JP6017149B2 - Spin injection magnetization reversal element and magnetoresistive random access memory - Google Patents

Description

  The present invention relates to a spin injection magnetization reversal element applied to a magnetoresistive effect element of a magnetoresistive random access memory, and to a magnetoresistive random access memory using the spin injection magnetization reversal element.

  A spin-injection magnetization reversal element has two or more magnetic films with an intermediate layer sandwiched between a non-magnetic film and an insulating film, and a current is supplied perpendicularly to the film surface from vertically connected electrodes (wiring). As a result, spin transfer magnetization (STT) (Non-patent Document 1) causes the magnetization direction of some of the magnetic films to rotate (reverse) by 180 °, so that the magnetization direction does not change. The direction is the same (parallel) or opposite (antiparallel) to the film. In this spin-injection magnetization reversal element, the resistance in the stacking direction changes depending on whether the magnetizations of the magnetic films are in the same direction or in different directions, so that 1-bit data is written / read as a magnetoresistive effect element. be able to. That is, the spin injection magnetization reversal element constitutes a magnetoresistive random access memory (MRAM) by two-dimensionally arranging memory cells provided with the spin injection magnetization reversal element. The spin-injection magnetization reversal element has a very small size (plan view size) of about 50 to 300 nm on a side and high-speed magnetization reversal operation. In particular, a TMR (Tunnel MagnetoResistance: tunnel magnetoresistive) element having an insulating film as an intermediate layer has been found to have a huge magnetoresistive effect due to a ferromagnetic tunnel junction (MTJ) (Non-Patent Document 2). MRAM has been developed (Patent Document 1).

A schematic diagram of such a spin injection magnetization reversal element is shown in cross-sectional view in FIG. As shown in FIG. 6, the spin injection magnetization reversal element 101 reverses the magnetization direction of the magnetization free layer 113 by connecting a pair of electrodes 31 and 32 up and down and being supplied with a current perpendicular to the film surface. be able to. Specifically, the spin injection magnetization switching element 101 is injected with electrons d _U 1 and d _D 1 in the direction in which current is supplied, and the magnetization direction of the magnetization free layer 113 is magnetized as shown in FIG. Either the same direction as the fixed layer 11, that is, the magnetization is parallel (P: Parallel), or the opposite direction (AP: Anti-Parallel) where the magnetization is antiparallel as shown in FIG. 6B. It can be. For example, when a value of “0” is recorded (written) in the spin injection magnetization switching element 101, a current is supplied from the magnetization free layer 113 side in order to make the magnetization parallel, and a value of “1” is recorded. In this case, a current is supplied from the magnetization fixed layer 11 side to make the magnetization antiparallel. That is, the spin injection magnetization switching element 101 performs writing by bipolar (bipolar) driving.

When data is read from the spin injection magnetization reversal element 101, a constant current smaller than the current for spin injection magnetization reversal is supplied from the electrodes 31 and 32, and the voltage between the electrodes 31 and 32 is supplied. Measure. The spin-injection magnetization reversal element 101 has a magnetization that is parallel or antiparallel, and the resistance changes to R101 _P and R101 _AP (> R101 _P ). Therefore, the magnitude is detected and the magnetization direction of the magnetization free layer 113 is read. be able to.

  Here, as described above, the MRAM includes memory cells arranged in a two-dimensional array, and the electrodes 31 and 32 are connected to wirings (word lines and bit lines) orthogonal to each other in a plan view. In addition, since a plurality of spin injection magnetization reversal elements 101 are connected in the row direction and the column direction, one spin injection magnetization reversal element 101 can be selected. In such an MRAM, when data is read out by selecting one spin-injection magnetization switching element 101, a current leaks to a non-selected spin-transfer magnetization switching element 101 connected to the same word line or bit line. As the number of mounted spin-injection magnetization reversal elements 101 increases, the resistance change amount of one spin-injection magnetization reversal element 101 detected at the time of data reading becomes smaller than the actual value, and the determination of “1” or “0” is made. It becomes difficult.

Therefore, in general, the MRAM includes a transistor such as a MOSFET (metal oxide semiconductor field effect transistor) in a memory cell, and one side of the spin-injection magnetization switching element 101, for example, the magnetization fixed layer 11 (electrode 31) and a wiring By making the connection / disconnection switchable between the two, the current is not leaked to the non-selected spin-injection magnetization switching element 101 (see, for example, Patent Document 1). An element that connects / disconnects to / from a wiring for each memory cell (spin injection magnetization switching element) like this transistor is referred to as an element selection circuit element. In such a select transistor type MRAM, since the write current supplied to the spin-injection magnetization switching element is large, for example, a current density of about 5 × 10 ⁶ A / cm ² , the MOSFET through which such a large current flows is a large plane. Even if the spin injection magnetization reversal element 101 is small, miniaturization of the memory cell is limited, and a cell selection wiring connected to the gate of the transistor is required in addition to the pair of wirings for writing / reading. It becomes.

