JP5280516B2 - Radio demultiplexer - Google Patents

Description

  The present invention relates to a radio wave demultiplexer using spin torque.

  In recent years, magnetic random access memory (MRAM) has been attracting attention as the possibility of replacing conventional dynamic random access memory (DRAM). In addition, the magnetization of the free layer can be reversed without using a magnetic field by simply passing a current of a certain level or more through a giant magnetoresistive (GMR) film or tunnel magnetoresistive (TMR) film used in a magnetic read head. This is theoretically shown in, for example, Journal of Magnetism and Magnetic Materials, 159, L1-6 (1996). Thereafter, for example, Physical Review Letters, Vol.84, No.14, pp.2149-2152 (2000) describes a diameter of 130 nm including a Co / Cu / Co multilayer film (GMR film) between two Cu electrodes. An example of a recording method in which the magnetization of the Co layer is reversed using spin torque applied to the magnetization of the Co layer from the spin of current flowing in the pillar is reported. Furthermore, as described in Applied Physics Letters, Vol. 84, pp. 2118-2120 (2004), spin torque magnetization reversal has been demonstrated using a nanopillar using a TMR film. In particular, spin torque magnetization reversal using a TMR film has attracted much attention because an output equivalent to or higher than that of a conventional MRAM can be obtained.

Recently, a method of using the spin torque effect for microwave band oscillation and reception has attracted attention. For example, a current I _dc smaller than the current required for the free layer to reverse the spin torque magnetization flows at both ends of the magnetoresistive effect element to excite precession in the magnetization of the free layer. For example, Nature, Vol. 425, pp. 382-385 (2003) proposed a spin torque oscillator that excites an alternating voltage at both ends of a device through a resistance effect. Furthermore, a new element called a spin torque diode, in which an alternating current with a GHz class frequency is passed through a magnetoresistive effect element via a bias T and a DC voltage V _dc is extracted, is disclosed in Nature, Vol. 438, pp.339, for example. -342 (2005). Since the size of these elements is as small as the μm class, it is expected to be applied to an extremely small size oscillator / receiver.
Journal of Magnetism and Magnetic Materials, 159, L1-6 (1996) Physical Review Letters, Vol.84, No.14, pp.2149-2152 (2000) Applied Physics Letters, Vol.84, pp.2118-2120 (2004) Nature, Vol.425, pp.382-385 (2003) Nature, Vol.438, pp.339-342 (2005) Nature Physics, Vol.4, pp.803-809 (2008)

  However, the conventional oscillator / receiver using spin torque has the following problems. First, the oscillator has a problem that the output is small. In the spin torque oscillator using the giant magnetoresistive effect that was originally proposed, the output was only a few nW. Recently, it was reported in Nature Physics, Vol.4, pp.803-809 (2008) that a μW class output was obtained using a tunnel magnetoresistive effect element using MgO as a barrier layer. However, in order to further increase the output, a tunnel magnetoresistive effect element having a magnetoresistance ratio exceeding 1000% is required, which is considered to be very difficult to realize. In addition, in order to use the spin torque effect as an oscillator, it is necessary to control the oscillation frequency with extremely high accuracy, but in reality, it is not easy to control the oscillation frequency due to the influence of variations in material characteristics and element shapes. . Therefore, it is considered industrially impractical to apply the spin torque effect to an oscillator.

  On the other hand, a spin torque diode can take out a direct-current voltage with high-frequency alternating current as an input, and thus can be used as a kind of receiver. However, since it is difficult to control the reception frequency with high accuracy, it is difficult to use the reception frequency as it is.

  The present invention provides an industrially producible receiver and radio wave demultiplexer that apply the spin torque effect.

  A radio wave demultiplexer according to the present invention includes a single bit line in which a direct current source and an antenna are connected in parallel, and a nonmagnetic layer, a fixed layer made of a ferromagnetic material, and a free layer made of a ferromagnetic material, respectively. A plurality of magnetoresistive effect elements connected to the bit line, a plurality of source lines connected to the plurality of magnetoresistive effect elements, and a plurality of source lines connected to the plurality of source lines, respectively. Amplifiers, mixers that mix the outputs of multiple amplifiers, multiple digit lines for applying magnetic fields independently to the free layers of multiple magnetoresistive elements, and a predetermined current applied to each digit line And a memory storing the magnitude of the current applied to the digit line. The direct current source supplies each of the free layers of the magnetoresistive effect element with a current that does not cause magnetization reversal due to the spin torque effect.

