MAGNETORESISTIVE RANDOM ACCESS MEMORY AND ITS WRITE CONTROL METHOD

Abstract

It is made possible to prevent the recording layer in the TMR element from assuming the intermediate state as perfectly as possible even if writing into the MRAM is conducted, as heretofore described. A write control method for a magnetoresistive random access memory including: applying a pulsative first magnetic field substantially parallel to the axis of easy magnetization of the recording layer and a pulsative second magnetic field substantially parallel to the axis of hard magnetization to the recording layer so as to cause a period of the pulsative first magnetic field and a period of the pulsative second magnetic field to overlap each other; and applying a pulsative third magnetic field having substantially the same direction as the pulsative first magnetic field to the recording layer at least once after applying the pulsative first magnetic field to the recording layer.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing current pulse waveforms used in a write control method according to a first embodiment of the present invention;

FIGS. 2A and 2B are sectional views showing a schematic configuration of a TMR element used in embodiments of the present invention;

FIG. 3 is a top view of a memory cell in an MRAM used in embodiments of the present invention;

FIG. 4 is a sectional view of a memory cell in an MRAM used in embodiments of the present invention;

FIG. 5 is a diagram showing a magnetic domain structure of a recording layer when a TMR element is in an intermediate state;

FIG. 6 is a diagram for explaining movement of a magnetic domain wall in a recording layer obtained when a magnetic field generated by a current pulse is made to act in a direction of axis of easy magnetization;

FIG. 7 is a waveform diagram showing write pulses used in a write control method of a comparative example of a first embodiment;

FIG. 8 is a diagram showing a relation between a low resistance value R0 of an MRAM and an MR ratio obtained when a write control method in the first embodiment is used for each bit of the MRAM;

FIG. 9 is a diagram showing a relation between a low resistance value R0 of an MRAM and an MR ratio obtained when a write control method in a comparative example is used for each bit of the MRAM;

FIG. 10 is a diagram showing current waveforms used in a write control method according to a second embodiment of the present invention;

FIG. 11 is a diagram showing current pulse waveforms used in a write control method according to a third embodiment of the present invention;

FIG. 12 is a sectional view showing a configuration of a TMR element of an MRAM in which a write control method according to a fourth embodiment of the present invention is used;

FIG. 13 is a diagram showing a current pulse waveform used in a write control method according to the fourth embodiment;

FIG. 14 is a circuit diagram of a magnetoresistive random access memory according to a fifth embodiment of the present invention;

FIG. 15 is a waveform diagram showing the case where data “0” is written in a magnetoresistive random access memory according to the fifth embodiment;

FIG. 16 is a waveform diagram showing the case where data “1” is written in a magnetoresistive random access memory according to the fifth embodiment; and

FIG. 17 is a circuit diagram of a magnetoresistive random access memory according to a sixth embodiment of the present invention.

Claims

1. A write control method for a magnetoresistive random access memory including at least one memory cell, the memory cell including a magnetoresistive effect element as a storage element, the magnetoresistive effect element including a recording layer having an axis of easy magnetization and an axis of hard magnetization and of which magnetization direction is changeable, a reference layer of which magnetization direction is pinned, and an insulation layer provided between the recording layer and the reference layer, the write control method comprising: applying a pulsative first magnetic field substantially parallel to the axis of easy magnetization of the recording layer and a pulsative second magnetic field substantially parallel to the axis of hard magnetization to the recording layer so as to cause a period of the pulsative first magnetic field and a period of the pulsative second magnetic field to overlap each other; andapplying a pulsative third magnetic field having substantially the same direction as the pulsative first magnetic field to the recording layer at least once after applying the pulsative first magnetic field to the recording layer.

2. The write control method according to claim 1, wherein the pulsative third magnetic field is, in magnitude, equal to or less than the pulsative first magnetic field applied to the recording layer.

3. The write control method according to claim 1, wherein applying the pulsative third magnetic field to the recording layer at least once further comprises applying a pulsative fourth magnetic field having substantially the same direction as the pulsative second magnetic field to the recording layer at least once so as to cause a period of the pulsative fourth magnetic field and a period of the pulsative third magnetic field to overlap each other.

4. The write control method according to claim 1, wherein applying the pulsative third magnetic field to the recording layer at least once further comprises continuously applying the pulsative second magnetic field to the recording layer.

5. The write control method according to claim 1, wherein applying the pulsative third magnetic field to the recording layer at least once comprises applying only the pulsative third magnetic field to the recording layer.

6. A write control method for a magnetoresistive random access memory including at least one memory cell, the memory cell including a magnetoresistive effect element as a storage element, the magnetoresistive effect element including a recording layer having an axis of easy magnetization and an axis of hard magnetization and of which magnetization direction is changeable, a reference layer of which magnetization direction is pinned, and an insulation layer provided between the recording layer and the reference layer, the write control method comprising: applying a pulsative first magnetic field substantially parallel to the axis of easy magnetization of the recording layer and a pulsative second magnetic field substantially parallel to the axis of hard magnetization to the recording layer so as to cause a period of the pulsative first magnetic field and a period of the pulsative second magnetic field to overlap each other;reducing a magnitude H1 of the pulsative first magnetic field to be a magnitude H2 which is zero or more and which is less than the magnitude H1; andapplying a pulsative third magnetic field having substantially the same direction as the pulsative first magnetic field and having a magnitude H3 to the recording layer at least once, a sum of the magnitude H3 and the magnitude H2 being equal to or less than the magnitude H1.

