MXPA01003347A - Process for improving leakage and dissipation factor of solid electrolytic capacitors employing conductive polymer cathodes - Google Patents

Abstract

The adhesion of a conductive polymer film to an oxidized porous pellet anode is improved by the incorporation of a silane coupling agent in the polymer impregnating solution. The incorporation of the silane coupling agent also decreases leakage current and dissipation factor. Suitable silanes are those of the general formula (R1-R3)-Si-(OR2)3. Each of R2 and R3 is a C1-C6 alkyl group such as methyl, ethyl, or propyl. R1 can be chosen from a wide variety of organic functional groups such as epoxy, glycidoxy, amino, and pyrrole. The most preferred silane is 3-glycidoxypropyltrimethoxysilane.

Description

PROCESS TO IMPROVE THE LEAK FACTOR AND DISPERSION OF SOLID ELECTROLYTIC CAPACITORS THAT USE CÁTODOS DE CONDUCTOR POLYMER Field of the Invention This invention relates to solid electrolytic capacitors and the methods for manufacturing them, and more particularly to electrolytic capacitors in which conductive polymers are used as solid electrolytes and which have a low equivalent series resistance.

BACKGROUND OF THE INVENTION A solid state electrolytic capacitor is made from a porous ball of sintered tantalum powder, a layer of dielectric tantalum oxide that is formed on the surface of the sintered tantalum powder, a solid state conductor that is impregnates within the volume of the ball, and external connections such as silver paint, and so on. The tantalum forms the positive electrode of the capacitor, and the solid-state conductor forms the negative electrode (which is also called the cathode or counter-electrode).

