JP4521354B2 - Magnetic random access memory - Google Patents

Description

  The present invention relates to a magnetic random access memory (MRAM) that uses a magneto-resistive element as a memory cell.

  Magnetic random access memories are attracting attention as next-generation memories, but in order to put them to practical use, problems such as reduction in write current and reduction in cell size must be solved.

  For example, if the value of the write current is too large, a write disturb occurs in a so-called half-selected cell, so that it is necessary to develop a technique for reversing the magnetization of the selected cell with a small write current.

  At the present stage, regarding the reduction of the write current, proposals have been made in terms of the cell shape, the write method, and the wiring structure.

  In terms of cell shape, shapes such as a cross, a bean, and a trapezoid have been proposed. However, in the approach based only on the cell shape, although a certain effect can be obtained with respect to the reduction of the write current, it is difficult to obtain sufficient erroneous write resistance by itself.

  Further, when the cell shape becomes complicated, it becomes difficult to stably and finely form the shape, which is disadvantageous for reducing the cell size.

  From the aspect of the writing method, methods such as toggle and spin-injection have been proposed (for example, see Patent Documents 1 and 2).

  However, the toggle method has a problem that it is difficult to reduce the write current although a certain effect can be obtained with respect to the erroneous write resistance. Further, in the spin injection method, since it is difficult to reduce the spin injection current (write current), problems such as thermal disturbance and element destruction occur.

  From the viewpoint of the wiring structure, a yoke structure has been proposed. The yoke structure is a structure in which a yoke material as a soft magnetic material is added to the surface of the write line, and has a certain effect in reducing the write current.

However, when the yoke structure is adopted, a strong magnetic field strength portion and a weak magnetic field strength portion are generated at the intersection of the two write lines, so that a magnetic field cannot be efficiently applied to the magnetoresistive effect element.
US Pat. No. 6,545,906 US Pat. No. 6,256,223

  In an example of the present invention, a magnetic random access memory capable of realizing a reduction in write current, a reduction in cell size, and an improvement in erroneous write resistance is proposed.

Magnetic random access memory according to the example of the present invention includes a first conductive line, the yoke material that covers the first and second side surfaces of the first conductive line, a second conductive line which crosses the first conductive line, a yoke material that covers the first and second side surfaces of the second conductive line, e Bei the first magnetoresistive element to have a composed free layer from a perpendicular magnetization film, the first of said first conductive line The gap existing at the intersection of the yoke material covering the side surface and the yoke material covering the first side surface of the second conductive line is defined as a first gap, and the yoke material covering the second side surface of the first conductive line and the The gap existing at the intersection of the second conductive line and the yoke material covering the second side surface is defined as a second gap, and the yoke material covering the second side surface of the first conductive line and the second conductive line The gap that exists at the intersection with the yoke material covering one side is the third gap. When the gap existing at the intersection of the yoke material covering the first side surface of the first conductive line and the yoke material covering the second side surface of the second conductive line is defined as the fourth gap, The magnetoresistive effect element is disposed in the first gap and is not disposed in the second to fourth gaps .

  According to the example of the present invention, in the magnetic random access memory, it is possible to realize a reduction in write current, a reduction in cell size, and an improvement in erroneous write resistance.

  The best mode for carrying out an example of the present invention will be described below in detail with reference to the drawings.

1. Overview
In the example of the present invention, writing is performed using a magnetic field (current magnetic field) generated by a write current flowing in a write line having a yoke structure. The magnetoresistive effect element is disposed in a gap between the yoke materials as a soft magnetic material covering the two write lines.

  In this gap, a magnetic field (vertical magnetic field) is generated in a direction from one yoke material to the other yoke material. Therefore, the magnetoresistive effect element is composed of a perpendicular magnetization film in which the magnetization direction (easy magnetization axis direction) is the thickness direction perpendicular to the film surface.

  According to such a configuration, since the magnetoresistive effect element is disposed in the gap between the yoke materials having the strongest magnetic field strength, it is possible to reduce the write current.

  Further, the magnetic field generated in the gap between the yoke materials is 2 in the direction from one yoke material to the other yoke material (for example, upward) and in the direction from the other yoke material to one yoke material (for example, downward). There will be only one.

  When this is referred to as a pole, in the example of the present invention, writing can be performed based on the direction of the pole, so that the resistance to erroneous writing can be improved.

  Further, since the magnetoresistive effect element is constituted by a perpendicular magnetization film, a simple shape such as a circle, a quadrangle, or a cross can be adopted as the shape, which can contribute to the reduction of the cell size.

  In addition, since there are four gaps between the yoke materials at the intersection of the two write lines, a maximum of four magnetoresistive elements can be arranged at one intersection, which increases the density of the memory cell. Can be realized.

2. Writing principle
First, the writing principle according to the example of the present invention will be described with reference to FIGS.

  The strength and direction of the vertical magnetic field generated in the four gaps 1, 2, 3, and 4 between the yoke materials at the intersection of the two write lines (up) and (down) are respectively indicated by these write lines (up) and (down) is determined according to the direction of the write currents Iw1 and Iw2.

(1) CASE 1
In CASE 1, as shown in FIG. 1, it is assumed that a write current Iw1 that flows to the right of the paper flows in the write line (up) and a write current Iw2 that flows downward in the paper flows to the write line (down).

