CN101246697A - Direct write method for magnetic memory cell and magnetic memory cell structure - Google Patents

Abstract

The invention discloses a direct write method of a magnetic storage unit. The magnetic memory cell includes a magnetically free stack having a lower ferromagnetic layer and an upper ferromagnetic layer. The lower ferromagnetic layer and the upper ferromagnetic layer both have bi-directional easy axes of substantially the same direction. The method includes applying a first magnetic field in a direction of the bi-directional easy axis and performing a write operation. When a first storage state is to be written, a second magnetic field is applied instead of the first magnetic field. The second magnetic field is oriented on a first side of the bi-directional easy axis and has a first angle. A third magnetic field is applied in place of the first magnetic field when a write operation is to write a second storage state. The third magnetic field is in the second side of the bidirectional easy axis and has a second angle. For example, at least one of the lower ferromagnetic layer and the upper ferromagnetic layer has a unidirectional easy axis and an angle with respect to a bidirectional easy axis.

Description

Direct writing method of magnetic memory cell and structure of magnetic memory cell

technical field

The present invention relates to the technology of a magnetic storage unit, and particularly relates to a writing method and structure of the magnetic storage unit.

Background technique

Magnetic memory, such as Magnetic Random Access Memory (Magnetic Random Access Memory, MRAM) is also a kind of non-volatile memory, which has the advantages of non-volatility, high density, high read and write speed, and radiation resistance. It utilizes the magnetization vectors of the magnetic substances adjacent to the tunneling insulating layer to record 0 or 1 data due to the magnitude of the magnetoresistance generated by the parallel or antiparallel arrangement. When writing data, the general method used is two current lines, such as the intersection of the bit line (Bit Line, BL) and the write word line (WWL) induced magnetic field to select the memory cell of the magnetic memory. At the same time, by changing the direction of the magnetization vector (Magnetization) of the free layer, its magnetoresistance value is changed. When reading the stored data, let the selected magnetic memory cells flow in current, and the digital value of the stored data can be determined from the read resistance value.

FIG. 1 shows the basic structure of a magnetic memory cell. Referring to FIG. 1 , in order to access the magnetic memory cell, current lines 100 and 102 need to be crossed and fed with appropriate current. According to the operation mode, they are also called write word lines and bit lines, for example. When the two wires are fed with current, magnetic fields in two directions will be generated to obtain the desired magnitude and direction of the magnetic field to be applied to the magnetic memory unit 104 . The magnetic memory unit 104 is a laminate structure, including a magnetic pinned layer having a fixed magnetization or total magnetic moment in a predetermined direction. Use the size of the magnetoresistance to read data. Also, through the output electrodes 106 and 108, the data stored in the memory cell can be read out. Details about the operation of the magnetic memory are well understood by those skilled in the art and will not be further described.

FIG. 2 illustrates the storage mechanism of the magnetic memory. In FIG. 2 , the magnetic pinned layer 104 a has a fixed magnetic moment direction 107 . The magnetic free layer 104c is located above the magnetic pinned layer 104a, and is separated by the insulating layer 104b. The magnetic free layer 104c has a magnetic moment direction 108a or 108b. Since the magnetic moment direction 107 is parallel to the magnetic moment direction 108a, the magnetic resistance generated by it represents, for example, the data of "0", otherwise the magnetic moment direction 107 is antiparallel to the magnetic moment direction 108b, and the magnetic resistance generated by it represents, for example, the data of "1". .

Generally, for the single-layer free layer 104c shown in FIG. 2, there is a possibility of access errors. In view of the above problems, in order to reduce the interference of adjacent cells when writing data, the improvement of the traditional technology is to replace the free layer with a ferromagnetic (FM) / non-magnetic metal (M) / ferromagnetic (FM) three-layer structure A single layer of ferromagnetic material constitutes a magnetically free laminated layer 166, the structure of which is shown in FIG. 3 . The two layers above and below the non-magnetic metal layer 152 are ferromagnetic metal layers 150, 154, which are arranged in anti-parallel to form closed magnetic force lines. The underlying magnetically fixed stack 168 is separated from the magnetically free stack 166 by a tunnel barrier layer (T) 156 . The magnetic pinned stack 168 includes a top pinned layer (TP) 158 , a non-magnetic metal layer 160 , and a bottom pinned layer (BP) 162 . There are fixed magnetization vectors in the upper pinned layer and the lower pinned layer. There is also a base layer 164 at the bottom, such as an antiferromagnetic layer.

