748,524 US Pat. No. 6,205,053 US Pat. No. 5,953,248 JP 2003-78112 A 24th Annual Meeting of the Japan Society of Applied Magnetics 12aB-3, 12aB-7, 24th Annual Meeting of the Japan Society of Applied Magnetics p.26-27

  An object of the present invention is to propose a magnetoresistive effect element that has a stable magnetic structure even when miniaturized, and can reduce a switching magnetic field while preventing erroneous writing of a half-selected cell during writing. There is.

Magnetoresistive element according to the embodiment of the present invention, the magnetoresistance effect element having a laminated structure made of a non-magnetic layer and disposed between the first and second ferromagnetic layers, two opposing sides A first curved surface that is recessed in one of the two, a second curved surface that is swollen in the other, and a planar shape in which ends of the first and second curved surfaces are coupled to each other. When the shape of the letter C is defined, the planar shape of the second ferromagnetic layer is the same direction, and the two or more letters C having the first and second curved surfaces oriented in the hard magnetization axis direction. The first ferromagnetic layer is a pinned layer and the second ferromagnetic layer is a free layer, and the magnetic field is at least in the hard axis direction. The magnetization pattern of the second ferromagnetic layer is two or more C-type when is zero To maintain the ward.

Magnetoresistive element according to the embodiment of the present invention, the magnetoresistance effect element having a laminated structure made of a non-magnetic layer and disposed between the first and second ferromagnetic layers, two opposing sides A first curved surface that is recessed in one of the two, a second curved surface that is swollen in the other, and a planar shape in which ends of the first and second curved surfaces are coupled to each other. When the shape of the letter C is defined, the planar shape of the second ferromagnetic layer is the two of the letters C having the opposite directions and the first and second curved surfaces facing the hard axis of magnetization. The second curved surface has a shape in which the second curved surface is shifted in the direction of the easy axis of magnetization and coupled back to back, the first ferromagnetic layer is a pinned layer, the second ferromagnetic layer is a free layer, and at least the magnetization When the magnetic field in the hard axis direction is zero, the magnetization pattern of the second ferromagnetic layer is 2 To maintain the C-shaped magnetic domains.

Magnetoresistive element according to the embodiment of the present invention, the magnetoresistance effect element having a laminated structure made of a non-magnetic layer and disposed between the first and second ferromagnetic layers, two opposing sides A first curved surface that is recessed in one of the two, a second curved surface that is swollen in the other, and a planar shape in which ends of the first and second curved surfaces are coupled to each other. When the shape of the letter C is defined, the plane shape of the second ferromagnetic layer is the same direction, and the two letter C shapes are oriented with the first and second curved surfaces in the hard axis direction. A second shape comprising a first shape that is arranged adjacent to each other in the direction of the easy axis of magnetization and coupled to each other, and a shape of the character C facing in the opposite direction to the shape of the character C in the first shape And the shape of the letter C in the first shape 2 curved surface and the second curved surface of the character C in the second shape are coupled to each other, the first ferromagnetic layer as a pinned layer, the second ferromagnetic layer as a free layer, At least when the magnetic field in the hard axis direction is zero, the magnetization pattern of the second ferromagnetic layer maintains three C-type magnetic domains .

Magnetoresistive element according to the embodiment of the present invention, the magnetoresistance effect element having a laminated structure made of a non-magnetic layer and disposed between the first and second ferromagnetic layers, two opposing sides A first curved surface that is recessed in one of the two, a second curved surface that is swollen in the other, and a planar shape in which ends of the first and second curved surfaces are coupled to each other. When the shape of the letter C is defined, the plane shape of the second ferromagnetic layer is the same direction, and the two letter C shapes are oriented with the first and second curved surfaces in the hard axis direction. A first shape that is aligned next to each other in the easy axis direction and joined together, and two letter C shapes that face the same direction and face the first and second curved surfaces in the hard axis direction, Pair with second shapes arranged side by side in the easy axis direction and coupled to each other The shape of the character C in the first shape and the shape of the character C in the second shape are opposite to each other, and the shape of the character C in the first shape The second curved surface and the second curved surface in the shape of the letter C in the second shape are coupled to each other, and the first ferromagnetic layer is a pinned layer and the second ferromagnetic layer is a free layer. And at least when the magnetic field in the hard axis direction is zero, the magnetization pattern of the second ferromagnetic layer maintains four C-type magnetic domains .

  According to an example of the present invention, there is provided a magnetoresistive effect element that has a stable magnetic structure even when miniaturized, and can reduce a switching magnetic field while preventing erroneous writing of a half-selected cell at the time of writing. Can be provided.

  Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to the drawings.

1. Overview
An example of the present invention is a so-called C-S in which the residual magnetization constitutes a C-type magnetic domain, and the magnetization pattern of the storage layer (free layer) changes from a C-type magnetic domain to an S-type magnetic domain during switching (magnetization reversal). The present invention relates to a magnetoresistive effect element having a shape suitable for switching.