  When a write current Iw1 directed rightward on the paper surface flows in the write line (up), the magnetic field generated by the write current Iw1 is a direction (upward) from the back side to the front side of the paper in the gaps 1 and 3, and in the gaps 2 and 4. , The direction from the front side to the back side (downward).

  When a write current Iw2 that flows downward on the writing line (down) flows in the writing line (down), the magnetic field generated by the writing current Iw2 is in the direction (upward) from the back side to the front side of the paper in the gaps 1 and 4, and the gap 2 3 is a direction (downward) from the front side to the back side.

  Therefore, in CASE 1, the magnetic field generated in the gap 1 is an upward strong vertical magnetic field, and the magnetic field generated in the gap 2 is a downward strong vertical magnetic field. Further, the magnetic fields generated in the remaining gaps 3 and 4 are zero or very weak vertical magnetic fields because the magnetic fields generated by the write currents Iw1 and Iw2 cancel each other.

  From the above, if a magnetoresistive element is arranged in the gaps 1 and 2 between the yoke materials at the intersection of the two write lines (up) and (down), the magnetoresistive element in the gaps 1 and 2 Each can write data.

  In CASE 1, the magnetoresistive effect elements in the gaps 1 and 2 can be used as reference cells, respectively.

(2) CASE 2
In CASE 2, as shown in FIG. 2, it is assumed that a write current Iw1 that flows to the left of the paper flows in the write line (up) and a write current Iw2 that flows upward in the paper flows to the write line (down).

  When a write current Iw1 that flows leftward on the paper line flows in the write line (up), the magnetic field generated by the write current Iw1 is a direction (downward) from the front side to the back side of the paper in the gaps 1 and 3, and in the gaps 2 and 4. The direction is from the back side of the paper to the front side of the paper (upward).

  Also, when a write current Iw2 that flows upward on the writing line (down) flows, the magnetic field generated by the write current Iw2 is in the direction (downward) from the front side to the back side of the paper in the gaps 1 and 4, and the gap 2, 3 is a direction (upward) from the back side to the front side.

  Therefore, in CASE 2, the magnetic field generated in the gap 1 is a downward strong vertical magnetic field, and the magnetic field generated in the gap 2 is an upward strong vertical magnetic field. Further, the magnetic fields generated in the remaining gaps 3 and 4 are zero or very weak vertical magnetic fields because the magnetic fields generated by the write currents Iw1 and Iw2 cancel each other.

  From the above, if a magnetoresistive element is arranged in the gaps 1 and 2 between the yoke materials at the intersection of the two write lines (up) and (down), the magnetoresistive element in the gaps 1 and 2 Each can write data.

  In CASE 2, as in CASE 1, the magnetoresistive elements in the gaps 1 and 2 can be used as reference cells, respectively.

(3) CASE 3
In CASE 3, CASE 1 and CASE 2 are used in combination.

  In this case, when the magnetic field generated in the gap 1 is upward, the magnetic field generated in the gap 2 is downward (FIG. 1). Conversely, when the magnetic field generated in the gap 1 is downward, the magnetic field generated in the gap 2 is upward. (FIG. 2).

  In CASE 3, complementary data is always stored in the magnetoresistive effect element in the gap 1 and the magnetoresistive effect element in the gap 2 at the same time. Therefore, for example, a 1-bit / 2-cell type memory cell excellent in read stability can be realized with a small area by using one as a data cell for data storage and the other as a reference cell.

  Alternatively, two magnetoresistive elements in the gaps 1 and 2 can be used to generate the reference voltage.

(4) CASE 4
In CASE 4, as shown in FIG. 3, it is assumed that a write current Iw1 that flows to the right of the paper flows in the write line (up) and a write current Iw2 that flows upward in the paper flows to the write line (down).

  When a write current Iw1 directed to the right side of the paper flows through the write line (up), the magnetic field generated by the write current Iw1 is a direction (upward) from the back side to the front side of the paper in the gaps 1 and 3, and in the gaps 2 and 4. , The direction from the front side to the back side (downward).

  When a write current Iw2 that flows upward in the drawing plane flows through the write line (down), the magnetic field generated by the write current Iw2 is in the direction (downward) from the front side to the back side of the page in the gaps 1 and 4, and the gap 2 3 is a direction (upward) from the back side to the front side.

  Therefore, in CASE 4, the magnetic field generated in the gap 3 is an upward strong vertical magnetic field, and the magnetic field generated in the gap 4 is a downward strong vertical magnetic field. The remaining magnetic fields generated in the gaps 1 and 2 are zero or very weak vertical magnetic fields because the magnetic fields generated by the write currents Iw1 and Iw2 cancel each other.

  As described above, if magnetoresistive elements are arranged in the gaps 3 and 4 between the yoke members at the intersections of the two write lines (up) and (down), the magnetoresistive elements in the gaps 3 and 4 can be compared. Each can write data.

  In CASE 4, the magnetoresistive elements in the gaps 3 and 4 can be used as reference cells, respectively.

(5) CASE 5
In CASE 5, as shown in FIG. 4, it is assumed that a write current Iw1 that flows to the left of the paper flows in the write line (up) and a write current Iw2 that flows downward in the paper flows to the write line (down).

  When a write current Iw1 that flows leftward on the paper line flows in the write line (up), the magnetic field generated by the write current Iw1 is a direction (downward) from the front side to the back side of the paper in the gaps 1 and 3, and in the gaps 2 and 4. The direction is from the back side of the paper to the front side of the paper (upward).

