JP2004193247A - Magnetic memory device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic memory device in which an MRAM element is sufficiently and magnetically shielded against a large outer magnetic field, an operation having no problem for the magnetic field from an environment to which the MRAM element is applied is guaranteed and an electronic unit can be miniaturized and lightened. <P>SOLUTION: The magnetic memory device composed as a magnetic random access memory (MRAM) 30 is formed of a TMR element 10 where magnetization fixing layers 4 and 6 in which magnetization directions are fixed and a magnetic layer (storage layer) 2 whose magnetization direction can be changed are laminated. The TMR element 10 is magnetically shielded by high saturation magnetization material layers 33 and 34 showing a high saturation magnetization of not less than 1.8 tesla (T). <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention provides an MRAM (Magnetic Random Access), which is a magnetic random access memory composed of a memory element in which a magnetization fixed layer whose magnetization direction is fixed and a magnetic layer whose magnetization direction can be changed are stacked. (Memory) or a magnetic memory device including a memory element having a magnetizable magnetic layer.
[0002]
[Prior art]
With the rapid spread of information and communication devices, especially small personal devices such as mobile terminals, devices such as memories and logics have higher performance such as higher integration, higher speed and lower power consumption. Is required.
[0003]
In particular, nonvolatile memories are considered to be indispensable in the ubiquitous era. The nonvolatile memory can protect important information including personal information even when power consumption or trouble occurs, or when the server and the network are disconnected due to some kind of failure. Also, recent portable devices are designed to minimize power consumption by placing unnecessary circuit blocks in standby mode. However, if a non-volatile memory that can serve as both high-speed work memory and large-capacity storage memory can be realized, In addition, power consumption and waste of memory can be eliminated. Also, if a high-speed, large-capacity nonvolatile memory can be realized, an “instant-on” function that can be started immediately when the power is turned on will be possible.
[0004]
Examples of the nonvolatile memory include a flash memory using a semiconductor and an FRAM (Ferroelectric Random Access Memory) using a ferroelectric.
[0005]
However, the flash memory has a drawback that the writing speed is as slow as the order of microsecond. On the other hand, in the FRAM, the number of rewritable times is 10 ¹² to 10 ¹⁴ , so that the endurance (Endurance) is small and the ferroelectricity is small to completely replace the SRAM with a Static Random Access Memory (SRAM) or a Dynamic Random Access Memory (DRAM). It has been pointed out that the fine processing of the body capacitor is difficult.
[0006]
Non-volatile memories that do not have these drawbacks and that have high speed, large capacity (high integration), and low power consumption have attracted attention, for example, Wang et al. , IEEE Trans. Magn. 33 (1997), 4498, which is a magnetic memory called an MRAM (Magnetic Random Access Memory), which has attracted attention due to recent improvements in the characteristics of TMR (Tunnel Magnetoresistance) materials. ing.
[0007]
An MRAM is a semiconductor magnetic memory that uses a magnetoresistance effect based on a spin-dependent conduction phenomenon peculiar to a nanomagnetic material, and is a nonvolatile memory that can hold data without supplying power from the outside.
[0008]
In addition, the MRAM has a simple structure, so that high integration is easy. In addition, since recording is performed by rotating a magnetic moment, the number of rewritable times is large, and the access time is very high. It is expected that R.O. Schuerlein et al, ISSCC Digest of Technical Papers, pp. 128-129, Feb. 2000 reported.
[0009]
The MRAM will be described in further detail. As shown in FIG. 11, a TMR element 10 serving as a storage element of a memory cell of the MRAM is provided on a support substrate 9 and has a magnetization layer which rotates relatively easily. 2 and fixed magnetization layers 4 and 6.
[0010]
The magnetization fixed layer has two magnetization fixed layers, a first magnetization fixed layer 4 and a second magnetization fixed layer 6, and a conductive layer between which these magnetic layers are antiferromagnetically coupled. 5 are arranged. For the storage layer 2 and the magnetization fixed layers 4 and 6, a ferromagnetic material made of nickel, iron or cobalt, or an alloy thereof is used. As a material of the conductor layer 5, ruthenium, copper, chromium, gold, silver Etc. can be used. The second magnetization fixed layer 6 is in contact with the antiferromagnetic layer 7, and the second magnetization fixed layer 6 has strong unidirectional magnetic anisotropy due to the exchange interaction acting between these layers. . As a material of the antiferromagnetic layer 7, a manganese alloy such as iron, nickel, platinum, iridium, and rhodium, cobalt, and nickel oxide can be used.
