JP2004193246A - Magnetic memory device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To easily form a magnetic shielding layer and to obtain a highly efficient magnetic shielding effect suitable for an MRAM. <P>SOLUTION: The magnetic random access memory (MRAM) 30 formed of a TMR element 10 where magnetization fixed layers 4 and 6 whose magnetization directions are fixed and a magnetic layer (storage layer) 2 whose magnetization direction can be changed are laminated is sealed with a sealing material 32 such as resin. Magnetic shielding layers 33 and 34 for magnetically shielding the MRAM 30 are brought into contact with one outer face and/or other outer face of the sealing material 32 and are particularly fixed to an upper/lower faces of a package by an adhesive and the like. <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) configured as a magnetic memory device.
[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 -10 ¹⁴ However, it has been pointed out that the endurance is small and it is difficult to finely process the ferroelectric capacitor in order to completely replace the SRAM (Static Random Access Memory) or the DRAM (Dynamic Random Access Memory) with a static random access memory.
[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 more detail. As illustrated in FIG. 18, a TMR element 10 serving as a storage element of a memory cell of an MRAM is provided on a support substrate 9 and has a storage layer whose magnetization is relatively easily rotated. 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. 19 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. 20 schematically shows a cross section of the memory cell, for example, a gate insulating film 15, a gate electrode 16, a source region 17, and a gate insulating film 15 formed in a p-type well region 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 a MESFET (Metal Semiconductor Field Transistor) can be used.
[0015]
FIG. 21 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]
FIG. 22 is an asteroid curve showing the write condition of the MRAM, showing the applied magnetic field H in the easy axis direction. _EA And the hard magnetic field H _HA Of the magnetization direction of the storage layer is shown in FIG. 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. Further, even in cells other than the intersection of the word line and the bit line through which a current flows, a magnetic field generated by the word line or the bit line alone is applied, and thus the magnitude of the magnetic field generated by the unidirectional switching magnetic field H _K In the above case, since the magnetization directions of the cells other than the intersections are also reversed, the selected cells 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, it is generally possible to write only the designated memory cell by reversing the magnetic spin using the asteroid magnetization reversal characteristic. It is a target. The resultant magnetization in a single storage area is determined by the magnetic field H _EA And the magnetic field in the hard axis direction H _HA Is determined by the vector composition with The write current flowing through the bit line applies a magnetic field H in the easy axis direction to the cell. _EA And a current flowing through the word line is applied to the cell by a magnetic field H in the hard axis direction. _HA Is applied.
[0018]
FIG. 23 illustrates a 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 reading, a reading 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 out to the sense line 21 via the reading field effect transistor 19 described above. By doing.
[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. The switching field in the easy axis direction and the switching field H in the hard axis direction described with reference to FIG. _SW Is 20 to 200 Oe (Oe), depending on the material, and is converted into a current of several mA (RH Koch et al., Phys. Rev. Lett. 84, 5419 (2000), JZ. Sun et al., 2001 8 ^th This is because it is as small as Joint Magnetics and Magnetic Material. 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, Co-coated γ-Fe ₂ O ₃ And a magnetic material having a large coercive force such as Ba ferrite. 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 the housing of an electronic device and is also assumed to be carried, it is necessary that the MRAM element be given the same resistance to external magnetism as magnetic cards, especially for the reasons described above. 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. For this purpose, it is best to completely cover the element with a magnetic shield layer. However, it is difficult to manufacture an actual shield structure, and a magnetic shield that can be easily manufactured is desired.
[0028]
However, when ferrite is used for the passivation film as in Patent Document 1 (US Pat. No. 5,902,690), since ferrite is an oxide magnetic material, oxygen deficiency is likely to occur when the film is formed by a sputtering method. It is difficult to use perfect ferrite as a passivation film. 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.
[0029]
In Patent Document 2 (U.S. Pat. No. 5,939,772), a cavity is provided in a package, and a magnetic material having a high magnetic permeability such as permalloy is integrated into an upper part and a lower part of a package surrounding an element. Although the mounting structure is shown, work such as design, processing, etc. is required when integrating them, which is troublesome.
