EP3033755A1

EP3033755A1 - Ferrite component for power applications and process for manufacturing the component

Info

Publication number: EP3033755A1
Application number: EP14745161.1A
Authority: EP
Inventors: Richard Lebourgeois; Gérard CIBIEN; Edouard BRUN
Original assignee: Thales SA
Current assignee: Thales SA
Priority date: 2013-08-14
Filing date: 2014-08-01
Publication date: 2016-06-22
Anticipated expiration: 2034-08-01
Also published as: EP3033755B1; FR3009764A1; WO2015022207A1; FR3009764B1

Abstract

The invention relates to an inductive component comprising a stack of layers, said stack comprising layers based on magnetic ferrite, characterised in that: - the magnetic ferrite respects the chemical formula: Ni_xMg_yZn_zCu_vCo_wFe_2-δO₄ where v is nonzero, 0<δ<0.1 and x+y+z+v+w = 1; and - said component comprises: ● tracks made of noble metal, possibly silver, gold or palladium/silver, distributed over the various levels formed by the surfaces of the layers, in order to form in each level a turn, the turns from one level to another level possibly being electrically connected or not; ● dielectric elements of amagnetic ferrite, which elements are positioned on at least some of said noble metal tracks between at least two layers of magnetic ferrite material, so that said dielectric elements are incorporated in the magnetic ferrite material; and ● a stack of said metal tracks forming said turns, in which each metal track is separated from the metal track of the layer above or below by a dielectric material made of amagnetic ferrite. The invention also relates to a process for manufacturing an inductive component according to the invention, comprising the production of tape casts and a co-sintering operation.

Description

Ferrite component for power application and method of

manufacture of the component. The field of the invention is that of multilayer magnetic components for inductance and transformer functions in power electronics and more precisely that of components comprising ferrite materials used at high and very high frequencies (between 1 MHz and 100 MHz) which can advantageously present low magnetic losses for large applied powers and for operations in a wide temperature range, typically between -50 ° C and + 150 ° C.

In this context, it has already been proposed to use "low loss" ferrite materials intended for high frequency applications (f> 1 MHz), it may especially be ferrites based on nickel, zinc and copper, cobalt. They are used as magnetic cores of various shapes (cores, pots, rods, etc.) and allow the realization of inductors or wound transformers, the winding portion being made using enamelled copper wire or coaxial conductor.

Their advantages are a low sintering temperature (T <950 ° C), an adjustable permeability between 10 and 1000, low magnetic losses at high and very high frequencies, a possible operation in a wide temperature range and a low manufacturing cost. .

Currently, the development of electronic equipment, both in civilian and military applications, is related to the miniaturization of passive and active components. Among these components, the largest are inductive passive components (inductance or transformer). When the volume of the inductive components is reduced, the power density increases, which leads to an increase in the operating temperature. Yields decrease as well as the life of electronic equipment.

In applications that use high electrical powers, the losses of the inductive component are essentially determined by the magnetic losses, said total losses of the magnetic material used for the realization of the core. Ferrites based on nickel, zinc, copper, cobalt are particularly well suited because of their adapted magnetic properties and their high electrical resistivity for this type of application. In addition, multilayer components can be produced from this type of magnetic ferrite material by the coffering technology.

In particular, it has already been proposed to use LTCC technology for "Low Temperature Cofired Ceramic" requiring prior to the realization of cast strips of Ni, Zn, Cu and Co ferrite material, to develop inductive components. For this, the shaping of the ceramic powder consists of producing strips with a thickness of 50 to 300 μιτι. It is then possible to deposit on these strips conductive inks, in particular based on silver, and then stack several strips to make integrated components as shown in Figures 1a and 1b. Ferrite layers 10 are covered with tracks, for example silver 11, interconnected from one layer to another by Via. FIG. 1b shows metal terminations connected to the turns 12.

In order to achieve micro-inductances, coils can be made from screen-deposited metal or other thick layer ceramics deposition technique. To avoid magnetic flux leakage, it is essential to magnetically isolate the turns of the winding or coils.