For the magnetic free stack 166 of the three-layer structure, the bit line BL and the write word line WWL are relative to the magnetic anisotropic axis (magnetic anisotropic axis) of the free stack 166, so that there is an included angle of 45 degrees, and the magnetic field anisotropic axis The direction is the so-called easy axis direction. In this way, the bit line BL and the write word line WWL can respectively apply a magnetic field with an angle of 45 degrees to the easy axis to the free stack 166 to rotate the magnetization vector of the free stack 166 . The data stored in the memory cell is determined by the directions of the two magnetization vectors of the ferromagnetic metal layer 154 and the upper pinned layer 158 .

In addition, in addition to changing the free layer into a three-layer structure, the conventional technology also proposes to rotate the magnetization vector of the free layer in a toggle mode of operation. FIG. 4 shows the effect of an external magnetic field on a three-layer structure. Referring to Fig. 4, the thick arrow represents the external magnetic field, and its length represents the magnitude. The two thin arrows represent the directions of the two magnetization vectors in the upper and lower ferromagnetic layers of the free stack. When the applied magnetic field is too small, the directions of the two magnetization vectors do not change. When the external magnetic field is large enough, the two magnetization vectors will have an angle. When the applied magnetic field is too large, the two magnetization vectors will follow the direction of the applied magnetic field. The operation of the button mode belongs to the second situation mentioned above.

FIG. 5 is a timing diagram of an applied magnetic field in the key mode. Referring to FIG. 5 , H1 and H2 represent the directions of two applied magnetic fields separated by 45 degrees from the direction of the easy axis, and the two arrows in the ellipse represent the directions of the two magnetization vectors. In the t ₀ stage, there is no external magnetic field, so the two magnetization vectors are in the direction of the easy axis. Then, the magnetic fields of H1 and H2 are activated according to the sequence shown in the figure, and the total magnetic fields of different time periods (t ₁ -t ₃ ) are obtained, and the directions of the two magnetization vectors are rotated. At time period _t4 , the application of the magnetic field is stopped and the directions of the two magnetization vectors are reversed once. That is to say, the data stored in the memory cell is changed by writing.

In addition, under the operating condition of the key-on mode, the write current is still relatively high, so the conventional technology also proposes a design of adding a magnetic field bias. FIG. 6 is a schematic diagram of a conventional technique for reducing operating current. Referring to FIG. 6, the basic structure of the memory cell is still similar to that of FIG. 3, as shown in the left figure, the main difference is that the total magnetic moment of the lower pinned layer 162 is increased relative to the total magnetic moment of the upper pinned layer 158, for example, increased thickness. Because the total magnetic moment of the lower pinned layer 162 and the upper pinned layer 158 is unbalanced, an external leakage magnetic field (fringemagnetic field) will be generated, and a magnetic field bias (bias filed) 184 will be generated to the free lamination layer 166, and the tether of the first quadrant can be The region of operation of the buckle is moved towards the zero point of the magnetic field, and as a result shrinks to a distance 186 . Therefore, since the required write magnetic field is small, the write operation current for generating the magnetic field can be reduced.

With regard to the above-mentioned traditional operation method, some improvements have been made to the mechanism for writing data into the corresponding magnetic storage unit, but the operation method still needs to read the current storage data of the magnetic storage unit in the _t2 stage. Write only when the data to be written is different. In this traditional write operation, since data needs to be read first, and the speed of reading data is relatively slow, the speed of the write operation is also slow. How to increase the speed of writing operations is still a subject of research and development.

Contents of the invention

The invention provides a direct writing method of the magnetic storage unit, which can directly write data into the magnetic storage unit without first reading the contents of the magnetic storage unit.

The invention proposes a direct writing method of a magnetic storage unit. The magnetic storage unit includes a magnetic free lamination layer, a lower ferromagnetic layer and an upper ferromagnetic layer. Both the lower ferromagnetic layer and the upper ferromagnetic layer have bidirectional easy axes in substantially the same direction. The method includes applying a first magnetic field in the direction of the bidirectional easy axis, and performing a write operation. When the first storage state is to be written, a second magnetic field is applied instead of the first magnetic field. The second magnetic field is on the first side of the two-way easy axis and has a first angle. A third magnetic field is applied instead of the first magnetic field when a write operation is to write into the second storage state. The third magnetic field is on the second side of the bidirectional easy axis, and has a second angle.

