JP4798895B2 - Ferromagnetic memory and its heat-assisted drive method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a nonvolatile memory using a ferromagnetic material, and more particularly to a heat-assisted driving method for a ferromagnetic memory.
[0002]
[Prior art]
In general, a ferromagnetic material has a characteristic that magnetization generated in the ferromagnetic material by a magnetic field applied from the outside remains even after the external magnetic field is removed (this is called residual magnetization). In addition, the electrical resistance of the ferromagnetic material changes depending on the direction of magnetization and the presence or absence of magnetization. This is called the magnetoresistive effect, and the rate of change of the electrical resistance value at that time is called a magnetoresistance ratio (MR ratio). Materials having a large magnetoresistance ratio include giant magnetoresistive (GMR) materials and super magnetoresistive (CMR) materials, such as metals, alloys, and complex oxides. For example, Fe, Ni, Co, Gd, or Tb, and alloys, there are materials such as composite oxide such as _{La X Sr 1-X MnO 9} , La X Ca 1-X MnO 9. If the residual magnetization of the magnetoresistive material is used, a nonvolatile memory that stores information by selecting an electrical resistance value depending on the magnetization direction and the presence or absence of magnetization can be configured. Such a nonvolatile memory is called a magnetic random access memory (MRAM).
[0003]
In recent years, many MRAMs being developed are storing information by the remanent magnetization of a ferromagnetic material of a giant magnetoresistive material, and the change in electrical resistance value caused by the difference in magnetization direction is converted into a voltage and stored. A method is adopted in which the read information is read out. Further, by changing the magnetization direction of the ferromagnetic memory cell by a magnetic field induced by passing a current through the write wiring, information can be written to the memory cell and the information can be rewritten.
[0004]
The MRAM cell has a tunnel magnetoresistive element (TMR: Tunnel Magneto-Resistance, MTJ: Magnetic Tunnel Junction) having a structure in which a tunnel insulating film is sandwiched between two ferromagnets. It is expected to be the device that is the closest to practical use.
[0005]
[Problems to be solved by the invention]
The conventional MRAM is based on the premise that information is held by the magnetization of a ferromagnetic material serving as a recording layer, a current is passed through the write wiring during information rewriting, and the magnetization direction of the recording layer is changed by a magnetic field induced by the current. It has become. However, as the cell area is reduced, the demagnetizing field of the ferromagnetic material increases, and it is necessary to apply a larger rewriting magnetic field. This results in an increase in the amount of current to be passed through the write wiring, and the current density of the write wiring increases dramatically as the cell area is reduced. For this reason, if the design rule becomes smaller than 0.2 μm, the write wiring may not be able to withstand the large current density.
[0006]
In order to solve this problem, a proposal has been made that an element heating means is provided in a magnetic memory element as disclosed in Japanese Patent Application Laid-Open No. 2000-285668. However, in heating the element, the heating element is overheated. This wiring has to be prepared separately, and the structure is complicated, which tends to be an obstacle to reducing the cell area.
[0007]
The present invention has been made to solve such an unsolved problem of the conventional technology, and has a simple structure and a ferromagnetic material capable of stably writing information even if the cell area is reduced. It is an object of the present invention to provide a heat assisted driving method for a memory.
[0008]
[Means for Solving the Problems]
In order to achieve the above object, each of the thermally assisted driving methods for a ferromagnetic memory according to the present invention includes first and second ferromagnetic films, and each of the first and second ferromagnetic films. A plurality of variable resistors having different electric resistance values depending on whether the magnetization directions are parallel and antiparallel, a plurality of bit lines parallel to each other, and a plurality of parallel crossing the bit lines. And a switching element formed on a semiconductor substrate with a control terminal connected to a predetermined word line and one terminal grounded, and a different electrical resistance value depending on the magnetization direction of the ferromagnetic material. The resistance value of the variable resistor is selected by a variable resistor having one terminal connected to the other terminal of the switching element and the other terminal connected to a predetermined bit line, and a magnetic field induced by passing a current. Write wiring and predetermined A signal detection circuit connected to the bit line to detect the resistance value of the variable resistor, and when writing information, a current is passed through the selected variable resistor, and the temperature of the variable resistor is raised above room temperature. Thus, information writing is performed.
