JP4633689B2 - Microwave oscillation device, method for manufacturing the same, and microwave oscillation device including the microwave oscillation device - Google Patents

Description

  The present invention relates to a microwave oscillating element, in particular, a microwave oscillating element using spin torque, a method for manufacturing the same, and a microwave oscillating device including the microwave oscillating element.

  In recent years, mobile terminals for wireless network communication systems typified by mobile phones have been commercialized in many cases corresponding to a plurality of communication devices such as WLAN, Blue tooth, RFID, and GPS. In order to handle frequencies corresponding to these many communication standards, a plurality of RF circuits corresponding to the respective frequencies are required. However, trying to incorporate a plurality of RF circuits into one device leads to an increase in the scale of the device.

  In order to realize a small and thin device, a technique for integrating these plural RF circuits into one and dealing with plural frequencies with one RF circuit has been vigorously developed. These are called tunable RF circuits. One of important techniques for realizing a tunable RF circuit is a microwave oscillating device that can vary the oscillation frequency.

  Recently, it has been reported that when a direct current is passed through an element using a magnetic multilayer film, microwave oscillation is caused by spin torque. Since the microwave oscillation element using this spin torque can change the oscillation frequency according to the magnetic field applied from the outside and the current value flowing through the element, it can be used as a microwave oscillation element for realizing the tunable RF circuit. There is expected.

  Here, the microwave oscillation element will be described with reference to FIG. FIG. 11 is a diagram for explaining the principle of a microwave oscillation element using spin torque. The microwave oscillation element 100 includes a first electrode 110a, a magnetization fixed layer 112 whose magnetization direction is fixed, an intermediate layer 113, and a magnetization free layer 114 that can change the magnetization direction on a substrate (not shown). And the second electrode 110b are stacked in this order. Here, the magnetization directions of the magnetization fixed layer 112 and the magnetization free layer 114 are the same.

  In this state, a voltage is applied between the electrodes 110a and 110b, and a direct current 131 is caused to flow from the first electrode 110a to the second electrode 110b. By flowing the direct current 131 in this manner, the electrons 132 (the direction in which electrons flow is opposite to the current) flow from the second electrode 110b to the first electrode 110a.

  At this time, electrons 132 whose spins have the same magnetic moment direction as the magnetization directions of the magnetization fixed layer 112 and the magnetization free layer 114 are coupled with the electron spin in the magnetization free layer 114 and the intermediate layer 113 in contact with the magnetization fixed layer 112. It is possible to flow toward the first electrode 110a while maintaining the spin direction without exerting an interaction.

  On the other hand, the electron 132 ′ whose spin magnetic moment is opposite to the magnetization direction of the magnetization free layer 114 causes exchange interaction with the electron spin in the magnetization free layer 114. For this reason, a spin torque acts between the spins of each electron, and precession begins to reverse the spin of the electrons in the magnetization free layer 114. When the generated spin torque is sufficiently large, the precession is amplified, and the spin of electrons in the magnetization free layer 114 is reversed (spin injection magnetization reversal). On the other hand, when the generated spin torque is small, or when the spin torque is suppressed by an external magnetic field, uniaxial anisotropy, etc., the spin cannot be reversed and only precession is performed.

  The microwave oscillation element using the spin torque may be a magnetoresistive element in which an electrode capable of flowing a current in a direction perpendicular to the film surface is provided in a multilayer film of the magnetization fixed layer 112, the intermediate layer 113, and the magnetization free layer 114. I can say that. The magnetoresistive element is an element whose resistance changes according to the relative angle of magnetization of the magnetization fixed layer 112 and the magnetization free layer 114.

  Therefore, when the electron spin in the magnetization free layer 114 starts precession due to the spin torque, the relative angle between the magnetization of the magnetization free layer 114 and the magnetization of the magnetization fixed layer 112 is the frequency of the precession (microwave region). Therefore, the resistance of the microwave oscillation element changes according to the frequency of precession.

  As shown in FIG. 11, when a constant direct current is input to the element and this resistance change is output as a voltage change applied to the element, a voltage signal oscillating at a high frequency can be obtained.

  As a feature of this microwave oscillation element, it is possible to change the precession frequency of the magnetization free layer 114 due to the spin torque by changing the magnitude of the current flowing through the element or the magnitude of the magnetic field applied from the outside. Therefore, it is possible to change the oscillation frequency of the microwave continuously and in a wide frequency range.

  FIGS. 12A and 12B show the configuration of the microwave oscillation element described in Non-Patent Documents 1 and 2. FIG.

  In the microwave oscillation element 400 illustrated in FIG. 12A, the magnetization free layer 114 and the second electrode 110 b are electrically connected through the nanocontact 118. On the other hand, in the microwave oscillation element 500 in FIG. 12B, the magnetization free layer 114 and the intermediate layer 113 are processed to have a size of about 100 nm, and are connected to the second electrode 10b on a nanoscale. . That is, both the microwave oscillation elements 400 and 500 in FIGS. 12A and 12B limit the cross-sectional area of the current flowing through the magnetization free layer 114 on the nanoscale order. This is because the current value required to induce precession of the magnetization free layer 114 due to spin torque is proportional to the volume of the magnetization free layer 114 through which the current flows. Therefore, reducing the cross-sectional area and increasing the current density leads to a reduction in the current required for microwave oscillation, and contributes to reducing power consumption as an element.

  However, the outputs of the microwave oscillating elements 400 and 500 shown in FIGS. 12A and 12B are about 1 nW, and it is necessary to further increase the output for practical use.

  In order to improve the output, a method of increasing the output by connecting a plurality of microwave oscillation elements shown in FIG. 12 in parallel and combining the outputs of the plurality of microwave oscillation elements is described in Non-Patent Documents 3 and 4 It is stated in.

  FIGS. 13A and 13B show microwave oscillators 400B and 500B in which a plurality of microwave oscillators 400 and 500 shown in FIGS. 12A and 12B are connected in parallel. As described above, by connecting the microwave oscillation elements in parallel, it is possible to improve the output by the number of elements connected in parallel.

Further, according to Non-Patent Documents 3 and 4, when the microwave oscillators connected in parallel are operated close to each other, the precession of the spin is phase-synchronized, and the generated microwave output is connected to the microwave oscillator element. It is stated that it will be larger than a few.
Physical Review B vol. 70 pp. 100406 Nature vol. 425 pp. 380 Nature vol. 437 pp. 389 Nature vol. 437 pp. 393

  As described above, the microwave oscillation element using the spin torque can change the oscillation frequency of the microwave continuously and in a wide frequency range, and oscillates at high output by connecting the elements in parallel. Therefore, application as a microwave oscillation element for realizing a tunable RF circuit is expected.

  However, in order to fabricate the element shown in FIGS. 13A and 13B, a magnetic free layer having a nanocontact structure or a fine structure with an electrode must be fabricated and the elements connected in parallel. Don't be. Examples of means for producing such a nanoscale microstructure include a microfabrication method such as EB lithography, but there are many processes for performing microfabrication, and there are problems in cost and mass productivity.

  The present invention has been made in view of the above problems, and its purpose is to use a simple contact process or film formation process without using microfabrication, and a nanocontact structure with an electrode or a magnetization free layer. To provide a microwave oscillating device that realizes a miniaturized structure and has high output, low cost, and excellent mass productivity, a method for manufacturing the same, and a microwave oscillating device including the microwave oscillating device. .

  In order to solve the above-described problem, a microwave oscillation device according to the present invention includes a magnetization fixed layer having a magnetization direction fixed between a first electrode and a second electrode, and a nonmagnetic material or an insulator. The intermediate layer and a magnetization free layer capable of changing the magnetization direction, and the intermediate layer is sandwiched between the magnetization fixed layer and the magnetization free layer, and from the first electrode, In the microwave oscillating device configured to allow a current to flow to the second electrode via the magnetization fixed layer, the intermediate layer, and the magnetization free layer, a predetermined path in the magnetization free layer is formed in the current path. It is characterized by having a plurality of nanoparticles for making the density of the current flowing in the region higher than the density of the current flowing in the region other than the predetermined region.

  According to the above configuration, the present invention can realize a microwave oscillating device excellent in high output, low cost, and mass productivity by a significantly simpler method as compared with the conventional configuration.

  Specifically, in the microwave oscillation device of the present invention, the density of the current flowing in a predetermined region in the magnetization free layer in the current path is set in a region other than the predetermined region in the magnetization free layer. Nanoparticles for increasing the density of the flowing current are used.