[0011]
A tunnel barrier layer 3 made of an insulator made of an oxide or a nitride of aluminum, magnesium, silicon, or the like is sandwiched between the storage layer 2 as a magnetic layer and the first magnetization fixed layer 4. In addition, it plays a role of cutting magnetic coupling between the storage layer 2 and the magnetization fixed layer 4 and flowing a tunnel current. These magnetic layers and conductor layers are mainly formed by a sputtering method. The tunnel barrier layer 3 can be obtained by oxidizing or nitriding a metal film formed by sputtering. The top coat layer 1 has a role of preventing interdiffusion between the TMR element 10 and a wiring connected to the TMR element, reducing contact resistance, and preventing oxidation of the storage layer 2, and is usually made of a material such as Cu, Ta, or TiN. Can be used. The base electrode layer 8 is used for connection with a switching element connected in series with the TMR element. The underlayer 8 may also serve as the antiferromagnetic layer 7.
[0012]
In the memory cell configured as described above, information is read out by detecting a change in tunnel current due to the magnetoresistance effect, as described later. The effect depends on the relative magnetization direction between the storage layer and the magnetization fixed layer.
[0013]
FIG. 12 is an enlarged perspective view showing a part of a general MRAM in a simplified manner. Here, the read circuit portion is omitted for simplicity, but includes, for example, nine memory cells, and has a bit line 11 and a write word line 12 that intersect each other. At these intersections, a TMR element 10 is arranged. To write to the TMR element 10, a current flows through the bit line 11 and the write word line 12, and the bit line 11 The writing is performed with the magnetization direction of the storage layer 2 of the TMR element 10 at the intersection of the write word line 12 and the magnetization direction parallel or anti-parallel to the fixed magnetization layer.
[0014]
FIG. 13 schematically shows a cross section of the memory cell, for example, a gate insulating film 15, a gate electrode 16, and a source region 17 formed in a p-type well region 14 formed in a p-type silicon semiconductor substrate 13. An n-type read field effect transistor 19 comprising a drain region 18 is disposed, and a write word line 12, a TMR element 10, and a bit line 11 are disposed thereon. A sense line 21 is connected to the source region 17 via a source electrode 20. The field effect transistor 19 functions as a switching element for reading, and a read wiring 22 drawn out between the word line 12 and the TMR element 10 is connected to the drain region 18 via a drain electrode 23. Note that the transistor 19 may be an n-type or p-type field-effect transistor, but various switching elements such as a diode, a bipolar transistor, and an MESFET (Metal Semiconductor Field Effect Transistor) can be used.
[0015]
FIG. 14 shows an equivalent circuit diagram of the MRAM, which includes, for example, six memory cells, and has a bit line 11 and a write word line 12 that intersect each other. 10, a field effect transistor 19 connected to the storage element 10 to select an element at the time of reading, and a sense line 21. The sense line 21 is connected to the sense amplifier 23 and detects stored information. In the drawing, reference numeral 24 denotes a bidirectional write word line current drive circuit, and reference numeral 25 denotes a bit line current drive circuit.
[0016]
Figure 15 is a asteroid curve indicating the write condition of MRAM, shows inversion threshold of the memory layer magnetization direction of the applied easy axis field H _EA and hard axis direction magnetic field H _HA. When a corresponding resultant magnetic field vector is generated outside this asteroid curve, a magnetic field reversal occurs, but the resultant magnetic field vector inside the asteroid curve does not reverse the cell from one of its current bistable states. Also in cells other than the intersections of word lines and bit lines are a current flows, a magnetic field generated by the word line or bit line alone is applied, if their size is more than one direction reversal magnetic field H _K Since the magnetization direction of the cell other than the intersection is also reversed, the selected cell can be selectively written only when the combined magnetic field is in the gray area in the figure.
