1. Field of the Invention
The present invention relates to a magnetoresistive effect element having an insulating layer and a metal layer between two ferromagnetic layers, a fabrication method thereof, a magnetic memory device provided with the magnetoresistive effect element and a fabrication method thereof.
2. Description of the Related Art
A magnetoresistive random access memory (MRAM) uses a magnetoresistive effect element having a tunneling magnetoresistive (TMR) effect in a cell unit for storing information. This magnetoresistive effect element is, for example, a magnetic tunnel junction (MTJ) element having a structure with an insulating layer (referred to as a tunnel barrier layer) inserted between two ferromagnetic layers.
The MTJ element for MRAM is used as a fixed magnetization layer in which the direction of magnetization of one of the two ferromagnetic layers holding the tunnel barrier layer is fixed not to change, while the other ferromagnetic layer is used as a memory layer with the direction of magnetization thereof easily reversed. The information can be stored by setting the state of the fixed magnetization layer and the memory layer parallel and antiparallel with each other in the direction of magnetization in correspondence with “0” and “1” of the binary notation.
In recent years, it has been pointed out that the use of MgO as a tunnel barrier layer can produce the MR ratio (magneto-resistance ratio) of several hundred %. The reason is considered to be that the lattice constant matches between the MgO (001) crystal at 45° and the Fe (001) crystal, and a magnetic layer, MgO and a magnetic layer are stacked in that order as a crystal structure.
Koji Tsunekawa, David D. Djayaprawira, Motonobu Nagai, Hiroki Maehara, Shinji Yamagata, Naoki Watanabe, Shinji Yuasa, Yoshishige Suzuki, and Koji Ando, APPLIED PHYSICS LETTERS, Vol. 87, No. 072503 (2005) (Nonpatent Document 1), for example, reports that in the case where Mg is arranged under MgO to form a film structure of Mg/MgO as a tunnel barrier layer, the MR ratio is improved in the area having a thin MgO and a low barrier resistance. The mere arrangement of Mg under MgO, however, cannot achieve the required life length before dielectric breakdown of the tunnel barrier.
U.S. Pat. No. 6,841,395, on the other hand, proposes to reduce the barrier resistance and improve the MR ratio by forming an oxygen-mixed metal layer after forming a pure metal layer followed by the processing with oxygen gas and thus preventing the oxidation of an underlying magnetic layer. In this method, however, extraneous oxygen atoms are generated in the oxygen-mixed metal layer above the tunnel barrier layer. Therefore, the passing conduction electrons are trapped to cause the likelihood of dielectric breakdown, or oxygen atoms are dispersed above the tunnel barrier layer at the time of annealing after the film-forming process thereby to oxidate the magnetic layer in the neighborhood of the boundary between the upper magnetic layer and MgO, resulting in increase in barrier resistance or decrease in MR ratio.
Also, U.S. Pat. No. 6,347,049 proposes a method in which a laminate barrier layer of different compounds such as MgO/Al2O3 is formed to prevent pinholes from being formed in the tunnel barrier layer and to improve the MR ratio with a low barrier resistance. In the case where different compounds are stacked with a very thin tunnel barrier layer not thicker than 1 nm required in the future, however, the lattice matching of the magnetic layer/tunnel barrier layer/magnetic layer would be disrupted, and a high MR ratio required in the future for the MRAM cannot be obtained.
Further, U.S. Patent Application No. 2004/0109347 proposes an example of a method related to the control of the boundary between MgO and the magnetic layer, in which the tunnel barrier layer having a low barrier resistance of not higher than 1.5 eV is used to suppress the leak current for a low applied voltage and supply a comparatively large current for a high applied voltage. Nevertheless, neither a specific method to form the tunnel barrier layer nor a specific method to control the boundary to reduce the barrier resistance is disclosed.
As described above, the conventional magnetoresistive effect element and the conventional fabrication method thereof fail to take the control of the boundary between the tunnel barrier layer and the magnetic layer sufficiently into consideration. As a result, the suppression of the progress of the dielectric breakdown with the energy release of the conduction electrons and the improvement in the MR ratio due to the prevention of oxidation of the magnetic layer are insufficient, thereby reducing the life length before dielectric breakdown and the MR ratio.