  As described above, the current value required to induce precession of the magnetization free layer due to spin torque is proportional to the volume of the magnetization free layer through which a current flows. That is, the current required for microwave oscillation can be reduced by reducing the cross-sectional area of the current flowing in the magnetization free layer and increasing the current density. Therefore, in the microwave oscillating device of the present invention, the above-described nanoparticles are used to increase the density of the current flowing in a predetermined region in the magnetization free layer. As described above, the present invention is compared with the conventional method of increasing the density of the current flowing in a predetermined region in the magnetization free layer by producing a magnetization free layer having a nano-contact structure or a fine structure with the electrode. Thus, the same effect as that of the conventional configuration can be realized by a remarkably simple method of providing nanoparticles. That is, according to the above configuration, it is possible to provide a microwave oscillation element that is lower in cost and superior in mass productivity.

  In particular, since a plurality of nanoparticles are used in the present invention, a microwave oscillator with high output can be realized, and a microwave oscillator corresponding to a high output with a conventional configuration that has to be provided with a plurality of fine structures. This can be realized by a much simpler method than the above.

  In the microwave oscillation device according to the present invention, the nanoparticles are conductive nanoparticles, and the second electrode includes an electrode layer and a connection layer in which the nanoparticles are surrounded by an insulator. The nanoparticles are preferably in contact with the electrode layer and the magnetization free layer. Specifically, the nanoparticles are preferably metal nanoparticles.

  If it is said structure, a nano contact is realizable between the nanoparticle comprised by the 2nd electrode, and the magnetization free layer. That is, by adopting the above configuration, the cross-sectional area of the current flowing in the magnetization free layer can be limited on the nano order. As a result, the current value required to induce precession of the magnetization free layer can be reduced.

For example, in the microwave oscillation element according to the present invention, the contact area of the nanoparticles between the electrode layer and the magnetization free layer is preferably more than 0 and 4900 nm ² or less. In particular, the contact area is preferably more than 0 and 70 nm × 70 nm or less.

  And the microwave oscillation element which concerns on this invention can provide the said 1st electrode, a magnetization fixed layer, an intermediate | middle layer, a magnetization free layer, and a 2nd electrode in this order.

  Further, in the microwave oscillation device according to the present invention, the nanoparticles are magnetic nanoparticles, and the magnetization free layer has a configuration in which the magnetic nanoparticles are surrounded by an insulator. The second electrode and the intermediate layer are preferably in contact with each other.

  With the above configuration, the nanoparticles are magnetic nanoparticles, and the magnetization free layer has a configuration in which the magnetic nanoparticles are surrounded by an insulator. Thereby, the cross-sectional area of the current flowing in the magnetization free layer can be limited in nano order. As a result, the current value required to induce precession of the magnetization free layer can be reduced.

  Further, in the microwave oscillation device according to the present invention, the nanoparticles are magnetic nanoparticles, the magnetization free layer has a configuration in which the magnetic nanoparticles are surrounded by an insulator, and the magnetization fixed layer includes: The first magnetization fixed layer and the second magnetization fixed layer having opposite magnetization directions are provided, and the magnetization free layer includes the first magnetization fixed layer and the second magnetization layer via the intermediate layer. It is preferable that the magnetic nanoparticles are in contact with each of the intermediate layers.

  As described above, by providing the first magnetization fixed layer and the second magnetization fixed layer whose magnetization directions are opposite to each other, it is compared with the microwave oscillation element of the present invention using a single magnetization fixed layer. As a result, microwave oscillation can be performed with a much smaller current value.

  Specifically, in the microwave oscillation device according to the present invention having the above-described configuration, the first magnetization fixed layer, the intermediate layer, the magnetization free layer, the intermediate layer, and the second magnetization fixed layer include When a voltage is applied to the first electrode and the second electrode, electrons pass through one of the magnetization fixed layers (here, tentatively referred to as the second magnetization fixed layer). , Passes through the intermediate layer, and goes to the magnetization free layer. At this time, the electrons have a spin having a magnetic moment in the same direction as the magnetization of the second magnetization fixed layer. When electrons with such spins flow into the magnetic nanoparticles in the free magnetic layer, the angular momentum of the spins is transmitted to the magnetic nanoparticles, and the spins of the electrons in the magnetic nanoparticles try to reverse. Begin.

  On the other hand, the magnetization direction of the first magnetization fixed layer is opposite to the magnetization of the second magnetization fixed layer. For this reason, an electron having a spin having a magnetic moment in the same direction as the magnetization of the second magnetization fixed layer is in contact with the first magnetization fixed layer at the interface where the electron flow enters the first magnetization fixed layer. Reflected by the layer. This reflected spin still affects the magnetization in the magnetic nanoparticles.

  That is, the electrons that have passed through the second magnetization fixed layer are reflected by the intermediate layer and then act again on the magnetization of the magnetic nanoparticles, so that the current value for generating the microwave is applied only to the magnetization fixed layer. It can be implemented with a smaller current value than the microwave oscillation element of the present invention used.

  In the microwave oscillating device according to the present invention, the magnetic nanoparticles preferably have a diameter of more than 0 and 100 nm or less.

  The microwave oscillation element according to the present invention preferably has an antiferromagnetic layer between the first electrode and the fixed magnetization layer. Alternatively, the microwave oscillating device according to the present invention has an antiferromagnetic property between the second electrode and the second magnetization fixed layer and between the first magnetization fixed layer and the first electrode. It is preferable to have a body layer.

  By having the antiferromagnetic material layer, the magnetization direction of the magnetization fixed layer can be reliably controlled in a predetermined direction.

  In addition, a microwave oscillation device according to the present invention includes a frequency variable unit having a microwave oscillation element having the above-described configuration and an external magnetic field generation unit.

  According to the above configuration, the present invention can realize a microwave oscillating device excellent in high output, low cost, and mass productivity by a remarkably simple technique as compared with the conventional configuration.

  In addition, in order to solve the above-described problem, a method for manufacturing a microwave oscillating device according to the present invention includes a magnetization fixed layer having a magnetization direction fixed between a first electrode and a second electrode, An intermediate layer that is a magnetic body or an insulator and a magnetization free layer capable of changing a magnetization direction, and the intermediate layer is sandwiched between the magnetization fixed layer and the magnetization free layer; A method of manufacturing a microwave oscillation element configured to allow a current to flow from one electrode to a second electrode through the magnetization fixed layer and the magnetization free layer, the second electrode having an electrode layer And a conduction step of electrically connecting each other with the magnetization free layer adjacent to each other, wherein the conduction step includes a plurality of conductive nanoparticles on one of the magnetization free layer and the electrode layer. Particles forming process, and particle forming process An insulator forming step of covering at least a part of the surface of the formed conductive nanoparticles with an insulator, the other of the magnetization free layer and the electrode layer, and the conductive nanoparticles electrically In order to make it conduct | electrically_connecting, the exposure process which removes a part of said insulator formed at the said insulator formation process and exposes the surface of this electroconductive nanoparticle is included.

  According to the above configuration, the present invention can realize a microwave oscillating device excellent in high output, low cost, and mass productivity by a significantly simpler method as compared with the conventional configuration.

  As described above, the current value required to induce precession of the magnetization free layer due to spin torque is proportional to the volume of the magnetization free layer through which a current flows. That is, the current required for microwave oscillation can be reduced by reducing the cross-sectional area of the current flowing in the magnetization free layer and increasing the current density.

  Then, if the manufacturing method of this invention is used, a nano contact can be implement | achieved between the nanoparticle comprised by the 2nd electrode, and a magnetization free layer. That is, by adopting the above configuration, the cross-sectional area of the current flowing in the magnetization free layer can be limited on the nano order. As a result, the current value required to induce precession of the magnetization free layer can be reduced. As described above, the present invention is compared with the conventional method of increasing the density of the current flowing in a predetermined region in the magnetization free layer by producing a magnetization free layer having a nano-contact structure or a fine structure with the electrode. Thus, a microwave oscillation device excellent in low cost and mass productivity can be realized by a remarkably simple method of providing nanoparticles.

  In particular, according to the present invention, since a plurality of conductive nanoparticles are formed, a microwave oscillator with high output can be realized, and a microwave oscillation corresponding to a high output of a conventional configuration in which a plurality of fine structures must be provided. This can be realized by a simpler method compared to the element.