[0017]
As described above, in the MRAM, by using the two write lines of the bit line and the word line, only the designated memory cell is selectively written by reversing the magnetic spin using the asteroid magnetization reversal characteristic. That is common. The resultant magnetization in the single storage area is determined by the vector composition of the magnetic field H _{EA in the} easy axis direction and the magnetic field H _{HA in the} hard axis direction applied thereto. A write current flowing through the bit line applies a magnetic field H _{EA in the} easy axis direction to the cell, and a current flowing through the word line applies a magnetic field H _HA in the hard axis direction to the cell.
[0018]
FIG. 16 illustrates the read operation of the MRAM. Here, the layer configuration of the TMR element 10 is schematically illustrated, the above-described magnetization fixed layer is illustrated as a single layer 26, and illustrations other than the storage layer 2 and the tunnel barrier layer 3 are omitted.
[0019]
That is, as described above, the information is written by reversing the magnetic spin of the cell by the synthetic magnetic field at the intersection of the bit line 11 and the word line 12 wired in a matrix, and changing the direction to “1” or “0”. Record as information. Reading is performed using the TMR effect that applies the magnetoresistance effect. The TMR effect is a phenomenon in which the resistance value changes depending on the direction of the magnetic spin. The information "1" and "0" are detected based on the low resistance state in which the magnetic spins are parallel. In this read operation, a read current (tunnel current) flows between the word line 12 and the bit line 11, and an output corresponding to the level of the resistance is read to the sense line 21 via the read field effect transistor 19 described above. Done by
[0020]
As described above, the MRAM is expected to be a high-speed and nonvolatile large-capacity memory. However, since a magnetic material is used for holding data, information is erased or rewritten due to an external magnetic field. Problem. Switching field _{H SW} switching field and hard axis direction of the easy magnetization axis direction described in FIG. 15, depending on the material is 20 to 200 oersteds (Oe), few mA in terms of current (R.H.. ^{Koch et al., Phys.Rev.Lett.84,5419 (2000} ), J.Z.Sun et al., since 2001 8 th Joint Magnetism and Magnetic Material reference) and small. In addition, since the coercive force (Hc) at the time of writing is, for example, about several Oe to 10 Oe, it is impossible to selectively write into a predetermined memory cell if an internal leakage magnetic field due to an external magnetic field exceeding that value acts. It may be.
[0021]
Therefore, as a step toward practical use of the MRAM, there is a long-awaited need for measures against external magnetism, that is, establishment of a magnetic shield structure for shielding the element from external electromagnetic waves.
[0022]
The environment in which the MRAM is mounted and used is mainly on a high-density mounting substrate and inside an electronic device. Depending on the type of electronic equipment, due to the recent development of high-density mounting, semiconductor elements, communication elements, micro motors, etc. are densely mounted on high-density mounting boards. , An antenna element, various mechanical components, a power supply, and the like are mounted at a high density to constitute one device.
[0023]
The fact that the mixed mounting is possible is one of the features of the MRAM as a nonvolatile memory. However, in an environment where a magnetic field component in a wide frequency range from DC to a low frequency to a high frequency is mixed around the MRAM. Therefore, in order to ensure the reliability of recording and holding of the MRAM, it is required to improve the resistance to an external magnetic field by devising a mounting method of the MRAM itself and a shield structure.
[0024]
As the magnitude of such an external magnetic field, for example, it is specified that a magnetic card such as a credit card or a bank cash card has resistance to a magnetic field of 500 to 600 Oe. For this reason, in the field of magnetic cards, a magnetic material having a large coercive force, such as Co-coated γ-Fe ₂ O ₃ or Ba ferrite, is used. Also, in the field of prepaid cards, it is necessary to have resistance to a magnetic field such as 350 to 600 Oe. Since the MRAM element is a device that is mounted in an electronic device housing and is also assumed to be carried, it is necessary to have resistance to a strong external magnetic field equivalent to that of magnetic cards. The magnitude of the magnetic field needs to be suppressed to 20 Oe or less, preferably 10 Oe or less.
[0025]
As a magnetic shield structure of an MRAM, it has been proposed to use an insulating ferrite (MnZn and NiZn ferrite) layer for a passivation film of an MRAM element to provide magnetic shield characteristics (see Patent Document 1 described later). A proposal has been made to attach a high-permeability magnetic material such as permalloy from above and below the package to provide a magnetic shielding effect and prevent magnetic flux from entering an internal element (see Patent Document 2 described later). Further, there is disclosed a structure in which a shield lid is placed on an element with a magnetic material such as soft iron (see Patent Document 3 described later).
