JP2003060172A - Magnetic memory cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve reliability by preventing a discontinuity due to electromigration by reducing the write current without lowering the reliability in a magnetic memory device (e.g. MRAM). SOLUTION: A magnetic memory cell comprises a magnetic material having a means for writing information by generating a magnetic field inversion according to a current magnetic field. The memory cell further comprises the write line for generating a magnetic field for writing (bit write line 11, word write line 21) having a composite structure of conductor layers 12, 22 made of nonmagnetic conductors, and magnetic material layers 13, 23 made of soft magnetic materials having high permeability in such a manner that the layers 13, 23 each has a specific resistance of four times or more as large as that of each of the layers 12, 22.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic storage element, and more particularly to a magnetic storage element characterized by a write line.

[0002]

2. Description of the Related Art With the rapid spread of information communication equipment, especially small personal equipment such as portable terminals, the memory elements and logic elements constituting them are highly integrated, high speed, low power consumption, etc. However, higher performance is required. In particular, increasing the density and capacity of non-volatile plating is becoming more and more important as a technology for replacing hard disks and optical disks that are essentially impossible to miniaturize due to the presence of moving parts.

Non-volatile memory includes a flash memory using a semiconductor and an FRAM (Ferro Ferro) using a ferroelectric.
electric Random Access Memory). However, the flash memory has a problem that the writing speed is low, on the order of μs. On the other hand, FRAM is
There is a problem that the number of rewritable times is small.

As a non-volatile memory that does not have the above-mentioned problems, for example, “Wang et al., IEEE Tran.
MR as described in s. Magn.33 (1997), 4498.
This is a magnetic memory called AM (Magnetic Random Access Memory), and has been used in recent years with TMR (Tunnel Magneto Resis
tance) Due to the improvement of the characteristics of materials, it is getting more and more attention.

Since the MRAM has a simple structure, it can be easily highly integrated, and since the recording is performed by the rotation of the magnetic moment, a sufficient number of rewritable times can be obtained. The access time is also expected to be extremely fast, and it has already been confirmed to operate in the nanosecond range.

In the MRAM, in order to record information in a specific bit in the element array, a bit write line and a word write line which traverse the array in the vertical and horizontal directions are provided, and only the element located in the intersection region is asteroid. A method of performing selective writing using characteristics (for example, Japanese Patent Laid-Open No. 10-11
No. 6490) is known.

Next, a general MRAM is replaced with the MRA of FIG.
An enlarged perspective view of a part of M will be described. Note that the read circuit portion is omitted in FIG. 3 for simplification.

As shown in FIG. 3, nine memory cells are shown in this MRAM circuit, and bit write lines 101, 102, 103 and word write lines 104, 105, 106 intersecting each other are provided. At the intersection of those writing lines, TMR (TMR is Tunnel Magneti
Magnetoresistive elements 111 to 119 made of a material or the like are arranged. The TMR element includes an information storage layer having a magnetic substance made of nickel, iron, cobalt, or an alloy of at least two or more thereof, and the magnetization of the information storage layer is magnetized by a magnetic field generated by a write current flowing in a write line. Information is written by changing the direction. Each write line is generally formed of a conductive material (metal) such as aluminum, copper, or an alloy thereof. Each write line is formed by selectively etching a chemically or physically deposited conductive material (metal).

The principle circuit of the MRAM described with reference to FIG. 3 will be described with reference to the circuit diagram of FIG.

As shown in FIG. 4, in this MRAM circuit, six memory cells are shown, and word write lines 104, 105, 10 corresponding to FIG.
6 and bit write lines 101 and 102.
At the intersection of these write lines, a TMR that becomes a storage element
Elements 111, 112, 114, 115, 117, 118
Are arranged, and the element selection is performed at the time of reading. The field effect transistor 121, which corresponds to each memory element,
122, 124, 125, 127, 128 are connected. Further, field effect transistors 121, 124, 1
A sense line 131 is connected to 27, and a sense line 132 is connected to the field effect transistors 122, 125, 128.