  In addition, in order to solve the above-described problem, another method for manufacturing a microwave oscillation device according to the present invention includes a magnetization fixed layer having a magnetization direction fixed between a first electrode and a second electrode. A nonmagnetic or insulating intermediate layer and a magnetization free layer capable of changing the magnetization direction, wherein the intermediate layer is sandwiched between the magnetization fixed layer and the magnetization free layer. A method of manufacturing a microwave oscillation device configured to allow a current to flow from a first electrode to a second electrode through the magnetization fixed layer, an intermediate layer, and a magnetization free layer, wherein the magnetization A magnetization free layer forming step of forming a free layer, wherein the magnetization free layer forming step includes: a particle forming step of forming a plurality of magnetic nanoparticles on the second electrode or the intermediate layer; and a particle forming step Table of the above magnetic nanoparticles formed by An insulator forming step of covering at least a part of the insulator with an insulator, and an exposing step of removing a part of the insulator formed in the insulator forming step to expose the surface of the conductive nanoparticles. It is a feature.

  According to the above configuration, the present invention can realize a microwave oscillating device excellent in high output, low cost, and mass productivity by a significantly simpler method as compared with the conventional configuration.

  As described above, the current value required to induce precession of the magnetization free layer due to spin torque is proportional to the volume of the magnetization free layer through which a current flows. That is, the current required for microwave oscillation can be reduced by reducing the cross-sectional area of the current flowing in the magnetization free layer and increasing the current density.

  Therefore, if the manufacturing method of the present invention is used, the magnetic free layer is formed using magnetic nanoparticles. That is, by adopting this configuration, the cross-sectional area of the current flowing in the magnetization free layer can be limited on the nano order. As a result, the current value required to induce precession of the magnetization free layer can be reduced. As described above, the present invention is compared with the conventional method of increasing the density of the current flowing in a predetermined region in the magnetization free layer by producing a magnetization free layer having a nano-contact structure or a fine structure with the electrode. Thus, a microwave oscillation device excellent in low cost and mass productivity can be realized by a remarkably simple method of providing nanoparticles.

  In particular, since a plurality of magnetic nanoparticles are formed in the present invention, a microwave oscillator having a high output can be realized, and a microwave oscillator corresponding to a high output having a conventional configuration that has to be provided with a plurality of fine structures. This can be realized by a simple method compared to the above.

  In addition, in order to solve the above-described problem, another method for manufacturing a microwave oscillation device according to the present invention includes a magnetization fixed layer having a magnetization direction fixed between a first electrode and a second electrode. A nonmagnetic or insulating intermediate layer and a magnetization free layer capable of changing the magnetization direction, wherein the intermediate layer is sandwiched between the magnetization fixed layer and the magnetization free layer. A method for manufacturing a microwave oscillation device configured to allow a current to flow from a first electrode to a second electrode through the magnetization fixed layer, the intermediate layer, and the magnetization free layer, A material containing an insulator matrix and a magnetic nanoparticle raw material is applied on any one of the two electrodes or the magnetization fixed layer, and the magnetic nanoparticles are separated from the magnetization fixed layer by the insulator matrix. Magnetic material from the raw material Forming the intermediate layer and the magnetization free layer, and removing the insulator on at least a part of the surface of the magnetic nanoparticle formed by the step to remove the conductive nanoparticle. And an exposure step for exposing the surface.

  With the above configuration, since the intermediate layer and the magnetization free layer can be formed simultaneously, that is, in one step, compared to the method of forming the intermediate layer and the magnetization free layer in each step, The manufacturing process can be simplified.

  As described above, the microwave oscillating device according to the present invention is configured such that the density of the current flowing in a predetermined region in the magnetization free layer in the current path is changed to a region other than the predetermined region in the magnetization free layer. It has a feature that it has a plurality of nanoparticles for making the density higher than the current flowing through the. In addition, as described above, the method for manufacturing a microwave oscillating device according to the present invention changes the magnetization direction between the first electrode and the second electrode, and the magnetization fixed layer in which the magnetization direction is fixed. A method of manufacturing a microwave oscillation device comprising a magnetization free layer capable of flowing current from a first electrode to a second electrode via the magnetization fixed layer and the magnetization free layer And a conduction step in which the second electrode having the electrode layer and the magnetization free layer are adjacent to each other to electrically conduct each other, and the conduction step is one of the magnetization free layer and the electrode layer. A particle forming step of forming a plurality of conductive nanoparticles on one layer, an insulator forming step of covering at least a part of the surface of the conductive nanoparticles formed by the particle forming step with an insulator, and the magnetization The other of the free layer and the electrode layer And exposing the surface of the conductive nanoparticles by removing a part of the insulator formed in the insulator forming step in order to electrically connect the conductive nanoparticles. It is characterized by including. In addition, as described above, another method for manufacturing a microwave oscillating device according to the present invention includes a magnetization fixed layer having a magnetization direction fixed between a first electrode and a second electrode, a non-magnetic An intermediate layer and a magnetization free layer capable of changing the magnetization direction, and current is passed from the first electrode to the second electrode via the magnetization fixed layer, the intermediate layer, and the magnetization free layer. A method of manufacturing a microwave oscillation element configured to flow, the method including a magnetization free layer forming step of forming the magnetization free layer, wherein the magnetization free layer forming step includes the second electrode, the magnetization fixed A particle forming step of forming a plurality of magnetic nanoparticles on any one of the layer and the intermediate layer, and insulation covering at least a portion of the surface of the magnetic nanoparticles formed by the particle forming step with an insulator Formed in the body forming step and the insulator forming step. It was is characterized by comprising an exposure step of exposing the surface of the part was removed conductive nanoparticles of the insulator. Furthermore, as described above, another method for manufacturing a microwave oscillation device according to the present invention includes a magnetization fixed layer having a magnetization direction fixed between the first electrode and the second electrode, and a nonmagnetic material. Alternatively, an intermediate layer that is an insulator and a magnetization free layer that can change the magnetization direction, and the intermediate layer is sandwiched between the magnetization fixed layer and the magnetization free layer, A method for manufacturing a microwave oscillation device configured to allow a current to flow from an electrode to a second electrode via the magnetization fixed layer, the intermediate layer, and the magnetization free layer, wherein the second electrode or A material containing an insulator matrix and a magnetic nanoparticle material is applied on any one of the magnetization fixed layers, and the magnetic nanoparticles are separated from the magnetization fixed layer by the insulator matrix. , Forming magnetic nanoparticles from the raw material Forming the intermediate layer and the magnetization free layer, and exposing the surface of the conductive nanoparticles by removing the insulator on at least a part of the surface of the magnetic nanoparticles formed by the step. And a process.

  In addition, as described above, the microwave oscillation device according to the present invention is characterized by including the frequency variable unit including the microwave oscillation element having the above-described configuration and the external magnetic field generation unit.

  With the above configuration, the present invention can realize a microwave oscillating device or a microwave device excellent in high output, low cost, and mass productivity by a significantly simpler method compared to the conventional configuration. .

[Embodiment 1]
An embodiment of a microwave oscillation device and a microwave oscillation device according to the present invention will be described. In the following description, various technically preferable limitations for implementing the present invention are given, but the scope of the present invention is not limited to the following embodiments and drawings.

  First, a microwave oscillation device according to the present invention will be described with reference to FIGS. 1 to 3A and 3B.

  FIG. 1 is a cross-sectional view showing the configuration of the microwave oscillating device according to this embodiment. As shown in FIG. 1, the microwave oscillation element 50a according to the present embodiment includes a first electrode 10a, an antiferromagnetic material layer 11, a magnetization fixed layer 12 whose magnetization is fixed in one direction, and an intermediate The layer 13, the magnetization free layer 14 having a variable magnetization direction, and the second electrode 10 b are stacked in this order.

  The second electrode 10 b includes a layer including a plurality of conductive nanoparticles 16 surrounded by an insulator layer 15 on the surface in contact with the magnetization free layer 14 and an electrode layer 17. The conductive nanoparticle 16 connects the magnetization free layer 14 and the electrode layer 17 with a nanocontact 18. That is, the magnetic free layer 14 and the second electrode 10 b are electrically nano-contacted by the conductive nanoparticles 16.

  The magnetization of the magnetization fixed layer 12 is fixed in one direction by the antiferromagnetic material layer 11.

  Instead of fixing the magnetization of the magnetization fixed layer 12 by the antiferromagnetic material layer 11, the magnetization fixed layer 12 may be formed of only a hard magnetic material in which magnetization reversal hardly occurs.

  The microwave oscillation element 50a in the present embodiment shown in FIG. 1 has an equivalent circuit similar to the microwave oscillation element 400B shown in FIG. Therefore, like the microwave oscillation element 400B of FIG. 13A, it is possible to oscillate with a larger output than the microwave oscillation element 400 shown in FIG. This will be described in detail below.