Manganese dioxide has been used as the selection cathode for solid tantalum capacitors since the commercial introduction of this style of capacitor in the early 1950s. A key property of manganese dioxide is its ability to self-repair. In the defective portions of the dielectric film, the manganese dioxide becomes non-conductive. This is because the manganese dioxide is transformed into a lower manganese oxide due to the heating of joule at the defective site. This mechanism allows capacitors with low leakage currents to be produced. It also allows small dielectric defects that occur during manufacture and use to be isolated. However, if the dielectric defect is too large, the dielectric can crack. Manganese dioxide is a powerful oxidizing agent. When placed in direct contact with the tantalum through a crack in the oxide, the capacitor can ignite, leading to the destruction of the capacitor and the possible destruction of other components in the circuit. It is desirable to replace manganese dioxide with a solid state conductor that does not cause the tantalum to ignite while maintaining the ability to self-repair. The use of tantalum capacitors in high frequency circuits has become more important. This has led to the need for tantalum capacitors that have a low equivalent series resistance (ESR). The best manganese dioxide has a resistance _________ k ___ iá ---- _-? ___. _ ^. L --... - -.- _? -,, _ _._ ^ __ ^ ^ ¡A-_. __. _. _ ^, _ ^ ktitt.lj specifies 0.5 to 10 ohm-cm. It is desirable to replace the manganese dioxide with a solid state conductor having a low specific strength. However, many metals and highly conductive oxides do not have a self-repairing capability and are therefore not suitable for solid state tantalum capacitors. Conductive polymers such as polypyrroles, polyanilines, and polythiophenes have specific resistances 10 to 100 times more than those of manganese dioxide. Because they are oxidizing agents much less powerful than manganese dioxide, these materials do not cause the capacitor to ignite after a fault. Polypyrrole has been shown to have a self-repair mechanism (Harada, NEC Technical Journal, 1996). Due to these favorable properties of the conductive polymer compounds, these compounds are being investigated as possible replacement materials for manganese dioxide in solid state tantalum capacitors. Three methods have been used to deposit the conductive polymer in the porous tantalum pellet: 1. Chemical oxidizing polymerization; 2. Electrolytic oxidation polymerization; and 3. Deposition of a polymer from a solution, followed by oxidation and / or softening. In chemical oxidation polymerization, they are reacting a monomer, an oxidizing agent and a softener inside the porous pellet to form the conductive polymer. The monomers include pyrrole, aniline, thiophene, and different derivatives of these compounds. The oxidizing agent can be either an anion or a cation. Typical anion oxidants are persulfate, chromate, and permanganate. Typical cations are Fe (III) and Ce (IV). The best softeners are anions of strong acids such as perchlorate, toluenesulfonate, dodecylbenzenesulfonate, and so on. The reaction between the monomer, the oxidizing agent, and the softener, can be carried out in a solvent such as water, an alcohol, a nitrile, or an ether. Different methods have been used to introduce the monomer, the oxidizing agent, and the softener, into the pellet and conduct the conversion to the conductive polymer. In one method, the pellet is first immersed in a solution of the oxidizing agent and the softener, dried and then immersed in a solution of the monomer. After the reaction is carried out, the pellet is washed and then the process is repeated until the desired amount of polymer is deposited in the pellet. In this method, it is difficult to control the morphology of the final polymer. It is also difficult to control the exact stoichiometry of the reaction between the monomer and the oxidizing agent. The control of the stoichiometry is critical to get the polymer of ,-AI"-,,. , - ,.). -. higher conductivity (Satoh et al., Synthetic Metals, 1994). Cross contamination of immersion solutions is a problem. Because the pellet must be submerged twice for each polymerization, the number of process steps is greatly increased. It is necessary to wash the reagents in excess and the reduced form of the oxidizing agent of the part. This adds even more process steps and complexity to the process. In a related method, the sequence is reversed so that the pellet is immersed in the monomer solution first and the solvent is evaporated. The pellet is then immersed in the oxidising agent / softening solution and the reaction is carried out. This method suffers from all the disadvantages of the previous method. In addition, some monomer may be lost in the evaporation step of the solvent. In yet another method, all the components are mixed together and the pellet is immersed in the combined solution. This method reduces the number of dives and allows a more precise control over the stoichiometry of the reaction. However, the monomer and oxidizing agent can react in the immersion bath, causing premature polymerization and loss of reagents. This adds complexity and additional cost to the process. This is especially a problem with the oxidizing agents of pyrrole monomer and Fe (III). To overcome this problem '____. É__i tát ---_? .-. - • &'- to a certain degree, the immersion bath can be maintained at cryogenic temperature (Nishiyama et al., U.S. Patent Number 5,455,736). However, the use of cryogenic temperatures adds considerable equipment and complexity of operation to the process. The pyrrole / Fe (III) can be replaced with a combination of monomer / oxidizing agent that is less active; for example, 3-ethylenedioxyphene and a Fe (III) salt of an organic acid (Jonas et al., U.S. Patent Number 4,910,645). In the electrolytic oxidation polymerization, the monomer is oxidized to the polymer at an electrode and the softener is incorporated from the electrolyte. This polymerization method produces polymer films of high conductivity. There is no chemical oxidant to wash the film after polymerization. Direct electrolytic oxidation from monomer to polymer is difficult due to the high strength dielectric oxide layer. Different methods have been proposed to avoid this problem. One method is to form the polymer on the tantalum and then to form the oxide layer (Saiki et al., United States Patent Number 5,135,618). In another method, the polymer or oxide layer is formed at the same time (Saiki et al., European Patent Application 0 501 805 Al). However, the -t B? lt'áilÍl'i-fÍÍnf fi ni-fc * ^ "^ '-'" - - ..... -.-. ... «.., _ _..__. _? __ ___ ^^ ____ ______ .- «- Uriiw-y. ^^ * __ .. .. ^ J__i_t?, Electrolites more appropriate for depositing the conductive polymer and tantalum oxide films are very different; therefore, these methods produce neither an optimal polymer nor an optimal oxide. Another method is to deposit a thin film of conductive material by chemical methods, followed by the contact of this layer with an electrode to perform the electrolytic oxidation polymerization. Manganese dioxide which was prepared by the pyrolysis of manganese nitrate (Tsuchiya et al., United States Patent Number 4,943,892), manganese dioxide which was prepared by the pyrolysis of permanganate (Kudoh et al. J. Power Sources, 1996), and the conductive polymer that was prepared by chemical oxidising polymerization (Yamamoto et al., Electronics and Communications in Japan, 1993), for this thin layer. The contact of this thin layer of conductive material with an auxiliary electrode is difficult to achieve in practice. In this way, Tsuchiya and collaborators propose to bridge the anode terminal with the conductive layer. This bridging layer should be removed after depositing the polymer by electrolytic oxidation polymerization. A complicated series of insulating scrubbers is used under the bridging layer to achieve this. Kojima et al. (United States Patent of __t_- A ______ --- you, jü_-.

