SUBSTRATES OF TANTAL-NIOBIO AND NIOBIO-SILICON FOR CONDENSER ANODES
FIELD AND BACKGROUND OF THE INVENTION The present invention relates to substrates for high dielectric constant capacitors and more specifically to tantalum and / or niobium based powder substrates made of porous masses that "form" electrolytically to establish a fine oxide of tantalum and / or niobium (usually tantalum and / or niobium pentoxide) as the dielectric layer. These are used with known solid or wet electrolyte systems. Tantalum / niobium powder substrates (primarily tantalum) have been used for half a century as optional materials for very high capacitance compact capacitors with low leakage, low electrical resistance in series and high levels of spark discharge, which responds well to demanding use and the quality control tests of the military, computer and telecommunications markets. The level of capacitance of the state of the art for electrolytic capacitors has passed in the last decade from less than 10,000 'microfarad volts per gram to more 50,000 by reducing the size of the powder substrate (with greater surface area of oxide formed in relation to the weight and anode volume, porosity control of the anode for effective access to the expanded zone, sintering controls, doping of the substrate with phosphorus and in some cases nitrogen, silicon or sulfur, as well as improvements in the production of conductive wires, union of the conductive wire to the anode, formation routines, electrolytic systems and packaging, however, these advanced systems of high capacitance have produced new expectations in terms of leakage, series resistance, polarization dependence, thermal stability in general, in the production and use of capacitors, frequency stability, disruptive discharge and stability g Generally, they have not been met or only have done so with high yield losses. Ta, Nb nitrurates and other modified forms of Ta, Nb have contributed to stability and ca-pacitancy, but insufficiently in relation to expectations. A main object of the invention is to provide a capacitor substrate system that provides better leakage, series resistance, polarization dependence, thermal stability in general in the production and use of capacitors, frequency stability, greater porosity that results in lower equivalent series resistance ("RSE") and low dissipation factor ("FD"), in relation to high CV / gram systems (30,000 and more). A related object is to achieve such stability reliably and with high yields. COMPENDIUM OF THE INVENTION The objects of the invention are fulfilled by new systems of tantalum-silicon and niobium-silicon formed preferably as mixtures of 90-98% by weight of Ta, Nb and 2-10% by weight of Si powders. mixed Si can also be added to a reactor for Na reduction of K2TaP7. Si-based wetting agents can also be used in suspensions of Ta as a means of introducing Si into Ta in appropriate amounts and forms. An improvement (decrease) in polarization dependence after heat treatment has been achieved and can be achieved reliably by the Ta-Si substrate system, and such a result is now reasonably projected for similar substrate systems of Ta / Nb-Yes. Electrolytic porous anode capacitors made with such systems can provide stable performance in high voltage arrays and in high frequency use conditions. The benefits of the present invention can also be realized in Ta / Nitride Nb systems and in Si systems with Ta / Nb; Nb / n-doped nitride with known capacitance-enhancing impurities such as P, Si, S. The benefits of the addition of silicon include control of the pore size of sintered anodes and optimized porosity with generally larger pores and greater uniformity of size pore to allow a more secure effective access of the electrolyte precursor, effective electrolyte conduction paths and less performance degradation of the condenser associated with variable porosity. A method of distributing Si homogeneously throughout the Ta or Nb produced is through the use of liquid organosilicon compounds. Due to the desire for a reduced content of oxygen and carbon, the preferred organo-silicon compound would be in the silicone family. These compounds which are formed primarily by SiOH bonds will decompose during the high temperature treatment of the Si powders in a reducing atmosphere. The reducing atmosphere can be obtained in the standard technology in the matter, but it is preferred that it be Mg or ¾ or NH to minimize contamination. Other objects, features