JP2003077268A - Ferromagnetic memory and its flashing drive method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent inversion of magnetization of a record layer by disturbance magnetic field. SOLUTION: In a ferromagnetic memory, a larger magnetic field than that at the time of information write operation is applied to a plurality of variable resistors having first and second ferromagnetic films respectively and indicating electric resistance values being different depending on the case of that magnetization directions of the first and second ferromagnetic films are parallel each other and the case of that they are anti-parallel, other than at the time of write operation and read operation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a storage memory for storing information, and more particularly to a non-volatile memory using a ferromagnetic material and its driving method.

[0002]

2. Description of the Related Art Generally, a ferromagnet has a characteristic that the magnetization generated in the ferromagnet by a magnetic field applied from the outside remains even after the external magnetic field is removed (this is called remanent magnetization). In addition, the electric resistance of the ferromagnetic material changes depending on the direction of magnetization and the presence / absence of magnetization. This is called the magnetoresistive effect, and the rate of change of the electric resistance value at that time is calculated as the magnetoresistive ratio (Magneto-Resista
nce Ratio; MR ratio). Giant magnetoresistive (GMR; Giant) is a material with a large magnetoresistive ratio.
Magneto-Rsistance (Material) and Colossal Magneto-Resistance (CMR)
Resistance) materials, such as metals, alloys, and complex oxides. For example, Fe, Ni, Co, Gd,
Tb and these alloys, La _X Sr _1-X MnO ₉ , L
There are materials such as composite oxide such as _{a X Ca 1-X MnO 9} . By utilizing the residual magnetization of the magnetoresistive material, it is possible to configure a non-volatile memory for storing information by selecting an electric resistance value depending on the magnetization direction and the presence or absence of magnetization. Such a non-volatile memory is a magnetic memory (MRAM).
cRandom Access Memory).

Most of MRAMs that have been developed in recent years store information by remanent magnetization of a ferromagnetic material of a giant magnetoresistive material, and change in electric resistance value caused by difference in magnetization direction is converted into voltage. Then, a method of reading the stored information is adopted. Further, by changing the magnetization direction of the ferromagnetic memory cell by a magnetic field induced by passing a current through the write wiring, it is possible to write information in the memory cell and rewrite the information.

As a cell of the MRAM, a tunnel magnetoresistive element (TMR; Tunnel Magneto-Re) having a structure in which a tunnel insulating film is sandwiched between two ferromagnetic materials.
science, MTJ; Magnetic Tun
high magnetic reluctance change rate (M)
R ratio) and is expected to be the most practical device.

[0005]

In the conventional MRAM, information is held by the magnetization of a ferromagnetic material which is a recording layer, and a magnetic field generated during operation or a disturbance magnetic field from the outside of the chip is
It is assumed that the magnetization can endure. However,
By repeating the magnetization reversal of the recording layer and receiving a disturbance magnetic field from the outside of the cell, a domain having a magnetization different from the magnetization direction for originally storing information is generated inside the recording layer. When such a domain occurs,
The magnetization of the recording layer is easily reversed by the disturbance magnetic field, and it becomes difficult to stably hold the memory.

The present invention has been made in order to solve the unsolved problems of the prior art, and an object of the present invention is to provide a ferromagnetic memory capable of holding a stable memory and a driving method thereof. I am trying.

[0007]

