WO2011083348A1

WO2011083348A1 - Tunable dielectric composite and method for the production thereof

Info

Publication number: WO2011083348A1
Application number: PCT/IB2009/055753
Authority: WO
Inventors: Paula Maria Lousada Silveirinha Vilarinho; Fu Zhi; Aiying Wu; Angus Kingon
Original assignee: Universidade De Aveiro
Priority date: 2009-12-11
Filing date: 2009-12-15
Publication date: 2011-07-14
Also published as: PT104881A

Abstract

The present invention relates to composite dielectric materials with low dielectric losses and high tunability of the relative dielectric permittivity, in the form of thick films to be used and integrated in circuits, as passive components of tunable devices, for application at radio and microwave frequencies, and methods for the production thereof, specifically with the combination of the electrophoretic deposition method with the sol gel method for manufacturing said thick composite films, composed of a dielectric phase with low dielectric losses (high Q), such as the rare earth barium titanates BaO-Re₂O₃-TiO₂ (Re = Nd, Sm, La, in particular), the neodymium titanate (BaNd₂Ti₅O₁₄, BNT), and of a dielectric phase with a tunable dielectric permittivity that is tunable by the electric field, as components of the solid solution between barium titanate and strontium titanate BaTiO₃ - SrTiO₃, such as (Ba_0.5 Sr_0.5) TiO₃ (BST), in particular.

Description

Title of Invention: COMPOSITE DIELECTRIC

TUNING AND MANUFACTURING PROCESS

Technical field of the invention

[1] The present invention relates to: (1) dielectric materials, more specifically relating to low dielectric loss composite dielectric materials and high tunability of relative dielectric permittivity by the action of the electric field in the form of thick films, not exceeding 10 microns and not less than 100 microns thick, on flexible metal substrates and rigid non-metallic substrates for application and circuit integration as passive components of tunable devices such as tunable oscillators, phase shifters phase displacement), varactors, among others, namely for use at radio frequencies and microwave frequencies, and (2) the method of manufacturing these same thick films, more specifically by combining the electrophoretic deposition process with the sun process gel for the manufacture of said film thick composites, consisting of a low dielectric loss (high Q) dielectric phase, such as rare earth barium titanates, BaO-Re ₂ 0 ₃ -Ti0 ₂ (where Re = Nd, Sm, La, among others), as neodymium (BaNd ₂ Ti ₅₀ 0i ₄ , BNT) among others and by a dielectric permittivity phase tunable by the action of the electric field as compounds of the solid solution between barium titanate and strontium titanate, BaTi0 ₃ - SrTi0 ₃ , such as (Bao. ₅ Sr ₀₅ ) TiO ₃ (BST), among others.

Summary of the invention

[2] The present invention is useful for: matching low dielectric losses in the same film with the tunability of dielectric permittivity, properties that do not exist in one material and are fundamental for devices operating at high frequencies; miniaturization of devices for microwave frequency applications; and the possibility of application to many other electroceramic systems, anticipating the expansion of existing applications and the manufacture of new electronic devices for application at high frequencies.

[3] The present invention describes a tunable composite dielectric having the

characterized in that it comprises a tunable dielectric material and comprises a non-tunable dielectric material composed of one or more of: tungsten bronzoid material, namely BaO-Re ₂ 0 ₃ -Ti0 ₂ , where Re = Nd, Sm, La, among others; MgT 10 ₃ ; Ba ₂ Ti ₉ O ₂₀ ; Zr ₀ .8 iSn ₀ . ₂ O4; Ba (Mgi _{/ 3} Ta _2/3 ) 0 ₃ ; or the like; or their compositions. [4] A preferred embodiment of the present invention has the feature that said non-tunable dielectric material is BaNd ₂ Ti _{50 0} ₄ , BNT.

[5] A preferred embodiment of the present invention has the feature that said tunable dielectric material comprises one or more of: the solid solution of barium strontium titanate, Ba _! . _x Sr _x TiO ₃ , BST; BaT 10 ₃ ; Pb (Zr, Ti) 0 ₃ ; or the like; or their compositions.

[6] A preferred embodiment of the present invention has the characteristic that said tunable dielectric material is (Bao. ₅ Sr ₀₅ ) TiO ₃ .

[7] A preferred embodiment of the invention has the characteristic comprises 80 to 95% by weight of said non - tunable dielectric material of low loss such as BaO-like Re ₂ 0 ₃ -Ti0 _2, wherein Re = Nd, Sm, La among others, and comprising 5 to 20% by weight of at least one additional high-tunability phase, such as solid barium and strontium titanate solutions.