  In place of the transistor, an MRAM having a diode connected to the spin injection magnetization switching element 101 has been developed (see, for example, Patent Document 2). The diode can have a size in plan view similar to that of the spin-injection magnetization switching element 101. However, since the current flows only in one direction, for example, the current flows only downward as shown in FIG. In this case, it is impossible to write “1” for each memory cell. Thus, a spin-injection magnetization reversal element has been proposed in which a unipolar (unipolar) drive magnetization reversal is realized by combining a perpendicular magnetization film and an in-plane magnetization film (see, for example, Patent Document 3). Further, as in Patent Document 3, a method using spin precession is used to form a magnetization free layer of an amorphous rare earth transition metal alloy whose magnetic properties change according to temperature, and to form a notch with a different shape at the periphery. There has been proposed a magnetic memory element (spin injection magnetization reversal element) provided in (see, for example, Patent Document 4).

JP 2001-156357 A JP 2004-179383 A JP 2006-128579 A International Publication No. 2009/157101

E.B.Mayer, D.C.Ralph, J.A.Katine, R.N.Louie, R.A.Buhrman, “Current-induced switching of domains in magnetic multilayer devices”, Science, 1999, Vol.285, pp.867-870 Shinji Yuasa, Taro Nagahama, Akio Fukushima, Yoshishige Suzuki, Koji Ando, “Giant room-temperature magnetoresistance in single-crystal Fe / MgO / Fe magnetic tunnel junctions”, Nature Materials, vol.3, p.868, Dec. 2004.

  In Patent Document 3, in order to perform writing with a forward bias current and a reverse bias current in which no current normally flows in a diode, similarly to a simple matrix type circuit without a selection circuit, the diode is also applied in the reverse direction. There is a possibility that a current flows and unintentional writing to an adjacent cell is performed, so that the function and reliability of the memory are remarkably lowered. Further, in Patent Document 4, inversion is caused by unipolar current by synchronizing the spin precession period and the pulse width of the pulse current causing the spin injection current. In this case, it is difficult to accurately write data due to variations in elements and variations in current pulse width, which is difficult to realize.

  The present invention has been devised in view of the above problems, and a spin-injection magnetization reversal element that allows reversal of magnetization in both parallel and antiparallel directions in units of cells and enables miniaturization of the memory cell, and the spin An object is to provide a magnetoresistive random access memory including an injection magnetization reversal element.

  In order to solve the above-mentioned problem, the present inventors have made a diode a device selection circuit element by using a unipolar drive spin-injection magnetization reversal element capable of reversing magnetization in a desired magnetization direction without changing the current supply direction. As a result, it was conceived that the memory cell can be miniaturized. By applying a ferrimagnetic material known as a perpendicular magnetic anisotropy material, by changing only the magnitude of the current and supplying it, the current in one direction can be changed from parallel to antiparallel. It has been found that magnetization can be reversed in both directions parallel to each other.

  That is, the spin-injection magnetization reversal element according to the present invention includes a magnetization fixed layer and a magnetization free layer stacked with an intermediate layer interposed therebetween, the magnetization free layer including a ferrimagnetic material, and the magnetization fixed layer and the magnetization free layer A magnetization direction of the magnetization free layer changes according to the magnitude of the current by connecting a pair of electrodes to the layer and changing the magnitude of the current to be supplied in one direction. To do.

  With this configuration, the spin-injection magnetization reversal element has a conventional spin-injection magnetization reversal by using, as a magnetization free layer, a ferrimagnetic body in which two magnetic bodies having magnetic moments that are antiparallel to each other and different in strength exist. By increasing the current in the same direction as one of the two, the spin injection magnetization reversal can be reversed in the opposite direction to the spin injection magnetization reversal, that is, two currents having the same direction but different sizes. , The magnitude of the resistance can be changed by reversing the spin injection magnetization in both directions.

Further, in the spin injection magnetization reversal element, the ferrimagnetic material is selected from a Tb—Fe—Co alloy, a Gd—Fe alloy, and a Mn—Ga alloy, and in particular, a Gd—Fe alloy of Fe: 78 to 81 at%. Is preferred.
With such a configuration, the spin injection magnetization reversal element is stable in reversal of spin injection magnetization in parallel and antiparallel, and can prevent erroneous writing.

  The magnetoresistive random access memory according to the present invention includes the spin injection magnetization reversal element in a memory cell, and the memory cell is two-dimensionally arranged. That is, in the magnetoresistive random access memory according to the present invention, the memory cell includes a pair of electrodes, and the spin-injection magnetization reversal element and the diode connected in series between the pair of electrodes.

