JPH07105648B2 - YIG thin film microwave device - Google Patents

Description

The present invention relates to a YIG thin film having means for applying a DC bias magnetic field to a microwave element using ferrimagnetic resonance of a YIG (yttrium / iron / garnet) thin film. Involved in microwave equipment.

[Outline of Invention]

The present invention provides a microwave device using the ferrimagnetic resonance of the YIG thin film, to which the YIG thin film microwave apparatus comprising a magnetic circuit composed of the permanent magnet for applying a bias magnetic field, a portion of the YIG of Fe ³⁺ ions A YIG thin film microwave device having an extremely good temperature characteristic is constructed by using a magnet having specific magnetic characteristics as a permanent magnet, with a configuration in which nonmagnetic ions are substituted.

[Conventional technology]

As a microwave device, YI which is a ferrimagnetic material on a GGG (gadolinium gallium garnet) non-magnetic substrate
A YIG thin film obtained by liquid phase epitaxial growth (hereinafter referred to as LPE) of a G thin film is processed into a required shape such as a circular shape or a rectangular shape by selective etching using a photolithography technique, and by utilizing the ferrimagnetic resonance of this, a filter, an oscillator, etc. What constitutes a microwave device has been proposed.

These microwave devices have an advantage that a microwave integrated circuit can be formed by using a microstrip line or the like as a transmission line, and hybrid connection with other microwave integrated circuits can be easily performed. Also,
The microwave device based on the YIG thin film magnetic resonance is excellent in mass productivity because it can be manufactured by the LPE and the photolithography technique as described above.

As described above, the microwave device using the YIG thin film magnetic resonance element has many practical advantages as compared with the conventional microwave device using the YIG sphere.

However, such a microwave device utilizing the ferrimagnetic resonance of the YIG thin film has a large practical problem that the temperature characteristic is poor because the temperature T of the ferrimagnetic resonance frequency f of the YIG thin film is highly dependent. There is.

This will be described below.

When the YIG thin film is placed in the gap of the magnetic circuit so that a DC magnetic field is applied perpendicularly to the film surface, its ferrimagnetic resonance frequency f has a small contribution of the anisotropic magnetic field, and if this is ignored, the kitel (Kittel) can be expressed by the following equation (1) using an equation.

f (T) = γ {Hg (T) −N _Z ^Y · 4π _S ^Y (T)} (1) where γ is the gyromagnetic ratio γ = 2.8MHz / 0e, Hg is the DC gap magnetic field, N _Z ^Y is the magnetic resonance diamagnetic field coefficient of the YIG thin film, which is a value calculated using magnetostatic mode theory, and 4πM _S ^Y is the saturation magnetization of YIG. Since both Hg and 4πM _S ^Y are functions of temperature T, the resonance frequency f is also a function of temperature. As a specific example, in the vertical resonance of a YIG disk with an aspect ratio (thickness / diameter) of 0.01, N _Z ^Y = 0.9774, and the bias magnetic field H
Assuming that g is constant regardless of temperature, 4πM _S ^Y is −20 ° C.
At 1916G (Gauss) and + 60 ° C, it becomes 1622G, so the resonance frequency f changes as much as 823MHz in this temperature range.

In such a YIG thin film microwave device, as a method of avoiding the fluctuation of the resonance frequency due to the ambient temperature, the YIG
Methods such as arranging the thin film magnetic resonance element in a constant temperature bath and keeping the element itself at an integrated temperature or keeping the resonance frequency of the element constant by changing the magnetic field depending on the temperature with an electromagnet have been considered. However, since these require external energy supply such as current control, their configuration is complicated.

[Problems to be solved by the invention]

The present invention solves the above-mentioned problems, that is, it does not require an external circuit for compensating the temperature characteristic, and further, there is no power consumption for compensating the temperature characteristic, and the fixed frequency, variable frequency The present invention can be applied to YIG thin film microwave devices of both frequencies, and enables good compensation of temperature characteristics in YIG thin film microwave devices of a wide range of operating frequencies.

Prior to the description of the present invention, in order to facilitate understanding of the present invention, a permanent magnet and a magnetic circuit will be described.

