JP2010232374A - Magnetoresistive element, and magnetic random access memory and spatial light modulator using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetoresistive element with vertical magnetic anisotropy which has superior magnetic characteristics by containing an RE-TM alloy, and can maintain the magnetic characteristics. <P>SOLUTION: The magnetoresistive element 1 has a magnetization fixed layer 11, an intermediate layer 12 and a magnetization reversal layer 13 laminated, wherein at least one of the magnetization fixed layer 11 and magnetization reversal layer 13 contains the RE-TM alloy, and an insulating layer 6 for insulating a pair of electrodes 2 and 3 connected above and below is disposed in contact with the magnetoresistive element 1 and made of silicon oxide. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a magnetoresistive element, a magnetic random access memory, or a spatial light modulator that utilizes the properties of a magnetic film.

  A film surface vertical conduction type magnetoresistive element (magnetoresistance effect element) includes two or more magnetic films, and spins by supplying current perpendicularly to the film surface from vertically connected electrodes (wiring). Due to the reversal of the injected magnetization, the magnetization direction of a part of the magnetic film is rotated by 180 ° to be the same direction as another magnetic film in which the magnetization direction does not change, or in the opposite direction. In this magnetoresistive element, the resistance between the upper and lower electrodes changes due to spin injection magnetization reversal (hereinafter referred to as magnetization reversal), and this can be used to write / read 1-bit data. . That is, the magnetoresistive element constitutes a magnetic random access memory (MRAM) by arranging memory cells including the magnetoresistive element in a matrix. Since the magnetoresistive element is extremely small in size and operates at a high speed of magnetization reversal, research and development of an MRAM and a magnetoresistive element as a large-capacity magnetic memory are underway.

  As a magnetic material of the magnetoresistive element, a Co—Fe alloy or the like that exhibits magnetization in the film surface direction has been conventionally studied, but recently, in order to further increase the capacity and power saving of the MRAM, Attention has been focused on magnetic materials that exhibit magnetization in the direction perpendicular to the film surface (having perpendicular magnetic anisotropy) that can further miniaturize the magnetoresistive element and reduce the current required for magnetization reversal. Among such perpendicular magnetic anisotropy materials, an alloy of rare earth metal and transition metal (RE-TM alloy) is attracting attention as a ferrimagnetic perpendicular magnetic anisotropy material. It is promising as an element material (see, for example, Patent Document 1).

  Another application of the magnetoresistive element is a light modulation element mounted on a pixel of a spatial light modulator. A magnetoresistive element as a light modulation element changes the direction of polarization of light reflected or transmitted by a magnetic film whose magnetization rotates by the magneto-optic effect. For this reason, research and development are being carried out as materials that can replace conventional liquid crystals (see, for example, Patent Document 2). For a magnetoresistive element used as a light modulation element, it is desirable to increase the change in the direction of polarization (increase the degree of light modulation). For this reason, it is desirable that the light modulation element increases the degree of light modulation by the polar Kerr effect by using a magnetoresistive element having perpendicular magnetic anisotropy and allowing light to enter the film surface substantially perpendicularly.

JP 2008-283207 A (Claim 6, Claim 11, Paragraph 0027) JP 2008-145748 A (Claim 6, FIG. 4)

In both the MRAM and the spatial light modulator, the magnetoresistive elements are two-dimensionally arranged in the film surface direction, and electrodes are connected from above and below. An insulating material is buried in this region so that the upper and lower electrodes are not short-circuited in a region where the magnetoresistive elements are separated from each other. The insulating material seals the side surface (end surface) of the magnetoresistive element in addition to the prevention of the short circuit, and silicon oxide (SiO ₂ ) is generally applied. Here, as described above, the RE-TM alloy is a particularly preferable material as the perpendicular magnetic anisotropic material, but has a property of being easily oxidized. Therefore, the magnetoresistive element is exposed at the end face of the magnetoresistive element exposed by supplying oxygen in the step of forming SiO ₂ in the space between the magnetoresistive elements when manufacturing the MRAM or the spatial light modulator. There is a possibility that the RE-TM alloy contained in the metal will oxidize and the magnetic properties of the RE-TM alloy and further of the magnetoresistive element will deteriorate. Also, after manufacturing, by interfacial RE-TM alloy (the end face of the magnetic resistance element) with SiO ₂ is in contact with the SiO _2, oxidation from the end face by the SiO ₂ oxygen (O) progresses, RE -There exists a possibility that the magnetic characteristic of TM alloy may deteriorate.

  The present invention has been devised in view of the above problems, and includes a magnetoresistive element that includes a RE-TM alloy that is preferable as a perpendicular magnetic anisotropy material and that can suppress deterioration of magnetic characteristics, and a magnetic random element that includes this magnetoresistive element. An object is to provide an access memory and a spatial light modulator.

In order to solve the above-mentioned problems, the present inventors do not apply a material containing oxygen (O) such as an oxide as an insulating material in place of SiO ₂ , but do not oxidize the RE-TM alloy and cause deterioration. We thought that it could be suppressed and found out that silicon nitride was applied.

  That is, a magnetoresistive element according to the present invention includes a spin injection magnetization reversal element including a magnetization fixed layer, an intermediate layer, and a magnetization reversal layer, and a pair of electrodes connected above and below the spin injection magnetization reversal element. The spin-injection magnetization reversal element includes at least one of a magnetization fixed layer and a magnetization reversal layer including an alloy of a rare earth metal and a transition metal, and the insulation layer includes: , In contact with the spin-injection magnetization switching element, and made of silicon nitride.

  With this configuration, since the spin-injection magnetization switching element includes the RE-TM alloy and has perpendicular magnetic anisotropy, it is possible to reduce the size and decrease the magnetization switching current, and stabilize the magnetization switching operation. Furthermore, these magnetic characteristics do not have the possibility that the RE-TM alloy is oxidized and deteriorated by making the insulating layer in contact with silicon nitride.