  With this configuration, the magnetoresistive random access memory can write data from 1 to 0 and 0 to 1 for each memory cell by miniaturizing the memory cell and supplying current only in one direction. Furthermore, the data reading operation is stabilized.

  According to the spin injection magnetization reversal element according to the present invention, the magnetization can be made parallel or antiparallel by unipolar drive, and the diode can be provided in the memory cell as an element selection circuit element. According to the magnetoresistive random access memory according to the present invention, data can be written / read for each memory cell by a pair of wirings orthogonal to each other in the vertical and horizontal directions, and stable at high speed.

1 is a plan view schematically showing a configuration of a recording apparatus including a magnetoresistive random access memory according to an embodiment of the present invention. FIG. 2 is a schematic diagram of a memory cell including a spin-injection magnetization reversal element according to an embodiment of the present invention, corresponding to the AA cross-sectional view of FIG. 1. It is a schematic diagram explaining operation | movement of the spin injection magnetization reversal element which concerns on one Embodiment of this invention. By the sample of induced magnetization switching device according to an embodiment of the present invention, a measured result indicating a relationship between the current value and the resistance, (a) the magnetization free layer is Gd _19.7 Fe _80.3, (b) is Gd _22.7 Fe _77.3 It is. It is a graph of the magnetization reversal probability with respect to the electric current value of the sample shown to Fig.4 (a). It is a schematic diagram explaining operation | movement of the conventional spin injection magnetization reversal element.

  Hereinafter, embodiments for realizing a spin-injection magnetization switching element and a magnetoresistive random access memory according to the present invention will be described with reference to the drawings.

[Spin injection magnetization reversal element]
The spin transfer magnetization reversal element according to the present invention is used as a 1-bit storage device of the memory cell 4 of the magnetoresistive random access memory (MRAM) 40 shown in FIG. In FIG. 1, a part of the bit line 52 (upper electrode 32) is cut away, and the spin-injection magnetization reversal element 1 disposed below the bit line 52 is shown.

  As shown in FIG. 2, the spin transfer magnetization switching element 1 according to an embodiment of the present invention is laminated in the order of a magnetization fixed layer 11, an intermediate layer 12, a magnetization free layer 13, and a protective layer 14 (not shown in FIG. 2). In this configuration, a pair of electrodes, ie, a lower electrode 31 and an upper electrode 32 (hereinafter appropriately referred to as electrodes 31 and 32) are connected in the vertical direction, and a current is supplied perpendicular to the film surface. The spin-injection magnetization reversal element 1 includes a magnetization fixed layer 11 whose magnetization is fixed in one direction and a magnetization free layer 13 whose magnetization direction is rotatable, with an intermediate layer 12 which is a nonmagnetic conductor or an insulator interposed therebetween. Spin injection magnetization reversal elements such as CPP-GMR (Current Perpendicular to the Plane Giant MagnetoResistance) elements and TMR (Tunnel MagnetoResistance) elements, especially TMR elements with a large magnetoresistance effect. Preferably there is. Further, the spin transfer magnetization switching element 1 is provided with a protective layer 14 as the uppermost layer in order to protect these layers from damage in the manufacturing process. Further, in order to increase the crystal orientation of the barrier layer used for the intermediate layer 12 and to increase the magnetoresistance ratio, a seed layer (underlayer) may be provided under the magnetization fixed layer 11 (lowermost layer) (not shown). ). Note that the magnetization order of the magnetization fixed layer 11 and the magnetization free layer 13 may be switched (not shown).

  In a plan view, the spin-injection magnetization reversal element 1 is about 50 to 100 nm × 100 to 300 nm in which the magnetization fixed layer 11 and the magnetization free layer 13 can easily form a single magnetic domain, like a general spin-injection magnetization reversal element. The corresponding area is preferable, and as shown in FIG. 1, it is a square (rectangular), but is not limited thereto. Although details will be described later in a method of manufacturing a magnetoresistive random access memory, each layer constituting the spin injection magnetization reversal element 1 has a lower electrode 31 formed thereon and, for example, a sputtering method or a molecular beam epitaxy (MBE) method. The film is continuously formed and laminated by a known method such as electron beam lithography and ion beam milling, and is processed into a desired planar view shape.

(Magnetic pinned layer)
The magnetization fixed layer 11 is a magnetic body, and the magnetization direction is fixed. Such a magnetization fixed layer 11 can be made of a known magnetic material used for a CPP-GMR element or a TMR element, and it is particularly preferable to apply a perpendicular magnetic anisotropic material. Specifically, a multilayer film such as a Co / Pd multilayer film in which transition metals such as Fe, Co, and Ni and noble metals such as Pd and Pt are repeatedly stacked, and a rare earth such as Tb—Fe—Co and Gd—Fe. ferrimagnetic material such as a metal and an alloy of the transition metal (RE-TM alloy), FePt was L1 ₀ type ordered alloys, FePd, and the like.