[0026]
[Patent Document 1]
U.S. Pat. No. 5,902,690 and drawings (column 5, FIG. 1 and FIG. 3)
[Patent Document 2]
U.S. Pat. No. 5,939,772 and drawings (column 2, FIGS. 1 and 2).
[Patent Document 3]
JP 2001-250206 A (page 5, right column, FIG. 6)
[0027]
[Problems to be solved by the invention]
In order to prevent the external magnetic flux from entering the memory cell of the MRAM, it is most important to provide a magnetic path having a high magnetic permeability around the element to prevent the magnetic flux from entering inside.
[0028]
However, when the passivation film of the element is formed of ferrite as in Patent Document 1 (US Pat. No. 5,902,690), the saturation magnetization of ferrite itself is low (0.2 to 0.5 in a general ferrite material). Tesla (T)), it is impossible to completely prevent the invasion of an external magnetic field. The saturation magnetization of the ferrite itself is about 0.2 to 0.35 T for NiZn ferrite and about 0.35 to 0.47 T for MnZn ferrite. However, since the magnitude of the external magnetic field penetrating the MRAM element is as large as several hundred Oe, At a degree of saturation magnetization, the magnetic permeability of the ferrite becomes almost 1 due to the magnetic saturation of the ferrite, and the ferrite does not function. Although there is no description of the film thickness in Patent Document 1, the effect is hardly expected because the passivation film is usually at most about 0.1 μm, which is too thin for a magnetic shield layer. Moreover, when ferrite is used for the passivation film, since the ferrite is an oxide magnetic material, oxygen deficiency is likely to occur when the film is formed by the sputtering method, and it is difficult to use complete ferrite as the passivation film.
[0029]
Patent Document 2 (U.S. Pat. No. 5,939,772) describes a structure in which the upper and lower portions of a package are covered with a permalloy layer. By using permalloy, a higher shielding performance than a ferrite passivation film can be obtained. However, although the permeability of Mu Metal disclosed in Patent Document 2 is as high as about μi = 100,000, the saturation magnetization is as low as 0.7 to 0.8 T, and is easily affected by an external magnetic field. Since the saturation occurs and μ = 1, there is a disadvantage that the thickness of the shield layer must be considerably large in order to obtain a complete magnetic shielding effect. Therefore, in practice, the structure for preventing the penetration of a magnetic field of several hundred Oe is incomplete as a magnetic shield layer because the saturation magnetization of permalloy is too small and its thickness is too thin.
[0030]
Patent Document 3 (Japanese Patent Application Laid-Open No. 2001-250206) discloses a magnetic shield structure using soft iron or the like. However, since this only covers the upper part of the element, the magnetic shield becomes incomplete and Soft iron has a saturation magnetization of 1.7 T and a magnetic permeability of about 300 μi, which is insufficient magnetic properties. Therefore, even if the magnetic shield is performed by the structure described in Patent Document 3, it is extremely difficult to completely prevent the invasion of the external magnetic field.
[0031]
SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its object to sufficiently shield an MRAM element magnetically even against a large external magnetic field and to provide an environment in which the MRAM element is applied. It is possible to guarantee a trouble-free operation with respect to the magnetic field of the electronic device, and to contribute to a reduction in size and weight of the electronic device.
[0032]
[Means for Solving the Problems]
That is, the present invention provides a magnetic memory device configured as a magnetic random access memory (MRAM) including a memory element in which a magnetization fixed layer having a fixed magnetization direction and a magnetic layer capable of changing the magnetization direction are stacked. 3. The magnetic memory device according to claim 1, wherein the memory element is magnetically shielded by a high saturation magnetization material layer having a high saturation magnetization of 1.8 Tesla (T) or more. Wherein the memory element is magnetically shielded by a high saturation magnetization material layer having a high saturation magnetization of 1.8 Tesla (T) or more. To provide.