In order to achieve the above object, a method of driving a ferromagnetic memory according to the present invention includes a first and a second ferromagnetic films, respectively. Two
A plurality of variable resistors showing different electric resistance values depending on whether the magnetization directions of the ferromagnetic films are parallel or antiparallel, and a magnetic field larger than that at the time of the information writing operation is applied to the plurality of variable resistors. Characterized in that it is applied at times other than a write operation and a read operation, and a plurality of bit lines parallel to each other and a plurality of word lines parallel to each other and intersecting the bit lines are formed in advance on a semiconductor substrate. And a switching element whose control terminal is connected to a predetermined word line and one terminal of which is grounded, and an electric resistance value can be selected by selecting the direction of magnetization of the ferromagnetic material. A variable resistor having one terminal connected to the terminal of the variable resistor and the other terminal connected to a predetermined bit line, and a resistance value of the variable resistor is selected by a magnetic field induced by flowing a current. A write wiring and a signal detection circuit for detecting the resistance value of the variable resistor, which is connected to the predetermined bit line and detects a signal on the bit line before and after the magnetization direction of the ferromagnetic material is inverted during a read operation. A signal detection circuit is provided, and in order to apply a magnetic field larger than that during the write operation to the variable resistor, a current larger than that during the write operation is periodically applied to the write wiring.

According to an embodiment of the present invention, in addition to the write line, a flushing dedicated wiring for generating a magnetic field larger than that in the write operation is provided, and a magnetic field larger than that in the write operation is applied to the variable resistor. In order to
A current may be periodically supplied to the wiring dedicated to flushing.

According to an embodiment of the present invention, the variable resistor may be a tunnel magnetoresistive element. Also, the magnetization direction of the ferromagnetic film of the tunnel magnetoresistive element is horizontal to the film surface, and the magnetization direction of the ferromagnetic film of the tunnel magnetoresistive element is perpendicular to the film surface. You may use what was said. In addition, the tunnel magnetoresistive element has a tunnel insulating film sandwiched between a first ferromagnetic material having a large coercive force and a second ferromagnetic material having a smaller coercive force than the first ferromagnetic material. May be used.

According to an embodiment of the present invention, the switching element may be a field effect transistor or a thin film transistor.

According to an embodiment of the present invention, as a method of applying a magnetic field larger than that during a write operation to the variable resistor, both or one of the operation time and the number of writes is measured, and the write line or A driving method in which a current is passed through the wiring dedicated to flushing may be used. Therefore, a peripheral circuit for measuring the operation time and the number of times of writing is provided.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will be described with reference to the drawings.

Embodiments of the present invention will be described in detail with reference to the drawings.

(First Embodiment) FIG. 1 shows a first embodiment of the present invention.
FIG. 3 is a configuration diagram of an in-plane magnetization type ferromagnetic memory showing the embodiment.

In the first embodiment of the present invention, the semiconductor substrate 1
A ground line 7 is connected via a plug 5 to the source of a field-effect transistor including an element isolation region 2, a source / drain region 3 formed by impurity diffusion, and a word line 4 functioning as a gate electrode. The local wiring 9 is connected to the drain via the plug 5, the metal layer 6, and the plug 8. Pin layer (ferromagnetic material) / on the local wiring 9
The lower electrode portion of the tunnel magnetoresistive element 11 composed of an insulating layer / recording layer (ferromagnetic material) is connected, and the bit line 12 is connected to the upper electrode of the tunnel magnetoresistive element 11. The write line 10 is arranged below the tunnel magnetoresistive element.

In this embodiment, a write current is passed through the write line 10, and the magnetic field generated by this current determines the magnetization direction of the recording layer included in the tunnel magnetoresistive element. During a write operation, a write current is passed through the write wiring 10 and at the same time a current is also passed through the bit line 12, and the magnetic field generated thereby acts to facilitate magnetization reversal in the recording layer.

The magnetic material forming the recording layer is preferably maintained in a state in which the magnetization directions are aligned as shown in FIG. 2A. However, by repeating the rewriting operation or receiving a disturbance magnetic field, As shown in FIG. 2B, a domain having a magnetization direction that does not contribute to memory retention is formed. When such a phenomenon occurs, the switching magnetic field fluctuates, and the magnetization direction is switched by the magnetic field strength that should not be reversed. The state shown in FIG. 2B can be returned to the state shown in FIG. 2A by applying a magnetic field stronger than the write magnetic field. The present invention provides this operation with a simple device structure and driving method.