North America Number 5,071,521) propose contacting the thin conductive layer with an auxiliary electrode, the use of an auxiliary electrode greatly increases the complexity of the process, especially with the sintered pellet type anodes, where an individual electrode must be provided for each single anode. The contact of the layer with an auxiliary electrode can cause damage to the oxide layer. In principle, the direct deposition of the polymer from the solution includes the immersion of the capacitor in the solution of the polymer and then the evaporation of the solvent to form a conductive film. This operation is repeated several times to deposit the required amount of the polymer in the pellet. This strategy will reduce the number of steps of the process compared to the approach of the chemical oxidation polymerization and eliminate the uncomfortable auxiliary electrodes that are used in the approach of the electrolytic oxidation polymerization. However, the efficiency of the capacitance is poor with this process due to the difficulty to impregnate the small pores with a liquid containing a dispersed solid phase. Additionally, the technical limitations on the conductive polymer solutions prevent this ideal process from being achieved in practice. For example, polyaniline is - faMIÍÉlti t lilÉN ** - »< ** - -M «» - .. .--. . > - - -.- ^ - J .. _J _, "» ._. .__.,. ______. __ «__? _ < _ ~ _. S ____ ?? _ soluble in NMP in the base form of emereldine (PANI-EB), but not in the smoothed form. A PANI-EB solution is impregnated into the pellet, followed by evaporation of the solvent to leave a PANI-EB film of low conductivity. The pellet should then be further soaked in a solution of a softener to change the film in the form of the conductive emereldine salt (ES, for its acronym in English). This softening reaction takes a considerable amount of time, and the excess softener should be washed from the pellet. In addition, PANI-EB solutions are very viscous at concentrations above 5 percent by weight and tend to settle with stagnation. Thus, Sakata et al. (U.S. Patent No. 5,457,862) state that PANI-EB in NMP can only be used to coat the outer part of the porous pellet and is not suitable for internal impregnation. Even after smoothing, the PANI-EB resistances that were prepared using this method are only about 1 ohm-cm. To avoid the problem of solidification, Abe et al. (U.S. Patent Number 5,436,796) use a solution of polyaniline in the white emereldine base form (PANI-EB). This allows higher PA deI concentrations to be used without the problems -__ ?? ___ ^ _____ ___ of solidification, and the last resistance is lower. However, with the aim of becoming the conductive PANI-EB form, the PANI-EB films must be oxidized and smoothed within the capacitor pellet. The oxidant / softener reaction takes a considerable amount of time, and both the excess softener and the excess oxidant must be washed from the pellet. Despite considerable research and development efforts to capitalize on the intrinsic advantages of the conductive polymer electrodes, only the devices manufactured with these materials have been achieved with limited commercial success. The application of stable, continuous, highly conductive adhesion films to the internal and external surfaces of the porous anodes presents numerous technical challenges. One of the difficulties associated with the solid electrolytes of the conductive polymer is the poor adhesion between the dielectric oxide and the conductive polymer, particularly after exposure to high humidity environments. As a consequence of the poor adhesion between the dielectric oxide and the electrolyte of the solid polymer, the efficiency of the capacitance is reduced. The capacitance efficiency is defined as the ratio of the dry capacitance of the capacitor after the application of the solid electrolyte, with the _____ *.? __._-____ l_ _. * ___ .. tJ-.L-t.JLJ Capacitance of the capacitor as measured in a suitable wet electrolyte, before the application of the solid electrolyte coating. Capacitance efficiencies less than 1.0 increase the manufacturing cost of tantalum capacitors, because additional tantalum is required to obtain the desired capacitance. The continuous inclination of the market towards the miniaturization of the electronic components, places a greater importance on the efficiency of the capacitance because a larger anode is required to compensate the loss of capacitance. Poor adhesion of the polymer film to the external surfaces of the porous tantalum anode results in cracking and debarking, creating a discontinuous external polymer film, the application of silver paint to a cracked outer film leads to a high leakage current . Poor adhesion of the polymer film to the dielectric surfaces of tantalum oxide can also cause an increase in the dispersion factor of the capacitor. Therefore, a method for improving the adhesion of the conductive polymer film to the dielectric surfaces is highly desirable. Arkles ("Tailoring Surfaces with Silanes", Chemtech 1, 766, 1977) reports the use of organosilanes to serve as coupling agents between oxides such as those of aluminum, zirconium, titanium, tin, and nickel and the organic phases . Wu et al., Writing in Chemistry of Ma terials, volume 9, number 2, February 1977, reported improved adhesion between polyaniline and glass slides. The glass surface was modified through the application of an amino silane prior to the deposition of the polyaniline on the glass substrate. Sato et al. Claim enhanced adhesion of the polypyrrole to anodized aluminum films in Japanese Patent Number 09246106. Sato et al. Describe the use of silane coupling agents as a pretreatment, but do not teach the incorporation of the silanes within the polymerization solution. Sakata et al. (U.S. Patent No. 5,729,428) discloses a solid electrolytic capacitor having a valve-acting metal body, an oxide film as a dielectric from the oxidation of the metal body, an organic layer electron donor that is formed from an organic compound having an electron donor group, and a conductive polymer layer as a solid electrolyte layer that covers the entire surface of the organic electron-donor compound. Sakata and colleagues also teach two ways to make the electron-donor organic layer in the capacitor that uses conductive polymers as solid electrolytes, and a method ? __ A__á _________ j ___ t, __ m. to manufacture the capacitor. The organic electron-donor layer taught by Sakata et al. May be comprised of fatty acids, aromatic carboxylic acids, anionic surface active agents, phenol and its derivatives, hydrolysates of silane coupling agents, titanium coupling agents, or of aluminum coupling covering the entire surface of the oxide film with a thickness of a monolayer to several layers. Sakata et al. Describe suitable silanes, which include 3-glycidoxypropyltrimethoxysilane. Sakata et al. Describe the formation of the organic electron donor layer either by contacting the oxide with the vapor of the organic electron-donor compound or by immersing the oxidized anode in an alcohol solution of the electron-donor compound (specifically a 2 weight percent solution of 3-glycidoxypropyltrimethoxysilane in methanol). The reference also shows that the water in the aqueous solutions tends to react with the oxide, thus preventing the reaction of the coupling agent (although the silane agents will allow the formation of a thin film when contained in an aqueous acidic solution). Sakata and colleagues describe that the purpose of the organic electron donor is to increase adhesion ÉM-ttWiWftiff ^ iiíliii - "'' - ^^" - ^ ---- --- ~ ----.- > - * ^ - ~ ¿- - * .-. + ?? between the oxide and the conductive polymer, avoiding by the same the reduction of the electrostatic capacitance and avoiding the deterioration in the dissipation factor at high temperatures. Sakata and co-workers also give warning to keep the thickness of the electron donor organic layer minimal, because the increased thickness leads to increased equivalent series resistance and reduced electrostatic capacitance, but does not teach the incorporation of the silane into the solution of polymerization.