  In CS switching, the magnetization pattern of the memory layer of the non-selected and half-selected magnetoresistive effect element that does not perform magnetization reversal constitutes a C-type magnetic domain that requires a large switching magnetic field for magnetization reversal, while magnetization reversal Since the magnetization pattern of the memory layer of the selected magnetoresistive effect element to be changed from a C-type magnetic domain to an S-type magnetic domain in which magnetization reversal can be performed with a small switching magnetic field, write disturb can be improved and erroneous writing can be prevented. Improved selectivity can be realized.

  In order to perform such C-S switching, specifically, magnetization reversal is performed by a combined magnetic field of a magnetic field in an easy axis direction and a hard axis direction of a magnetoresistive effect element. In this case, a planar shape of a magnetoresistive effect element that can maintain two or more C-type magnetic domains in the magnetization pattern of the storage layer in a region where the magnetic field in the hard axis direction is zero or small may be proposed.

  As such a planar shape, a rough shape in which two or more characters C are combined can be considered. For example, when these two or more characters C are facing the same direction, the overall shape of the magnetoresistive element is the character E, the character M, or a plurality of characters E or a plurality of characters M combined. The approximate shape (E type, M type, continuous E type, and continuous M type) is obtained.

  Further, for example, when these two or more characters C are directed in different directions, the overall shape of the magnetoresistive effect element is an approximate shape obtained by combining these two or more characters C back to back, the characters Z, Or it becomes the approximate shape (deformation H type, Z type with a decoration, continuous deformation H type, and Z type with a continuous decoration) approximated to the shape which combined these two or more.

  Here, the character H is referred to as a modified H type because the two vertical lines of the character H are curved in opposite directions. In addition, the letter Z is referred to as “decorated Z type” because, in detail, the planar shape is a rough shape having a convex part (decoration part) at the center of the letter Z.

  In addition, a planar shape obtained by intersecting two or more parallelograms can also form two or more C-shaped magnetic domains, so that the shape is suitable for performing CS switching. In addition, in this case, since two or more parallelograms are combined instead of two or more quadrangles, the tip of the memory layer of the magnetoresistive effect element has a tapered shape that is cut off obliquely.

  Therefore, since the magnetization pattern of the memory layer of the non-selected magnetoresistive effect element can effectively maintain two or more C-type magnetic domains even during switching, it is possible to prevent erroneous writing and improve selectivity.

  As described above, the magnetoresistive effect element according to the example of the present invention has a planar shape in which the remanent magnetization and the magnetization pattern when the magnetization reversal is not performed constitute two or more C-type magnetic domains, respectively. is doing. Therefore, write disturb can be improved by CS switching, and erroneous writing can be prevented and selectivity can be improved.

  In order to increase the difference between the wide writing window, that is, the value of the switching magnetic field of the selected magnetoresistive effect element that performs magnetization reversal and the value of the switching magnetic field of an unselected magnetoresistive effect element that does not perform magnetization reversal. In addition, at least one of the storage layer and the reference layer of the magnetoresistive effect element may be formed of two different types of ferromagnetic layers (soft layer and hard layer).

  Further, at least one of the storage layer and the reference layer of the magnetoresistive effect element is disposed between two different types of ferromagnetic layers (soft layer and hard layer) and these two different types of ferromagnetic layers. You may comprise from a nonmagnetic layer.

  In this case, an asteroid curve extending long in the hard axis direction can be obtained in the single domain model by two different types of ferromagnetic layers being ferromagnetically or antiferromagnetically coupled to each other. For this reason, a wide writing window can be realized by combining such a structure with CS switching.

  The “two different types” mentioned here mean “different magnetic characteristics”, and different magnetic characteristics include, for example, the thickness of the ferromagnetic layer, film formation conditions, material, and structure (soft layer, hard layer). It can be realized by.

2. Embodiment
Hereinafter, a plurality of embodiments that are considered to be optimal in carrying out the examples of the present invention will be described.

  A magnetic memory element that is an object of an example of the present invention is a magnetoresistive effect element having a magnetoresistive effect, for example, an MTJ (Magneto Tunnel Junction) element having a tunnel magnetoresistive effect. First, the basic structure of the MTJ element will be described.

  As shown in FIG. 1, the magnetic tunnel junction of the MTJ element is composed of two ferromagnetic layers 1a and 1b and a thin insulating layer 2 sandwiched between them. One of the ferromagnetic layers is a reference layer (pinned layer) 1a in which the magnetization pattern (magnetization direction) is fixed by the antiferromagnetic layer 3, and the other one is a magnetization pattern ( This is a storage layer (free layer) 1b whose magnetization direction is changed. The insulating layer 2 disposed between the reference layer 1a and the storage layer 1b is called a tunnel barrier.

Usually, the ferromagnetic layers 1a and 1b are made of Ni, Fe, Co, an alloy of these metals, an amorphous magnetic material such as CoFeB, or the like. Further, as the ferromagnetic layers 1a and 1b, a Mn oxide such as LaMnO ₃ or a half metal typified by a Heusler alloy such as NiMnSb may be used.

