JP2003115577A - Nonvolatile magnetic thin film memory - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a magnetic thin film memory employing a magnetoresistive effect element 41 as a memory element in which erroneous writing or incomplete writing due to saturation magnetization of a magnetic film or variation of coercive force incident to variation working temperature dependent significantly on the environment is reduced. SOLUTION: The nonvolatile magnetic thin film memory uses a magnetoresistive effect element 41 having a vertical magnetization film as a memory element, employs a ferrimagnetic body where rare earth element magnetization is dominant in the vertical magnetization film and has a compensation temperature between a room temperature and a Curie point. A magnetic thin film memory comprises means for controlling the level of a current required for writing information stepwise, and a temperature sensor sensing the temperature of the magnetoresistive effect element. In the recording/reproducing method of the magnetic thin film memory, test writing of information in the memory cell is performed before the information is recorded and normal data is recorded after recording the test writing is confirmed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nonvolatile magnetic thin film memory device using a magnetoresistive effect element,
In particular, the present invention relates to a non-volatile magnetic thin film memory device corresponding to a change in coercive force of a perpendicularly magnetized film with temperature.

[0002]

2. Description of the Related Art Conventionally, a magnetic thin film memory is known as a solid-state memory having no moving part, like a semiconductor memory. Such a magnetic thin film memory satisfies the conditions that information is not lost even when power is cut off, the number of times information is repeatedly rewritten is unlimited, and there is no risk of information being lost even when radiation is incident. However, it has many advantages over conventional semiconductor memories.

Among them, a tunnel magnetic resistance (TMR; Tunnel Magne) which has been recently proposed.
The magnetic thin film memory utilizing the to Resistive effect has been particularly attracting attention because it can obtain a larger output than the conventional magnetic thin film memory utilizing the anisotropic magnetoresistive effect and the giant magnetoresistive effect.

In a magnetic thin film memory utilizing the tunnel magnetoresistive effect, two ferromagnetic layers are separated by a thin insulating layer (tunnel barrier layer), and the magnetoresistance according to the difference in spin polarizability between the two ferromagnetic layers. Occurs. The magnitude of the tunnel current depends on whether the magnetizations of the two ferromagnetic layers are relatively parallel,
Depends on antiparallel.

FIG. 11 is a schematic diagram showing an example of the configuration of a conventional magnetic thin film memory utilizing the tunnel magnetoresistive effect.

As shown in FIG. 11, a tunnel barrier layer 112 is sandwiched between magnetic layers 111 and 113 having different coercive forces.

In the magnetic thin film memory configured as described above, when a voltage 114 is applied between the magnetic layers 111 and 113, electrons from one magnetic layer penetrate the tunnel barrier layer 112 and the other magnetic layer is magnetized. The tunnel current is generated by entering the layer. The magnitude of this tunnel current depends on the applied voltage. The resistance depends on the state of magnetization of both layers of the magnetic layers 111 and 113, and takes a minimum resistance value when both layers are relatively parallel and a maximum resistance value when they are antiparallel. This phenomenon has been confirmed both when the magnetic layers 111 and 113 are in-plane magnetized films and when they are perpendicular magnetized films (Journal of Japan Society for Applied Magnetics).
24, 563-566 (2000)).

As a magnetic thin film memory utilizing such a phenomenon, an MRAM (Magnetic Random) is used.
There is a non-volatile magnetic storage device called an Access Memory.

Although a tunnel magnetoresistive effect element using an in-plane magnetized film having a large in-plane magnetic anisotropy such as Fe, Co, or Ni as a ferromagnetic layer of the tunnel magnetoresistive effect film has been actively developed. Japanese Laid-Open Patent Publication No. 11-213650 discloses a magnetoresistive effect element using a perpendicular magnetization film.
It has been shown that the magnetoresistive effect element using the perpendicular magnetization film is advantageous for miniaturization because the demagnetizing field does not occur even if the element size is reduced.

A tunnel magnetoresistive effect element using a perpendicular magnetization film is driven by a field effect transistor.