and advantages will be apparent from the following detailed description of preferred embodiments taken in conjunction with the accompanying drawings in which: BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a graph of Ta-Si capacitance as a function of high capacitance of a capacitor of the Ta type (50K) with sintering at various temperatures of 1300 to 1550 ° C. Figure 2 compares similar materials in terms of polarization dependence at various test polarization voltages. Figures 3-4 plot the capacitance and the leak depending on the sintering temperature (as in Figure 1) comparing Ta-Si with Ta and also with TaN + Si. Figures 5-6 compare (as in Figure 2) the polarization dependence of Ta, Ta-Si, Ta + Si3N4, TaN-Si3N4 and TaN-Si. And Figures 7-8 compare the incremental volume according to the characteristics of pore diameter for Ta as a function of Ta-Si, and TaN as a function of TaN-Si. BRIEF DESCRIPTION OF PREFERRED EMBODIMENTS United States Patent ("USP") 4,432,035 of February 14, 1984, by Hsieh (IBM), describes Ta9Si2 (instead of a2If previously tried) in thin film capacitors, but has never The technique provided a way to useful powder substrates for sintered anodes of electrolytic capacitors. The present invention starts from the separate way of recognizing, from the work of T. Tripp et al., USP 4.957.541 (tantalum powder of capacitor quality; see also references cited therein), the adequate function of tantalum nitride by providing a new series of useful powder substrates. Example 1 Initial tests demonstrated a leakage of Ta-Si dust substrate systems approximately similar to Ta dust substrate systems (no gain), but the capacitance was improved for Ta-Si as a function of Ta even at higher sintering temperature for Ta-Si and slightly lower at lower sintering temperatures. It seemed that Si was acting as a retarder of sintering. The tests involved a group of four average pellets for each of the Ta, Ta-Si systems. Ta was a standardized 50K-9010 product made from reduced potassium heptafluorotantalo with leach artifacts, size fines, doping and deoxidization known in the art. The Ta-Si was prepared by mixing 0.333 gm of pure Si powder of 60 mesh to 99.999% with 9.667 gm of powder of Ta 50K-9010, as an approximation to TagSi2. The powders of both systems were compressed into pellets and sintered at 1500 ° C for the first sets of pellets formed at 16, 30, 40, 50, 80 and 100 volts of forming voltage, Vf, and the second sets were sintered to several temperatures from 1,350 to 1,550 ° C. The preparation conditions and the experimental results are tabulated as follows: TABLE I Summary of pellet preparation, formation and test conditions
Condition Value (s) Pellet mass (g) 0.14 Press density (g / cc) 5.0 Sintering temperature (° C) 1350, 1450, 1550 Sintering time (minutes) 20 Formation temperature (° C ) 80 Formation voltage (V) 16, 30, 40, 50, 80, 100, 120 Formation current (mA / g) 100 Retention time (hours) 2 hours, or 5 minutes Electrolyte formation 0.1V / V % H3PO4 DCL test voltage (% Vf) 70 Polarization voltage (v) 0-20V LDC impregnation time (minutes5)
TABLE II Electrical results for silica tantalum mixture (maintained for 5 minutes)
TABLE III Capacitance (μG-V / g)
Temperatu50 -9010 LFS-001 50K-9010 LFS-001 sin-50Vf 50Vf 120Vf 120Vf Termination 1350 41,500 31,400 1,450 30,600 24,300 19,000 20,900 1550 16,100 19,300 TABLE IV Leakage (nA / ^ F-V / g)
Temperatu50K-9010 LFS-001 50K-9010 LFS-001 ra of sin- 50Vf 50Vf 120Vf 120Vf terization 1350 0,322 0, 512 1450 0,275 0,249 0, 608 0, 946 1550 0, 067 0, 065
TABLE V 140 volts capacitance formation (μG-V / g) and Leakage
The results are represented graphically in Figure 1 where it is seen that the capacitance of the Ta-Si powder substrate capacitors (LFS) is of the same range as the Ta (50K) powder substrate capacitors, but shows less decrease at increasing sintering temperatures, a number of better stability and delay rates, but given ambiguous proximity of the values. Example 2 Other samples were prepared as in Example 1, but extending to Ta-Si, TaN-Si and Ta-Si3N4: - 0.333 gm 60M 99.999% Si with 9.667 gm 50K-9010; - 0.3106 gm 60M 99.999% Si with 9.689 gm TaN-003 - 0.545 gm Si3M with 9.456 gm 50 -9010 - 0.507 gm Si3N4 with 9.43 gm TaN-003 All the mixtures had a Ta / Si ratio of 9/2 . The following were also included as controls: - Pure TaN-003 - Pure 50K-9010 The conditions of the experimental procedure and the results are set forth in Tables VI-VII.