[0033]
As a result of intensive studies, the present inventor has focused on the saturation magnetization of the magnetic shield layer in a magnetic memory device, particularly an MRAM, and has set the memory element to an externally applied magnetic field for the first time as a specific high saturation magnetization of 1.8 T or more. It has been found that the magnetic field (internal magnetic field) acting on the surface can be significantly reduced to 10 Oe or less. The magnetic permeability of such a magnetic shield layer is such a value that the magnetic shield layer is magnetized by an externally applied magnetic field, but the saturation magnetization is 1.8 T or more to avoid magnetic saturation of the magnetic shield layer. Must be high. By applying such a magnetic shield layer to an MRAM element, the present invention provides an extremely useful and high-performance magnetic memory for an MRAM which is particularly susceptible to an externally applied magnetic field (in particular, a coercive force at the time of writing is 10 Oe or less). This achieves a shielding effect.
[0034]
BEST MODE FOR CARRYING OUT THE INVENTION
In the magnetic memory device of the present invention, the high saturation magnetization material layer exhibiting a high saturation magnetization of 1.8 T or more is composed of 2 to 3% by weight of Si, the balance of Fe: 47 to 50% by weight of Co, and the balance of Fe: 35 to 40% by weight of Co. 23 to 27% by weight of Co, Fe balance; and 48 to 50% by weight of Co, V1 to 3% by weight, and the balance of Fe; and at least one soft magnetic material selected from the group consisting of: Is desirable.
[0035]
In order for the high saturation magnetization material layer to effectively exhibit its magnetic shield effect, the upper and / or lower portions of the memory element in the package or / and the upper part of the package of the memory element on the outer surface of the package And / or desirably at the bottom.
[0036]
In addition, the high-saturation magnetic material layer has a flat film shape or a plate shape, and in order to more effectively suppress its magnetic saturation, a film or plate shape with irregularities, or a mesh or a slit is used. It is good to have a shape with a through hole.
[0037]
Although the present invention is suitable for an MRAM, such an MRAM has an insulator layer or a conductor layer sandwiched between the magnetization fixed layer and the magnetic layer, and is provided on an upper surface and a lower surface of the memory element. Information is written by magnetizing the magnetic layer in a predetermined direction with a magnetic field induced by flowing a current through each of wirings as a bit line and a word line, and the written information is written in the tunnel magnetoresistance effect (TMR effect) between the wirings. ).
[0038]
Hereinafter, preferred embodiments of the present invention will be specifically described with reference to the drawings.
[0039]
1 to 3 exemplify MRAM packages having various magnetic shield structures according to the present embodiment.
[0040]
In these examples, the MRAM element (chip including the memory cell section and the peripheral circuit section) 30 shown in FIGS. 11 to 13 is provided on the die pad 40 and external leads connected to a mounting board (not shown). Except for the MRAM 31, it is sealed with a sealing material 32 such as a mold resin (for example, epoxy resin). (Here, the MRAM element 30 has the same structure and operation principle as the MRAM described above. It is omitted, and a lead frame including the die pad 40 is shown in a simplified manner). Then, the magnetic shield layers 33 and 34 having a high saturation magnetization of 1.8 T or more according to the present invention are embedded in the sealing material 32 in contact with the upper part of the MRAM element 30 and the lower part of the die pad 40, respectively (FIG. 1). Alternatively, an example in which each is buried in a non-contact manner (FIG. 2) and an example in which the magnetic shield layers 33 and 34 are disposed on the upper surface and the lower surface of the sealing material 32 (FIG. 3) are shown.
[0041]
The magnetic shield layers 33 and 34 are previously adhered on the MRAM element 30 and below the die pad 40 at the time of sealing with the sealing material 32, or are arranged in a mold, or the upper surface of the sealing material 32 after sealing. And the lower surface. In any case, the MRAM element 30 has a sandwich structure arranged between the magnetic shield layers 33 and 34, and the magnetic shield layers 33 and 34 are integrated with the MRAM package. This is the most desirable structure considering the implementation of
[0042]
Each of the magnetic shield structures shown in FIGS. 1 to 3 has an effect of magnetically shielding the MRAM element 30 more than an externally applied magnetic field. In this case, although the magnetic shield layers 33 and 34 do not form a closed magnetic circuit with the outside, the magnetic shield layers 33 and 34 can effectively collect an externally applied magnetic field and magnetically shield the magnetic field. The magnetic shield layers 33 and 34 are preferably provided above and below the MRAM element 30, respectively. However, even if they exist on at least one of them (especially on the surface side of the MRAM element), the shielding effect is exhibited.
