JP4139348B2 - Element using carrier-induced ferromagnet or high-frequency element - Google Patents

Description

  The present invention relates to a method for controlling a ferromagnetic resonance frequency using a carrier-induced ferromagnet, and more particularly to a microwave device using a ferromagnetic resonance frequency that changes based on carrier control using a magnetic semiconductor.

  2. Description of the Related Art In recent years, electronic devices have been remarkably developed, and with their digitization / IC conversion, mutual interference in the circuit due to noise generated by the electronic circuit, or influence on other electronic devices has become a major problem. As a countermeasure, an inductance component is used as a filter to increase a high frequency impedance Z value, thereby attenuating a noise component including a high frequency component and transmitting only a low frequency signal component. In response to the demand for miniaturization of electronic components with miniaturization of electronic circuits, chip inductors in which ferrite layers and coil conductors are alternately printed and laminated are used. Ferrite-based materials have a low saturation magnetic flux density, but their electrical resistivity is much higher than that of metal-based materials, and magnetic losses due to eddy currents are relatively small up to high frequencies.

Therefore, the magnetic permeability is maintained up to a high frequency. Ferrite materials are also used as noise filters of 10 MHz or higher because they have the advantage that they can be easily made in complex shapes and are low in cost. Since ferromagnetic resonance of the ferromagnetic material occurs in the frequency band of the GHz band, it can be used as an element operating in the microwave band (see, for example, Patent Document 1). Recently, proposals have also been made regarding high-frequency notch filters using ferromagnetic resonance in ferromagnetic materials.
Japanese Patent Laid-Open No. 08-250334 Gary A. Prinz, “Hybrid Ferromagnetic-semiconductor Structure” Science vol.250, p.1092 (1990).

  In recent years, high-frequency communication such as wireless LAN has become mainstream among communication technologies. In a wireless LAN, a high frequency band such as 2.4 GHz band or 5 GHz band is used, and a high frequency ferrite (which is suitable for noise suppression in the vicinity of 300 MHz) that has been conventionally used is not sufficient as a high frequency filter for noise suppression. is there. This is because high-frequency ferrite has a small spontaneous magnetization in a zero magnetic field in ferrimagnetism.

  In addition, as described above, even in the case of an element using the resonance frequency of ferromagnetic resonance in an element using a conventionally proposed metal ferromagnet, the resonance frequency is determined by the g factor, magnetization, magnetic anisotropy, It is a unique value determined by an external magnetic field, and the resonance frequency can be controlled only by the magnetic field and temperature.

  An object of the present invention is to provide a microwave device effective for noise countermeasures at high frequencies such as the GHz band. Another object of the present invention is to provide a frequency filter that can modulate the resonance frequency by external control.

  The element according to the present invention includes a carrier-induced ferromagnet and control means for performing control to modulate the carrier concentration of the carrier-induced ferromagnet. By modulating the carrier concentration, the ferromagnetic resonance frequency can be controlled. In order to control the ferromagnetic resonance frequency, the anisotropic magnetic field of the carrier-induced ferromagnet is modulated, or the magnetization of the carrier-induced ferromagnet is modulated. The carrier-induced ferromagnet adjusts the material and the carrier concentration so as to appear near the operating temperature, or uses paramagnetism.

  The high-frequency element according to the present invention includes a carrier-induced ferromagnet and a control unit that controls a resonance frequency that depends on an anisotropic magnetic field and magnetization when the DC magnetic field is substantially constant. Since the anisotropic magnetic field changes due to the change in magnetization, the resonance frequency changes continuously as a function of the electric field. The carrier-induced ferromagnet is a ferromagnetic semiconductor obtained by adding a magnetic element to a semiconductor. The control means is means for applying an electric field or irradiating light to the ferromagnetic semiconductor.

  The filter element according to the present invention is a ferromagnetic semiconductor having uniaxial anisotropy, and has a fine wire structure extending in the same direction as the uniaxial anisotropy, and the ferromagnetic semiconductor And a control means for performing control for modulating the carrier concentration.

