CA2562986A1

CA2562986A1 - Multi-layer ceramic polymer capacitor

Info

Publication number: CA2562986A1
Application number: CA002562986A
Authority: CA
Inventors: David A. Kelly
Original assignee: Individual
Current assignee: Individual
Priority date: 2006-10-06
Filing date: 2006-10-06
Publication date: 2008-04-06
Also published as: WO2008040114A1

Abstract

A method of capacitor construction using ceramic powder with a polymer binding agent, in a multi-layered structure. Each layer has an electrode formed on a dielectric layer, which is then assembled such that each electrode layer has at least one dielectric layer separating an adjacent electrode. During manufacture the ceramic polymer dielectric is supported by a carrier layer forming part of the capacitor structure and often supporting the electrodes of the capacitor. The dielectric is composed of a principal ingredient, a fine dielectric powder and a second ingredient that acts as a binding agent. The construction is highly modified to that of a polymer film capacitor through the addition of high K ceramic polymer layers.

Description

FIELD OF THE INVENTION
The field of the invention relates to a ceramic dielectric polymer capacitor construction with special electrodes that provide a degree of self healing and external circuit protection. The capacitor design has energy storage capability far exceeding current polymer film technology and approaches that of current double layer low voltage super capacitors. The capacitor fabrication is highly modified over that used in conventional polymer film capacitor manufacture.

BACKGROUND OF THE INVENTION
Traditionally, batteries of many different types and construction has filled the role of electric energy storage devices, but they suffer from a limited life and a slow rate of recharge. The development and demand by the public for pure electric or hybrid cars, electric scooters and renewable energy sources such as solar or wind power has created the need for an inexpensive, long lived, fast to recharge electric storage device. The development of various super capacitor technologies has tried to fill the need for such an electrical device. Each of the various super capacitor technologies developed have specific technical limits to their operation and often a high cost of manufacture. Lower cost super capacitor designs are constantly being researched with the goal of developing and meeting the public's requirement for such an inexpensive device.
Various industries require the continued development of inexpensive capacitors and electric energy storage devices. Research into high K dielectric materials, for example relaxor ferro-electric ceramics, has lead to the discovery of materials with properties that are well suited for use in a capacitor, with dielectric values up to 100,000 but, a number of the best materials are not compatible with current ceramic capacitor manufacturing technology. Further, problems have been recognized with existing ceramic super capacitor technology currently under development, where a short circuit across a dielectric layer between oppositely charged electrodes results in sudden destruction of the capacitor and at times the destruction of the capacitor assembly being used as an electrical energy storage device. Another problem with ceramic capacitors is the development of internal cracks, across the dielectric insulating layers, caused by thermal shock or a sudden voltage surge or mechanical stress from improper handling and the manufacturing process. These cracks represent weak spots within the dielectric insulating layer and a location where an electrical short circuit may develop during normal operation. To reduce the risk of an electrical short circuit manufacturers have to substantially increase the thickness of the dielectric layer making the ceramic capacitor larger and more expensive than a crack resistant or self healing insulating dielectric material would require.
A ceramic super capacitor energy storage device, manufactured using the traditional ceramic capacitor method of construction, often uses thousands of capacitors connected in a parallel arrangement, with each capacitor having hundreds of insulating dielectric layers. This means that each energy storage device contains hundreds of thousands of insulating dielectric layers where a short in a single layer would result in the discharge of the whole energy storage device into a single capacitor, destroying the capacitor and the energy storage device.