SUMMARY OF THE INVENTION It is an objective of the present invention to reduce the dissipation factor (DF) of solid electrolytic capacitors impregnated with counter electrodes of conductive polymers. It is another object of the present invention to decrease the equivalent series resistance (ESR) of the electrolytic capacitors impregnated with counter electrodes of conductive polymers. It is still another object of the present invention to reduce the leakage current of the electrolytic capacitors impregnated with counter electrodes of conductive polymers. It is a further object of the present invention, Improve adhesion between metal oxides and conductive polymers. In one aspect of the invention, a solid electrolytic capacitor comprises: (a) a porous pellet anode; (b) a dielectric oxide film that is formed by oxidizing a surface of the porous pellet; (c) a conductive polymer counter electrode that adheres to the oxide film, the conductive polymer having a silane coupling agent that is incorporated therein. In another aspect of the invention, a process for preparing a solid electrolytic capacitor having a conductive polymer counter electrode comprises: (a) providing an oxidized porous capacitor pellet; (b) immersing the pellet in a solution comprising a solvent, a monomer, an oxidizing agent, a softener, and a silane coupling agent; and (c) applying heat to the pellet in order to evaporate the solvent, thereby forming a conductive polymer film having the silane coupling agent incorporated therein. The porous pellet can be made from tantalum, aluminum, niobium, titanium, zirconium, hafnium, or alloys of these elements, and is preferably made to i-tAjt-r.1- ^ ftt- '' -ff l from tantalum. Suitable monomers for preparing conducting polymers include pyrrole, thiophene, and derivatives thereof. The preferred monomer is 3,4-ethylenedioxythiophene. Suitable solvents include ketones and alcohols, and preferably a mixed solvent of 1-butanol and 2-propanol is used. Oxidants for the polymerization of thiophenes and pyrroles include Fe (III) salts of organic and inorganic acids, alkali metal persulfates, ammonium persulfates, and others. The preferred oxidant is Fe (III) tosylate. Preferably, p-toluenesulfonate is used as a softener. The most preferred silane is 3-3-glycidoxypropyltrimethoxysilane. It was found that the incorporation of a silane coupling agent in the polymer impregnation solution unexpectedly improves the adhesion of the polymer film to the oxidized porous anode and unexpectedly decreases the leakage current and the dissipation factor of the polymer. capacitor.