[0030]
Also, in Patent Document 3 (Japanese Patent Application Laid-Open No. 2001-250206), a magnetic shield plate is provided on the upper side via a wall member surrounding the element. , Processing and the like are required, and a technique of mounting a magnetic shield plate in consideration of deflection due to impact or the like is required.
[0031]
The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a magnetic shield layer easily and realize a high-performance magnetic shield effect suitable for an MRAM.
[0032]
[Means for Solving the Problems]
That is, the present invention provides a magnetic random access memory (MRAM) comprising 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 laminated, and a sealing material such as a resin. A magnetic shield layer for magnetically shielding the memory element,
In contact with one outer surface and / or the other outer surface of the sealing material, or at least one side of the inside of the sealing material in a non-contact state with the memory element
Provided
The present invention relates to a magnetic memory device (hereinafter, referred to as a first magnetic memory device of the present invention).
[0033]
According to the first magnetic memory device of the present invention, noting that the MRAM is mainly used as a package molded with a sealing material such as a resin, one of the package sealing materials in which the magnetic shield layer is molded is used. Is attached to the outer surface (for example, the upper surface of the package on the chip surface side of the memory element) or the other surface (for example, the lower surface of the package on the back surface side of the memory element) with an adhesive or the like, so that the magnetic shield is effective. The magnetic shield layer processed into a shape can be easily attached or detached, or at a predetermined position in the sealing material on at least one side of the memory element simply by disposing the magnetic shield layer in the mold at the time of molding. It can be easily buried. For this reason, a high-performance magnetic shield can be easily realized for the MRAM, and the mounting work related to the magnetic shield can be simplified. In addition, this package has a structure and shape suitable for mounting on a circuit board. It becomes.
[0034]
According to the present invention, 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 is formed using a sealing material such as a resin. A magnetic memory device, wherein a magnetic shield layer for magnetically shielding the memory element is provided on the chip back side of the memory element inside the encapsulant (hereinafter, a second embodiment of the present invention). (Hereinafter referred to as a magnetic memory device).
[0035]
According to the second magnetic memory device of the present invention, paying attention to the fact that the MRAM is mainly used as a package molded with a sealing material such as a resin, the magnetic shield layer is fixed between the substrate and the memory element. The magnetic shield layer processed into a shape effective for the magnetic shield can be easily buried at a predetermined position in the sealing material on the back surface side of the chip of the memory element simply by disposing the magnetic shield layer in the mold in the state as described above. For this reason, a high-performance magnetic shield can be easily realized for the MRAM, and the mounting work related to the magnetic shield can be simplified. In addition, this package has a structure and shape suitable for mounting on a circuit board. It becomes.
[0036]
The present invention further provides a magnetic random access memory (MRAM) comprising 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 laminated by using a sealing material such as a resin. A magnetic shield layer for magnetically shielding the memory element,
At least one of the outer surface and the outer surface of the encapsulant may be in contact with the memory element and / or in contact with the memory element inside the encapsulant.
On the other side,
It is also provided on the chip back side of the memory element inside the sealing material.
To
A magnetic memory device (hereinafter, referred to as a third magnetic memory device of the present invention) is also provided.
[0037]
According to the third magnetic memory device of the present invention, focusing on the fact that the MRAM is mainly used as a package molded with a sealing material such as a resin, one of the package sealing materials in which the magnetic shield layer is molded. Is attached to the outer surface (for example, the upper surface of the package on the chip surface side of the memory element) or the other surface (for example, the lower surface of the package on the back surface side of the memory element) with an adhesive or the like, so that the magnetic shield is effective. A magnetic shield layer having a shape can be easily attached or detached, and / or a predetermined position in a sealing material on at least one side of a memory element simply by disposing the magnetic shield layer in a mold at the time of molding. It can be easily embedded and placed in a mold with the magnetic shield layer fixed between the substrate and the memory element. In, the chip back side of the memory element can be easily embedded a magnetic shield layer effective shape to a predetermined position in the sealing material for magnetic shield. For this reason, a high-performance magnetic shield can be easily realized for the MRAM, and the mounting work related to the magnetic shield can be simplified. In addition, this package has a structure and shape suitable for mounting on a circuit board. It becomes.
