CZ20032169A3 - Tantalum-silicon and niobium-silicon substrates for capacitor anodes - Google Patents

Abstract

The allows: Ta-Si, Nb-Si, TaN-Si, NbN-Si and variants are used as enhanced powder anode substrates for electrolytic capacitor anodes (sintered powder masses) with dielectric oxide formation at walls of the internal pores.

Description

Tantalum silicon and niobium silicon substrates for capacitor anodes

Technical field

The invention relates to substrates for high permittivity capacitors and in particular to tantalum and / or niobium-based powder substrates processed into a porous mass which is formed to obtain a thin dielectric layer of tantalum and / or niobium oxide (normally tantalum and / or niobium oxide). . These are used in well known solid or wet electrolyte systems.

BACKGROUND OF THE INVENTION

Substrates based on tantalum / niobium powder (mainly based on tantalum powder) have been used for half a century as selection materials for high capacity capacitors with low dispersion, low ballast resistance and high breakdown voltage to meet their application requirements and quality control tests in the military, computer and telecommunications areas.

The capacitance of electrolytic capacitors has increased from less than 10,000 microfaradvolts per gram to 50,000 microfaradvolts per gram over the last decade due to reduced particle size of the powder substrate (larger surface area of oxide relative to mass and volume)

9 ···· Anodes) controlled porosity to achieve better access to the expanded region, control sintering and doping of the substrate with phosphorus and, in some cases, nitrogen, silicon or sulfur. There has also been an improvement in lead wire production, lead wire connection to the anode, molding process, electrolytic systems and packaging systems.

However, even these improved high-capacity systems are expected to improve further in terms of scattering, ballast resistance, biasing, thermal stability in production and use, frequency stability, breakdown voltage, and overall stability not yet achieved or only achieved at the expense of high yield losses. By using tantalum and niobium nitrides and other forms, tantalum and niobium modifications have brought about an improvement in stability and capacity, but insufficiently with respect to the desired values.

It is an object of the present invention to provide a capacitor substrate system that provides improved scattering, resistivity, bias, thermal stability in the manufacture and use of capacitors, frequency stability, increased porosity resulting in lower equivalent series resistance (ESR) ) and a low Dissipation Factor (DF) for high CV / gram systems (30,000 and above).

Another object of the invention is to achieve said stability in a reproducible manner and at high yields.

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SUMMARY OF THE INVENTION

The above objects of the invention are met by new tantalum silicon and niobium silicon systems, which are preferably formed as mixtures of 90 to 98% by weight of tantalum powder, niobium and 2 to 10% by weight of silicon powder, which are mixed with each other. Silicon may also be added to ₂ TaP ₇ . Silicon-based wetting agents can also be used in tantalum suspensions as a means of introducing silicon and tantalum in suitable amounts and form.

An improvement (reduction) of the bias after heat treatment has been achieved, which improvement can be achieved reproducibly and reliably with the Ta-Si substrate system, and this result is now rationally designed for similar Ta / Nb-Si substrate systems. Porous anode electrolytic capacitors obtained using such systems can provide stable power at high voltages and under high frequency use conditions.

Progress can also be achieved within the invention by using Ta / Nb-nitride systems and Si / Nb, Ta / Nb-nitride systems doped with known capacity enhancing impurities such as phosphorus, silicon and sulfur.

The added benefit of silicon addition is to control the pore size of the sintered anodes and achieve optimum porosity generally with larger pores and greater pore size uniformity, thereby allowing for more efficient electrolyte precursor access, a more efficient electrolyte conductive path and less capacitor degradation associated with varying porosity.

One method of homogeneous distribution of silicon in the tantalum or niobium produced is the use of liquid organosilicon compounds. Due to the requirement of reduced oxygen and carbon content, the preferred organosilicon compound should be selected from the group of silicones. These compounds, which are mainly composed of SiOH bonds, will decompose into Si at high processing temperatures of powders in a reducing atmosphere.

Said reducing atmosphere may be produced by standard technology known in the art, but due to minimization of contamination, the reducing environment is achieved using Mg or H ₂ or NH.

Other objects, features and advantages of the invention will be apparent from the following detailed description of a preferred embodiment of the invention based on the accompanying drawings. This detailed description is illustrative only and is not intended to limit the scope of the invention, which is clearly defined by the definition of the claims and the description.

