EP1829061A1

EP1829061A1 - Ferrite material with low hyperfrequency losses and production method

Info

Publication number: EP1829061A1
Application number: EP05821798A
Authority: EP
Inventors: Richard Lebourgeois; Ludovic Pinier; Michel Pate
Original assignee: Thales SA
Current assignee: Thales SA
Priority date: 2004-12-20
Filing date: 2005-12-16
Publication date: 2007-09-05
Also published as: FR2879593A1; FR2879593B1; US20090321677A1; WO2006067088A1

Abstract

The invention relates to a ferrite material with a garnet structure based on yttrium and iron and comprising copper enabling the sintering time thereof to be reduced substantially in comparison with conventional ferrite garnet-type materials, corresponding to the following chemical formula: YaTRbFecAldlneCafCugZrhViCojSikO12±y wherein TR = a rare earth or combination of rare earths and 3 (a+b+c+d+e) + 2 (f+g+j) + 4 (h+k) + 5i = 24 ± 2y 1=a=3,5; 0=b=1.5; 4=c=5; 0=d=1,5; 0=e<0.8; 0=f=1; 0=g=0,05; 0=i<0.8; 0=j=0.5; 0=k=0.5. Applications: hyperfrequency components, passive inductive low-loss components operating at Gigahertz frequencies.

Description

FERRITE MATERIAL HAS LOW MICROFREQUENCY LOSSES AND

MANUFACTURING PROCESS

The invention relates to ferrite materials with low magnetic losses, particularly suitable for producing microwave components and in particular low loss passive inductive components operating at frequencies of the order of a few Gigahertz. Such components are particularly sought for both for civil telecommunications applications and for radar applications typically operating in frequency ranges between a few Gigahertz and a few tens of Gigahertz. They may be inductive passive components that perform, in microwave communication systems, functions such as filters, phase-shifters, circulators or insulators.

For this purpose, the passive components may typically comprise an element made of ferrite material in which an electromagnetic wave propagates. The previously magnetized ferrite material has a magnetic anisotropy which acts differently on the electromagnetic wave according to whether it is polarized in one direction or the other. This well known principle of non-reciprocity is based on gyromagnetic resonance or ferromagnetic resonance. For these applications, the performance of the component is conditioned by low losses (magnetic and dielectric). The magnetic losses are directly related to the saturation magnetization which must be adjusted according to the frequency band of the application. For low frequency operations (1 to 20 GHz), it is necessary to look for magnetizations with low saturation (less than 0.2 Tesla), otherwise the magnetic losses are important. For operations with a higher frequency (20 to 100 GHz), it is necessary to look for higher magnetizations (typically between 0.2 Tesla and 0.55 Tesla) to obtain better efficiencies, the magnetic losses being reduced.

Families of ferrite materials particularly suitable for these applications are ferrite materials of garnet structure which correspond to a particular crystalline organization. The structure crystallographic garnets is cubic. The crystallographic sites are tetrahedral (corresponding to an environment of 4 oxygen ions), octahedral (corresponding to an environment of 6 oxygen ions) and dodecahedral (corresponding to an environment of 8 oxygen ions). For example, yttrium-iron (YIG) garnet of chemical formula: {Y ³⁺ ₃ [Fe ³⁺ ] ₂ (Fe ³⁺ J ₃ O ₁₂ in which the symbols {}, [] and () respectively indicate the dodecahedral, octahedral and tetrahedral sites and the values ³⁺ the valence of the ions These ferrites have low saturation magnetizations which make it possible to limit the magnetic losses at low frequency (1 to 20 GHz) as well as the low dielectric losses. ferrite ferrite yttrium and iron of generic formula: YsFe ₅ Oi ₂ allows for example ferromagnetic resonance line widths of less than 4000 A / m at 10 GHz and tangents of dielectric loss less than or equal to 10 ⁴ to 10 GHz.

The problem with this type of ferrite lies in the very high manufacturing temperatures which necessarily generate high costs of developing components incorporating this type of ferrite. This is why the invention proposes a new family of garnet-type ferrites whose manufacture can be carried out at lower temperatures, thanks to the presence of copper whose proportions have been optimized.

Indeed, according to the invention, low levels of copper are claimed in order to reduce the dielectric losses as well as the low power magnetic losses.

In general, the ferrites are manufactured according to a conventional method comprising the following steps: a weighing step of the raw materials;

a step of mixing and grinding the raw materials;

- a heat treatment step called chamottage high temperature typically 1200 ⁰ C aiming to synthesize the garnet phase in powder form; a second grinding and pressing step; very high temperature sintering of the re-milled chamfered powder whose purpose is to densify the ceramic while conferring on it the desired shape.

