Low power consumption magnetic memory and magnetic information recording device

A highly integrated magnetic memory with low power consumption is provided. A first element portion which has a free layer, a first pinned layer formed in the film thickness direction of the free layer, and an insulation barrier layer formed between the free layer and the first pinned layer, and a second element portion which has the aforementioned free layer, a second pinned layer formed in the film surface direction of the free layer, and a non-magnetic layer formed between the free layer and the second pinned layer are provided. A current IW flows in the film surface direction of the second element portion for writing the magnetic information and a current IR flows in the film thickness direction of the first element portion for reading the magnetic information.

CLAIM OF PRIORITY

The present application claims priority from Japanese application JP 2004-279648 filed on Sep. 27, 2004, the content of which is hereby incorporated by reference into this application.

FIELD OF THE INVENTION

The present invention relates to a low power consumption and high output magnetic memory and magnetic information recording device which has both a switching function and a spin torque magnetization reversal function.

BACKGROUND OF THE INVENTION

A magnetic memory of the prior art consists of a memory cell1in which a tunneling magnetoresistive element (TMR element) is formed on a MOSFET, as shown inFIG. 13. The TMR element of the memory cell1((T. Miyazaki and N. Tezuka, J. Magn. Magn. Mater. 139, L231 (1995)) consists of a free layer31, an insulation barrier layer32, and a pinned layer33, and is connected to a bit line212and an electrode circuit46. The electrode circuit46is connected to the source electrode22of MOSFETs12to14through the electrodes42to45, and the drain electrode21is connected to the word line211through the electrode41. Switching is a means, using a MOSFET, in which the magnetization direction of the free layer31of the TMR element is rotated by using a current-induced space magnetic field which is generated by passing a current between the bit line212and the word line211to write the information, and the information is read by the output voltage of the TMR element. Moreover, except for the magnetization rotation using the above-mentioned current-induced space magnetic field, there is a so-called spin transfer torque magnetization reversal method in which the magnetization of the free layer is rotated by passing a current directly through the magnetoresistive element, and they are disclosed, for instance, in U.S. Pat. No. 5,695,864 and JP-A No. 305337/2002.

SUMMARY OF THE INVENTION

In order to achieve low power consumption in a magnetic memory, developing the above-mentioned spin transfer torque magnetization reversal method is one of the important subjects. However, the conventional spin torque magnetization reversal method was one where a current flows in a three-layer structure film, in which a ferromagnetic layer, a non-magnetic layer, and a ferromagnetic layer were stacked in order, in a direction perpendicular to the film surface (along the stacking direction). In this case, a model was proposed by J. Z. Slonzewski in which magnetization was rotated in the direction of current flow and the current (Ic: threshold current) which is required for the magnetization reversal is proportional to the demagnetizing field of the recording magnetic layer. The ferromagnetic layer which performs magnetization reversal was a thin film and the influence of the demagnetizing field in the direction perpendicular to the film surface was great, so that a problem arose in that it was impossible to drastically reduce the current which was necessary to perform the magnetization reversal.

It is an objective of the present invention to provide a low power consumption magnetic memory cell in which the current required for the spin transfer torque magnetization reversal is greatly reduced.

According to the present invention, Icof the spin transfer torque magnetization is drastically reduced by separately forming a stacked film of a ferromagnetic layer, a non-magnetic layer, and a ferromagnetic layer in a film surface and reducing the demagnetizing field of the recording magnetic layer, resulting in the above-mentioned objective being achieved.

A magnetic memory of the present invention comprises a first element portion which has a free layer, a first pinned layer formed in the film thickness direction of the free layer, and an insulation barrier formed between the free layer and the first pinned layer, a second element portion which has the aforementioned free layer, a second pinned layer formed in the film surface direction of the free layer, and a non-magnetic layer formed between the free layer and the second pinned layer, a means for flowing a current IRin a film thickness direction of the first element portion, and a means for flowing a current IWin a film surface direction of the second element portion. The current IWin the film surface direction is used for writing the magnetic information and the current IRin the film thickness direction is used for reading the magnetic information.

A magnetic memory of the present invention comprises a writing method using a spin torque magnetization in the film surface which does not use a magnetic field induced by a current and a reading method using a TMR element, and can reduce the threshold current for the spin torque magnetization by decreasing the demagnetizing field, resulting in a high output magnetic memory with extremely low power consumption being achieved.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereafter, the preferred embodiments of the present invention will be explained with reference to the drawings. The same code is affixed to the same component part, and redundant explanations are omitted in the following figures.