  When a write current Iw2 that flows downward on the writing line (down) flows in the writing line (down), the magnetic field generated by the writing current Iw2 is in the direction (upward) from the back side to the front side of the paper in the gaps 1 and 4; 3 is a direction (downward) from the front side to the back side.

  Therefore, in CASE 5, the magnetic field generated in the gap 3 is a downward strong vertical magnetic field, and the magnetic field generated in the gap 4 is an upward strong vertical magnetic field. The remaining magnetic fields generated in the gaps 1 and 2 are zero or very weak vertical magnetic fields because the magnetic fields generated by the write currents Iw1 and Iw2 cancel each other.

  As described above, if magnetoresistive elements are arranged in the gaps 3 and 4 between the yoke members at the intersections of the two write lines (up) and (down), the magnetoresistive elements in the gaps 3 and 4 can be compared. Each can write data.

  In CASE 5, as in CASE 4, the magnetoresistive elements in the gaps 3 and 4 can be used as reference cells, respectively.

(6) CASE 6
In CASE 6, CASE 4 and CASE 5 are used in combination.

  In this case, when the magnetic field generated in the gap 3 is upward, the magnetic field generated in the gap 4 is downward (FIG. 3). Conversely, when the magnetic field generated in the gap 3 is downward, the magnetic field generated in the gap 4 is upward. (FIG. 4).

  In CASE 6, complementary data is always stored in the magnetoresistive effect element in the gap 3 and the magnetoresistive effect element in the gap 4 at the same time. Therefore, for example, a 1-bit / 2-cell type memory cell excellent in read stability can be realized with a small area by using one as a data cell for data storage and the other as a reference cell.

  Alternatively, two magnetoresistive elements in the gaps 3 and 4 can be used to generate a reference voltage.

(7) CASE 7
In CASE 7, CASE 1, 2, 4, 5 are used in combination.

  For example, when magnetoresistive elements are arranged in the gaps 1 and 3, binary data (“0” / “1”) can be independently written into these magnetoresistive elements.

  That is, for the magnetoresistive effect element in the gap 1, writing can be executed independently of the magnetoresistive effect element in the gap 3 by using CASE 1 (FIG. 1) and CASE 2 (FIG. 2). For the magnetoresistive effect element in the gap 3, writing can be executed independently of the magnetoresistive effect element in the gap 1 by using CASE 3 (FIG. 3) and CASE 4 (FIG. 4).

  Similarly, for example, when magnetoresistive elements are arranged in the gaps 2 and 4, binary data can be independently written to these magnetoresistive elements.

  That is, for the magnetoresistive effect element in the gap 2, writing can be executed independently of the magnetoresistive effect element in the gap 4 by using CASE 1 (FIG. 1) and CASE 2 (FIG. 2). For the magnetoresistive effect element in the gap 4, writing can be performed independently of the magnetoresistive effect element in the gap 2 by using CASE 3 (FIG. 3) and CASE 4 (FIG. 4).

(8) CASE 8
In CASE 8, all of CASE 1 to CASE 7 are used in combination.

  Magnetoresistive elements are arranged in all four gaps 1, 2, 3, 4 between the yoke members at the intersections of the two write lines (up), (down).

  In this case, two 1-bit / 2-cell type memory cells are arranged at one intersection. That is, 2-bit data can be stored by four magnetoresistive elements arranged at one intersection.

2. Embodiment
Next, some preferred embodiments will be described.

(1) Circuit example
FIG. 5 shows a circuit example of a magnetic random access memory according to the example of the present invention.

  The memory cell array 10 is composed of a plurality of memory cells 11 arranged in an array. The memory cell 11 includes, for example, a magnetoresistive effect element 12 and a selection element 13 connected in series. The magnetoresistive effect element 12 is composed of, for example, an MTJ (magnetic tunnel junction) element, and the selection element 13 is composed of, for example, an N-channel MOS transistor.

  One end of the magnetoresistive element 12 is connected to, for example, a write bit line 14 extending in the column direction. One end of the write bit line 14 is connected to the write driver / sinker 15A, and the other end is connected to the write driver / sinker 15B.

  The write drivers / sinkers 15A and 15B have a decoder function and select one column in the memory cell array 10 at the time of writing. The write drivers / sinkers 15A and 15B control the generation / cutoff of the write current and determine the direction of the write current flowing through the write bit line 14 according to the value of the write data.

  The write bit line 14 also functions as a read bit line.

  The other end of the write bit line 14 is connected to the sense amplifier 21 via the selection element 20.

  The selection element 20 is composed of, for example, an N channel MOS transistor. A column selection signal φCSL for selecting one column in the memory cell array 10 is input to the gate of the N-channel MOS transistor as the selection element 20 at the time of reading.

  The sense amplifier 21 is composed of, for example, a differential amplifier, determines the value of data read from the selected memory cell 11 based on the reference voltage Vref, and outputs an output signal Vout.

  In the vicinity of the magnetoresistive effect element 12, for example, a write word line 16 extending in the row direction is disposed. One end of the write word line 16 is connected to the write driver / sinker 17A, and the other end is connected to the write driver / sinker 17B.

  The write drivers / sinkers 17A and 17B have a decoder function and select one row in the memory cell array 10 at the time of writing. The write drivers / sinkers 17A and 17B control the generation / cutoff of the write current and determine the direction of the write current flowing in the write word line 16 according to the value of the write data.

