WO2016003306A1

WO2016003306A1 - Method for manufacturing ferroelectric capacitors

Info

Publication number: WO2016003306A1
Application number: PCT/RU2014/000476
Authority: WO
Inventors: Игорь Владимирович ЩЕРБАКОВ; Сергей Николаевич РЯЗАНЦЕВ
Original assignee: Общество С Ограниченной Ответственностью "Элемент 22"
Priority date: 2014-06-30
Filing date: 2014-06-30
Publication date: 2016-01-07

Abstract

This invention relates to a technique for manufacturing capacitors with a dielectric made from a barium titanate-based ceramic that is coated with a metal by vacuum evaporation deposition. The present method for manufacturing ferroelectric capacitors comprises moulding a ceramic substrate, preferably based on barium titanate, applying a dopant coating, vacuum depositing copper electrodes and vacuum annealing the composite material. What is novel is that the dopant coating is applied in a liquid phase by condensation from a vapour stream of a metal evaporated in a vacuum, said metal being selected from among: titanium, vanadium, chromium, manganese and niobium, at a substrate temperature of 150-350°C, whereupon the substrate with a dopant coating is subjected to vacuum annealing, and copper electrodes are subsequently applied directly to the composite substrate, which is heated to a temperature not greater than 600°C. By comparison with the prior art, the proposed technical solution provides, on average, a sixfold increase in the specific capacity of a ferromagnetic capacitor and a 3.6-fold increase in breakdown voltage with no increase in dielectric loss.

Description

PREPARATION METHOD

FERROELECTRIC CAPACITORS

Technical field

The invention relates to a technology for manufacturing capacitors with a dielectric made of ceramic based on barium titanate coated with a metal by atomization by vacuum evaporation.

State of the art

The level of this technical field characterizes described in the book of Rene V. T. "Electric capacitors", ed. 3, M.: Energy, 1969, p. 73-75 a method for manufacturing an electric capacitor comprising a plate of ferroceramic material with electrodes in the form of a double-sided coating with an electrically conductive material.

As an electrically conductive material, silver is used, which is applied to the substrate in the form of a paste.

The adhesion of the functional coating to the substrate is provided by heat treatment in which silver diffuses into the surface layer.

The main disadvantage of this method is the reduction in the capacitance of the capacitor due to the partial restoration of ceramics in the diffusion zones and the subsequent degradation of the capacitance and a decrease in breakdown voltage

A more advanced technical solution, the closest to the proposed one, is a method of manufacturing ferroceramic capacitors containing a ceramic dielectric based on barium titanate, on the metallized surfaces of which fixed electrode current collectors described in patent RU 2354632, 2007

The known method includes the operation of forming a ceramic plate (substrate), on the surface of which a mixture is applied in equal proportions of finely dispersed (1-50 μm) copper powder with the substrate material, and then by hot pressing a plate with a surface composite layer is formed, which serves as an adhesive for fixing copper electrodes.

Then, predominantly a third of the surface composite layer is ground, exposing copper particles for subsequent vacuum deposition at a pressure of 10 ^{~ 4} Pa of copper as an electrode layer.

After that, the prepared ferroceramic plate, on the surfaces of which a copper layer is deposited, is heated in vacuum, conducting photon annealing for fusion into a monolith of the electrode layer with a copper inclusion of an adhesive layer.

Upon reaching the melting of the metal in the upper electrode coating layer of the ceramic substrate in a vacuum chamber, in an argon atmosphere, the pressure is changed to atmospheric pressure within 15 minutes, cooling the product to a temperature of 25-30 ° C without oxygen.

The method provides a 35-40% increase in the adhesion strength of the metal to the surface of the ceramic substrate.

However, the known method does not significantly increase the capacitance of a ferro-ceramic capacitor.

In addition, a wide (up to 50 μm) top layer of the substrate is saturated with copper particles, creating bridges of conductivity and internal ionization, which leads to a sharp decrease in voltage. SUMMARY OF THE INVENTION

The technical problem to which the present invention is directed is to improve the known method for high-performance manufacturing of ferro-ceramic capacitors with increased specific capacitance and breakdown voltage.

The required technical result is achieved by the fact that in the method of manufacturing ferroelectric capacitors, including forming a ceramic substrate, mainly based on barium titanate, applying an alloying coating, vacuum deposition of copper electrodes and vacuum annealing of the composite material according to the invention, the alloying coating is applied in the liquid phase by condensation from the vapor stream of vacuum-evaporated metals of a series: titanium, vanadium, chromium, manganese, niobium, at a substrate temperature of 150-350 ° C, after which ku alloying with coating is subjected to vacuum annealing, and the subsequent deposition of copper electrodes carried on directly heated to a temperature not higher than 600 ° C composite substrate.

The differences of the proposed method provide, in comparison with existing analogues, an increase by an average of 6 times the specific capacitance of a ferro-ceramic capacitor and 3.5 times the breakdown voltage.