  ADVANTAGE OF THE INVENTION According to this invention, the microwave element of GHz band which can control a ferromagnetic resonance frequency electrically and optically can be provided. Since the anisotropic magnetic field is large, even a zero magnetic field can be used in the high frequency region.

In this specification, the carrier-induced ferromagnet refers to a ferromagnet in which the concentration of the magnetic metal added to the magnetic semiconductor is adjusted to a concentration suitable for expressing carrier-induced ferromagnetism. Magnetization is the value per unit of magnetic moment induced by an external magnetic field. Magnetization causes Larmor precession at a frequency proportional to the effective magnetic field. FIG. 1 is a diagram illustrating the principle of a ferromagnetic resonance phenomenon of a ferromagnet based on Larmor precession. As shown in FIG. 1, when an effective magnetic field H _eff is applied to the ferromagnetic material F, the magnetization M rotates around the effective magnetic field H _eff based on the torque T determined by the effective magnetic field H _eff and the magnetization M. When the ferromagnetic material F gives a high frequency magnetic field (field modulation) H _AC, so-called ferromagnetic resonance phenomenon precession continues to occur. In other words, in a state where a certain external magnetic field H _eff is applied to the ferromagnetic material F, a so-called filtering effect of absorbing a high frequency of a specific frequency is exhibited. This frequency is called the resonance frequency and is represented by ω.

ここで、γはジャイロ係数と呼ばれる係数である。
（１）式より、次の（２）式が導入される。

Here, γ is a coefficient called a gyro coefficient.
From the formula (1), the following formula (2) is introduced.

Here, _Han is _an anisotropic magnetic field based on the anisotropy of a single crystal. That is, it can be seen that a ferromagnetic single crystal film can be used as a high-frequency notch filter. From equation (2), the resonance frequency ω can be controlled by externally applied magnetization (the magnetic flux density generated by the crystal), that is, the resonance frequency and the on / off of the filter are controlled by the external magnetization direction. You can see that

In addition to the above knowledge, the inventor can use carrier-induced ferromagnets, in which ferromagnetism is induced by carriers, that is, magnetic semiconductors, to modulate the carrier concentration by external control means. Since the isotropic magnetic field _Han and the magnetization M can be changed, it was considered that the ferromagnetic resonance frequency can be controlled. The external control means is, for example, an electric field or light irradiation. By changing the magnitude of magnetization or anisotropy by electric field or light irradiation, the ferromagnetic resonance frequency can be controlled electrically and optically over a wide range. The magnetization value of the ferromagnetic semiconductor is smaller than the magnetization value of the ferromagnetic metal. However, since the anisotropic magnetic field is relatively large, it can be applied in a high frequency region even with a zero magnetic field. .

  Based on the above consideration, the ferromagnetic resonance frequency control method and the high-frequency filter element according to the embodiment of the present invention will be described with reference to the drawings. First, as an applicable material, a magnetic semiconductor in which ferromagnetism is induced by carriers is used. For example, a magnetic semiconductor in which a magnetic atom (transition metal or rare earth metal) is added to a III-V group compound semiconductor such as GaAs, InAs, or GaN. It is also possible to use a ferromagnetic semiconductor in which a magnetic atom (transition metal or rare earth metal) is added to a group IV semiconductor such as Si or Ge. Furthermore, a ferromagnetic semiconductor obtained by adding a magnetic element (transition metal or rare earth metal) to a II-VI group semiconductor may be used. The concentration of the magnetic element to be added is a concentration suitable for expressing carrier-induced ferromagnetism.

  Next, an outline of the element structure will be described. The structure of the ferromagnetic resonance control element according to the present embodiment has the following configuration, for example. Detailed configuration will be described in the following examples.