[8] A preferred embodiment of the present invention is that it comprises dielectric and tunable phases with thicknesses between 5 and 100 microns, preferably between 10 and 80 microns, even more preferably with thicknesses between 50 and 80 microns.

[9] A preferred embodiment of the present invention has the feature of further comprising a metallic substrate such as platinum, gold, silver, copper, nickel, among others; or non-metallic substrate such as alumina, A1 ₂ 0 ₃ , among others, for depositing said low dielectric loss thick layer, BNT.

[10] Preferred embodiments of the present invention comprise devices.

electronic devices, comprising varactors, tunable filters, phase-shifting, co-planar and linear devices, and phase-array antennas, thick film multilayer capacitors, planar capacitors having the feature of comprising one or more tunable dielectric composites as previously described. .

[11] The present invention further describes a process for manufacturing said tunable composite dielectric which has the feature of combining the electrophoretic deposition process with the sol gel deposition to achieve a combination of a low loss non-tunable dielectric material and of a tunable dielectric material, namely the solid solution of barium strontium titanate, Ba _! _x Sr _x Ti0 ₃ , BST, in particular (Bao. ₅ Sr ₀₅ ) TiO ₃ or compositions thereof.

[12] A preferred embodiment of the present invention has the feature of comprising the following steps:

- Thick layer electrophoretic deposition of the non-tunable low dielectric loss dielectric matrix, such as BaO-Re ₂ 0 ₃ -Ti0 ₂ , where Re = Nd, Sm, La, among others, or compositions thereof; infiltration by tunable phase phase sol gel methodology of said tunable dielectric material in the matrix layer;

- sintering of the composite film for densification.

[13] A preferred embodiment of the present invention has the feature of comprising for depositing said thick layer of the low dielectric loss phase matrix, BNT: metal substrates such as platinum, gold, silver, copper, nickel, among others; or non-metallic substrates such as alumina, A1 ₂ 0 ₃ , among others.

[14] A preferred embodiment of the present invention has the feature of comprising the following steps:

- synthesis of the ceramic matrix powders by the preparation of composite thick films which involves the prior preparation of ceramic powders of the matrix composition, which for the particular case of BaNd ₂ Ti ₅ 0i ₄ powders, precursors of BaC0 ₃ , Nd ₂ 0 5 and TiO ₂ are mixed in appropriate proportions to obtain the subject compound in zirconia milling ball mills for about 24 hours in aqueous or alcoholic medium, the resulting mixture being dried and calcined for synthesis of said compound;

- Preparation of stable suspension of matrix powders for electrophoretic deposition by preparation of the stabilized suspension by different suspending media, such as acetone, (CH ₃ ) 2 CO,> 99.9, ethanol, C ₂ H ₅ OH,> 99.9 , and acetic acid CH ₃ COOH,> 99.9, which for acetone I ₂ > 99.8%, dissolved in isopropanol, C ₃ H ₇ OH,> 99.9%, is used as an additive to adjust the pH value. suspension, in this case of BNT, and the suspensions used have the

10g / liter concentration of BNT powders and are ultrasonicated to complete dispersion of the powders;

- electrophoretic thick layer deposition of the matrix composition, the substrates being selected from a group of flexible metals comprising Pt, Ni, Cu and others, and from a group of rigid oxides comprising A1 ₂ 0 ₃ ; others, whereby the thick layer of the matrix material is deposited by electrophoretic deposition, that under the action of an electric field the charged particles suspended in the suspending medium move towards the opposite charge electrode and deposit on the substrate forming a continuous layer, the film thickness being dependent on the suspension concentration, applied voltage and time, and films of 10 to 80 microns thickness can be deposited under 40 V to 600 V in 30 s 10 min, and the films deposited dried at 90 ° C for up to 24 h.