The magnetization directions of the fixed layer and the free layer of the magnetoresistive element are substantially perpendicular. The magnetoresistive element can be a tunnel magnetoresistive element or a giant magnetoresistive element. Further, the magnetic resonance frequency f _i of the i-th magnetoresistive element is used as the magnetic field of magnitude H _i generated by the current flowing through the digit line disposed adjacent to the i-th magnetoresistive element. To set.

  According to the present invention, it is possible to configure a small-sized radio wave demultiplexer that applies the spin torque effect and can easily control the reception frequency.

It is a figure which shows the electromagnetic wave duplexer of this invention which applied the spin torque effect. It is a figure which shows the basic structure of the magnetoresistive effect element which comprises a splitter. It is a model diagram of an element including a digit line for adjusting the resonance frequency of the magnetoresistive effect element. It is a figure which shows the relationship between the resonance frequency of a magnetoresistive effect element, and the magnitude | size of an applied magnetic field. It is a figure which shows the example of a setting of the resonant frequency. It is a figure which shows the planar shape of a magnetoresistive effect element.

Explanation of symbols

1 Current Driver 2 Memory 3 Digit Line 4 DC Power Supply 5 Inductance 6 Capacity 7 Antenna 8 Bit Line 9 Magnetoresistive Element 10 Amplifier 21 Radio Wave 22 Bias T
23 Free layer 24 Barrier layer 25 Fixed layer 31 Magnetic field generated by digit line current 32 Metal plate 33 Source line

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Although a giant magnetoresistive element can be used as the magnetoresistive element, an example using a tunnel magnetoresistive element capable of obtaining a large output will be described below.

  FIG. 1 shows a circuit diagram of a radio wave demultiplexer to which a spin torque according to the present invention is applied. 1 is a current driver, 2 is a memory for storing the magnitude of a current flowing through a digit line, 3 is a digit line through which a current for generating a magnetic field applied to the magnetoresistive effect element is passed, 4 is a direct current source, and 5 is a direct current Inductance to be passed, 6 is a capacity for passing only alternating current, 7 is an antenna, 8 is a bit line, 9 is a magnetoresistive effect element, 10 is an amplifier, and 11 is a mixer. FIG. 2 is a diagram showing the portion of the magnetoresistive effect element in more detail. 21 is a radio wave, 22 is a bias T composed of an inductance 5 and a capacitor 6, 23 is a free layer in which magnetization precesses due to the spin torque effect, 24 is a barrier layer, 25 is the direction of magnetization, and the magnetization of the free layer It is a fixed layer fixed perpendicular to the direction. The direct current source 4 supplies a direct current of a magnitude that does not cause magnetization reversal due to the spin torque effect to each free layer 23 of the magnetoresistive effect element. FIG. 3 is a schematic diagram of an actual device. The magnetoresistive effect element 9 is formed between the bit line 8 and the metal plate 32. A digit line 3 for generating a magnetic field 31 to be applied to the free layer 23 is formed immediately below the magnetoresistive effect element 9 in a direction perpendicular to the bit line. A signal generated by the magnetoresistive effect element 9 is guided to the amplifier 10 manufactured in the peripheral portion of the receiving device body through the source line 33.