1) A ferromagnetic semiconductor multilayer structure in which an insulating semiconductor layer is stacked on a conductive or semi-insulating substrate, and the above-described ferromagnetic semiconductor is stacked on the insulating semiconductor layer. 2) The ferromagnetic semiconductor multilayer structure is produced by a thin film production technique such as molecular beam epitaxy, metal organic vapor phase epitaxy, or sputtering. 3) An insulating layer is stacked on the ferromagnetic semiconductor layer. 4) A gate electrode (electric field applying means) as a control means by an electric field or a light irradiation device as a control means by light is provided. In the high frequency filter element, a conductive substrate is used, and a strip line structure having a parallel metal plate structure composed of a conductive substrate and a gate electrode is formed.

Since the resonance frequency ω of the carrier-induced ferromagnet depends on _Han and M, by modulating the carrier concentration of the carrier-induced ferromagnetic semiconductor by a control means that can control the carrier concentration, the resonance frequency ω is Can be changed. For example, if the carrier concentration is controlled to increase, _Han and M increase. Accordingly, the resonance frequency ω is also increased. When the control is performed so that the carrier concentration is lowered, the resonance frequency ω is reduced. The control means is not particularly limited as long as the carrier concentration can be controlled, but an element with good controllability can be easily formed by using the means listed in the following examples. .

  As described above, the resonance frequency can be modulated by modulating the carrier concentration of the carrier-induced ferromagnetic semiconductor by the control means capable of controlling the carrier concentration. At this time, absorption at a desired frequency can be caused by changing the control amount by the control means. That is, a frequency filter that can be controlled from the outside can be configured.

The first embodiment relates to a technique for controlling a ferromagnetic resonance frequency by a field effect, for example, a technique for controlling a ferromagnetic resonance frequency by a field effect using GaMnAs. FIG. 2 is a schematic cross-sectional view showing a cross-sectional structure of the ferromagnetic resonance control element according to this embodiment. As shown in FIG. 2, the ferromagnetic resonance control device according to the first embodiment, for ^example, n i-Ga on the conductive or GaAs semi-insulating substrate 1 made of _{+ -GaAs-1 y Al y As} (0 ≦ y ≦ 1: y is omitted in the figure, the same applies hereinafter), and then a ferromagnetic semiconductor (a semiconductor in which GaAs is doped with Mn, which is a magnetic element) Ga _1-x Mn _x It has a multilayer structure in which a thin film 5 of an As layer (x is omitted in the figure, the same applies hereinafter) is laminated thereon. The Mn concentration x in the GaAs layer is x ≧ 0.03, which is a concentration indicating metallic electrical conduction. An insulating film such as Al ₂ O ₃ or SiO ₂ is formed on the Ga _1-x Mn _x As layer 5. As the insulating layer 7, an insulating semiconductor thin film, for example, an undoped AlGaAs layer (insulating layer) may be stacked on the Ga _1-x Mn _x As layer 5. A metal electrode (made of Au, Al, etc.) 11 for applying an electric field is formed on the insulating film 7. The structure shown in FIG. 2 can be manufactured by a general method such as a molecular beam epitaxy method (MBE method), a metal organic chemical vapor deposition method (MOCVD method), or a sputtering method. When a conductive substrate is used, the substrate is grounded, and when a semi-insulating substrate is used, the Ga _1-x Mn _x As layer 5 is grounded.

  A resonance control method of the ferromagnetic resonance control element having the above structure will be described below. First, a DC magnetic field is applied in the magnetization (easy axis) direction ([110]). The DC magnetic field may be zero. Next, the element is irradiated with microwaves. When the electric field vector is parallel to the magnetization (the magnetic field is perpendicular), it is coupled with the magnetization, and when the electric field vector is orthogonal to the magnetization, it is not coupled with the magnetization. Microwave absorption occurs at a resonance frequency ω (equation (2)) determined by an external magnetic field, magnetization, and anisotropy constant.