  In addition, the magnetization fixed layer 11 has a coercive force Hcp sufficiently higher than the coercive force Hcf of the magnetization free layer 13 so that the magnetization of the magnetization fixed layer 11 is fixed even if the magnetization direction of the magnetization free layer 13 rotates. Each material is selected so as to be larger than the magnetization free layer 13 or thicker than the magnetization free layer 13. Specifically, the thickness of the magnetization fixed layer 11 is preferably designed in the range of 3 to 50 nm. In particular, the spin injection magnetization reversal element 1 according to the present invention is supplied with a larger current in addition to the current for the conventional spin injection magnetization reversal operation, as will be described later. The coercive force Hcp is designed to be sufficiently large so that the magnetization is not reversed by such a current.

(Middle layer)
The intermediate layer 12 is provided between the magnetization fixed layer 11 and the magnetization free layer 13. If the spin injection magnetization reversal element 1 is a TMR element, the intermediate layer 12 is made of a laminated film containing an insulator such as MgO, Al ₂ O ₃ , and HfO ₂ or an insulator such as Mg / MgO / Mg. The thickness is preferably 0.1 to 2 nm. If the spin transfer magnetization switching element 1 is a CPP-GMR element, the intermediate layer 12 is made of a nonmagnetic metal such as Cu, Ag, or Al, and preferably has a thickness of 1 to 10 nm. As described above, since the spin transfer magnetization switching element 1 is preferably a TMR element, the intermediate layer 12 preferably includes an insulator.

(Magnetization free layer)
The magnetization free layer 13 is made of a ferrimagnetic material among known magnetic materials used for CPP-GMR elements and TMR elements. Specific examples include alloys of rare earth metals and transition metals such as Tb—Fe—Co and Gd—Fe (RE-TM alloy), Mn—Ga alloys, and the like, and particularly Gd—Fe alloys (hereinafter referred to as GdFe alloys). ) Is preferred. Further, the magnetization free layer 13 is formed thinner than the magnetization fixed layer 11 in order to suppress the coercive force Hcf so as to easily reverse the magnetization, and specifically, the thickness is designed in the range of 1 to 20 nm. It is preferable.

  In the GdFe alloy, the transition metal Fe shows a magnetic moment in one direction (+ z direction), whereas the rare earth metal Gd shows a magnetic moment in the opposite direction (−z direction). Show. When a RE-TM alloy is applied as a magnetic layer of a spin-injection magnetization reversal element, for example, for a Tb-Fe-Co alloy, a composition (compensation composition) in which the respective magnetic moments of TM and RE are offset. In contrast, the RE-TM alloy as a whole has a low saturation magnetization and a magnetic moment in the -z direction, which easily exhibits perpendicular magnetic anisotropy and ensures the necessary coercive force. ing. On the other hand, for the GdFe alloy, the reversal current when applied to the magnetization free layer is not small in the vicinity of such a compensation composition, although the coercive force is small compared to other RE-TM alloys. The Fe content is increased so that the magnetic moment in the + z direction is shown as a whole. Furthermore, in the GdFe alloy applied to the magnetization free layer 13 of the spin transfer magnetization reversal element 1 according to the present invention, as will be described later, the magnetization reversal is stable not only in the normal spin transfer magnetization reversal but also in the reverse direction. Therefore, it is preferably 78 at% or more. On the other hand, in the GdFe alloy, when the Fe content exceeds 81 at%, the magnetic moment in the + z direction of Fe becomes dominant, the saturation magnetization becomes excessive, and the perpendicular magnetic anisotropy is not exhibited. When the GdFe alloy having such a limited composition is formed by sputtering, for example, a target made of a GdFe alloy having a composition corresponding to the desired composition of the magnetization free layer 13 may be used. Note that the composition of the target and the composition of the film to be formed do not necessarily match, so the target composition is determined after investigation in advance.

(Protective layer)
The protective layer 14 has a surface (upper surface) in order to protect the magnetization free layer 13 and the like from damage during manufacture of the spin injection magnetization reversal element 1 and particularly when the magnetization free layer 13 contains an easily oxidizable RE-TM alloy. It is provided in the uppermost layer in order to prevent oxidation. The protective layer 14 is composed of a single layer of Ta, Ru, Cu, or two layers of Cu / Ta, Cu / Ru. In addition, when setting it as the said 2 layer structure, all make Cu inside (lower layer). When the thickness of the protective layer 14 is less than 1 nm, it is difficult to form a continuous film. On the other hand, even if the thickness exceeds 10 nm, the effect of protecting the magnetization free layer 13 and the like in the manufacturing process is further improved. do not do. Therefore, the thickness of the protective layer 14 is preferably 1 to 10 nm.