[0009]
By making the temperature of the variable resistor higher than room temperature, it is possible to reduce the magnetic field required for the magnetization reversal of the ferromagnetic material. This is because the remanent magnetization gradually weakens as the ferromagnetic material approaches the Curie temperature, and becomes a paramagnetic material at a temperature higher than the Curie temperature and loses the remanent magnetization. That is, it is possible to easily reverse the magnetization by lowering the temperature while heating the ferromagnetic material to an abnormal Curie temperature and applying even a weak magnetic field.
[0011]
The variable resistor may be a tunnel magnetoresistive element.
[0012]
The switching element may be a field effect transistor or a thin film transistor.
[0013]
The variable resistor may be one in which the magnetization direction of the ferromagnetic film of the tunnel magnetoresistive element is horizontal with respect to the film surface, or one in which the magnetization direction is vertical.
[0014]
Further, the tunnel magnetoresistive element includes a first ferromagnetic material having a large coercive force and a second ferromagnetic material having a coercive force smaller than that of the first ferromagnetic material, and a tunnel insulating film sandwiched between them. It may be used.
[0015]
Furthermore, the temperature of the variable resistor during the write operation may be higher than the Curie temperature of the recording layer ferromagnetic material.
The ferromagnetic memory according to the present invention is driven by any one of the methods described above .
The co-magnetic memory according to another aspect of the present invention includes a first and second ferromagnetic films, respectively, and the magnetization directions of the first and second ferromagnetic films are parallel to each other; Provided with a plurality of variable resistors showing different electric resistance values when they are anti-parallel, when writing information, a current is passed through the selected variable resistor, and the temperature of the variable resistor is higher than room temperature Thus, information writing is performed.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Next, embodiments of the present invention will be described in detail with reference to the drawings.
[0017]
FIG. 1 is a configuration diagram of an in-plane magnetization type ferromagnetic memory showing an embodiment of the present invention. The in-plane magnetization type ferromagnetic memory according to the embodiment has a field effect comprising an element isolation region 2, a source / drain region 3 formed by impurity diffusion, and a word line 4 functioning as a gate electrode on a semiconductor substrate 1. Type transistor 13, ground line 7 connected to its source via plug 5, local line 9 connected to its drain via plug 5, metal layer 6 and plug 8, and local line 9 A tunnel magnetoresistive element 11 composed of a pinned layer (ferromagnetic material) / insulating layer / recording layer (ferromagnetic material) and connected to the lower electrode part, and a bit line connected to the upper electrode of the tunnel magnetoresistive element 11 12 and a write line 10 disposed below the tunnel magnetoresistive element 11.
[0018]
In addition, a heat generating layer may be disposed on the lower electrode portion so as to be in contact with the tunnel magnetoresistive element 11.
[0019]
In this embodiment, in the in-plane magnetization type ferromagnetic memory, a write current is supplied to the write line 10 and the bit line 12, and a magnetic field generated by the current flowing in the bit line 12 is included in the tunnel magnetoresistive element 11. The magnetization direction of the layer is determined, and the magnetic field generated by the current flowing through the write line 10 makes it easy to reverse the magnetization of the recording layer of the tunnel magnetoresistive element 11. During a write operation, a write current is supplied to the write line 10 and simultaneously a current is supplied to the bit line 12. Further, a voltage is applied to the word line 4 to turn on the field effect transistor 13 that functions as a switching element. The branched current passes through the tunnel magnetoresistive element 11 and flows to the ground line 7. By this operation, when the recording layer of the tunnel magnetoresistive element 11 is heated to near the Curie temperature, the magnetization is very easily reversed. From this state, when the field effect transistor 13 is turned off and the through current does not flow through the tunnel magnetoresistive element 11, the temperature is rapidly lowered so that the current flowing in the bit line 12 is along the direction of the magnetic field induced. The magnetization direction of the recording layer is determined.