- stable sol preparation of the second phase composition, wherein the phase sun is prepared using as starting precursors Ba (CH ₃ COO) ₂ ,> 99.9%, Sr (CH ₃ COO) ₂ - ½H ₂ 0,> 99.9 %, and Ti (OC ₄ H ₉ ) _4, > 99.9%, with glacial acetic acid CH ₃ COOH, > 99.9, and ethylene glycol, HOCH ₂ CH ₂ OH,> 99.9, are used as solvents, and acetylketone C ₅ H ₈ 0 _2, > 99.9 as Ti stabilizer, being Ba (CH 3COO) ₂ powders and Sr (CH ₃ COO) ₂ * 1 / 2H ₂ 0 with a molar ratio of 5: 5 dissolved in acetic acid under constant stirring at 80 ° C, Ti (OC ₄ H ₉ ) _{4 being} stabilized with ethylene glycol and acetyl acetone and this solution mixed with the Ba (Ac) ₂ / Sr (Ac) _{2 solution} with a 1: 1 molar ratio under constant agitation, and after mixing for 2 hours the solution concentration is adjusted to 0.25 mol / 1. and stirred for an additional 1 hour;

- scattering infiltration, spin coating, of the second phase sun, after drying the films are infiltrated by spreading with the tunable dielectric phase sun, and after infiltration the films are dried and pyrolyzed at 350 ° C for 5 minutes. minutes on a hot plate, this cycle being repeated up to 10 times;

- sintering the composite films in air atmosphere between 1100 and 1300 ° C for different time periods, depending on the substrate, to densify the composite. Background of the Invention

[15] Wireless applications, based in part on devices operating at

radio frequencies (RF) and integrated circuits are rapidly expanding and are an important market for semiconductor manufacturers [1]. These applications include mobile phones, blue tooth (personal wireless connections), Office voice (digital voice business communications), video, data transmission over wireless local area networks (WLAN), global positioning systems (GPS). and car safety control, among others [2].

[16] In terms of materials, the need to use microwave frequencies in miniaturized circuits has resulted in a continuous and increasing demand for tunable passive components under the action of the electric field, such as tunable oscillators, phase shifters. phase), varactors, among others [3] [4]. For these applications are critical aspects one permittivity DIELEC trophic and _R moderate to high (the size of the dielectric resonator is proportional to 1 / _r ^m), associated with low dielectric loss (0.005 <tan <0.01) (high factor Q) and high dielectric tunability,> 10 [5, 6].

[17] Quality factor Q (defined as the inverse of dielectric loss 1 / tan d) is considered to be the most important parameter of the dielectric behavior of a material for a microwave frequency operating device. Parameter Q has a significant effect on the speed and quality of the electromagnetic wave passing through the component, contributing to noise reduction, a high Q allows signal distribution or storage with minimal loss. The use of high Q dielectric materials thus results in less operating power consumption, increased battery life and battery life, and reduced device size and weight. It is acknowledged that future communications will require a bandwidth frequency hopping for communication using frequency hopping techniques so that a large amount of data can be transmitted for each bandwidth. Under these circumstances fast-acting tunable filters are a key component [7].

[18] However, achieving low dielectric losses simultaneously with dielectric permittivity and high tunability in the same material has been shown

problematic, so far no material meeting these characteristics is known, since the combination of these two properties is fundamentally difficult to achieve [6]. In general dielectric materials which have high dielectric permittivity (> 500) and good dielectric permittivity tunability, of which ferroelectric materials are a good example, concurrently exhibit high dielectric losses, which drastically limit their use to microwave frequencies. . There is thus in practice a compromise between the tunability of dielectric permittivity and the dielectric loss of a given material.

[19] Of the ferroelectric materials, it is known that barium strontium solid solution (Bai_ _x Sr _x Ti0 ₃ ) (BST) compositions are promising candidates for applications in tunable devices for use at microwave frequencies such as filters. , phase shifters, varactors, and others [8]. The maximum dielectric permittivity that occurs near ambient temperature and the ability to modify it by changing the solid solution stoichiometry of Ba _! . _x Sr _x Ti0 ₃ make this family of potential materials candidates for such applications. However, there are numerous problems associated with the use of high frequency BST compositions, in particular related to the high dielectric losses that characterize these materials [9,10]. They have been conducted various studies with the aim of reducing the dielectric loss BST [11], for example by the addition of additives such as MgO, A1 ₂ 0 _3, among others, known as Q promoters [7, 12, 13]. However these additives may react chemically with BST, making their properties at microwave frequencies markedly dependent on processing parameters that may damage device performance.