  The magnetization direction of the magnetoresistive effect element 12 is determined by the combined magnetic field of the magnetic field generated by the write current flowing through the write bit line 14 and the magnetic field generated by the write current flowing through the write word line 16.

  The other end of the magnetoresistive effect element 12 is connected to, for example, the ground terminal Vss via the selection element 13.

  The gate of the N channel MOS transistor as the selection element 13 is connected to the read word line 18. For example, the read word line 18 extends in the row direction, and one end thereof is connected to a row decoder 19 for selecting one row in the memory cell array 10 at the time of reading.

(2) Memory cell example
FIG. 6 shows an example of the device structure of the memory cell 11 of FIG. 7 is a cross-sectional view taken along line VII-VII in FIG.

  A double well region including an N type well region (N-well) 22B and a P type well region (P-well) 22C is formed in the P type silicon substrate (P-sub) 22A.

  An element isolation layer 23 having an STI (shallow trench isolation) structure is formed in the P-type well region 22C. In the element region surrounded by the element isolation layer 23, an N channel MOS transistor as the selection element 13 is formed.

  The N-channel MOS transistor includes source / drain regions 24A and 24B in the P-type well region 22C and a gate electrode 25 on the channel region between the source / drain regions 24A and 24B. The gate electrode 25 is connected to the read word line 18.

  Contact plugs 26 and 28 and intermediate layers 27A and 27B are formed on the source / drain region 24B.

  The magnetoresistive effect element (MTJ) 12 is disposed on the lower electrode 29. The lower electrode 29 is electrically connected to the source / drain region 24B via the contact plugs 26 and 28 and the intermediate layers 27A and 27B.

  The write bit line 14 extends in the column direction and includes, for example, a conductive line 14A made of a metal such as Al or Cu, and a yoke material (soft magnetic material) 14B surrounding the conductive line 14A.

  The write word line 16 extends in the row direction, and includes a conductive line 16A made of a metal such as Al or Cu, and a yoke material 16B surrounding the conductive line 16A.

  The yoke material 14B covers the side surface and the upper surface of the conductive wire 14A, and the yoke material 16B covers the side surface and the lower surface of the conductive wire 16A. The yoke members 14B and 16B have a function of converging the lines of magnetic force generated by the write current flowing through the write bit line 14 and the write word line 16.

  Between the yoke members 14B and 16B, four gaps are formed that serve as paths for the converged magnetic field lines. The magnetoresistive effect element 12 is disposed in one of these four gaps, and is connected to the write bit line 14 via a cap layer 30 made of, for example, a conductive material.

  The planar shape of the magnetoresistive effect element 12 is set to a simple shape, for example, a circle. Further, the magnetoresistive effect element 12 is laid out so that at least its central portion exists in the gap between the yoke members 14B and 16B.

  The magnetic free layer and the magnetic pinned layer of the magnetoresistive effect element 12 are each composed of a ferromagnetic film (perpendicular magnetization film) whose magnetization direction is a thickness direction perpendicular to the film surface. Is done.

  The magnetization direction (upward / downward) of the magnetic free layer can be changed by a magnetic field (current magnetic field) generated by a write current flowing through the write bit line 14 and the write word line 16.

(3) Example of magnetoresistance effect element
An example of a magnetoresistive element will be described.

FIG. 8 shows a first example of a magnetoresistive effect element.
In the first example, the magnetoresistive effect element 12 includes a magnetic free layer, a tunnel barrier layer, a magnetic pinned layer, and an anti-ferromagnetic layer (AF).

  In the bottom pin type of FIG. 5A, an antiferromagnetic layer (pin layer) is formed on a silicon substrate, a magnetic pinned layer is formed on the antiferromagnetic layer, and a tunnel is formed on the magnetic pinned layer. A barrier layer (tunneling barrier layer) is formed, and a magnetic free layer is formed on the tunnel barrier layer.

  In the top pin type of FIG. 4B, a magnetic free layer is formed on a silicon substrate, a tunnel barrier layer is formed on the magnetic free layer, a magnetic pinned layer is formed on the tunnel barrier layer, and the magnetic pinned layer is formed on the magnetic pinned layer. Thus, an antiferromagnetic layer is formed.

  The magnetization direction of the magnetic pinned layer is pinned upward or downward by the antiferromagnetic layer, and the magnetization direction of the magnetic free layer changes upward or downward depending on the current magnetic field.

FIG. 9 shows a second example of the magnetoresistive effect element.
The second example is different from the first example in that the magnetic free layer of the magnetoresistive effect element 12 has a SAF (synthetic anti-ferromagnetic) structure.

  Therefore, the magnetic free layer includes a first free layer (ferromagnetic layer), a second free layer (ferromagnetic layer), and a non-magnetic layer between them. For example, the first and second free layers are antiferromagnetically coupled to each other.

  8A corresponds to the bottom pin type of FIG. 8A, and the SAF type magnetoresistive element of FIG. 8B corresponds to the top pin type of FIG. It corresponds to.

FIG. 10 shows a third example of the magnetoresistive effect element.
The third example relates to the planar shape of the magnetoresistive effect element.

  In the example of the present invention, the magnetoresistive effect element is disposed in the gap at the intersecting portion of the yoke material covering the two write lines intersecting each other.