  Each of the ferromagnetic layers 1a and 1b is formed by a sputtering method, an MBE method, or the like, and its thickness is set to a value in the range of 0.1 nm or more and 50 nm or less.

  The insulating layer 2 is made of, for example, an oxide such as AlOx or MgO, or a nitride such as AlN. As for the insulating layer 2, a semiconductor such as Si or Ge may be used instead.

  The thickness of the insulating layer 2 is set to 10 nm or less. The thickness of the insulating layer 2 is preferably as thin as possible. In recent years, the insulating layer 2 is set to 2 nm or less, more preferably 1 nm or less.

  The example of the present invention relates to the shape of the magnetoresistive effect element as described in the section of the outline above, but specifically relates to the planar shape of the storage layer (free layer) of the magnetoresistive effect element. That is, in the example of the present invention, it is necessary that at least the planar shape of the memory layer has a shape in which two or more characters C are combined, a shape in which two parallelograms intersect, and the like.

  Therefore, in the following plurality of embodiments, only the storage layer of the magnetoresistive effect element is taken out and the planar shape of the storage layer will be described.

  The planar shape of the magnetoresistive effect element as a whole including the reference layer and the storage layer may be the same as the planar shape of the storage layer, or may be different from the planar shape of the storage layer.

(1) First embodiment
FIG. 2 shows the planar shape of the memory layer of the magnetoresistive effect element according to the first embodiment of the present invention.

  In this example, the memory layer of the magnetoresistive effect element has a planar shape in which two letters C are combined. Specifically, the two letters C face the same direction, have a curved surface in the hard axis direction, and are arranged side by side in the easy axis direction. The two characters C as a whole have a planar shape that approximates the character E or the character M.

  In this case, the magnetization pattern in the region where the residual magnetization of the memory layer of the magnetoresistive effect element and the magnetic field in the hard axis direction are zero or small are each composed of two C-type magnetic domains.

  FIG. 3 shows a switching curve of the magnetoresistive effect element having the planar shape of FIG. FIG. 4 shows a switching curve (asteroid curve) obtained by the single magnetic domain model.

  3 and FIG. 4, the switching curve of the magnetoresistive effect element having the planar shape of FIG. 2 is a single domain model in a region where both a magnetic field in the easy axis direction and a magnetic field in the hard axis direction exist. It is recessed from the resulting switching curve. That this dent is large means that a switching magnetic field (reversal magnetic field) is small.

  Therefore, according to the magnetoresistive effect element having the planar shape of FIG. 2, erroneous writing can be prevented by increasing the switching magnetic field in a region where the magnetic field in the hard axis direction is zero or small (in the case of non-selection). At the same time, in a region where both a magnetic field in the easy axis direction and a magnetic field in the hard axis direction are present (in the case of selection), the switching magnetic field can be reduced to reduce the current consumption by reducing the write current.

  Note that the size of the depression also depends on the thickness of the storage layer.

  The depression of the switching curve itself can be formed by setting the thickness of the memory layer to 50 nm or less. However, considering the recent high integration and low current consumption of memory elements, the thickness of the memory layer considering the depression of the switching curve is a value in the range of 2 nm or more and 20 nm or less, and further 3 nm or more, It is preferable to set the value within a range of 14 nm or less.

  The aspect ratio of the planar shape of the storage layer is preferably set so that longitudinal (hard magnetization axis direction): horizontal (easy magnetization axis direction) is a value within a range from 1: 1 to 1:10. Actually, the value is set to a value within a range from 1: 2 to 1: 4 (in this example, approximately 1: 2) from the viewpoint of high integration of memory elements.

(2) Second embodiment
FIG. 5 shows the planar shape of the memory layer of the magnetoresistive effect element according to the second embodiment of the present invention.

  In this example, as in the first embodiment, the memory layer of the magnetoresistive effect element has a planar shape in which two characters C are combined. However, unlike the first embodiment, the two characters C face different directions. Specifically, the two letters C are coupled back to back and are oriented in opposite directions. In addition, the curved surface of the letter C faces the hard magnetization axis direction and is slightly shifted in the easy magnetization axis direction. The two characters C as a whole have a planar shape that approximates the character Z.

  Even in this case, the magnetization pattern in the region where the residual magnetization of the memory layer of the magnetoresistive effect element and the magnetic field in the hard axis direction are zero or small are each composed of two C-type magnetic domains.

  FIG. 6 shows a switching curve of the magnetoresistive effect element having the planar shape of FIG.

  This switching curve is substantially the same as the switching curve of FIG. That is, in the region where both the magnetic field in the easy axis direction and the magnetic field in the hard axis direction are present, the region is recessed from the switching curve obtained by the single domain model shown in FIG.