[20] Another approach referred to in the literature, because it is intuitively believed that dielectric losses of ferroelectrics can be improved by combining with linear behavior and low loss dielectrics is the 'combination' of these materials. By combining a series non-tunable low dielectric loss dielectric material with tunable BST, the dielectric losses and tunability of the layered structure have been anticipated [14]. [21] In terms of linear dielectric materials that may be used to microwave frequencies they must also exhibit low Q or high loss, high dielectric permittivity and low temperature coefficient of permittivity _R CT (CT _r avoids deviations low frequency due to temperature variations) [15]. Within the linear dielectrics of low dielectric losses, the family of titanium, barium and rare earth bronzoids, BaO-Re ₂ 0 ₃ -Ti0 ₂ (where Re = Nd, Sm, La, among others) represents a commercial family of materials with important applications in microwave due to high values of _R (85), lower tan d (0.0005) to ~ 1 MHz and low CT _r (-113 ppm / ° C) (data for Band ₂ ₄ Ti ₅ 0i) [16]

General Description of the Invention

[22] In the context of the manufacture of low dielectric materials with low dielectric losses and high tunability of relative dielectric permittivity in the form of thick films, the combination of BaO-Re ₂ 0 ₃ -Ti0 ₂ compositions with Bai- _x compositions Sr _x Ti0 _3i not mentioned so far may result in materials with low dielectric losses and high tunability of dielectric permittivity.

[23] From a manufacturing standpoint, this growing wireless industry needs low cost manufacturing technologies that enable the manufacture of devices with high density, small component and low weight [17]. Miniaturization of planar circuits, antennas, filters, couplers, are some examples of current needs. And, because of this current volume reduction requirement, one of the solutions to consider will be the manufacture of ceramic dielectric film (thick or thin) to replace current monolithic ceramic dielectrics, which is also a force driving demand for mass production processes associated with low production costs [18].

[24] Thick film preparation techniques are usually based on

densification of porous films. A layer of powders is obtained after deposition of a suspension on a substrate and the distinction between the different methodologies is made on the basis of the methodology used to deposit the powder on the substrate and includes tape casting, screen printing ( 'screen printing', jet printing and electrophoretic deposition (EPD) [19].

[25] Thus, dielectric thick films fabricated by strapping or screen printing have high potential for use as elements of hybrid radio frequency / microwave circuits because of the associated low costs. It has been stated that the principles that assist in the design and operation of components / devices of functional materials (dielectric and ferroelectric) for microwave frequency operation can be applied to devices made from thick film with minor adjustments [20]. However, to date, the high losses and Technological limitations in linear dimensions associated with thick film technology continue to limit the use of thick films of functional materials in tunable devices. At the same time, planar devices made from thick films are expected to exhibit lower tunability than thin films, as only the top of the thick film will effectively contribute to tuning, while the remaining film can be considered as a non-tunable region of capacity parallel to the top of the film [9, 10].

[26] In terms of methodologies for thick film deposition, the importance of electrophoretic deposition stems from its unique characteristics, of which it is worth emphasizing the ability to conform over a wide range of complex and porous three-dimensional shapes and structures. Additionally, and not least for the manufacture of the above mentioned devices, it is a simple, versatile, low cost manufacturing method and easily adaptable to an industrial scale of production. And when compared to other thick film manufacturing methods, electrophoretic deposition allows for the production of very uniform layers with easy thickness control [21].

[27] In this context, the present invention is designed to overcome the difficulty associated with the lack of material that combines low dielectric losses with high tunability of dielectric permittivity and to contribute to the development of versatile, low cost manufacturing techniques without geometric limitations. , enabling the manufacture of miniaturized devices at competitive costs. Thus, the present invention combines in a composite material composed of two materials each having optimized properties: one characterized by low dielectric losses (high Q) and the other by a high dielectric permittivity tunability. On the other hand, the present invention combines the electrophoretic deposition method with the sun gel deposition for the manufacture of thick composite films of controlled thicknesses and on substrates of variable geometries.

[28] The present invention is intended to manufacture thick films of dielectric materials of optimized properties (low dielectric losses, high Q and tunability) for use in, for example, tractors, tunable filters, phase shifters. co-planar and linear and phase array antennas. The present invention can also produce multi-layer thick film capacitors to enable the manufacture of high capacity, low cost tunable vertical capacitors. These capacitors as well as planar capacitors form the basis of high power tunable filters and resonators.