Detailed Description of the Invention A porous pellet was prepared, for example, by pressing charged powder and sintering to form a porous body. The preparation of the porous pellets is well known in the art, for example as taught in U.S. Patent No. 5,729,428 to Sakata et al., Which is incorporated herein by reference in its entirety. The pellet can be made from any suitable material such as tantalum, aluminum, niobium, titanium, zirconium, hafnium, or alloys of these elements. Tantalum is the preferred material. The porous pellet can be of any size that is suitable for producing a surface mount capacitor 0 styled lead. The body of the porous pellet typically has a thickness of about 0.5 millimeters to 3 millimeters, a width of about 0.9 millimeters to 5 millimeters, and a length of about 1 mm to 5.5 mm. Then an oxide film was formed on the pellet. The oxide film can be formed using any suitable electrolyte solution, such as a phosphoric acid solution or containing phosphate. A voltage of about 14 V to about 150 V was applied. The formation voltage fluctuated from 2.5 to 4.5 times the nominal voltage of the part and more preferably from 3 to 3.5 times the rated voltage of the part. After the oxide film was formed, the pellet was immersed in an impregnation solution. The impregnation solution contained a monomer, an oxidizing agent, a softener and a silane coupling agent. The selection of a suitable solvent for the solution is well within the level of experience in the art. Examples of the solvents include acetones and alcohols such as acetone, pyridine, tetrahydrofuran, methanol, ethanol, 2-propanol, and 1-butanol. Preferably, a mixed 1-butanol and 2-propanol solvent is employed at a ratio of from about 1:15 to about 1.2: 1, preferably about 1: 2. The monomer concentration can be from about 1.5 weight percent, to about 8 weight percent, more preferably from about 4 weight percent to about 8 weight percent, and most preferably is about 6 percent by weight. Suitable monomers for preparing the conducting polymers include, but are not limited to, aniline, pyrrole, thiophene, and derivatives thereof. The monomers for preparing the conducting polymers are well known in the art, for example as taught in United States Patent Number 4,910,645 to Jonas et al., Which is incorporated herein by reference. The preferred monomer is 3,4-ethylenedioxythiophene. The concentration of the oxidizing agent can be from about 6 weight percent to about 45 weight percent, most preferably ? _í__tt ___? ^ a_t ^ __ ^ _ í_. _.__ t __- ^ íJi ___.___.__ i_ ^. The most preferred is from about 16 weight percent to about 42 weight percent, and most preferably about 24 weight percent. Oxidizing agents for preparing the conducting polymers are well known in the art. U.S. Patent No. 4,910,645, for example, teaches different oxidants for the polymerization of thiophenes and inorganic acids, alkali metal persulfates, ammonium persulfates, and others. The preferred oxidant is Fe (III) tosylate. The softener concentration can be from about 5 weight percent to about 30 weight percent, more preferably from about 12 weight percent to about 25 weight percent, and most preferably is about 21 percent by weight. Any suitable softener can be used, such as dodecylbenzenesulfonate, p-toluenesulfonate, or chloride. The preferred softener is p-toluenesulfonate. The silane concentration can range from about 0.25 weight percent to about 10 weight percent, more preferably from about 0.5 weight percent to about 4 weight percent, and most preferably from about 0.5 percent by weight up to approximately ^ l- - ^^ íj_S ^ Autt ______? _ ^ MÍ ^ t_ _ ^ l ^ 1_? d? Í ___ t_? t_ ^ J J 2 percent by weight. Deionized water can be added to the solution for the purpose of causing the hydrolysis of the alkoxy groups in silanol groups. Preferably, the concentration of deionized water is from about 0.5 weight percent to about 3 weight percent, more preferably about 1 weight percent. Suitable silanes are those of the general formula (R1-R3) -Si- (OR2) 3 as taught by Edwin P. Plueddemann, Silane Coupling Agents, Plenum Press (1982). Each of R2 and R3 is an alkyl group of 1 to 6 carbon atoms, more preferably methyl, ethyl or propyl. R3 is more preferred propyl. R1 can be selected from a wide variety of organic functional groups such as epoxy, glycidoxy, amino, and pyrrole. The most preferred silane is 3-glycidoxypropyltrimethoxysilane. The anodized pellets were immersed in the impregnating solution and then cured at a temperature of from about 65 ° C to about 160 ° C, further preferably from about 80 ° C to about 120 ° C, more preferably about 110 ° C, followed by washing in deionized water or other solvent. A lower silane concentration (ie, 0.5 percent by weight) that was used in the initial dives (ie, the first 6 dives) is effective for __kj _? ____ i _____ Í.t, _______ ra h iiIÉIÜlti - I I IG »^ * '- ^ .-- ^^ --.- ^« ^ - ^^ ^ __. ___u L __, __ reduce the dissipation factor and equivalent series resistance. The silane concentration can be increased for subsequent dives (i.e., 1 weight percent for dives 7-12), and further increased (i.e., 2 weight percent) to apply the external polymer coating to in order to effectively reduce the leakage current.