Typically with a garnet of YsFesO ^ type, the sintering is carried out at a temperature between 145O ⁰ C and 155O ⁰ C.

By adding calcium and vanadium components, this temperature can be lowered to about 135 ^° C.

The ferrite materials according to the invention comprising copper have a sintering temperature significantly lower, of the order of 1050 to 1070 ^° C. Copper has the advantage of being substituted in particular for vanadium which is a toxic substance. Thus it is possible to develop ferrites at lowered sintering temperature, while decreasing the content of toxic element. Their industrial synthesis is thus easier to implement. Their low sintering temperature reduces their manufacturing cost and makes it possible to co-sinter with other types of materials such as certain metals such as gold or silver-palladium alloys or other ceramics that go into the manufacturing process. components such as ferrites for permanent magnets or dielectric materials such as those based on alumina. For example, ferrite according to the known art, constituting the heart of the circulator is metallized with silver deposited most often by screen printing. One or two polar pieces (which create the polarizing magnetic field) are then formed and consist of a permanent magnet of the hexaferrite type or a samarium-cobalt or neodymium-iron-boron alloy. Indeed according to the state of the art it is impossible to co-sinter a ferrite ferrite with a metal because the minimum sintering temperatures for garnets are incompatible with the melting temperatures of the main metals used in microelectronics (962 ⁰ C for money, 1064 ⁰ C for gold ...).

In addition, the advantage of having lowered sintering temperatures is to minimize the solid phase diffusion reactions of the species present and thus preserve the starting chemical compositions while mechanically combining the different materials. In this way, it is possible to avoid machining and assembly steps and thus to manufacture low-cost microwave components. According to the known art, from the basic formulation of YsFe ₅ Oi ₂ many compositions have been optimized according to the intended applications and the desired characteristics.

According to the operating frequencies and the powers involved, the following characteristics of the material are adapted: saturation magnetization, low power magnetic losses (linewidth

ΔH or ΔHe _ff ) magnetic losses with high power level (ΔH _k ), dielectric losses, temperature stability. Each type of application (frequency band, power level, operating temperature and temperature stability) leads to a compromise between all these parameters. Let us quote for the substitutions which gave rise to developments of materials:

- The substitutions by aluminum (Al) which lead to the following formulations: Y3Fe _5- 5χAl5χOi ₂ , x ranging from 0 to 0.3. They make it possible to reduce the saturation magnetization of the ferrite without increasing the magnetic losses, and thus to adapt the material to the operating frequency.

- The substitutions by gadolinium (Gd) which lead to the following formulations: Y _3- 3yFe5Gd ₃ yOi2, y ranging from 0 to 0.5. They make it possible to reduce the saturation magnetization of the ferrite without reducing the Curie temperature. The power handling (ΔH _k ) is also improved.

Mixed substitutions by aluminum (Al) and gadolinium (Gd) which lead to the following formulations: Y _3-3 yGd ₃ yFe _5-

5xAI _5x Oi2, x varying from 0 to 0.3 and y varying from 0 to 0.5. The combined effects described above are thus obtained.

- Substitutions of indium (In) or with calcium-zirconium (Ca-Zr) which lead to the following formulations: Y ₃ Fe _{_5-z} ln _z θi2 orY _3- ZCA _z Fe _{_5-z} zzr Oi2, z variant from 0 to 0.6. This increases the saturation magnetization.

- The substitutions by calcium-indium-vanadium which lead to the following formulations: Y ₃ - ₂ χCa ₂ χFe _5-x- _y ln _y V _z O 1 ₂ , z varying from 0 to 0.5. They make it possible to increase the saturation magnetization and to reduce the magnetic losses at low power level.

- Substitutions with cobalt (Co) which is associated with silicon or germanium which gives the following formulations: Y3Fe _5- 2uMe _u CθuOi2, Me being Si or Ge and u varying from 0 to 0.2. They allow high power operation at the expense of low power performance (increase of ΔH).

substitutions by gadolinium and / or magnetic rare earth ions such as dysprosium or holium whose formulations are the following: Ys-sx-szFes-syGdsxMeszAlsyO ^. They also allow high power operation but for low substitution rates, low losses also improve.

Another advantage of the invention lies in the fact that in particular for applications at frequencies used in the telecommunications field, the ferrite must have relatively high molar percentages of yttrium and / or gadolinium. By using a copper-substituted ferrite, interesting properties are obtained by decreasing the levels of yttrium and / or gadolinium, since copper substitutes for these elements in the ferrite according to the invention.

Another advantage of the invention is that copper makes it possible to overcome the presence of vanadium, which is a toxic element.