[0043]
The magnetic shield layers 33 and 34 shown in FIGS. 1 to 3 are made of a flat film, a foil, or a flat plate, but are not limited to this. For example, as shown in FIG. As shown in FIG. 4B, a shape having a through-hole 36 such as a net shape or a slit shape may be used. The magnetic shield layer having the shape shown in FIG. 4 generates a demagnetizing field with respect to an externally applied magnetic field due to the shape anisotropy not only at its peripheral end but also at the irregularities and through-hole portions, and is hardly magnetically saturated. It has an effect.
[0044]
In each of the magnetic shield structures shown in FIGS. 1 to 4, the saturation magnetization of the magnetic shield layers 33 and 34 is 1.8 T or more, which is much larger than that of conventional ferrite, permalloy, or the like. Since it can be easily and accurately arranged at a predetermined position on the stopper, even if an externally applied magnetic field of 300 Oe to 500 Oe acts, the internal magnetic field with respect to the MRAM element 30 is always suppressed to 10 Oe or less, and sufficient normal operating conditions are obtained. Can be filled in half.
[0045]
Therefore, the inventor of the present invention has proposed a performance such that even if a large DC external magnetic field from 300 Oe to a maximum of 500 Oe is applied, the internal (MRAM element portion) has a performance of 10 Oe or less in order to guarantee the normal operation of the MRAM element. An experiment was performed for the purpose of obtaining. FIG. 5 shows a schematic diagram of the experiment. For example, two magnetic shield layers 33 and 34 each having a size of 10 mm × 10 mm are arranged at an interval of 0.4 mm, and a Gauss meter 37 is provided at the center (cavity). By disposing the DC magnetic field of 300 Oe and 500 Oe in parallel with the magnetic shield layer and moving the Gauss meter 37 in parallel with the magnetic shield layer, the internal magnetic field strength from the end to the center (from the magnetic shield layer) Leakage magnetic field strength) was measured, and an effective magnetic shield material was examined.
[0046]
Among the various types of magnetic shield materials used in this experiment, Fe-10Si-6Al (Sendust), which is a soft magnetic material having the highest magnetic permeability, and Fe-, which is a soft magnetic material having the highest saturation magnetization, are typical materials. FIG. 6 shows representative values of various physical properties of 49Co-2V (Permendur). Fe-10Si-6Al has a high initial permeability μi = 40,000 and a maximum permeability μm = 100,000, whereas the saturation magnetization Ms = 0.85T and a low saturation magnetization value. On the other hand, Fe-49Co-2V has μi = 1,200 and a maximum magnetic permeability μm = 11,000, which is about 1/10 that of Fe-10Si-6Al, whereas Ms = 2. It has a high saturation magnetization of 3T.
[0047]
FIG. 7 shows the distribution of the internal magnetic field strength when the external applied magnetic field is 300 Oe and 500 Oe for each magnetic shield material. Here, a magnetic shield layer (shield foil) having a thickness of 100 μm is used, and the internal magnetic field strength shows the shield length, that is, distribution within 10 mm from one end to the other.
[0048]
According to the result, the internal magnetic field strength shows a large value at the shield end and the center, and the value increases as the applied magnetic field increases. The increase in the internal magnetic field strength at the center is due to the magnetic saturation of the material. When Fe-10Si-6Al having a high magnetic permeability is used as a magnetic shielding material when the applied magnetic field is 300 Oe, the internal central magnetic field strength is 185.5 Oe, while the Fe-49Co having a high saturation magnetization is used. The central magnetic field intensity at -2 V is 7.5 Oe, which indicates an excellent magnetic shielding effect. Similarly, when the applied magnetic field is 500 Oe, the central magnetic field intensity in the case of Fe-10Si-6Al is 389.9 Oe, whereas the central magnetic field intensity in the case of Fe-49Co-2V is as small as 154.3 Oe. Become.
[0049]
Next, FIGS. 8 and 9 show the results of measuring the central magnetic field strength inside the sandwich shield structure with respect to the thickness of the magnetic shield layer of each material. FIG. 8 shows the case where the externally applied magnetic field is 300 Oe, and FIG. 9 shows the case where the externally applied magnetic field is 500 Oe.