(Magnetization reversal operation of spin injection magnetization reversal element)
Next, the magnetization reversal operation of the spin injection magnetization reversal element in the present embodiment will be described with reference to FIG. In FIG. 3, the protective layer 14 is not shown. In the spin injection magnetization reversal element 1, the magnetization fixed layer 11 has its magnetization fixed upward. In addition, the diode 2 is connected to the magnetization fixed layer 11 (lower electrode 31), and the spin injection magnetization reversal element 1 is supplied with current only downward.

First, when the magnetization free layer 13 has a downward magnetization (see FIG. 3C), the spin transfer magnetization reversal element 1 has a magnetization reversal current I _STS of the magnetization free layer 13 as shown in FIG. When the current −I _W 1 having the above magnitude is supplied, the state changes to a state showing the upward magnetization that is the same as the magnetization direction of the magnetization fixed layer 11 as in the conventional spin transfer magnetization switching element 101 (see FIG. 6A). (Magnetization reversal). Specifically, when a current −I _W 1 is supplied from the magnetization free layer 13 side, electrons are injected from the magnetization fixed layer 11 side, and the magnetization fixed layer 11 has a downward spin opposite to the magnetization of the magnetization fixed layer 11. Electrons d _D 1 are discriminated, and only electrons d _U 1 having an upward spin are injected from the lower electrode 31 into the magnetization fixed layer 11 and further injected into the magnetization free layer 13. Since the electron d _U 1 has a spin torque with a strength that reverses the spin of the internal electrons of the magnetization free layer 13, the magnetization free layer 13 is inverted in magnetization upward by the electron d _U 1.

Here, as described above, the ferrimagnetic material has two magnetic moments in opposite directions and different in strength. For example, when the magnetization free layer 13 is made of a GdFe alloy, the whole magnetization free layer 13 exhibits downward magnetization because the magnetic moment of strong Fe is downward, and the magnetic moment of Gd weaker than Fe is opposed upward. It is. In the conventional spin injection magnetization reversal as described with reference to FIG. 3A, the magnetic moment of Fe is reversed in response to the torque of the electron d _U 1 having an upward spin in which the magnetic moment is antiparallel. Become. Then, the magnetic moment of Gd coupled with Fe follows and reverses as much as possible to be antiparallel to the magnetic moment of Fe, and the magnetization free layer 13 undergoes magnetization reversal so as to exhibit upward magnetization as a whole.

In contrast, the spin injection magnetization reversal element 1, when the magnetization free layer 13 is the upward magnetization, as shown in FIG. 3 (b), a larger current -I _W than the current -I _W 1 When 2 is supplied, the following operation is performed. Specifically, in the same manner as when the current −I _W 1 is supplied (see FIG. 3A), the magnetization fixed layer 11 causes an electron d _D 2 having a downward spin opposite to the magnetization of the magnetization fixed layer 11 to be generated. As a result of discrimination, only electrons d _U 2 having an upward spin are injected into the magnetization free layer 13.

When the magnetization free layer 13 exhibits upward magnetization, the magnetic moment of Fe (represented by “Fe” in the figure) is also upward. Therefore, the magnetic moment of Fe does not receive the torque of the electron d _U 2 having parallel upward spins, and the direction does not change. However, when the torque of the electron d _U 2 is stronger than a certain value, the anti-parallel Gd magnetic moment (indicated by the symbol “Gd” in the figure) tries to reverse upward due to this strong torque. It is considered that the exchange coupling between Gd and Fe is temporarily released. That is, as shown in FIG. 3B, when electrons d _U 2 are injected into the magnetization free layer 13, both magnetic moments of Fe and Gd are upward. When the supply of the current −I _W 2 is stopped in this state, as shown in FIG. 3C, the electron d _U 2 disappears from the magnetization free layer 13, and Gd and Fe return to the coupled state, and the mutual magnetic properties It is considered that the magnetic moment of Fe is reversed so that the moment is antiparallel. As a result, the magnetic moment of Fe is downward, and the magnetization free layer 13 is reversed in magnetization so as to exhibit downward magnetization as a whole.

As described above, the spin injection magnetization reversal element 1 according to the present invention supplies the two currents I _W 1 and I _W 2 in one direction, thereby reversing the magnetization in both parallel and antiparallel directions. Can be made. The spin transfer magnetization reversal element 1 has a magnetization that is parallel or antiparallel, and the resistance changes to R1 _P and R1 _AP (> R1 _P ), similarly to the conventional spin transfer magnetization reversal element 101 (see FIG. 6). To do. Therefore, as will be described later, the spin transfer magnetization reversal element 1 can be configured as an MRAM memory cell by connecting a diode that allows current to flow only in one direction (forward direction) as an element selection circuit element.