In addition, (2) Formula is a formula when it has uniaxial anisotropy and a magnetic field is applied in the easy axis direction. Assuming simple uniaxial anisotropy ([110] easy axis) (H _an = 2K _u / M, a = 2.2 × 10 ⁵ m / As), 4 GHz (H _an ≈0. 2T, K _u ≈5 × 10 ³ Jm ⁻³ , and M≈0.07T (Mnx = 0.05)). Here, the value of magnetization is changed by applying an electric field to the element. It can be modulated from a ferromagnetic state to a paramagnetic state by an electric field. Note that in the zero magnetic field, M = 0 to N _m gμ _B S _m (N _m : concentration of magnetic element, g: g factor of magnetic element, μ _B : Bohr magneton, S _m : magnetic moment of magnetic element). Due to the change in magnetization, the anisotropic magnetic field and the demagnetizing field in the equation (2) change, and the resonance frequency continuously changes as a function of the electric field. This is shown in FIG. 3 and FIG.

As shown in FIG. 3, when the electric field is changed from E = 0 to E ₁ to E ₄ (E ₁ and E ₂ are negative, and E ₃ and E ₄ are positive), the electric field depends on the applied electric field. Thus, the frequency position of the transmittance notch decreases (ω ₃ , ω ₄ ) or increases (ω ₁ , ω ₂ ), respectively. FIG. 4 is a diagram illustrating the relationship between the electric field E and the resonance frequency. As shown in FIG. 5, the resonance frequency ω decreases almost monotonously with respect to the electric field E, and the resonance frequency can be controlled based on the electric field E. Note that in a state in which a strong positive electric field is applied and no ferromagnetism is present (M = 0), resonance cannot be obtained with a zero magnetic field, and in this case, the state is turned off. In the first embodiment, GaMnAs is used as the ferromagnetic semiconductor. However, even if another ferromagnetic semiconductor, for example, InMnAs, is used, the ferromagnetic resonance frequency can be controlled by the field effect. For example, when a paramagnetic semiconductor in which GaMnAs is doped with electrons and the hole concentration in GaMnAs is effectively reduced is used, ferromagnetism develops when a negative electric field is applied in an off state (M = 0) when no electric field is applied. Then, the on state (M ≠ 0) is established, and resonance occurs. In the on state, the resonance frequency can be controlled by the electric field. The paramagnetic state is a paramagnetic state at the operating temperature by adding holes of n-type impurities such as Sn, Si, and GaTe to compensate for holes and lowering the hole concentration during preparation under the sample preparation conditions exhibiting ferromagnetism. Can be realized.

Next, a second embodiment of the present invention will be described. 2nd Example is an Example regarding the control technique of the ferromagnetic resonance frequency by light irradiation using GaMnAs. A configuration example of the ferromagnetic resonance control element according to the present embodiment is shown in FIG. Basically, the structure is the same as that shown in FIG. 2, but since GaMnAs is irradiated with light instead of voltage, SiO ₂ and Au are not required. That is, for ^example, by laminating the insulating layer 23 made of _{i-Ga 1-y} on the conductive or GaAs semi-insulating substrate 21 made of _{n + -GaAs Al y As (0} ≦ y ≦ 1), then the ferromagnetic A semiconductor (a semiconductor in which GaAs is doped with Mn as a magnetic element) has a multilayer structure in which a thin film 25 of a Ga _1-x Mn _x As layer is stacked thereon.

Next, the operation of the ferromagnetic resonance control element will be described. First, a DC magnetic field is applied in the magnetization (easy axis) direction ([110]). The DC magnetic field to be applied may be a zero magnetic field. Next, the ferromagnetic semiconductor is irradiated with microwaves. When the electric field vector generated by the microwave is parallel to the magnetization (the magnetic field is orthogonal), it is combined with the magnetization, and when the electric field vector is orthogonal (parallel to the magnetic field), it is not combined with the magnetization. Thereby, the absorption of the microwave of the resonance frequency (the above-mentioned formula (2)) determined by the external magnetic field H, the magnetization M, and the anisotropy constant occurs. In addition, (2) Formula has a uniaxial anisotropy, and is a formula at the time of applying a magnetic field to an easy axis direction. Here, if simple uniaxial anisotropy ([110] easy axis) is assumed (H _an = 2K _u / M, γ = 2.2 × 10 ⁵ m / As), 4 GHz (H _an ≒ 0.2T, K _u ≈5 × 10 ³ Jm ⁻³ , M≈0.07T (Mnx = 0.05). By generating carriers (holes) by light irradiation, the value of magnetization increases and the demagnetizing field changes as the ferromagnetic interaction between Mn increases. The change in carrier concentration (2) anisotropic magnetic field H _an, also the resonance frequency ω is changed to change of absorption occurs frequency continuously varies as a function of the irradiation light intensity.