[0020]
FIG. 2 schematically shows the fluctuation state of the voltage and current pulse applied to each wiring in this write operation.
[0021]
FIG. 3 is a configuration diagram of a perpendicular magnetization type ferromagnetic memory showing an embodiment of the present invention. The perpendicular magnetization type ferromagnetic memory of the present embodiment has a field effect comprising an element isolation region 2, a source / drain region 3 formed by impurity diffusion, and a word line 4 functioning as a gate electrode on a semiconductor substrate 1. Type transistor 13, ground line 7 connected to the source via plug 5, drain electrode connected to lower electrode 14 via plug 5, metal layer 6 and plug 8, and lower electrode 14 A tunnel magnetoresistive element 11 comprising a pinned layer (ferromagnetic material) / insulating layer / recording layer (ferromagnetic material), a bit line 12 connected to the upper electrode of the tunnel magnetoresistive element 11, and a tunnel magnetoresistive element 11 and a write line 10 arranged on the lower side.
[0022]
In addition, a heat generating layer may be disposed on the lower electrode 14 so as to be in contact with the tunnel magnetoresistive element 11.
[0023]
In this embodiment, a write current is passed through the write line 10 and the bit line 12, and the magnetic field generated by the current flowing through the write line 10 determines the magnetization direction of the recording layer included in the tunnel magnetoresistive element 11, and the bit line 12. Makes it easier for the magnetic field generated by the current flowing through the tunneling magnetoresistive element 11 to reverse the magnetization of the recording layer.
[0024]
The information rewriting operation is the same as in the case of the in-plane magnetization type ferromagnetic memory.
[0025]
By realizing the driving method of the present invention, information can be stably rewritten with a simple structure and an easy driving method even in a ferromagnetic memory with a small design rule.
[0026]
Next, a specific example of the ferromagnetic memory according to the present embodiment will be shown.
(First specific example)
In the first specific example, a variable resistance whose electric resistance value is variable by selecting a TMR element having a structure in which a tunnel insulating film is sandwiched between two ferromagnetic thin films so that the magnetization direction of the ferromagnetic substance can be changed is selected. Used as a container.
[0027]
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. Since this magnetization direction is maintained unless a magnetic field is applied from the outside, a nonvolatile memory can be realized.
[0028]
First, the memory trial process in the first specific example will be described.
[0029]
As shown in FIG. 4, on a p-type silicon substrate 15, an embedded element isolation region 16 made of SiO ₂ , an n-type diffusion region 17 serving as a drain and a source of a field effect transistor functioning as a switching element, and SiO 2 _{2 A} gate insulating film 18 and a polysilicon gate electrode 19 are formed.
[0030]
Next, as shown in FIG. 5, an interlayer insulating film is formed, the surface is planarized, contact holes are opened, and a plug 20 is formed by embedding tungsten. Next, a wiring layer made of Ti / AlCuSi / Ti is formed, and via 21 and ground line 22 are formed through a photolithography process.
[0031]
Next, as shown in FIG. 6, after an interlayer insulating film is formed and the surface is flattened, a groove is formed in a portion where the wiring is to be formed, and a write wiring 23 mainly made of copper is embedded. A plating method is used for this method. The upper surface of the write wiring 23 and the interlayer insulating film is planarized by CMP (Chemical Mechanical Polishing). Although this write line 23 is not shown in FIG. 7, it is separately connected to a write current control transistor.
[0032]
Next, as shown in FIG. 7, after an interlayer insulating film having a thickness of about 50 nm is formed, contact holes are formed, plugs 24 made of tungsten are formed, and the surface is flattened. Next, a local wiring layer mainly made of TiN is formed, and after the photolithography process, the local wiring 25 is formed.
