JPH01235316A - Microwave element - Google Patents

Abstract

PURPOSE:To eliminate the mismatching of a lattice constant and to enhance the quality by a method wherein a specific epitaxial film is grown on a specific garnet substrate single crystal and an oxide garnet single crystal is constituted. CONSTITUTION:A film expressed by a composition formula of (LaYFeGa)8O12 is grown epitaxially on a garnet substrate single crystal expressed by a composition formula of (YGdGa)8O12; an oxide garnet single crystal is constituted. In a microwave element obtained in this manner, its temperature dependence of a resonance frequency is little; a lattice constant between the substrate single crystal and an epitaxial growth layer is not mismatched. A pit is not produced in the grown epitaxial filmy an element having an excellent characteristic as the microwave element can be obtained.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention provides a novel device useful as a microwave device, particularly a microwave device used in a microwave band with a frequency of 100 MHz to several tens of GHz, such as an isolator or a circulator. The present invention relates to a microwave element made of oxide garnet single crystal having a magnetic film.

(Conventional technology and its problems) Conventionally, YIG crystals grown by the flux method have been used as magnetic materials for microwave devices, but microwave devices made by the flux method are said to be expensive to manufacture. Because of these disadvantages, it has been proposed to use YIG crystals grown by a liquid phase epitaxial method applying wafer process technology developed in the semiconductor industry.

However, this YIG crystal has a drawback that the temperature dependence of the resonance frequency becomes large when constructing a microwave element because the temperature dependence of the saturation magnetization is large.
Part of the iron in the composition of the IG crystal is replaced by Ga, which becomes non-magnetic ions.
However, when some of the iron in the YIG crystal is replaced with Ga, the mismatch in lattice constant between the epitaxial film and the GGG single crystal, which is the substrate crystal, occurs even when the substitution amount is O. This mismatch leads to an increase in strain and, in extreme cases, the disadvantage of cracking of the epitaxial film.

For this reason, in order to match the lattice constants of the epitaxial film and the substrate crystal, 1) adding La element with a large ionic radius to the epitaxial film, and 2) changing the substrate crystal to GG, which is normally used for this type of application.
Methods have been proposed in which a part of the Gd element in GGG is replaced from a G crystal with a Y element with a small ionic radius (YGd), and a Ga, 0□2 crystal is created. Method 1) As the amount of gallium in the Ebitaxel membrane increases, it is necessary to increase the amount of lanthanum substituted in the Ebitaxel membrane. However, as the amount of lanthanum substituted increases, there is a problem in that focusing tends to occur in the Ebitaxel membrane. ), it is necessary to increase the yttrium substitution amount in the substrate crystal as the gallium substitution amount in the Ebitaxi cell film increases, but if the yttrium substitution amount increases, cell growth will occur during substrate single crystal growth. It turns out that there is a problem with it being easy.

(Structure of the Invention) The present invention relates to a high-quality microwave device that solves these disadvantages, and is based on a garnet substrate single crystal having the composition formula (% formula %).
It is characterized by being made of an oxide garnet single crystal formed by growing a film represented by Y Fe Ga), 01 □ by Ebitaxel.

In other words, the inventors have determined that the temperature dependence of the resonant frequency and!
As a result of various studies on the development of a microwave device that does not have a mismatch in lattice constant between the tI plate crystal and the Ebitaxel growth layer and does not generate bits in the grown film, we found that the above-mentioned (Y Gd Ga), 0□2 was used as the substrate material. This has a lattice constant of 12.367 to 12.38.
It is a relatively small one within the range of 3 people, and Ebitaxicell is grown on this substrate (described later) (La Y Fe
Ga), Oo.

The epitaxial film to be grown on this substrate is (La Y Fe Ga) sOtz, and the large amount of iron is 4.1 to 3. 6, since iron ions mainly at the (d) site in YIG are replaced with nonionic gallium elements, the temperature dependence of saturation magnetization due to iron ions at the (d) site can be reduced. In addition, if this material is grown on the above-mentioned substrate and the lanthanum substitution amount is 0.1 or less, it is possible to grow an epitaxial film that is difficult to cause focusing and has no temperature dependence of saturation magnetization. Check and
The present invention was completed by conducting research on a microwave device using this.