The sense line 131 is the sense amplifier 133.
, And the sense line 132 is connected to the sense amplifier 134 to detect the information stored in each element. Write line bidirectional current sources 141 and 142 are connected to both ends of the bit write line 101, and write line bidirectional current sources 14 are connected to both ends of the bit write line 102.
3, 144 are connected. Further, the word write line 104 has a bidirectional current source 151 for the word write line.
The word write line 105 is connected to the word write line bidirectional current source 152, and the word write line 106 is connected to the word write line bidirectional current source 153.

The sectional structure of a single cell of the MRAM corresponding to FIGS. 3 and 4 will be described with reference to the schematic sectional view of FIG.

As shown in FIG. 5, a field effect transistor 215 composed of a gate region 212, a source region 213 and a drain region 214 is arranged on a semiconductor substrate 211, and a word write line 221 and a TMR element layer 231 are formed on the field effect transistor 215. , Bit write lines 241 are arranged.
A sense line 251 is connected to the drain region 214 via a plug 216.

Next, the structure of the TMR film used for the memory cell will be described with reference to the schematic perspective view of FIG.

As shown in FIG. 6, the TMR film 310 includes a storage layer 311 whose magnetization rotates relatively easily and a magnetization fixed layer. The magnetization fixed layer includes the first magnetization fixed layer 313 and the second magnetization fixed layer 313.
Of the magnetic pinned layer 315 and the magnetic pinned layer 315, and the conductor layer 314 is arranged between them so that these magnetic layers are antiferromagnetically coupled. As a material of the conductor layer 314, ruthenium (Ru), copper (Cu), chromium (Cr), gold (Au), silver (Ag), or the like can be used.

The second magnetization fixed layer 315 is the antiferromagnetic layer 3
16 and is formed in contact with the second magnetization fixed layer 315.
The second magnetic pinned layer 315 has strong unidirectional magnetic anisotropy due to the exchange interaction between the antiferromagnetic material layer 316 and the antiferromagnetic material layer 316. As a material of the antiferromagnetic material layer 316, a manganese alloy such as iron (Fe), nickel (Ni), platinum (Pt), iridium (Ir) or rhodium (Rh), or an oxide such as cobalt or nickel is used. it can.

The storage layer 311 and the first magnetization fixed layer 3 are also provided.
A tunnel barrier layer 312 made of an insulating layer made of an oxide or a nitride of aluminum, magnesium, silicon or the like is arranged between the storage layer 311 and the magnetic layer 13 of the first magnetization fixed layer 313. It has a role to cut the static coupling and to pass a tunnel current. The respective films other than the tunnel barrier layer 312 are mainly formed by a sputtering method, and the tunnel barrier layer 312 can be obtained by oxidizing or nitriding a metal film formed by sputtering.

In the memory cell having the above structure, a change in tunnel current due to the magnetoresistive effect is detected and information is read out. The effect depends on the relative magnetization direction between the storage layer and the magnetization fixed layer.

As described above, in the MRAM array, the memory cells are arranged at the intersections of the grids of bit write lines and word write lines. In case of MRAM,
By using the word write line and the bit write line, it is common to selectively write in individual memory cells by utilizing the asteroid magnetization reversal characteristic.

The combined magnetization in a single memory area is the magnetic field H _EA and the hard axis magnetic field H _EA applied to it.
Determined by vector composition with _HA . The current flowing through the bit write line applies a magnetic field in the easy axis direction (H _EA ) to the cell, and the current flowing through the word write line applies a magnetic field in the hard axis direction (H _HA ).

The asteroid curve shown in FIG. 7 shows the reversal threshold value of the magnetization direction of the storage layer due to the applied easy-axis direction magnetic field H _EA and hard-axis direction magnetic field H _HA . When a synthetic magnetic field vector corresponding to the outside of the asteroid curve is generated, magnetic field reversal occurs. The resultant magnetic field vector inside the asteroid curve does not invert the cell from one of its current bistable states. In addition, since the magnetic field generated by the word line or the bit line alone is applied to cells other than the intersection of the word line and the bit line that are passing current, when the magnitude of these is greater than or equal to the one-way reversal magnetic field H _K. Since the magnetization directions of the cells other than the intersections are also inverted, the selected cell can be selectively written only when the combined magnetic field is in the shaded portion 401.