It is therefore advisable to use dielectric strips that are compatible with ferrite-silver cofiring at 900 ° C. Nevertheless, problems of interdiffusion and of different thermal expansion coefficients make it difficult to produce such components in the presence of intermediate dielectric elements. .

In this context, the present invention proposes to use a dielectric material, which can form cast strips for the elaboration of dielectric elements, integrated in the component and does not disturb the composition of the elements in the presence during the operation of co-curing of all the constituents of the component: cast strips of ferrite material, metal tracks, cast strips of dielectric material.

Thus, the proposed solution consists in using a non-magnetic ferrite, of the same family as the magnetic ferrite chosen, so as to keep the same elements in a similar way, even identical, for magnetic and dielectric parts, and so to assemble ceramic materials whose coefficients of shrinkage and expansion are close.

More precisely, the subject of the invention is an inductive component comprising a stack of layers, said stack comprising layers based on magnetic ferrite, characterized in that:

magnetic ferrite meets the chemical formulation:

Ni _x Mg _y Zn _z CuvC0wFe ₂ -5O ₄ with v not zero, 0 <δ <0.1 and x + y + z + v + w = 1;

said component comprises:

o noble metal tracks that can be silver, gold or palladium-silver, distributed on different levels constituted by the surfaces of the layers, to form at each level a turn, the turns of a level to a other level that can be electrically connected or not;

non-magnetic ferrite dielectric elements, positioned on at least a portion of said noble metal tracks and between at least two layers of magnetic ferrite material, so that said dielectric elements are incorporated in magnetic ferrite material;

o a stack of said metal tracks constituting said turns, wherein each metal track is separated from the metal track of the upper or lower level by a non-magnetic ferrite dielectric material.

According to a variant of the invention, the dielectric elements are based on a nonmagnetic ferrite ceramic having a sintering temperature of between 800 and 1000 ° C.

According to a variant of the invention, the dielectric elements are based on non-magnetic ferrite comprising nickel, zinc and copper.

According to a variant of the invention, the non-magnetic ferrite corresponds to the following formula: Mg _a Ni _b Co _e ZncCu _of Fe ₂ -50 ₄ with:

c> 0.5, d> 0.1, 0 <δ <0.1 and a + b + c + d + e = 1. According to a variant of the invention, w is non-zero.

The invention also relates to a micro-inductor comprising an inductive component according to the invention, characterized in that it comprises coil elements positioned on at least one set of magnetic ferrite material layers, so as to perform a winding integrated in said component, said coil elements being electrically connected to each other.

The subject of the invention is also a transformer comprising an inductive component according to the invention, characterized in that it comprises at least two series of coil elements positioned on at least one set of layers of magnetic ferrite material, so as to making windings integrated in said component, in each series the coil elements being electrically connected.

The invention also relates to an electronic system comprising at least one inductive component, or a micro-inductor or a transformer and at least one capacitor and an electronic control, characterized in that the inductive component or the micro-inductor or the transformer is according to the invention.

According to a variant of the invention, the capacitor comprises a nonmagnetic ferrite material or a permittivity dielectric greater than or equal to 20.

The subject of the invention is also a method for manufacturing an inductive component according to the invention, characterized in that it comprises the following steps:

the production of cast strips of magnetic ferrite material corresponding to the following formula: Ni _x Mg _y Zn _z CuvCOwFe ₂ - δ0 ₄ with v not zero, 0 <δ <0.1 and x + y + z + v + w = 1 ;

the production of metal tracks based on noble metal that may be silver, gold or palladium on the surface of at least a portion of said magnetic ferrite material cast strips;

the production of cast strips based on non-magnetic ferromagnetic dielectric material;

- Cutting elements in said cast strips based on nonmagnetic ferrite material; the positioning of said elements at the level of the metal tracks on the surface of said cast strips of ferrite material;

the addition of magnetic ferrite elements at the periphery of the dielectric elements and at the surface so as to incorporate said dielectric elements in said component;

- An operation of cofreating all the cast strips of magnetic ferrite material integrating the metal tracks, and dielectric elements so as to form said inductive component.

