JP2003060173A - Method for terminal auxiliary drive of ferromagnetic memory - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem that, when a cell area of a conventional MRAM is reduced, a diamagnetic field of a ferromagnetic material is increased, it is necessary to impart a larger rewriting magnetic field, and hence a current to flow to the write wiring is increased with the result that as the cell area is decreased, a current density of the write wiring is remarkably increased. SOLUTION: A method for thermal auxiliary drive of a ferromagnetic memory comprises the steps of supplying currents to a selected variable resistors of a plurality of variable resistors, in the case of writing information in the resistors indicating different electric resistance values of the case that magnetizing directions of first and second ferromagnetic films are parallel, and the case that the magnetizing directions of the first and second ferromagnetic films are anti-parallel; raising the temperature of the variable resistor to a temperature higher than the ambient temperature; and writing information in the resistor.

Description

Detailed Description of the Invention

[0001]

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

[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 expressed by the magnetoresistive ratio (MR).
Ratio). Giant Magneto-Resistance (GMR) materials and Colossal Magneto-Resistance (CMR) materials have a large magneto-resistance ratio.
There are 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. 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 nonvolatile memory is called a magnetic memory (MRAM; Magnetic Random 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 an MRAM, a tunnel magnetoresistive element (TMR; Tunnel Magneto-Resistance, MT) having a structure in which a tunnel insulating film is sandwiched between two ferromagnetic materials is used.
J; Magnetic Tunnel Junction) has a high magnetoresistance change rate (MR 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, a current is passed through a write wiring when the information is rewritten, and a magnetic field induced by the current causes a magnetic field in the recording layer to change. It is assumed that the magnetization direction is changed. 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 in the write wiring increases dramatically as the cell area is reduced. Therefore, if the design rule is smaller than 0.2 μm, the write wiring may not be able to withstand the high current density.

In order to solve this problem, Japanese Patent Laid-Open No. 2000-
As disclosed in Japanese Patent No. 285668, it has been proposed to provide a magnetic memory element with an element heating means. However, in order to heat the element, it is necessary to separately prepare wiring for overheating a heating element. However, there is a drawback that it is complicated and tends to become an obstacle when reducing the cell area.

The present invention has been made to solve the above-mentioned unsolved problems of the conventional technique, and has a simple structure and can stably write information even if the cell area is reduced. It is an object of the present invention to provide a thermally assisted driving method for a ferromagnetic memory.

[0008]

In order to achieve the above-mentioned object, a method of thermally assisting a ferromagnetic memory according to the present invention has first and second ferromagnetic films, respectively. And a plurality of variable resistors having different electric resistance values when the magnetization directions of the second ferromagnetic film are parallel and antiparallel, and a plurality of bit lines which are parallel to each other in advance, and A plurality of word lines that are parallel to each other and intersect the bit line, a switching element that is formed on a semiconductor substrate, has a control terminal connected to a predetermined word line and one terminal is grounded, and a magnetization direction of a ferromagnetic material. A variable resistor that enables selection of different electrical resistance values, one terminal of which is connected to the other terminal of the switching element and the other terminal of which is connected to a predetermined bit line, and a magnetic field induced by flowing a current. The resistance of the variable resistor It has a write wiring to be selected and a signal detection circuit connected to a predetermined bit line to detect the resistance value of the variable resistor.When writing information, a current is passed through the selected variable resistor to change the resistance. It is characterized in that the temperature of the resistor is set higher than room temperature to write information.

By making the temperature of the variable resistor higher than room temperature, it is possible to reduce the magnetic field required for reversing the magnetization of the ferromagnetic material. This is because when the ferromagnetic material approaches the Curie temperature, the remanent magnetization gradually weakens, and when the temperature rises above the Curie temperature, it becomes a paramagnetic material and loses the remanent magnetization. That is, the magnetization can be easily reversed by heating the ferromagnetic material to an abnormal Curie temperature and applying a weak magnetic field while lowering the temperature.

According to an embodiment of the present invention, a heating layer is arranged separately from the variable resistor so as to be in contact with the variable resistor, and a current is supplied to the selected variable resistor and the heating layer during a write operation. Alternatively, the temperature of the variable resistor may be made higher than room temperature to perform the information writing operation.

The variable resistor may be a tunnel magnetoresistive element.

The switching element may be a field effect transistor or a thin film transistor.

Further, as the variable resistor, one in which the magnetization direction of the ferromagnetic film of the tunnel magnetoresistive element is horizontal to the film surface may be used, or one in which it is vertical may be used. .

Further, in the tunnel magnetoresistive element, a tunnel insulating film is 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. You may use what is.