  In addition, a magnetic random access memory according to the present invention is configured by including, in a memory cell, a spin-injection magnetization reversal element containing the RE-TM alloy and a pair of electrodes connected to the upper and lower sides thereof. That is, a magnetic random access memory including a plurality of two-dimensionally arranged memory cells, which is in contact with the spin injection magnetization reversal element and insulates between adjacent spin injection magnetization reversal elements and the pair of electrodes. An insulating layer made of nitride is provided.

  With this configuration, the magnetic random access memory can reduce the spin injection magnetization reversal element for recording 1 bit as perpendicular magnetic anisotropy, reduce the drive current, and stabilize the data write / read operation. To do. Furthermore, these characteristics can suppress deterioration by providing silicon nitride as an insulating layer in a region in contact with the spin injection magnetization switching element.

  A spatial light modulator according to the present invention uses the spin-injection magnetization switching element including the RE-TM alloy as a light modulation element, and a pair of electrodes connected above and below the spin-transfer magnetization switching element. Are provided in a pixel. That is, a plurality of pixels arranged two-dimensionally, a pixel selection unit that selects one or more pixels from the plurality of pixels, and a current supply unit that supplies a predetermined current to the pixels selected by the pixel selection unit, A spatial light modulator that emits light by changing the polarization direction of light incident on the pixel selected by the pixel selection means in a specific direction, and is adjacent to the spin injection magnetization switching element and An insulating layer made of silicon nitride that insulates between the magnetization reversal elements and the pair of electrodes is provided.

  With this configuration, the spatial light modulator can increase the degree of light modulation by the polar Kerr effect, with the magnetoresistive element constituting the light modulation element provided in the pixel as the perpendicular magnetic anisotropy. Further, the current for pixel selection operation can be reduced, and the operation is stabilized. Furthermore, deterioration of these characteristics can be suppressed by providing silicon nitride as an insulating material on the side surface of the magnetoresistive element.

  According to the magnetoresistive element of the present invention, it is possible to obtain a magnetoresistive element having perpendicular magnetic anisotropy that can reduce the magnetization reversal current, stabilize the magnetization reversal operation, and hardly deteriorate the magnetic characteristics thereof. According to the magnetic random access memory according to the present invention, the capacity can be increased, the data writing / reading operation can be performed stably at high speed, and the characteristics can be hardly deteriorated. . Further, according to the spatial light modulator according to the present invention, it is possible to achieve high definition, high speed response, and excellent pixel selectivity, and further, these characteristics can be hardly deteriorated.

It is sectional drawing of the magnetoresistive element which concerns on one Embodiment of this invention. It is a perspective view explaining typically operation of a magnetoresistive element concerning one embodiment of the present invention. It is a top view which shows typically the structure of the spatial light modulator which concerns on one Embodiment of this invention. FIG. 4 is a schematic diagram for explaining the pixel selection operation of the spatial light modulator shown in FIG. It is a top view which shows typically the structure of the recording device provided with the magnetic random access memory which concerns on one Embodiment of this invention. 6 is a cross-sectional view of a magnetoresistive element and a memory cell including the magnetoresistive element according to an embodiment of the present invention, and is a cross-sectional view taken along line BB of FIG. It is a graph which shows the magnetic characteristic of the magnetoresistive element of an Example.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for realizing a magnetoresistive element, a magnetic random access memory, and a spatial light modulator according to the present invention will be described with reference to the drawings.

[Magnetic resistance element]
As shown in FIG. 1, a magnetoresistive element (spin injection magnetization reversal 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 reversal layer 13, and a protective layer 14. It is a structure and is connected to the upper electrode 2 and the lower electrode 3 which are a pair of electrodes in the vertical direction, and a current is supplied perpendicular to the film surface. Further, an insulating layer 6 is embedded in a gap between the upper electrode 2 and the lower electrode 3 (hereinafter appropriately referred to as electrodes 2 and 3), that is, a region adjacent to the side surface of the magnetoresistive element 1. The magnetoresistive element 1 is a CPP-GMR having a magnetization fixed layer 11 whose magnetization is fixed in one direction and a magnetization reversal layer 13 whose magnetization direction is rotatable, with an intermediate layer 12 which is nonmagnetic or insulating, sandwiched between them. Spin injection magnetization reversal elements such as (Current Perpendicular to the Plane Giant MagnetoResistance) elements and TMR (Tunnel MagnetoResistance) elements, and to protect these layers from damage in the manufacturing process In addition, a protective layer 14 is provided as the uppermost layer. Each layer constituting the magnetoresistive element 1 is formed with a lower electrode 3 and is continuously formed and laminated by a known method such as a sputtering method or a molecular beam epitaxy (MBE) method. And it is processed into a desired planar view shape by an ion beam milling method or the like. Hereinafter, details of each layer constituting the magnetoresistive element 1 will be described.

  The magnetization fixed layer 11 and the magnetization reversal layer 13 can be made of a known magnetic material as a magnetization fixed layer and a magnetization reversal layer such as a CPP-GMR element or a TMR element having perpendicular magnetic anisotropy, respectively. In the embodiment, at least one includes an alloy (RE-TM alloy) of a rare earth metal and a transition metal. Examples of transition metals include Fe, Co, Ni, and examples of rare earth metals include Sm, Eu, Gd, and Tb. The RE-TM alloy is a ferrimagnetic material, and since the apparent saturation magnetization Ms is low, the magnetic field leaking to the outside can be reduced. Note that including the RE-TM alloy may constitute the entire magnetization fixed layer 11 or the magnetization reversal layer 13, or may include a part such as a multilayer structure laminated with other materials. Good.

  The magnetization fixed layer 11 preferably has a thickness of 1 to 50 nm. When the magnetization pinned layer 11 includes a RE-TM alloy, the saturation magnetization Ms is low. Therefore, the magnetoresistive element 1 reduces the magnetic field leaking from the magnetization pinned layer 11 to the magnetization switching layer 13 and spin injection. The phenomenon that the magnetization reversal characteristic shifts to one side in the current axis direction can be suppressed, and a stable spin injection magnetization reversal operation can be obtained by setting the positive magnetization reversal current and the negative magnetization reversal current to substantially the same magnitude. Examples of other materials include transition metals such as Fe, Co, and Ni, alloys containing them, and [Fe / Pt] × n and [Co / Pt] × n multilayer films.