A magnetoresistive effect element according to a first aspect of the present invention comprises: a first ferromagnetic layer formed above a substrate; a second ferromagnetic layer formed above the first ferromagnetic layer; an insulating layer interposed between the first ferromagnetic layer and the second ferromagnetic layer and formed of a metal oxide; and a first nonmagnetic metal layer interposed between the insulating layer and the second ferromagnetic layer and in contact with a surface of the insulating layer on the side of the second ferromagnetic layer, the first nonmagnetic metal layer containing the same metal element as the metal oxide.
A magnetoresistive effect element manufacturing method according to a second aspect of the present invention comprising: forming a first ferromagnetic layer above a substrate; depositing an insulating layer formed of a metal oxide above the first ferromagnetic layer; forming a first nonmagnetic metal layer containing the same metal element as the metal oxide on the insulating layer; and forming a second ferromagnetic layer on the first nonmagnetic metal layer.
[1] Dependency of Barrier Resistance on Stress Application Time
The present inventors have studied the dependency of the barrier resistance on the stress application time under a constant voltage stress exerted on a tunnel barrier layer of a magnetoresistive effect element (MTJ element). As a result, the present inventors have acquired the knowledge described below.
As shown in
As shown in
As shown in
In the second reference example, however, comparison between
Based on this knowledge and in view of the fact that the boundary between the upper magnetic layer and MgO in the tunnel barrier layer of the magnetoresistive effect element should be controlled in a superior state, the progress of the dielectric breakdown due to the energy release of the conduction electrons is suppressed while at the same time preventing the oxidation of the magnetic layer to improve the life length before dielectric breakdown and the MR ratio.
Embodiments of the invention configured based on the aforementioned knowledge will be explained below with reference to the drawings. In the description that follows, common parts are designated by the same reference numerals, respectively.
[2] Magnetoresistive Effect Element and the Surrounding Structure
As shown in
An upper wiring layer 105 is formed on and connected to the memory layer 104. The upper wiring layer 105 and the lower wiring layer 101 are insulated from each other by insulating layers 106, 107. The upper wiring layer 105 and the lower wiring layer 101 are formed of such a material as Al, Al-Cu, Cu, Ta, W or Ag. The insulating layers 106, 107, on the other hand, are formed of such a material as a silicon oxide film (SiOx) or a silicon nitride film (SiNx).
The insulating layer 107 is formed with a contact hole 108 reaching the memory layer 104. A conductive member is buried in the contact hole 108. The upper wiring layer 105 and the memory layer 104 are electrically connected to each other by a contact plug formed of this conductive member.
As shown in
The fixed magnetization layer 102 has the film structure described below. Specifically, the fixed magnetization layer 102 is formed as a laminate structure including the lower wiring connection layer 201, the antiferromagnetic layer 202, the ferromagnetic layer 203, the insertion layer 204 and the ferromagnetic layer 205.
The lower wiring connection layer 201 is formed of Ta, for example, 5 nm thick. The antiferromagnetic layer 202 is formed of, for example, Pt—Mn 15 nm thick. The ferromagnetic layer 203 is formed of Co—Fe, for example, 2 nm thick. The direction in which the ferromagnetic layer 203 is magnetized is fixed by the antiferromagnetic layer 202. The insertion layer 204 is formed of a nonmagnetic metal such as Ru 1 nm thick. The ferromagnetic layer 205 is formed of Co—Fe—B, for example, 2 nm thick. The ferromagnetic layer 203, the insertion layer 204 and the ferromagnetic layer 205 make up a laminate ferri-pinned structure. The magnetization of the ferromagnetic layer 205 is bonded with the magnetization of the ferromagnetic layer 203 by the insertion layer 204, and therefore, the direction in which the ferromagnetic layer 205 is magnetized is fixed.
The memory layer 104 has the film structure described below. Specifically, the memory layer 104 is formed of a laminate structure having the ferromagnetic layer 209, the cap layer 210 and the upper wiring connection layer 211.
The ferromagnetic layer 209 is formed of Co—Fe—B, for example, 2 nm thick. The direction in which the ferromagnetic layer 209 is magnetized is variable. The cap layer 210 is formed of Ta, for example, 5 nm thick. The upper wiring connection layer 211 is formed of Ru, for example, 7 nm thick, and has the function of protecting the surfaces of the etching mask and the magnetoresistive effect element 100.