Description of the drawings

In the attached drawings:

Figure 1 is a graph of the capacity of Ta-Si and the high-capacity tantalum (50K) capacitor type versus sintering temperature varying from 1300 to 1550 ° C;

Fig. 2 compares the same materials in terms of their bias dependence at different test biases;

Figures 3 and 4 show the dependence of capacity and scattering on the sintering temperature (similar to Figure 1), comparing the Ta-Si system to the Ta system as well as to the TaN + Si system;

Fig. 5 and Fig. 6 compare (similar to Fig. 2) the bias dependence of the Ta, Ta-Si, Ta + Si ₃ N ₄ , TaN-Si ₃ N ₄ and TaN-Si systems; and Figures 7 and 8 compare the volume contributions as a function of the pore diameter, comparing the Ta system against the Ta-Si system and the TaN system against the TaN-Si system.

US Pat. No. 4,432,035 to Priority 14/02/1984 describes a Ta ₂ Si _{2 system} (instead of the previously tested Ta ₂ Si system) for a thin film capacitor, but nowhere is a suitable type of powder substrate for sintered electrolytic capacitor anodes .

The invention is based on a self-recognized understanding of the role of tantalum nitride in providing a new range of useful 0 000000000.

* Η · 0 · 00 · 00 · 00 ^U 0000 000 00 «0 · _# pulverulent substrates (work T.Trippa et al., U.S. 4,957,541, tantalum powder of capacitor grade).

DETAILED DESCRIPTION OF THE INVENTION

Example 1

Initial tests have shown that the dispersion of Ta-Si powder systems is basically the same as the dispersion of a Ta powder system (ie no progress in this respect), but the Ta-Si system had better capacity compared to the Ta system, even at higher sintering temperatures and slightly lower and low temperatures. It turned out that silicon acted as a sintering delaying agent.

The test results obtained are the average of the results obtained for each of the four pellets of the Ta and Ta-Si systems. The Ta system is a standard 50K-9010 product obtained by reducing sodium heptafluorotantalate and conventional leaching, fine particle conversion, doping and deoxidation. In contrast, the Ta-Si system was prepared by mixing 0.333 g of silicon powder (60 mesh particle size) with a purity of 99.999% with 9.667 g of tantalum powder 50K-9010 to achieve approximately Ta ₂ Si ₂ .

The powders of both systems were compressed into pellets and sintered at 1500 ° C for the first set of pellets formed at a forming voltage of Vf 16, 30, 40, 50, 80, and 100 V, and for the second set of pellets sintered at different temperatures from 1350 ° C to 1550 ° C.

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Preparation conditions and obtained by the following Tables I to V.

results are shown

Table I «« · I I I I I I I I I I I I I I I I I I ·· ··· * «·»

Preparation conditions and conditions formation pellets, as well as testovací Conditions Values Pellet weight (g) 0.14 Density after pressing (g / cm ³ ) 5.0 Sintering temperature (° C) 1350, 1450, 1550 Sintering time (min) 20 May Formation temperature (° C) 80 Formation voltage (V) 16, 30, 40, 50 120 80, 100, Formation current (mA / g) 100 ALIGN! Stamina (h) 2 hours or 5 minutes Formation electrolyte 0.1% (v / v) H ₃ PO ₄ DCL-Test Voltage ( ;% Vf) 70 Preload (V) 0 to 20 DLC Heating time (min) 5

Table II

Electrical results for tantalum-silicon mixture (duration: 5 minutes) • 999999

9 9 9 9 9 9

9 9 9 9 9 9 9 9 9 β · ··· ♦ · & · ········ · · 9 9 9 9 99

500 ° C CV / g (9gF.V / g) 1500 ° C / L (nA / gF.V) 16 32 400 0,884 30 25 100 ALIGN! 0.422 40 24 300 0.385 50 23 800 0.560 80 23 800 3,576 100 ALIGN! 22nd 500 2,326

Table III

Capacity (gF.V / g) Sintering temperature 50K-9010 LFS-001 50K-9010 120 Vf LFS-001 12 0 Vf 50 Vf 50 Vf 1350 ° C 41 500 31 400 1450 ° C 30 600 24 300 19 000 20 900 1550 ° C 16 100 ALIGN! 19 Dec 300

• 9

Table IV 9 9 9 9 9 9 9 9 9 9 9 9 99 99 99 99 99 99 99

Dispersion (nA / pF.V / g)