Most of the magnetic properties of magnetic materials are shown by the magnetization curve and the magnetic hysteresis curve. As is well known, when a magnetic field is applied from the outside to a material that is not magnetized at all and the strength of the magnetic field is changed in various ways, the situation of the magnetic flux density induced in the material is By following the path indicated by the magnetization curve shown in the figure, a so-called magnetic hysteresis curve, that is, a magnetic hysteresis curve is drawn. Permanent magnets utilize the remaining magnetism by removing the magnetic field once magnetized to saturation, so the magnetic state is Br (indicated by Or called Remanence).

Since the permanent magnet is used for the purpose of supplying a magnetic field to the outside, a magnetic air gap (magnetic gap) is always provided in the magnetic circuit. A magnetic field, that is, a demagnetizing field will be generated. Therefore, the operating point of the permanent magnet is
It comes to the second quadrant of the magnetic hysteresis curve in the figure, that is, a curve called a demagnetization curve from the point of remanence Br to the coercive force Hc. The demagnetization characteristics of ferrite and rare earth magnets consist of two parts, a linear part having a slope almost equal to the magnetic permeability of vacuum, that is, a recoil magnetic permeability μ _r, and a linear part that droops drastically. The point of inflection is called a knick point.

Further, the magnetic field calculation for the magnetic circuit 2 in which the closed magnet circuit 1 is formed by disposing the permanent magnet 4 in the magnetic gap g of the yoke 3 as shown in FIG. 7 will now be described.

In this case, Maxwell's equation Is applied to the circuit of FIG.

Here, the cross-sectional area of the permanent magnet 4 is Am, the cross-sectional area of the magnetic gap is Ag, the thickness of the permanent magnet 4 is 1/2 lm, the magnetic gap length is lg, and the magnetic flux density in the permanent magnet 4 and the magnetic gap g is permanent. Assuming that the magnetic fields in the magnet 4 and the magnetic gap g are Hm and Hg and the magnetic permeability of the yoke is infinite, the magnetic field in the yoke is 0. In this case Am = Ag, [Means for Solving Problems] FIG. 1 is a block diagram of a YIG thin film microwave device (1)
Is a microwave element made of a YIG thin film, (2) is a magnetic circuit for applying a bias magnetic field to this microwave element (1), and this magnetic circuit (2) is, for example, a U-shaped yoke (3) and its both end portions relative to each other. Permanent magnets (4) each having a thickness of 1/2 lm are arranged on the facing surfaces, and a gap lg is provided between both magnets (4) and (4).
A magnetic gap g is formed with the microwave element (1) arranged in the magnetic gap g.

Then, as proposed in Japanese Patent Application No. 60-150431 application filed by the present applicant, in this magnetic circuit (2), fo is a used frequency, γ is a gyromagnetic ratio, and N _Z ^Y is a YIG thin film. Demagnetizing factor,
▲ 4π M ^Y _SO ▼ (o) is saturation magnetization at room temperature when the amount of nonmagnetic ion substitution with Fe ^{3+ of} YIG described later is zero, and α ₁ ^Y (o) is the same when the amount of substitution is zero When the first-order temperature coefficient of the saturation magnetization of YIG near room temperature is, the remanence Br of the permanent magnet (4) at room temperature is (fo / γ) + N _Z ^Y · ▲ 4πM ^Y _SO ▼ (o) or more. , And the first-order temperature coefficient of Br near room temperature The above permanent magnet is used.

It should be noted that here, the used frequency fo refers to this frequency when the used frequency of the microwave device is fixed, and when it is variable, it is superimposed on a fixed bias magnetic field and not shown in the magnetic circuit. The bias magnetic field is varied by controlling the energization of the electromagnetic coil. The frequency when the energizing current to the electromagnetic coil is turned off is referred to.

And, particularly in the present invention, the microwave element (1)
The YIG composition, so-called substituted YIG for substituting part of the Fe ³⁺ ions in the non-magnetic ions, i.e. for example Ga ³⁺ some trivalent nonmagnetic ions Fe ³⁺ ions, Al ^3+, etc. Or a divalent ion such as Ca ²⁺ and a tetravalent ion such as Ge ⁴⁺ are substituted and substituted with a trivalent ion to obtain a substitution type YIG equivalent to the temperature characteristic of the resonance frequency. To do.