6 and 7 are diagrams illustrating absorption characteristics (transmittance) with respect to different light irradiation intensities P. FIG. As shown in FIG. 6, the frequency at which the notch of the transmittance corresponding to the resonance frequency ω is different at P = 0, P ₁ , P ₂ , and the resonance frequency ω is controlled by the intensity of the irradiated light (ω ₀ , ω ₁ , ω ₂ ). FIG. 7 is a diagram showing the relationship of the resonance frequency with respect to the light intensity P. In FIG. As shown in FIG. 7, it can be seen that the resonance frequency ω can be controlled by the light intensity P. If a paramagnetic element whose hole concentration is lowered by adding an n-type impurity is used, it can be modulated from paramagnetism (M = 0, off state) to ferromagnetism (M ≠ 0, on state) by light irradiation. In the ferromagnetic state, the ferromagnetic resonance frequency can be controlled by light irradiation.

  As described above, according to this example, it was found that the carrier can be modulated by the irradiation light and the resonance frequency of the ferromagnetic material can be controlled. For example, even when InMnAs is used, ferromagnetic resonance frequency control by light irradiation can be performed in the same manner.

  Next, a third embodiment of the present invention will be described with reference to the drawings. The present embodiment relates to a notch filter element that can operate at a microwave frequency, and is a notch filter element that can control the absorption frequency over a wide range by a field effect using the above-described ferromagnetic resonance control element. is there.

FIG. 8 is a perspective view showing a configuration example of the notch filter element according to the present embodiment. As shown in FIG. 8, a conductive substrate (e.g., ⁿ + -GaAs) over 41, the insulating layer _{(undoped (i) -Ga 1-} y Al y As (0 ≦ y ≦ 1) layer) 43 was laminated, A multilayer structure in which a Ga _1-x Mn _x As thin film 45 is laminated thereon is formed. The Mn concentration x to be added is x ≧ 0.03 indicating metallic electrical conduction. Next, the direction of magnetization is controlled by processing the microstrip line into a thin line. By processing into a fine line shape and increasing the aspect ratio, the magnetization M is directed in the direction in which the fine line extends. Here, the magnetization M can be directed in a specific direction (thin line direction) by utilizing the magnetic anisotropy unique to GaMnAs. For example, if a sample having a high carrier concentration is selected, the uniaxial anisotropy between [110] / [11-0] is dominant. Using this, a fine line is produced in the [110] direction. An insulating film 46 is formed on the Ga _1-x Mn _x As layer 45 (Al ₂ O ₃ , SiO _2, etc.). Alternatively, GaMnAs layer 45 insulating semiconductor thin film on (e.g. _{undoped (i) -Ga 1-y} Al y As (0 ≦ y ≦ 1)) may be stacked. Next, a metal electrode (Au or Al or the like) 47 for applying an electric field is formed on the insulating semiconductor thin film layer 46. An electrode material may be formed on the GaMnAs thin film 45, and the electrode material and GaMnAs may be processed simultaneously to form a fine line. Next, electrodes E1 and E2 are formed at both ends of the strip line made of the GaMnAs layer 45, and then, for example, a coaxial cable 51 is connected to guide microwaves.

  In the above structure, by applying an electric field to the GaMnAs layer 45 by the metal electrode 47, the carrier concentration in the GaMnAs is modulated and the resonance frequency ω is adjusted, thereby filtering high frequency signals passing through the coaxial cable 51. It can be performed. The high-frequency filter element can also be manufactured using InMnAs, for example.

  As described above, according to the embodiment or example of the present invention, it is possible to obtain a notch filter that operates with microwaves and that can control an absorption frequency over a wide range by a field effect or light irradiation.