Thus, more specifically, the subject of the invention is a ferrite material based on yttrium and iron, characterized in that it corresponds to the following chemical formula:

YaTR _b FecAl _d ln _θ CafCUgZrhViCθjSi _k Oi2 ± γ with: TR: a rare earth or a combination of rare earths and

3 (a + b + c + d + e) + 2 (f + g + j) + 4 (h + k) + 5i = 24 ± 2γ 1 <a <3.5; 0 <b <1, 5; 4 <c <5; 0 <d <1, 5; O≤e≤O.8; 0 <f <1; 0 <g <0.05; O≤i≤O.8; O≤j≤O.5; 0 <k <0.5.

Advantageously, the rare earths can be of the gadolinium (Gd), dysprosium (Dy) or holmium (Ho) type.

The invention also relates to a composite material based on ferrite characterized in that it comprises a material according to the invention cofired with one or more materials of metal type or of dielectric type or ferroelectric type.

The invention also relates to a magnetic component comprising a magnetic core made of ferrite material according to the invention and a magnetic component characterized in that it comprises a circulator or a microwave phase shifter, made of ferrite material, according to the invention, which can operate in a frequency range of about 0.5 Gigahertz to about 20 Gigahertz.

Finally, the subject of the invention is a process for manufacturing a ferrite material according to the invention, characterized in that it comprises the following steps:

• the weighing of oxides or carbonates raw materials to obtain the composition of the ferrite material;

• mixing and first grinding of the raw materials;

• chamotte at a temperature between about 800 and 1050 ⁰ C, in one or more steps;

A second grinding of the powder obtained, followed by pressing; Sintering said regrind powder at a temperature of between about 900 ^° C. and 1100 ° C.

The subject of the invention is also a method for manufacturing the material, characterized in that it comprises the following steps: • the weighing of oxides or carbonates raw materials to obtain the composition of the ferrite material;

> the mixing and a first grinding of the raw materials;

• chamotte at a temperature between about 800 and 1100 ⁰ C, in one or more steps;

A second grinding of the powder obtained;

• the mixture of said regrind powder with organic products (binders, deflocculants, surfactants ...) for the production of a paste; "the deposit in thick layers of this paste by casting or screen printing;

The production of a multilayer structure consisting of a stack of layers of hard ferrite (permanent magnet), metal (silver, silver-palladium, gold) and ferrite according to claim 3;

Sintering said multilayer structure at a temperature of between 850 and 1100 ^° C.

The hard ferrite may advantageously be hexaferrite type. Advantageously, the first grinding can be carried out in a humid medium.

The invention will be better understood and other advantages will appear on reading the description which follows. In general, the ferrite material according to the invention corresponds to the chemical formula:

YaTR _b Fecal _d ln _θ CafCUgZrhViCθjSi _k Oi2 ± γ with

TR: a rare earth or a combination of rare earths and

3 (a + b + c + d + e) + 2 (f + g + j) + 4 (h + k) + 5i = 24 ± 2γ

1 <a <3.5; 0 <b <1, 5; 4 <c <5; 0 <d <1, 5; O≤e≤O.8;

0 <f <1; 0 <g <0.05;O≤i≤O.8;O≤j≤O.5; O≤k≤O.5. In general, the ferrite material is produced according to the steps described below:

Step 1 All the oxides and / or carbonates raw materials are weighed so as to produce the appropriate garnet ferrite.

2nd step

All the raw materials are mixed-milled for example with a ball mill (hermetic container filled with stainless steel balls or any other hard non-polluting material) or by attrition

(Rotary system filled with balls in contact which grind the powder by shearing) so as to constitute a first powder.

Step 3

The first powder is heat-treated at a temperature between about 800 ⁰ C and 1100 ⁰ C, preferably under air, under nitrogen or oxygen, in one or more times.

This step corresponds to the conventional step of chamotte or calcination during the manufacture of ferrite material which aims to partially form the desired crystalline phase.

Step 4

The calcined powder is again milled under conditions similar to those of step 2.

Step 5

The regrind powder is then pressed by axial or isostatic pressing with pressures of the order of 1000 to 2000 bar to promote densification at the time of sintering.

Step 6

The regrind and pressed powder is then heated to high temperature. This so-called sintering operation is aimed at the complete formation of the garnet crystalline phase as well as the densification of the ceramic. It is carried out at temperatures between about 900 ⁰ C and 115O ⁰ C and preferably under air or under oxygen.