FIG. 12 is a diagram showing an example of the structure of a magnetic thin film memory using a perpendicular magnetization film for the tunnel magnetoresistive effect element.

The magnetic thin film memory of FIG. 12 has a gate and a source of a transistor 121 on a substrate, and further uses a tunnel magnetoresistive effect element 122 as a storage element.
Writing is performed by the current magnetic field in the direction perpendicular to the film surface generated from the write line 123. Although only a single-bit memory cell is shown in this figure, a plurality of memory cells are actually arranged on the substrate, and each memory cell is electrically isolated by the interlayer insulating film.

[0013]

Generally, the coercive force of a magnetic material changes with an increase in temperature. When the temperature of the tunnel magnetoresistive effect element that constitutes the above-mentioned nonvolatile magnetic thin film memory device rises and the coercive force of the magnetic layer, which is one component of the element, changes, when the coercive force decreases, crosstalk between adjacent cells may occur. When the coercive force rises, a problem such as writing failure occurs.

Particularly in an MRAM in which a magnetic field generated by a current is applied to record information, it is difficult to prevent the magnetic field from being applied to a memory cell in the periphery of a memory cell in which information is to be written. When it is applied to a portable device or the like, the operating temperature is various, and due to the influence of temperature, erroneous writing may occur frequently in the peripheral memory cells.

In addition, the coercive force of the tunnel magnetoresistive effect element using the perpendicular magnetization film is generally large. Therefore, the current value due to the write line for writing to the element becomes very large, and the heat generation of the entire device is remarkable.

The present invention has been made to solve the above problems, and an object thereof is to provide a non-volatile magnetic thin film memory device which operates stably even when the temperature of the device rises.

[0017]

In view of the above-mentioned problems, the present invention reduces the temperature dependence of the coercive force within the operating temperature range so that the composition of the perpendicular magnetization film, which is one component of the magnetoresistive effect element, is reduced. To adjust.

Therefore, the magnetoresistive effect element has a perpendicular magnetization film, and the perpendicular magnetization film is an alloy thin film of a rare earth metal and a transition metal, and is made of a ferrimagnetic material in which the rare earth element magnetization is dominant.
By using a magnetoresistive effect element having a compensation temperature between room temperature and Curie temperature as a memory element,
It is possible to provide a non-volatile magnetic thin film memory device having small temperature dependence.

Further, at the time of writing information to the magnetoresistive effect element, a temperature sensor senses a temperature change, and the data of the temperature change of the coercive force provided separately is compared with a reference current value of a device in which each temperature is compared. It is characterized in that an appropriate write current value is flowed.

Further, before writing information on the magnetoresistive effect element and at regular time intervals, test recording is performed on the test recording element to find a current value that does not cause erroneous recording. .

For these magnetoresistive effect elements, it is more preferable to use a tunnel magnetoresistive effect film because the magnetoresistive change rate is large.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the nonvolatile magnetic memory device of the present invention will be described in detail below. (First Embodiment 1) FIG. 1 is a diagram showing a temperature change of saturation magnetization of a magnetic film which is a constituent element of the tunnel magnetoresistive effect element of the first embodiment. Further, FIG. 2 is a diagram showing a temperature change of the coercive force in the magnetic film of the first embodiment.

The magnetic film shown in FIGS. 1 and 2 is a perpendicular magnetization film at room temperature without an applied magnetic field. An alloy thin film of Tb as a rare earth metal and Fe and Co as a transition metal is used.

As shown in FIG. 3, the magnetic layer of this embodiment has T
The sublattice magnetization direction of b and the sublattice magnetization directions of Fe and Co are magnetically coupled in an antiparallel state at room temperature.

When the temperature of the magnetic layer is raised, as shown in FIG. 1, the magnitude of the magnetization of Tb becomes equal to the magnitudes of the magnetizations of Fe and Co, and there is a compensation temperature for canceling each other. There is a Curie temperature at which the magnetization disappears.