The intermediate layer 103 has the film structure described below. Specifically, the intermediate layer 103 has a laminate structure having the metal layer 206, the insulating layer 207 and the metal layer 208.
The insulating layer 207 is desirably formed of any one of a metal oxide, a metal nitride and a metal oxynitride. The metal layers 206, 208 desirably contain the same metal element as the insulating layer 207. The fact that the metal layers 206, 208 and the insulating layer 207 have the same component metal makes it difficult to disrupt the lattice matching in the boundary between the metal layer 206 and the insulating layer 207 and the boundary between the metal layer 208 and the insulating layer 207. Incidentally, the metal element and the metal element unit making up the metal layers 206, 208 are not limited to the same ones as those of the insulating layer 207, but any compound containing the particular metal element as a main component may be used. The metal layers 206, 208 and the insulating layer 207 are nonmagnetic layers.
According to this embodiment, the insulating layer 207 is formed of, for example, MgO, and the metal layers 206, 208 of, for example, Mg. Nevertheless, the insulating layer 207 may alternatively be formed of AlOx, AlN, AlON, AlHfOx, AlZrOx or AlFOx, in which case the metal layers 206, 208 are desirably formed of Al.
The metal layers 206 and 208 may be formed of materials different from each other. For example, one of the metal layers 206 and 208 may be formed of a metal unit and the other a metal compound. Also in this case, however, the metal layers 206, 208 desirably contain the same metal element as the insulating layer 207 as a main component.
The insulating layer 207 has a thickness of, for example, 1 nm. The thickness of the metal layer 206, on the other hand, is 0.4 nm, for example. The thickness of the metal layer 208 is, for example, 0.6 nm. The metal layers 206, 208 desirably have the thickness of 0.2 to 2.0 nm as described later.
The metal layers 206, 208 may have the same thickness, or the metal layer 206 may be either thicker or thinner than the metal layer 208. Similarly, the metal layers 206, 208 may have the same thickness as the insulating layer 207. Alternatively, either the metal layers 206, 208 may be thicker than the insulating layer 207 or the insulating layer 207 may be thicker than the metal layers 206, 208.
The surface of the insulating layer 207 near the metal layer 206 is desirably in direct contact with the metal layer 206, and the surface of the insulating layer 207 near the metal layer 208 is desirably in direct contact with the metal layer 208. This is by reason of the fact that the metal layers 206, 208 improve the crystallinity in the boundary between the metal layer 206 and the insulating layer 207 and the boundary between the metal layer 208 and the insulating layer 207, respectively.
In the intermediate layer 103 shown in
The metal layer 208 “above” the insulating layer 207 is defined as the metal layer 208 deposited after forming the insulating layer 207 in the fabrication process. Thus, this includes a case in which after forming the magnetoresistive effect element 100, the magnetoresistive effect element 100 is turned upside down and attached to another substrate X leading to the final structure in which the metal layer 208 is located “under” the insulating layer 207 with respect to the substrate X.
With regard to the direction of magnetization of the fixed magnetization layer 102 and the memory layer 104, the magnetoresistive effect element 100 may be of either an in-plane magnetization type (parallel magnetization type) in which the direction of magnetization is parallel to the film surface or a perpendicular magnetization type in which the direction of magnetization is perpendicular to the film surface.
The magnetoresistive effect element 100 described above may be modified in various ways. The thickness of each layer making up the magnetoresistive effect element 100, for example, may be appropriately adjusted within the range of 0.1 nm to several tens of nm. Also, each layer of the magnetoresistive effect element 100 may be configured of a material different from the one described above. Further, what is called “the top-pin structure” with the magnetoresistive effect element 100 arranged in the vertically opposite position with respect to the substrate may be formed. Furthermore, the fixed magnetization layer 102 may be formed of a single layer. Also, the memory layer 104 may be formed of a plurality of ferromagnetic layers. Further, a ferromagnetic double-tunnel junction structure having a plurality of tunnel barrier layers may be employed. In the case where one of the two tunnel barrier layers is formed of an insulating layer of MgO and the other tunnel barrier layer of a metal such as Cu, for example, the metal layer 208 may be formed at least on the upper surface (the surface far from the semiconductor substrate) of the tunnel barrier layer formed of an insulating layer.