[0038]
BEST MODE FOR CARRYING OUT THE INVENTION
In the first and third magnetic memory devices of the present invention, the pair of magnetic shield layers sandwich the sealing material in a state of being in contact with the one outer surface and the other outer surface of the sealing material, respectively. It is good to be provided in.
[0039]
In addition, a pair of the magnetic shield layers are provided so as to sandwich the sealing material in a state of being in contact with the one outer surface and the other outer surface of the sealing material, and the third magnetic shield layer is provided with the third magnetic shield layer. Preferably, it is provided on the back surface of the chip.
[0040]
Further, the magnetic shield layer is provided on the chip surface side of the memory element in contact with the one outer surface of the sealing material, and is also provided on the chip back side, and the memory element is provided from both sides. It is also good to have a structure of sandwiching.
[0041]
In the first, second, and third magnetic memory devices according to the present invention, the magnetic shield layer has a flat film shape or a plate shape, and effectively suppresses magnetic saturation. It is preferable that the film has a shape of a film or plate having irregularities, or a shape having a through hole such as a mesh or a slit.
[0042]
When the sealing material contains a soft magnetic filler such as a ferrite filler, the magnetic shielding effect can be further enhanced.
[0043]
In addition, as a shield material for forming the magnetic shield layer, pure iron, Fe-Ni-based, Fe-Co-based, Fe-Ni-Co-based, Fe-Si-based, Fe-Al-Si-based, and ferrite-based And the like. Among them, it is desirable to use a material having not only a certain degree of magnetic permeability but also a high saturation magnetization which is not easily saturated with an external magnetic field. As such a material, a material having a saturation magnetization of 1.8 Tesla (T) or more, particularly, Si 2 to 3% by weight, Fe balance; Co 47 to 50% by weight, Fe balance; Co 35 to 40% by weight, Fe balance 23 to 27% by weight of Co and the balance of Fe; 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.
[0044]
In the MRAM to which the present invention is applied, an insulator layer or a conductor layer is sandwiched between the magnetization fixed layer and the magnetic layer, and a bit line and a word line provided on an upper surface and a lower surface of the memory element are provided. The magnetic layer is magnetized in a predetermined direction by a magnetic field induced by applying a current to the wiring to write information, and the written information is read by a tunnel magnetoresistance effect (TMR effect) between the wirings. Is good.
[0045]
Hereinafter, preferred embodiments of the present invention will be specifically described with reference to the drawings.
[0046]
1 and 2 illustrate MRAM packages having various magnetic shield structures according to the present embodiment, respectively.
[0047]
In these examples, the MRAM element (chip including the memory cell section and the peripheral circuit section) 30 shown in FIGS. 18 to 20 is provided on the die pad 41 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 the lead frame including the die pad 41 is shown in a simplified manner). Then, based on the present invention, an example in which the magnetic shield layers 33, 34, or 33 are fixed to the upper surface and the lower surface of the sealing material 32 constituting the package by an adhesive (FIG. 1), respectively, the upper surface of the sealing material 32 FIG. 2 shows an example (FIG. 2) of fixing with only an adhesive.
[0048]
The magnetic shield layers 33 and 34 can be easily adhered to predetermined positions above, below, or above the sealing material 32 after sealing (after molding) with the sealing material 32. In this case, the magnetic shield layers 33 and 34 may be detachable. In each case, the MRAM element 30 has a sandwich structure disposed 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 in consideration of mounting on a substrate.
[0049]
Each of the magnetic shield structures shown in FIGS. 1 and 2 has an effect of sufficiently shielding the MRAM element 30 from 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 field can be effectively collected and magnetically shielded even with the outside. Although the magnetic shield layers 33 and 34 are preferably provided above and below the MRAM element 30 as shown in FIG. 1, even if they exist only on the chip surface side of the MRAM element as shown in FIG. The effect is exhibited.
[0050]
The present inventor conducted experiments and studies on a shielding effect when a magnetic shield layer was mounted on a package as shown in FIGS. 1 and 2 in order to confirm the guarantee of normal operation of the MRAM element.