  Therefore, as shown in the figure, the magnetoresistive effect element 12 has a planar shape such as a circle (Fig. (A)), a square (Fig. (B)), a cross (Fig. (C)), etc. A simple shape can be adopted.

  Here, the magnetoresistive effect element 12 is laid out so that at least the center thereof exists in the gap between the yoke materials.

(4) Operation
The operation of the magnetic random access memory shown in FIGS. 5 to 10 will be described.

  Writing is performed by controlling the direction of the write current flowing in the write bit line 14 and the write word line 16 in the selected memory cell 11.

  First, a write current is supplied to the write bit line 14 in the selected column using the drivers / sinkers 15A and 15B, and writing is performed on the write word line 16 in the selected row using the drivers / sinkers 17A and 17B. Apply current.

  In “0” -writing, for example, a write current is passed in the direction from the driver / sinker 15A toward the driver / sinker 15B, and the write current is caused to flow in the direction from the driver / sinker 17A toward the driver / sinker 17B.

  At this time, for example, in the cross-sectional view of FIG. 7, a write current flows from the back side to the front side of the drawing on the write bit line 14 and the write word line 16 and is arranged in the gap between the soft magnetic materials 14B and 16B. The magnetization direction of the magnetic free layer of the magnetoresistive effect element 12 changes upward.

  Thereby, for example, the magnetization direction of the magnetic free layer and the magnetization direction of the magnetic pinned layer of the magnetoresistive element 12 are both upward (parallel state), and “0” -writing is completed.

  In “1” -write, for example, a write current is supplied in the direction from the driver / sinker 15B to the driver / sinker 15A, and the write current is supplied in the direction from the driver / sinker 17B to the driver / sinker 17A.

  At this time, for example, in the cross-sectional view of FIG. 7, a write current flows from the front side to the back side of the drawing on the write bit line 14 and the write word line 16 and is arranged in the gap between the soft magnetic materials 14B and 16B. The magnetization direction of the magnetic free layer of the magnetoresistive effect element 12 changes downward.

  As a result, the magnetization direction of the magnetic free layer of the magnetoresistive effect element 12 is directed downward, and the magnetization direction of the magnetic pinned layer is directed upward (anti-parallel state), thereby completing “1” -writing.

  Reading is performed by flowing a read current through the magnetoresistive effect element 12 and detecting the resistance value of the magnetoresistive effect element 12 by the sense amplifier 21.

  First, using the row decoder 19, the read word line 18 in the selected row is set to “H”, and the selection element 13 in the memory cell 11 is turned on. Next, a column is selected by the column selection signal φCSL, and a read current is sent from the sense amplifier 21 to the memory cell 11 via the write bit line (read bit line) 14.

  In “0” -reading, the magnetoresistive effect element 12 is in a parallel state and its resistance value is low. For example, when a read current is passed through the magnetoresistive effect element 12, the input voltage Vin of the sense amplifier 21. Becomes smaller than the reference voltage Vref.

  Thereby, it is detected that the magnetoresistive effect element 12 in the selected memory cell 11 is in a parallel state.

  In “1” -reading, the magnetoresistive effect element 12 is in an anti-parallel state and its resistance value is high. For example, when a read current is passed through the magnetoresistive effect element 12, the input voltage of the sense amplifier 21 Vin becomes larger than the reference voltage Vref.

  Thereby, it is detected that the magnetoresistive effect element 12 in the selected memory cell 11 is in the anti-parallel state.

(5) Modification
Next, a modification of the device structure of FIG. 7 will be described.

FIG. 11 shows a first modification.
The first modification is different from the example of FIG. 7 in that the write bit line 14 is disposed below the magnetoresistive effect element 12 and the write word line 16 is disposed above the magnetoresistive effect element 12. .

  In this case, the magnetoresistive effect element 12 is connected to the write bit line 14 via the cap layer 30 made of a conductive material.

  Thus, the positional relationship between the write bit line 14 and the write word line 16 can be reversed.

FIG. 12 shows a second modification.
The second modification is different from the example in FIG. 7 in that the yoke members 14B and 16B surrounding the conductive wires 14A and 16A have a horn structure.

  That is, the yoke material 14B protrudes below the lower surface of the conductive wire 14A, and the yoke material 16B protrudes above the upper surface of the conductive wire 16A.

  By adopting such a horn structure, a current magnetic field can be applied to the magnetoresistive effect element 12 more efficiently.

  As another modification, for example, a sense amplifier can be connected to a write word line. In this case, one end of the magnetoresistive effect element is connected not to the write bit line but to the write word line.

3. Application examples
An application example of the magnetic random access memory of the example of the present invention will be described.

(1) First application example
FIG. 13 shows a first application example.

  The first application example relates to a magnetic random access memory to which CASE 8 of the write principle is applied.

  Four gaps of yoke materials 14B and 16B are formed at the intersection between the write bit line 14 and the write word line 16, and the magnetoresistive effect elements 12 (R1) and 12 (R2) are respectively formed in these four gaps. ), 12 (L1), 12 (L2).

  The magnetoresistive effect elements 12 (R1) and 12 (L1) form a pair, and the two magnetoresistive effect elements 12 (R1) and 12 (L1) store 1-bit data. That is, one of the magnetoresistive effect elements 12 (R1) and 12 (L1) is used as a data cell, and the other is used as a reference cell.