In this embodiment, the compensation temperature is higher than room temperature,
A magnetic film lower than the Curie temperature is used. Furthermore, it is preferable that the compensation temperature is 100 [° C.] or higher.
By adjusting the composition of the TbFeCo alloy thin film so as to satisfy such conditions, as shown in FIG. 2, the change amount of the coercive force within the operating temperature range of −20 [° C.] to 100 [° C.] is 10 [. It was possible to control within Oe].

Although only TbFeCo is given as an example here, when it is desired to control the magnitude of coercive force to be small, a magnetic film containing Gd may be used.
Also in that case, the temperature dependence of the saturation magnetization and the coercive force may be appropriately controlled depending on the composition and film forming conditions.

The transition metal may contain Ni and the rare earth metal may contain Dy. This also makes it possible to control the temperature dependence of saturation magnetization and coercive force. (Second Embodiment) In this embodiment, a MOS-FET is provided at the end of the memory cell array of the MRAM to serve as a temperature sensor.

FIG. 4 is a simplified diagram showing the structure of the MRAM in the second embodiment. FIG. 5 is a flow chart showing the flow of a recording process of detecting the environmental temperature of the MRAM and recording information under the optimum recording condition in the second embodiment, and FIG. 6 is a diagram showing the configuration of a temperature sensor used for detecting the environmental temperature. FIG. 7 is a diagram showing the temperature dependence of the gate electrode threshold voltage used in the temperature sensor. In FIG. 7, as an example, p-MOS
3 shows the temperature dependence of the threshold voltage when using.

As shown in FIG. 4, MRA in the present embodiment.
M is the temperature sensor 46 and the tunnel magnetoresistive effect element 4
1, a write line 42 for writing information in the tunnel magnetoresistive effect element, a write line decoder 44 for controlling the write line 42, a bit line 43 for reading information in the tunnel magnetoresistive effect element, and a bit line And a bit line decoder 45 for controlling 43.

The temperature sensor 46 in this embodiment is a MOS-F provided below the tunnel magnetoresistive effect element 41.
Use ET.

As shown in FIG. 6, an extra MOS-FET is provided at a location separated from the memory cell array 64. In this embodiment, this MOS-FET is used as the temperature sensor 6
Use as 5.

As shown in FIG. 7, the threshold value of the gate electrode of the MOS-FET exhibits temperature dependence.

The temperature detection of the temperature sensor 65 shown in FIG.
Temperature detection is performed with the structure of the field effect transistor unchanged. Since the characteristics of the transistor change sensitively with respect to temperature, this temperature dependence can be used for temperature detection, and it is preferable because it can be formed on the substrate in the same process as the transistor provided for driving.

Actually, since the gate voltage of the gate 63 is not raised, a current is passed between the source 61 and the drain 62. When the gate voltage becomes higher than the threshold voltage, a current flows between the source 61 and the drain 62. Therefore, the voltage at that time is read to detect the operating temperature.

In this way, if the ambient temperature is detected by the temperature sensor 65 before writing the regular information and writing is performed with the optimum writing current, problems such as crosstalk and writing failure due to changes in operating temperature can be solved. You can

As shown in FIG. 5, the ambient temperature is measured by the temperature sensor before the normal data writing (step S51), and the temperature-dependent data of the gate electrode threshold of the MOS-FET is stored. The optimum write current value is detected by comparing with the data in the comparator (step S52). The optimum write current value can be obtained from the data of the temperature change of the coercive force of the tunnel magnetoresistive effect element and the ambient temperature. The temperature change of the coercive force of the tunnel magnetoresistive effect element may be recorded in advance in a device separately provided.

After that, if the write current value is controlled to write the normal data (step S53), the write can be performed normally.

In this embodiment, the threshold voltage of the gate electrode of the lower MOS-FET portion in the MRAM is used as the temperature sensor, but the gate electrode, drain electrode,
It is also possible to use the temperature sensor by utilizing the temperature change of the resistance value of the source electrode.