In the drawings other than
[3] Method of Fabricating Magnetoresistive effect Element
As shown in
The eight film-forming conditions include (1) second reference example, (2) Mg on MgO, (3) processing MgO with O2, (4) smoothing the lower CoFeB, (5) processing with O2, and upper Mg, (6) smoothing, and upper Mg, (7) smoothing and processing with O2, and (8) smoothing, processing with O2 and upper Mg.
The condition (1) corresponds to the film-forming process for the structure shown in
Incidentally, the process of forming each layer of the magnetoresistive effect element 100 using sputtering in the example of the fabrication method described below is modifiable, and may use, for example, the vapor deposition, the atomic layer deposition (ALD) or the chemical vapor deposition (CVD).
[3-1] First Example of Fabrication Method
First, as shown in
Next, as shown in
Then, as shown in
In the process shown in
Specifically, in the case where the insulating layer 207 is an oxide layer, the barrier oxidation process may be performed after the direct sputtering of a compound target (for example, MgO target), the reactive sputtering (for example, O2 gas introduction) of a metal target (for example, Mg target) or the forming of a metal layer (for example, Mg layer). The barrier oxidation uses an oxygen plasma, an oxygen radial, ozone or oxygen gas atmosphere.
In the case where the insulating layer 207 is a nitride layer, on the other hand, the nitridation atmosphere such as nitrogen plasma, nitrogen radical, nitrogen, ammonia, NO, NO2 or N2O may be used for barrier nitridation after reactive sputtering of the metal target or the forming of the metal layer.
In the case where the insulating layer 207 is an oxynitride layer, on the other hand, the atmospheres for the nitridation of a metal oxide layer, the oxidation of a metal nitride layer and the oxynitridation may be used in any appropriate combination.
[3-2] Second Example of Fabrication Method
First, as shown in
Next, as shown in
The smoothing step 301 can be executed by any of the three methods described below. A first method consists in the gas-phase etching, in which the silicon oxide film is etched with argon gas plasma at a low rate of about 2 nm per 60 seconds. A second method involves the gas exposure process, in which by exposure in the gas atmosphere of hydrogen gas or nitrogen gas, for example, the surface condition of the ferromagnetic layer 205 is changed or the surface contamination with water, organic materials, etc. is removed. According to a third method, the crystalline structure of the ferromagnetic layer 205 is changed by the rapid thermal annealing (RTA) by radiation of the lamp light or heating of the substrate (not shown) with the heater. Incidentally, the process parameters such as the type, mixing ratio, pressure and temperature of the processing gas, the discharge output and the processing time for the plasma, if used, may be changed appropriately.
Next, as shown in
As shown in
In a method of oxygen processing step 302, the surface of the insulating layer 207 is exposed to the oxidation atmosphere of oxygen gas, ozone or oxygen plasma. For example, the insulating layer 207 is exposed for 30 seconds to the oxygen gas atmosphere under the pressure up to 2 Pa. In order to improve the reactivity between the oxidating gas and the oxygen atom defect, the sample may be heated with RTA or heater. In the case where the insulating layer 207 is formed of a metal nitride, the nitridation atmosphere may be used in place of the oxidation atmosphere described above. In the case where the insulating layer 207 is formed of a metal oxynitride, on the other hand, any one of the following methods may be employed: (a) a method in which the oxide film formed by sputtering is exposed to the nitrogen atmosphere, (b) a method in which the nitride film formed by sputtering is exposed to the oxygen atmosphere, and (c) a method in which the oxide film, the nitride film or the metal film formed by sputtering is exposed to the oxynitridation atmosphere. Also, the process parameters such as the type, mixing ratio, pressure and the temperature of the processing gas, the discharge output for the plasma, if used, and the processing time may be appropriately changed.
Next, as shown in
As shown in
In this second example of the fabrication method, assume that the insulating layer 207 of MgO originally has many oxygen atoms. The oxygen processing step 302 shown in
Incidentally, the first and second examples of the fabrication method include the film-forming steps under the conditions (2) and (8) of
[4] Method of Fabricating Magnetic Memory Device
First, as shown in
After forming the full-stack structure, the substrate may be annealed, as required, in a magnetic or nonmagnetic field. Instead of the exemplary condition of 360° C., 2 hours and 1 T, the condition including other temperature, time and magnetic field may be used. Also, the RTA heating process may be used.