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Detailed Description of the Invention

[51] The present invention comprises in particular:

(i) the manufacture of low dielectric loss thick (high Q) dielectric composite films of less than 0.001 to 1 MHz, intermediate dielectric permittivity between 70 and 300 and high tunability of dielectric permittivity, tunability greater than 14 percent to 2 kV / cm electric fields in which the phase responsible for the low losses belongs to the BaO-Re ₂ 0 ₃ -Ti0 ₂ tungsten bronzoid family (Re = Nd, Sm, La, among others), such as BaNd ₂ Ti ₅₀ 0i ₄ (BNT) and the phase responsible for high tuning is from the solid solution family BaTi0 ₃ - SrTi0 ₃ , as (Bao. ₅ Sr ₀₅ ) TiO ₃ (BST), allowing: 1) to make low film compatible dielectric losses with the tunability of the dielectric permittivity, properties that do not exist in one material and fundamental for devices operating at high frequencies, 2) the miniaturization of devices for applications at the frequencies of 3) the possibility of application to many other electroceramic systems, anticipating the extension of existing applications and the manufacture of new electronic devices for application at high frequencies;

ii) the development of manufacturing method of said composites by combining the electrophoretic deposition methodology for deposition of a thick layer of the low dielectric loss (BNT) matrix on metallic substrates such as platinum, gold, silver, copper , nickel, among others and non-metallic substrates such as alumina (A1 ₂ 0 ₃ ) and others, with the sol gel methodology, for infiltration of the tunable phase (in this case BST) in this thick layer, so that the final properties of the composite controlled by the thickness and proportion of each of the phases in the composite.

Brief presentation of the invention

[52] Thick composite dielectric films are revealed that combine the properties of low dielectric loss (high Q) and intermediate dielectric permittivity with the tunability of dielectric permittivity and the method of manufacture of these same films. Thick composite dielectric films with these characteristics are intended for applications in phased array antenna systems, filters and similar devices for high frequency operation.

[53] Their principle is the combination in the composite film of a low dielectric loss phase, namely the barium and rare earth titanate family ( BaO-Re ₂ 0 ₃ -Ti0 ₂ (where Re = Nd, Sm, La, among others) as BaNd ₂ Ti ₅ 0i ₄ (BNT), with a highly tunable phase of dielectric permittivity, namely the solid solution family Bai_ _x Sr _x Ti0 ₃ , which makes it possible to combine features of dielectric permittivity with low dielectric losses in a single film, characteristics that cannot be matched to a single material, thus filling a material technology gap for microwave frequency applications and opening up the possibility of developing new devices.

[54] A method of making low dielectric loss-tunable thick composite dielectric films of 5 to 80 micron thickness, preferably 10 to 50 micron thickness, is disclosed by combining electrophoretic deposition and sol gel methodology, on metallic substrates such as platinum, gold, silver, copper, nickel, among others and non-metallic substrates such as alumina (A1 ₂ 0 ₃ ) and others, comprising:

1) thick dielectric matrix deposition of the low dielectric loss by electrophoretic deposition,

2) infiltration by soluble phase gel methodology of tunable characteristics, in the matrix layer,

3) sintering of the composite film for its densification.

[55] Composite films consist of about 80 to 95% by weight of low loss (high Q) dielectric phase material such as barium and rare earth titanates and about 5 to 20% by weight of hair. least one additional phase of high tunability, such as solid barium and strontium titanate solutions. The final properties of the thick composite film can be controlled by the thickness and proportion of each phase in the composite.

[56] The relevance of the invention relates to: (i) the possibility of making low dielectric losses compatible with dielectric permittivity, which are non-existent in one material and fundamental for devices operating at high frequencies, ii) the possibility of miniaturization of the devices and iii) the possibility of application to many other systems of

electroceramics, anticipating the widening of existing applications and the manufacture of new electronic devices for application at high frequencies.

Detailed Description of Preferred Accomplishments

[57] In order to fill a current material gap

At high frequency tunable dielectrics, the present invention discloses thick composite films and manufacturing methodology of said low dielectric loss and tunable films. Thick dielectric composite films have several advantages over materials for tunable applications in normal use. frequently. These advantages include: (i) the possibility of matching the high Q phase with the high tunability phase in a single film, characteristics not existing in one material, ii) the possibility of manipulating the final dielectric characteristics of the film by manipulating the process variables. iii) the possibility of integrating several circuit elements into the same substrate and iv) miniaturization of the devices.