[0050]
From FIG. 8, when a magnetic field of 300 Oe is applied, in order to suppress the magnetic field strength penetrating into the inside to 10 Oe or less, Fe-10Si-6Al having a high magnetic permeability requires a shield thickness of 300 μm, It has been found that a shield thickness of 80 μm can sufficiently cope with Fe-49Co-2V having a saturation magnetization. FIG. 9 also shows that when a magnetic field of 500 Oe is applied, a shield thickness of 500 μm is required for Fe-10Si-6Al having a high magnetic permeability, whereas Fe-49Co-2V having a high saturation magnetization is required. It was found that a shield thickness of 150 μm could sufficiently cope with the problem.
[0051]
From the above results, it can be seen that the magnetic shielding effect depends more on the saturation magnetization than on the magnetic permeability, and the use of a high saturation magnetization material of 1.8 T or more as the magnetic shielding material has a much better effect. It was found that the magnetic shield structure could be designed, manufactured, and mounted.
[0052]
FIG. 10 shows the relationship between the internal magnetic field strength and the saturation magnetization value Ms at a magnetic shield layer thickness of 200 μm when the externally applied magnetic field is 500 Oe. The materials used here were Fe-45Ni: Ms = 1.45T (μm = 70,000), Fe-50Ni: Ms = 1.55T (μm = 100,000), Fe-49Co-2V: Ms = 2 0.3T (μm = 11,000), Fe: Ms = 1.7T (μm = 8,000), Fe-3Si: Ms = 1.9T (μm = 30,000), Fe-10Si-6Al: Ms = 0.85T (μm = 100,000).
[0053]
As shown in FIG. 10, the higher the saturation magnetization, the better the shielding effect and the lower the internal magnetic field strength. In particular, in a material having a saturation magnetization of 1.8 T or more, the internal magnetic field strength can be reliably suppressed to less than 10 Oe. On the other hand, with a saturation magnetization material of less than 1.8 T, the internal magnetic field intensity sharply increases and exceeds 10 Oe, making it impossible to guarantee the operation of the MRAM.
[0054]
As the high saturation magnetization material, a material of 1.8 T or more, in particular, Si 2 to 3% by weight, Fe balance: Co 47 to 50% by weight, Fe balance: Co 35 to 40% by weight, Fe balance: Co 23 to 27% by weight, Fe balance And at least one soft magnetic material selected from the group consisting of 48 to 50% by weight of Co, 1 to 3% by weight of V, and the balance of Fe.
[0055]
By using such a highly saturated magnetized material according to the present invention for a magnetic shield, a high magnetic permeability material such as Sendust or a permalloy (Ni-Ni-Ni) as described in the above-mentioned Patent Document 2 (US Patent No. 5,939,772). The shield thickness can be designed to be less than half as compared with the case where a high magnetic permeability material made of Fe-based material is used as the magnetic shield material, which can greatly contribute to the reduction in size and weight of electronic devices.
[0056]
In addition, by using the magnetic shield structure according to the present invention, a good magnetic shield effect is exhibited even with a large applied magnetic field that cannot be completely shielded with a high magnetic permeability material, and an environment in which the operation of the MRAM element can be guaranteed. Can be made.
[0057]
The embodiments described above can be variously modified based on the technical idea of the present invention.
[0058]
For example, the composition and type of the above-described high saturation magnetization material, the thickness and arrangement of the magnetic shield layer, the structure of the MRAM, and the like may be variously changed. The magnetic shield layer may be located on both the top and / or bottom of the MRAM device or package, as well as on the top and / or bottom of the MRAM device, and / or on the top and / or bottom of the package of the MRAM device.
[0059]
Although the present invention is suitable for an MRAM, it is also applicable to other magnetic memory devices including a memory element having a magnetizable magnetic layer.
[0060]
Effects of the Invention
According to the present invention, as described above, in a magnetic memory device, particularly an MRAM, the saturation magnetization of the magnetic shield layer is set to a specific high saturation magnetization of 1.8 or more. The internal magnetic field can be significantly reduced to 10 Oe or less, which is extremely useful for an MRAM which is particularly susceptible to an externally applied magnetic field.
[Brief description of the drawings]
FIG. 1 is a schematic sectional view of an MRAM package according to an embodiment of the present invention.