  Therefore, according to the magnetoresistive effect element having the planar shape of FIG. 5, erroneous writing can be prevented by increasing the switching magnetic field in a region where the magnetic field in the hard axis direction is zero or small (in the case of non-selection). At the same time, in a region where both a magnetic field in the easy axis direction and a magnetic field in the hard axis direction are present (in the case of selection), the switching magnetic field can be reduced to reduce the current consumption by reducing the write current.

  Note that the size of the depression of the switching curve depends on the thickness of the memory layer, as in the first embodiment. That is, the depression of the switching curve itself can be formed by setting the thickness of the memory layer to 50 nm or less, but the actual thickness of the memory layer is a value within the range of 2 nm or more and 20 nm or less, and further 3 nm As described above, the value is set within a range of 14 nm or less.

  As for the aspect ratio of the planar shape of the storage layer, as in the first embodiment, the longitudinal (hard magnetization axis direction): lateral (easy magnetization axis direction) is a value within the range from 1: 1 to 1:10. Is set to be Actually, it is set to a value within a range from 1: 2 to 1: 4 (in this example, approximately 1: 2).

(3) Third embodiment
FIG. 7 shows the planar shape of the memory layer of the magnetoresistive effect element according to the third embodiment of the present invention.

  Also in this example, the memory layer of the magnetoresistive effect element has a planar shape in which two letters C are combined. The two letters C are oriented in different directions, are joined back to back, and are oriented in opposite directions. In other words, the memory layer of this example has a shape in which two parallelograms are crossed.

  Since the storage layer has a shape in which two parallelograms are crossed, the shape of the tip of the storage layer is not a square but a tapered shape that is cut off obliquely.

  Note that the angle of the front end portion (acute angle portion) of the memory layer is set to a value within the range of 20 ° or more and less than 90 °.

  Here, the angle of the tip of the storage layer means the angle at the corresponding portion of the mask used when processing the storage layer. Regarding the memory layer actually formed, the tip is rounded with a certain curvature, not an acute angle, depending on the accuracy of photolithography, processing accuracy, and the like.

  In order to determine this angle from the shape of the actually formed storage layer, for example, the straight line portion that is the side of the storage layer is stretched straight, and the intersection angle of the portion where the straight line intersects is the angle of the tip of the storage layer. To do.

  Even in such a case, the magnetization pattern in the region where the remanent magnetization of the memory layer of the magnetoresistive effect element and the magnetic field in the hard axis direction are zero or small are each composed of two C-type magnetic domains.

  In this example, the planar shape of the memory layer of the magnetoresistive effect element is symmetric with respect to the center point. For example, as shown in FIGS. 8 and 9, the shape is asymmetric with respect to the center point. And two C-shaped magnetic domains may be easily formed.

  Moreover, as shown in FIG. 10, it is good also as a rough shape which crossed one parallelogram and one square. When the shape shown in FIG. 10 is actually applied to an MTJ element, for example, a rough shape as shown in FIGS. 11 and 12 is obtained.

  Note that the switching curve of the magnetoresistive effect element having the planar shape of FIGS. 7 to 12 is also a curve having a depression as shown in FIG. 6, for example.

  Therefore, even in the magnetoresistive effect element having the planar shape of FIGS. 7 to 12, the switching magnetic field is increased to prevent erroneous writing in a region where the magnetic field in the hard axis direction is zero or small (in the case of non-selection). In addition, in a region where both a magnetic field in the easy axis direction and a magnetic field in the hard axis direction exist (in the case of selection), the switching magnetic field can be reduced to reduce the current consumption by reducing the write current. it can.

  Note that the thickness and aspect ratio of the storage layer are the same as those in the first embodiment, and therefore the description thereof is omitted here.

(4) Fourth embodiment
FIG. 13 shows the planar shape of the memory layer of the magnetoresistive effect element according to the fourth embodiment of the present invention.

  In this example, the memory layer of the magnetoresistive effect element has a planar shape in which three letters C are combined. Specifically, the three letters C are arranged side by side in the same direction, facing a curved surface in the hard axis direction, and in the easy axis direction. The three characters C as a whole have a planar shape that approximates a shape in which a plurality of characters E or a plurality of characters M are combined.

  In this case, the magnetization pattern in the region where the remanent magnetization of the memory layer of the magnetoresistive effect element and the magnetic field in the hard axis direction are zero or small are each composed of three C-type magnetic domains.

  The memory layer of the magnetoresistive element may be formed to have a planar shape in which more than three letters C are combined.

  FIG. 14 shows a switching curve of the magnetoresistive effect element having the planar shape of FIG.

  Also in the magnetoresistive effect element having the planar shape of FIG. 13, in a region where the magnetic field in the hard axis direction is zero or small (in the case of non-selection), the switching magnetic field can be increased to prevent erroneous writing and In a region where both a magnetic field in the easy axis direction and a magnetic field in the hard axis direction are present (in the case of selection), the switching magnetic field can be reduced to reduce the current consumption by reducing the write current.

  Note that the thickness and aspect ratio of the storage layer are the same as those in the first embodiment, and therefore the description thereof is omitted here.