Next, as shown in
The etching process of the fixed magnetization layer 102, the intermediate layer 103 and the memory layer 104 is not limited to the collective processing described above. Alternatively, the etching process may be stopped at the upper surface of the insulating layer 207 making up the intermediate layer 103, for example, and the fixed magnetization layer 102 may not be etched.
Next, as shown in
In the next step, a mask member (not shown) having a planar pattern corresponding to that of the lower wiring layer 101 is formed on the insulating layer 106 using CVD or lithography. Next, the insulating layer 106 and the lower wiring layer 101 are selectively etched by the RIE process using the mask member. In the process, the parts located on this side and in the depth through the page of
Next, as shown in
As shown in
An alternative method of forming the upper wiring layer 105 may be employed, in which the contact hole 108 is buried with the conductive material and flattened to such an extent as to expose the insulating layer 107 thereby to form a contact plug, after which a film of the conductive material is formed on the insulating layer 107 and the contact plug, followed by etching.
[5] MR Ratio and Life Length before Dielectric Breakdown due to Thickness Change of Mg on MgO
Under the conditions shown in
The graph of
The result shown in
The thickness of Mg on MgO is desirably in the range of 0.2 nm to 2.0 nm. In this range, both the MR ratio and the life length before dielectric breakdown can be maintained at a higher level than when Mg on MgO is not formed.
The thickness of Mg on MgO is desirably in the range of 0.4 nm to 1.0 nm. In this range, the highest MR ratio can be maintained. More desirably, the thickness of Mg on MgO is 0.8 nm.
The thickness of Mg on MgO is desirably in the range of 0.2 nm to 0.6 nm. In this range, the longest life length before dielectric breakdown can be maintained. More desirably, the thickness of Mg on MgO is 0.2 nm.
[6] MR Ratio and Life Length before Dielectric Breakdown with Change in Film-Forming Condition
The cause of improvement in the life length before dielectric breakdown under the conditions (2) to (8) is considered as described below.
The reason why the life length before dielectric breakdown is improved by “Mg on MgO” will be described later with reference to
The reason why the life length before dielectric breakdown is improved by “processing MgO with O2” is that the oxygen atom defect in MgO of the insulating layer 207 is repaired by O atoms of O2.
The reason why the life length before dielectric breakdown is improved by “smoothing lower CoFeB” is that the insulating layer 207 formed just above the smoothed ferromagnetic layer 205 is smoothed, and therefore, the local concentration of the electric field due to roughness is suppressed.
[7] Effects of Forming Mg on MgO
In the magnetoresistive effect element 100, two possible effects are obtained by forming Mg on MgO.
[7-1] First Effect
The first effect is that as shown in
The provision of the metal layer 206 of Mg under the insulating layer 207 of MgO can prevent the oxidation of the ferromagnetic layer 205 with the diffusion of the 0 atoms from the insulating layer 207 to the ferromagnetic layer 205 at the time of annealing after forming the layers.
[7-2] Second Effect
The possible second effect is that as shown in
In view of the fact that the metal layer 208 of Mg changes to the Mg-rich MgO layer as described above, the boundary structure of MgO/magnetic layer is formed, and the trap source due to the energy release from the conduction electrons is prevented from being formed. The insulating layer 207 of MgO supplying O atoms is estimated to be more reduced in effective thickness than before the diffusion of O atoms. Thus, the barrier resistance can be reduced while keeping the boundary structure of the MgO/magnetic layer in satisfactory state.
The specific effects of conversion of the metal layer 208 of Mg into the Mg-rich MgO layer are as follows:
Once the insulating layer (MgO) 207 underlying the metal layer (upper Mg) 208 is deprived of the extraneous O atoms by the metal layer (upper Mg) 208, the concentration of the extraneous atoms liable to be charged negatively is reduced, and so is the height of the barrier (the height of the energy barrier against the conduction electrons) of the insulating layer (MgO) 207.