  The magnetization switching layer 13 preferably has a thickness of 1 to 20 nm. When the magnetization reversal layer 13 includes a RE-TM alloy, the saturation magnetization Ms is low. Therefore, the magnetoresistive element 1 can reduce the magnetization reversal current density Jc to reduce the magnetization reversal current. Other materials include transition metals such as Fe, Co, Ni, and alloys containing them, CoPt, CoCr based alloys (CoCr, CoCrPt, CoCrTa, etc.), [Fe / Pt] × n, [Co / Pt] × n. And a ferromagnetic metal such as MnBi.

  Also in the RE-TM alloy or other materials, at least one of the magnetization fixed layer 11 and the magnetization switching layer 13 has a spin polarization factor such as a transition metal such as CoFe or a transition metal alloy at the interface with the intermediate layer 12. It is preferable to stack a high material with a thickness of about 1 nm. As a result, the spin polarization at the interface is increased, and the spin torque caused by the spin injected into the magnetization switching layer 13 injected through the intermediate layer 12 is increased. The required current can be reduced.

The intermediate layer 12 is provided between the magnetization fixed layer 11 and the magnetization switching layer 13. If the magnetoresistive element 1 is a TMR element, the intermediate layer 12 is made of an insulator such as MgO, Al ₂ O ₃ , HfO ₂ or a laminated film containing an insulator such as Mg / MgO / Mg. The thickness is preferably 0.1 to 2 nm. If the magnetoresistive element 1 is a CPP-GMR element, the intermediate layer 12 is made of a nonmagnetic metal such as Cu, Au, or Ag, and the thickness is preferably 1 to 10 nm.

  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 switching 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.

  As described above, according to the magnetoresistive element according to the present embodiment, a magnetoresistive element that exhibits perpendicular magnetic anisotropy, can be easily miniaturized, can reduce a magnetization reversal current, and has a stable magnetization reversal operation. can do. Here, the magnetization reversal operation of the magnetoresistive element 1 will be described with reference to FIG. In FIG. 2, the protective layer 14 is not shown. The magnetoresistive element 1, which is a spin injection magnetization reversal element, reverses the magnetization direction of the magnetization reversal layer 13 by injecting electrons having spins in the reverse direction, that is, by supplying current in the opposite direction (spin injection magnetization). Reversal (hereinafter referred to as magnetization reversal as appropriate), so that the magnetization direction of the magnetization fixed layer 11 is the same or 180 ° different. As described above, since the magnetization fixed layer 11 and the magnetization switching layer 13 have perpendicular magnetic anisotropy, the magnetization thereof indicates an upward or downward direction. In this specification, in FIGS. 2 (a) and 2 (b) As indicated by the arrows, the magnetization of the magnetization fixed layer 11 is always fixed upward.

  As shown in FIG. 2A, when the upper electrode 2 is set to “+” and the lower electrode 3 is set to “−”, and a current is supplied downward from the magnetization switching layer 13 side to the magnetization fixed layer 11, the magnetization switching layer 13 Is in the same upward direction as the magnetization direction of the fixed magnetization layer 11. Hereinafter, this state is referred to as that the magnetization of the magnetoresistive element 1 is parallel (P: Parallel). On the contrary, when the upper electrode 2 is set to “−” and the lower electrode 3 is set to “+” and current is supplied upward from the magnetization fixed layer 11 side to the magnetization switching layer 13, the magnetization of the magnetization switching layer 13 is changed to the magnetization fixed layer 11. The downward direction is opposite to the magnetization direction. Hereinafter, this state is referred to as anti-parallel (AP) in which the magnetization of the magnetoresistive element 1 is antiparallel.

  If the magnetization of the magnetoresistive element 1 exhibits either parallel or antiparallel magnetization, the magnetization is retained by the coercive force of the magnetization reversal layer 13 until a current for reversing the magnetization is supplied. Thus, since the magnetization is retained in the magnetoresistive element 1, a current that temporarily reaches the current value that reverses the magnetization direction, such as a pulse current, is used as the current supplied to the magnetoresistive element 1. Can do. As will be described later, the magnetoresistive element 1 generally has a pixel array of a magnetic random access memory (MRAM) or a spatial light modulator by two-dimensionally arranging a plurality of elements in the film surface direction. By supplying a predetermined current from 2 and 3, any one or more magnetoresistive elements 1 can be selectively reversed in magnetization.

  Note that the magnetoresistive element according to the present embodiment is configured to include one magnetization fixed layer, one intermediate layer, and one magnetization reversal layer. However, the present invention is not limited to this. A magnetoresistive element including two magnetization fixed layers with an intermediate layer interposed between the upper and lower sides may be used.

  Here, as described above, when a plurality of magnetoresistive elements 1 are two-dimensionally arranged to form a pixel array of an MRAM or a spatial light modulator, the upper and lower electrodes 2 and 3 of the magnetoresistive element 1 are adjacent to each other. An insulating material (insulating layer 6 in FIG. 1) needs to be embedded in the gap between the magnetoresistive elements 1 and 1 to prevent a short circuit. Hereinafter, the insulating material will be described together with a spatial light modulator and an MRAM configured by arranging magnetoresistive elements.

[Spatial light modulator]
Hereinafter, an embodiment of a spatial light modulator provided in a pixel using the magnetoresistive element according to the present invention as a light modulation element will be described. In addition, the pixel in this specification refers to a means for displaying information (bright / dark) in the minimum unit of display by the spatial light modulator.

  A spatial light modulator 10 according to an embodiment of the present invention selects a pixel array 40 composed of pixels 4 arranged in a two-dimensional array as shown in FIG. 3 and one or more pixels 4 from the pixel array 40. And a current control unit 80 to be driven. The plane (upper surface) in this specification is a light incident surface of the spatial light modulator, and the spatial light modulator 10 reflects light incident on the pixel 4 (pixel array 40) from above and modulates the light. Thus, the reflective spatial light modulator is emitted upward.