The operation of the duplexer of the present invention will be described below. A radio signal to be received is first caught by an antenna 7 outside the receiver. This radio signal is a signal in which information such as a video signal and an audio signal is superimposed at a lower frequency on a high frequency of a preset frequency f (frequency band is usually set to 1 to 30 GHz). The direct current generated by the direct current source 4 is superimposed on the signal received by the antenna 7 via the capacitor 6 and the inductance 5 at the bias T 22 and guided to the bit line 8. This signal current is applied to all the magnetoresistive effect elements 9 from the bit line 8 to the channels 1 to n. At this time, both ends of the tunnel magnetoresistive element 9 of the channel i (i = 1 to n)
V _i = I _i sin (2πf _i t) × ΔR · sin (2πf _i t + φ)
In the voltage V _j represented it is excited by the spin torque effect. Here, f _i is the ferromagnetic resonance frequency of the free layer of the magnetoresistive effect element connected to the i-th channel, φ is the phase difference between the input signal and the ferromagnetic resonance vibration, and I _i is generated by a DC power source. After the direct current I is divided into n channels, the value of the current flowing into the i-th channel, ΔR, is the amount of resistance change due to the tunnel magnetoresistance effect. If the values of f and f _i match, V _i = (1/4) I _i ΔRcos (φ)
If there is no match, the output is zero. Thus, the ferromagnetic resonance frequency f _i of each channel, by setting the frequency of the frequency f that carry signals such as video signals and audio signals, only the signal superimposed on a specific frequency demultiplexes the detection it can.

The frequency f _i of the ferromagnetic resonance of each magnetoresistive element can be set as follows corresponding to the saturation magnetization Ms of the free layer and the magnetic field H _i generated by the current flowing through the digit line. In the equation, γ is a magnetic rotation ratio, and μ ₀ is a vacuum permeability.

f _i -γ / (2π) μ ₀ H _i ^1/2 Ms ^1/2
FIG. 4 shows an example of the relationship between the external magnetic field H _i and the ferromagnetic resonance frequency f _i . It can be seen that the resonance frequency can be changed from 3.2 GHz to 20 GHz by changing the magnetic field from 1 mT to 10 mT. Since the resonance line width of ferromagnetic resonance is usually about several tens of MHz, about _ten resonance frequencies from resonance frequencies f ₁ to f ₁₀ can be dispersed between 3.2 GHz and 20 GHz as shown in FIG. It is. Thus, it is possible to demultiplex and detect about 10 different radio signals using this demultiplexer.

When a duplexer is actually fabricated, the resonance frequency shifts for each duplexer due to manufacturing variations of magnetoresistive elements. A method of matching this with a preset frequency f _i is as follows. Before the duplexer is manufactured and shipped, a current superimposed with a sine wave having the set frequency f _i is applied to the bit line 8. Next, the value of the current that maximizes the output from the i-th channel while flowing the current through the digit line 3 installed immediately below the i-th channel magnetoresistive effect element 9 and adjusting the magnitude of the current. Is recorded in the memory 2. This operation is performed for all the channels from the first channel to the tenth channel, and the information is recorded in the memory 2. When actually used as a duplexer, the recorded information is read from the memory 2 and transferred to the current driver 1, and a predetermined current value is applied to the digit line for each channel. By doing so, it is possible to configure a duplexer that can always demultiplex only the signal superimposed on the set frequency f _i regardless of the manufacturing error of the magnetoresistive effect element.

  Hereinafter, specific examples of the film structure of the magnetoresistive effect element will be described. The most standard configuration is a tunnel magnetoresistive element composed of a CoFeB fixed layer / MgO barrier layer / CoFeB free layer capable of realizing a high magnetoresistance ratio. Further, a CoFeB fixed layer is formed on an antiferromagnetic film such as MnIr or PtMn, and the magnetization of the fixed layer is fixed in one direction. Further, if the fixed layer has a laminated ferrimagnetic structure having a three-layer structure of CoFe, Ru, and CoFeB, the device characteristics are further stabilized. The above is the basic configuration, but the free layer may be formed of a multilayer film of NiFe, CoFe, or NiFe / CoFe depending on the frequency to be set. The fixed layer can also have a CoFe or CoFe / Ru / CoFe laminated ferrimagnetic structure. The shape of the tunnel magnetoresistive element 9 is such that the direction parallel to the bit line 8 in FIG. 3 is long, the direction perpendicular thereto is shortened, and the easy axis is parallel to the bit line 8 in FIG. The length ratio, that is, the aspect ratio, is preferably about 1.5 to 2.5 as a ratio of long side / short side. This is to stabilize the motion of free layer magnetization due to ferromagnetic resonance excited by the spin torque effect. Further, the planar shape of the magnetoresistive effect element is desirably an octagon or a hexagon in which four vertices of an ellipse or a rectangle are cut off as shown in FIG. Thereby, the motion of the free layer magnetization due to ferromagnetic resonance is further stabilized.