First Embodiment

FIG. 1is a cross-sectional schematic drawing illustrating an example of a configuration of a magnetic memory and a switching portion of a memory cell. A C-MOS transistor11consists of two n-type semiconductors12and13and a p-type semiconductor14. The electrode21to be a drain is electrically connected to the n-type semiconductor12and connected to the ground through the electrode41and the electrode47. The electrode22to be a source is connected to the n-type semiconductor13. Moreover,23is a gate electrode, and on/off operation of the current flowing between the source electrode22and the drain electrode21is controlled by on/off operation of this gate electrode23. The electrode45, electrode44, electrode43, and electrode42are stacked on the source electrode22, and the free layer311is connected to the electrode42. The tunneling magnetoresistive element (TMR element) of the memory cell1consists of a stacked layer of the free layer311, the insulation barrier layer312, and the first pinned layer313. The non-magnetic conduction layer314and the second pinned layer315are connected to this free layer311in the film surface. The word line211is connected on the pinned layer315to flow a current from the second pinned layer315to the free layer311, which is different from a conventional magnetic memory where a word line is connected to a drain electrode of a MOSFET (refer toFIG. 13).

In this embodiment, the free layer311is composed of CoFe (2 nm), the insulation barrier layer312of Al oxide film (2 nm), and the first pinned layer313of CoFe (5 nm). The non-magnetic conduction layer314is composed of Cu (2 nm), and the second pinned layer315is composed of CoFe (2 nm). The composition of CoFe is controlled to have a Co content between 50 and 90%. The area of the free layer311is controlled to be 50 nm×150 nm, the area of the non-magnetic conduction layer314100 nm×150 nm, and the area of the second pinned layer315100 nm×150 nm. The product of the magnetic moment and volume of the free layer311is 2.7×104(T·nm3) and it is smaller than 5.4×104(T·nm3) which is the product of the magnetic moment and volume of the second pinned layer315, so that the magnetization of the free layer311is rotated by a spin transfer torque. The shape of the above-mentioned element is formed by using typical lithography and an electron beam lithography system, RIE (reactive ion etching), and ion milling.

Hf, Ta, Mg, and Ti oxides, except for Al oxide, may be used for the insulation barrier layer312. Moreover, a CoFe/Ru/CoFe multi-layered film may be used for the first pinned layer313and the second pinned layer315. Since the magnetization direction can be fixed by a strong magnetic field using this multi-layered film, it is possible to reverse the spin torque magnetization reversal efficiently and stably. Au, Cr, Ag, Ru, Al, and Pt, except for Cu, may be used for the non-magnetic conduction layer, and a material including at least one selected from these materials may be used. The bit line212is formed on the TMR element2through the electrode46and is used for a circuit which flows a current while reading the magnetic information written in the free layer311of the TMR element.

FIG. 2shows an example illustrating a method for reading/writing magnetic information to the free layer311. For instance, when the magnetization directions of the free layer311and the first pinned layer313are assumed to be parallel and information is written as a “0”, a write current Iwflows from the second pinned layer315to the free layer311through the non-magnetic layer314, as shown inFIG. 2A. On the other hand, when the magnetization directions of the free layer311and the first pinned layer313are assumed to be opposite and information is written as a “1”, a write current Iwflows from the free layer311side to the second pinned layer315through the non-magnetic layer314, as shown inFIG. 2B.

Since the relationship between the write current Iwand the resistance of the TMR element2is of a manner as shown inFIG. 3, the low resistance state is the electrical signal “0” in which the magnetizations of the free layer311and the second pinned layer313are in a parallel arrangement, and the high resistance state is the electrical signal “1” in which the magnetizations of the free layer311and the second pinned layer313are in an anti-parallel arrangement. A read current IRflows to the TMR element2to read the recorded information. Then, the information can be read as an electrical signal which is caused by the difference of the resistances of the TMR element in the “0” state and the “1” state.

Here, it is know that the threshold current density of the flux reversal caused by a spin torque magnetization method is shown as follows.
JC∝MV(Han+Hd)  (1)
M is the saturation magnetization of a magnetic material which performs magnetization reversal, V the volume of the magnetic material, Hanthe anisotropic magnetic field of the magnetic material, Hdthe demagnetizing field of the magnetic film in the direction in which a current flows.

Therefore, it is understood that JCis proportional to Han+Hd. Hanof CoFe is on the level of several tens of Oersteds. Regarding Hd, for instance,FIG. 4shows a plot of the cell aspect ratio (diameter/film thickness) of a magnetization-reversing CoFe film and the magnitude of the demagnetizing field Hd. In a conventional method in which a current flows in a direction perpendicular to the film surface, the demagnetization field Hdis greater than 10000 Oe. However, since the aspect ratio of the recording layer of this embodiment is 20 in the longitudinal direction in which the current flows, the demagnetizing field can be reduced to about 1/100th compared with the conventional method. That is, great energy was required in the conventional spin torque flux reversal because the spin torque works in a mode which lets the magnetization rotate in the direction perpendicular to the film surface. However, in a method of the present invention, great energy such as that required in the film surface perpendicular method is not required because the spin torque works in a mode which lets the magnetization rotate in the film surface. As a result, according to the present invention, it is possible to reduce the threshold current density to about 1/100th compared with the conventional method as shown inFIG. 5.