According to the connection and writing method described in the embodiments of the present invention, for example, at least one of the lower ferromagnetic layer and the upper ferromagnetic layer has a unidirectional easy axis, and has an included angle with the bidirectional easy axis.

Also, the present invention proposes another direct writing method for a magnetic storage unit, which is suitable for accessing a magnetic storage unit. The coupling intermediate layer and the upper ferromagnetic layer are stacked. The lower ferromagnetic layer and the upper ferromagnetic layer have substantially the same two-way easy axis, and the two-way easy axis is close to perpendicular and sandwiched by nearly 45 degree of the first magnetic field and the second magnetic field to be added to generate the operating magnetic field.

The method includes, when the operating magnetic field is to write into a first storage state: applying the first magnetic field, the first magnetic field is a first magnetic field level waveform, and has a first pulse of a first width. Also, the second magnetic field is applied substantially simultaneously, the second magnetic field is a second magnetic field level waveform, and has a second pulse of a second width, wherein the first width is smaller than the second width, and the first pulse and the The second pulse has substantially the same magnetic field strength, and the operating magnetic field returns to the low magnetic field level after the second pulse ends.

The first magnetic field is applied when the operating magnetic field is to write into the second storage state, and the first magnetic field is a third magnetic field level waveform with a third pulse of a third width. Also, the second magnetic field is applied substantially simultaneously, the second magnetic field is a fourth magnetic field level waveform, a fourth pulse with a fourth width, wherein the third width is greater than the fourth width, and the third pulse and the The fourth pulse has substantially the same magnetic field strength, and the operating magnetic field returns to the low level of the magnetic field after the third pulse ends.

According to another write-in method described in the embodiment of the present invention, for example, at least one of the lower ferromagnetic layer and the upper ferromagnetic layer has a unidirectional easy axis, and has an included angle with the bidirectional easy axis.

The invention proposes a magnetic storage unit structure, which includes: a magnetically fixed laminated layer, a tunnel barrier layer, a magnetically free laminated layer, and a first antiferromagnetic layer. The tunnel barrier layer is located on the magnetic fixed stack. The magnetic free lamination layer is located on the tunnel barrier layer, wherein the magnetic free lamination layer includes a lower ferromagnetic layer and an upper ferromagnetic layer, each having substantially the same easy axis in both directions. The first antiferromagnetic layer, adjacent to one of the lower ferromagnetic layer and the upper ferromagnetic layer, is referred to as a first adjacent ferromagnetic layer, wherein the magnetic pair alignment line of the first antiferromagnetic layer is aligned with the There is a first included angle between the bidirectional easy axes to generate a first unidirectional easy axis on the first adjacent ferromagnetic layer.

In order to make the above and other objects, features and advantages of the present invention more comprehensible, preferred embodiments will be described in detail below together with the accompanying drawings.

Description of drawings

[Simple description of the diagram]

FIG. 1 shows the basic structure of a magnetic memory cell.

FIG. 2 illustrates the storage mechanism of the magnetic memory.

FIG. 3 is a schematic diagram of a cross-sectional structure of a conventional magnetic memory unit.

FIG. 4 shows the effect of an external magnetic field on the free layer of the three-layer structure.

FIG. 5 is a timing diagram of an applied magnetic field in the key mode.

FIG. 6 is a schematic diagram of a conventional technique for reducing operating current.

FIG. 7 shows a magnetic field writing waveform in a first state according to an embodiment of the present invention.

FIG. 8 shows a magnetic field writing waveform in a second state according to an embodiment of the present invention.

FIG. 9 shows another case where the magnetization vector is deflected by an external magnetic field.

FIG. 10 is a schematic diagram illustrating the structure of a magnetic memory unit according to an embodiment of the present invention.

FIG. 11 illustrates a situation where an external magnetic field deflects a magnetization vector according to an embodiment of the present invention.

FIG. 12 illustrates another magnetic field operation waveform according to an embodiment of the present invention.