[58] The thick composite films object of this invention preferably comprise a matrix of (BaO-Re ₂ 0 ₃ -Ti0 ₂ (where Re = Nd, Sm, La, among others) as BaNd ₂ Ti ₅₀ 0i ₄ (BNT), and a second phase of high tunability of the dielectric permittivity, namely the solid solution family of Ba _! _x Sr _x Ti0 ₃ , for example Bao. ₅ Sr ₀₅ Ti0 _3. However, other low dielectric loss dielectric materials may be partially or wholly used in place of BaO-Re ₂ 0 ₃ -Ti0 ₂ (where Re = Nd, Sm, La, among others) such as MgTi0 ₃ , Ba ₂ Ti ₉ O ₂₀ , Zr _{0 8} TiSn ₀₂ O ₄ , Ba (Mgi _{/ 3} Ta _2/3 ) 0 ₃ and the like, and the tunable dielectric permittivity phase may include (Bai_ _x Sr _x ) Ti0 ₃ , BaTi0 ₃ , Pb (Zr, Ti) 0 ₃ and the like.

[59] The preparation of these thick composite films comprises the following steps:

1) synthesis of ceramic matrix powders: the preparation of thick composite films involves the preparation of ceramic powders of the matrix composition. For the particular case of powders band ₂ Ti ₅ 0i _4, precursors BaC0 _3, Nd ₂ 0 ₅ and Ti0 ₂ are mixed in appropriate proportions to obtain the compound concerned in ball mills with grinding media of zirconia for about 24 hours in aqueous or alcoholic medium. The resulting mixture is dried and calcined for synthesis of said compound. The calcination temperature is determined by thermogravimetric analysis and the sintering temperature, determined by dilatometric analysis, is chosen to ensure the maximum densification of the composite film.

2) preparation of stable suspension of matrix powders for deposition

electrophoretic: preparation of the stabilized suspension may be carried out by different suspending media, such as acetone ((CH ₃ ) 2 CO,> 99.9), ethanol (C ₂ H ₅ OH,> 99.9%), and acetic acid (CH ₃ COOH,> 99.9%). For acetone I ₂ (> 99.8%, Aldrich) dissolved in iso-propanol (C ₃ H ₇ OH,> 99.9%) is used as an additive to adjust the pH value of the suspension, in this case NTB. Suspension stability is analyzed by UV light transmittance, mean particle size distribution and zeta potential of the suspension. Based on the variation of zeta potential, the pH of the suspension is adjusted to obtain the optimum suspension homogenization which will ensure the quality of the final films. The suspensions used have a concentration of 10g / liter of BNT powders and are ultrasonicated until complete dispersion of the powders.

3) thick layer electrophoretic deposition of the matrix composition: the substrates are selected from a group comprising flexible metals Pt, Ni, Cu and others , and from a group of oxides comprising governed A1 ₂ 0 _3, among others. The thick layer of matrix material is deposited by electrophoretic deposition. Under the action of an electric field the charged particles suspended in the suspending medium move towards the opposite charge electrode and deposit on the substrate forming a continuous layer. Film thickness depends on suspension concentration, applied voltage and time. Under the present conditions, films 10 to 80 microns thick can be deposited under 40 V to 600 V within 30 s to 10 min. Deposited films are dried at 90 ° C for up to 24 h.

4) stable sol preparation of the second phase composition: The phase sun is prepared using as starting precursors Ba (CH ₃ COO) ₂ (> 99.9), Sr (CH ₃ COO) 2 · ½H ₂ 0 (> 99.9% ) and Ti (OC ₄ H ₉ ) ₄ (> 99.9%). Glacial Acetic Acid (CH ₃ COOH)

(> 99.9%) and ethylene glycol (HOCH ₂ CH ₂ OH,) (> 99.9%) are used as solvents, and acetyl acetone (C ₅ H ₈ 0 ₂ ) (> 99.9%) as a stabilizer for Ti alkoxide. (CH ₃ COO) ₂ and Sr (CH ₃ COO) ₂ * 1 / 2H ₂ 0 with a molar ratio of 5: 5 are dissolved in acetic acid under constant stirring and at 80 ° C. Ti (OC ₄ H ₉ ) ₄ is stabilized with ethylene glycol and acetylacetone and this solution mixed with Ba (Ac) ₂ / Sr (Ac) _{2 solution} with a 1: 1 molar ratio under constant stirring. After mixing for 2 hours, the solution concentration is adjusted to 0.25 mol / l and stirred for a further 1 hour.

5) Second phase sun spin coating: After drying the films are infiltrated with the tunable dielectric phase sun. After infiltration the films are dried and pyrolyzed at 350 ° C for 5 minutes in hot plate. This cycle is repeated up to 10 times.

6) sintering of composite films as described below: thick composite films are sintered in air atmosphere between 1100 and 1300 ° C for different time periods, depending on the substrate, to densify the composite.