  A portion surrounded by a dotted line in the microwave oscillator 50a shown in FIG. 1 is connected to the magnetization free layer 14 and the first layer by the conductive nanoparticles 16 as in the conventional microwave oscillator 400 shown in FIG. Two electrodes 10 b are connected by a nano contact 18. That is, the portion surrounded by the dotted line has an equivalent circuit similar to that of the conventional microwave oscillator 400 shown in FIG. 12A, and can perform microwave oscillation in the same manner.

  Furthermore, in the microwave oscillation element 50 a in the present embodiment, the magnetization free layer 14 and a large number of nanocontacts 18 are formed by the plurality of conductive nanoparticles 16. Therefore, the microwave oscillating device 50a has a structure in which a plurality of microwave oscillating devices 400 shown in FIG. 12A are connected in parallel, like the microwave oscillating device 400B shown in FIG. Will be. The equivalent circuit of the microwave oscillating device 50a in FIG. 1 is the same as the microwave oscillating device 400B shown in FIG. 13A, and an output larger than that of the microwave oscillating device 400 in FIG. Is possible.

  Further, as described above, when the interval between the conductive nanoparticles 16 is reduced, the microwave oscillation elements connected in parallel oscillate in phase synchronization. That is, when the interval between the conductive nanoparticles 16 is narrowed, the precession of the spin of electrons in the magnetization free layer 14 that is induced immediately below the nanocontact 18 is phase-synchronized between adjacent nanocontact portions. This makes it possible to oscillate the microwave with a larger output.

  Next, materials for forming each element of the microwave oscillation element 50a in the present embodiment will be described in detail.

As a material of the magnetization fixed layer 12 and the magnetization free layer 14, any of the following (1) to (3) can be used.
(1) An alloy containing at least one element selected from the group consisting of Fe, Co, Ni, or Fe, Co, Ni, Mn, and Cr. (2) NiFe-based alloy called “Permalloy”, CoNbZr-based alloy. , FeTaC alloys, CoTaZr alloys, FeAlSi alloys, FeB alloys, CoFeB alloys, and other soft magnetic materials (3) Heusler alloys, CrO ₂ , Fe ₃ O ₄ , La _1-X Sr _X MnO _3, etc. Metal Magnetic Material As materials for the magnetization fixed layer 12 and the magnetization free layer 14, a material having magnetic characteristics according to the use may be appropriately selected and used.

Moreover, as the material of the intermediate layer 13, the following can be used.
(1) Cu, Au, Ag, Ru, or an alloy containing at least one of these (2) At least one element selected from the group consisting of Al, Ti, Ta, Co, Ni, Si, Mn, and Fe Insulator made of oxide or nitride containing (3) fluoride. The intermediate layer 13 may be doped with a different element such as oxygen.

  As a material of the electrode layer 17 of the first electrode 10a and the second electrode 10b, a conventionally known electrode material can be used.

  Moreover, as a material of the electroconductive nanoparticle 16, what is necessary is just to have electroconductivity, for example, Pt, Au, Cu etc. can be used.

  The shape of the conductive nanoparticles 16 is not particularly limited as long as it can be nano-contacted with the magnetization free layer 14 and the second electrode 10b, and may be spherical, elliptical, or polyhedral. .

As a material of the insulating layer 15 may be, for example, _{SiO 2, Al 2 O 3,} SiN or the like. Among them, SiN is preferable because it has a smaller proportion of H ₂ O in the film than SiO _{2 and the} like, and is excellent in the effect of preventing intrusion of O ₂ and H ₂ O from the outside.

  In the present embodiment, the magnetization of the magnetization fixed layer 12 is fixed by the antiferromagnetic material layer 11. As a material of the antiferromagnetic material layer 11 that can be used in this case, FeMn, PtMn, PdMn, PdPtMn, IrMn, PtIrMn, and the like are desirable. In addition, as an intermediate layer (disposed between the pinned magnetic layer 12 and the antiferromagnetic layer 11) when fixed using interlayer coupling, Cu, Au, Ag, Ru, or any two or more of these are used. Alloys containing are preferred.

  A method for manufacturing the microwave oscillation element 50a according to the present embodiment will be described below.

  FIG. 2 is a diagram for explaining a method of manufacturing the microwave oscillating device according to this embodiment.

  First, Cu (film thickness: 60 nm) is formed as a first electrode 10a on a substrate such as Si (FIG. 2A). Specifically, as shown in the top view of FIG. 2A ′, after Cu (film thickness 60 nm) is formed, a resist is applied, patterned, and a predetermined dimension (for example, using ion milling) In this example, a thin wire having a width of 30 μm and a length of 100 μm is formed between two electrode pad portions of 80 μm × 80 μm).

Next, an IrMn alloy layer (film thickness: 15 nm) is formed as the antiferromagnetic material layer 11 on the first electrode 10a. Further thereon, a NiFe alloy layer (film thickness 5 nm), which is a soft magnetic material having a saturation magnetization Bs of about 1 T, is formed as the magnetization fixed layer 12. Further, an AlO _x layer (film thickness: 1.4 nm) is formed as the intermediate layer 13, and an FeCoNi alloy layer (film thickness: 5 nm) having a saturation magnetic flux density of 2.3 T is formed thereon as the magnetization free layer.

  Next, a 5 nm Ta layer is formed as a protective layer.

  Next, a layer including the conductive nanoparticles 16 surrounded by the insulator layer 15 is formed. For the conductive nanoparticles, a method using a so-called SK (Stranski-Krastanov) mode or VW (Volmer-Weber) mode growth that appears at an early stage of the thin film growth process is used. In both the SK mode and the VW mode, in the thin film growth process, crystal nuclei are generated and grown (island growth) to form a thin film. If the thin film formation is stopped during the crystal nucleus growth process, innumerable nanoparticles formed by the crystal nucleus growth can be obtained on the substrate surface. In addition, it has been proved by recent semiconductor processes that the size of the nanoparticles can be formed in a uniform size although there is some distribution. Further, in order to control the fine particle interval / position, a method of putting stress distribution or dislocation on the substrate surface has been devised, but in this embodiment, there is no particular problem with respect to the interparticle distance / position. . This is because the microwave oscillating elements are connected in parallel by the conductive nanoparticles even if the interparticle distance / position varies. This method does not require fine processing such as electron beam lithography and etching, and can form nanoparticles by a simple process. After Pt is formed into nanoparticles having a diameter of about 50 nm to 100 nm by using SK mode or VW mode growth, SiN is formed as an insulator layer 15 so as to cover the conductive nanoparticles 16. The thickness of SiN is about several nm.

Another method for forming a layer including the conductive nanoparticles 16 covered with the insulator layer 15 is a compound called “granular structure”, in which metal particles are deposited or formed in an amorphous matrix. The body structure is used. The “granular structure” can be obtained by simultaneously forming a metal material such as Cu or Pt and an insulator such as SiO ₂ or Al ₂ O ₃ by sputtering. Therefore, when using the “granular structure” to form a layer including the conductive nanoparticles 16 covered with the insulator layer 15 necessary for the microwave oscillation element, the conductive nanoparticles 16 and the insulator layer are formed. 15 can be formed simultaneously. Therefore, the number of steps is one less than the method of forming the conductive nanoparticles 16 in the SK mode and the VW mode described above and then forming the insulating layer.

  Next, the conductive nanoparticles surrounded by the insulator layer 15 from the antiferromagnetic material layer 11 formed on the first electrode 10a by using ion milling to a predetermined size as in the first electrode 10a. Up to the layer including the material is processed into a predetermined dimension (for example, 50 μm × 50 μm) (FIG. 2B).

  Next, in order to prevent a short circuit with the second electrode 10b, the insulating film 20 is covered so as to cover the layer including the conductive nanoparticles 16 surrounded by the insulating layer 15 from the antiferromagnetic material layer 11 processed previously. As a result, SiN is formed.

  Thereafter, a contact hole 21 between the electrode layer 17 and the conductive nanoparticles 16 in the second electrode 10b is created. The contact hole 21 is formed by applying a resist and patterning, and removing the insulating film by wet etching with hydrofluoric acid or ion milling. At this time, the surface portion of the insulator layer 15 covering the conductive nanoparticles 16 is also removed, and a part of the conductive nanoparticles 16 is exposed on the surface (FIG. 2C). Here, the area of the exposed conductive nanoparticles 16 becomes the contact area of the nanocontacts 18. As described above, when the cross-sectional area of the current path is reduced, the current density increases, so that the effect of reducing the magnitude of the current required for microwave oscillation is obtained. Therefore, it is desirable that the contact area is small.