(5) Fifth embodiment
FIG. 15 shows the planar shape of the memory layer of the magnetoresistive effect element according to the fifth embodiment of the present invention.

  In this example, the memory layer of the magnetoresistive effect element has a planar shape in which three letters C are combined. Specifically, the memory layer has a planar shape in which one specific character C and a character C facing the same direction and a character C facing a different direction with respect to the specific one character C are combined.

  In this case, the magnetization pattern in the region where the remanent magnetization of the memory layer of the magnetoresistive effect element and the magnetic field in the hard axis direction are zero or small are each composed of three C-type magnetic domains.

  Also in the magnetoresistive effect element having the planar shape of FIG. 15, in the region where the magnetic field in the hard axis direction is zero or small (in the case of non-selection), the switching magnetic field can be increased to prevent erroneous writing and In a region where both a magnetic field in the easy axis direction and a magnetic field in the hard axis direction are present (in the case of selection), the switching magnetic field can be reduced to reduce the current consumption by reducing the write current.

  Note that the thickness and aspect ratio of the storage layer are the same as those in the first embodiment, and therefore the description thereof is omitted here.

(6) Sixth embodiment
FIG. 16 shows the planar shape of the memory layer of the magnetoresistive effect element according to the sixth embodiment of the present invention.

  In this example, the memory layer of the magnetoresistive effect element has a planar shape in which four letters C are combined. Specifically, the memory layer has a planar shape in which one specific character C and a character C facing the same direction and a character C facing a different direction with respect to the specific one character C are combined. The four characters C have a shape that approximates the character H as a whole.

  In this case, the magnetization pattern in the region where the residual magnetization of the memory layer of the magnetoresistive effect element and the magnetic field in the hard axis direction are zero or small are each composed of four C-type magnetic domains.

  Also in the magnetoresistive effect element having the planar shape of FIG. 16, in the region where the magnetic field in the hard axis direction is zero or small (in the case of non-selection), the switching magnetic field can be increased to prevent erroneous writing and In a region where both a magnetic field in the easy axis direction and a magnetic field in the hard axis direction are present (in the case of selection), the switching magnetic field can be reduced to reduce the current consumption by reducing the write current.

  Note that the thickness and aspect ratio of the storage layer are the same as those in the first embodiment, and therefore the description thereof is omitted here.

(7) Seventh embodiment
This embodiment relates to, for example, the structure of the ferromagnetic layer (memory layer, reference layer) of the magnetoresistive effect element according to the first to sixth embodiments described above.

  For example, the ferromagnetic layer serving as the memory layer of the magnetoresistive effect element includes two different types of magnetic layers, that is, a soft magnetic layer (soft layer) and a hard magnetic layer (hard layer). When the memory layer is composed of a stack of such a soft magnetic layer and a hard magnetic layer, the switching curve greatly extends in the hard axis direction. By applying this property to the example of the present invention, for example, a switching curve as shown in FIG. 24 can be obtained.

  With such a switching curve, the magnetization state of the so-called half-selected memory element can be stabilized, and erroneous writing can be effectively prevented. Further, in this case, since the switching curve is sufficiently away from the hard axis, the influence of the shift of the switching curve due to the Neel coupling or the leakage magnetic field from the reference layer is reduced, and the switching curve is strongly affected.

  17 and 18 show a first example of the planar shape of the memory layer of the magnetoresistive effect element according to the seventh embodiment.

  This example is characterized in that the memory layer of the magnetoresistive effect element in FIG. 2 is composed of a soft magnetic layer (soft layer) and a hard magnetic layer (hard layer).

  The soft magnetic layer and the hard magnetic layer are ferromagnetically coupled or antiferromagnetically coupled. The magnetization in the soft magnetic layer and the magnetization in the hard magnetic layer may be in the same direction as shown in FIG. 17, or may be in opposite directions as shown in FIG.

  FIG. 19 shows a second example of the planar shape of the memory layer of the magnetoresistive effect element according to the seventh embodiment.

  This example is characterized in that the memory layer of a C-type magnetoresistive effect element having a planar shape consisting of one letter C is composed of a soft magnetic layer (soft layer) and a hard magnetic layer (hard layer).

  The soft magnetic layer and the hard magnetic layer are ferromagnetically coupled or antiferromagnetically coupled.

  In the case of this example, the magnetization in the soft magnetic layer and the magnetization in the hard magnetic layer can be in the same direction, but as shown in FIG.

  FIG. 20 shows a third example of the planar shape of the memory layer of the magnetoresistive effect element according to the seventh embodiment.

  This example is characterized in that the memory layer of the cross-shaped magnetoresistive effect element is composed of a soft magnetic layer (soft layer) and a hard magnetic layer (hard layer).

  The soft magnetic layer and the hard magnetic layer are ferromagnetically coupled or antiferromagnetically coupled.

  Also in the case of this example, the magnetization in the soft magnetic layer and the magnetization in the hard magnetic layer can be in the same direction, but as shown in FIG.