[Description of main component symbols]

100, 102: Current wires 104: Magnetic storage unit

104a: Magnetic pinning layer 104b: Insulating layer

104c: Magnetic free layer 106, 108: Electrodes

107, 108a, 108b: Magnetic moment direction 150: Ferromagnetic metal layer

152: Non-magnetic metal layer 154: Ferromagnetic metal layer

156: Tunneling insulation layer 158: Upper fixed layer

160: Non-magnetic metal 162: Lower fixed layer

164: Base layer 166: Magnetic free lamination

168: Magnetic fixed stack 170: Upper magnetization vector

172: Lower magnetization vector 174a: Applied magnetic field

174b: Applied magnetic field 174c: Applied magnetic field

184: Magnetic field bias 186: Distance

190: Magnetic fixed stack 192: Tunneling barrier

194: lower ferromagnetic layer 196: metal layer

198: upper ferromagnetic layer 200: magnetic free lamination

202: Two-way easy axis 204: Two-way easy axis

206: Metal layer 208: Antiferromagnetic layer

210: Antiferromagnetic easy axis direction 212: Antiferromagnetic layer

Detailed ways

The invention proposes a direct writing method of the magnetic storage unit, which can directly write data into the magnetic storage unit without first reading the contents of the magnetic storage unit.

The invention also cooperates with the proposed structure of the magnetic memory unit. The magnetically free stacked layers in the memory cell structure include, for example, a lower ferromagnetic layer and an upper ferromagnetic layer, respectively having substantially the same easy axes in both directions. The first antiferromagnetic layer, adjacent to one of the lower ferromagnetic layer and the upper ferromagnetic layer, is referred to as a first adjacent ferromagnetic layer, wherein the magnetic pair alignment line of the first antiferromagnetic layer is aligned with the There is a first included angle between the bidirectional easy axes to generate a first unidirectional easy axis on the first adjacent ferromagnetic layer.

Also, the structure may also include, for example, a second antiferromagnetic layer adjacent to the other of the lower ferromagnetic layer and the upper ferromagnetic layer, referred to as a second adjacent ferromagnetic layer, wherein the second antiferromagnetic There is a second included angle between the magnetic pair alignment line of the layer and the bidirectional easy axis to generate a second unidirectional easy axis on the second adjacent ferromagnetic layer, and between the first unidirectional easy axis and the The anisotropy strength of the second unidirectional easy axis is different.

Some examples are given below for illustration, but the present invention is not limited to the examples given.

FIG. 7 shows a magnetic field writing waveform in a first state according to an embodiment of the present invention. Referring to FIG. 7 , during the period t ₀ , the magnitudes of the magnetic fields H1 and H2 are zero, that is, the initial state without an external magnetic field. As another example, the upper ferromagnetic layer has a magnetization vector 170, and the lower ferromagnetic layer has a magnetization vector 172, both of which are substantially on the easy axis, but arranged antiparallel. During the time period _t1 , the magnetic fields H1 and H2 are activated simultaneously. In a preferred situation, for example, the strengths of the magnetic fields H1 and H2 are substantially equal, so the magnetic field resultant vector 174a is on the easy axis. At this time, the two magnetization vectors 170, 172 and the resultant magnetic field 174a reach a balanced state. Then during the period _t2 , the magnetic field H2 is turned off, that is, only the magnetic field H1, ie, the magnetic field 174b, is applied. During the period _t2 , the two magnetization vectors 170, 172 are deflected counterclockwise relative to the magnetic field 174b. During the period _t3 , the magnetic field H1 is then turned off, that is to say, no external magnetic field is applied. Therefore, the two magnetization vectors 170 , 172 will fall into a stable state, which is, for example, the first state, and for example represents "0". The first state in this embodiment is that the magnetization vector 170 is in the positive direction of the easy axis.