[0051]
Due to the development of high-density packaging, the MRAM is practically used in a multi-pin package together with other functional elements. The package structure, QFP (QuadFlat Package), LQFP (Low Profile Quad Flat Package), BGA (BallGrid Array Package), LFBGA (Low Profile Fine Pitch Ball Grid Array Package), LFLGA (Low Profile Fine Pitch Land Grid Array Package) And the like. FIG. 3 shows a package structure 50 of a 160-pin QFP type. A 160 pin QFP type package is about 28 mm x 28 mm and has a thickness of about 3.45 mm.
[0052]
The present inventor has studied the magnetic shielding effect in consideration of this package structure. FIG. 4 shows a schematic diagram of an experiment employed in examining the magnetic shielding effect. Modeling the case where the magnetic shield layers 33 and 34 are installed above and below a 160-pin QFP type package as shown in FIG. 3, two shield layers of 28 mm × 28 mm are arranged at an interval of 3.45 mm, and a Gauss meter 37 is provided at the center thereof. Was installed. Then, by applying a DC external magnetic field 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 (leakage magnetic field strength from the magnetic shield layer) is reduced. It was measured.
[0053]
FIG. 5 shows the measurement results of the internal penetration magnetic field strength with respect to the external magnetic field strength in a structure (sandwich structure) in which the upper and lower sides of a molded MRAM element built-in semiconductor package are sandwiched between magnetic shield layers 33 and 34. As a shield material, Fe-49Co-2V having a high saturation magnetization of Ms = 2.3T and a high saturation magnetization was used, and the thickness of the magnetic shield layer was 300 μm.
[0054]
From FIG. 5, it was confirmed that this magnetic shield structure can suppress the internal magnetic field strength to less than 20 Oe with respect to an external magnetic field of 400 Oe or less. Moreover, the internal magnetic field strength can be suppressed to less than 10 Oe with respect to an external magnetic field of 200 Oe or less.
[0055]
FIG. 6 shows the measurement results of the internal penetration magnetic field strength with respect to the external magnetic field strength in the structure in which the magnetic shield layer 33 is provided only on the upper part of the molded semiconductor package containing the MRAM element. As a shield material, Fe-49Co-2V was used, and the shield thickness was 1000 μm.
[0056]
From FIG. 6, it was confirmed that the magnetic shield structure can suppress the internal magnetic field strength to less than 20 Oe for an external magnetic field of 100 Oe or less and the internal magnetic field strength to less than 10 Oe for an external magnetic field of 50 Oe or less. .
[0057]
From the above, it was found that a large shielding effect was exhibited in the sandwich structure including the upper and lower two magnetic shield layers 33 and 34. It was also confirmed that a certain degree of magnetic shielding effect was obtained even when only one magnetic shield layer 33 was provided on the upper part.
[0058]
In consideration of this result, it is expected that a magnetic shield effect is obtained even when a shield layer is provided on the back surface of the MRAM chip. FIG. 7 shows a schematic diagram of the structure. Here, the distance between the magnetic shield layer 40 and the MRAM element on the chip surface was set to 200 μm (a chip having a thickness of 200 μm was used), and the chip area was set to 15 mm × 15 mm.
[0059]
FIG. 8 shows the measurement results of the internal penetration magnetic field strength with respect to the external magnetic field strength at a magnetic shield layer thickness of 10 to 30 μm. Fe-49Co-2V was used as a shielding material.
[0060]
As shown in FIG. 8, when the external magnetic field is 20 Oe, the internal leakage magnetic field intensity (magnetic field intensity affecting the MRAM element) can be reduced to about 10 Oe or less, and the case where the magnetic shield layer 40 is provided on the back surface of the chip It can be seen from FIG.
[0061]
Further, by using this structure together with the structure in which the magnetic shield layer is provided only on the upper and lower portions or the upper portion of the package, a further shielding effect can be obtained. As an example, as shown in FIG. 9, using a 160-pin QFP type package as a model, two magnetic shield layers 33 and 34 each having a size of 28 mm × 28 mm and a thickness of 300 μm are arranged at an interval of 3.45 mm. The experiment was performed with a structure in which a 15 mm × 15 mm chip having a thickness of 200 μm was provided, in which a magnetic shield layer 40 having a thickness of 20 μm was provided on the back surface of the chip between the layers.