In the present invention, a current larger than the current value flowing in the write line 10 during the write operation is supplied to the write line 10 separately from the write operation.
This operation is called a flushing operation. As an example,
An operation is performed in which a current of 3 mA is applied to the write line 10 during the write operation, but an electric current of 5 mA is applied during the flushing operation. By this operation, the domain that does not contribute to the record retention generated in the recording layer can be eliminated or reduced and initialized.

The flushing operation is not limited to the case where a larger current is supplied to the write line 10 than that during the write operation, and the larger current may be supplied to the bit line 12 than that during the write operation. Alternatively, as shown in FIG. 3, a dedicated flushing line 13 may be provided and an operation of flowing a current larger than the write current during the flushing operation may be performed.

(Second Embodiment) FIG. 4 shows a second embodiment of the present invention.
FIG. 3 is a configuration diagram of a perpendicular magnetization type ferromagnetic memory showing the embodiment of FIG.

In the second embodiment, on the semiconductor substrate 1,
Element isolation region 2, source formed by impurity diffusion /
Drain region 3 and word line 4 functioning as a gate electrode
The source of the field-effect transistor consists of a plug 5
Connect the ground wire 7 via the
The lower electrode 14 is connected via the metal layer 6 and the plug 8. A tunnel magnetoresistive element 1 comprising a pin layer (ferromagnetic material) / insulating layer / recording layer (ferromagnetic material) on the local wiring 9.
1 is connected to the lower electrode portion of the tunnel magnetoresistive element 1
A bit line 12 is connected to the upper electrode of 1. In addition, the write line 10 is arranged below the tunnel magnetoresistive element. Similar to the in-plane magnetization type ferromagnetic memory, a current larger than the current value flowing in the write line 10 during the write operation is supplied to the write line 10 separately from the write operation. Further, not only when a larger current is supplied to the write line 10 than during a write operation, but a larger current may be supplied to the bit line 12 than during a write operation. Further, the dedicated wiring 13 for flushing may be separately provided, and an operation of flowing a current larger than the write current during the flushing operation may be performed.

By providing a circuit for measuring both or one of the operating time and the number of times of writing, and periodically supplying a current to the write line or the dedicated wiring for flushing at every certain operating time and every certain number of writes, the stored information is stored. Can be stably held.

According to the flushing operation of this embodiment, it is possible to suppress the generation of the magnetization domain that does not contribute to the memory retention and to initialize it, and it is possible to stably retain the memory information.

Next, a specific example of the ferromagnetic memory of the present invention will be shown.

(First Specific Example) FIGS. 5 to 13 show a first example.
It is a figure for explaining a concrete example of.

In the first specific example, a TMR element having a structure in which a tunnel insulating film is sandwiched between two ferromagnetic thin films is selected so that the magnetization direction of the ferromagnetic material can be changed so that the electric resistance value can be changed. It is used as a variable resistor.

Here, the variable resistor (TMR layer) has a structure in which a tunnel insulating film is sandwiched between a hard layer having a large coercive force and a soft layer having a smaller coercive force, and is in-plane magnetized. The resistance value of the TMR layer differs depending on whether the magnetization directions of the hard layer and the soft layer are parallel or antiparallel.
Then, this magnetization direction is maintained unless a magnetic field is externally applied, so that a nonvolatile memory can be realized.

First, the process of trial manufacture of the memory of the first specific example will be described.

As shown in FIG. 5, p-type silicon substrate 15
On top of this, a buried element isolation region 16 made of SiO _{2 is formed.}
And an n-type diffusion region 1 serving as a drain and a source of a field effect transistor that functions as a switching element.
7. A SiO ₂ gate insulating film 18 and a polysilicon gate electrode 19 are formed.

Next, as shown in FIG. 6, an interlayer insulating film is formed, the surface is flattened, contact holes are opened, and a plug 20 is formed by burying tungsten. Next, a wiring layer made of Ti / AlCuSi / Ti is formed, and a via 21 is formed through a photolithography process.
And the ground wire 22 is formed.