  Similarly, the magnetoresistive effect elements 12 (R2) and 12 (L2) form a pair, and the two magnetoresistive effect elements 12 (R2) and 12 (L2) store 1-bit data. That is, one of the magnetoresistive effect elements 12 (R2) and 12 (L2) is used as a data cell, and the other is used as a reference cell.

  One ends of the magnetoresistive effect elements 12 (R1), 12 (R2), 12 (L1), and 12 (L2) are connected to the write bit line 14 in common.

  The other end of the magnetoresistive effect element 12 (R1) is connected to a ground point via an N channel MOS transistor as the lower electrode 29 (R1) and the selection element 13 (R1). The gate of the N channel MOS transistor as the selection element 13 (R1) is connected to the read word line 18 (R1).

  The other end of the magnetoresistive effect element 12 (L1) is connected to a ground point via an N channel MOS transistor as the lower electrode 29 (L1) and the selection element 13 (L1). The gate of the N-channel MOS transistor as the selection element 13 (L1) is connected to the read word line 18 (L1).

  Similarly, the other end of the magnetoresistive effect element 12 (R2) is connected to the ground point via the lower electrode 29 (R2) and an N-channel MOS transistor as the selection element 13 (R2). The gate of the N channel MOS transistor as the selection element 13 (R2) is connected to the read word line 18 (R2).

  The other end of the magnetoresistive effect element 12 (L2) is connected to the ground point via the lower electrode 29 (L2) and an N-channel MOS transistor as the selection element 13 (L2). The gate of the N channel MOS transistor as the selection element 13 (L2) is connected to the read word line 18 (L2).

(2) Second application example
FIG. 14 shows a second application example.

  The second application example is characterized in that the planar shape of the magnetoresistive effect elements 12 (R1), 12 (R2), 12 (L1), and 12 (L2) in the first application example is a cross shape.

  Here, the magnetoresistive effect elements 12 (R1), 12 (R2), 12 (L1), and 12 (L2) have a shape (cross shape) that matches a cross shape constituted by the yoke members 14B and 16B. Is laid out.

  In this case, the magnetoresistive elements 12 (R1), 12 (R2), 12 (L1), 12 (in accordance with the portion where the magnetic field strength of the magnetic field strength distribution at the intersection of the write bit line 14 and the write word line 16 is strong. Since L2) can be arranged, the writing efficiency is improved.

(3) Third application example
FIG. 15 shows a third application example.

  The third application example relates to a magnetic random access memory to which CASE 3 or CASE 6 of the write principle is applied.

  Four gaps of yoke materials 14B and 16B are formed at the intersection of the write bit line 14 and the write word line 16, and two gaps existing on the diagonal line at the intersection of these four gaps are Magnetoresistive elements 12 (R) and 12 (L) are arranged, respectively.

  The magnetoresistive effect elements 12 (R) and 12 (L) form a pair, and the two magnetoresistive effect elements 12 (R) and 12 (L) store 1-bit data. That is, one of the magnetoresistive elements 12 (R) and 12 (L) is used as a data cell, and the other is used as a reference cell.

  Alternatively, the magnetoresistive elements 12 (R) and 12 (L) can both be used to generate this reference voltage when data is read out.

  For example, when the magnetoresistive effect elements 12 (R) and 12 (L) are connected in parallel between a write bit line as a reference bit line and a ground point at the time of reading, “0” is applied to the reference bit line. It is possible to generate a reference voltage as an intermediate voltage between data and “1” -data.

(4) Fourth application example
FIG. 16 shows a fourth application example.

  The fourth application example relates to a magnetic random access memory to which CASE 7 of the write principle is applied.

  Four gaps of yoke materials 14B and 16B are formed at the intersection of the write bit line 14 and the write word line 16, and two of these four gaps adjacent to each other in the column direction are respectively magnetoresistive. Effect elements 12 (R) and 12 (L) are arranged.

  Data is independently written in the magnetoresistive elements 12 (R) and 12 (L). That is, each of the magnetoresistive effect elements 12 (R) and 12 (L) is used as a data cell.

  In addition, you may arrange | position the magnetoresistive effect elements 12 (R) and 12 (L) in two gaps adjacent to each other at the intersection in the row direction.

(5) Fifth application example
FIG. 17 shows a fifth application example.

  The fifth application example is a modification of the third application example.

  The feature of the fifth application example is the layout of the lower electrodes 29 (L) and 29 (R), and the other points are the same as those of the third application example.

  That is, the lower electrodes 29 (L) and 29 (R) are arranged so that their long axes are parallel to the direction in which the write bit line 14 extends. When the write word line 16 is disposed above the write bit line 14, the major axes of the lower electrodes 29 (L) and 29 (R) are parallel to the direction in which the write word line 16 extends. You may arrange in.

  The fifth application example can be applied to the embodiment shown in FIG. 6, the fourth application example shown in FIG. Moreover, it is applicable also to the 1st and 2nd application example shown in FIG.13 and FIG.14 on the condition that lower electrodes do not contact.

  The direction in which the lower electrodes 29 (L) and 29 (R) are drawn out can be freely selected within a range of 0 ° (parallel) to 90 ° (vertical) with respect to the write bit line 14 or the write word line 16.

4). material
(1) The perpendicular magnetization film (free layer, pinned layer) is made of the following materials.