[0062]
As a result, when an external magnetic field of 400 Oe was applied, the internal magnetic field intensity could be reduced to 7.5 Oe, and a high magnetic shielding effect was obtained.
[0063]
From the above experimental results, a structure (sandwich structure) in which the upper and lower portions of the molded semiconductor package with a built-in MRAM element are sandwiched by shield layers, a structure in which a magnetic shield layer is provided only on the upper portion, or a magnetic shield layer on the back surface of the chip It has been found that the structure provided with can provide a magnetic shielding effect against an external magnetic field. Furthermore, it was found that a further magnetic shielding effect can be obtained by adopting a structure combining the above.
[0064]
Although the magnetic shield layers 33 and 34 shown in FIGS. 1 and 2 can be easily adhered (or adhered) to the upper surface and / or lower surface of the sealing material 32 after molding, the magnetic shield layers shown in FIG. The mold 40 can be easily installed if it is molded in a state sandwiched between the die pad 41 and the MRAM element 30 in advance.
[0065]
In addition, an example in which the magnetic shield layer 34 is buried in the encapsulant 32 in contact with the MRAM element 30 below the die pad 41 (FIG. 10) or the respective magnetic shield layers 33 and 34 are formed in the MRAM element Also in the example (FIG. 11) buried in non-contact with 30, there is a magnetic shielding effect.
[0066]
In this case, the magnetic shield layers 33 and 34 may be previously adhered below the die pad 41 at the time of sealing with the sealing material 32 or may be arranged in a mold. Also in the case of FIG. 11, 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 a desirable structure in consideration of mounting on a (circuit board).
[0067]
Any of the magnetic shield structures described above 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 field can be effectively collected and magnetically shielded even with the outside. The magnetic shield layers 33 and 34 preferably exist above and below the MRAM element 30, respectively, but the shielding effect is exhibited even if they exist on at least one of them (especially on the front side of the MRAM element).
[0068]
Further, the magnetic shield layers 33 and 34 described above are made of a flat film, foil or flat plate, but are not limited to this. For example, as shown in FIG. As shown in B), a shape having a through-hole 36 such as a net shape or a slit shape may be used.
[0069]
The magnetic shield layer having the shape shown in FIG. 12 generates a demagnetizing field with respect to an externally applied magnetic field due to the shape anisotropy not only at the peripheral edge but also at the irregularities and the through-hole portions, and is hardly magnetically saturated. It has an effect. The magnetic shield layer having such a shape is prepared in a shape and size most effective for a magnetic shield, and can be easily fixed to a package with an adhesive or the like (this is shown in FIG. 12 and other drawings). The same applies to the magnetic shield layer.)
[0070]
Examples of the shield material of the magnetic shield layers 33 and 34 include pure iron, Fe-Ni, Fe-Co, Fe-Ni-Co, Fe-Si, Fe-Al-Si, and ferrite. No. Among them, it is desirable to use a material having not only a certain degree of magnetic permeability but also a high saturation magnetization which is not easily saturated with an external magnetic field. As such a material, a material having a saturation magnetization of 1.8 Tesla (T) or more, particularly, Si 2 to 3% by weight, Fe balance; Co 47 to 50% by weight, Fe balance; Co 35 to 40% by weight, Fe balance 23 to 27% by weight of Co and the balance of Fe; 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.
[0071]
In each of the above examples, the magnetic shield layer 33, 34, or 40 is provided on the upper, lower, or inner side of the package. However, the filler of the soft magnetic material as described above is contained in the sealing material 32. It was found that when used together, the magnetic shielding effect was further improved.
[0072]
For example, as shown in FIG. 13, the sealing material 42 in which the ferrite filler 51 is dispersed and contained in FIG. 1, and as shown in FIG. 14, the sealing material 42 in which the ferrite filler 51 is dispersed and contained in FIG. As shown in FIG. 15, a package is formed by the sealing material 42 in which the ferrite filler 51 is dispersed and contained in FIG. 7, and as shown in FIG. 16, the sealing material 42 in which the ferrite filler 51 is dispersed and contained in FIG.