Next, as shown in FIG. 7, after forming an interlayer insulating film and flattening the surface, a groove is formed in a portion where a wiring is to be formed so that the write wiring 23 mainly made of copper is buried. Form. A plating method is used for this method. The CMP (Che (Che)
medical Mechanical Polish
It is flattened in g). Although not shown in FIG. 7, the write line 23 is separately connected to the write current control transistor.

Next, as shown in FIG. 8, after forming an interlayer insulating film with a thickness of about 50 nm, a contact hole is opened, a plug 24 made of tungsten is formed, and the surface is flattened. Next, after forming a local wiring layer mainly made of TiN and performing a photolithography process, a local wiring 25 is formed.

Next, as shown in FIG. 9, Cu / CoFe
After forming a laminated structure 26 of / Al ₂ O ₃ / γ-MnFe and forming an interlayer insulating film, the upper Cu electrode is exposed by a CMP process. The γ-MnFe layer is used as a pinned layer and CoFe is used as a recording layer.

Next, as shown in FIG. 10, a bit line 27 mainly made of copper is formed by a copper plating and CMP burying process, and a protective film 28 is formed to complete the process.

A sense amplifier was manufactured as a peripheral circuit.

A memory having such a structure was designed according to a rule of 0.5 μm (minimum processing dimension is 0.5 μm), and a test chip having 4 × 4 cells was manufactured. A schematic of the circuit is shown in FIG. One cell (C11, C12, C1
3. ． ． ． ． ) Is one field effect transistor (F
ET; T11, T12, T13. ． ． ． ． ) And a variable resistor (TMR; R1 connected to its drain terminal).
1, R12, R13. ． ． ． ． ) And the other end of the variable resistor is connected to bit lines (BL1, BL2, BL3, BL
4), the source terminal of the FET is grounded,
The gate electrode terminals of the FET are word lines (WL1, WL
2, WL3, WL4). Further, each bit line is connected to a sense amplifier (SA1, SA2, SA3, SA4) for comparing its potential with a reference voltage (Ref.). In addition, write lines (WRL1, WRL2, WR
L3 and WRL4) are arranged immediately below each TMR. In addition, each bit line has a grounding transistor (T1, T2,
A ground potential can be obtained by T3 and T4).

FIG. 12 shows a state where the cell portion of the test chip is viewed from above. In the figure, one mass indicated by a dotted line represents the minimum processing dimension of 0.5 μm. The variable resistor (TMR) has a rectangular shape with an aspect ratio of 3, has an easy axis of magnetization in the longitudinal direction, and magnetizes in the longitudinal direction. The direction of magnetization of TMR is determined by the direction of the current flowing through the bit line (BL), and the current flowing through the write line (WRL) is TM
It has a role of generating a magnetic field perpendicular to the axis of easy magnetization of R and generating an auxiliary magnetic field for facilitating reversal of magnetization.

The operation of writing "1" in the cell C22 in FIG. 11 will be described. A current is passed through the write line WRL2 and the bit line BL2 (T2 is turned on at this time), and the magnetization of the recording layer of the TMR (R22) is reversed so that the magnetization directions of the recording layer and the pinned layer are antiparallel. . The current value at this time was 5 mA, respectively. By this operation, TMR (R22) can be brought into a high resistance state. Next, in order to read the information of the cell C22, the selection transistor T22 is turned on, a constant current is passed through BL2, and the bit line BL2 and the reference voltage are connected to the sense amplifier SA2.
Compare by. In this case, since R22 is in a high resistance state, the potential of BL2 becomes higher than the reference voltage, and SA2
Outputs a "Hi" signal.