  Next, a specific structure of the ferromagnetic layer composed of the soft magnetic layer and the hard magnetic layer will be described.

  FIG. 21 shows an example in which the memory layer of the magnetoresistive effect element is composed of a soft magnetic layer / a hard magnetic layer.

  The arrows of the soft magnetic layer (soft layer) and the hard magnetic layer (hard layer) indicate the magnetization direction patterns, and there are four patterns as indicated by numbers 1 to 4. The state (0 or 1) of the magnetoresistive effect element is determined by the magnetization direction of the reference layer and the magnetization direction of the soft magnetic layer.

  22 and 23 are examples in which the memory layer of the magnetoresistive effect element is composed of a soft magnetic layer / non-magnetic layer / hard magnetic layer.

  Numbers 1 to 4 indicate four patterns of magnetization directions of the soft magnetic layer (soft layer) and the hard magnetic layer (hard layer).

  By disposing a nonmagnetic layer between two ferromagnetic layers (soft magnetic layer and hard magnetic layer), a coupling called interlayer coupling occurs between these ferromagnetic layers. Interlayer coupling causes ferromagnetic coupling or antiferromagnetic coupling between two ferromagnetic layers, depending on the thickness of the nonmagnetic layer.

  For example, when antiferromagnetic coupling occurs between two ferromagnetic layers, the switching curve greatly extends in the hard axis direction as shown in FIG.

  With such a switching curve, the magnetization state of the so-called half-selected memory element can be stabilized, and erroneous writing can be effectively prevented. Further, in this case, since the switching curve is sufficiently away from the hard axis, the influence of the shift of the switching curve due to the Neel coupling or the leakage magnetic field from the reference layer is reduced, and the switching curve is strongly affected.

  Note that the example of FIG. 22 is a case where the nonmagnetic layer is a conductor, and the example of FIG. 23 is a case where the nonmagnetic layer is an insulator.

  When a conductor is used as the nonmagnetic layer, the nonmagnetic layer uses a nonmagnetic metal such as Cu, Ag, Au, Ti, Ta, Ru, Re, and Rh. When an insulator is used as the nonmagnetic layer, for example, an oxide insulator such as AlO or MgO or a nitride such as AlN is used for the nonmagnetic layer.

  The arrows of the soft magnetic layer (soft layer) and the hard magnetic layer (hard layer) indicate the magnetization direction patterns, and there are four patterns. The state (0 or 1) of the magnetoresistive effect element is determined by the magnetization direction of the reference layer and the magnetization direction of the soft magnetic layer.

(8) Other
The shapes related to the first to seventh embodiments described above can be easily realized by devising the shape of the mask used when processing the ferromagnetic layer.

  However, as the MTJ element is miniaturized, the shape of the mask and the shape of the MTJ element do not completely match. For example, the processing of the memory layer is performed by transferring the shape of the mask to the memory layer by photolithography and etching. At this time, at the acute angle portion, the focus at the time of photolithography is blurred, or the etching amount at the time of etching There will be more.

  Accordingly, here, it is sufficient that the outline of the MTJ element has a shape as shown in the first to seventh embodiments described above. It is assumed to be included in the outline of the MTJ element shown in the first to seventh embodiments.

3. Application examples
The magnetoresistive effect element according to the example of the present invention can be applied to a memory cell of a magnetic random access memory.

  Since the magnetoresistive effect element according to the example of the present invention can sufficiently reduce a switching magnetic field, the maximum effect can be exhibited when applied to a storage layer in a memory cell of a magnetic random access memory.

  Hereinafter, some examples of the magnetic random access memory will be described.

  FIG. 25 shows a cross-point type memory cell array.

  The read / write word line WL and the read / write bit line BL intersect each other, and the magnetoresistive element C is disposed at the intersection. The magnetoresistive element C is electrically connected to the read / write word line WL and the read / write bit line BL.

  A diode D is disposed between the magnetoresistive element C and the read / write word line WL. The diode D has a function of preventing a so-called sneak current at the time of reading / writing unique to the cross-point type memory cell array. The sneak current is avoided, for example, by applying a bias voltage to the diode D, the non-selected read / write word line WL, and the non-selected read / write bit line BL.

  For example, a sense amplifier SA is connected to the read / write word line WL via a selection transistor STw. For example, a power source is connected to the read / write bit line BL via a selection transistor STB.

  FIG. 26 shows a ladder type memory cell array.

  A plurality of magnetoresistive elements C are arranged in a ladder shape between the write bit line BLw and the read bit line BLr. The write bit line BLw and the read bit line BLr extend in the same direction.

  A write word line WL is arranged immediately below the magnetoresistive element C. The write word line WL is arranged away from the magnetoresistive element C by a certain distance and extends in a direction intersecting the write bit line BLw.

  For example, a resistance element R is connected to the read bit line BLr via a selection transistor ST. The sense amplifier SA senses read data by detecting the voltage generated across the resistance element R. A power supply is connected to one end of the write bit line BLw, and a ground point is connected to the other end via, for example, a selection transistor ST.