[0073]
Then, as shown in FIG. 1, the magnetic shield layers 33 and 34 are provided in a package containing no ferrite filler, and as shown in FIG. 13, the NiZn ferrite filler (average particle diameter 20 μm, addition amount 60 vol. FIG. 17 shows the difference in the internal magnetic field strength between the case where the magnetic shield layers 33 and 34 were provided in the package containing the%). FIG. 17 shows the measurement results of the internal penetration magnetic field strength with respect to the package length (measurement distance) in these two structures. As a shield material, Fe-49Co-2V having a high saturation magnetization of Ms = 2.3T and a high saturation magnetization was used, the thickness of the magnetic shield layer was 300 μm, and the externally applied magnetic field strength was 500 Oe.
[0074]
17, it is confirmed that the internal magnetic field intensity of the shield structure of FIG. 1 is 146.9 Oe and the internal magnetic field intensity of the shield structure of FIG. 13 can be suppressed to 70.4 Oe at an external magnetic field of 500 Oe. did it.
[0075]
In this experiment, NiZn ferrite was used as the ferrite filler, but the ferrite filler is not limited to this, and any oxide magnetic material such as MnZn ferrite, Ba ferrite, or Sr ferrite may be used. In addition, it is expected that a filler having the same or higher magnetic shielding effect can be obtained even if a filler obtained by insulating the surface of a metal soft magnetic powder is used. It is desirable that the average particle size of such a filler is 1 to 50 μm and the amount of addition is 20 to 85% by volume. If the content of the ferrite filler is less than 20% by volume with respect to the package, a good shielding effect cannot be expected. On the other hand, if the content exceeds 85% by volume, the melt viscosity at the time of molding becomes high, and as a package resin, May lack moldability.
[0076]
The embodiments described above can be variously modified based on the technical idea of the present invention.
[0077]
For example, the composition and type of the above-described magnetic shield material, the thickness and arrangement of the magnetic shield layer, the structure of the MRAM, and the like may be variously changed. The above-described magnetic shield structure may be appropriately combined. For example, the structure shown in FIGS. 2 and 7 or the structure shown in FIGS. 7 and 10 can be combined. In FIG. 11, the lower magnetic shield layer 34 is omitted. Is also good.
[0078]
Effects of the Invention
The present invention, as described above, has a structure in which a magnetic shield layer is attached to one outer surface or the other surface of a molded package sealing material with an adhesive or the like, so that a shape effective for a magnetic shield is formed. The magnetic shield layer can be easily attached or detached, and / or can be easily positioned at a predetermined position in the encapsulant on at least one side of the memory element simply by disposing the magnetic shield layer in the mold at the time of molding. The magnetic shield can be buried, and the magnetic shield layer is fixed between the substrate and the memory element, and it is simply placed in the mold. The layer can be easily embedded at a predetermined position in the sealing material. For this reason, a high-performance magnetic shield can be easily realized for the MRAM, and the mounting work related to the magnetic shield can be simplified. In addition, this package has a structure and shape suitable for mounting on a circuit board. It becomes.
[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 plan view and a side view of the MRAM package according to the embodiment;
FIG. 4 is a schematic cross-sectional view at the time of measuring the internal magnetic field strength between the magnetic shield layers.
FIG. 5 is a table showing a measurement result of an internal penetration magnetic field intensity with respect to an external magnetic field intensity in a structure in which upper and lower portions of a semiconductor package having a built-in MRAM element are sandwiched between magnetic shield layers (sandwich structure).
FIG. 6 is a table showing measurement results of an internal penetration magnetic field strength with respect to an external magnetic field strength in a structure in which a magnetic shield layer is provided only above a semiconductor package having a built-in MRAM element.
FIG. 7 is a schematic sectional view of another MRAM package according to the present embodiment.