Next, the work of writing "0" (constant resistance state) and "1" (high resistance state) is repeatedly performed in R22.
At this time as well, similar to the above, 5 mA is applied to WRL2 and BL2. FIG. 13 shows the relationship between the number of rewrites and the bit line-reference voltage difference (standard value). When the number of times of rewriting increased, the difference between the bit line and the reference voltage decreased, and when rewriting 10 ¹⁰ times, the sense amplifier could not detect. At this time,
As a flushing operation, 10 are applied to the WRL2 and BL2.
When the operation of flowing mA was performed, the bit line-reference voltage difference was almost recovered as at point A in FIG.

From this, the effect of the flushing operation was confirmed.

(Second Specific Example) FIG. 14 is a plan layout view showing a ferromagnetic memory configuration of the second specific example.

In the second specific example, a memory cell as shown in FIG. 14 was manufactured by the same steps as the first specific example. The difference from the first specific example is that TbFe / Al ₂ O ₃ /
The TMR layer 29 made of a GdFe laminated film is formed, and the structure is employed in which the write line 23 is provided beside the TMR layer 29 and perpendicularly magnetized.

As a result of conducting an operation test on this memory cell in the same manner as in the first specific example, the effect of the flushing operation was confirmed similarly.

(Third Concrete Example) FIG. 15 is a plan layout view showing a ferromagnetic memory configuration of the third concrete example.

As a third specific example, a memory cell as shown in FIG. 15 was manufactured by the same steps as the second specific example. The difference from the second specific example is that a flushing wiring is added separately.

For this memory cell, when flushing, 1 is applied to each of BL2, WRL2 and flushing wiring.
As a result of conducting an operation test similar to that of the second specific example by applying 0 mA, it was possible to confirm the effect of a good flushing operation.

[0047]

As described above, according to the present invention,
By providing the flushing operation, it is possible to maintain a good operation by the problem that the resistance change rate becomes small and the signal strength becomes small by repeatedly performing the rewriting operation.

[Brief description of drawings]

FIG. 1 is a sectional view showing the configuration of a ferromagnetic memory according to a first embodiment of the present invention.

2 is a TM of in-plane magnetization in the ferromagnetic memory of FIG.
It is an explanatory view for explaining an example of magnetization of an R element.

FIG. 3 is a sectional view showing a configuration of a ferromagnetic memory according to a second embodiment of the present invention.

FIG. 4 is a sectional view showing a configuration of a ferromagnetic memory according to a first example of the present invention.

FIG. 5 is a cross-sectional view showing a trial manufacturing process of a first specific example.

FIG. 6 is a cross-sectional view showing a trial manufacturing process of a first specific example.

FIG. 7 is a cross-sectional view showing a trial manufacturing process of a first specific example.

FIG. 8 is a cross-sectional view showing a trial manufacturing process of a first specific example.

FIG. 9 is a cross-sectional view showing a prototype process of the first specific example.

FIG. 10 is a cross-sectional view showing a prototype process of the first specific example.

FIG. 11 is a circuit diagram showing a ferromagnetic memory configuration of a first specific example.

FIG. 12 is a plan layout view showing a ferromagnetic memory configuration of a first specific example.

FIG. 13 is a graph showing the rewriting endurance of the first specific example.

FIG. 14 is a plan layout view showing a ferromagnetic memory configuration according to a second example of the present invention.

FIG. 15 is a plan layout view showing a ferromagnetic memory configuration according to a third example of the present invention.

[Explanation of symbols]

1 semiconductor substrate 2 element isolation region 3 source / drain region 4 word line 5 plug 6 metal layer 7 ground line 8 plug 9 local wiring 10 write wiring 11 tunnel magnetoresistive element 12 bit line 13 flushing dedicated wiring 14 lower electrode 15 p-type silicon Substrate 16 Embedded element isolation region 17 n-type diffusion region 18 SiO ₂ gate insulating film 19 polysilicon gate electrode 20 tungsten plug 21 via 22 ground line 23 copper write line 24 tungsten plug 25 TiN local wiring 26 Cu / CoFe / Al2O3 / γ -MnFe 27 Copper bit line 28 Protective film 29 TbFe / Al2O3 / GdFe stack