Furthermore, the temperature of the variable resistor during the write operation may be higher than the Curie temperature of the recording layer ferromagnetic material.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION Next, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block 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 including a device 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, a ground line 7 connected to the source thereof via the plug 5, a local wiring 9 connected to the drain thereof via the plug 5, the metal layer 6 and the plug 8, and a local wiring 9 A tunnel magnetoresistive element 11 formed of a pinned layer (ferromagnetic material) / insulating layer / recording layer (ferromagnetic material) and connected to a lower electrode portion, and a bit line connected to an upper electrode of the tunnel magnetoresistive element 11. 12
And a write line 10 arranged below the tunnel magnetoresistive element 11.

In addition to this, a heating layer may be arranged in the lower electrode portion so as to be in contact with the tunnel magnetoresistive element 11.

In this embodiment, in the in-plane magnetization type ferromagnetic memory, a write current is passed through the write line 10 and the bit line 12, and a magnetic field generated by the current flowing through the bit line 12 is applied to the tunnel magnetoresistive element 11. The magnetization direction of the included recording layer is determined, and the magnetic field generated by the current flowing through the write line 10 facilitates reversal of the magnetization of the recording layer of the tunnel magnetoresistive element 11. 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 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 flows through the tunnel magnetoresistive element 11 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 extremely likely to be reversed. From this state, when the field effect transistor 13 is turned off and a through current stops flowing through the tunnel magnetoresistive element 11, the temperature thereof rapidly decreases,
The magnetization direction of the recording layer is determined so as to be along the magnetic field direction induced by the current flowing through the bit line 12.

FIG. 2 schematically shows how the voltage and current pulse applied to each wiring change during this write operation.

FIG. 3 is a block diagram of a perpendicular magnetization type ferromagnetic memory showing an embodiment of the present invention. The perpendicular magnetization type ferromagnetic memory according to the present embodiment has a field effect composed of 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, a ground line 7 connected to the source via the plug 5, a lower electrode 14 connected to the drain via the plug 5, the metal layer 6 and the plug 8, and a lower electrode 14 A tunnel magnetoresistive element 11 composed of a pinned layer (ferromagnetic material) / insulating layer / recording layer (ferromagnetic material), a bit line 12 connected to an upper electrode of the tunnel magnetoresistive element 11, and a tunnel magnetoresistive element. 11 and a write line 10 arranged on the lower side of the line 11.

Besides, a heating layer may be arranged on the lower electrode 14 so as to be in contact with the tunnel magnetoresistive element 11.

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 causes the tunnel magnetoresistive element 1 to operate.
1 determines the magnetization direction of the recording layer included in the bit line 12
The magnetic field generated by the current flowing in the magnetic field makes it easy to reverse the magnetization of the recording layer of the tunnel magnetoresistive element 11.

The information rewriting operation is the same as in the case of the in-plane magnetization type ferromagnetic memory.

By implementing the driving method of the present invention,
Even in a ferromagnetic memory having a small design rule, information can be stably rewritten with a simple structure and an easy driving method.

Next, a specific example of the ferromagnetic memory of this embodiment will be shown. (First Specific Example) 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 used.
This is used as a variable resistor in which the electric resistance value is made variable by selecting the magnetization direction of the ferromagnetic material to be changeable.

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 in the first specific example will be described.

As shown in FIG. 4, 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 17 serving as a drain and a source of a field effect transistor that functions as a switching element.
Then, the SiO ₂ gate insulating film 18 and the polysilicon gate electrode 19 are formed.

Next, as shown in FIG. 5, 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. 6, 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 embedded. Form. A plating method is used for this method. The write wiring 23 and the upper surface of the interlayer insulating film are CMP (Chemic
flattening by al Mechanical Polishing). Although not shown in FIG. 7, the write line 23 is separately connected to the write current control transistor.

Next, as shown in FIG. 7, after forming an interlayer insulating film having 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. 8, 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. 9, a bit line 27 mainly made of copper is formed by a copper plating and burying process by CMP, 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. The outline of the circuit is shown in FIG. One cell (C11, C12, C13 ...
・) Is one field effect transistor (FET; T1)
1, T12, T13 ...) and one variable resistor (TMR; R11, R12, R) connected to its drain terminal.
13 ...) and the other end of the variable resistor is connected to the bit lines (BL1, BL2, BL3, BL4),
The source terminal of T is grounded, and the gate electrode terminal of FET is connected to the word lines (WL1, WL2, WL3, WL4). The potential of each bit line is set to the reference voltage (Re
f. ) Sense amplifiers (SA1, SA)
2, SA3, SA4). In addition, the write lines (WRL1, WRL2, WRL3, WRL4) are connected to each T
It is located directly below the MR. Further, each bit line can be set to the ground potential by the grounding transistors (T1, T2, T3, T4).