  The present invention can be applied to a GHz band notch filter, a microwave switching element, or the like that cuts noise of a specific frequency.

It is a figure which shows the principle of the ferromagnetic resonance phenomenon of the ferromagnetic material based on a Larmor precession. It is a figure which shows the example of the layer structure of the element by 1st Example of this invention. It is a figure which shows the frequency dependence of the transmittance | permeability of the element by 1st Example about a different electric field. It is a figure which shows the electric field dependence of the resonant frequency of the element by 1st Example. It is a figure which shows the example of the layer structure of the element by 2nd Example of this invention. It is a figure which shows the frequency dependence of the transmittance | permeability of the element by 2nd Example about different light intensity. It is a figure which shows the optical intensity dependence of the resonant frequency of the element by 2nd Example. It is a perspective view which shows the structural example of the notch filter element by 3rd Example of this invention.

Explanation of symbols

1 ... GaAs semi-insulating substrate, 3: insulating layer, a thin film of _{5 ... Ga 1-x Mn x} As layer, 7 ... insulating film, 11 ... metal electrodes for electric field application, 21 ... GaAs semi-insulating substrate, 23 ... Insulating layer, 25 ... Ga _1-x Mn _x As thin film, 41 ... conductive substrate, 43 ... insulating layer, 45 ... Ga _1-x Mn _x As thin film, 46 ... insulating semiconductor thin film layer, 47 ... Metal electrode for electric field application, 51 ... Coaxial cable.

Claims (9)

A ferromagnetic semiconductor having uniaxial anisotropy and having a thin wire structure extending in the same direction as the uniaxial anisotropy;
An element or a high-frequency element having control means for controlling the carrier concentration in the ferromagnetic semiconductor. A ferromagnetic semiconductor having uniaxial anisotropy and having a thin wire structure extending in the same direction as the uniaxial anisotropy;
Element or a high frequency device and a control means for controlling for modulating the magnetization ferromagnetic semiconductor anisotropy field at a carrier concentration. A ferromagnetic semiconductor having uniaxial anisotropy and having a thin wire structure extending in the same direction as the uniaxial anisotropy;
An element or a high-frequency element having control means for controlling a resonance frequency of the ferromagnetic material depending on an anisotropic magnetic field and magnetization at a substantially constant temperature by carrier concentration modulation . A ferromagnetic semiconductor having uniaxial anisotropy and having a thin wire structure extending in the same direction as the uniaxial anisotropy;
An element or a high-frequency element having control means for controlling the resonance frequency depending on the anisotropic magnetic field and the magnetization by carrier concentration modulation when the DC magnetic field is substantially constant. The element or high-frequency element according to any one of claims 1 to 4, wherein the carrier-induced ferromagnet is a ferromagnetic semiconductor obtained by adding a magnetic element to a semiconductor. 6. The element or high-frequency element according to claim 5 , wherein the control means is means for controlling the ferromagnetic semiconductor so as to modulate a carrier concentration in the ferromagnetic semiconductor. The element or high-frequency element according to any one of claims 1 to 6, wherein the control means is means for applying an electric field or irradiating light to the ferromagnetic semiconductor. A conductive substrate;
A first insulating layer formed on the substrate;
A laminated structure of a carrier-induced ferromagnetic layer formed on the first insulating layer, a second insulating layer formed on the ferromagnetic layer, and a conductive layer formed on the insulating layer. A laminated structure having a thin wire structure extending in the same direction as the uniaxial anisotropy of the ferromagnetic layer;
First and second electrodes respectively formed on both ends of the thin wire;
Means for applying high frequency power between the first electrode and the second electrode;
An element or a high-frequency element comprising input means for inputting at least one of application of an electric field and irradiation of light to the stacked structure. The element or high-frequency element according to any one of claims 1 to 8, wherein the carrier-induced ferromagnet changes from a paramagnetic semiconductor to a carrier-induced ferromagnet by controlling the carrier concentration.

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