Second Embodiment

FIG. 6is a cross-sectional schematic drawing illustrating another example of a memory cell and a switching portion of a magnetic memory of the present invention. This embodiment corresponds to one in which the first anti-ferromagnetic layer316and the second anti-ferromagnetic layer317are stacked to fix the magnetization directions of the first pinned layer313and the second pinned layer315, respectively, in one direction in the configuration of the memory cell1shown inFIG. 1.

In this embodiment, PtMn (12 nm) was used for the first anti-ferromagnetic layer316and the second anti-ferromagnetic layer317. Herein, except for PtMn, FeMn and IrMn may be used for the anti-ferromagnetic layer. In this embodiment, since the magnetic domains of the pinned layer are controlled to be oriented in one direction due to the anti-ferromagnetic layer, parallel and anti-parallel states of the relative angle of the magnetization direction with the free layer can be achieved stably. Additionally, an increase in the output of the read signal obtained at the TMR element2and writing by using the stable spin torque magnetization can be achieved.

FIG. 7shows an example illustrating a method of reading/writing magnetic information to the free layer311. The method of reading/writing magnetic information is the same as that of the first embodiment. When the magnetization direction of the free layer311of the TMR element2is made parallel to the magnetization direction of the first pinned layer313, a write current Iwflows from the second pinned layer315to the free layer311through the non-magnetic layer314as shown inFIG. 7A. On the other hand, when the magnetization direction of the free layer311is made anti-parallel to the magnetization direction of the first pinned layer313, a write current Iwflows from the free layer311side to the second pinned layer315through the non-magnetic layer314as shown inFIG. 7B. A read current IRflows to the TMR element2to read the recorded information.

Third Embodiment

FIG. 8is a cross-sectional schematic drawing illustrating another example of a memory cell and a switching portion of a magnetic memory of the present invention. This embodiment shows an example of the configuration, in which the first pinned layer313is formed on the transistor11side through the insulation barrier layer312, in the configuration of the memory cell1shown inFIG. 1. A magnetic memory of this embodiment can be deposited without breaking the vacuum atmosphere in a manufacturing process of the magnetic memory portion and a high quality TMR element can be fabricated, so that the output of the read signal can be increased.

FIG. 9shows an example illustrating a method of reading/writing magnetic information to the free layer311. The method of reading/writing magnetic information is same as that of the first embodiment. When the magnetization direction of the free layer311of the TMR element2is made parallel to the magnetization direction of the first pinned layer313, a write current Iwflows from the second pinned layer315to the free layer311through the non-magnetic layer314as shown inFIG. 9A. On the other hand, when the magnetization direction of the free layer311is made anti-parallel to the magnetization direction of the first pinned layer313, a write current Iwflows from the free layer311side to the second pinned layer315through the non-magnetic layer314as shown inFIG. 9B. A read current IRflows to the TMR element2to read the recorded information.

Fourth Embodiment

FIG. 10is a cross-sectional schematic drawing illustrating another example of a memory cell of a magnetic memory and a switching portion of the present invention. This embodiment shows an example of a configuration in which the first anti-ferromagnetic layer316and the second anti-ferromagnetic layer317are stacked next to each other to fix the magnetization directions of the first pinned layer313and the second pinned layer315, respectively, in one direction in the configuration of the memory1shown inFIG. 8. In this embodiment, since the magnetic domains of the pinned layer are controlled to be oriented in one direction due to the anti-ferromagnetic layer, parallel and anti-parallel states of the relative angle of the magnetization direction with the free layer can be achieved stably. Additionally, an increase in the output of the read signal obtained at the TMR element2and writing by using the stable spin torque magnetization reversal can be achieved.

FIG. 11shows an example illustrating a method of reading/writing magnetic information to the free layer311. The method of reading/writing magnetic information is the same as that of the first embodiment. When the magnetization direction of the free layer311of the TMR element2is made parallel to the magnetization direction of the first pinned layer313, a write current Iwflows from the second pinned layer315to the free layer311through the non-magnetic layer314as shown inFIG. 11A. On the other hand, when the magnetization direction of the free layer311is made anti-parallel to the magnetization direction of the pinned layer313, a write current Iwflows from the free layer311side to the second pinned layer315through the non-magnetic layer314as shown inFIG. 11B. A read current IRflows to the TMR element2to read the recorded information.

FIG. 12is an example of a magnetic random access memory in which the above-mentioned memory cell1is provided. The write word line211and the bit line212are electrically connected to the memory cell1. The magnetic memory could be operated with low power consumption by providing the magnetic memory cell described in the above-mentioned embodiments.