In the case of the present embodiment, the contact area of the nanocontact is determined in consideration of the current distribution in the magnetization free layer 14 from the nanocontact 18. In general, the value of the current density necessary to apply the spin torque is reported to be about 10 ⁷ A / cm ^3, and the value of the current flowing through one element connected in parallel is about 0.5 mA. For example, the contact area is determined to be 70 nm × 70 nm. Considering the current distribution, that is, the spread of the current in the magnetization free layer 14, a nanocontact junction area of at least 70 nm × 70 nm or less is required. As described above, since the diameter of the conductive nanoparticle 16 forming the nanocontact 18 is about 50 nm to 100 nm, the insulating film 20 and the surface of the insulator layer 15 covering the conductive nanoparticle 16 are included. By removing the portion, a nanocontact having a size of 70 nm × 70 nm or less can be formed. If necessary, whether or not a nanocontact of a desired size is formed may be confirmed by looking at the particle shape using an AFM (atomic force microscope) or the like.

  Finally, the electrode layer 17 in the second electrode 10b is formed and processed into a predetermined dimension as in the first electrode 10a (FIG. 2D).

  The manufacturing method described in the present embodiment is a method of stacking from the first electrode 10a toward the second electrode 10b, but the present invention is not limited to this, and the second electrode 10b. Alternatively, a method of stacking from the first electrode 10a toward the first electrode 10a may be used.

  As described above, in the microwave oscillation element 50a in the present embodiment, the magnetization free layer 14 and the second electrode 10b electrically form a plurality of nanocontacts by the plurality of conductive nanoparticles 16. ing. These are equivalent to the microwave oscillation element 400B shown in FIG. 13A in which the microwave oscillation elements 400 shown in FIG. 12A are connected in parallel, and show a large output.

  Further, in the microwave oscillating device 50a in the present embodiment, a plurality of nanocontacts 18 are formed by using a plurality of conductive nanoparticles 16, so that fine processing that requires nanoscale accuracy is not necessary. It is possible to manufacture a low-cost device with excellent mass productivity.

  Next, an oscillation device provided with the microwave oscillation element in the present embodiment will be described.

  3 (a) and 3 (b) show a microwave oscillation device including the microwave oscillation element 50a according to the embodiment of the present invention. FIG. 3A shows a configuration of a microwave oscillation device 60 using the microwave oscillation element 50a of the present invention. The microwave oscillation device 60 includes a power supply unit 51, a frequency variable unit 52, and a signal amplification unit 53. The power supply unit 51 includes four power supplies V1, V2, V3, and V4 that can arbitrarily control voltage (current). The power sources V1, V2, and V3 are connected to the frequency variable unit 52, and the power source V4 is connected to the signal amplifying unit 53. Further, an AC signal 54 is output from the frequency variable unit 52 to the signal amplifying unit 53.

  FIG. 3B shows the frequency variable unit 52 in FIG. 3A in more detail. As shown in FIG. 3B, the frequency variable unit 52 includes the microwave oscillation element 50a in the present embodiment, and in addition to this, the frequency variable unit 52 is formed of at least an external magnetic field generation unit 56 (for example, a Cu fine wire or a Cu fine wire). Coil). A power source V1 is connected to the first electrode 10a of the microwave oscillating device 50a. By controlling this V1, the magnitude of the applied voltage, that is, the device current is controlled. The external magnetic field generator 56 is connected to power sources V2 and V3, and can control the magnitude and direction of the external magnetic field applied to the microwave oscillation element 50a. By controlling these power supplies V1, V2 and V3, the oscillation frequency is changed. The output from the frequency variable unit 52 is used as a predetermined signal output by the signal amplifying unit 53. As such a device for generating a reference frequency, a VCO (voltage controlled oscillator) is used in a mobile phone.

In other words, it can be said that the microwave oscillation device and the microwave oscillation device using the same according to the present invention are characterized by the following configurations.
That is, the microwave oscillating element and the microwave oscillating device using the same can change the magnetization direction of the first electrode, the magnetization fixed layer whose magnetization direction is fixed, the non-magnetic intermediate layer, and the like. In other words, in the microwave oscillation element in which the magnetization free layer and the second electrode are stacked in this order, the second electrode includes nanoparticles.
In the above configuration, the second electrode includes a plurality of conductive nanoparticles surrounded by an insulator on a surface in contact with the magnetization free layer, and the magnetization free layer and the first electrode It is preferable that the two electrodes form a plurality of nanocontacts electrically by the conductive nanoparticles or the aggregated aggregated nanoparticles.
Furthermore, in said structure, it is preferable that the contact area of the said nano contact is 70 nm x 70 nm or less.
Moreover, in said case, it is preferable that the said electroconductive nanoparticle is a metal particle.

[Embodiment 2]
Another embodiment according to the present invention will be described below with reference to FIGS. In this embodiment, in order to explain differences from the first embodiment, members having the same functions as the members described in the first embodiment are denoted by the same member numbers for convenience of explanation. The description is omitted.

  FIG. 4 is a cross-sectional view showing the configuration of the microwave oscillating device according to the present embodiment. As shown in FIG. 4, the microwave oscillation element 50b according to the present embodiment includes a first electrode 10a, an antiferromagnetic material layer 11, a magnetization fixed layer 12 whose magnetization is fixed in one direction, and an intermediate The layer 13, the magnetization free layer 24 having a variable magnetization direction, and the second electrode 10 b are stacked in this order.

  In addition, the magnetization free layer 24 in the present embodiment is composed of magnetic nanoparticles 26 surrounded by an insulator layer 25. The magnetic nanoparticles 26 have a role similar to that of the magnetic free layer 114 processed into the nanoscale in the microwave oscillation elements 500 and 500B illustrated in FIGS. 12B and 13B.

  Further, the magnetization of the magnetization fixed layer 12 is fixed in one direction by the antiferromagnetic material layer 11. Instead of fixing the magnetization of the magnetization fixed layer 12 by the antiferromagnetic material layer 11, the magnetization fixed layer 12 may be formed of only a hard magnetic material that is difficult to cause magnetization reversal.

  The microwave oscillation element 50b in the present embodiment shown in FIG. 4 has an equivalent circuit similar to the microwave oscillation element 500B shown in FIG. Therefore, like the microwave oscillator 500B of FIG. 13B, it is possible to oscillate with a larger output than the microwave oscillator 500 shown in FIG. This will be described in detail below.

  In the microwave oscillating device 50b shown in FIG. 4, the magnetic nanoparticles 26 and the second electrode 10b are electrically connected at a portion surrounded by a dotted line. In FIG. 12B, the magnetization free layer finely processed on the nanoscale and the second electrode are electrically connected on the nanoscale. As described above, in the present embodiment, the magnetic nanoparticle 26 and the magnetization free layer 114 shown in FIG. 12 can be regarded as the same, and therefore, in a portion surrounded by a dotted line, FIG. It has an equivalent circuit similar to the conventional microwave oscillation device 500 shown, and can perform microwave oscillation in the same manner.

  Furthermore, in the microwave oscillation element 50b in the present embodiment, the plurality of magnetic nanoparticles 26 and the second electrode 10b are electrically connected. Accordingly, the microwave oscillating device 50b has a structure in which a plurality of microwave oscillating devices 500 shown in FIG. 12B are connected in parallel, similarly to the microwave oscillating device 500B shown in FIG. 13B. Yes. The equivalent circuit of the microwave oscillating device 50b in FIG. 4 is the same as the microwave oscillating device 500B shown in FIG. 13B, and a larger output than the microwave oscillating device 500 shown in FIG. 12 can be obtained. it can.

  Further, as the interval between the magnetic nanoparticles 26 is reduced, the microwave oscillation elements connected in parallel oscillate in phase synchronization. That is, when the interval between the magnetic nanoparticles 26 is narrowed, the precession of the spins of the electrons of the adjacent magnetic nanoparticles 26 in the magnetization free layer 14 is phase-synchronized. This makes it possible to oscillate with a larger output.

  Next, materials for forming each element of the microwave oscillation element 50b in the present embodiment will be described.

  The magnetic nanoparticles 26 are made of the same material as the magnetization free layer 14 described in the first embodiment.

  The insulator layer 25 can be formed using a material similar to that of the insulator layer 15 described in Embodiment 1.

  Further, the materials used for other portions are the same as those in the first embodiment.

  Hereinafter, a method for manufacturing the microwave oscillation element 50b according to the present embodiment will be described.

  FIG. 5 is a diagram for explaining a method of manufacturing the microwave oscillator 50b according to the present embodiment.