To reduce the threat of destruction of a ceramic super capacitor energy storage device, by such a common failure mode, the addition of external fuse elements to each capacitor or group of capacitors is required. The purpose of the fuse device is to disconnect the failed capacitor from the energy storage device in such a way that the energy storage device will continue to function, even though one or more elements have failed. The over design of the ceramic super capacitor and addition of fuse devices increase the size and expense of an energy storage device using ceramic capacitors.
Plastic film capacitors of current manufacture are technologically mature, efficiently utilize available dielectric material, are low cost to manufacture and may be designed to be self healing, such that an internal dielectric short circuit clears in such a way that the capacitor continues to function as intended. The mechanical and electrical performance of plastic film capacitors are ideal in all ways except the dielectric constant of plastic film is only 1/1000 that of a high K ceramic material. The focus of current research has been to develop methods of combining the high K
dielectric properties of ceramic capacitors with the ease of manufacture of the film capacitor. The progress to date has been of only limited success with blends of polymer film material with added ceramic particles, exhibiting dielectric constants up to 50 or a 4 fold improvement.
Research and development of ceramic polymer capacitors have found solutions to the ceramic capacitor cracking problem and methods of incorporating self-healing properties to the dielectric layers in a manner that will prevent premature device failure. The use of a suitable ceramic polymer material where the ceramic content is typically greater than 85%
allows much thinner dielectric sections and a number of ways to incorporate self healing properties combined with a lower cost of manufacture. However, the technology still doesn't match the simplicity of plastic capacitor manufacture.
There are many different patents that provide information about current state of the art in plastic film and ceramic capacitor design and manufacture. US7,033,406 is an example of a high energy electrical storage unit that uses state of the art ceramic capacitor technology in its manufacture. The ceramic capacitor used in the ESU have no mention of fuse elements or other electrode technology to provide a degree of self healing. The capacitor design relies on a void free ceramic glass matrix where the structure is about 10% by volume a special glass. The absence of any form of self healing or fuse element in the ceramic structure makes the capacitor at risk of melting or become severely damaged, should a dielectric layer fail. The use of ceramic glass composite matrix improves some properties but still leaves the capacitor sensitive to cracking if subjected to mechanical stress.
US4,247,881, 7,027,288 and 7,099,141 demonstrate two different methods of self healing, should an insulating dielectric layer fail. For plastic capacitors, self healing design practices are represented by US4,049,859, 4,131,931 and 4,685,026.
An example of a method used to increase the power capability of a cylindrical plastic film capacitor is represented in US4,719,539. US6,426,861 is a good example of a hybrid film capacitor where one or more plastic materials are blended together to form the dielectric insulating layer.
Figure 1 represents prior art from the inventor's September 2006, Canadian patent application. The drawing represents different electrode structures formed on top of either ceramic or ceramic polymer layers. Both the electrodes represented by numbers 102, 104, 106, 108, 111, 113, 116 and ceramic or ceramic polymer layers shown by 101, 105, 109, 112, 117 may be formed using any conventional manufacturing technique compatible with the material being formed. The ceramic or polymer ceramic dielectric layers for example may be formed using conventional tape casting, screen printing, spraying or other compatible process. The electrodes placed on the dielectric layers for example may be formed through screen printing, evaporation, sputtering, direct printing as a few of the many methods that are currently used.

Figure 2, 3 and 4 represents prior art from the inventor's September 2006, Canadian patent application. They are constructed from ceramic polymer tapes made in a manner similar to conventional ceramic capacitors. These figures show how the electrodes from Figure 1 may be stacked to form various capacitor structures. Figure 2 shows a conventional capacitor made by stacking ceramic polymer tape layers on top of each other, which are then pressed together to form a capacitor structure. Figure 3 and 4 represent a capacitor structure that has the capability to self heal if a portion of the dielectric should fail. These last two figures are fabricated using a ceramic polymer tapes which are fabricated, then stacked and pressed together to form the desired capacitor structure.

SUMMARY OF THE INVENTION
The main object of the present invention is to substitute a ceramic polymer dielectric in place of the polymer dielectric used in polymer (plastic) film capacitors. The present invention is a ceramic polymer capacitor method of manufacture that is inexpensive, self healing and offers energy densities up to and exceeding 1000 times that of conventional plastic film capacitors, of a similar physical size. The method of manufacture is compatible with all ceramic dielectric compounds including those that are currently not compatible with conventional ceramic capacitor fabrication methods. The method of manufacture resolves the many problems encountered when high densities of ceramic dielectric powder is combined with a polymer compound to form an insulating dielectric layer. A capacitor designed and fabricated using the present invention is capable of exceeding the energy densities of current ceramic capacitor technology and through the use of new high K
ceramics, currently not useable in conventional ceramic capacitors, is capable of exceeding the energy density of the best storage battery technology. A capacitor manufactured according to the current invention may be constructed to have any desired electrical performance and environmental capabilities of current ceramic or polymer film capacitor technology.
The dielectric used by the preferred embodiment is comprised of a suitable ceramic powder, often comprised of but not limited to 2 predominant sized particles typically 1 micron in diameter or less, where the smaller particles are no more than 1/2 the size of the larger particles. The ceramic powder is dried then combined with a polymer compound that includes a compatible solvent and other selected additives to adjust the viscosity and impart desired properties to the mixture. The percentage by volume of ceramic to polymer, after removal of the solvent, is typically but not limited to 92%. The polymer compound may be either a cured resin dissolved in a suitable solvent;
alternately activated so it can be cured during a later process stage. The mixture is processed to remove residue gasses, moisture or other undesired substances. The resulting ceramic polymer solvent mixture is then applied to a either a suitable substrate or previous capacitor layer, using any process that provides the desired film thickness and properties. The solvent is then sufficiently removed to leave the ceramic polymer mixture with properties that are compatible with the next step in the capacitor manufacturing process.
In one embodiment the substrate is a thin polymer film which has the desired electrode structure already deposited on its surface. The substrate with the ceramic polymer compound, less solvent is then either wound onto a cylindrical form if the desired capacitor is to be axial or layered onto a suitable substrate to be later cut into a rectangular or other desired shape.