[Action]

In the magnetic circuit shown in FIG. 1, all the magnetic flux passes through the magnetic gap g, the magnetic field in this gap g is uniform, and the permeability of the yoke is infinite. The following equation is established by Well's equation. However, the cgs unit was used here.

Bm = Bg (2) lmHm = lgHg (3) However, Bm and Bg are permanent magnets (4), magnetic flux density in the magnetic gap, and Hm and Hg are permanent magnets (4), respectively. In the magnetic field in the magnetic gap g, the direction of Hm is opposite to that of Hg, Bm, Bg.

Further, as defined in FIG. 6, if the permanent magnet (4) does not have a knick point and the demagnetization characteristic with a constant recoil permeability μr shows linearity, the following equation ( 4) is established.

From the expressions (3) and (4), the magnetic field Hg in the magnetic gap g of the magnetic circuit (2) is obtained as a function of the temperature T as follows.

From the equations (1) and (5), in order for the resonance frequency to become the constant value fo regardless of the temperature T, the following equation (6) must be established.

On the other hand, the remanence Br of the permanent magnet (4) and the saturation magnetization 4πM _S ^Y of the YIG thin film microwave element (1) are the temperature coefficient α ₁ ^B up to the second order in a temperature range of ± several tens of degrees around room temperature To.
, And α ₂ ^B can be taken into account and can be expressed with sufficient accuracy. _{That, Br (T) = B r} o {1 + α 1 B (T-To) + α 2 B (T-To) 2} ‥‥
(7) 4πM _S ^Y (T) = ▲ 4πM ^Y _SO ▼ {1 + α ₁ ^Y (T-To) + α ₂ ^Y (T-T
o) ² } ... (8) Substituting equations (7) and (8) into equation (6), and making the 0th, 1st, and 2nd terms of temperature T on both sides equal. The following equation is obtained by

From the equation (9), it can be seen that the condition of strength of the permanent magnet (4) is that B _r ^o > (fo / f) + N _Z ^Y · ▲ 4πM ^Y _SO ▼. And looking at equations (10) and (11),
The optimum values of the first and second temperature coefficients of Br are the resonance frequency,
It is found that it can be obtained only from the magnetic resonance diamagnetic field coefficient of the YIG thin film, the saturation magnetization of YIG and its temperature coefficient. As a specific example,
The vertical resonance of a YIG disk with an aspect ratio (film thickness / diameter) of 0.01 is N _Z ^Y = 0.9774, and the saturation magnetism of YIG at To = 20 ° C and its temperature coefficient are ▲ 4πM ^Y _SO ▼ = 1771.8G,
α ₁ ^Y = −2.07 × 10 ⁻³ , α ₂ ^Y = −0.996 × 10 ⁻⁶ , and the results of calculating the primary and secondary temperature coefficients of Br from these values are shown in the table of FIG. However, in practice, it is extremely difficult to prepare a permanent magnet that satisfies both equations (10) and (11) at the same time.
G Consider only the condition of Eq. (10) that makes the temperature characteristics of the thin film device zero. Since the value of α ₁ ^B is determined by the permanent magnet used, the resonance frequency that satisfies equation (10) is uniquely determined. As a specific example, the resonance frequency at which the slope of the temperature characteristic becomes zero is α ₁ ^B = 1.12 × 10 ^-3
4.11GHz with a permanent magnet of Nd ₂ Fe ₁₄ B, α ₁ ^B = −0.9 × 10
^-3 CeCo ₅ permanent magnet, 6.30GHz, α ₁ ^B = −0.5 × 1
A permanent magnet with 0 ^-3 SmCo ₅ gives a frequency of 15.2 GHz. As described above, when the existing permanent magnet is used, there are restrictions on the operating frequency of the YIG thin film that can realize good temperature characteristics.