Examples of realization:

Example 1

To demonstrate the interest of the invention, five formulations were synthesized using the same procedure:

YsFesO ^ (reference A)

YaCu ₉ Fe ₅ Oi ₂ ; a = 2.98 and g = 0.02 (reference B)

YaCu ₉ Fe ₅ Oi ₂ ; a = 2.97 and g = 0.03 (reference C)

YaCu ₉ Fe ₅ Oi ₂ ; a = 2.96 and g = 0.04 (reference D)

YaCu ₉ Fe ₅ Oi ₂ ; a = 2.951 and g = 0.049 (reference E)

The raw materials are industrial oxides CuO, Y2O _{3 and} Fe ₂ O ₃ .

The grindings are carried out by attrition for 30 minutes at a speed of 500 revolutions / min. The grinding balls are made of zirconia, the grinding bowl is made of stainless steel.

The chamissage is carried out at 1050 ^° C. for the formulations containing copper, at 1200 ^° C. for the formulation (A) without copper.

X-ray analysis indicates that the garnet crystalline phase is obtained for the formulations.

The sintering is carried out at 1070 ^° C. or at 1080 ^° C. under oxygen for the formulations with copper and at 148 ^° C. for that without copper, a difference of 41 ^° C. The densities measured after sintering are given below:

Higher densities are obtained with the copper-containing formulations despite lower sintering temperatures of 350 or 360 ^° C.

The saturation magnetic moment per gram is respectively:

(uem being the electromagnetic unit per gram)

Comparison of magnetic losses at low power level between ferrites A, B, C, D and E:

The magnetic losses measured as the width of the gyromagnetic resonance line at 10 GHz (ΔH) are respectively:

Magnetic losses near resonance are higher for samples containing copper but are largely acceptable for the microwave applications under consideration.

Magnetic losses far from resonance are lower for samples containing little copper. They are compatible microwave applications considered such as circulators or microwave insulators.

The high frequency (10 GHz) dielectric losses, tanδ _ε , are:

Dielectric losses are lower for samples containing little copper. They are compatible microwave applications considered such as circulators or microwave insulators.

Claims

Ferritic ferrite structure based on yttrium and iron, characterized in that it corresponds to the following chemical formula:

YaTR _b Fecal _d ln _θ CafCUgZrhViCθjSi _k Oi2 ± γ with

TR: a rare earth or a combination of rare earths and

3 (a + b + c + d + e) + 2 (f + g + j) + 4 (h + k) + 5i = 24 ± 2γ

1 <a <3.5; 0 <b <1, 5; 4 <c <5; 0 <d <1, 5; O≤e≤O.8; 0 <f <1; 0.2-SgO ₁ OO; O≤i≤O.8; O≤j≤O.5; O≤k≤O.5.

2. ferrite material according to claim 1, characterized in that the rare earth or rare earths are of type Gd, Dy or Ho.

3. Composite material based on ferrite, characterized in that it comprises a ferrite material according to one of claims 1 or 2, co-cured with one or more materials of metal type or dielectric type or ferroelectric type.

Magnetic component comprising a ferrite magnetic core according to one of claims 1 to 3.

5. Magnetic component characterized in that it comprises a circulator or a microwave phase shifter, of ferrite material according to one of claims 1 to 3.

6. Magnetic component according to one of claims 4 or 5, operating in a frequency range of about 0.5 Gigahertz to about 20 Gigahertz.

7. A method of manufacturing a material according to one of claims 1 or 2, characterized in that it comprises the following steps: • Weighing oxides or carbonates raw materials to obtain the composition of the ferrite material;

• mixing and first grinding of the raw materials; ^" The chamotte at a temperature between about 800 and 1050 ⁰ C;

• A second grinding of the powder obtained, followed by pressing;

Sintering said regrind powder at a temperature between about 900 and 1100 ^° C.

8. Manufacturing process according to claim 7, characterized in that the first grinding is carried out in a humid medium.

9. The manufacturing method according to one of claims 7 or 8, characterized in that the sintering of the regrind powder is carried out under air or oxygen.

10. Manufacturing process according to one of claims 7 to 9, characterized in that the grinding operations are performed with a ball mill and / or attrition.

1 1. A method of manufacturing the material according to claim 3, characterized in that it comprises the following steps:

• Weighing oxides or carbonates raw materials to obtain the composition of the ferrite material;

• mixing and first grinding of the raw materials;

• The chamotte at a temperature between about 800 and 1100 ° C; • A second grinding of the powder obtained, followed by pressing;

• The mixture of said regrind powder with organic products (binders, deflocculants, surfactants ...) for the production of a paste;

• Thick deposition of this paste by casting or screen printing; • The production of a multilayer structure consisting of a stack of layers of hard ferrite (permanent magnet), metal (silver, silver-palladium, gold) and ferrite according to claim 3;

Sintering of said multilayer structure at a temperature of between approximately 850 and 1100 ^° C .;

12. The manufacturing method according to claim 11, characterized in that the hard ferrite is hexaferrite type.