FIG. 11 shows a state where the cell portion of the test chip is viewed from above. In the figure, one mass indicated by a fine 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 the TMR magnetization 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, facilitating the reversal of the magnetization. Has a role of generating an auxiliary magnetic field.

The operation of writing "1" in the cell C22 in FIG. 10 will be described. A current is passed through the write line WRL2 and the bit line BL2 (at this time, T2 is turned on), 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 of TMR (R22) is reversed so that the magnetization directions of the recording layer and the pinned layer are antiparallel. Bit line BL2 and word line WL2 at this time
The value of the current flowing through each was 5 mA. Also, T
The value of the through current flowing through the MR (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 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 compared by the sense amplifier SA2. In this case, since R22 is in the high resistance state, the potential of BL2 becomes higher than the reference voltage, and SA2 outputs the “Hi” signal.

On the other hand, at the time of writing, when the field effect transistor T22 was kept off and the write operation was completed without passing through current to TMR (R22), that is, without heating, no information was rewritten.

This confirmed the effectiveness of the operation according to the present invention. (Second Specific Example) A memory cell as shown in FIG. 12 was experimentally manufactured by the same manufacturing process as in the first specific example. The difference from the first specific example is that the TMR layer 29 made of a TbFe / Al ₂ O ₃ / GdFe laminated film is formed, and the write line 23 is provided beside the TMR layer 29 to vertically magnetize. It is a point.

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 operation according to the present invention was similarly confirmed.

[0042]

According to the present invention, it is possible to rewrite information in a ferromagnetic memory with a simple structure and an easy method even if the design rule becomes small.

[Brief description of drawings]

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

FIG. 2 is an explanatory diagram showing a method of applying a voltage and a current during driving of the present invention.

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

FIG. 4 is a sectional view (1) showing a trial production process of the first specific example.

FIG. 5 is a sectional view (2) showing a trial manufacturing process of the first specific example.

FIG. 6 is a sectional view (3) showing a trial manufacturing process of the first specific example.

FIG. 7 is a sectional view (4) showing a trial manufacturing process of the first specific example.

FIG. 8 is a sectional view (5) showing a trial manufacturing process of the first specific example.

FIG. 9 is a sectional view (6) showing a trial manufacturing 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]

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 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

Claims (10)

[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. A method of driving a ferromagnetic memory having a plurality of variable resistors showing an electric resistance value, wherein when writing information, a current is passed through the selected variable resistor so that the temperature of the variable resistor is higher than room temperature. A thermally assisted driving method of a ferromagnetic memory for increasing information writing. 2. 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 word having a predetermined control terminal. A switching element connected to a line and one terminal of which is grounded, and a different electric resistance value that enables selection of different electrical resistance values depending on the direction of magnetization of the ferromagnetic material, and one terminal of which is connected to the other terminal of the switching element. A variable resistor having the other terminal connected to the bit line, a write wire for selecting the resistance value of the variable resistor by a magnetic field induced by flowing a current, and a write wire connected to a predetermined bit line. And a signal detection circuit for detecting the resistance value of the variable resistor.When writing information, a current is passed through the selected variable resistor to raise the temperature of the variable resistor above room temperature, Ferromagnetic heat-assisted method for driving a memory according to claim 1 for writing. 3. The ferromagnetic memory has a heating layer so as to be in contact with the variable resistor separately from the variable resistor, and when the information is written, the selected variable resistor and the generated heat are generated. 3. An information write is performed by passing a current through the layer to raise the temperature of the variable resistor above normal temperature.
A thermally assisted driving method for a ferromagnetic memory according to claim 1. 4. The variable resistor is a tunnel magnetoresistive element.
Alternatively, the heat assisted driving method of the ferromagnetic memory according to claim 2. 5. The heat-assisted driving method for a ferromagnetic memory according to claim 2, wherein the switching element is a field effect transistor. 6. The heat assisted driving method for a ferromagnetic memory according to claim 2, wherein the switching element is a thin film transistor. 7. The magnetization direction of the ferromagnetic film of the tunnel magnetoresistive element is horizontal to the film surface.
5. A heat assisted driving method for a ferromagnetic memory according to claim 4. 8. The magnetization direction of the ferromagnetic film of the tunnel magnetoresistive element is perpendicular to the film surface.
5. A heat assisted driving method for a ferromagnetic memory according to claim 4. 9. 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. 6. A method of thermally assisting a ferromagnetic memory according to claim 1, wherein 10. When writing information, a current is caused to flow 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. A thermally assisted driving method for a ferromagnetic memory according to claim 1.