The metal layer (upper Mg) 208, on the other hand, is lower in barrier than the originally O-rich insulating layer (MgO) 207 even in the case where O atoms are diffused from the insulating layer (MgO) 207.
As a result, the average height of the barrier as a whole (intermediate layer 103) according to this embodiment is lower than in the absence of the metal layer (upper Mg) 208. According to this embodiment, therefore, the conduction electrons are easily passed through the barrier, so that the physical thickness corresponding to the same barrier resistance is larger than in the first and second reference examples.
With the increase in the physical thickness with the applied voltage and the barrier resistance remaining constant, the electric field in the barrier is decreased, and the degeneration and breakdown of the barrier by the electric field are suppressed for an improved life length before dielectric breakdown. Alternatively, the barrier resistance can be reduced without reducing the physical thickness.
The extraneous Mg in the Mg-rich MgO is considered to pose no problem of the barrier characteristic including the life length before dielectric breakdown and the MR ratio. The reason is that since Mg is larger than MgO in lattice constant, the crystalline lattice is shrunk in the case where the extraneous O atoms are diffused from the insulating layer (MgO) 207 into the metal layer (upper Mg) 208 and the Mg-rich MgO barrier is formed.
The MgO in the Mg-rich MgO, like the underlying insulating layer (MgO) 207, becomes the MgO crystalline lattice having the bcc(001) structure. With the shrinkage of the crystalline lattice, on the other hand, the extraneous Mg atoms come to exist in the MgO crystalline lattice and share the valence electrons with the MgO crystalline lattice. The Mg atoms are heavier than the O atoms, and therefore, as compared with the extraneous O atoms in the O-rich MgO, the extraneous Mg atoms are harder to move in the MgO crystalline lattice and hence to deform the MgO crystalline lattice. Thus, the extraneous Mg atoms are isolated into Mg2+ ions but never become a trap source or a leak spot. Once this satisfactory Mg-rich MgO is formed in the boundary between the upper magnetic layer 209 and the insulating layer (MgO) 207, a trap source is more difficult to form in MgO than in the conventional O-rich MgO. Even in the case where the conduction electrons that have passed through the MgO barrier release the extraneous energy corresponding to the applied voltage, therefore, the trap generation by the particular energy is suppressed and the life length before dielectric breakdown improved.
The second effect shows that the intermediate layer 103 desirably has the film composition described below.
In the case where the intermediate layer 103 has a double-layer structure including the metal layer 208 and the insulating layer 207, a Mg-rich MgO layer is formed on the upper surface of the boundary between the intermediate layer 103 and the ferromagnetic layer 209. As a result, the metal comes to exist in the upper part (metal layer 208) of the intermediate layer 103 in a greater proportion than in the lower part (insulating layer 207) of the intermediate layer 103. More desirably, the metal exists in the upper part (metal layer 208) of the intermediate layer 103 in a proportion at least 1.001 times greater than in the lower part (insulating layer 207) of the intermediate layer 103 to produce a special effect.
In the case where the intermediate layer 103 has a triple-layer structure including the metal layers 208, 206 and the insulating layer 207, on the other hand, a Mg-rich MgO layer is formed on the upper surface of the boundary between the intermediate layer 103 and the ferromagnetic layer 209, while another Mg-rich MgO layer is formed on the lower surface of the boundary between the intermediate layer 103 and the ferromagnetic layer 205. As a result, the upper part (insulating layer 208) and the lower part (metal layer 206) of the intermediate layer 103 contain the metal in a greater proportion than the intermediate part (insulating layer 207) of the intermediate layer 103. More desirably, the upper part (metal layer 208) and the lower part (metal layer 206) of the intermediate layer 103 contain the metal in proportion at least 1.001 times more than the intermediate part (insulating layer 207) of the intermediate layer 103 to produce a special effect.
Considering the intermediate layer 103 as a whole, the addition of Mg to MgO causes the average metal content ratio of the intermediate layer 103 to approach a layer (Mg>1O<1) higher than the stoichiometric ratio. More desirably, the average metal content ratio of the intermediate layer 103 is at least 1.001 times greater in proportion than the stoichiometric ratio to produce a special effect.