Garnet substrate single crystal (Y Gd Ga) constituting the oxide garnet single crystal of the present invention, 01. is the compositional formula % Formula % ≧a>Olb is a number expressed by 3.1≧b>3.0, which means that (c) Y and Gd at the site, [a]
It is assumed that part of Y and Ga are arranged at the site (d), and Ga is arranged at the (d) site, and an example of this is shown by the formula %. This one is for example Y2O
, 3,5 to 7.5 mol%, Gd, 030 to 34 mol%, and Ga2O, 61 to 63 mol% were placed in a crucible, heated to 1,730°C by high frequency induction to melt, and then extracted from this solution. It can be obtained by pulling a single crystal using the Ralski method.

When a wafer cut from this single crystal was etched with, for example, hot phosphoric acid, the lattice constant was measured to be 12.367 to 12.383.

In addition, the epitaxial film (La Y Fe Ga) grown on this single crystal substrate, 0□□, has a compositional formula of x y
-x z 8-y-z Denoted by O12・This x.

LaYFeGa y, z is 0.1≧x > O13, 1>y>3
, 0.4゜1 > z > 3,6, which means (c) La and Y at site, (,) F at site
Part of e and Y and part of Ga, (d) Fe and 68 at the site
, which has the formula Laa1+4Y11.0
OFe18! Ga1.1lol! + 1-aal”1
97Fe3. ? , lGa11zO+z are exemplified. This material is said to have a lattice constant of 12.363 to 12,372, but the lattice constant of the substrate single crystal on which Ebitaxi Cell is grown is 12.367 to 1 as described above.
It is said that there are 2°383 people, and the lattice constant of both is ±0.00.
Since they match within the range of three people, there is no mismatch, and Ebitaxicel can be easily grown, and the obtained Ebitaxicel growth layer does not have any cracks.

In addition, regarding this epitaxial film, if this is a conventionally known YIG, in this YIG, the (a) site has approximately 2
．． There is an iron ion with a formula weight of 0, and an iron ion with a formula weight of about 3.0 at the (d) site, and since the [a] and (d) sites are mostly occupied by iron ions, the saturation magnetization is about 1. .0
A value of 1.760G corresponding to the formula weight is generated, and the iron ion at the (d) site causes the saturation magnetization to have a strong temperature dependence. However, the above composition formula used in the present invention In the case of YIG, the iron ions mainly at the (d) site are replaced with gallium element so that the amount Z value of iron ions becomes 4.1>Z>3.6. It is said that the temperature dependence of saturation magnetization is small.

In addition, it is known that lanthanum element is further added to products in which iron ions are replaced with gallium element in this way, and the lanthanum substitution amount X value is set to 0, 24 > x > 0, 13, (La Y Fe Ga),
0□.

If the lanthanum value in the crystal is set like this, many pits will occur in the Ebitaxicel film, so in the present invention, the X value is set to 0.1≧x>O, so that no pits are generated. There is.

This shrimp taxicel growth can be carried out by liquid phase method, therefore, it can be done by La, 03, Y2O2, Fc40i, Ga,
O, PbO as a flux component, and 8□03 are placed in a platinum crucible, heated to 950 to 1.100°C to melt, and the above-described single crystal substrate is immersed in this melt. The thickness of the epitaxial layer produced by this epitaxial cell growth method varies depending on the frequency used in the target microwave device, but it is usually in the range of 57 m to 404 m.

The microwave device of the present invention obtained by the method described above has a small temperature dependence of the resonant frequency, there is no mismatch in lattice constant between the substrate single crystal and the epitaxy cell growth layer, and furthermore, it is possible to focus on the grown epitaxial film. Since it does not generate any In addition to being excellent as an element, it is also useful as an isolator and circulator.

Next, examples of the present invention will be described. In the examples, the measurement of the resonance magnetic field value, the calculation of the saturation magnetization, and the calculation of the temperature coefficient quantitatively indicating the temperature dependence of the saturation magnetization were performed as follows.

[Measurement of resonance magnetic field value]

A small piece of 2.6 x 2.6 mm was cut out from the sample, and using a ferromagnetic resonance apparatus with a temperature variable device, the resonant magnetic field values were measured when the direction of the applied magnetic field was horizontal and perpendicular to the sample temperature. Measure while changing.

[Calculation of saturation magnetization]

It is calculated from the resonance magnetic field value measured above using the following formula.

This\4π Ms...saturation magnetization, Ha...Anisotropic magnetic field.

H... Resonant magnetic field value when the epitaxial film is placed perpendicular to the applied magnetic field, Hll... Resonant magnetic field value when the epitaxial film is placed parallel to the applied magnetic field.