Conversely, if the second state is to be written, the waveform of the magnetic field to be written will have some changes. FIG. 8 shows a magnetic field writing waveform in a second state according to an embodiment of the present invention. Referring to FIG. 8 , the _t0 period and the _t1 period are the same as the situation in FIG. 7 , but during the _t2 period, the magnetic field H1 is turned off, that is, only the magnetic field H2 is applied, which is the magnetic field 174c. The two magnetization vectors 170, 172 are deflected clockwise relative to the magnetic field 174c. During the period _t3 , since the magnetization vector 170 is closer to the negative direction of the easy axis, the magnetization vector 172 is closer to the positive direction of the easy axis. Therefore, when there is no external magnetic field, the directions of the magnetization vectors 170 , 172 are opposite to those of the magnetization vectors 170 , 172 during the period t3 in FIG. 7 . That is to say, when the magnetization vector 170 is in the negative direction of the easy axis, it is called the second state, for example. Therefore, according to the magnetic field waveform of FIG. 8, a desired second state, such as "1", can be written. Of course, it can be understood that the first state and the second state are only used to represent different states that can be distinguished, and the actual content of the first state and the second state is not limited to the embodiment. For example, the aforementioned first state may also be referred to as a second state, while the described second state is referred to as a first state.

Regarding the above operation waveforms, generally speaking, the first state or the second state can be written as expected. However, since the initial state in the t ₀ period is not necessarily the state as shown, or the magnetization vectors 170, 172 have deviated from the easy axis in the initial state, this will cause the state in the t ₁ period to be uncertain, and therefore May cause write errors. An example is given below, as shown in FIG. 9 . Referring to FIG. 9 , assuming the initial state at time period t ₀ , its magnetization vector 170 is oriented in the negative direction of the easy axis. During the period _t1 , although the applied magnetic field 174a is in the positive direction of the easy axis, the equilibrium state of the magnetization vectors 170 and 172 may be that the magnetization vector 172 is more biased towards the direction of H2. If, for example, with the magnetic field waveform of FIG. 7, the first state is to be written, but the second state ends up being written, an error is caused.

Therefore, in combination with the structural design of the magnetic storage unit, the present invention can ensure the stability of the state during the _t1 period. That is to say, no matter what the initial state is, it can ensure the same state during the period t ₁ , thus also ensuring that the magnetization vectors 170 , 172 can subsequently deflect in the expected direction. FIG. 10 is a schematic diagram illustrating the structure of a magnetic memory unit according to an embodiment of the present invention.

Referring to FIG. 10 , the embodiment of the magnetic memory cell structure proposed by the present invention may include, for example, a magnetic fixed stack 190 , a tunnel barrier 192 , a magnetic free stack 200 , and an antiferromagnetic layer 212 . The tunneling barrier layer 192 is located on the magnetic fixed stack 190 . A magnetically free stack 200 is located on the tunneling barrier layer 192 , wherein the magnetically free stack 200 includes, for example, a lower ferromagnetic layer 194 , a metal layer 196 , and an upper ferromagnetic layer 198 . The ferromagnetic layers 194, 198 have substantially the same bidirectional easy axes 202, 204, respectively. According to this embodiment, the antiferromagnetic layer 208 is adjacent to the upper ferromagnetic layer 198 . But in general, the antiferromagnetic layer 208 can be adjacent to either the lower ferromagnetic layer or the upper ferromagnetic layer. There may also be two antiferromagnetic layers 208 adjacent to the lower ferromagnetic layer 194 and the upper ferromagnetic layer 198 respectively. Also, the antiferromagnetic layer 208 may form a layer stack 212 with the metal layer 206, for example.

It should be noted here that there is an included angle between the easy axis direction 210 of the antiferromagnetic layer 208 and the bidirectional easy axis 204 , so as to generate a unidirectional easy axis on the adjacent ferromagnetic layer 198 . In other words, the magnetization vector of the ferromagnetic layer 198 tends to fall in the direction of the unidirectional easy axis during the period _t1 .

Since the antiferromagnetic layer 208 causes a unidirectional easy axis, the direction of the magnetization vector of the ferromagnetic layer 198 can be ensured, which is less affected by the initial position, thereby ensuring subsequent deflection results. As shown in FIG. 11 , when the magnetic field 174a is on the easy axis in both directions, the magnetization vector 170 of the ferromagnetic layer 198 will be on the left.

Generally speaking, the included angle between the easy axis direction 210 and the bidirectional easy axis 204 is preferably 45 degrees. However, the included angle may be substantially less than 90 degrees, for example. It has been verified by simulation that it can still work accurately at an included angle of 60 degrees.