On the other hand, in the present invention, the substitution amount δ of non-magnetic ions for Fe ³⁺ ions in the YIG thin film is controlled, and thus the YIG thin film in a wide range of operating frequencies can be used even with the existing permanent magnet. Good temperature characteristics can be realized in the microwave device. Next, this will be described.

First, Y 3 is obtained by substituting Fe ³⁺ ions of YIG with nonmagnetic ions.
The change in IG saturation magnetization will be described. Now, looking at a pure YIG single crystal, three Fe ³⁺ ions out of 5 Fe ³⁺ magnetic ions in Y ₃ Fe ₅ O ₁₂ enter the tetrahedral position, and 2
Number of Fe ³⁺ ions enters the octahedral position, of the tetrahedral position Fe ³⁺
The ions and the Fe ³⁺ ions at the octahedral position are antiparallel to each other due to the strong superexchange interaction. As a result, 5 Bohr magnetone (5 μB) possessed by one Fe ³⁺ ion
Min magnetic moment contributes to the YIG saturation magnetization.
Now, some of YIG's Fe ³⁺ ions are non-magnetic ions. Ga
Considering the case of substitution with ³⁺ , when the substitution amount δ is not so large, 100% of Ga ³⁺ is replaced with Fe ^{3+ at the} tetrahedral position, so the magnetic moment per molecular formula is 5 μB × {(3-δ ) −2} = 5 (1−δ) μB, and the saturation magnetization decreases. The saturation magnetization of Ga-substituted YIG has been reported in detail in the literature: Journal of Applied Physics Vol.45, No.6 PP2728-2732, June, 1974, and (1)-( FIG. 3 shows the result of calculating the saturation magnetization with respect to temperature change by changing the Ga substitution amount in Y ₃ Fe ₅ −δ Ga ₁₂ using the equation 4).
Then, in FIG. 4, the central temperature is 20 ° C. with respect to the Ga substitution amount δ.
The values of the saturation magnetization of 4πM _S ^Y and the primary and secondary temperature coefficients α ₁ ^Y and α ₂ ^Y at −20 ° C. to + 60 ° C. are shown. As is clear from FIG. 4, the value of the saturation magnetization of YIG at room temperature is
However, the value of the first-order temperature coefficient α ₁ ^Y of the saturation magnetization is almost constant regardless of the substitution amount δ.

On the other hand, in the conditional expressions (9) and (10) for the permanent magnet, the saturation magnetization of YIG at room temperature and the first-order temperature coefficient of the saturation magnetization as a function of the substitution amount δ are calculated by ▲ 4πM ^Y _SO ▼, respectively.
When (δ) and α ₁ ^Y (δ), it is rewritten as follows.

Here, the value of (4πM ^Y _SO ) (δ) decreases monotonically as the substitution amount δ increases, as described above, If the condition of is satisfied, there exists a solution of the thickness lm of the permanent magnet that satisfies the expression (9 ′) regardless of the value of δ. Also,
In equation (10 '), α ₁ ^B and α ₁ ^Y (δ) are both negative values, and as mentioned above, α ₁ ^Y (δ) is almost constant regardless of the value of δ. , ▲ 4π M ^Y _SO ▼ (δ) decreases monotonically with the value of δ, so the coefficient of α ₁ ^Y (δ) N _Z ^Y・ ▲
4πM ^Y _SO ▼ (δ) / {(fo / γ) + H _Z ^Y・ ▲ 4πM ^Y _SO
It can be seen that the value of ▼ (δ)} is positive and decreases monotonically as δ increases.

Therefore, If the condition of is satisfied, by selecting the replacement amount δ (1
It becomes possible to satisfy the condition of the expression 0 '). That is,
Even with the existing permanent magnet material, the required temperature characteristics can be realized by adjusting the substitution amount δ of nonmagnetic ions of Fe ^{3+ in} the YIG thin film.

Incidentally, when the values of α ₁ ^B , fo, H _Z ^Y are given, the value of δ satisfying the expression (10 ′) cannot be analytically obtained, and therefore it is calculated by computer simulation. However α ₁ ^Y
Assuming that δ dependence of (δ) is small, ▲ 4πM ^Y _SO ▼
The change of (δ) is expressed by a quadratic equation: ▲ 4πM ^Y _SO ▼ (δ) = ▲ 4πM ^Y _SO ▼ (o) (1 + β ₁ δ + β ₂ δ ² ) ...
If approximated by (14), the approximate value of the optimum replacement amount δ can be obtained from the following equation.