According to a variant of the method, the realization of metal tracks is performed by a screen printing operation.

According to a variant of the method, the metal tracks are deposited by ink jet.

According to a variant of the process, the co-sintering operation is carried out at a temperature of between approximately 800 ° C. and 1000 ° C.

the production of magnetic ferrite inks, non-magnetic ferrites and noble metals;

- Making layers of said stack by jet deposits using said inks.

The invention will be better understood and other advantages will become apparent on reading the description which follows given by way of non-limiting example and by virtue of the appended figures among which:

- Figures 1a and 1b illustrate a micro-inductance of the prior art;

FIGS. 2a and 2b illustrate a transformer structure of the invention comprising a stack of metal turns produced on the surface of magnetic ferrite cast strips, said turns being covered with non-magnetic ferromagnetic dielectric; FIG. 3 illustrates the losses measured at the primary level of a transformer whose structure comprises a stack of strips which are cofired with a conventional dielectric and with a nonmagnetic ferrite dielectric, as a function of the applied voltage;

FIG. 4 illustrates a component variant according to the invention, in which the dielectric element completely covers a coil element;

FIGS. 5a and 5b illustrate an example of a component according to the invention highlighting the insulation of two turns via non-magnetic ferrite elements;

FIGS. 6a and 6b illustrate an example of a connection diagram of 2 turns, respectively on the primary side and the secondary side in an exemplary transformer;

FIG. 7 illustrates the losses measured at the primary level of a transformer comprising a component similar to that illustrated in FIG. 4, as a function of the applied voltage;

FIG. 8 illustrates the dimensions of a conventional commercial transformer core used to establish performance comparisons with a component of the invention;

FIG. 9 illustrates a block diagram of an electronic system based on a multifunctional ceramic substrate.

In general, the inductive component of the present invention is a component comprising layers of magnetic ferrite material having the formula: Ni _x Mg _y Zn _z CuvC0wFe ₂ -5O ₄ with v not zero, 0 <δ <0.1 and x + y + z + v + w = 1.

It may advantageously be a material based on Ni, Zn, Cu and Co but without limitation.

Indeed, multilayer components made from ferrites

NiZnCuCo have two important advantages:

- very low losses at high frequency.

the possibility of being sintered at a low temperature, around 900 ° C., ie 400 ° C., below the sintering temperature of the conventional ferrites, allowing them to be co-cured with dielectrics and metals such as gold or silver. Thus, in an inductive component of the invention, the coils can be made from silver deposited by screen printing or another technique, for example by ink jet. It should be noted that all the ceramic deposits can also use the inkjet technique.

To avoid magnetic flux leakage, a non-magnetic ferrite, also based on Ni, Zn and Cu (nonmagnetic ferrite may also comprise Co) is used so as to retain the same chemical elements for the magnetic and non-magnetic parts, and so to assemble ceramic materials whose expansion coefficients are close.

For this, by adjusting the composition of the ferrite, it is possible to modulate the Curie temperature, so as to lower it and that below the ambient temperature. It is thus possible to render a non-magnetic ferrite above ambient temperature and to enable it to provide an insulation function and thus make it possible to prevent magnetic flux leakage by adjusting the composition thereof.

The windings are made from silkscreened silver and covered with non-magnetic ferromagnetic dielectric elements to prevent magnetic flux leakage.

The combination of NiZnCuCo ferrites with low-temperature sintering dielectrics and silver-based metallizations thus enables the production of high-performance, cost-effective magnetic components.

It is thus easy to realize inductance and transformer functions that are necessary for the proper functioning of energy converters or power amplifiers.

Embodiment of a transformer according to the invention

A multilayer transformer was made from a cast NiZnCuCo ferrite. The schema of the structure is given in FIGS. 2a and 2b. Stack 4 layers as described in top view in Figure 2b alternating the side where out the silver tracks. We close then with thicker layers of ferrites. We finally end with the connections of the turns between them.