[60] Although thick composite films have already been manufactured for

Tungsten bronzoid compositions such as BaNd ₂ Ti ₅₀ 0i ₄ and other low dielectric loss (high Q) dielectrics have not yet been combined in the form of thick films with proprietary compositions, oxides or additives. tunability of dielectric permittivity across the electric field to adjust the electronic properties of the tunability / phaser of thick film

Description of the Figures

[61] For an easier understanding of the invention, attached are figures which represent preferred embodiments of the invention which, however, are not intended to limit the scope of the present invention.

[62] Figure 1 illustrates X-ray diffractograms of BNT - BST on Pt and sintered substrates at 1300 ° C / lh. For comparison purposes the X-ray diffraction spectra of the individual members of the solid solution BNT and BST are also represented. JCPDS 33-0166 diffraction strips are indicated at the bottom of the figure.

[63] The thickness of composite films is variable and depends on processing parameters, with thicknesses of about and above 50 micron being the most advisable. Figure 2 illustrates the microstructure of thick BNT - BST composite films on Pt and sintered substrates at 1300 ° C / lh (a) and (b) and also the elemental chemical analysis (c) of electron diffraction strontium.

[64] Figure 3 illustrates the dependence on dielectric permittivity (a) and loss

(b) as a function of frequency of thick BNT-BST composite films over Pt and sintered at 1300 ° C / lh. The individual electrical response of each member of the solid solution is given for comparison purposes.

[65] thick composite films of Ti band ₂ to ₄ ₅ 0i 5 percent by weight Bao _.5 Sr .5 ₀ ₃ Ti0 exhibit dielectric constant of 280 at 1 MHz, the dielectric loss of 0.0014 at 1 MHz, and 14 percent tunability at 2 kV / cm. The tunability of these thick films can reach 30 percent depending on the composition of the thick composite film and the applied electric field.

[66] Figure 4 illustrates the dependence of relative dielectric permittivity and DC field dielectric loss of (a) BST, (b) BNT-BST and (c) BNT sintered at 1300 ° C / 1.

[67] Figure 5 represents the temperature permittivity dependence of films

thick BNT-BST composites on Pt and sintered at 1300 ° C / lh.

Claims

Tunable composite dielectric comprising a tunable dielectric material and comprising a non-tunable dielectric material comprising one or more of: tungsten bronzoid family material,

namely BaO-Re ₂ 0 ₃ -Ti0 ₂ , where Re = Nd, Sm, La, among others; MgT 10 ₃ ; Ba ₂ Ti ₉ 0 ₂ o; Zr ₀ . ₈ TiSno. ₂₀ ₄ ; Ba (Mgi / ₃ TA _{_2/3)} 03; or the like; or their compositions.

Tunable composite dielectric according to the preceding claim, characterized in that said non-tunable dielectric material is BaNd ₂ Ti ₅₀ 0i ₄ , BNT.

Tunable composite dielectric according to any one of the preceding claims, characterized in that said tunable dielectric material comprises one or more of: the solid solution of barium strontium titanate, Ba _! _x Sr _x Ti ₃ , BST; BaT 10 ₃ ; Pb (Zr, Ti) 0 ₃ ; or the like; or their compositions.

Tunable composite dielectric according to the preceding claim, characterized in that said tunable dielectric material is (Ba ₀₅ Sr ₀₅ ) TiO ₃ .

A tunable composite dielectric according to any one of the preceding claims, comprising 80 to 95% by weight of said low loss non-tunable dielectric material, such as BaO-Re ₂ 0 ₃ -Ti 0 ₂ , where Re = Nd, Sm, La, among others, and comprising 5 to 20% by weight of at least one additional high tunable phase, such as solid solutions of barium and strontium titanate.

A tunable composite dielectric according to any one of the preceding claims, characterized in that it comprises dielectric and tunable phases with thicknesses between 5 and 100 microns, preferably between 10 and 80 microns, even more preferably with thicknesses between 50 and 80 microns.

A tunable composite dielectric according to any one of the preceding claims, further comprising a metal substrate such as platinum, gold, silver, copper, nickel, among others; or non-metallic substrate such as alumina, A1 ₂ 0 ₃ , among others, for depositing said low dielectric loss thick layer, BNT. An electronic device comprising varactors, tunable filters, co-planar and linear phase shift devices, and phase array antennas, multi-layer thick film capacitors, planar capacitors according to any one of the preceding claims, comprising one or more more composite dielectrics

tunable as previously described.