[0022]

However, for the write line, a conductor thin film such as aluminum or copper which is usually used in semiconductor devices is used. For example, a 0.25 μm line width element is used for a switching field of 20 Oe. A writing current of about 2 mA was required to write with the writing line. When the thickness of the write line is equal to the line width, the current density at that time is 3.2 MA / cm ² , which is close to the breaking limit value due to electromigration.

In principle, the write current can be reduced by reducing the coercive force of the recording area.
This method has a limit because the reliability of the information recording element is deteriorated by external magnetic disturbance. Therefore, MR
Reducing the write current has become an important issue in AM.

[0024]

The present invention is a magnetic memory device made to solve the above problems.

The magnetic memory element of the present invention uses a magnetic material having means for writing information by causing magnetic field inversion by a current magnetic field, and the write line for generating the magnetic field for writing is non-magnetic. In a magnetic memory element having a composite structure of a conductor layer made of a conductor and a magnetic layer made of a soft magnetic material having a high magnetic permeability, the magnetic layer has a specific resistance that is four times or more that of the conductor layer. It is a thing.

In the above magnetic memory element, the write line for generating a magnetic field for writing has a composite structure of a conductor layer made of a non-magnetic conductor and a magnetic layer made of a soft magnetic material having a high magnetic permeability. In addition, since the magnetic layer has a resistivity that is four times or more that of the conductor layer, it is possible to suppress a decrease in current use efficiency during writing, and thus it is possible to reduce the current during writing.

[0027]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of a magnetic memory element of the present invention will be described with reference to the schematic perspective view showing the main part of FIG.

As shown in FIG. 1, the magnetic memory element (MRAM) of the present embodiment uses magnetic bodies having means for writing information by causing magnetic field reversal by a current magnetic field, and mutually. Bit write lines 11 that intersect
And a word write line 21, and a magnetoresistive effect element 31 is arranged at the intersection of the bit write line 11 and the word write line 21.

The magnetoresistive element 31 is, for example, TM
R (TMR is an abbreviation for Tunnel Magnetic Resistance) is composed of materials such as nickel, iron or cobalt,
Alternatively, the magnetization direction of the information storage layer is changed by a magnetic field generated by a write current flowing through the bit write line 11 and the word write line 21 including an information storage layer having a magnetic body made of an alloy of at least two of them. By doing so, the information is written.

The bit write line 11 has a composite structure of a conductor layer 12 made of a non-magnetic conductor and a magnetic layer 13 made of a soft magnetic substance having a high magnetic permeability.
Are arranged on the surface of the bit write line 11 opposite to the magnetoresistive effect element 31 side. Then, the magnetic layer 13
Has a specific resistance that is at least four times that of the conductor layer 12.

The word write line 21 has a composite structure of a conductor layer 22 made of a non-magnetic conductor and a magnetic layer 23 made of a soft magnetic material having a high magnetic permeability.
3 is arranged on the surface of the word write line 21 opposite to the magnetoresistive effect element 31 side. And the magnetic layer 2
3 has a resistivity that is four times or more that of the conductor layer 22.

The bit write line 11 is a conductor layer 1 made of aluminum, copper or an alloy thereof by a sputtering method, a plating method or a chemical vapor deposition method.
After depositing 2, the magnetic layer 13 is deposited by sputtering or plating. After that, a desired pattern is formed by ion milling or reactive ion etching. The word write line 21 is formed into a desired pattern by ion milling or reactive ion etching after forming the film in the reverse order of the bit write line 11. In this example, the two-layer structure is applied to both the bit write line 11 and the word write line 21, but it is also effective to use only one of them.

With such a writing structure, the current during writing can be reduced.

By the way, the magnitude of the magnetic field generated from the bit write line 11 and the word write line 21 having the above-described structure is almost inversely proportional to the distance between the current center and the recording element. Therefore, in order to efficiently apply a magnetic field with a constant current, it is better to bring the current center closer to the element.

Next, the reason why the magnetic layer has a specific resistance that is at least four times that of the conductor layer will be described.