  27 and 28 each show a one-transistor-1MTJ type memory cell array.

  The write word line WL and the read / write bit line BL intersect each other, and the magnetoresistive element C is disposed at the intersection. The magnetoresistive element C is electrically connected to the read / write bit line BL. A write word line WL is arranged immediately below the magnetoresistive element C. The write word line WL is separated from the magnetoresistive element C by a certain distance.

  One end of the magnetoresistive element C is connected to, for example, the sense amplifier SA via the selection transistor ST2. The read / write bit line BL is connected to the power supply via the selection transistor ST1.

  In the structure of FIG. 28, one end of the magnetoresistive element C is connected to the lower electrode L as a lead line. For this reason, even if the selection transistor ST2 is disposed immediately below the magnetoresistive effect element C, the write word line WL can be disposed in the vicinity of the magnetoresistive effect element C.

  As described above, the representative example of the magnetic random access memory to which the magnetoresistive effect element according to the example of the present invention is applied has been described. However, the example of the present invention can also be applied to a magnetic random access memory other than these representative examples.

  The easy axis of magnetization of the magnetoresistive effect element may be parallel to the write word line or may be parallel to the write bit line. Further, the easy axis direction of magnetization of the magnetoresistive effect element may be oriented at 45 ° with respect to the direction in which the two write lines (write word / bit line) extend.

4). Other
According to the example of the present invention, in the selected state that is the target of magnetization reversal, the switching magnetic field at the writing point (recessed portion) of the switching curve is small, and in the semi-selected state and the non-selected state that is not the target of magnetization reversal. A magnetoresistive effect element having a stable magnetization state can be provided.

  When this magnetoresistive effect element is used as a memory cell of a magnetic random access memory, a write current for generating a switching magnetic field necessary for magnetization reversal can be reduced, and a low current consumption can be realized. Thus, according to the example of the present invention, it is possible to provide a magnetic memory that consumes less power, can be highly integrated, and can perform switching (magnetization reversal) at high speed.

  The examples of the present invention are not limited to the above-described embodiments, and can be embodied by modifying the components without departing from the scope of the invention. Various inventions can be configured by appropriately combining a plurality of constituent elements disclosed in the above-described embodiments. For example, some constituent elements may be deleted from all the constituent elements disclosed in the above embodiments, or constituent elements of different forms may be appropriately combined.

The figure which shows the cross-section of the magnetoresistive effect element in connection with the example of this invention. The figure which shows the planar shape of the memory | storage layer of the magnetoresistive effect element in connection with 1st Embodiment. The figure which shows the switching curve of the magnetoresistive effect element of FIG. The figure which shows the switching curve obtained by a single magnetic domain model. The figure which shows the planar shape of the memory | storage layer of the magnetoresistive effect element in connection with 2nd Embodiment. The figure which shows the switching curve of the magnetoresistive effect element of FIG. The figure which shows the planar shape of the memory | storage layer of the magnetoresistive effect element in connection with 3rd Embodiment. The figure which shows the modification of the magnetoresistive effect element of FIG. The figure which shows the modification of the magnetoresistive effect element of FIG. The figure which shows the modification of the magnetoresistive effect element of FIG. The figure which shows the modification of the magnetoresistive effect element of FIG. The figure which shows the modification of the magnetoresistive effect element of FIG. The figure which shows the planar shape of the memory | storage layer of the magnetoresistive effect element in connection with 4th Embodiment. The figure which shows the switching curve of the magnetoresistive effect element of FIG. The figure which shows the planar shape of the memory layer of the magnetoresistive effect element in connection with 5th Embodiment. The figure which shows the planar shape of the memory layer of the magnetoresistive effect element in connection with 6th Embodiment. The figure which shows the structure of the memory | storage layer of the magnetoresistive effect element in connection with 7th Embodiment. The figure which shows the structure of the memory | storage layer of the magnetoresistive effect element in connection with 7th Embodiment. The figure which shows the structure of the memory | storage layer of the magnetoresistive effect element in connection with 7th Embodiment. The figure which shows the structure of the memory | storage layer of the magnetoresistive effect element in connection with 7th Embodiment. The figure which shows the cross-section of the magnetoresistive effect element in connection with 7th Embodiment. The figure which shows the cross-section of the magnetoresistive effect element in connection with 7th Embodiment. The figure which shows the cross-section of the magnetoresistive effect element in connection with 7th Embodiment. The figure which shows the switching curve of the magnetoresistive effect element in connection with 7th Embodiment. The figure which shows the example of a magnetic random access memory. The figure which shows the example of a magnetic random access memory. The figure which shows the example of a magnetic random access memory. The figure which shows the example of a magnetic random access memory.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1a: Ferromagnetic layer (reference | standard layer), 1b: Ferromagnetic layer (memory layer), 2: Tunnel barrier, 3: Antiferromagnetic layer, C: Magnetoresistive element, D: Diode, R: Resistive element, SA: Sense amplifier, STw, STB, ST, ST1, ST2: Select transistor, BL: Read / write bit line, WL: Write word line, BLw: Write bit line, BLr: Read bit line.