Tunable composite dielectric manufacturing process characterized by combining the electrophoretic deposition process with the sun gel deposition in order to obtain a combination of a low loss non-tunable dielectric material and a tunable dielectric material, namely the solid titanate solution. barium and strontium, Ba _! . _x Sr _x Ti0 ₃ , BST, in particular (Bao.5 Sr ₀ .5) TiO ₃ or its compositions.

Tunable composite dielectric manufacturing process according to the preceding claim, comprising the following steps:

The. thick layer electrophoretic deposition of the non-tunable low dielectric loss dielectric matrix of the tungsten bronzoid family, namely BaO-Re ₂ 0 ₃ -Ti0 ₂ , where Re = Nd, Sm, La, among others, or compositions thereof;

B. methodically soluble phase gel filtration of said tunable dielectric material into the matrix layer;

ç. sintering of the composite film for densification.

Tunable composite dielectric manufacturing process according to the preceding claim, comprising comprising deposition of said thick layer of the low dielectric loss phase matrix, BNT: metal substrates such as platinum, gold, silver, copper, nickel, among others; or non-metallic substrates such as alumina, A1 ₂ 0 ₃ , among others. Tunable composite dielectric manufacturing process according to the preceding claim, comprising the following steps:

The. synthesis of the matrix ceramic powders by the preparation of thick composite films which involves the prior preparation of ceramic powders of the matrix composition, which for the particular case of BaNd ₂ Ti 5O14 powders, precursors of BaC0 ₃ , Nd ₂ 0 ₅ and Ti0 ₂ are mixed in suitable proportions to obtain the compound concerned in zirconia milling ball mills for about 24 hours in aqueous or alcoholic medium, the resulting mixture being dried and calcined for synthesis of said compound;

B. preparation of stable suspension of matrix powders for electrophoretic deposition by preparation of the stabilized suspension by different suspending media such as acetone, (CH ₃ ) 2 CO,> 99.9, ethanol, C ₂ H ₅ OH,> 99.9, and acetic acid CH ₃ COOH,> 99.9, which in the case of acetone I ₂ > 99.8%, dissolved in isopropanol, C ₃ H ₇ OH,> 99.9%, is used as an additive to adjust the pH value of suspension, in this case of NTB, where the suspensions used have a concentration of 10g / liter of TNB powders and are filtered until complete dispersion of the powders;

ç. thick-layer electrophoretic deposition of the matrix composition, the substrates being selected from a group of flexible metals comprising Pt, Ni, Cu among others, and from a group of regulated oxides comprising A1 ₂ 0 ₃ , among others. wherein the thick layer of matrix material is deposited by electrophoretic deposition, which under the action of an electric field the charged particles suspended in the suspending medium move towards the opposite charge electrode and deposit on the substrate forming a The film thickness depends on the suspension concentration, applied voltage and time, and 10 to 80 microns thick films can be deposited under 40 V to 600 V in 30 s to 10 min. at 90 ° C for time periods up to 24 h.

d. stable sun preparation of the second phase composition, wherein the phase sun is prepared using as starting precursors Ba (CH ₃ COO) ₂ ,> 99.9%, Sr (CH ₃ COO) ₂ -½H ₂ 0,> 99.9% , and Ti (OC ₄ H ₉ ) _4, > 99.9%, with glacial acetic acid CH ₃ COOH> 99.9%, and ethylene glycol, HOCH ₂ CH ₂ OH,> 99.9%, are used as solvents, and acetylacetone C ₅ H ₈ 0 _2i > 99.9%, as Ti alkoxide stabilizer, being powders of Ba (CH ₃ COO) ₂ and Sr (CH ₃ COO) ₂ · 1 / 2H ₂ 0 with a molar ratio of 5: 5 dissolved in acid under constant stirring at 80 ° C, Ti (OC ₄ H ₉ ) _{4 being} stabilized with ethylene glycol and acetyl acetone and this solution mixed with Ba (Ac) ₂ / Sr (Ac) _{2 solution} with a molar ratio of 1 : 1 under constant stirring and after mixing for 2 hours the solution concentration is adjusted to 0.25 mol / 1 and stirred for 1 more hour;

and. scattering infiltration, spin coating, of the second phase sun, and after drying the films are infiltrated by scattering with the tunable dielectric phase sun, and after infiltration the films are dried and pyrolyzed at 350 ° C for 5 minutes. on a hot plate, this cycle being repeated up to 10 times;

f. sintering of the composite films in air atmosphere between 1100 and 1300 ° C for different time periods, depending on the substrate, to densify the composite.