In another embodiment, the spin injection magnetization reversal element 1 may be supplied with current upward, that is, from the magnetization fixed layer 11 side, and the diode 2 is connected in the direction opposite to that shown in FIG. The stacking order of the magnetization fixed layer 11 and the magnetization free layer 13 of the magnetization switching element 1 may be switched. In this case, electrons are directly injected from the upper electrode 32 into the magnetization free layer 13, but electrons d _U 1, d _U 2 having the same upward spin as the magnetization of the magnetization fixed layer 11 in the magnetization fixed layer 11. Therefore, electrons d _D 1 and d _D 2 having a downward spin accumulate in the magnetization free layer 13. Therefore, contrary to FIG. 3A, FIG. 3B, and FIG. 3C, when the current + I _W 1 is supplied, the anti-parallel magnetization is shown as in FIG. When + I _W 2 is supplied, it shows parallel magnetization.

Regarding the magnitudes of the two currents I _W 1 and I _W 2 for reversing the magnetization of the spin injection magnetization reversal element 1 in parallel and antiparallel, the current I _W 1 is _{equal to} or greater than the magnetization reversal current I _STS of the magnetization free layer 13 as described above. If it is. On the other hand, the current I _W 2 has a strong antiferromagnetic material that forms the magnetization free layer 13 and has a magnetic moment that is antiparallel to each other, for example, the bond between the rare earth metal (RE) and the transition metal (TM) is released. The size is such that electrons having spin torque are injected. In order for the spin-injection magnetization reversal element 1 to stably reverse the magnetization by supplying the current I _W 2, the ferrimagnetic material forming the magnetization free layer 13 has the above-mentioned current I _W 2 by the constant current I _W 2. It is preferable to set the composition or the like so that the bond is surely released.

  As described above, according to the spin-injection magnetization reversal element according to the present invention, the unipolar drive spin-injection magnetization reversal element that can supply current only in one direction to make the magnetization parallel or anti-parallel. can do. As will be described later, the spin-injection magnetization reversal element 1 constitutes a magnetoresistive random access memory (MRAM) by arranging a plurality of two-dimensionally in the film surface direction as a magnetoresistive effect element. Therefore, the diode can be used as an element selection circuit element.

[Magnetic resistance random access memory]
Next, an embodiment of a magnetoresistive random access memory provided with a spin injection magnetization reversal element according to the present invention in a memory cell will be described with reference to the drawings.
As shown in FIG. 1, a magnetoresistive random access memory (MRAM) 40 according to the present invention includes memory cells 4 arranged in a two-dimensional array on a substrate 7, and constitutes a recording apparatus 10 together with a controller 90. It is a part.

  In the present embodiment, the MRAM 40 is exemplified by a configuration including 16 memory cells 4 of 4 rows × 4 columns for the sake of brevity. The MRAM 40 has four word lines 51 extending in the Y direction (vertical direction in FIG. 1) in plan view, and an X direction (horizontal direction in FIG. 1) orthogonal to the word line 51 in plan view. The memory cell 4 is provided at each intersection of the word line 51 and the bit line 52. As shown in FIG. 2, the MRAM 40 is provided with a word line 51 on the substrate 7. In the memory cell 4, the diode 2 is connected to the word line 51 through the barrier layer 23, and further through the lower electrode 31. Thus, the spin transfer magnetization reversal element 1 is connected, and the upper electrode 32 connected to the spin transfer magnetization reversal element 1 forms the bit line 52. In the MRAM 40, an insulating layer 6 is formed between adjacent word lines 51, 51, between bit lines 52, 52, and between word lines 51 and bit lines 52, that is, between spin injection magnetization reversal elements 1, 1. Yes.

  The control unit 90 is a well-known component that writes to and reads from the MRAM 40. As an example, as shown in FIG. 1, the control unit 90 controls the bit line selection unit 92 that selects the bit line 52, the word line selection unit 91 that selects the word line 51, and the selection units 91 and 92. And a write / read drive unit 93 including a power source for supplying a write current and a read current to the bit line 52 and the word line 51, a voltmeter for reading, and the like. The cell selection unit 94 selects, for example, one or more specific memory cells 4 of the MRAM 40 based on an external signal (not shown), and selects a bit line 52 and a word line 51 connected to the selected memory cell 4. The unit 92 and the word line selection unit 91 are selected. The write / read drive unit 93 supplies an appropriate voltage / current and measures the voltage for operating the spin transfer magnetization reversal element 1 provided in the selected memory cell 4.

(Spin injection magnetization reversal element)
The spin-injection magnetization switching element 1 has the configuration already described and will not be described. In all the spin-injection magnetization switching elements 1 provided in the MRAM 40, the magnetization fixed layer 11 is unified in the same magnetization direction, and is fixed upward here (see FIG. 3).

(Electrode, wiring)
The lower electrode 31 and the upper electrode 32 (bit line 52) and the word line 51 are formed of a general metal electrode material such as a metal such as Cu, Al, Au, Ag, Ta, Cr, or an alloy thereof. The Then, it is processed into a desired shape such as a stripe shape by a known method such as a sputtering method, by film formation, photolithography, etching, lift-off method, or the like.