Claims (8)

In the magnetoresistive effect element having a laminated structure including the first and second ferromagnetic layers and the nonmagnetic layer disposed therebetween,
The first curved surface has a first curved surface that is recessed in one of two sides facing each other, the second curved surface swells in the other, and the ends of the first and second curved surfaces are When the planar shape coupled to each other is defined as the shape of the letter C, the planar shape of the second ferromagnetic layer is the two oriented in the same direction and the first and second curved surfaces in the hard magnetization axis direction. the above said character C shape, are arranged next to each other in the direction of the easy magnetization axis have a shape conjugated with each other,
The first ferromagnetic layer is a pinned layer, and the second ferromagnetic layer is a free layer,
A magnetoresistive element, wherein the magnetization pattern of the second ferromagnetic layer maintains two or more C-type magnetic domains at least when the magnetic field in the hard axis direction is zero . In the magnetoresistive effect element having a laminated structure including the first and second ferromagnetic layers and the nonmagnetic layer disposed therebetween,
The first curved surface has a first curved surface that is recessed in one of two sides facing each other, the second curved surface swells in the other, and the ends of the first and second curved surfaces are When the planar shape coupled to each other is defined as the shape of the letter C, the planar shape of the second ferromagnetic layer is two opposite directions, the first and second curved surfaces facing the hard axis of magnetization. the second curved surface of the shape of the letter C, and shifting the easy axis direction have a shape conjugated to one another back to back,
The first ferromagnetic layer is a pinned layer, and the second ferromagnetic layer is a free layer,
A magnetoresistive effect element , wherein the magnetization pattern of the second ferromagnetic layer maintains two C-type magnetic domains at least when the magnetic field in the hard axis direction is zero . In the magnetoresistive effect element having a laminated structure including the first and second ferromagnetic layers and the nonmagnetic layer disposed therebetween,
The first curved surface has a first curved surface that is recessed in one of two sides facing each other, the second curved surface swells in the other, and the ends of the first and second curved surfaces are When the planar shape coupled to each other is defined as the shape of the letter C, the planar shape of the second ferromagnetic layer is the same in two directions with the first and second curved surfaces facing the hard axis. A first shape in which the shapes of the characters C are arranged adjacent to each other in the easy axis direction and coupled to each other, and a shape of the characters C facing in the opposite direction to the shape of the characters C in the first shape It is composed of a combination of a second shape comprising a said second curved surface of the character C shape of the first of the character in the C of the second curved surface and the second shape of the shape of the shape Are combined with each other,
The first ferromagnetic layer is a pinned layer, and the second ferromagnetic layer is a free layer,
A magnetoresistive effect element , wherein the magnetization pattern of the second ferromagnetic layer maintains three C-type magnetic domains at least when the magnetic field in the hard axis direction is zero . In the magnetoresistive effect element having a laminated structure including the first and second ferromagnetic layers and the nonmagnetic layer disposed therebetween,
The first curved surface has a first curved surface that is recessed in one of two sides facing each other, the second curved surface swells in the other, and the ends of the first and second curved surfaces are When the planar shape coupled to each other is defined as the shape of the letter C, the planar shape of the second ferromagnetic layer is the same in two directions with the first and second curved surfaces facing the hard axis. The first shape in which the shape of the letter C is aligned next to each other in the easy axis direction and joined together is the same as the first shape, and the first and second curved surfaces are directed in the hard axis direction. The shape of the letter C is composed of a combination of a second shape that is arranged adjacent to each other in the direction of the easy axis of magnetization and coupled together, and the shape of the letter C in the first shape and the shape in the second shape the shape of letter C, the reverse orientation, the form of the letter C of the first in shape It said second curved surface of the character C shape of the second curved surface and the second in shape is coupled to each other,
The first ferromagnetic layer is a pinned layer, and the second ferromagnetic layer is a free layer,
A magnetoresistive effect element , wherein the magnetization pattern of the second ferromagnetic layer maintains four C-type magnetic domains at least when the magnetic field in the hard axis direction is zero . At least one of the first and second ferromagnetic layers includes two magnetic layers, and the two magnetic layers are ferromagnetically coupled or antiferromagnetically coupled to each other. The magnetoresistive effect element according to any one of claims 1 to 4 . At least one of the first and second ferromagnetic layers includes two magnetic layers and a nonmagnetic layer between the two magnetic layers, and the two magnetic layers are strong against each other. the element according to any one of claims 1 to 4, characterized in that it is a magnetic coupling or antiferromagnetic coupling. The thickness of the first and second ferromagnetic layers, 0.1 nm or more, the magnetoresistance effect according to any one of claims 1 to 6, characterized in that it is set to the value of the range 50nm element. Magnetic random access memory characterized by using a magnetoresistance effect element according as a memory cell in any one of claims 1 to 7.

Images