FIG. 2 is a schematic sectional view of another MRAM package according to the embodiment;
FIG. 3 is a schematic sectional view of another MRAM package according to the embodiment;
FIG. 4 is a schematic sectional view of still another MRAM package according to the embodiment;
FIG. 5 is a schematic cross-sectional view when the internal magnetic field strength between the magnetic shield layers is measured.
FIG. 6 is a table showing various physical property values of Fe-10Si-6Al as a high magnetic permeability material and Fe-49Co-2V as a high saturation magnetization material.
FIG. 7 is a distribution diagram of an internal magnetic field intensity when an externally applied magnetic field is 300 Oe and 500 Oe when a magnetic shield layer (shield foil) having a thickness of 100 μm is used.
FIG. 8 is a table showing the central magnetic field strength with respect to the thickness of the magnetic shield layer when the externally applied magnetic field is 300 Oe.
FIG. 9 is a table showing the central magnetic field strength with respect to the thickness of the magnetic shield layer when the externally applied magnetic field is 500 Oe.
FIG. 10 is a graph showing a change in internal magnetic field strength with respect to a saturation magnetization value.
FIG. 11 is a schematic perspective view of a TMR element of the MRAM.
FIG. 12 is a schematic perspective view of a part of a memory cell unit of the MRAM.
FIG. 13 is a schematic sectional view of a memory cell of the MRAM.
FIG. 14 is an equivalent circuit diagram of the MRAM.
FIG. 15 is a diagram showing a magnetic field response characteristic during writing in the MRAM.
FIG. 16 is a diagram illustrating a read operation principle of the MRAM.
[Explanation of symbols]
1 top coat layer, 2 storage layer, 3 tunnel barrier layer,
4 a first magnetization fixed layer, 5 an antiferromagnetic coupling layer, 6 a second magnetization fixed layer,
7: antiferromagnetic layer, 8: underlayer, 9: support substrate,
10: memory cell (TMR element), 11: bit line,
12 write word line, 13 silicon substrate, 14 well region,
15 gate insulating film, 16 gate electrode, 17 source region,
18 ... Drain region,
19: Field effect transistor for reading (transistor for selection),
20 ... source electrode, 21 ... sense line, 22 ... readout wiring,
23: drain electrode, 26: magnetization fixed layer,
30: MRAM element (with built-in TMR element), 31: external lead, 32: sealing material,
33, 34: High saturation magnetization magnetic shield layer, 37: Gauss meter,
40 ... Die pad

Claims (6)

In a magnetic memory device configured as a magnetic random access memory including a memory element in which a magnetization fixed layer having a fixed magnetization direction and a magnetic layer capable of changing the magnetization direction are stacked, the memory element includes: A magnetic memory device characterized by being magnetically shielded by a high saturation magnetization material layer having a high saturation magnetization of 8 Tesla or more. A magnetic memory device comprising a memory element having a magnetizable magnetic layer, wherein the memory element is magnetically shielded by a high saturation magnetization material layer exhibiting a high saturation magnetization of 1.8 Tesla or more. apparatus. The high saturation magnetization material layer contains 2 to 3% by weight of Si, the balance of Fe; 47 to 50% by weight of Co, the balance of Fe; 35 to 40% by weight of Co, the balance of Fe; 23 to 27% by weight of Co, the balance of Fe; and 48 to 50% by weight of Co. 3. The magnetic memory device according to claim 1, wherein the magnetic memory device is formed of at least one soft magnetic material selected from the group consisting of V, 1 to 3% by weight, and the balance of Fe. 3. The method according to claim 1, wherein the high saturation magnetization material layer is disposed above and / or below the memory element in a package and / or above and / or below the memory element on the outer surface of the package. 4. A magnetic memory device as described. 3. The magnetic memory device according to claim 1, wherein the high saturation magnetization material layer has a flat or uneven film or plate shape, or a shape having a through hole such as a mesh or a slit. An insulator layer or a conductor layer is sandwiched between the magnetization fixed layer and the magnetic layer, and the magnetic layer is generated by a magnetic field induced by flowing a current through wirings provided on an upper surface and a lower surface of the memory element, respectively. 2. The magnetic memory device according to claim 1, wherein the information is written by magnetizing the data in a predetermined direction, and the written information is read out by a tunnel magnetoresistance effect between the wirings.

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