TABLE VI Summary of pellet preparation, training and test conditions
TABLE VII Capacitance (mF-V / g)
TABLE VIII Leakage (nA / mF-V) Temperature 50K- TaN-003 Ta + Si TaN + Si TaN + Si3N of sinteri9010 4 ation 50 Vf 1350 0, 272 0, 881 0,565 1, 006 41,900 1450 0, 064 1,079 0,458 0,434 6,726 1550 0, 062 0,954 0, 058 0,164 0, 157 1450-lOOVf 0, 701 - 0, 880 1,332 11,413 The results are represented graphically in the figures
3-8. Figures 3-4 show TaN and TaN-Si with the lowest capacitance loss within a variable sintering temperature, but with leakage improvement (decrease) for TaN-Si at increasing sintering temperatures. A favorable balance of the characteristics of Ta-Si is also shown. Figures 5-6 show (in test products sintered at 1450 ° C and 1350 ° C) that at several polarization voltages from 0 to 20 volts the capacitance declines further to increasing polarization for Ta, much less for Ta-Si and still less for Ta-Si3N4 and less for TaN-Si. Figures 7-8 with porometry test results show a benefit of incremental volume as a function of pore diameter for Ta-Si as a function of Ta (Figure 7) and TaN-Si (Figure 8). This can lead to a reduction in series electrical resistance and better performance in high frequency use. The general results indicate a need. Example 3 Niobium silicon (Nb-Si) systems were also processed as for Ta above. These behaved differently from the Ta-Si system. There was no improvement in thermal stability and polarization dependence, but something different was observed. There was a general increase in capacitance with the addition of approximately 1% Si. There was also a decrease in the leak. The percentage increase in capacitance arose with the increasing sintering temperature, decreased in L / C and remained stable in general.
TABLE IX
There was an increase in porosity in Nb as seen in Ta, but the sample used had very good porosity of So there was no significant decrease in CSR. X-rays were passed in a sintered Ta-Si mix pellet and the result was that alloy was actually produced and there was not only one mixture. Explanation The present invention uniquely and unexpectedly establishes a different change of the powder substrate sintering characteristic of Ta-Si (and / or TaN-Si) as a function of Ta (or TaN) that can be linked to the temperature of higher quality sintering leading to capacitors of high capacitance beneficial and low leakage with several areas of better stability in terms of voltage polarization, frequency RSE, heat treatment. Example 4 Silanes were used to add silicon to tantalum as described below in parts (a) and (b) below, and the resultant silicon-doped tantalum was tested with results indicated in (c). (a) APST Tantalum powder was wetted with an aqueous solution of APST-amino propyl silane, triol, ie, C3HnW03Si, as a means of adding silicon and nitrogen dopants to the powder. The doping was performed at a level necessary to generate 500 ppm of silicon. The tantalum used was a typical 50,000 hp / gm powder (50 K). This level of doping should have theoretically generated an additional 249 ppm of nitrogen to the powder, a desired result. APST is soluble in water, and therefore conventional phosphorus additive can be added using techniques known to those skilled in the art. In this Example, the powder was actually doped simultaneously with 100 ppm of phosphorus dissolved in the same solution. After the addition of dopan-te, the powder was dried, and then heat treated (agglomerated) at 1320 ° C for 30 minutes under vacuum. (b) THSMP Tantalum powders were wetted with an aqueous solution of sodium THSMP -3-trihydrosilylmethylphosphonate, ie, CHi2Na06Si, as a means of adding silicon and phosphorus dopants, at a level to generate about 500 ppm of silicon. Again, the tantalum powder used was a typical 50,000 hp / gm class powder. It would be expected that this level of dopant would provide an additional level of 550 ppm phosphorus, a relatively high level of phosphorus for this type of powder. Therefore, no additional phosphorus was added. Like APST, THSMP is soluble in water, and can also be added using the typical methods for adding phosphorus known to those skilled in the art. After addition and drying, the powder was thermally treated under