The component thus comprises a ferrite core 20, around which is deposited a coil element 30, covered with a dielectric element 40, of the invention is a nonmagnetic ferrite, and then are deposited in a complementary manner magnetic ferrite elements 21 around of the dielectric element 40 of nonmagnetic ferrite.

To achieve this type of structure, cast strips are produced:

- Of magnetic ferrite material, on which are printed the silver coil elements;

- Amagnetic, dielectric ferrite material;

cutting elements of dielectric material and of magnetic ferrite material, arranged in the same plane.

The whole is cofritté at 900 ° C under air for 2 hours so as to realize the transformer.

After sintering, electrical measurements were made at the input inductance (called the primary) and the output inductance (so-called secondary), in terms of power losses. More precisely, a power is injected into the component and the dissipated power is measured.

Two types of structures were tested after production according to the process described above: one using commercial dielectric strips (reference: ULF140 from AFM Microelectronics Inc.), the other, nonmagnetic ferrite strips, of composition: Nio.05Cuo _.2 Zno.75 e1.96O4

It is found that the primary inductances are low and quite comparable between the two transformers, and the leakage inductances relatively large, these leakage inductances accounting for the coupling between the primary and secondary.

The evolution of the losses at 2 MHz, as a function of the applied rms voltage, was measured for these two transformer structures, on the primary side. The results are given in FIG. 3. The curve 3a relates to the structure with the ULF dielectric 140, the curve 3b relates to the structure with the nonmagnetic ferrite dielectric.

It is found that the losses are higher when ULF140 dielectric is used, which can be explained by the presence of stresses generated by the difference of the shrinkage coefficients.

To reduce the leakage inductance and further improve the coupling, the Applicant has made structures for which the output of the silver conductors does not pass through the magnetic ferrite, for a transformer referenced TC, as illustrated in FIG. 4. According to this variant, the dielectric element 40 'covers the entirety of the coil element 30.

Figures 5a and 5b show two sectional views of an inductive component in a basic or more elaborate form, having tracks forming two turns isolated by means of nonmagnetic ferrite elements. Such a configuration can be achieved by a succession of magnetic ferrite layers C _fmii nonmagnetic ferrite elements 40 thus isolate the two turns 30, and 30 _{i +} i from each other.

FIGS. 6a and 6b illustrate an example of a connection diagram of the two turns respectively on the primary side and on the secondary side, illustrated as representatives of the portions of solenoids.

The primary and leakage inductances have been measured, the values obtained are given below for the CT transformer:

There is a clear decrease in leakage inductance indicating better coupling.

The power losses were measured for the CT transformer under the same conditions as for transformers TA and TB. We here too, a clear improvement, with a gain of more than a factor of 3 compared to the previous best result. The Applicant was then able to measure up to 15 V rms.

Figure 7 illustrates the total losses for the CT transformer, as a function of the applied rms voltage, measured on the primary side.

To evaluate the performance of this component in relation to the state of the art, the Applicant has chosen to compare it with a 2: 2 transformer, having 2 turns at the primary and 2 turns at the secondary made with copper wire of diameter. 300 μιτι on a Ferroxcube ferrite core 4F1. This choice is justified by the following remarks:

the transformer TC being of small size, the inductance values are low and to obtain similar values with a larger core, it is necessary to choose an even lower permeability, which prevents the use of Mn-Zn ferrites. ;

- This ferrite is a high frequency power ferrite therefore perfectly suited to the present comparison;

- its losses at 3 MHz and 10 mT, given by the manufacturer, are 200 mW / cm ³ .

The Ferroxcube ferrite core 4F1 retained is a core type E22, the letter E corresponding to the shape of the core as shown in the diagram of Figure 8, illustrating the ribs.

Dimensions are given in mm. The effective parameters for a core consisting of 2 E contiguous are shown in the table below:

The E22 core at 4F1 was wound with 2 turns for the primary and 2 turns identical to the secondary. The Applicant measured the primary and leakage inductances that were compared to those of the CT transformer. The coupling coefficient was also measured in comparing primary and secondary voltages for fixed primary excitation.