FIG. 8 is a table showing a measurement result of an internal penetration magnetic field intensity with respect to an external magnetic field intensity in a structure in which a magnetic shield layer is provided on the back surface of the chip.
FIG. 9 is a schematic sectional view of another MRAM package according to the embodiment of the present invention.
FIG. 10 is a schematic sectional view of another MRAM package according to the embodiment;
FIG. 11 is a schematic sectional view of another MRAM package according to the embodiment;
FIG. 12 is a schematic sectional view of another MRAM package according to the embodiment;
FIG. 13 is a schematic sectional view of another MRAM package according to the embodiment;
FIG. 14 is a schematic sectional view of another MRAM package according to the embodiment;
FIG. 15 is a schematic sectional view of another MRAM package according to the embodiment.
FIG. 16 is a schematic sectional view of still another MRAM package according to the embodiment.
FIG. 17 shows a structure (sandwich structure) in which the upper and lower portions of a semiconductor package with a built-in MRAM element are sandwiched between magnetic shield layers, in a case where a ferrite filler is used as a package material and a case where a ferrite filler is not used. It is a graph which shows the measurement result of an internal penetration magnetic field intensity.
FIG. 18 is a schematic perspective view of a TMR element of the MRAM.
FIG. 19 is a schematic perspective view of a part of a memory cell portion of the MRAM.
FIG. 20 is a schematic sectional view of a memory cell of the MRAM.
FIG. 21 is an equivalent circuit diagram of the MRAM.
FIG. 22 is a diagram illustrating a magnetic field response characteristic during writing in the MRAM.
FIG. 23 is a diagram illustrating the principle of a read operation of an 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, 40: magnetic shield layer, 37: Gauss meter,
41: die pad, 42: sealing material containing ferrite filler,
51 ... Ferrite filler

Claims (9)

A magnetic random access memory composed of a memory element in which a magnetization fixed layer having a fixed magnetization direction and a magnetic layer whose magnetization direction can be changed is laminated is sealed with a sealing material. The magnetic shield layer for shielding,
A magnetic memory device provided on at least one side thereof in contact with one outer surface and / or the other outer surface of the encapsulant or inside the encapsulant in a non-contact state with the memory element. A magnetic random access memory composed of a memory element in which a magnetization fixed layer having a fixed magnetization direction and a magnetic layer whose magnetization direction can be changed is laminated is sealed with a sealing material. A magnetic memory device, wherein a magnetic shield layer for shielding is provided on the chip back surface side of the memory element inside the sealing material. A magnetic random access memory composed of a memory element in which a magnetization fixed layer having a fixed magnetization direction and a magnetic layer whose magnetization direction can be changed is laminated is sealed with a sealing material. The magnetic shield layer for shielding,
The memory element is provided on at least one side thereof in a non-contact state with the memory element in contact with one outer surface and / or the other outer surface of the sealing material and / or inside the sealing material,
A magnetic memory device provided inside the sealing material also on the chip back side of the memory element. 4. The magnetic device according to claim 1, wherein the pair of magnetic shield layers are provided so as to sandwich the sealing material in a state of being in contact with the one outer surface and the other outer surface of the sealing material, respectively. 5. Memory device. A pair of the magnetic shield layers are provided so as to sandwich the sealing material in a state of being in contact with the one outer surface and the other outer surface of the sealing material, and a third magnetic shield layer is provided on the chip back surface. The magnetic memory device according to claim 3, wherein A structure in which the magnetic shield layer is provided in contact with the one outer surface of the sealing material on the chip surface side of the memory element and also provided on the chip back side, and sandwiches the memory element from both sides 4. The magnetic memory device according to claim 3, wherein: 4. The magnetic memory device according to claim 1, wherein the magnetic shield layer has a flat or uneven film or plate shape, or a shape having a through hole such as a mesh or a slit. 4. The magnetic memory device according to claim 1, wherein the sealing material contains a soft magnetic filler. 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 current through wirings provided on an upper surface and a lower surface of the memory element, respectively. 4. The magnetic memory device according to claim 1, wherein the magnetic memory device is configured to magnetize in a predetermined direction to write information and read the written information by a tunnel magnetoresistance effect between the wirings.

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