EXAMPLES The following illustrative examples are provided for a better understanding of the invention. These examples are illustrative of the preferred aspects of the invention and are not presented to limit the scope of the invention.

EXAMPLE 1 Charge tantalum powder 26,000 CV / g was pressed into pellets and sintered to form a porous body with dimensions of 0.81 millimeters in thickness, 2.92 millimeters in width, and 3.94 millimeters in length. The pellets (anodes) were sintered and then anodized in a 28 volt phosphoric acid electrolyte. Three impregnation solutions containing the monomer of 3,4-ethylenedioxythiophene, the Fe (III) oxidant, and the p-toluenesulfonate softener were prepared. The first solution contained 4 weight percent monomer, 16 percent by weight iron toluensulfonate, 16 percent by weight butanol, and the 2-propanol balance. Half a gram of 3-glycidoxypropyltrimethoxysilane and 2 grams of deionized water were added per 100 grams of the impregnation solution. The second solution was identical to the first solution, except that the concentration of 3-glycidoxypropyltrimethoxysilane was increased to 1 gram per 100 grams of the solution. The third solution contained 6 weight percent monomer, 24 weight percent iron toluenesulfonate, 24 weight percent butanol, and the balance 2-propanol. Two grams of 3-glycidoxypropyltrimethoxysilane and 2 grams of deionized water per 100 grams of impregnating solution number 3 were added. A group of anodes was repeatedly immersed in the first impregnation solution and cured. The anodes were washed in deionized water at 80 ° C and dried after each curing cycle. The anodes were processed through a series of 6 of these steps for each impregnation solution. After the final impregnation cycle, the anodes were examined microscopically. An adherent, continuous film was observed that covered the entire external dielectric surface of the anodes. After the application of a layer of silver paint to the outside of the anodes, the capacitance, the dissipation factor, the equivalent series resistance, and the leakage current of the devices were recorded.