  As shown in FIG. 3, the pixel array 40 includes a plurality of upper electrodes 2, 2... Striped in plan view, and a plurality of lower electrodes 3, 3 that are also striped and orthogonal to the upper electrode 2 in plan view. ,..., And one pixel 4 is provided at each intersection of the upper electrode 2 and the lower electrode 3. Accordingly, the pixels 4 are arranged in a two-dimensional array on the light incident surface of the spatial light modulator 10 to constitute the pixel array 40. In the present embodiment, the pixel array 40 is exemplified by a configuration including 16 pixels 4 of 4 rows × 4 columns. The upper electrode 2 and the lower electrode 3 are collectively referred to as electrodes 2 and 3 as appropriate. As shown in FIGS. 3 and 4, the pixel 4 includes an upper electrode 2 and a lower electrode 3 as a pair of electrodes in the pixel 4, and a magnetoresistive element 1 sandwiched between these electrodes 2 and 3 from above and below. Is provided. Further, the insulating layer 6 is filled between the adjacent upper electrodes 2 and 2, the magnetoresistive elements 1 and 1, and the lower electrodes 3 and 3.

  As shown in FIG. 3, the current control unit 80 controls the upper electrode selection unit 82 that selects the upper electrode 2, the lower electrode selection unit 83 that selects the lower electrode 3, and the electrode selection units 82 and 83. A pixel selection section (pixel selection means) 84 and a power supply (current supply means) 81 that supplies current to the electrodes 2 and 3 are provided. These may be known ones and supply appropriate voltages and currents to reverse the magnetization of the magnetoresistive element 1.

  The upper electrode selection unit 82 selects one or more of the upper electrodes 2, and the lower electrode selection unit 83 selects one or more of the lower electrodes 3, and each supplies a predetermined current from the power source 81. The pixel selection unit 84 selects one or more specific pixels 4 of the pixel array 40 based on, for example, an external signal (not shown), and connects the electrodes 2 and 3 connected to the selected pixel 4 to the electrode selection units 82 and 83. To select. The power supply 81 supplies an appropriate voltage / current to reverse the magnetization of the magnetoresistive element 1 provided in the selected pixel 4. With such a configuration, a specific pixel 4 is selected, and a predetermined current is supplied to the magnetoresistive element 1 of this pixel 4 to reverse the magnetization. In FIG. 3, the power supply 81 is connected to one end of each of the electrodes 2 and 3 via the electrode selection units 82 and 83, but may be connected to both ends. By connecting to both ends, the response speed can be increased and the operation variation between pixels can be reduced.

  Details of the configuration of the pixel 4 of the spatial light modulator 10 will be described with reference to FIGS. The upper electrode 2 is disposed on the magnetoresistive element 1 as shown in FIG. 4 and extends in a strip shape in the lateral direction as shown in FIG. One upper electrode 2 supplies a current to each of the magnetoresistive elements 1 of the plurality of pixels 4, 4,... Arranged in one horizontal row. On the other hand, the lower electrode 3 is disposed under the magnetoresistive element 1 and extends in a strip shape in the vertical direction. One lower electrode 3 supplies a current to each of the magnetoresistive elements 1 of the plurality of pixels 4, 4,... Arranged in one vertical column. The upper electrode 2 is made of a transparent electrode material so as not to block incident light and outgoing light of the magnetoresistive element 1. On the other hand, the lower electrode 3 is made of an electrode metal material having excellent conductivity. The pixels 4 are formed on the pixel array 40 by being arranged on a known substrate such as a Si substrate whose surface is thermally oxidized.

  As shown in FIG. 3, the magnetoresistive element 1 is arranged in a portion where the upper electrode 2 and the lower electrode 3 overlap in a plan view, and is sandwiched and connected to the electrodes 2 and 3 from above and below. Although the magnetoresistive element 1 has a function as a light modulating element in the spatial light modulator 10, the configuration thereof is the same as the magnetoresistive element 1 according to the present invention shown in FIG. To do. The planar view shape of the magnetoresistive element 1 is a square in the present embodiment, but is not limited to this. In addition, one magnetoresistive element 1 is arranged for one pixel 4. For example, a plurality of magnetoresistive elements such as (1 × 3), (2 × 2), and the like are provided in one pixel 4 in the surface direction. Element 1 may be provided.

The upper electrode 2 is made of a transparent electrode material so that light can pass therethrough. Transparent electrode materials include, for example, indium zinc oxide (IZO), indium tin oxide (ITO), tin oxide (SnO ₂ ), antimony oxide-tin oxide (ATO), oxidation zinc (ZnO), fluorine-doped tin oxide (FTO), consisting of a known transparent electrode material such as indium oxide (in ₂ O _3). In particular, IZO is most preferable in terms of specific resistance and ease of film formation. These transparent electrode materials are formed into a film by a known method such as a sputtering method, a vacuum deposition method, or a coating method.

  When the electrode (wiring) is made of a transparent electrode material, it is preferable to provide a metal film between the electrode and the magnetoresistive element 1 connected to the electrode. That is, in the upper electrode 2 made of a transparent electrode material, it is preferable to laminate a metal film as a base layer between the magnetoresistive element 1 (not shown). By interposing a metal film between the magnetoresistive element 1 and the upper electrode 2 made of a transparent electrode material having a resistance higher than that of the electrode metal material, the contact resistance between the upper electrode 2 and the magnetoresistive element 1 is reduced. To increase the response speed.

  As the metal constituting the underlayer, for example, Au, Ru, Ta, or an alloy composed of two or more of these metals can be used, and these metals are formed by a known method such as a sputtering method. The In order to further reduce the contact resistance by improving the adhesion between the underlying layer and the layer above it, that is, the transparent electrode, the metal film serving as the underlying layer is formed continuously in a vacuum processing chamber with the transparent electrode material. It is preferred that If the thickness of the underlayer is less than 1 nm, it is difficult to form a continuous film, while if it exceeds 10 nm, the amount of transmitted light is reduced. Therefore, the preferable thickness of the underlayer is 1 to 10 nm.