As shown in
The effects of the upper Mg shown in
As shown in
As long as the MgO formed on the substrate surface is rich in O, the extraneous O atoms liable to become negative ions make up an electron trap source by capturing electrons or a leak spot source passing the conduction electrons, thereby reducing the life length before dielectric breakdown or the MR ratio of MgO.
In the upper Mg 0.6 shown in
Incidentally, the ideal MgO having the relation [Mg]>[O] can be formed by optimizing the MgO-forming conditions as rich in O and substantially in the relation Mg:O=1:1 and also by optimizing the various film-forming conditions such as the forming of the corresponding upper Mg, the processing in the oxidation atmosphere and the smoothing process.
[8] Application to Magnetic Random Access Memory
The magnetoresistive effect element 100 described above can be used as a storage element of a magnetic random access memory. The magnetic random access memory includes a plurality of memory cells each having the magnetoresistive effect element described above thereby to form a memory cell array.
For example, the lower wiring layer 101 shown in
Data can be written in the magnetic random access memory in any one of two methods, roughly speaking. According to one method called the magnetic field write method, the direction of magnetization of the memory layer 104 is reversed by a magnetic field generated with a current supplied to a write wiring arranged in the neighborhood of the magnetoresistive effect element 100. In the other method called the spin injection write method, a write current is supplied to the magnetoresistive effect element 100 and the conduction electrons arranged in the same spin direction by the fixed magnetization layer 102 are supplied to the memory layer 104 thereby to reverse the magnetization of the memory layer 104. According to this embodiment, the magnetoresistive effect element 100 is usable for both the magnetic field write method and the spin injection write method. The application to the latter, however, is more desirable and can produce the effects of this embodiment more easily.
In the spin injection write method, the directions of magnetization of the fixed magnetization layer 102 and the memory layer 104 are parallel or antiparallel with each other in accordance with the direction of the current flowing between the fixed magnetization layer 102 and the memory layer 104. For this reason, the direction of the current supplied is defined as described below.
In the case where “1” data is written, the current is supplied from the fixed magnetization layer 102 to the memory layer 104. In other words, electrons are injected from the memory layer 104 side to the fixed magnetization layer 102 side. As a result, the directions of magnetization of the fixed magnetization layer 102 and the memory layer 104 are opposite to and antiparallel with each other. This high resistance state Rap is defined as “1” data.
In the case where “0” data is written, on the other hand, the current is supplied from the memory layer 104 of the MTJ element MTJ toward the fixed magnetization layer 102. Specifically, electrons are injected from the fixed magnetization layer 102 side to the memory layer 104 side. As a result, the directions of magnetization of the fixed magnetization layer 102 and the memory layer 104 are arranged in the same direction and in parallel to each other. This low resistance state Rp is defined as “0” data.
In the read operation, the transistor connected to the lower wiring layer 101 shown in
[b 9] Effects
With the magnetoresistive effect element 100 according to an embodiment of this invention, the metal layer 208 of Mg, for example, is formed on the insulating layer 207 of MgO. Also, the surface of the uppermost layer (ferromagnetic layer 205) of the fixed magnetization layer 102 is smoothed before forming the lowest layer (metal layer 206) of the intermediate layer 103. Also, after processing the surface of the insulating layer 207 in the oxidation atmosphere, the metal layer 208 is formed on the particular surface.
As a result, the boundary of the intermediate layer 103 with the upper ferromagnetic layer 209 is prevented from forming a trap source which would otherwise be formed due to the energy release by the conduction electrons, thereby making it possible to form a tunnel barrier high in smoothness with the oxygen atom defect repaired. Thus, a magnetoresistive effect element high in MR ratio and a withstanding voltage, long in the life length before dielectric breakdown and suppressed in generation of minority faulty elements with a low withstanding voltage can be realized.
Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.
Number | Date | Country | Kind |
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2007-104161 | Apr 2007 | JP | national |
This application is a continuation of and claims the benefit of priority under 35 U.S.C. §120 from U.S. Ser. No. 12/100,097 filed Apr. 9, 2008, and claims the benefit of priority under 35 U.S.C. §119 from Japanese Patent Application No. 2007-104161 filed Apr. 11, 2007, the entire contents of each of which are incorporated herein by reference.
Number | Date | Country | |
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Parent | 12100097 | Apr 2008 | US |
Child | 13172516 | US |