In the magnetic memory device having the structure shown in FIG. 1, the write efficiency is set to 90 in order to write efficiently.
It must be at least%. As shown in FIG. 2, the conductor layer 12 (22) and the magnetic layer 13 (23) each have a thickness of 0.1 μm, a line width of 0.25 μm, and the recording layer is a conductor layer 12 (22). When they are in close contact, the ratio of the magnetic field applied to the element when the specific resistance of the magnetic layer is infinite is the writing efficiency, and this writing efficiency and (specific resistance of magnetic layer) / (specific resistance of conductive layer) From the relationship between the specific resistance ratio between the magnetic material layer and the conductive material layer represented by), in order to prevent the writing efficiency from being reduced to 90% or less in the above recording structure, the specific resistance of the magnetic material layer is the specific resistance of the conductive material layer. It can be seen that the resistance needs to be about four times or more.

Aluminum is a commonly used conductor material in semiconductor devices. The specific resistance of bulk aluminum is 2.65 μΩ · cm, and in order to satisfy the above condition, the specific resistance of the magnetic material is approximately 10 μΩ · c.
must be at least m. It is more desirable that the specific resistance of the magnetic layer is 25 μΩ · cm or more, which is about 9 times or more the specific resistance of the conductive layer. In this case, it is possible to suppress the decrease in current use efficiency in writing to 5% or less.

For the above reason, the magnetic layer 13 (23) shown in FIG. 1 has a resistivity that is four times or more that of the conductor layer 12 (22).

The conductor layers 12, 2 which can be used in the present invention
In addition to aluminum, 2 is a conductive substance (metal) such as copper, an alloy of copper and aluminum, or tungsten.
Can be formed with.

Magnetic layer 13 (23) usable in the present invention
As a material that can be used for, there is a material in which an additive such as tantalum (Ta) or niobium (Nb) is added to a nickel iron alloy (for example, permalloy) to have a specific resistance of 25 μΩ · cm or more. For example, the specific resistance of a Ni _0.8 Fe _0.2 alloy ((Ni _0.8 Fe _0.2 ) _0.95 Ta _0.05 ) added with 5 at% of tantalum formed by a sputtering method is 100.
It is μΩcm, and can be sufficiently used. Also,
When these additive elements are added in an amount of 0.5 at% or more, the specific resistance becomes 25 μΩ · cm or more, and thus it can be used. In addition to the above tantalum and niobium, as an additive element,
At least one element selected from boron, carbon, aluminum, silicon, phosphorus, titanium, vanadium, chromium, zirconium, niobium, molybdenum, hafnium, tungsten and yttrium can be used. As a method for forming the film, an electroplating method, a vapor deposition method, or the like can be used in addition to the sputtering method.

The above permalloy has a composition of 5 depending on its composition.
There is a material such as Ni _0.55 Fe _0.45 alloy having a specific resistance of about 0 μΩ · cm, and this can also be used.
Further, a material having a high iron content, such as a Ni _0.45 Fe _0.55 alloy called 45 permalloy, can also be used. These materials can be formed into a film by a film forming method such as a plating method, a sputtering method, or a vapor deposition method.

In addition, an amorphous magnetic material having a specific resistance of about 100 μΩ · cm is generally suitable, for example, CoZr, CoHf, CoZrTa, CoNbT.
a, CoFeB, CoFeC, FeC, FeB, FeN
Materials such as bB, FeNbC, CoTaB and CoTaC can be used. These materials can be formed into a film by a film forming method such as a plating method, a sputtering method, or a vapor deposition method.

Oxides, nitrides or oxynitrides based on iron or cobalt alloys can be used because they have a specific resistance of 40 μΩ · cm to 100 μΩ · cm or more. These materials can be formed into a film by sputtering in gas. For example, FeO-N,
CoO-N, CoFeN, CoFeO, CoFeO-N
Etc. can be used, and 5% to 30% of argon gas is used at the time of film formation.
% Oxygen gas, nitrogen gas, or a mixed gas of oxygen and nitrogen, a sputtering method, an evaporation method, or the like can be used. Further, it is possible to form a film by a plating method. In addition, additives such as boron and carbon are added to these materials at 1 at%
By adding 5 at%, it is possible to promote granularity and further increase resistance.