Also, it is not easy to control because the magnetic fields H1 and H2 should be activated absolutely simultaneously during the time period _t1 . However, it has also been verified by simulation that the simultaneous activation time between the magnetic fields H1 and H2 can have some tolerance, for example, there is still an operating region under 2 ns, which can meet the requirement of accurate writing. In other words, after various simulation verifications, the present invention can be determined to be an effective design, allowing some tolerance in process and operating conditions, without requiring precise fabrication and operation.

Also, as previously described in FIG. 6, in order to reduce the magnetic field bias proposed by the operating current, or the magnetic field bias generated in other ways can also be incorporated into the magnetic memory cell design of the present invention, which are also features of the present invention. coverage.

Also, the magnetic fields H1 and H2 in FIG. 7 and FIG. 8 are positive values and operate in the first quadrant. However, under the same mechanism, the magnetic fields H1 and H2 can also operate in the third quadrant, that is to say, H1 and H2 are negative values, as shown in FIG. 12 . The effect is still the same.

The operating magnetic field waveform proposed by the embodiment of the present invention can save the reading operation that needs to read data first in the traditional writing operation, so the writing operation can be accelerated. In addition, in order to improve the accuracy of the writing operation, it is proposed to generate a unidirectional easy axis in the free ferromagnetic layer, and its direction has a proper angle with the bidirectional easy axis. Since the unidirectional easy axis will cause the magnetization vectors to form the same state during the period t1, subsequent write operations can write data more accurately.

Although the present invention has been disclosed above with preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art may make some changes and modifications without departing from the spirit and scope of the present invention. Therefore, The scope of protection of the present invention should be defined by the claims.

Claims (24)