  The lower electrode 3 is made of a general electrode metal material such as a metal such as Cu, Al, Au, Ag, Ta, Cr, or an alloy thereof. Then, it is processed into a stripe shape by a known method such as a sputtering method, by film formation, photolithography, etching, lift-off method, or the like.

The insulating layer 6 is disposed between the adjacent upper electrodes 2 and 2 (not shown in FIG. 4) and the lower electrodes 3 and 3 to insulate them from each other, and is a region where the magnetoresistive element 1 is not present in plan view. In order to insulate between the electrodes 2 and 3 and to seal the side surface of the magnetoresistive element 1, the magnetoresistive elements 1 and 1 are disposed. Here, when an oxide such as SiO ₂ is disposed as the insulating layer 6 between the magnetoresistive elements 1 and 1, an oxygen (O) -containing film such as an oxide is usually supplied with an atmospheric gas containing oxygen. While forming the film. At this time, the RE-TM alloy contained in the magnetization fixed layer 11 or the magnetization reversal layer 13 is oxidized on the exposed end face (side surface) of the magnetoresistive element 1 to change its magnetic characteristics, and the magnetization reversal of the magnetoresistive element 1 is changed. There is a risk of affecting the operation. Specifically, the rare earth metal of the RE-TM alloy is oxidized to change to a composition having a high proportion of transition metal, so that the coercive force is reduced, the apparent saturation magnetization Ms is increased, and the oxidation further proceeds. Then, the properties as a ferrimagnetic material cannot be maintained, and the perpendicular magnetic anisotropy is lost. Further, the heat treatment in the process after the film formation of SiO ₂ and the heat generated during the operation cause the RE-TM alloy to be oxidized by the oxygen (O) of SiO ₂ from the interface or side surface in contact with SiO ₂ of the magnetoresistive element 1. There is a risk of progress.

Therefore, in the spatial light modulator 10 according to the present invention, silicon nitride is applied as the insulating layer 6 between the magnetoresistive elements 1 and 1 that are in particular in contact with the magnetoresistive element 1. Silicon nitride mainly has a composition of Si ₃ N ₄ and is represented by Si—N in this specification. Thus, by arranging Si—N between the magnetoresistive elements 1, 1, the RE-TM alloy contained in the magnetoresistive element 1 can be maintained without being oxidized. A conventionally known insulating material such as SiO ₂ or Al ₂ O ₃ is applied to the insulating material disposed in the region not in contact with the magnetoresistive element 1 such as between the upper electrodes 2 and 2 and between the lower electrodes 3 and 3. May be.

  After the magnetoresistive element 1 is processed into a desired plan view shape, the insulating layer 6 is formed by sputtering Si-N or chemical vapor deposition (CVD) before forming the upper electrode 2 (forming an electrode material). ) And the like, and deposited between the magnetoresistive elements 1 and 1, and then Si—N on the magnetoresistive element 1 is removed by etching, CMP (Chemical Mechanical Polishing), or the like. Can be formed. Alternatively, Si-N may be deposited with the resist used as a mask remaining in the processing of the magnetoresistive element 1, and the entire Si-N may be removed (lift-off).

(Spatial light modulator pixel selection operation)
Next, the pixel selection operation of the spatial light modulator 10 will be described with reference to FIG. The electrodes 2 and 3 are connected to the current control unit 80 as described above. As shown in FIG. 4, a light source 93 that irradiates light toward the pixel array 40 and a light source 93 that irradiates light above the pixel 4 (pixel array 40) of the spatial light modulator 10 according to the present embodiment. An incident polarizing filter 91 that converts the emitted light into polarized light before entering the pixel array 40, an outgoing polarizing filter 92 that transmits only polarized light in a specific direction from the light reflected and emitted from the pixel array 40, and an outgoing polarizing filter A detector 94 for detecting the light transmitted through 92 is disposed.

  Since light (laser light or the like) emitted from the light source 93 includes various polarization components, the light is transmitted through the incident polarization filter 91 in front of the pixel array 40 to be light of one polarization component. Hereinafter, light of one polarization component is referred to as polarization. This polarized light (incident polarized light) is incident on all the pixels 4 of the pixel array 40 at a predetermined incident angle. In each pixel 4, the incident polarized light passes through the upper electrode 2 and enters the magnetoresistive element 1, is reflected by the magnetization reversal layer 13 of the magnetoresistive element 1, is emitted as outgoing polarized light, and passes through the upper electrode 2 again. Then, the light is emitted from the pixel 4. All outgoing polarized light emitted from each pixel 4 reaches the outgoing polarization filter 92. The outgoing polarization filter 92 transmits only specific polarized light, here polarized light whose angle θap is rotated with respect to incident polarized light, and this transmitted outgoing polarized light is incident on the detector 94. Each of the polarizing filters 91 and 92 is a polarizing plate, and the detector 94 is an image display means such as a screen, a camera, or the like.

  When light incident on the magnetoresistive element 1 is reflected by the magnetization reversal layer 13 which is a magnetic material and emitted, the direction of polarization of the incident light changes (rotation) due to the Kerr effect (magnetic Kerr effect). As described above, the magnetoresistive element 1 undergoes magnetization reversal according to the direction of the current supplied from the electrodes 2 and 3, and the magnetization is parallel / antiparallel for each pixel 4, that is, the magnetization of the magnetization reversal layer 13 is An upward / downward direction is shown (see FIGS. 2A and 2B). As described above, when the magnetization direction of the magnetization reversal layer 13 is different by 180 °, the incident light is rotated in the opposite directions at the same rotation angle, that is, the Kerr rotation angle θk of the magnetization reversal layer 13 and emitted. If the optical rotation angles in the magnetoresistive element 1 with magnetization parallel and antiparallel are expressed as θp and θap, respectively, θp = + θk and θap = −θk, and the direction from the magnetoresistive element 1 depends on the current direction from the electrodes 2 and 3. The difference in the polarization direction of the emitted light, that is, the difference in optical rotation angle | θp−θap | is 2θk.