Sintering 50K-9010 LFS-001 50K-9010 LFS-001 temperature 50 Vf 50 Vf 120 Vf 120 Vf 1350 ° C 0.322 0.512 1450 ° C 0.275 0.249 0, 608 0,946 1550 ° C 0,067 0,065

Table V

Sintering temperature 50K-9010 capacity LFS001 capacity 50K-9010 L / C LFS-001L / C 1450 ° C 16 900 16 000 1,230 0, 960 1500 18 600 0.500 Listed results are displayed graphically FIG. 1, of who he is apparently, that capacitance to bases powdered substrate (LFS) lies in the same range as

capacitance of tantalum powder capacitors (SOK), but shows smaller deviations with increasing sintering

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temperature of the degree of improved stability and degree of retardation, although this finding is problematic due to the proximity of the respective values.

Example 2

Following the procedure of Example 1, additional samples were prepared, in this case samples of Ta-Si, TaN-Si and Ta-Si ₃ N _{4 systems} . These samples were prepared by mixing the following proportions of the individual components:

0.333 g Si 60M with a purity of 99.999% with 9.667 g of 50K-9010;

0.3106 g Si 60M with a purity of 99.999% with 9.689 g TaN-003;

0.545 g Si ₃ N ₄ with 9.456 g 5OK.9010;

0.507 g Si ₂ N ₄ with 9.43 g TaN-003.

All these mixtures had a Ta / Si ratio of 9/2.

Pure TaN-003 and pure 50K-9010 were also included as control subjects.

The conditions of the experimental procedures and their results are shown in Tables VI to VIII below.

Table I

Μ · Φ φ φφφφφφ • ΦΦΦ φφφ * φ · ·

Preparation conditions and conditions formation pellets as well as test pellets Conditions Values Pellet weight (g) 0.14 3 Density after pressing (g / cm) 5.0 Sintering temperature (° C) 1350, 1450, 1550 Sintering time (min) 20 May Formation temperature (° C) 80 Formation voltage (V) 50, 120 Formation current (mA / g) 100 ALIGN! Stamina (h) 2 hours Formation electrolyte 0.1% (v / v) H ₂ PO ₄ DCL-Test Voltage ( % Vf) 70 Preload (V) 0 to 20 DLC Heating time (min) 5

0 0 0

0 «0 0 0 0 00 00 00 0000 00 · 00 000000 • 0 00 0000« «0

0 000000 • 00 «00 000 0 0 00 00

Table VII

Capacity (mG.V / g)

Sintering temperature 50K- 9010 TaN-00 3 Ta + Si TaN + Si TaN + Si ₃ N ₄ Ta + Si ₃ N 1350 ° C 40959 31220 31666 33985 31194 30634 1450 29260 30634 23581 30608 29946 25594 1550 14910 26714 17588 26828 25253 19915 1450-100Vf 18564 - 21336 18398 18060 14318

Table VIII

Variance (nA / inF.V)

Sintering temperature 50K-9010 50Vf TaN-003 Ta + Si TaN + Si TaN + Si ₃ N 1350 ° C 0.272 0, 881 0.565 1,006 41900 1450 ° C 0,064 1,079 0.458 0.434 6,726 1550 ° C 0,062 0,954 0,058 0.164 0.157

1450 ° C

100 Vf 0.701

0.880 1.332 11.413 • fc · · fc «

Fcfc fcfcfc fcfcfc

The results obtained are shown graphically in Figures 3 to 8.

Giant. 3 and 4 show the TaN and TaN-Si systems with the lowest capacity loss with varying sintering temperature but with an improvement in the scattering (decrease) of the TaN-Si system at increasing sintering temperature. Favorable balance characteristics are also shown.

5 and 6 show (on test products sintered at 1450 ° C and 1350 ° C) that at different biases from 0 to 20 V, the capacity deviates the most with increasing bias for the Ta system, much less for the Ta- system. Si and even less for the Ta-Si ₃ N ₄ system and at least for the TaN-Si system.

Figures 7 and 8 showing the results of porosity testing show the volume-pore diameter contributions for Ta-Si versus Ta systems (Figure 7) and for TaN-Si versus TaN systems (Figure 8). These results can lead to reduced electrical ballast resistance and improved performance in high frequency applications.