Comparative Example 1 Í¡, The capacitors were prepared from the same batch of anodes as in Example 1. A solution of 95 volume percent 2-propanol in 5 percent deionized water was prepared. Two grams of 3-glycidoxypropyltrimethoxysilane were added per 100 grams of the alcohol-water solution. The anodized anodes were immersed in the silane solution for 1 minute. The anodes were dried in a forced convection oven at 110 ° C for 10 minutes. Monomer solutions at four and six percent by weight were prepared, in which the monomer (3,4-ethylenedioxythiophene), the oxidant (Fe (III)), and the softener (p-toluenesulfonate) were mixed together in the proportions that are provided in Example 1. A poly (3, 4-ethylenedioxythiophene) conductive polymer film was applied to the anodes through a chemical oxidising polymerization process, as described in Example 1. After the application of the conductive polymer film, the anodes were examined microscopically. The outer film cracked and peeled, revealing bare dielectric surface areas. After the microscopic examination, the anodes were immersed in a silver paint, and the capacitance, the dissipation factor, the equivalent series resistance, and the i___l_____________ - .. -vi * -..--. . * --- * ____________._ _.,. _- _. . - _. ^ _. ... ____ __ leakage current, Table 1 compares the performance between the capacitors that have the previous treatment with silane with those that have the silane incorporated in the impregnation solution.

Table 1: Previous Treatment with Silane vs. Incorporation of Silane in the Impregnator Solution Where "cap" is capacitance, "DF" is a dissipation factor, and "ESR" is equivalent series resistance.

EXAMPLE 2 A group of anodized pellets was impregnated, as described in Example 1, with a poly (3, 4-ethylenedioxythiophene) conductive polymer film. This impregnation was achieved through a process of chemical oxidation polymerization in which the monomer (3,4-ethylenedioxythiophene), the oxidant (Fe (III)), and the softener (p-toluenesulfonate) were mixed together in an impregnating solution as described above. The -i.- »jn-aat ...., .. - .- .- *. .. - concentration of monomer in this solution was 4 percent by weight. The ratio of oxidant and softener to the monomer for this 4 weight percent solution was identical to that used in the 1 6 weight percent solution described in Example 1. A series of 12 dives was applied. of impregnation to coat the internal surfaces of the dielectric with the conductive polymer. To determine the effect of the addition of the silane to the final dips on the leakage current, the anodes were divided into 2 groups for the application of 6 weight percent dips to build the thickness of the outer film. An anode group was treated with an impregnation solution with the composition as in Example 1. The other anode group was treated with an impregnation solution that did not contain silane. After the application of the external polymer coating, silver paint was applied and the DC leakage of each group was measured. Table 2 below shows these results.

Table 2: Capacitor Performance with Silane in the External Polymer Coating Solution _________ __, ____ t ____, _______, ---- T t iim - and ^^ -, J.A..J- > ___, ____ «_.___ _____, ___ _________ ..

Where "cap" is capacitance, "DF" is a dissipation factor, and "ESR" is equivalent series resistance. The data clearly indicate that the leakage current was reduced by the incorporation of 3-glycidoxypropyltrimethoxysilane in the solution that was used to apply the external polymer coating.

Example 3 in order to test the effect of the incorporation of 3-glycidoxypropyltrimethoxysilane into the impregnation solution for the initial dives, another experiment was run using the anodes that were prepared as in Example 1. The anodes were immersed 12 times in a 4 weight percent impregnation solution, as described in Example 2. A silane concentration of 0.5 was used. percent by weight for the initial six dips (all impregnation solutions containing silane, also contained 1 percent deionized water). A 1 weight percent concentration was used for dives 7-12. A silane concentration of 2 weight percent was used in the 6 weight percent dips to provide an external polymer coating. For comparison, a group of anodes from the same batch was impregnated with solutions that did not contain silane. In Table 3 are l ifii I ti-li? i iH? l ttiit., * .._. & _ * ____. & . the data for the experiment. These data demonstrated that the incorporation of silane into the conductive polymer impregnation solution for the initial dives, reduces the DF and the ESR. As in the previous example, the leakage current was reduced by the addition of silane to the 6 weight percent solutions that were used to provide an external polymer coating for the capacitor.