The application of the alloying metal to the substrate in the liquid phase from the vapor stream and the subsequent vacuum annealing of the composite material provide effective mass transfer (thermal diffusion) of the alloying metal (dopant) to the substrate while combining surface and bulk diffusion of the alloying metal into the ceramic substrate. In this case, due to activation and mixing of the melt in the liquid bath, the dopant interacts with ferroceramics, forming solid solutions and chemical compounds.

Alloying elements diffusing into barium titanate grains

(bulk diffusion), increase the polarization of the substrate domains, increasing the dielectric constant, and fill vacancies along the grain boundaries of barium titanate (surface diffusion), forming intergranular insulating layers, which increases the breakdown voltage of a ferro-ceramic capacitor material.

The solubility of dopant metals and thermal diffusion into the substrate of their atoms in the liquid state is much higher than in the solid state, therefore, the dielectric constant of doped ferroceramics significantly increases.

So, with a thickness of a ceramic substrate plate of 300 mm, the diffusion zone is 120-150 μm, which, when double-sided doping, provides through doping of the substrate volume and the achievement of maximum targets.

When a dopant layer is deposited, the temperature of the substrate array is maintained in the range of 150-350 ° C, while the temperature on the substrate surface reaches the melting temperature of the dopant due to the heat of condensation of the alloying material from the vapor stream, which ensures the state of the dopant on the substrate surface in the liquid phase during alloying .

Doping with a dopant of a ceramic plate heated to a temperature of 150-350 ° C ensures the active interaction of the alloying metal in a liquid bath with barium titanate, increasing the penetration depth of the alloying elements into the plate, that is, the combination of surface and volume diffusion of the dopant.

If the heating temperature of the ceramic substrate during alloying is below 150 ° C, a strong adhesive bond of the alloying metal layer to the ferroceramic material is not ensured.

If the temperature of heating the ceramic substrate during alloying during alloying is higher than 350 ° C, the dielectric loss in the formed capacitor sharply increases.

In order for the diffusion of the alloying metal-dopant to complete saturation, a vacuum annealing is carried out, in which the dopant penetrates deep into the ferroceramics. In this case, due to surface diffusion of the dopant along the grain boundaries, barrier layers are formed that increase the breakdown voltage, in addition, the dopant fills the pores that cause ionization breakdown. The diffusion process continues until the chemical potentials of the components of the entire prepared structure are equalized.

Annealing in vacuum is combined with the application of an alloying metal to maintain the required diffusion temperature, excluding the oxidation of dopant.

The use of a series of metals as dopant: titanium, vanadium, chromium, manganese, niobium is explained by the fact that they have an ion radius of less than 0.066 μm, close in size to the ions of the crystal lattice of barium titanate, and an ionization energy of more than 6.7 eV, which allows alloying elements diffuse into the crystal lattice of the substrate material, thereby increasing the capacitance of the capacitor material while shifting the position of the titanium ion in the lattice. In the barium titanate lattice, a special role is played by a titanium ion, occupying a central but somewhat shifted position, and the polarization of the dielectric is due to the displacement of the titanium ion when an external electric field is applied. The incorporation into the lattice of ions close in radius to the ions of the lattice of barium titanate leads to an increase in the capacitance of the ferroceramic capacitor.

When a ceramic substrate is doped with metals with an ion radius greater than 0.066 nm and an ionization energy of less than 6.7 eV, the effect of increasing the capacitance does not occur due to the larger size of the ion, which cannot penetrate the barium titanate lattice, or due to the lack of energy for penetration into the lattice.

The higher ionization energy ensures the activation of the dopant when the barium titanate melt is mixed on the surface of the ceramic substrate when the molten bath is mixed, increasing the polarization of the domains of the composite base and the depth of diffusion, which multiply increases the purpose of the ferroelectric, in particular, breakdown voltage.

To illustrate the above, the radii of some metals are given:

Ti ⁴⁺ - 0.64A, Cr ⁶⁺ - 0.35A, Mn ²⁺ - 0.52A, V ⁵⁺ - 0.59A, Nb ⁵⁺ - 0.6bA;

Ni ²⁺ - 0.79A, Fe ²⁺ - 0.8θΑ, Co ²⁺ - 0.80A, Cu ²⁺ - 0.8θΑ, Zr ⁴⁺ - 0.82A, Y ³⁺ - 0.97A, respectively suitable and unsuitable for alloying according to the proposed method for the manufacture of ferroelectric condensers.

A feature of the proposed method is that the alloying dopant layer formed on the surface of the ceramic plate serves as an adhesive layer on which the electrode layer of copper deposited is directly formed vacuum spraying, without breaking the process stream in a vacuum chamber.

In this case, the temperature of the doped substrate does not exceed 600 ° C in order to exclude the interaction of copper with the material of the adhesive layer monolithically bonded to the ceramic base, thereby preventing the deterioration of the performance of the capacitor.

Preferred Embodiments

The essence of the proposed method is illustrated by examples of its implementation.

Example N2 1.