[A] Magnetic material with high coercive force and magnetic anisotropy energy density of 1 × 10 ⁶ erg / cc or more-Example 1
An alloy containing at least one element of Fe (iron), Co (cobalt), and Ni (nickel) and at least one element of Cr (chromium), Pt (platinum), and Pd (palladium)
This alloy includes both ordered alloys and irregular alloys. Examples of ordered alloys include Fe (50) Pt (50), Fe (50) Pd (50), Co (50) Pt (50) (numbers in parentheses are percentages), and irregular alloys include CoCr There are alloys, CoPt alloys, CoCrPt alloys, CoCrPtTa alloys, CoCrNb alloys and so on.

・ Example 2
A structure in which at least one element of Fe, Co, Ni or an alloy containing the element and an alloy containing one element of Pt or Pd or an alloy containing the element are alternately stacked.
Examples of this structure include a Co / Pt artificial lattice, a Co / Pd artificial lattice, and a CoCr / Pt artificial lattice.

・ Example 3
An amorphous alloy comprising at least one element of rare earth metals, for example, Tb (terbium), Dy (dysprosium), Gd (gadolinium) and at least one element of transition metals
For example, there are TbFe, TbCo, TbFeCo, DyTbFeCo, GdTbCo and the like.

[B] Magnetic material obtained by adjusting the composition ratio and thickness and adding impurities to the material shown in [A]-Example 1
An alloy containing at least one element of Fe, Co, Ni and at least one element of Cr, Pt, Pd, Cu, Ag, Cr, B, V, Ta, Nb, SiO ₂ , MgO, TiN For example, an ordered alloy such as Fe (50) Pt (50), Fe (50) Pd (50), Co (50) Pt (50), etc. When an impurity such as Cu, Cr or Ag is added, the magnetic anisotropy energy density decreases. In addition, increasing the proportion of nonmagnetic elements in materials such as CoCr alloy, CoPt alloy, CoCrPt alloy, CoCrPtTa alloy, and CoCrNb alloy as disordered alloys decreases the magnetic anisotropic energy density.

・ Example 2
In a structure in which at least one element of Fe, Co, Ni or an alloy containing the element and one element of Pt or Pd or an alloy containing the element are alternately stacked, the thickness adjustment or impurity concentration For example, such a material has an optimum value at which the magnetic anisotropy energy density is the highest, and the magnetic anisotropy energy density decreases as the value deviates from the optimum value. In addition, when an impurity element such as Cu or Ag, an alloy thereof, or an insulator is added to an alloy constituting a Co / Pt artificial lattice, a Co / Pd artificial lattice, or a CoCr / Pt artificial lattice, the magnetic anisotropic energy density is reduced. descend.

・ Example 3
The magnetic anisotropy energy density is reduced by adjusting the composition ratio of an amorphous alloy composed of at least one element of rare earth metals, for example, Tb, Dy, Gd and at least one element of transition metals. By adjusting the composition ratio of amorphous alloys such as TbFe, TbCo, TbFeCo, DyTbFeCo, and GdTbCo, the magnetic anisotropy energy density can be reduced.

・ Other
Such a material having a reduced magnetic anisotropic energy density can be used as a free layer of a magnetoresistive element.

(2) The nonmagnetic layer is composed of the following materials.
・ Ta
・ TiN, CrRu, Co-Cr-Pt (The total ratio of Cr and Pt should be 50% or more so as to be non-magnetic), Au, Ag, Pt, Pd, Ir, Fe, Cr, MgO
By forming a nonmagnetic layer using these materials and forming a perpendicular magnetization film on the nonmagnetic layer, the orientation of the perpendicular magnetization film can be enhanced and its characteristics can be improved.

・ CrTi, CrNb, CrV, CoCrPt, CrRu
(3) Other
When the magnetoresistive effect element is formed on the yoke material (soft magnetic material), a buffer layer having a function of preventing diffusion of atoms and a function of not exchange-coupling them is formed between them.

  The buffer layer is composed of a conductive layer such as Ta, TiN, or TaN.

  For example, when an ordered alloy such as FePt or CoPt is used as the free layer, a buffer layer is disposed between the yoke material and the free layer in order to generate perpendicular magnetic anisotropy thereto.

  This buffer layer can be made of a material such as MgO.

  For example, when a Co / Pt artificial lattice is used as the free layer, the coercive force of the magnetoresistive element can be adjusted by adjusting the thicknesses of Co and Pt.

  For example, when an ordered alloy such as FePt or CoPt is used as the free layer, a functional layer is added to the free layer. As the functional layer, for example, a material having the same crystal structure as that of the free layer and having a lattice constant close to that of the free layer, for example, FeRh is used.

  For example, even when a Co / Pt artificial lattice or a Co / Pd artificial lattice is used as the free layer, FeRh can be used as a functional layer.

  For example, when an ordered alloy such as FePt or CoPt is used as the pinned layer, it is necessary to orient the fct (001) plane in order to generate perpendicular magnetic anisotropy thereto. Therefore, for example, an ultrathin layer made of MgO having a thickness of several nm is formed as the control layer for crystal orientation.

  In addition to MgO, the ultrathin layer is composed of, for example, an element or compound having a fcc structure or bcc structure having a lattice constant of 2.8 angstrom, 4.0 angstrom, 5.6 angstrom, such as Pt, Pd, Ag, Au, Al, Cu, Cr, Fe or the like or an alloy thereof can be used.