[Embodiment] In the configuration of FIG. 1, the gap lg of the magnetic gap g is 3 mm.
As the permanent magnet (4), any one of Nd ₂ Fe ₁₄ B magnet, CeCo ₅ magnet and SmCo ₅ magnet was used. FIGS. 5A to 5C show the simulation results by the equation (15) for each operating frequency f of the YIG thin film microwave device at this time. Here, δ is the optimum replacement amount that makes the slope of the temperature characteristics of the YIG thin film microwave device zero, and lm is the required permanent magnet (4).
The total thickness, Δf, is the frequency variation considering the second-order temperature coefficient in the temperature range of −20 ° C. to + 60 ° C. According to FIG. 5, by controlling the substitution amount δ of nonmagnetic ions for Fe ³⁺ ions of YIG, good temperature characteristics can be obtained for YIG thin film devices with a wide range of operating frequencies by using existing permanent magnets. It turns out that can be realized.

In the example described above, the present invention is applied to a microwave device whose operating frequency is fixed. The magnetic circuit (2)
Although not shown in the yoke (3), it can be applied to a variable YIG thin film microwave device in which a coil is wound.

〔The invention's effect〕

As described above, according to the present invention, a microwave device having a good temperature characteristic can be realized, and as described at the beginning, the characteristics of the microwave device using the YIG thin film, which is excellent in mass productivity, can be utilized to further utilize the microwave device. The industrial profit is great.

[Brief description of drawings]

FIG. 1 is a block diagram of an example of a YIG thin film microwave device according to the present invention, FIG. 2 is a table showing temperature coefficients to be taken by a permanent magnet for each frequency, and FIG. 3 is saturation with a substitution amount δ as a parameter. Magnetization temperature characteristic curve diagram, Fig. 4 is a table showing the relation of each value to Ga substitution amount of YIG, and Fig. 5 is Ga substitution amount with respect to frequency, magnet thickness, frequency variation Δf, curvature of temperature characteristic curve 6 is a table showing the shape, FIG. 6 is a magnetization curve diagram, and FIG.
The figure is a magnetic circuit diagram. (1) is a microwave element, (2) is a magnetic circuit, g is its magnetic gap, (3) is a yoke, and (4) is a permanent magnet.

Continuation of front page (56) References 1979 IEEE MTT-S INTERNATIONAL MICROWAVE SYMPOSIUM DIGEST P.P. 160-161. Materials Research Bulletin, Pergamon Press Vol. 12, Number 7, July, 1977 PP. 735-740

Claims (1)

[Claims] 1. A microwave device utilizing ferrimagnetic resonance of a YIG thin film, (b) a magnetic circuit comprising a permanent magnet for applying a DC magnetic field to the microwave device, and (c) the above. The composition of the YIG thin film that constitutes the microwave element is obtained by substituting a part of Fe ³⁺ ions with non-magnetic ions, and (d) the above-mentioned permanent magnet uses fo (frequency in a fixed frequency device, its frequency, variable frequency). In the device, the frequency in a state where no current is passed through the electromagnet coil for frequency control), γ is the gyromagnetic ratio, Nz ^Y is the magnetic resonance diamagnetic field coefficient of the YIG thin film, and 4πMso ^Y (0) is the replacement of the nonmagnetic ion. Saturation magnetization of YIG thin film at room temperature when the amount is zero, α
_{When 1} ^Y (0) is the first-order temperature coefficient of saturation magnetization near room temperature of the YIG thin film when the amount of substitution is zero, the remanence Br of the permanent magnet at room temperature is (fo / γ) + Nz ^Y 4π
Above Mso ^Y (0), the first-order temperature coefficient of Br near room temperature is [Nz ^Y · 4πMso ^Y (0) / {(fo / γ) + Nz ^Y · 4πMso ^Y
(0)] × α ₁ ^Y (0) or above YIG
Thin film microwave device.