[0033]
Next, as shown in FIG. 8, a stacked structure 26 of Cu / CoFe / Al ₂ O ₃ / γ-MnFe is formed, an interlayer insulating film is formed, and then the upper Cu electrode is exposed by a CMP process. The γ-MnFe layer is the pinned layer and CoFe is the recording layer.
[0034]
Next, as shown in FIG. 9, a bit line 27 mainly made of copper is formed by a copper plating and CMP filling process, and a protective film 28 is formed to complete the process.
[0035]
A sense amplifier was fabricated as a peripheral circuit.
[0036]
A memory having such a structure was designed with a 0.5 μm rule (minimum processing size of 0.5 μm), and a test chip having 4 × 4 cells was produced. An outline of the circuit is shown in FIG. One cell (C11, C12, C13...) Has one field effect transistor (FET; T11, T12, T13...) And one variable resistor (TMR) connected to its drain terminal. R11, R12, R13..., And the other end of the variable resistor is connected to the bit lines (BL1, BL2, BL3, BL4), the FET source terminal is grounded, and the FET gate electrode terminal is the word Connected to lines (WL1, WL2, WL3, WL4). Each bit line is connected to a sense amplifier (SA1, SA2, SA3, SA4) for comparing the potential with a reference voltage (Ref.). Further, the write lines (WRL1, WRL2, WRL3, WRL4) are arranged immediately below each TMR. Each bit line can be set to the ground potential by the grounding transistors (T1, T2, T3, T4).
[0037]
FIG. 11 shows a state where the cell portion of the test chip is viewed from above. In the figure, one square indicated by a fine dotted line represents a 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 in the longitudinal direction, and is magnetized in the longitudinal direction. The direction of the magnetization of the TMR is determined by the direction of the current flowing through the bit line (BL), and the current flowing through the write line (WRL) generates a magnetic field perpendicular to the easy axis of TMR and makes it easy to reverse the magnetization. For generating an auxiliary magnetic field.
[0038]
The operation of writing “1” to the cell C22 in FIG. 10 will be described. A current is passed through the write line WRL2 and the bit line BL2 (T2 is turned on at this time), then the voltage of the word line WL2 is raised to turn on the field effect transistor T22 and a through current is passed through TMR (R22). By heating, the magnetization of the recording layer is reversed so that the magnetization directions of the TMR (R22) recording layer and the pinned layer are antiparallel. At this time, the current values flowing through the bit line BL2 and the word line WL2 were 5 mA, respectively. The through current value flowing through TMR (R22) is about 60 μA. By this operation, TMR (R22) can be brought into a high resistance state.
Next, in order to read the information in the cell C22, the selection transistor T22 is turned on, a constant current is supplied to BL2, and the bit line BL2 is compared with the reference voltage by the sense amplifier SA2. 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.
[0039]
On the other hand, at the time of writing, when the field effect transistor T22 was kept off and no writing current was passed through TMR (R22), that is, the writing operation was terminated without heating, information was not rewritten.
[0040]
As a result, the effectiveness of the operation according to the present invention was confirmed.
(Second specific example)
A memory cell as shown in FIG. 12 was made by a trial production process similar to that of the first specific example. The difference from the first specific example is that a TMR layer 29 made of a TbFe / Al ₂ O ₃ / GdFe laminated film is formed, and a write line 23 is provided beside the TMR layer 29 and perpendicularly magnetized. Is a point.
[0041]
As a result of performing an operation test similar to that of the first specific example on this memory cell, the effect of the operation according to the present invention was confirmed.
[0042]
【The invention's effect】
According to the present invention, even if the design rule is reduced, it is possible to rewrite information in the ferromagnetic memory with a simple structure and an easy method.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing a configuration of a ferromagnetic memory according to an embodiment of the present invention.
FIG. 2 is an explanatory diagram for illustrating a method of applying voltage and current during driving according to the present invention.