  Alternatively, the polarized light incident on the magnetoresistive element 1 is transmitted through the magnetization reversal layer 13, the intermediate layer 12, and the magnetization fixed layer 11, reflected at the upper surface of the lower electrode 3, and again the magnetization fixed layer 11, the intermediate layer 12, the magnetization The structure which permeate | transmits and inject | emits the inversion layer 13 may be sufficient. In this case, by passing through the magnetization reversal layer 13 and the magnetization fixed layer 11 which are magnetic materials, the direction of the polarized light depends on the respective predetermined angles (optical rotation) of the magnetization reversal layer 13 and the magnetization fixed layer 11 due to the Faraday effect. Rotate (rotate) to (angle). However, since the magnetization direction of the fixed magnetization layer 11 is constant, the change in the polarization of the light emitted from the magnetoresistive element 1 is determined by the Faraday rotation angle θF of the magnetization switching layer 13. Since the emitted light passes through the magnetization switching layer 13 twice, the difference in optical rotation angle | θp−θap | is 4θF.

  The outgoing polarized light from the left and right pixels 4 and 4 in FIG. 4 rotated by an angle θap with respect to the incident polarized light passes through the outgoing polarizing filter 92 and reaches the detector 94. Therefore, the pixel 4 is bright (white). ) Is displayed on the detector 94. On the other hand, since the outgoing polarized light from the central pixel 4 is blocked by the outgoing polarizing filter 92, the pixel 4 is dark (black) and displayed on the detector 94. Thus, light / dark (white / black) can be separated for each pixel, and light / dark can be switched by switching the direction of the current. As an initial state of the spatial light modulator 10, for example, all the upper electrodes 2 are “-” so that the magnetizations of the magnetoresistive elements 1 of all the pixels 4 are anti-parallel so that the whole is displayed white. All of the lower electrode 3 may be set to “+” to supply an upward current.

  Here, the Kerr rotation angle θk and the Faraday rotation angle θF of the magnetization switching layer 13 are larger as the incident angle of light is closer to the film surface that is the magnetization direction of the magnetization switching layer 13 as described above. Therefore, it is desirable that the incident angle be 90 ° in order to maximize the optical rotation angle difference | θp−θap |. However, in this case, the optical path of the outgoing polarized light coincides with the optical path of the incident polarized light. Therefore, the incident polarization filter 92, the detector 94, the light source 93, and the incident polarization filter 91 are arranged so as not to block the optical paths of the incident polarized light and the outgoing polarized light, respectively, by tilting the incident angle from 90 ° by about 5 ° to 30 °. To do. That is, the incident angle of polarized light is preferably 60 ° to 85 ° with respect to the pixel array 40. Alternatively, the incident angle may be 90 °, and a half mirror may be disposed between the incident polarizing filter 91 and the pixel array 40 to reflect only the outgoing polarized light laterally. In this case, the output polarization filter 92 and the detector 94 are arranged on the side of the pixel array 40. Since the RE-TM alloy has a large Kerr rotation angle and Faraday rotation angle, the magnetoresistive element 1 is configured to include the RE-TM alloy in the magnetization reversal layer 13 so that the difference in optical rotation angle | θp−θap. | Can be made larger.

In another embodiment, the spatial light modulator according to the present invention may be a reflective spatial light modulator that enters from below as a configuration in which the top and bottom are switched. That is, the lower electrode is made of a transparent electrode material and the upper electrode is made of an electrode metal material. Light incident from below is transmitted through the lower electrode and reflected by the magnetoresistive element 1 or the upper electrode, and the lower electrode is again formed. Transmits and exits. Accordingly, the polarizing filters 91 and 92, the light source 93, and the detector 94 are disposed below the pixel array 40. In this case, the lower electrode is preferably provided with a base layer, which is a metal film, between the magnetoresistive element 1 and the contact resistance is reduced as in the case where the upper electrode is made of a transparent electrode material. In addition, the magnetoresistive element 1 is laminated by switching the positions of the magnetization fixed layer 11 and the magnetization inversion layer 13. Further, the substrate is made of a transparent substrate material such as SiO ₂ , Al ₂ O ₃ , MgO or the like so that light enters the pixel 4 from below and light emitted from the pixel 4 is irradiated again downward. Apply.

  As yet another embodiment, both the upper electrode and the lower electrode may be made of a transparent electrode material to form a transmissive spatial light modulator. At this time, the substrate is made of the transparent substrate material so that light transmitted through the pixel from above is further irradiated downward. In addition, the magnetoresistive element 1 may be stacked by switching the positions of the magnetization fixed layer 11 and the magnetization switching layer 13. In such a spatial light modulator, the light source 93 and the incident polarizing filter 91 are disposed immediately above the pixel array 40, and the outgoing polarizing filter 92 and the detector 94 are disposed immediately below the pixel array 40, respectively, with an incident angle of 90 °. can do. Alternatively, a transmissive spatial light modulator that emits light from below and emits upward may be used.

  Furthermore, as a modification of each of these embodiments, for the upper electrode and the lower electrode that are made of a transparent electrode material and transmit light, the wiring portion is a hole in a region overlapping with the magnetoresistive element 1 in plan view as a metal material for an electrode The transparent electrode material may be provided only inside the hole (not shown). By using such an electrode, light can be incident on the magnetoresistive element 1 using a low-resistance metal material, so that a voltage drop due to wiring resistance is suppressed to save power and reduce operation variation between pixels. it can.

  As described above, according to the spatial light modulators according to the embodiments of the present invention and the modifications thereof, the magnetoresistive element including the RE-TM alloy is used as the light modulation element, and the pixel selection is performed with high definition and high speed response. It becomes a spatial light modulator with excellent properties. In addition, when the insulating material embedded between the magnetoresistive elements is Si—N, the RE-TM alloy contained in the magnetoresistive elements can be maintained without being oxidized.