[Calculation of temperature coefficient]

From the graph of the temperature dependence of saturation magnetization for each sample, a temperature coefficient indicating the temperature dependence of saturation magnetization in the range of -30° C. to 80° C. is calculated from the following equation.

(Note) 4π Ms (80°C)... Saturation magnetization at 80°C 4π Ms (-30°C)... Saturation magnetization at -30°C Example 1 (1) La as a component that forms an epitaxial film
,0. , Y2O3, Fe, 0. and Ga, 0. was charged into a platinum crucible, and 1'bO,B□0. 1,100 after preparing
℃ to melt it, and then the formula Y is added to the melt.
A single garnet substrate wafer indicated by lLsGd, GaassO□ is immersed and the formula L is applied to its (111) direction.
aaa*L. . Fe3.5scacx. An epitaxial film indicated by 0□2 was grown to a thickness of about 27 m.

The lattice constant of this oxide garnet single crystal is 12°366
, degree of mismatch between the substrate crystal and the epitaxial film (in)
The results were obtained for O1 and its temperature coefficient of -0.2 G/°C. In addition, this epitaxial film has a small number of pits and is of good quality, and its temperature coefficient is -3, 2G/" compared to YIG.
It was confirmed that the amount was very small compared to C.

(2) Next, (La
YFeGa)sexs/ (YGdGa)sOx
Using z substrate as material, (La Y Fe Ga), O□
A high-frequency tunable filter using a magnetostatic forward volume wave (MsFvw) propagating through a membrane was constructed (Fig. 1a).
(See b)), MSFVw The aluminum electrodes for excitation and detection were created by a normal photolithography method. Figure 2 shows the frequency characteristics of this element, and the center frequency of this high frequency tunable filter can be varied from 0.3 to 10 GI by controlling the current value of the frequency variable coil.
It is variable with Iz. Next, using this, the temperature dependence of the center frequency of the filter (T
CP) was determined from the measured values at frequencies of 60° C., 20° C., and -20° C., and the results shown in curve A in FIG. 3 were obtained. Note that the external magnetic field generator used in this example is one that can generate any constant magnetic field regardless of the ambient temperature.

Also, for comparison, conventionally known Y IG/GGG
The temperature dependence of the substrate shown in curve B in FIG. 3 confirms that the substrate of the present invention exhibits extremely excellent TCP.

Example 2 Using the high frequency tuner pull filter of Example 1, the fourth
Configure a high frequency tuner pull oscillator with the structure shown in the figure,
When the oscillation spectrum of this oscillator was observed, the results shown in FIG. 5 were obtained.

This oscillator showed an arbitrary frequency output from 0.3 to 10 GHz by controlling the current value of the frequency variable coil. ) at 60℃, 20
C. and -20.degree. C., the same results as curve A in FIG. 3 in Example 1 were obtained. In this example, an external magnetic field that can generate an arbitrary constant magnetic field regardless of the ambient temperature was used for generating the external magnetic field.

In addition, for comparison, when a conventionally known YIG/GGG substrate was used, its TCP was determined using the same method, and this showed the same result as curve B in FIG. 3 in Example 1. 1. The product of the present invention has excellent T.
It was confirmed that it was indicative of CP.

[Brief explanation of the drawing]

FIG. 1(a) is a perspective view of a high frequency tuner pull filter made of the microwave element of the present invention, FIG. 1(b) is a longitudinal sectional view thereof, and FIG. A graph showing an example of the characteristics of a high frequency tuner pull filter, Figure 3 shows the high frequency tuner pull filter of Figures 1 (a) and (b) and as a comparative example! This is a graph showing the frequency temperature dependence (TCP) of a filter using 1G/GGG, and FIG. 4 is a longitudinal cross-sectional view of a high frequency tuner pull oscillator using the filter of FIGS. FIG. 5 shows the oscillation spectrum of the high frequency tuner pull oscillator shown in FIG. 1st figure: 1st figure: 1st figure, 1st cell piece, base ((b) 2nd figure: □ Shuji ■ Length (GH2I 3rd figure: 41'L (GH21) 4th figure: Micro 5 melon 7 shear □ 5LS intersection (GH2)

Claims (1)

[Claims] 1. The composition formula (LaY
A microwave device characterized in that it is made of an oxide garnet single crystal formed by epitaxially growing a film represented by FeGa)_5O_1_2.