FIG. 3 is a cross-sectional view showing a configuration of a ferromagnetic memory according to an embodiment of the present invention.
FIG. 4 is a cross-sectional view (1) showing a trial production process of a first specific example;
FIG. 5 is a cross-sectional view (2) showing a trial manufacturing process of a first specific example;
FIG. 6 is a cross-sectional view (3) showing a trial production process of the first specific example;
FIG. 7 is a cross-sectional view (4) showing a trial production process of the first specific example;
FIG. 8 is a cross-sectional view (5) showing a trial production process of the first specific example;
FIG. 9 is a sectional view (6) showing a trial production process of the first specific example;
FIG. 10 is a circuit diagram showing a ferromagnetic memory configuration of a first specific example;
FIG. 11 is a plan layout view showing a ferromagnetic memory configuration of a first specific example;
FIG. 12 is a cross-sectional view showing a ferromagnetic memory configuration of a second specific example.
[Explanation of symbols]
DESCRIPTION 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 line 11 Tunnel magnetoresistive element 12 Bit line 13 Field effect transistor 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 writing line 24 Tungsten plug 25 TiN local wiring 26 Cu / CoFe / Al 2 O 3 / γ-MnFe
27 Copper bit line 28 Protective film 29 TbFe / Al 2 O 3 / GdFe

Claims (11)

  Each has first and second ferromagnetic films, and the first and second ferromagnetic films have different electric resistance values when the magnetization directions are parallel and antiparallel. A method of driving a ferromagnetic memory having a plurality of variable resistors, wherein when information is written, a current is supplied to the selected variable resistor, and the temperature of the variable resistor is set to be higher than room temperature, and information is written. A heat-assisted driving method for a ferromagnetic memory for performing writing. The ferromagnetic memory is formed on a semiconductor substrate with 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 control terminal is connected to the predetermined word line It is possible to select different resistance values depending on the direction of magnetization of the ferromagnetic material and the switching element whose terminal is grounded, and one terminal is connected to the other terminal of the switching element, and the other terminal is connected to the predetermined bit line. Connected to the variable resistor, a write wiring for selecting a resistance value of the variable resistor by a magnetic field induced by flowing a current, and a resistance value of the variable resistor connected to the predetermined bit line A signal detection circuit for detecting information, and when writing information, a current is passed through the selected variable resistor, and the temperature of the variable resistor is raised above room temperature to write information. Ferromagnetic heat-assisted method for driving a memory of claim 1.   3. The method according to claim 1, wherein the variable resistor is a tunnel magnetoresistive element.   3. The method according to claim 2, wherein the switching element is a field effect transistor.   3. The method according to claim 2, wherein the switching element is a thin film transistor. 4. The method according to claim 3, wherein the magnetization direction of the ferromagnetic film of the tunnel magnetoresistive element is a horizontal direction with respect to the film surface. 4. The method according to claim 3, wherein the magnetization direction of the ferromagnetic film of the tunnel magnetoresistive element is perpendicular to the film surface. The tunneling magnetoresistive element, the first and the ferromagnetic large coercive force, according to claim 3 comprising sandwiched tunnel insulating film in the second ferromagnetic smaller coercive force than the first ferromagnetic material A heat-assisted driving method of the ferromagnetic memory as described.   2. The ferromagnetic material according to claim 1, wherein when writing information, a current is passed through the selected variable resistor so that the temperature of the variable resistor is higher than the Curie temperature of the recording layer ferromagnetic material. Memory heat-assisted drive method. A ferromagnetic memory driven by the method according to claim 1. Each has first and second ferromagnetic films, and the first and second ferromagnetic films have different electric resistance values when the magnetization directions are parallel and antiparallel. A ferromagnetic memory comprising a plurality of variable resistors, wherein when information is written, a current is passed through the selected variable resistor, and the temperature of the variable resistor is raised from room temperature to perform information writing.

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