Example 3

In the same manner as the above Ta-systems, Nb-Si systems were also prepared and tested. These systems behaved differently with respect to Ta-Si systems. There is no improvement in thermal stability and bias, although some difference has been observed. There was an overall increase in capacity with an addition of about 1% Si. There was also a 9 9 9 9 9 9 · Φ Φ Φ Φ Φ Φ Φ Φ Φ 9 Φ Φ

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9999 ΦΦΦ ΦΦΦ · Φ 99 99 dispersion drop. There is a percentage increase in liquidity with increasing sintering temperature and a percentage decrease in L / C with increasing temperature while maintaining stability in general.

Table IX

Sintering temperature Increase capacity Reduction L / C 1100 ° C 1% 41% 1200 ° C 4% 36% 1300 ° C 25% 33% It happened here for Ta-systems, porosity the increase in porosity that was observed but the sample used was very good to observe a slight decrease in ESR.

X-ray spectroscopy of the sintered pellet of the Ta-Si mixture was performed, and it was found that the alloy actually formed and was not a mixture.

Discussion

Within the scope of the invention, it is exclusively and surprisingly possible to obtain a different change in the sintering characteristics of the Ta-Si (or / and TaN-Si) powder substrate compared to the Ta (or TaN) powder substrates, which may be related to the fact that capacitance and low dispersion having regions of increased stability in terms of bias, ESR frequency and heat treatment.

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Example 4

For the purpose of delivering silicon to tantalum, silanes were used as described in the following sections a) and b), and the obtained silicon-doped Ta-systems were tested to achieve the results set forth in section c) below.

a) APST

The tantalum powders were wetted with an aqueous solution of APST (which is an aminopropylsilantriol of the formula C ₂ H _{x 1} NO ₃ Si) used as a means to deliver the silicon and nitrogen dopants to the powder. This doping was performed to the level required to deliver 500 ppm silicon. The tantalum used was typically 50,000 CV / g powder (50 K). This level of doping should theoretically provide a powder of 249 ppm nitrogen to achieve the desired effect. APST is water soluble and thus can be added with a conventional phosphorus additive using techniques known in the art. In this example, the powder was actually simultaneously doped with 100 ppm of phosphorus dissolved in the same solution. After the dopants were added, the powder was dried and heat treated (agglomerated) at 30 minutes under vacuum.

b) THSMP

17 • · • · 9 9 9 9999 9 99 9 9 9 9 9 9 9 9 9 9 9 999 999 99 9 • · · · · • « • · 9 9 9 9 9 9 99 Tantalum pills were dipped solution THSMP (3-trihydrosilylmethylphosphonate) sodium summary formulas PC ₄ H ₁₂ NaO ₆ Si) used as a resource for delivery

silicon and phosphorus dopant to the powder in an amount providing about 500 ppm silicon. Again, the tantalum powder was a typical 50,000 CV / g powder. This doping level is expected to provide an additional amount of 550 ppm phosphorus, which is a relatively high phosphorus content for this type of powder. No additional phosphorus is added. Like APST, THSMP is a water-soluble substance and can thus be added using conventional procedures for adding phosphorus. After dopant addition, the powder is heat treated under the same conditions as described for APST.

(c) Test results

The doped powders of (a) and (b) were tested to determine their surface area (SA, cm / g), the bulk density by Scot (SBD, cm / g), the mean particle diameter by Fisher (FAPD, μιη), the flowability (g / g). s), carbon (C) content in ppm as well as nitrogen (Ν), oxygen (O), phosphorus (P) and silicon (Si) content, the results are given in Table X below for APST treated powders and THSMP and 50K tantalum powder were also tested as a control subject. The determined silicon and nitrogen contents were very accurate (close to the calculated contents), with a lower agreement for phosphorus, but this was in any case provided in excess, as also seen from the higher surface of the 50K + THSMP sample compared to the other samples . Sodium added together with THSMP was substantially dissipated during subsequent thermal agglomeration.

Table X

Powder SA SBD FAPD Teku- tost C N 0 P Si 50K 9172 27.2 2.64 0.384 32 60 10330 92 71 50K + APST 10097 27.3 2.76 0.396 365 266 11010 78 405 50K + THSMP 11423 24.3 1.7 0.211 652 66 11880 317 500

The same powders in the agglomerated state were tested in a Malvern Mastersizer particle size measuring apparatus using a laser scattering measurement on the particles suspended in a water bath, and the results are shown in Table XI below. The table shows the results obtained for the 50K control subject, APST doped powder and THSMP doped powder, and the agglomerated particle size within the 10, 50 and 90 weight percent fractions, mean (MV) in micrometers, calculated surface area (CS) in M / g and the percentage by weight of particles having a size of 11 microns or less (fine particles). Obviously, doping serves as a significant sintering retardant for both APST and THSMP.