The results are similar, with slightly better performance for the cofired CT transformer.

To finalize the comparison, the Applicant measured the losses at 2 MHz according to the applied voltage. For an effective voltage of 15 V (sinusoidal signal), the results are as follows:

- 540 mW for the cofired CT transformer;

- 480 mW for the transformer in 4F1.

Similar losses (about 10% less for the transformer in 4F1) were obtained but for a cofritted structure of volume 6 times lower. If one compares neither the real volumes but the apparent volumes, one obtains a gain of a factor 10, demonstrating by the same, the potential of the cofired components realized. This type of inductive component of the present invention which is efficient, of small size, can advantageously be integrated into more complex systems comprising all the passive functions based on ceramics (inductances, transformers, capacitors, filters) in a substrate thanks to the use of compatible materials and coffering technology. On one side of the substrate can be reported discrete components and on the other side, a cooled plate.

Such a system is illustrated in FIG. 9, which shows, on a ceramic substrate 100, a co-sintered multilayer structure 101, elementary layers 102, a cooled plate 300, an electrical control 400 and a function to be fed 500. The set of layers components of inductive components and capacitors are thus advantageously made of magnetic ferrite material and non-magnetic ferrite.

Claims

1. An inductive component comprising a stack of layers, said stack comprising layers based on magnetic ferrite characterized in that:

magnetic ferrite meets the chemical formulation:

said component comprises:

2. Inductive component according to claim 1, characterized in that the dielectric elements are based on a nonmagnetic ferrite ceramic having a sintering temperature between 800 and 1000 ° C.

3. Inductive component according to one of claims 1 or 2, characterized in that the dielectric elements are based on nonmagnetic ferrite comprising nickel, zinc and copper.

4. Inductive component according to claim 3, characterized in that the nonmagnetic ferrite has the following formula: Ni _a Mg _b ZncCu _d Co _e Fe ₂ - ₅ 0 ₄ with:

c> 0.5, d> 0.1, 0 <δ <0.1 and a + b + c + d + e = 1.

5. inductive ferrite-based component according to one of claims 1 to 4, characterized in that w is non-zero.

6. Micro-inductor comprising an inductive component according to one of claims 1 to 5, characterized in that it comprises coil elements positioned on at least one set of magnetic ferrite material layers, so as to achieve an integrated winding said component, said coil elements being electrically connected to each other.

7. Transformer comprising an inductive component according to one of claims 1 to 5, characterized in that it comprises at least two sets of coil elements positioned on at least one set of magnetic ferrite material layers, so as to achieve windings integrated in said component, in each series the coil elements being electrically connected.

An electronic system comprising at least one inductive component, or a micro-inductor or a transformer and at least one capacitor and an electronic control, characterized in that the inductive component or the micro-inductor or the transformer responds to one of the Claims 1 to 7.

9. Electronic system according to claim 8, characterized in that the capacitor comprises a nonmagnetic ferrite material or a dielectric permittivity greater than or equal to 20.

10. A method of manufacturing an inductive component according to one of claims 1 to 5, characterized in that it comprises the following steps: the production of cast strips of magnetic ferrite material corresponding to the following formula: Ni _x Mg _y Zn _z CuvCOwFe ₂ - δ0 ₄ with v not zero, 0 <δ <0.1 and x + y + z + v + w = 1 ;

- Cutting elements in said cast strips based on nonmagnetic ferrite material;

the positioning of said elements at the level of the metal tracks on the surface of said cast strips of ferrite material;

1 1. Method of manufacturing an inductive component, according to claim 10, characterized in that the production of metal tracks is performed by a screen printing operation.

12. Method of manufacturing an inductive component, according to claim 10, characterized in that the metal tracks are deposited by ink jet.

13. The method of manufacturing an inductive component according to one of claims 10 to 12, characterized in that the cofinding operation is carried out at a temperature between about 800 ° C and 1000 ° C.

14. Method of manufacturing an inductive component according to one of claims 1 to 5, characterized in that it comprises the following steps:

- Making layers of said stack by jet deposits using said inks.