7. The write control method according to claim 6, wherein applying the pulsative third magnetic field to the recording layer at least once further comprises applying a pulsative fourth magnetic field having substantially the same direction as the pulsative second magnetic field to the recording layer at least once so as to cause a period of the pulsative fourth magnetic field and a period of the pulsative third magnetic field to overlap each other.

8. The write control method according to claim 6, wherein applying the pulsative third magnetic field to the recording layer at least once further comprises continuously applying the pulsative second magnetic field to the recording layer.

9. The write control method according to claim 6, wherein applying the pulsative third magnetic field to the recording layer at least once comprises applying only the pulsative third magnetic field to the recording layer.

10. A write control method for a magnetoresistive random access memory including at least one memory cell, the memory cell including a magnetoresistive effect element as a storage element, the magnetoresistive effect element including a recording layer of which magnetization direction is changeable, a reference layer of which magnetization direction is pinned, and an insulation layer provided between the recording layer and the reference layer, the write control method comprising: injecting a spin-polarized pulse current into the recording layer a plurality of times, when conducting writing by injecting a spin-polarized pulse current into the recording layer.

11. A magnetoresistive random access memory comprising: a first wiring;a second wiring;a memory cell including a magnetoresistive effect element as a storage element, the magnetoresistive effect element being provided so as to be associated with an intersection region of the first wiring and the second wiring, the magnetoresistive effect element including a recording layer having an axis of easy magnetization and an axis of hard magnetization and of which magnetization direction is changeable, a reference layer of which magnetization direction is pinned, and an insulation layer provided between the recording layer and the reference layer;a first current generation circuit which generates a first pulse current and causes the first pulse current to flow through the first wiring in order to generate a first magnetic field substantially parallel to a direction of the axis of easy magnetization of the recording layer to be applied to the recording layer; anda second current generation circuit which generates a second pulse current and causes the second pulse current to flow through the second wiring in order to generate a second magnetic field substantially parallel to a direction of the axis of hard magnetization of the recording layer to be applied to the recording layer,whereinthe first and second current generation circuits generate the first and second pulse currents so as to cause periods of the first magnetic field and the second magnetic field to overlap each other, andafter generation of the first pulse current, the first current generation circuit generates a third pulse current at least once so as to cause a third magnetic field having substantially the same direction as a direction of the first magnetic field, the third magnetic field being applied to the recording layer.

12. The magnetoresistive random access memory according to claim 11, comprising: an array having a plurality of the memory cells; anda selection circuit which selects at least one memory cell from the plurality of memory cells,whereinthe first current generation circuit generates the first and third pulse currents so as to cause the first and third magnetic fields to be applied to the recording layer in the selected memory cell, andthe second current generation circuit generates the second pulse current so as to cause the second magnetic field to be applied to the recording layer in the selected memory cell.

13. The magnetoresistive random access memory according to claim 11, wherein the second current generation circuit generates a fourth pulse current in order to cause a fourth magnetic field which has substantially the same direction as a direction of the second magnetic field and a period of which overlaps a period of the third magnetic field, the fourth magnetic field being applied to the recording layer at least once, when causing the third magnetic field to be applied to the recording layer at least once.

14. The magnetoresistive random access memory according to claim 11, wherein the second current generation circuit generates the second pulse current in order to cause the second magnetic field to continue to be applied to the recording layer, when causing the third magnetic field to be applied to the recording layer.

15. The magnetoresistive random access memory according to claim 11, wherein the second current generation circuit does not cause a pulse current to flow, when causing the third magnetic field to be applied to the recording layer.

16. The magnetoresistive random access memory according to claim 11, wherein the third magnetic field is, in magnitude, equal to or less than the first magnetic field.

17. A magnetoresistive random access memory comprising: a first wiring;a second wiring;a memory cell including a magnetoresistive effect element as a storage element, the magnetoresistive effect element including a recording layer of which magnetization direction is changeable, a reference layer of which magnetization direction is pinned, and an insulation layer provided between the recording layer and the reference layer, one end of the magnetoresistive effect element being electrically connected to the first wiring, the other end of the magnetoresistive effect element being electrically connected to the second wiring;a first current generation circuit which generates a first pulse current a plurality of times and causes a spin-polarized pulse current to flow through the magnetoresistive effect element via the first wiring a plurality of times, when writing a first value into the memory cell; anda second current generation circuit which generates a second pulse current a plurality of times and causes a spin-polarized pulse current to flow through the magnetoresistive effect element via the second wiring a plurality of times, when writing a second value into the memory cell.

18. The magnetoresistive random access memory according to claim 17, comprising: an array having a plurality of the memory cells; anda selection circuit which selects at least one memory cell from the plurality of memory cells,whereinthe first current generation circuit generates the first pulse current for the selected memory cell a plurality of times, when conducting writing into the selected memory cell, andthe second current generation circuit generates the second pulse current for the selected memory cell a plurality of times, when conducting writing into the selected memory cell.

19. The magnetoresistive random access memory according to claim 17, wherein a selection transistor is provided between one of the first wiring and the second wiring and the magnetoresistive effect element.