It is also possible to provide a temperature sensor for each bit line and write line to detect the temperature and control the current value for each column or row. Of course, an arbitrary area may be set and the value of the current flowing in each area may be controlled.

According to the present embodiment, since the temperature change in the memory cell array is detected and the information is recorded, it is possible to reduce the erroneous writing and the writing failure due to the temperature change. (Third Embodiment) In the third embodiment, the memory cells in the margin area of the memory cell array of the MRAM are trial-written as the trial-write memory cells, and the writing of information is controlled stepwise according to the environmental temperature. To do.
That is, writing is performed in an arbitrary memory cell at a certain current value, recording is confirmed, and then an information recording operation is started. The condition of the memory cell can be determined by confirming whether the normal recording operation is performed during the trial writing.

FIG. 8 is a simplified diagram showing the structure of the MRAM in the third embodiment. FIG. 9 is a flow chart showing the flow of a recording process for recording information under the optimum recording condition for each environmental temperature of the MRAM in the third embodiment, and FIG. 10 is a diagram showing the configuration of the trial write tunnel magnetoresistive effect element.

As shown in FIG. 8, MRA in the present embodiment.
M is a trial write memory cell 86, a tunnel magnetoresistive effect element 81 in which normal data is written, a write line 82 for writing information in the tunnel magnetoresistive effect element 81, and a write line for controlling the write line 82. A decoder 84, a bit line 83 for reading information from the tunnel magnetoresistive effect element 81, and a bit line decoder 85 for controlling the bit line 83 are provided. In this embodiment,
Before writing regular data, test write memory cell 86
Data writing is performed on the data, and after confirming whether the data is normally written, regular data writing is performed.

As shown in FIG. 10, a trial write memory cell 8 having a trial write tunnel magnetoresistive effect element 102.
6 is provided in the margin area of the normal data memory cell 101.

As shown in FIG. 9, first, the write line decoder in the margin area, that is, the area for trial writing is turned on.
(Step S91). Next, recording is performed in the trial writing memory cell 86 (step S92). Next, the test writing memory cell 86 recorded in step S92,
The test writing memory cell 86 adjacent to the test writing memory cell 86 is reproduced (step S93), and it is confirmed whether or not there is a write failure (step S94).

When memory cells are arranged in a matrix like MRAM and a specific memory cell is selected by a magnetic field by a current to record information, a memory cell adjacent to a memory cell to be written is selected. It is unavoidable that a magnetic field is applied up to. Therefore, if the coercive force of the magnetic film is reduced due to temperature change or the like, the possibility of erroneous writing increases. Therefore, when confirming the recording, it is necessary to confirm that neither the memory cell for trial writing for recording or the memory cell adjacent thereto is erroneously written.

If there is a write error, the write current value is changed, the process returns to step S91, and the same operation is repeated until normal writing can be confirmed.

If there is no write failure, the write current value is determined (step S95), and the normal data is written (step S96).

By writing the above information, the normal data could be written normally.

[0050]

As described above, according to the nonvolatile magnetic thin film memory device of the present invention, even if the environmental temperature changes, the tunnel magnetoresistive effect element or the information write current is set to the optimum condition. There is an effect that information can be accurately recorded.

[Brief description of drawings]

FIG. 1 is a diagram showing a temperature change of a saturation magnetization of a magnetic film which is a constituent element of a tunnel magnetoresistive effect element of a first embodiment.

FIG. 2 is a diagram showing a change in coercive force of the magnetic film of Example 1 with temperature.

FIG. 3 is a diagram showing a spin state of the magnetic layer of the first example.

FIG. 4 is a simplified diagram showing a configuration of an MRAM in a second embodiment.

FIG. 5 is a flowchart showing the flow of a recording process of detecting the environmental temperature of the MRAM and recording information under the optimum recording condition in the second embodiment.

FIG. 6 is a diagram showing a configuration of a temperature sensor used for detecting an environmental temperature.

FIG. 7 is a diagram showing temperature dependence of a gate electrode threshold voltage used in a temperature sensor.