In the above plating method, for example, a plating solution prepared by adding a sulfate, such as nickel, iron, or cobalt, or a salt oxide, to which a sodium salt such as vanadium or chromium, or an ammonium salt is added, is used. For example, (Ni _0.8 Fe _0.2 )
_As a plating solution for forming a _0.95 Ta _0.05 alloy film, a plating solution obtained by adding sodium tantalate to a solution of nickel sulfate and iron sulfate is used. The temperature of the plating solution is set to room temperature (for example, 20 ° C) to 60 ° C. The pH of the plating solution is adjusted with hydrochloric acid, for example, about 2.0 to 4.0.

In the above-mentioned sputtering method, for example, an RF magnetron sputtering apparatus is used, and as an example, the film forming atmosphere is an argon atmosphere of 0.2 Pa, and the input power is set to 500 W to form the film. As the target, an alloy target prepared to have a composition capable of obtaining a film having a desired composition is used. The substrate temperature during film formation is set appropriately.

To form a granular film by a sputtering method, a mixed gas of argon and 30% oxygen or 30% nitrogen is used as a sputtering gas.

The film formation by the vapor deposition method is performed by, for example, electron beam vapor deposition using a vapor deposition source prepared to have a composition capable of obtaining a film having a desired composition.

[0048]

As described above, according to the magnetic memory device of the present invention, it is possible to write information with a small word write current, so that the write current can be reduced as compared with the conventional one, and the magnetic memory device. It is possible to obtain effects such as a reduction in power consumption, a reduction in electromigration breakage of the write line, an improvement in reliability, and a reduction in the write line driver circuit to reduce a chip area.

[Brief description of drawings]

FIG. 1 is a perspective view of a schematic configuration of a main part showing an embodiment of a magnetic memory element of the present invention.

FIG. 2 is a diagram showing a relationship between a magnetic field applied to an element and a ratio of specific resistances of a magnetic layer and a conductive layer.

FIG. 3 is a schematic configuration perspective view showing a simplified part of the configuration of the MRAM.

FIG. 4 is a circuit diagram showing a principle circuit of an MRAM.

FIG. 5 is a schematic configuration sectional view showing a sectional configuration of a single cell of the MRAM.

FIG. 6 is a schematic configuration perspective view showing a configuration of a TMR film used for a memory cell.

FIG. 7: Easy axis magnetic field H _EA and hard axis magnetic field H
₃ is an asteroid curve showing the reversal threshold of the magnetization direction of the memory layer by _HA .

[Explanation of symbols]

11 ... Bit write line, 12 ... Conductor layer, 13 ... Magnetic layer, 21 ... Word write line, 22 ... Conductor layer, 23
... Magnetic layer

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 5E049 AA01 AA04 AA07 AA09 AC01                       AC10 BA16                 5F033 HH08 HH09 HH11 HH15 HH16                       MM05 PP06 PP15 PP27 VV16                       WW04 XX03 XX05 XX33                 5F083 FZ10 GA05 GA30 JA31 JA36                       JA37 JA60 KA01 PR03 PR21                       PR22

Claims (4)

[Claims] 1. A magnetic material having a means for writing information by causing magnetic field reversal by a current magnetic field, wherein a write line for generating a magnetic field for writing is
In a magnetic memory element having a composite structure of a conductor layer made of a non-magnetic conductor and a magnetic layer made of a soft magnetic material having a high magnetic permeability, the magnetic layer has a specific resistance of 4 times or more that of the conductor layer. A magnetic storage element having: 2. The magnetic layer is an alloy composed of one of iron, cobalt and nickel, or an alloy composed of at least two of these, and includes boron, carbon, aluminum, silicon, phosphorus, 0.5 or more of at least one element selected from titanium, vanadium, chromium, zirconium, niobium, molybdenum, hafnium, tantalum, tungsten and yttrium.
The magnetic memory element according to claim 1, wherein the magnetic memory element contains at% or more. 3. The magnetic layer is made of an amorphous magnetic material.
The magnetic storage element described. 4. The magnetic memory element according to claim 1, wherein the magnetic layer is made of a granular magnetic substance of nitride, oxide or oxynitride.