  First, Cu (film thickness 60 nm) is formed as a first electrode 10a on a substrate 19 such as Si (FIG. 5A). Specifically, as shown in the top view of FIG. 5A ′, after Cu (film thickness 60 nm) is formed, a resist is applied, patterned, and a predetermined dimension (using ion milling) For example, a thin wire having a width of 30 μm and a length of 100 μm is formed between two electrode pad portions of 80 μm × 80 μm).

  Next, an IrMn alloy layer (film thickness: 15 nm) is formed as the antiferromagnetic material layer 11 on the first electrode 10a. Further thereon, a NiFe alloy layer (film thickness 5 nm), which is a soft magnetic material having a saturation magnetization Bs of about 1 T, is formed as the magnetization fixed layer 12. Further, an AlOx layer (film thickness 1.4 nm) is formed as the intermediate layer 13.

  Next, a layer including magnetic nanoparticles 26 surrounded by the insulator layer 25 is formed.

  The magnetic nanoparticles 26 use a method utilizing so-called SK mode or VW mode growth that appears in the early stage of the thin film growth process. This method does not require fine processing such as electron beam lithography and etching, and can form nanoparticles by a simple process. After FeCoNi is formed into nanoparticles using SK mode or VW mode growth, SiN as an insulator layer 25 is formed so as to surround the magnetic nanoparticles 26. In addition, in order to control the nanoparticle spacing and position, a method of putting stress distribution or transfer on the substrate surface has been devised. In this embodiment, the distance between nanoparticles is the same as in the first embodiment. -There is no particular problem with the location. This is because the microwave oscillation elements are connected in parallel by the magnetic nanoparticles even if the inter-particle distance / position varies.

As another method for forming a layer including the magnetic nanoparticles 26 covered with the insulator layer 25, a composite structure called “granular film” in which the magnetic nanoparticles 26 are deposited or formed in an amorphous matrix. Is used. The “granular film” can be obtained by simultaneously forming a ferromagnetic metal and Al ₂ O ₃ constituting the magnetic nanoparticle 26 in the present embodiment by a sputtering method or the like. When the “granular film” is used, it is not necessary to form the intermediate layer 13 made of Al ₂ O ₃ . This is because the magnetic nanoparticles 26 in the granular film are covered with an amorphous matrix made of Al ₂ O ₃ . Therefore, when the granular film is formed, Al ₂ O ₃ is formed between the magnetization fixed layer 12 and the magnetic nanoparticles 26 and serves as the intermediate layer 13. Therefore, it is not necessary to form Al ₂ O ₃ as the intermediate layer 13 in advance.

FIG. 6 shows a microwave oscillation element 50b ′ using a granular film, and the intermediate layer 13 is omitted as compared with the microwave oscillation element 50b shown in FIG.

Here, the size of the magnetic nanoparticles 26 will be described. As described above, in the microwave oscillation elements 500 and 500B of FIGS. 12B and 13B, the magnetization free layer 114 is miniaturized to reduce the cross-sectional area of the current path. As a result, the current density is increased, which has the effect of reducing the amount of current required for microwave oscillation. Further, the reason why the magnetization free layer 14 is miniaturized is that the magnetization free layer 14 has a single magnetic domain, a current distribution, and a uniform temperature distribution due to Joule heat. In the case of the present embodiment, the size of the magnetic nanoparticle 26 determines the cross-sectional area of the current path. Moreover, the dimension for making the magnetic nanoparticle 26 into a single magnetic domain is about 100 nm in diameter. Therefore, in order to make the magnetic nanoparticles 26 have a single magnetic domain and increase the current density to reduce the current required for microwave oscillation, the diameter of the magnetic nanoparticles 26 needs to be 100 nm or less.

Next, as with the first electrode 10a, ion milling is used to a predetermined dimension, and a predetermined dimension (from the antiferromagnetic material layer 11 to the layer containing conductive nanoparticles surrounded by the insulator layer 15) ( For example, it is processed to 50 μm × 50 μm). (Fig. 5 (b))
Next, in order to prevent a short circuit with the second electrode 10 b, SiN is formed as the insulating film 20 so as to cover the layer including the magnetic nanoparticles 26 surrounded by the insulating layer 25 from the antiferromagnetic material layer 11. .

  Thereafter, a contact hole 21 between the electrode layer 17 and the magnetic nanoparticles 26 in the second electrode 10b is created. The contact hole 21 is formed by applying a resist and patterning, and removing the insulating film by wet etching with hydrofluoric acid or ion milling. At this time, the surface portion of the insulator layer 15 covering the magnetic nanoparticles 26 (the surface portion of the magnetization free layer 14) is also removed, and a part of the magnetic nanoparticles is exposed on the surface (FIG. 5C).

  Finally, the second electrode 10b is formed and processed into a predetermined dimension in the same manner as the first electrode 10a (FIG. 5D).

  As described above, in the microwave oscillation element in the present embodiment, the plurality of magnetic nanoparticles 26 and the second electrode 10b are electrically connected. These are equivalent to the microwave oscillator 500B shown in FIG. 13B in which the microwave oscillators 500 shown in FIG. 12B are connected in parallel, and show a large output.

  In the microwave oscillation element 50b in the present embodiment, the plurality of magnetic nanoparticles 26 perform the same function as the finely processed magnetization free layer 114 in FIG. The required microfabrication is not required, and it is possible to manufacture a low-cost element with excellent mass productivity.

In other words, it can be said that the microwave oscillation device and the microwave oscillation device using the same according to the present invention are characterized by the following configurations.
That is, the microwave oscillating element and the microwave oscillating device using the same can change the magnetization direction of the first electrode, the magnetization fixed layer whose magnetization direction is fixed, the non-magnetic intermediate layer, and the like. In other words, in the microwave oscillation element configured by laminating the magnetization free layer and the second electrode in this order, it can be said that the magnetization free layer includes nanoparticles.
In the above configuration, the magnetization free layer is composed of a plurality of magnetic fine particles surrounded by an insulator, and the second electrode and the magnetic fine particles electrically form a plurality of nanocontacts. Is preferred.

[Embodiment 3]
Another embodiment according to the present invention will be described below with reference to FIGS. In this embodiment, in order to explain the difference from the second embodiment, for the sake of convenience of explanation, members having the same functions as those described in the second embodiment are denoted by the same member numbers. The description is omitted.

  FIG. 7 is a sectional view showing the configuration of the microwave oscillating device according to the present embodiment. The microwave oscillation element 50c of the present embodiment includes an intermediate layer 22 and a second layer between the magnetization free layer 14 and the second electrode 10b of the microwave oscillation element 50b described in FIG. 4 of the second embodiment. The antiferromagnetic layer 11b and the magnetization fixed layer 12b are formed.

  That is, as shown in FIG. 7, the microwave oscillation element 50c according to the present embodiment includes the first electrode 10a, the first antiferromagnetic layer 11a, and the first whose magnetization is fixed in one direction. Magnetization fixed layer 12a, intermediate layer 22, magnetization free layer 24 with variable magnetization direction, intermediate layer 22, second magnetization fixed layer 12b, second antiferromagnetic material layer 11b, second layer The electrodes 10b are stacked in this order.

  In addition, the magnetization free layer 24 in the present embodiment is composed of magnetic nanoparticles 26 surrounded by an insulator layer 25.

  The magnetization directions of the magnetization fixed layers 12a and 12b are opposite to each other and are fixed by the antiferromagnetic layers 11a and 11b. Instead of fixing the magnetizations of the magnetization fixed layers 12a and 12b by the antiferromagnetic layers 11a and 11b, the magnetization fixed layers 12a and 12b may be formed of only a hard magnetic material in which magnetization inversion hardly occurs.

  The material of the second magnetization fixed layer 12b is made of the same material as that of the first magnetization fixed layer 12a, and the material of the magnetization fixed layer 12 described in the first embodiment can be used.

  In the present embodiment, a PtMn alloy layer can be used as the first antiferromagnetic material layer 11a, and an IrMn alloy layer can be used as the second antiferromagnetic material layer 11b.

  For the intermediate layer 22, the material of the intermediate layer 13 described in the first embodiment can be used.

In addition, the magnetization free layer 24 in this Embodiment can also be comprised using the granular film mentioned above. When the granular film is formed, Al ₂ O ₃ is formed between the first and second magnetization fixed layers 12 a and 12 b and the magnetic nanoparticles 26 to serve as the intermediate layer 22. Therefore, it is not necessary to form Al ₂ O ₃ as the intermediate layer 22 in advance (see FIG. 8).

  The microwave oscillation element 50c in the present embodiment shown in FIG. 7 oscillates at a smaller current value than the microwave oscillation elements 50b and 50b ′ (FIGS. 4 and 6) in the second embodiment. It is excellent in that it becomes possible. This will be described in detail below.