FIG. 8 is a simplified diagram showing a configuration of an MRAM in a third embodiment.

FIG. 9 is a flowchart showing the flow of a recording process of recording information under the optimum recording condition for each environmental temperature of the MRAM in the third embodiment.

FIG. 10 is a diagram showing a configuration of a trial writing tunnel magnetoresistive effect element.

FIG. 11 is a schematic diagram showing a configuration example of a magnetic thin film memory utilizing a conventional tunnel magnetoresistive effect.

FIG. 12 is a diagram showing a configuration example of a magnetic thin film memory using a perpendicular magnetization film for a tunnel magnetoresistive effect element.

[Explanation of symbols]

41 Tunnel Magnetoresistive Element 42 Writing line 43 bit line 44 Decoder for write line 45 bit line decoder 61 Source 62 drain 63 gates 64 memory cell array 65 Temperature sensor 81 Tunnel Magnetoresistive Element 82 writing line 83 bit line 84 write line decoder 85-bit line decoder 86 Memory cell for trial writing Steps S51 to S53, S91 to S96

Claims (13)

[Claims] 1. A nonvolatile magnetic thin film memory comprising a transistor, a magnetoresistive effect element, and a metal wiring for applying a magnetic field to the magnetoresistive effect element on a substrate, wherein the magnetoresistive effect element has a perpendicular magnetization film. A non-volatile magnetic thin film memory device, wherein the perpendicularly magnetized film is an alloy thin film of a rare earth metal and a transition metal, is made of a ferrimagnetic material in which rare earth element magnetization is predominant, and has a compensation temperature between room temperature and Curie temperature. 2. The rare earth metal is composed of at least one element selected from Tb, Dy, and Gd, and the transition metal is composed of at least one element selected from Fe, Ni, and Co. Item 3. A non-volatile magnetic thin film memory device according to item 1. 3. The ferrimagnetic material has an operating temperature of −20.
In the range of [° C] to 100 [° C], the change amount of coercive force is 10
2. The non-volatile magnetic thin film memory device according to claim 1, wherein the non-volatile magnetic thin film memory device is [Oe] or less. 4. A non-volatile magnetic thin film memory comprising a transistor, a magnetoresistive effect element, and a metal wiring for applying a magnetic field to the magnetoresistive effect element on a substrate, wherein the value of current flowing through the metal wiring is controlled stepwise. And a temperature sensor for sensing the temperature of the magnetoresistive effect element. 5. The non-volatile magnetic thin film memory according to claim 4, wherein the current value control means controls the current flowing through the metal wiring according to the temperature sensed by the temperature sensor. 6. The non-volatile magnetic thin film memory device according to claim 4, wherein the temperature sensor comprises a MOS-FET circuit. 7. The non-volatile magnetic thin film memory device according to claim 4, wherein the temperature sensor is a component of a memory cell array. 8. The non-volatile magnetic thin film memory device according to claim 4, wherein the temperature sensor detects from a temperature change of a threshold voltage of a gate of a MOS-FET circuit. 9. The magnetic thin film memory device according to claim 1, wherein the magnetoresistive effect element is a tunnel magnetoresistive effect element. 10. In a recording / reproducing method of a non-volatile magnetic thin film memory device having a substrate, a plurality of memory cells having a magnetoresistive element provided on the substrate, and a transistor, before recording information, A recording / reproducing method for a non-volatile magnetic thin film memory device, comprising: performing trial writing of information in a memory cell, confirming recording of the trial writing, and then recording regular data. 11. The recording / reproducing method of a non-volatile magnetic thin film memory device according to claim 10, wherein trial writing of information is performed to a trial writing memory cell for performing trial writing. 12. The non-volatile magnetic thin film memory recording according to claim 10, wherein when the recording confirmation of the trial writing is performed, the recording confirmation of the information of the memory cell adjacent to the memory cell trial-written is similarly performed. How to play. 13. The recording / reproducing method of a non-volatile magnetic thin film memory device according to claim 11, wherein the test write memory cell is located at a side end portion of the memory cell array.