Table XI

Powder 10% 50% 90% MV CS 11 micrometers 50K 13.4 53.7 149.26 69,923 0.211 7.51 50K + APST 16, 9 77.89 214.94 103.4 0.17 5.62 50K + THSMP 8.68 58.52 177.28 78,051 0.297 12.73

Despite the sodium present in the THSMP, after the vacuum heat treatment, the sodium content of the 50K + THSMP sample is comparable to that of the control subject. It should also be noted that although silicon is introduced in the form of a compound, it is converted into elemental form during agglomeration heat treatment and converted into an alloys with a host tantalum.

It should be noted that the same effects can be expected when the same silicon doping is applied to niobium and to tantalum and niobium alloys, including alloys and compounds of one or both of these metals, including nitrides and subnitrides. Other silicon-containing compounds and solutions (e.g., water glass) may also be used for the silicon doping described above and, if desired, secondary doping, such as secondary doping with nitrogen and / or phosphorus, may also be used.

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The agglomerated particles (or resulting anode compacts) may be subjected to a known deoxidation treatment, for example exposure to alkali or alkaline earth metals or aluminum vapors, preferably exposure to magnesium or calcium vapors, while heating the powder to a temperature of 600 to 1200 ° C, preferably to a temperature greater than 800 ° C, according to the instructions provided, for example, in U.S. Patent 4,483,819 issued July 19, 1982 and U.S. Patent 4,537,641 issued August 27, 1985.

The deoxidation process also provides a method for improving the conversion of silicon compounds to elemental silicon and its transition into an alloy with a host refractory metal.

Deoxidation can be performed during thermal agglomeration (reactive agglomeration). Often, deoxidation is followed by inorganic acid treatment carried out to remove residues from the reduction reaction (e.g., magnesium oxide).

It is also known that other host refractory metal impurities can be removed by a deoxidation process, whereby a lower temperature at which temperature agglomeration is performed can be used.

Combinations of chemical and thermal factors of the doping stage, agglomeration stage, deoxidation stage and optionally sintering stage can be optimized for each specific case of doping with silicon alone or in combination with other additives to improve the physical and electrical properties of the capacitors.

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manufactured using porous anode compact parts made of such agglomerated powders.

It will be apparent to one of ordinary skill in the art that other embodiments, improvements, details and uses are possible that are consistent with the spirit and content of the foregoing description and are within the scope of the invention based on the doctrine of equivalents. claims.

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Claims (5)

ΆΜ / Ι -Μ?] PATENT CLAIMS ·· ·· Powder metal substrate alloys containing tantalum and / or niobium or nitrides thereof in which a silicon component is incorporated in the form of a mixture or an alloy. A substrate according to claim 1, characterized in that it is in the form of sintered into a porous anode mass with improved porosity of substantially uniform higher pore sizes compared to sintered masses of Ta, Nb or NbN alone. Anode composition according to claim 2, characterized in that it is formed to form a dielectric oxide of the alloy on the pore walls. 4. A fully packaged electrolytic capacitor comprising the anode of claim 3. Products according to any one of claims 1 to 4 with a weight ratio of about (Ta, Nb) _g Si ₂ and the presence or absence of nitrogen. Represented by: • · 9 $ · · 99 9999 • • • · · 9 9 9 • « • · · 9 ···· • · « 999 ·· 99 99 Ta-Si and 50K systems at changing sintering temperature (50V _f ) - • Jt-'50K-S010Cap - * - LFS-OO1 Cap - - · --KK-SOIOL / C FIG Relative capacity (C / C Pre-bias dependence after heat treatment FIG. 2 ·· ···· / čwvv? »I« · • fcfcfc • fc · fc fc • fcfcfc fcfcfc fcfcfc · fc · • · fcfcfc 4 4 • · * · fc I fcfc fcfcfcfc • fcfc fcfc fc · FIG.5 1450 ° C - Pre-bias after heat treatment —O — 50K-9010 —B — TaN-003 —ώ — Ta + Si — O — Ta + Si3N4 —X — TaN + Si3N4 - (- TaN + Si 1350 ° C - Pre-bias after heat treatment + J • H o (0 Cu <0 Ή c >