  The following is an example of a tunnel magnetoresistive effect element made of CoFe (3 nm) / Ru (0.8 nm) / CoFeB (2.5 nm) / MgO (1 nm) / CoFeB (3 nm) which can obtain a particularly high tunnel magnetoresistance ratio. Detailed operating conditions will be described. Here, the inside of () represents a film thickness. The size of the tunnel magnetoresistive effect element was an ellipse of 80 × 160 nm.

When the current density J _c at which spin torque magnetization reversal occurs by changing the current pulse width t used for spin torque magnetization reversal, the spin torque magnetization reversal is performed with a pulse width of 1 ns from the plot of J _c against ln (t). The current density (threshold current density) and the thermal stability index Δ can be obtained. The tunnel magnetoresistive element of this example had a threshold current density of 2 MA / cm ² and a thermal stability city index of 60. Therefore, the threshold current value of the spin torque magnetization reversal is about 200 μA. When ferromagnetic resonance is caused by using the spin torque effect, it is necessary to apply a direct current that is about half the threshold current value of the spin torque magnetization reversal. In this embodiment, the current I _i per channel is 100 μA. It was. Therefore, the value of the current I energized by the DC power supply 4 is only 1 mA when demultiplexing for 10 channels.

The resistance of the tunnel magnetoresistive element when the magnetizations of the free layer 23 and the fixed layer 25 are orthogonal is about 400Ω, and the resistance of the tunnel magnetoresistive element when the magnetizations of the free layer 23 and the fixed layer 25 are parallel is 200Ω. The resistance in the case of antiparallel is 600Ω, and the so-called tunnel magnetoresistance ratio is 200%. Resonant frequency of the excited ferromagnetic resonance by spin torque effect, a current flowing through the digit line is changed as shown in FIG. 4 with respect to the magnetic field H _i generated. The cross sectional dimension of the digit line was a rectangle of 500 nm × 500 nm. The distance between the free layer 23 of the tunnel magnetoresistive element and the center of the digit line is about 300 nm. At this time, the current value for generating a magnetic field of 1 mT is 750 μA, and the current value for generating a magnetic field of 10 mT is 7.5 mA. In this embodiment, a current of about 750 μA is applied to the digit line immediately below channel 1 and a current of 7.5 mA is applied to the digit line immediately below channel 10. At this time, as shown in FIG. The resonance frequency of the tunnel magnetoresistive effect element 1 is 3.2 GHz, and the resonance frequency of the tunnel magnetoresistive effect element of the channel 10 is 20 GHz. The resonance frequencies of the other channels were set by adjusting the value of the current flowing through the digit line so that the interval between the resonance frequencies of adjacent resonance lines was 1.87 GHz.

  The signal obtained from each channel is about 1 mV, and this was amplified several tens of times by an amplifier, and various signals superimposed on high-frequency radio waves could be detected. For example, if a ferromagnetic thin film such as NiFe is formed on the three surfaces excluding the upper surface of the digit line, the current value necessary for generating the magnetic field can be further halved to further reduce power consumption. I can do it. In addition, the size of the demultiplexer is extremely small as a few tens of μm × several tens of μm as a whole, and can be formed on a semiconductor substrate on which peripheral circuits such as amplifiers are formed by using a lithography process, thereby reducing manufacturing costs. There is an advantage that you can.

Next, an example in which a giant magnetoresistive element is used as the magnetoresistive element is shown. The film configuration is CoFe (3 nm) / Ru (0.8 nm) / CoFe (2.5 nm) / Cu (3 nm) / CoFe (1 nm) / NiFe (2 nm). Here, the inside of () represents a film thickness. The size of the giant magnetoresistive element was an ellipse of 80 × 160 nm. When the current density J _c at which spin torque magnetization reversal occurs by changing the current pulse width t used for spin torque magnetization reversal, the spin torque magnetization reversal is performed with a pulse width of 1 ns from the plot of J _c against ln (t). The current density (threshold current density) and the thermal stability index Δ can be obtained. The giant magnetoresistive element of this example had a threshold current density of 8 MA / cm ² and a thermal stability city index of 60. Therefore, the threshold current value of the spin torque magnetization reversal is about 800 μA.