(diode)
As the diode 2, for example, a general one such as a silicon (Si) diode is applied, and it may have a configuration corresponding to the write current and the read current of the spin injection magnetization switching element 1. In FIG. 2, since the n layer 21 is stacked below and the p layer 22 is stacked in this order, the current flows only downward, that is, when the bit line 52 is “+” and the word line 51 is “−”. Flows and is supplied to the spin-injection magnetization switching element 1 (see FIG. 3). The n layer 21 and the p layer 22 may be interchanged so that current is supplied upward. Further, it is preferable to provide a barrier layer 23 made of a semiconductor such as Ti—N between the word line 51 so that a metal such as Cu in the word line 51 is not diffused. In FIG. 2, the shape is the same as that in the plan view of the spin transfer magnetization switching element 1, but the shape is not limited thereto.

(substrate)
The substrate 7 is a base for two-dimensionally arranging the memory cells 4, and is a broad substrate for manufacturing the wirings 51 and 52, the diode 2, and the spin transfer magnetization switching element 1. As such a substrate 7, a known substrate material can be applied. Specifically, a Si substrate on which a surface is thermally oxidized to form a SiO ₂ film is suitable. Alternatively, a known insulating substrate such as a GGG (gadolinium gallium garnet) substrate, SiC (silicon carbide) substrate, MgO (magnesium oxide) substrate, or Ge (germanium) single crystal substrate may be used as a transparent substrate material. it can. Thus, since the MRAM according to the present invention does not include a transistor, the substrate 7 is not limited to Si or the like. The substrate 7 is at least a surface of an insulator so that the word lines 51 and 51 formed thereon are not short-circuited.

(Insulating layer)
The insulating layer 6 is formed between the adjacent word lines 51 and 51, between the bit lines 52 and 52, and between the word line 51 and the bit line 52, that is, between the spin transfer magnetization reversal elements 1 and 1 and between the diodes 2 and 2. , Each provided for insulation. For the insulating layer 6, for example, an oxide film such as SiO ₂ or Al ₂ O ₃ or a known insulating material such as Si—N can be applied. However, in the region in contact with the spin transfer magnetization switching element 1, ferrimagnetic properties are applicable. When a RE-TM alloy that easily oxidizes is included as a body, it is preferable to apply a non-oxide such as Si-N.

(Memory cell operation)
Regarding the operation of the spin injection magnetization reversal element 1 in the memory cell 4, the writing, that is, the magnetization reversal operation is as described with reference to FIG. In FIG. 3, current is supplied from the electrodes 31 and 32, but in the memory cell 4 (MRAM 40), the spin injection magnetization switching element 1 is driven by supplying current from the bit line 52 and the word line 51. On the other hand, when reading data, if a current of a predetermined magnitude is supplied between the bit line 52 and the word line 51 and the voltage flowing through the spin-injection magnetization reversal element 1 is measured as in the known MRAM. Good. At this time, a reverse current is supplied to the non-selected memory cell 4, that is, a voltage higher than that of the bit line 52 is applied to the word line 51 so that the current does not leak to the spin transfer magnetization switching element 1. May be.

[Method of manufacturing magnetoresistive random access memory]
The magnetoresistive random access memory (MRAM) according to the present invention is manufactured in the same manner as a known manufacturing method. As an example, first, the word line 51 is formed on the substrate 7 by sputtering or etching, and the insulating layer 6 is embedded between the word lines 51 and 51. Next, the barrier layer 23, the n layer 21, the p layer 22, the lower electrode 31, the magnetization fixed layer 11, the intermediate layer 12, the magnetization free layer 13, and the protective layer 14 are arranged at the planar view position of the memory cell 4 on the word line 51. The material for forming each layer is continuously formed and processed into the shape of each memory cell 4 as shown in FIG. 1 to form the spin transfer magnetization reversal element 1 and the diode 2, and the lower electrode 31 therebetween. . Then, an insulating layer 6 is embedded between the spin injection magnetization switching elements 1 and 1. Finally, the bit line 52 and the insulating layer 6 between the bit lines 52 and 52 are formed, and the MRAM 40 is manufactured.

  As described above, according to the magnetoresistive random access memory according to the embodiment of the present invention, the memory cell is miniaturized and simplified by using the diode as the element selection circuit element, and the pair of word lines Therefore, a recording device having a simple configuration can be obtained.

  As mentioned above, although each embodiment for implementing the spin-injection magnetization switching element and the magnetoresistive random access memory of the present invention has been described, the present invention is not limited to these embodiments, and is described in the claims. Various changes can be made within the range.