Disks with a diameter of 6 mm and a thickness of 300 μm made of molded and sintered capacitor ferroceramics based on barium titanate of the Y5V temperature stability group (according to the Russian classification of the H30 group) are applied by electron beam spraying with a 8 μm thick alloy layer.

In this case, a dopant - titanium (ion radius of 0.064 nm and an ionization energy of 6.82 eV) is applied to sample H30-1 at a substrate temperature of 200 ... 250 ° C, and a dopant - vanadium (ion radius of 0.059 is applied to the NZO-2 sample nm and ionization energy of 6.71 eV) at a substrate temperature of 190 ... 230 ° C, and a dopant - chromium (ion radius 0.35 nm and ionization energy of 6.764 eV) at a substrate temperature of 150 is applied to sample H30-3. .220 ° C.

Similarly, a layer of dopant is applied to the second side of the ceramic discs.

Then, the dopant layer on the surface of the NZO-1, N30-2, and NZO-3 samples is heated in vacuum from the thermoblock and annealed to obtain barium titanate-based material doped in bulk. Then, a double-sided copper coating is applied to the surface of the samples of the composite material doped with dopant by means of vacuum electron beam deposition at a substrate temperature of not more than 600 ° C.

The result is a ceramic capacitor of group H30 in the form of a plate of doped ferroceramics with copper electrodes.

Comparison sample NZO-4 is a ceramic capacitor made of molded and sintered capacitor ferroceramics based on barium titanate of the Y5V temperature stability group (according to the Russian classification of the NZO group) without an alloying additive and with silver electrodes deposited by thermal diffusion according to the prototype.

The test results of the samples are shown in the Table.

JNb2 example.

On disks with a diameter of 6 mm and a thickness of 300 μm from a molded and sintered capacitor ferroceramics based on barium titanate of the Y5V temperature stability group (according to the Russian classification of the H70 group), a 10 μm thick alloying layer is deposited by electron beam electron beam sputtering.

In this case, a dopant - titanium (ion radius of 0.064 nm and an ionization energy of 6.82 eV) is applied to sample H70-1 at a substrate temperature of 250 ... 300 ° C, and a dopant - vanadium (ion radius of 0.059 is applied to sample H70-2 nm and ionization energy of 6.71 eV) at a substrate temperature of 200 ... 250 ° C, and a dopant - chromium (ion radius 0.35 nm and ionization energy of 6.76 eV) at a substrate temperature of 170 is applied to sample H70-3 ... 250 ° C. Similarly, a layer of dopant is applied to the second side of the ceramic discs.

Then the dopant layer on the surface of samples H70-1, H70-2, and H70-3 is heated in vacuum from the fuser and annealed to obtain 5 barium titanate-based material doped in bulk.

Then, a double-sided copper coating is applied to the surface of the samples of the composite material doped with dopant by means of vacuum electron beam deposition at a substrate temperature of not more than 600 ° C.

0 As a result, a ceramic capacitor of the H70 group is obtained in the form of a plate of doped ferroceramics with copper electrodes.

Comparison sample H70-4 is a ceramic capacitor made of molded and sintered capacitor ferroceramics based on 5 barium titanate of the group for temperature stability Y5V (according to the Russian classification of group H70) without alloying additive and with silver electrodes deposited by thermal diffusion according to the prototype.

The test results of the samples are shown in the Table.

Table

resistance> 5 10 ³ > 5 10 ³ > 5 · 10 ³ > 3 · 10 ³ > 5 · 10 ³ > 5 10 ³ > 5 10 ³ > 3-isolation, mOhm

dielectric 5932 6780 7627 1 160 18780 18644 25423 37: permeability

The table shows that as a result of doping the ferroceramics of the NZO group by the proposed method, compared with the prototype, the dielectric constant (hence, capacity) increased depending on the dopant by 5.0-6.6 times with a simultaneous increase in breakdown voltage by 3.2 -3.6 times.

For group H70, the growth in capacitance was from 5 to 6.8 times with a simultaneous increase in breakdown voltage by 3.6-4.0 times.

In this case, the dielectric loss did not increase.

A comparative analysis of the proposed technical solution with identified analogues of the prior art, from which the invention clearly does not follow for a specialist in electrical engineering, showed that it is unknown, and given the practical feasibility of serial production of ferroelectric capacitors on existing equipment, we can conclude that the criteria for patentability are met.

Claims

CLAIM

A method of manufacturing ferroelectric capacitors, including forming a ceramic substrate, mainly based on barium titanate, applying an alloying coating, vacuum deposition of copper electrodes and vacuum annealing of a composite material, characterized in that the alloying coating is applied in the liquid phase by condensation from a vapor stream of vacuum-evaporated metal from range: titanium, vanadium, chromium, manganese, niobium, at a substrate temperature of 150-350 ° C, after which the substrate with an alloying coating is subjected to vacuum annealing y, and subsequent deposition of copper electrodes carried on directly heated to a temperature not higher than 600 ° C composite substrate.