the same conditions as the APST sample. (c) Results of the test The surface area (AS, cm squared / gm), Scott volumetric density (DVS, cc / gm), Fisher mean particle diameter (DPMF, microns), flow (gm / second), carbon content (C) in ppm and equally content of nitrogen (N), oxygen (O), phosphorus (P) and silicon (Si) of the doped powders of (a) and (b), and the results are set out in Table X below for powders treated with APST and THSMP, with the tantalum powder base 50K as control checked equally. The uptake of silicon and nitrogen was very accurate (closely corresponding to the calculated one) and lower for phosphorus, but had been provided in excess in any case, as also indicates the highest surface of the 50K + THSMP sample compared to the other . The sodium added by the THSMP was substantially dissipated in the thermal agglomeration post-treatment. TABLE X
The same powders, agglomerates, were checked on a Malvern Mastersizer particle size measuring instrument using laser diffraction measurements of particles suspended in an aqueous bath, and the results are set forth in Table XI below. The tabulated results are shown for each of the control 50, powder treated with APST and with THSMP, the particle size of agglomerated particles up to fractions of 10, 50, 90% by weight, average value (MV) in microns, calculated surface area (CS) in m squared / gm, and% in weight of llmicra and under fines (fine particles). It is seen that doping served as a considerable retarder of sintering in both cases of APST and THSMP. TABLE XI
Powder 10% 50% 90% MV CS llmicra s 50K 13.4 53, 7 149.26 69, 923 0, 211 7.51 50K + 16, 9 77, 89 214, 94 103.4 0.17 5.62 APST 50K + 8.68 58.52 177.28 78.051 0.297 12.73 THSMP Despite the sodium present in the THSMP after the heat treatment in vacuo, the Na present in the sample 50 + THSMP was comparable to the control. It can also be seen that although the silicon is introduced into a composite form, it becomes elemental in the course of the heat treatment for agglomeration and is alloyed with the tantalum host. It should be understood that similar effects can be expected if silicon doping similar to niobium, tantalum or niobium alloys, including alloys, and compounds of one or both of these metals including nitrides and subnutrides are applied. Other silicon-containing compounds and solutions (eg, water glass) can also be used to provide silicon doping benefits described above and, if desired, also to provide secondary benefits from other dopants, eg, doped with nitrogen and / or phosphorus The agglomerated (or resulting anode compact) particles can be subjected to known deoxidation treatments such as exposure to vapors of alkali metals or alkaline earth metals or aluminum, preferably magnesium or calcium, during heating of the powders at 600-1200 ° C. , preferably more than 800 ° C, as described, for example, WW Al-brecht et al., US Patents 4,483,819, issued July 19, 1982, and 4,537,641, issued August 27, 1985. The deoxidation heating also provides a way to advance the conversion of silicon compounds to elemental silicon and its alloy with the host refractory metal. The deoxidation can be applied during the thermal agglomeration (reactive agglomeration). Deoxidation is often followed by a treatment with an inorganic acid to remove residue from the reduction reaction (for example, magnesium oxide). It is also known that other impurities of the refractory host metal can be removed by the deoxidation process and that thermal agglomeration temperatures can be reduced because of such a process. The combination of chemical and thermal factors of doping, agglomeration, deoxidation and possible sintering stops can be optimized for each situation of doping with silicon, alone or with other additives, to improve the physical and electrical properties of capacitors made with compact anodes porous made of such agglomerated powders. It will now be apparent to those skilled in the art that other embodiments, improvements, details and uses may be consistent with the letter and spirit of the foregoing description and within the scope of this patent, which is limited only by the following claims, interpreted according to patent law, including the doctrine of equivalents.