1. A direct writing method of a magnetic storage unit, the magnetic storage unit comprises a magnetic free stack, and the magnetic free stack is formed by stacking a lower ferromagnetic layer, a non-magnetic coupling intermediate layer, and an upper ferromagnetic layer , the lower ferromagnetic layer and the upper ferromagnetic layer respectively have bidirectional easy axes in substantially the same direction, the method comprising: applying a first magnetic field in the direction of the bidirectional easy axis; and performing a write operation to write the first storage state or the second storage state to the magnetic memory unit, Wherein when the write operation is to be written into the first storage state: applying a second magnetic field instead of the first magnetic field, wherein the second magnetic field is on a first side of the bidirectional easy axis and subtends a first angle; and stopping the second magnetic field, Wherein when the write operation is to be written into the second storage state: applying a third magnetic field instead of the first magnetic field, wherein the third magnetic field is on a second side of the bidirectional easy axis at a second angle, wherein the first side is opposite the second side; and The third magnetic field is stopped. 2. The direct writing method of a magnetic memory cell as claimed in claim 1, wherein the first angle and the second angle are substantially equal and substantially less than 90 degrees. 3. The direct writing method of a magnetic memory unit as claimed in claim 2, wherein the first angle and the second angle are substantially close to 45 degrees. 4. The direct writing method of the magnetic memory unit as claimed in claim 1, wherein one of the lower ferromagnetic layer and the upper ferromagnetic layer of the magnetic memory unit has a unidirectional easy axis, wherein the unidirectional easy axis is in line with the There is an included angle between the easy axes in both directions. 5. The direct writing method of a magnetic memory unit as claimed in claim 4, wherein the included angle is substantially less than 90 degrees. 6. The direct writing method of a magnetic memory unit as claimed in claim 4, wherein the included angle is substantially close to 45 degrees. 7. The direct writing method of the magnetic storage unit as claimed in claim 1, wherein the lower ferromagnetic layer and the upper ferromagnetic layer of the magnetic storage unit have two unidirectional easy axes with different anisotropic strengths respectively, and respectively There is an included angle with the easy axis in both directions. 8. The direct writing method of a magnetic memory unit as claimed in claim 7, wherein the included angle is substantially less than 90 degrees. 9. The direct writing method of a magnetic memory unit as claimed in claim 8, wherein the included angle is substantially close to 45 degrees. 10. The direct writing method of a magnetic memory cell as claimed in claim 7, wherein the first angle and the second angle are substantially equal and substantially less than 90 degrees. 11. The direct writing method of a magnetic memory cell as claimed in claim 10 , wherein the first angle and the second angle are substantially close to 45 degrees. 12. A direct writing method of a magnetic storage unit, suitable for accessing a magnetic storage unit, the magnetic storage unit includes a magnetic free stack, and the magnetic free stack is composed of a lower ferromagnetic layer, a non-magnetic coupling intermediate layer, and the upper ferromagnetic layer, the lower ferromagnetic layer and the upper ferromagnetic layer respectively have substantially the same two-way easy axis, wherein the first The magnetic field and the second magnetic field are added to generate an operating magnetic field, and the method includes: When the operating magnetic field is to write the first storage state: applying the first magnetic field, the first magnetic field is a first magnetic field level waveform, and has a first pulse of a first width; applying the second magnetic field substantially simultaneously, the second magnetic field being a second magnetic field level waveform, having a second pulse of a second width, wherein the first width is less than the second width, and the first pulse and the second the pulses have substantially the same field strength, and the operating field returns to the low field level after the second pulse ends; and When the operating magnetic field is to be written into the second storage state: applying the first magnetic field, the first magnetic field is a third magnetic field level waveform, and has a third pulse of a third width; Applying the second magnetic field substantially simultaneously, the second magnetic field is a fourth magnetic field level waveform, a fourth pulse with a fourth width, wherein the third width is greater than the fourth width, and the third pulse is the same as the fourth pulse The pulses have substantially the same magnetic field strength, and the operating magnetic field returns to the low magnetic field level after the third pulse ends. 13. The direct writing method of the magnetic storage unit as claimed in claim 12, wherein one of the lower ferromagnetic layer and the upper ferromagnetic layer of the magnetic storage unit has a unidirectional easy axis, wherein the unidirectional easy axis is in line with the There is an included angle between the easy axes in both directions. 14. The direct writing method of a magnetic memory unit as claimed in claim 13, wherein the included angle is substantially less than 90 degrees. 15. The direct writing method of a magnetic memory cell as claimed in claim 13 , wherein the included angle is substantially close to 45 degrees. 16. The direct writing method of the magnetic storage unit as claimed in claim 12, wherein the lower ferromagnetic layer and the upper ferromagnetic layer of the magnetic storage unit have two unidirectional easy axes with different anisotropic strengths respectively, and respectively There is an included angle with the easy axis in both directions. 17. The direct writing method of a magnetic memory cell as claimed in claim 16, wherein the included angle is substantially less than 90 degrees. 18. The direct writing method of a magnetic memory cell as claimed in claim 16, wherein the included angle is substantially close to 45 degrees. 19. A magnetic memory cell structure comprising: Magnetic fixed lamination; a tunneling barrier layer on the magnetic pinned stack; A magnetically free stack, located above the tunneling barrier, wherein the magnetically free stack includes a lower ferromagnetic layer and an upper ferromagnetic layer, respectively having substantially the same easy axis in both directions; and The first antiferromagnetic layer, adjacent to one of the lower ferromagnetic layer and the upper ferromagnetic layer, is referred to as a first adjacent ferromagnetic layer, wherein the magnetic pair alignment line of the first antiferromagnetic layer is aligned with the There is a first included angle between the bidirectional easy axes to generate a first unidirectional easy axis on the first adjacent ferromagnetic layer. 20. The magnetic memory cell structure as claimed in claim 19, wherein the first included angle is substantially less than 90 degrees. 21. The magnetic memory cell structure of claim 19, wherein a nonmagnetic layer is further included between the first antiferromagnetic layer and the first adjacent ferromagnetic layer. 22. The magnetic memory cell structure of claim 19, further comprising a second antiferromagnetic layer adjacent to the other one of the lower ferromagnetic layer and the upper ferromagnetic layer, referred to as a second adjacent ferromagnetic layer, Wherein there is a second included angle between the magnetic pair alignment line of the second antiferromagnetic layer and the bidirectional easy axis, so as to generate a second unidirectional easy axis on the second adjacent ferromagnetic layer, and in the first A unidirectional easy axis has a different anisotropic strength than the second unidirectional easy axis. 23. The magnetic memory cell structure as claimed in claim 22, wherein the second included angle is substantially less than 90 degrees. 24. The magnetic memory cell structure of claim 22, wherein a nonmagnetic layer is further included between the second antiferromagnetic layer and the second adjacent ferromagnetic layer.

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