[Magnetic random access memory]
As shown in FIG. 5, a magnetic random access memory (MRAM) 70 according to an embodiment of the present invention is a component that constitutes the recording device 9 together with the current control unit 80A. The MRAM 70 includes a plurality of bit lines 2A, 2A,... Striped in plan view, and a plurality of word lines 5, 5,... That are also striped and orthogonal to the bit line 2A in plan view. One memory cell 7 is provided for each intersection of 2A and the word line 5. In the present embodiment, the MRAM 70 is exemplified by a configuration including 16 memory cells 7 of 4 rows × 4 columns.

  As shown in FIG. 5, the current control unit 80A includes a bit line selection unit 82A that selects the bit line 2A, a word line selection unit 85 that selects the word line 5, and cells that control these selection units 82A and 85. A selection unit 84A and a power supply 81A for supplying current to the bit line 2A and the word line 5 are provided. The cell selection unit 84A selects, for example, one or more specific memory cells 7 of the MRAM 70 based on an external signal (not shown), and selects the bit line 2A and the word line 5 connected to the selected memory cell 7 as a bit line. The part 82A and the word line selection part 85 are selected. The power supply 81A supplies an appropriate voltage / current for operating the magnetoresistive element 1 and the MOSFET provided in the selected memory cell 7.

  As shown in FIG. 6, one memory cell 7 includes one magnetoresistive element 1 on the MOSFET. Specifically, the lower electrode 3A of the magnetoresistive element 1 is connected to the drain of the MOSFET via a wiring layer. In the memory cell 7, the upper electrode of the magnetoresistive element 1 constitutes the bit line 2 </ b> A of the MRAM 70. The configuration of the magnetoresistive element 1 is the same as that of the magnetoresistive element 1 according to the present invention shown in FIG. Therefore, in the MRAM 70, in the layered direction region where the magnetoresistive element 1 and the bit line 2A and the lower electrode 3A connected to the upper and lower sides thereof are formed, the lower electrode 3A is not extended in the vertical direction in plan view. Otherwise, the configuration is the same as the pixel array 40 of the spatial light modulator 10 shown in FIG.

  In the MOSFET, for example, a source and a drain are formed on a p-type substrate made of silicon (Si). On the p-type substrate between the source and the drain, a gate electrode is formed via an insulating layer 6. In addition, contacts are formed and connected between the drain-wiring layer and between the wiring layer-lower electrode 3A. On the other hand, the word line 5 is connected to the source via a contact, and the word line 5 is grounded.

  These wirings, that is, the bit line (upper electrode) 2A, the lower electrode 3A, the wiring layer, the gate electrode, and the word line 5 are general metals such as Cu, Al, Au, Ag, Ta, Cr, and alloys thereof. It is made of a typical electrode metal material. Therefore, in the MRAM 70, unlike the pixel array 40 of the spatial light modulator 10, both electrodes connected to the top and bottom of the magnetoresistive element 1 are made of a metal material.

The insulating layer 6 is arranged between the blank portion in FIG. 6 and between the adjacent bit lines 2A and 2A (not shown in FIG. 6) to insulate the wirings from each other, and seals the side surface of the magnetoresistive element 1 To do. Here, Si-N is applied to the insulating layer 6 disposed at least between the magnetoresistive elements 1, 1, that is, between the bit line 2 </ b> A and the lower electrode 3 </ b> A, as in the pixel array 40 of the spatial light modulator 10. Thereby, the RE-TM alloy contained in the magnetization fixed layer 11 or the magnetization reversal layer 13 of the magnetoresistive element 1 is oxidized on the side surface of the magnetoresistive element 1 during or after the formation of the insulating layer 6 (film formation). Therefore, characteristics such as magnetization reversal operation of the magnetoresistive element 1 can be maintained. A conventionally known insulating material such as SiO ₂ or Al ₂ O ₃ is applied to the insulating material disposed between the bit lines 2A and 2A, between the lower electrodes 3A and 3A, between the other wirings and in the MOSFET region. Also good.

(Memory cell operation)
Next, the operation of the magnetoresistive element 1 in the memory cell 7 will be described with reference to FIGS. In the memory cell 7 (MRAM 70), the magnetization of the magnetoresistive element 1 is reversed in parallel / antiparallel by the current supply from the bit line 2A and the word line 5. As shown in FIG. 2A, the magnetoresistive element 1 having parallel magnetization has a low resistance in the direction perpendicular to the film surface, and a value of “0” is recorded at this time. On the other hand, as shown in FIG. 2B, the magnetoresistive element 1 having the antiparallel magnetization has a high resistance and a value of “1” is recorded. In the initial state of the memory cell 7, the magnetoresistive element 1 is in a state in which this magnetization is antiparallel.

  In this initial state, when a predetermined voltage is applied to the gate electrode to turn on the MOSFET and the current control unit 80A causes a current to flow downward from the bit line 2A to the MOSFET, The element 1 undergoes magnetization reversal and the magnetization becomes parallel, and a value of “0” is written. Conversely, when a current is supplied from the word line 5 to the bit line 2A upward via the MOSFET to the magnetoresistive element 1, the magnetization of the magnetoresistive element 1 becomes antiparallel again and a value of “1” is written. In reading, a predetermined voltage may be applied between the bit line 2A and the word line 5 to detect the magnitude of the current flowing through the magnetoresistive element 1.

  As described above, according to the magnetic random access memory according to the embodiment of the present invention, a recording apparatus having a large capacity and an excellent high-speed response can be obtained using the magnetoresistive element including the RE-TM alloy. In addition, when the insulating material embedded between the magnetoresistive elements is Si—N, the RE-TM alloy contained in the magnetoresistive elements can be maintained without being oxidized.

  As mentioned above, although each embodiment for implementing the magnetoresistive element, the spatial light modulator, and the magnetic random access memory of the present invention has been described, the present invention is not limited to these embodiments. Various modifications are possible within the range shown in.