Table 3: Performance of the Capacitor with Silane Incorporated in the Initial Dives Where "cap" is capacitance, "DF" is a dissipation factor, and "ESR" is equivalent series resistance. It will be apparent to those skilled in the art that various modifications and variations may be made in the compositions and methods of the present invention, without departing from the spirit or scope of the invention. Therefore, it is intended that the present invention cover the modifications and variations of this invention, provided they are within the scope of the appended claims and their equivalents.

Claims (19)

1. A solid electrolytic capacitor comprising: (a) a porous pellet anode; (b) a dielectric oxide film by means of oxidizing a surface of the porous pellet; and (c) a conductive polymer counter electrode that adheres to the oxide film, the conductive polymer having a silane coupling agent incorporated therein. The solid electrolytic capacitor of claim 1, wherein the porous pellet is made from a material that is selected from the group consisting of tantalum, aluminum, niobium, titanium, zirconium, hafnium, and alloys thereof . 3. The process of claim 1, wherein the silane coupling agent is of the general formula (R1-R3) -Si- (OR2) 3, wherein R1 is selected from the group consisting of epoxy, glycidoxy , amino, and pyrrole; and R2 and R3 are each alkyl of 1 to 6 carbon atoms. 4. The process of claim 3, wherein R2 is selected from the group consisting of methyl, ethyl and propyl, and wherein R3 is propyl. 5. The solid electrolytic capacitor of claim 1, wherein the coupling agent of _¡'ALÁÍ, - & At * .-,? Já_i: -i: .-. 3. M-_tiA¿_. . . I. ..--- ". , ... _ ¿.. - £., ^ ... ^ ._ .. ^ _., -..._ í -. ^ .. a _.__ "i,, ^, ^ s _?,? .. ^,.,, _. . ^ .. ^ __1¡.Í .Í: .É_. silane is 3-glycidoxypropyltrimethoxysilane. 6. The solid electrolytic capacitor of claim 1, wherein the conductive polymer is selected from the group consisting of polyanilm, polythiophene, polypyrrole, and derivatives thereof. 7. The solid electrolytic capacitor of claim 1, wherein the conductive polymer is poly- (3,4-ethylenedioxythiophene). 8. A process for preparing a solid electrolytic capacitor having a conductive polymer counter electrode, the process comprising: (a) providing a pellet of the oxidized porous capacitor; (b) immersing the pellet in a solution comprising a solvent, a monomer, an oxidizing agent, a softener, and a silane coupling agent; and (c) applying heat to the pellet so as to evaporate the solvent, thereby forming a conductive polymer film having the silane coupling agent incorporated therein. The process of claim 8, wherein the porous pellet is made from a material that is selected from the group consisting of tantalum, aluminum, niobium, titanium, zirconium, hafnium, and alloys thereof. The process of claim 8, wherein the silane coupling agent is of the general formula (R-R3) -Si- (OR2) 3, wherein R1 is selected from the group consisting of epoxy, glycidoxy , amino, and pyrrole; and R2 and R3 * i are each alkyl of 1 to 6 carbon atoms. 11. The process of claim 10, wherein R2 is selected from the group consisting of methyl, ethyl and propyl, and wherein R3 is propyl. The process of claim 8, wherein the silane coupling agent is 3-glycidoxypropyl-10-trimethoxysilane. The process of claim 8, wherein the silane coupling agent is present in the solution in a concentration of from about 0.25 to about 10 percent by weight. 14. The process of claim 8, wherein the silane coupling agent is present in the solution in a concentration of from about 0.5 to about 4 percent by weight. 15. The process of claim 8, wherein the silane coupling agent is present in the solution in a concentration of from about 0.5 to about 2 percent by weight. 16. The process of claim 8, wherein the monomer is selected from the group consisting of 25 aniline, pyrrole, thiophene, and derivatives thereof. Lti.? A -? - UA. Í ..? _to_-. The process of claim 8, wherein the monomer is 3,4-ethylenedioxythiophene. 18. The process of claim 8, wherein the oxidizing agent is Fe (III) tosylate. 19. The process of claim 8, wherein the softener is p-toluenesulfonate. t-l-jtjLj .--- * --- »» ..