In order to confirm the effect of the present invention, a sample of a spin transfer magnetization switching element (see FIG. 2) according to an embodiment of the present invention was produced. Using a Si substrate with a thermal oxide film on the surface, forming a lower electrode with a Cu film, laminating an Ag film (20 nm), further providing Ru (3 nm) as a base film, and then reversing the spin injection magnetization As elements, from the lower electrode side, magnetization fixed layer: TbFeCo (10 nm) / CoFe (1 nm), intermediate layer: Ag (6 nm), magnetization free layer: GdFe (8.9 nm), protective layer: Ru (3 nm), Films were continuously formed and stacked by a DC magnetron sputtering method. Next, a rectangular resist mask of 100 nm × 300 nm is formed, and each layer of the spin-injection magnetization switching element and the Cu film (lower electrode) are processed by an ion beam milling method, and then SiO ₂ / Si− is formed on the resist. N was deposited, and the resist was removed together with the SiO ₂ / Si—N (lift-off) thereon to form an insulating layer around (side surfaces) of the spin transfer magnetization switching element. And Cu was formed into a film as an upper electrode on a spin injection magnetization reversal element, and it was set as the sample of an example. Samples were prepared by forming a GdFe alloy of a magnetization free layer with two compositions of Fe: _{80.3 at} % (Gd _19.7 Fe _80.3 ) and Fe: _{77.3 at} % (Gd _22.7 Fe _77.3 ).

  An initialization magnetic field of 1 kOe was applied to the prepared sample, and the magnetization directions of the whole (magnetization fixed layer and magnetization free layer) were aligned upward. Then, assuming that the lower electrode is “+” and the upper electrode is “−”, a negative direct current pulse current (pulse width 10 μs) in which electrons flow from the magnetization fixed layer to the magnetization free layer under the condition of a magnetic field −70 Oe at the time of spin injection, While supplying the size (absolute value) gradually increasing and decreasing, the resistance between the electrodes was measured by a four-terminal method using a lock-in amplifier. When the resistance decreased and increased, that is, when the magnetization was reversed, the current value was measured 100 times for each magnetization reversal from antiparallel to parallel (AP-P) and parallel to antiparallel (P-AP). FIG. 4 shows measurement results of current and resistance.

  As shown in FIGS. 4A and 4B, the spin-injection magnetization reversal element is antiparallel to parallel (resistance drops) and parallel to antiparallel even when a current is supplied only in one direction (negative direction). Unipolar driving was confirmed by reversing the magnetization in both directions (increasing resistance). In particular, as shown in FIG. 4 (a), a sample using an Fe: 80.3 at% GdFe alloy as the magnetization free layer has a magnetization reversal from antiparallel to parallel at -4.5 mA and 100% at about -5 mA. When the current becomes parallel and further increased, the magnetization is reversed from parallel to antiparallel at -10.5 mA, and almost 100% antiparallel at -11 mA, resulting in a spin injection magnetization reversal element with extremely stable operation. It was. FIG. 5 is a graph showing the magnetization reversal probability with respect to the current value in this sample. From this, the GdFe alloy of Fe: 80.3 at% has a conventional spin injection magnetization reversal in which the magnetic moment of Fe is reversed and the magnetic moment of Gd is reversed following the current supply of −4 mA. However, if a current supply of −11 mA, which is larger than this, is estimated that the coupling between Gd and Fe is released and the magnetic moment of Gd is reversed.

DESCRIPTION OF SYMBOLS 10 Recording apparatus 1 Spin-injection magnetization inversion element 11 Magnetization fixed layer 12 Intermediate layer 13 Magnetization free layer 14 Protective layer 2 Diode 31 Lower electrode (electrode)
32 Upper electrode (electrode)
40 MRAM (Magnetoresistive Random Access Memory)
4 Memory cells 51 Word line (electrode)
52 Bit line (electrode)
6 Insulating layer 7 Substrate 90 Control unit

Claims (4)

A spin-injection magnetization reversal device comprising a magnetization fixed layer and a magnetization free layer stacked with an intermediate layer interposed therebetween,
The magnetization free layer comprises a ferrimagnetic material;
By connecting a pair of electrodes to the magnetization fixed layer and the magnetization free layer and changing the magnitude of the current to be supplied in one direction, the magnetization of the magnetization free layer according to the magnitude of the current A spin-injection magnetization reversal element characterized in that the direction changes.   The spin injection magnetization reversal element according to claim 1, wherein the ferrimagnetic material is one selected from a Tb-Fe-Co alloy, a Gd-Fe alloy, and a Mn-Ga alloy.   The spin injection magnetization reversal element according to claim 1, wherein the ferrimagnetic material is a Gd—Fe alloy of Fe: 78 to 81 at%. A magnetic random access memory comprising a plurality of memory cells arranged two-dimensionally,
4. The magnetoresistive random element comprising: a pair of electrodes; and the spin-injection magnetization switching element and the diode according to claim 1, which are connected in series between the pair of electrodes. 5. Access memory.