  FIG. 9 is a diagram for explaining the principle of microwave generation in this embodiment. In FIG. 9, for easy understanding, a part of the microwave oscillation element in FIG. 7 is shown in an enlarged manner, and the other parts are not shown.

  In order to generate a microwave, a voltage is applied between the electrode 10a and the electrode 10b, and a current 31 flows from the electrode 10a to the magnetization free layer 24 through the antiferromagnetic layer 11a and the magnetization fixed layer 12a. Shed. By flowing the current 31 in this way, the electrons 32 that have passed through the magnetization fixed layer 12b (the direction in which electrons flow are opposite to the current) have spins having a magnetic moment in the same direction as the magnetization of the magnetization fixed layer 12b ( In the same figure, it has a left direction). When electrons having such a spin flow into the magnetic nanoparticle 26 in the magnetization free layer 24, the angular momentum of the spin is transmitted to the magnetic nanoparticle 26, and the spin of the electron in the magnetic nanoparticle 26 is reversed. And start precession.

  On the other hand, the magnetization direction of the other magnetization fixed layer 12a is opposite to the magnetization of the magnetization fixed layer 12b. For this reason, electrons having a spin having a magnetic moment in the same direction as the magnetization of the magnetization fixed layer 12b are reflected by the intermediate layer in contact with the magnetization fixed layer 12a at the interface where the flow of electrons enters the magnetization fixed layer 12a. This reflected spin also affects the magnetization in the magnetic nanoparticles 26.

  That is, since the electrons that have passed through the magnetization fixed layer 12b are reflected by the intermediate layer 22 and then act again on the magnetization of the magnetic nanoparticles 26, the current value for generating microwaves is determined from the second embodiment. This can be implemented with a small current value.

  Also in the present embodiment, a microwave oscillation element is manufactured using a plurality of magnetic nanoparticles 26 as in the second embodiment. Therefore, a structure in which the microwave oscillation elements are connected in parallel is taken, and a large output is shown. Further, since the magnetic nanoparticles 26 are used, a microwave oscillation element can be formed without fine processing.

  In addition, among the materials forming the elements of the microwave oscillating device 50c in the present embodiment, configurations other than those described above can be the same as the materials in the second embodiment.

  FIG. 10 is a diagram for explaining a method for manufacturing a microwave oscillation element according to this embodiment. A method for manufacturing the microwave oscillation element 50c according to the present embodiment will be described below.

  First, Cu (film thickness 60 nm) is formed as a first electrode 10a on a substrate 19 such as Si (FIG. 10A). Specifically, as shown in the top view of FIG. 10A ′, after Cu (film thickness 60 nm) is formed, a resist is applied, patterned, and a predetermined dimension (using ion milling) For example, a thin wire having a width of 30 μm and a length of 100 μm is formed between two electrode pad portions of 80 μm × 80 μm).

  Next, a PtMn alloy layer (film thickness: 15 nm) is formed as the first antiferromagnetic material layer 11a on the first electrode 10a. Furthermore, a NiFe alloy layer (film thickness: 5 nm), which is a soft magnetic material having a saturation magnetization Bs of about 1 T, is formed thereon as the first magnetization fixed layer 12a. Further, an AlOx layer (film thickness 1.4 nm) is formed as the intermediate layer 22.

  Next, a layer including magnetic nanoparticles 26 surrounded by the insulator layer 25 is formed. The magnetic nanoparticles 26 use a method utilizing so-called SK mode or VW mode growth that appears in the early stage of the thin film growth process. This method does not require fine processing such as electron beam lithography and etching, and can form nanoparticles by a simple process. After forming FeCoNi on the nanoparticles using SK mode or VW mode growth, SiN is deposited to cover the magnetic nanoparticles. In addition, in order to control the nanoparticle interval and position, a method of putting stress distribution, dislocation, etc. on the substrate surface has been devised. In this embodiment, the nanoparticle is the same as in the first and second embodiments. There is no particular problem regarding the distance and position. This is because the microwave oscillation elements are connected in parallel by the magnetic nanoparticles even if the interparticle distance / position varies.

  As described above, the layer containing the magnetic nanoparticles 26 covered with the insulator layer 25 may be formed as a granular film.

  Here, the size of the magnetic nanoparticles 26 will be described.

  As described above, in the microwave oscillation elements 500 and 500B of FIGS. 12B and 13B, the magnetization free layer 114 is miniaturized to reduce the cross-sectional area of the current path. As a result, the current density is increased, which has the effect of reducing the amount of current required for microwave oscillation. Further, the reason why the magnetization free layer is miniaturized is that the magnetization free layer has a single magnetic domain, a current distribution, and a uniform temperature distribution due to Joule heat. In the case of the present embodiment, the size of the magnetic nanoparticle 26 determines the cross-sectional area of the current path. The size for making the magnetic nanoparticles 26 into a single magnetic domain is about 100 nm in diameter. Therefore, in order to make the magnetic nanoparticle 26 have a single magnetic domain and increase the current density to reduce the current required for microwave oscillation, the size of the magnetic nanoparticle 26 needs to be 100 nm or less.

  Next, an AlOx layer (film thickness 1.4 nm) is formed as the intermediate layer 22. Then, as the second magnetization fixed layer 12b, the second magnetization fixed layer 12b is formed of a soft magnetic material made of a NiFe alloy layer (film thickness 5 nm) having a saturation magnetization Bs of about 1T. Further, an IrMn alloy layer (film thickness: 15 nm) is formed as the second antiferromagnetic layer 11b.

  Next, heat treatment is performed while applying an external magnetic field in the plane of the substrate 19. That is, in FIG. 10, heat treatment is performed at 270 ° C. for 10 hours while applying an external magnetic field of 10 kOe to the right. Thereby, the magnetization of the first magnetization fixed layer 12a (soft magnetic NiFe alloy layer) adjacent to the first antiferromagnetic material layer (PtMn alloy layer) 11a can be fixed in the right direction in the drawing.

  Further, in FIG. 10, heat treatment is applied at 200 ° C. for 1 hour while applying an external magnetic field in the left direction. Thereby, the magnetization of the second magnetization fixed layer (soft magnetic NiFe alloy layer) 12b adjacent to the second antiferromagnetic material layer (IrMn alloy layer) 11b can be fixed in the left direction of the drawing.

  Next, similarly to the first electrode 10a, ion milling is performed to a predetermined dimension, and the predetermined dimension (for example, 100 μm × 100 μm) (FIG. 10B).

  Next, SiN is formed as an insulating film 20 so as to prevent a short circuit with the second electrode 10b so as to cover the first antiferromagnetic layer 11a processed from the first antiferromagnetic layer 11b previously processed. .

  Thereafter, a contact hole 21 that connects the second electrode 10b and the antiferromagnetic material layer 11b is formed. The contact hole 21 is formed by applying a resist and patterning, and removing the insulating film by wet etching with hydrofluoric acid or ion milling (FIG. 10C).

  Finally, the second electrode 10b is formed and processed into a predetermined dimension in the same manner as the first electrode 10a (FIG. 10D).

  As described above, by using the first magnetization fixed layer 12a and the second magnetization fixed layer 12b whose two magnetization directions are antiparallel, the first and second magnetization fixed layers 12a and 12b pass through. The magnetic nanoparticle 26 is used even in a structure in which the angular momentum possessed by the spin of electrons can be efficiently applied to the magnetization of the magnetic nanoparticle 26 to reduce the current value required for microwave oscillation. Thus, since the microwave oscillation element 50c is manufactured, fine processing that requires nanoscale accuracy is unnecessary, and the element can be manufactured at low cost.

In other words, it can be said that the microwave oscillation device according to the present invention is characterized by the following configuration.
That is, the microwave oscillation element includes a first electrode, a magnetization fixed layer with a fixed magnetization direction, a nonmagnetic intermediate layer, a magnetization free layer capable of changing the magnetization direction, and a second electrode. In the microwave oscillation device configured by stacking in this order, the magnetization free layer includes nanoparticles, and the magnetization free layer includes a plurality of magnetic fine particles surrounded by an insulator, and the second electrode In other words, a second magnetization fixed layer having a fixed magnetization direction is arranged between the magnetization free layer and the magnetization free layer.

  The present invention is not limited to the above-described embodiments, and various modifications can be made within the scope of the claims, and obtained by appropriately combining technical means disclosed in different embodiments. Such embodiments are also included in the technical scope of the present invention.