  In the case of the bottom pin structure, a control layer for crystal orientation is disposed between the yoke material and the pin layer. For example, a buffer layer made of Ta, TiN, TaN, or the like is disposed between the control layer and the yoke material.

  In the case of the top pin structure, MgO with the fcc (100) plane oriented is used for the barrier layer. In this case, a control layer for crystal orientation may be further stacked on condition that the MR ratio does not deteriorate.

  Similarly, when an ordered alloy such as FePt or CoPt is used as the free layer, it is necessary to orient the fct (001) plane.

  In the case of a top pin (bottom free) structure, a control layer for crystal orientation is disposed between the yoke material and the pin layer. For example, a buffer layer made of Ta, TiN, TaN, or the like is disposed between the control layer and the yoke material.

  In the case of a bottom pin (top free) structure, MgO in which the fcc (100) plane is oriented is used for the barrier layer. In this case, a control layer for crystal orientation may be further stacked on condition that the MR ratio does not deteriorate.

5). Other
According to the example of the present invention, an efficiency of 40 Oe / mA or more can be realized in the gap of the yoke material. In this case, the write current can be set to several mA or less, and the switching magnetic field (reversal magnetic field) of the magnetoresistive effect element is raised to a level at which the magnetic shield is not required, that is, an erroneous write does not occur due to the external magnetic field. be able to.

  For example, if the distance from the magnetoresistive effect element to the lower yoke material is 100 nm, the distance from the magnetoresistive effect element to the upper yoke material is 100 nm, and the magnetic field in the gap of the yoke material is 40 Oe / mA, the simulation is free. The switching magnetic field of the layer (perpendicular magnetization film) can be set to about 200 Oe, and the value of the write current can be set to 4 to 5 mA.

  The example of the present invention is not limited to the above-described embodiment, and can be embodied by modifying each component 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-described embodiments, or constituent elements of different embodiments may be appropriately combined.

The figure which shows the writing principle in connection with the example of this invention. The figure which shows the writing principle in connection with the example of this invention. The figure which shows the writing principle in connection with the example of this invention. The figure which shows the writing principle in connection with the example of this invention. 1 is a circuit diagram showing a magnetic random access memory according to an example of the present invention. The top view which shows the example of a memory cell. Sectional drawing which follows the VII-VII line of FIG. Sectional drawing which shows the structural example of a magnetoresistive effect element. Sectional drawing which shows the structural example of a magnetoresistive effect element. Sectional drawing which shows the example of the planar shape of a magnetoresistive effect element. Sectional drawing which shows a 1st modification. Sectional drawing which shows a 2nd modification. The top view which shows a 1st application example. The top view which shows the 2nd application example. The top view which shows the 3rd application example. The top view which shows the 4th application example. The top view which shows the 5th application example.

Explanation of symbols

  10: memory cell array, 11: memory cell, 12: magnetoresistive effect element, 13, 20: selection element, 14: write bit line, 14A, 16A: conductive line, 14B, 16B: yoke material (soft magnetic material), 15A 15B: Write bit line driver / sinker, 16: Write word line, 17A, 17B: Write word line driver / sinker, 18: Read word line, 19: Row decoder, 21: Sense amplifier, 22A: P-type silicon substrate 22B: N-type well region, 22C: P-type well region, 23: Device isolation layer, 24A, 24B: Source / drain region, 25: Gate electrode, 26, 28: Contact plug, 27A, 27B: Intermediate layer, 29: Lower electrode, 30: cap layer.

Claims (5)

A first conductive line; a yoke material covering first and second side surfaces of the first conductive line; a second conductive line intersecting the first conductive line; and first and second side surfaces of the second conductive line . comprising a yoke material that covers, and a first magneto resistive effect element which have a composed free layer from a perpendicular magnetization film,
The gap present at the intersection of the yoke material covering the first side surface of the first conductive line and the yoke material covering the first side surface of the second conductive line is defined as a first gap, and the first conductive line The yoke material that covers the second side surface of the first conductive line is defined as a gap that exists at the intersection of the yoke material that covers the second side surface and the yoke material that covers the second side surface of the second conductive line. Between the yoke material covering the first side surface of the first conductive line and the yoke material covering the first side surface of the first conductive line. When the gap existing at the intersection with the yoke material covering the second side surface is the fourth gap,
The magnetic random access memory according to claim 1, wherein the first magnetoresistive element is disposed in the first gap and is not disposed in the second to fourth gaps . 2. The magnetic random access memory according to claim 1, further comprising a free layer composed of a perpendicular magnetization film, disposed in the second gap, and not disposed in the first, third, and fourth gaps. A magnetic random access memory comprising a second magnetoresistance effect element. The first and second magnetoresistive elements are on a diagonal line at the intersection of the first and second conductive lines, and 1-bit data is stored by the first and second magnetoresistive elements. 3. The magnetic random access memory according to claim 2, wherein: 2. The magnetic random access memory according to claim 1, further comprising a free layer composed of a perpendicular magnetization film, disposed in the third gap, and not disposed in the first, second, and fourth gaps. A magnetic random access memory comprising a second magnetoresistance effect element. The first and second magnetoresistive elements are adjacent to each other in a row direction or a column direction at an intersection of the first and second conductive lines, and data is independently transmitted to the first and second magnetoresistive elements. 5. The magnetic random access memory according to claim 4 , wherein the magnetic random access memory is written.

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