Claims (11)

[Claims] 1. Each has a first and a second ferromagnetic film, and is different depending on whether the magnetization directions of the first and the second ferromagnetic films are parallel and antiparallel. In a method of driving a ferromagnetic memory having a plurality of variable resistors having electric resistance values, a magnetic field larger than that during an information writing operation is applied to the plurality of variable resistors except during a writing operation and a reading operation. And method for driving a ferromagnetic memory. 2. A ferromagnetic memory having a plurality of bit lines parallel to each other, a plurality of word lines parallel to each other and intersecting the bit lines, and a word line formed on a semiconductor substrate and having a predetermined control terminal. A switching element whose one terminal is grounded and an electric resistance value can be selected by selecting the direction of magnetization of the ferromagnetic material, and one terminal is connected to the other terminal of the switching element to a predetermined value. Of the variable resistor, the other terminal of which is connected to the bit line, write wiring for selecting the resistance value of the variable resistor by the magnetic field induced by flowing a current, and the resistance value of the variable resistor are detected. As a signal detection circuit to be provided, a signal detection circuit which is connected to a predetermined bit line and which detects a signal of the bit line before and after the magnetization direction of the ferromagnetic material is inverted during a read operation is provided. The large magnetic field from the operation write attempts to apply to the variable resistor, periodically, characterized in that a large current flows from the write operation to the write wiring claim 1
A method for driving the ferromagnetic memory described. 3. A plurality of bit lines which are parallel to each other, a plurality of word lines which are parallel to each other and intersect the bit lines, and a control terminal which is formed on a semiconductor substrate and whose control terminal is connected to the predetermined word line. , The electric resistance value can be selected by selecting the switching element grounded and the direction of magnetization of the ferromagnetic material, and one terminal is connected to the other terminal of the switching element and the other is connected to the predetermined bit line. As a variable resistor connected to the terminal, a write wiring for selecting the resistance value of the variable resistor by a magnetic field induced by flowing a current, and a signal detection circuit for detecting the resistance value of the variable resistor, A signal detection circuit that is connected to the predetermined bit line and that detects a signal of the bit line before and after the magnetization direction of the ferromagnetic material is inverted during a read operation, and separately from the write line, For generating a large magnetic field from the operation write attempts, and having a flushing-grade wire, ferromagnetic memory. 4. A current is periodically supplied to the flushing-dedicated wiring according to claim 3, in order to apply a larger magnetic field to the variable resistor than during a write operation.
The method for driving a ferromagnetic memory according to claim 2. 5. The method for driving a ferromagnetic memory according to claim 2, wherein the variable resistor is a tunnel magnetoresistive element. 6. The method for driving a ferromagnetic memory according to claim 2, wherein the switching element is a field effect transistor. 7. The method of driving a ferromagnetic memory according to claim 2, wherein a thin film transistor is used as the switching element. 8. The method of driving a ferromagnetic memory according to claim 2, wherein the direction of magnetization of the ferromagnetic film of the tunnel magnetoresistive element is horizontal to the film surface. 9. The method for driving a ferromagnetic memory according to claim 2, wherein the direction of magnetization of the ferromagnetic film of the tunnel magnetoresistive element is perpendicular to the film surface. 10. A tunnel magnetoresistive element has a tunnel insulating film sandwiched between a first ferromagnetic material having a large coercive force and a second ferromagnetic material having a smaller coercive force than the first ferromagnetic material. 5. The method for driving a ferromagnetic memory according to claim 2 or 4. 11. In order to apply a larger magnetic field to a variable resistor than during a writing operation, both or one of the operating time and the number of times of writing is measured, and a current is periodically passed through a writing line or a flushing-dedicated wiring. 5. The method for driving a ferromagnetic memory according to claim 2, which is characterized in that.