  According to the present invention, it is possible to improve the output of microwaves, and it is possible to manufacture a microwave oscillation element by a method that is excellent in low cost and mass productivity. Therefore, it is possible to improve the possibility that the microwave oscillation element using the spin torque of the present invention is mounted as a microwave oscillation element used in an RF circuit capable of dealing with a plurality of frequencies.

  Therefore, since it can oscillate in the microwave region, it can contribute to the practical application of various devices using millimeter waves, such as millimeter wave radars and superheaters using millimeter waves.

It is sectional drawing which shows the structure of the microwave oscillation element concerning the 1st Embodiment of this invention. It is a figure which shows the manufacturing process of the microwave oscillation element shown in FIG. (A) is a figure which shows the structure of the microwave oscillation apparatus provided with the microwave oscillation element shown in FIG. 1, (b) is a part of structure of the microwave oscillation apparatus shown to (a). It is a figure shown in detail. It is sectional drawing which shows the structure of the microwave oscillation element concerning the 2nd Embodiment of this invention. It is a figure which shows the manufacturing process of 2nd Embodiment microwave oscillation element shown in FIG. It is sectional drawing which shows the other structure of the microwave oscillation element concerning the 2nd Embodiment of this invention. It is sectional drawing which shows the structure of the microwave oscillation element concerning the 3rd Embodiment of this invention. It is sectional drawing which shows the other structure of the microwave oscillation element concerning the 3rd Embodiment of this invention. It is a figure explaining the principle of the microwave oscillation element concerning the 3rd Embodiment of this invention. It is a figure which shows the manufacture process of the microwave oscillation element of 3rd Embodiment shown in FIG. It is a figure for demonstrating the principle of the microwave oscillation element using a spin torque. (A) * (b) is sectional drawing shown about the structure of the microwave oscillation element of a prior art. FIG. 13 is a cross-sectional view showing a state in which a plurality of the conventional microwave oscillation elements shown in FIGS. 12A and 12B are used and connected in parallel.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1a Microwave oscillator 1b * b 'Microwave oscillator 1c Microwave oscillator 10a 1st electrode 10b 2nd electrode 11 Antiferromagnetic material layer 11a 1st antiferromagnetic material layer 11b 2nd antiferromagnetic material Body layer 12 magnetization fixed layer 12a first magnetization fixed layer 12b second magnetization fixed layer 13 intermediate layer 14 magnetization free layer 15 insulator layer 16 conductive nanoparticles 17 electrode layer 18 nanocontact 19 substrate 20 insulating film 21 contact hole 22 Intermediate Layer 24 Magnetization Free Layer 25 Insulator Layer 26 Magnetic Nanoparticle 31 Current 32 Electron 51 Power Supply Unit 52 Frequency Variable Unit 53 Signal Amplifying Unit 54 AC Signal 56 External Magnetic Field Generation Unit 60 Microwave Oscillator Bs Saturation Magnetization V1 to V4 Power Supply

Claims (15)

Between the first electrode and the second electrode,
A magnetization fixed layer with a fixed magnetization direction;
A non-magnetic or insulating intermediate layer;
A magnetization free layer capable of changing the magnetization direction,
The intermediate layer is sandwiched between the magnetization fixed layer and the magnetization free layer,
In the microwave oscillation device configured to allow a current to flow from the first electrode to the second electrode via the magnetization fixed layer, the intermediate layer, and the magnetization free layer,
The current path has a plurality of nanoparticles for making the density of the current flowing in a predetermined region in the magnetization free layer higher than the density of the current flowing in a region other than the predetermined region. A microwave oscillation element characterized by the above. The nanoparticles are conductive nanoparticles,
The second electrode has an electrode layer and a connection layer in which the nanoparticles are surrounded by an insulator,
The microwave oscillation element according to claim 1, wherein the nanoparticles are in electrical contact with the electrode layer and the magnetization free layer. The microwave oscillation element according to claim ² , wherein a contact area of the nanoparticles between the electrode layer and the magnetization free layer is more than 0 and 4900 nm ² or less.   The microwave oscillation element according to claim 3, wherein the contact area is greater than 0 and equal to or less than 70 nm x 70 nm.   5. The device according to claim 1, wherein the first electrode, the magnetization fixed layer, the intermediate layer, the magnetization free layer, and the second electrode are provided in this order. The microwave oscillation element of description.   The microwave oscillation element according to claim 1, wherein the nanoparticles are metal nanoparticles. The nanoparticles are magnetic nanoparticles,
The magnetization free layer has a configuration in which the magnetic nanoparticles are surrounded by an insulator,
The microwave oscillation element according to claim 1, wherein the magnetic nanoparticles are in contact with the second electrode and the intermediate layer. The nanoparticles are magnetic nanoparticles,
The magnetization free layer has a configuration in which the magnetic nanoparticles are surrounded by an insulator,
The magnetization fixed layer includes a first magnetization fixed layer and a second magnetization fixed layer whose magnetization directions are opposite to each other,
The magnetization free layer is configured to be sandwiched between the first magnetization fixed layer and the second magnetization fixed layer via the intermediate layer,
The microwave oscillation element according to claim 1, wherein the magnetic nanoparticles are in contact with the intermediate layers.   The microwave oscillation element according to claim 7 or 8, wherein the magnetic nanoparticles have a diameter of more than 0 and 100 nm or less.   10. The microwave oscillation device according to claim 1, further comprising an antiferromagnetic layer between the first electrode and the fixed magnetization layer. 11.   An antiferromagnetic layer is provided between the second electrode and the second magnetization fixed layer and between the first magnetization fixed layer and the first electrode. The microwave oscillation device according to claim 9 or 10.   A microwave oscillation device comprising a frequency variable unit having the microwave oscillation element according to any one of claims 1 to 11 and an external magnetic field generation unit. Between the first electrode and the second electrode, a magnetization fixed layer whose magnetization direction is fixed, an intermediate layer that is a non-magnetic material or an insulator, and a magnetization free layer that can change the magnetization direction And the intermediate layer is sandwiched between the magnetization fixed layer and the magnetization free layer, and the second electrode passes through the magnetization fixed layer, the intermediate layer, and the magnetization free layer from the first electrode. A method of manufacturing a microwave oscillation device configured to allow current to flow through an electrode,
A conduction step of causing the second electrode having the electrode layer and the magnetization free layer to be adjacent to each other and electrically conducting each other;
The conduction step is
A particle forming step of forming a plurality of conductive nanoparticles on one of the magnetization free layer and the electrode layer;
An insulator forming step of covering at least a part of the surface of the conductive nanoparticles formed by the particle forming step with an insulator;
In order to electrically connect the other layer of the magnetization free layer and the electrode layer and the conductive nanoparticles, a part of the insulator formed in the insulator formation step is removed. An exposure step of exposing the surface of the conductive nanoparticles. Between the first electrode and the second electrode, a magnetization fixed layer whose magnetization direction is fixed, an intermediate layer that is a non-magnetic material or an insulator, and a magnetization free layer that can change the magnetization direction And the intermediate layer is sandwiched between the magnetization fixed layer and the magnetization free layer, and the second electrode passes through the magnetization fixed layer, the intermediate layer, and the magnetization free layer from the first electrode. A method of manufacturing a microwave oscillation device configured to allow current to flow through an electrode,
Including a magnetization free layer forming step of forming the magnetization free layer,
The magnetization free layer forming step includes
A particle forming step of forming a plurality of magnetic nanoparticles on the second electrode or the intermediate layer;
An insulator forming step of covering at least a part of the surface of the magnetic nanoparticles formed by the particle forming step with an insulator;
And a exposing step of exposing a surface of the conductive nanoparticles by removing a part of the insulator formed in the insulator forming step. Between the first electrode and the second electrode, a magnetization fixed layer whose magnetization direction is fixed, an intermediate layer that is a non-magnetic material or an insulator, and a magnetization free layer that can change the magnetization direction And the intermediate layer is sandwiched between the magnetization fixed layer and the magnetization free layer, and the second electrode passes through the magnetization fixed layer, the intermediate layer, and the magnetization free layer from the first electrode. A method of manufacturing a microwave oscillation device configured to allow current to flow through an electrode,
A material containing an insulator matrix and a raw material of magnetic nanoparticles is applied on any one of the second electrode and the magnetization fixed layer, and the magnetic nanoparticles are converted into the magnetization fixed layer by the insulator matrix. Forming magnetic nanoparticles from the raw material so as to be spaced apart from each other, and forming the intermediate layer and the magnetization free layer;
And a step of exposing the surface of the conductive nanoparticles by removing the insulator on at least a part of the surface of the magnetic nanoparticles formed by the step. .

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