When ferromagnetic resonance is caused by using the spin torque effect, it is necessary to apply a direct current that is about half the threshold current value of the spin torque magnetization reversal. In this embodiment, the current I _i per channel is 400 μA. It was. Therefore, the value of the current I energized by the DC power supply 4 is only 4 mA when performing demultiplexing of 10 channels. The resistance of the giant magnetoresistive element when the magnetization of the free layer and the fixed layer is orthogonal is about 50Ω, and the resistance of the tunnel magnetoresistive element when the magnetization of the free layer and the fixed layer is parallel is 50Ω, antiparallel The resistance in this case is 55Ω, and the so-called tunnel magnetoresistance ratio is 10%. Resonant frequency of the excited ferromagnetic resonance by spin torque effect, a current flowing through the digit line is changed as shown in FIG. 4 with respect to the magnetic field H _i generated. The cross sectional dimension of the digit line was a rectangle of 500 nm × 500 nm. The distance from the free layer of the giant magnetoresistive element to the center of the digit line is about 300 nm. At this time, the current value for generating a magnetic field of 1 mT is 750 μA, and the current value for generating a magnetic field of 10 mT is 7.5 mA. In this embodiment, a current of about 750 μA is passed through the digit line immediately below channel 1 and a current of 7.5 mA is passed through the digit line directly below channel 10. At this time, the resonant frequency of the tunnel magnetoresistive element of channel 1 is 3.2 GHz, and the resonant frequency of the tunnel magnetoresistive element of channel 10 is 20 GHz. The resonance frequencies of the other channels were set by adjusting the value of the current flowing through the digit line so that the interval between the resonance frequencies of adjacent resonance lines was 1.87 GHz.

  The signal obtained from each channel is about 1 nV, which was amplified several thousand times by an amplifier, and various signals superimposed on the high-frequency radio wave could be detected. For example, if a ferromagnetic thin film such as NiFe is formed on the three surfaces excluding the upper surface of the digit line, the current value necessary for generating the magnetic field can be further halved to further reduce power consumption. I can do it. In addition, the size of the demultiplexer is extremely small as a few tens of μm × several tens of μm as a whole, and can be formed on a semiconductor substrate on which peripheral circuits such as amplifiers are formed by using a lithography process, thereby reducing manufacturing costs. There is an advantage that you can.

Claims (5)

A bit line in which a direct current source and an antenna are connected in parallel;
Each has a structure in which a nonmagnetic layer is sandwiched between a fixed layer made of a ferromagnetic material and a free layer made of a ferromagnetic material, and a plurality of magnetoresistance effect elements connected to the bit line,
A plurality of source lines respectively connected to the plurality of magnetoresistive elements;
A plurality of amplifiers respectively connected to the plurality of source lines;
A mixer for mixing the outputs of the plurality of amplifiers;
A plurality of digit lines for independently applying a magnetic field to the free layers of the plurality of magnetoresistive elements;
A current driver for applying a predetermined current to each digit line;
A memory storing the magnitude of the current applied to the digit line,
The direct current source supplies a direct current having a magnitude that does not cause magnetization reversal due to the spin torque effect to each free layer of the magnetoresistive effect element.   2. The radio wave demultiplexer according to claim 1, wherein magnetization directions of the fixed layer and the free layer of the magnetoresistive effect element are substantially perpendicular.   3. The radio wave demultiplexer according to claim 1, wherein the nonmagnetic layer is an insulating barrier layer.   3. The electromagnetic wave demultiplexer according to claim 1, wherein the nonmagnetic layer is a conductive metal layer. 5. The radio wave demultiplexer according to claim 1, wherein a magnetic rotation ratio is γ, a vacuum magnetic permeability is μ ₀ , and a saturation magnetization of a ferromagnetic material in a free layer is Ms. The magnetic resonance frequency f _i of the tunnel magnetoresistive element uses a magnetic field of magnitude H _i generated by a current flowing through a digit line arranged adjacent to the i-th tunnel magnetoresistive element, A radio demultiplexer characterized by the following formula.
f _i -γ / (2π) μ ₀ H _i ^1/2 Ms ^1/2

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