In order to confirm the effect of the present invention, a sample of the magnetoresistive element (see FIG. 1) according to the embodiment of the present invention was produced. The magnetoresistive element includes, from the lower electrode side, a magnetization fixed layer: Tb—Fe—Co (20 nm) / Co—Fe (1 nm), an intermediate layer: Cu (6 nm), a magnetization reversal layer: Gd—Fe (10 nm), protection Layer: A CPP-GMR element in which Ru (3 nm) was laminated. In the sample, only one magnetoresistive element was provided, the shape in plan view was a rectangle of 120 nm × 120 nm, and Cu was applied to the upper electrode and the lower electrode. Specifically, first, Cu and each layer of the magnetoresistive element were sequentially formed and stacked on a Si substrate whose surface was thermally oxidized as a lower electrode. Next, a resist mask for the lower electrode that is larger than the planar shape of the magnetoresistive element is formed, and each layer of the magnetoresistive element and Cu (lower electrode) are processed by an ion beam milling method. ₂ was formed, and the resist was removed together with the SiO ₂ thereon (lift-off) to form an insulating layer around the lower electrode. Next, each layer of the magnetoresistive element is processed in the same manner as described above using the resist mask having a plan view shape of the magnetoresistive element (to the surface of the lower electrode) to form the magnetoresistive element, and then Si—N And an insulating layer around the magnetoresistive element (side surface) was formed by lift-off. And the upper electrode was formed on the magnetoresistive element, and it was set as the sample of the Example. Further, as a comparative example, a sample having the same magnetoresistive element and having SiO ₂ formed as an insulating layer around the magnetoresistive element instead of Si—N was produced.

  A uniform magnetic field was applied from the outside to the manufactured sample so that the magnetization of the magnetoresistive element was parallel as an initial state. A magnetic field was gradually applied from the outside while measuring the resistance of the magnetoresistive element between the upper and lower electrodes, and the magnetic field at which the magnetizations of the magnetization reversal layer and the magnetization fixed layer were reversed was measured. FIG. 7 shows a graph of a change in resistance of the magnetoresistive element due to an external magnetic field.

As shown in FIG. 7, in both the example and comparative samples, the magnetoresistive element changed to high resistance when the magnetic field reached around ± 1 kOe. This indicates that the magnetization reversal layer is reversed and the magnetization of the magnetoresistive element is antiparallel. When the magnetic field was further increased, in the comparative example, when the magnetic field reached around ± 3 kOe, the magnetoresistive element changed to a low resistance comparable to the initial state (returned). This indicates that the magnetization of the magnetization fixed layer is inverted and becomes parallel to the magnetization direction of the magnetization inversion layer that has been previously inverted, that is, the magnetization of the magnetoresistive element is again parallel. On the other hand, in the example, when the magnetic field was increased to around ± 5 kOe, the magnetization of the magnetization fixed layer was reversed. From these results, the RE-TM alloy included in the magnetoresistive element, in particular, the Tb—Fe—Co alloy of the magnetization fixed layer, is oxidized in the case of film formation of SiO ₂ that is in contact with the side surface and has a coercive force. It can be assumed that it has declined. On the other hand, it can be said that the original magnetic properties of the RE-TM alloy were maintained by applying Si—N to the insulating layer in the examples.

10 Spatial light modulator 1 Magnetoresistive element (spin injection magnetization reversal element)
DESCRIPTION OF SYMBOLS 11 Magnetization fixed layer 12 Intermediate layer 13 Magnetization inversion layer 14 Protective layer 2 Upper electrode 2A Bit line (upper electrode)
3, 3A Lower electrode 40 Pixel array 4 Pixel 5 Word line 6 Insulating layer 70 MRAM (magnetic random access memory)
7 Memory cell 80 Current control unit 81 Power supply (current supply means)
84 Pixel selection unit (pixel selection means)
9 Recording device

Claims (3)

A spin-injection magnetization reversal element comprising a stack of a magnetization fixed layer, an intermediate layer, and a magnetization reversal layer, a pair of electrodes connected above and below the spin-injection magnetization reversal element, and an insulating layer that insulates between the pair of electrodes A magnetoresistive element comprising:
In the spin-injection magnetization switching element, at least one of the magnetization fixed layer and the magnetization switching layer includes an alloy of a rare earth metal and a transition metal,
The magnetoresistive element according to claim 1, wherein the insulating layer is disposed in contact with the spin injection magnetization switching element and is made of silicon nitride. A magnetic random access memory comprising a plurality of memory cells arranged two-dimensionally,
The memory cell includes a spin injection magnetization reversal element comprising a magnetization fixed layer, an intermediate layer, and a magnetization reversal layer stacked, and a pair of electrodes connected to the top and bottom of the spin injection magnetization reversal element,
In the spin-injection magnetization switching element, at least one of the magnetization fixed layer and the magnetization switching layer includes an alloy of a rare earth metal and a transition metal,
A magnetic random access memory comprising an insulating layer made of silicon nitride in contact with the spin-injection magnetization reversal element to insulate between the adjacent spin-injection magnetization reversal elements and between the pair of electrodes. A plurality of pixels arranged two-dimensionally, pixel selection means for selecting one or more pixels from the plurality of pixels, and current supply means for supplying a predetermined current to the pixels selected by the pixel selection means. A spatial light modulator that emits light by changing the polarization direction of the light incident on the pixel selected by the pixel selection means to a specific direction,
The pixel includes a spin injection magnetization reversal element including a magnetization fixed layer, an intermediate layer, and a magnetization reversal layer, and a pair of electrodes connected above and below the spin injection magnetization reversal element,
In the spin-injection magnetization switching element, at least one of the magnetization fixed layer and the magnetization switching layer includes an alloy of a rare earth metal and a transition metal,
A spatial light modulator comprising: an insulating layer made of silicon nitride that is in contact with the spin injection magnetization reversal element and insulates between the adjacent spin injection magnetization reversal elements and the pair of electrodes.