In another embodiment a suitable substrate is used to form the ceramic polymer dielectric layer, which is then subjected to further manufacturing processes. The substrate is removed at an appropriate point during the manufacturing process and is not part of the finished capacitor structure. The ceramic polymer dielectric compound is either wound into an axial capacitor or layered onto a suitable substrate to be cut later into a rectangular or other desired shape.
In the preferred embodiment the capacitor structure is completed; then heated in combination with a DC voltage, that is in proportion to the final capacitor working voltage, is applied across the capacitor electrical terminations (electrodes) with pressure to enhance the dielectric and electrical properties of the capacitor and complete the curing of the polymer.
In another embodiment an electric field of desired intensity is applied perpendicular to the plane of the ceramic polymer dielectric during the solvent evaporation process.
Yet in another embodiment electric charge is applied to at least one of the electrodes located on the substrate film, an electrode on the ceramic polymer layer or directly on the ceramic polymer layer itself during the solvent removal process.
In an embodiment in keeping with the preferred embedment, where the ceramic polymer compound is applied by a method of spraying, electrostatic charge is injected to the spray to create a more uniform layer often enhancing the ceramic polymer dielectric properties.
In the preferred embodiment, after the capacitor is fabricated, one process is to subject the capacitor to a suitable voltage profile, under appropriate environmental conditions, to break down any intermediate weak areas of the capacitor. The suitable voltage profile is at least DC and may include AC of varying amplitude and frequency, that is capable of breaking down any areas of the ceramic polymer dielectric that does not meet the desired capacitor voltage specification.
Yet another aspect of the invention where a capacitor electrically insulating dielectric layer is composed principally of a ceramic dielectric powder, typically smaller than 1 micron in size, bound together into a void free solid matrix with a polymer compound, where the polymer compound is a soft elastic compound such as a silicone gel, acrylic or other adhesive that adheres to the ceramic powder after curing.
An aspect of the invention where an electrically insulating dielectric layer is composed principally of a ceramic dielectric powder, typically smaller than 1 micron in size, bound together into a void free solid matrix with a polymer compound, where: the electrically insulating dielectric material is stacked with alternating electrode layers, where a number if not all the electrodes are connected to one of at least two common electrodes located on different sides of the capacitor, and each common electrode is electrically isolated from each other and comprise one part of the capacitor electrical circuit.
In the preferred embodiment of the invention where an electrically insulating dielectric layer is composed principally of a ceramic dielectric powder, bound together into a void free solid matrix with a polymer compound, where: the electrically insulating ceramic polymer dielectric material is formed on a thin polymer film substrate with at least one electrode layer deposited on its surface.
The electrode is often high resistance 1 to 1000 ohm aluminum 10's of angstroms thick. During normal operation of the capacitor occasionally weak sections of the dielectric layer may arc or short.
The energy of the dielectric short circuit converts the very thin aluminum in the area of the arc into an electrical insulator which then acts to isolate the failed section of dielectric from the undamaged parts of the capacitor. This clearing action is a form of self repair, commonly referred to as a "self-healing capacitor". The ability of the ceramic polymer dielectric capacitor to self-heal in the preferred embodiment allows the use of much thinner ceramic polymer dielectric layers than possible in convention ceramic capacitor manufacturing, making the capacitor smaller and less expensive to manufacture.
Another embodiment of the invention removes the ceramic polymer dielectric carrier film or substrate before or during the formation of the capacitor structure. In this embodiment the ceramic polymer dielectric carrier film or substrate is not part of the finished capacitor structure.
Another embodiment of the invention that may be applied to the new method of capacitor construction and conventional ceramic capacitors design is, where at least one set of electrodes are made from a PTC (Positive Temperature Coefficient) high resistive material, which limits the current applied to a dielectric short circuit. If the short circuit is permanent, the highly resistive PTC
electrode will greatly increase in resistance as the electrode increases in temperature, as power is dissipated in the short circuit, limiting the power dissipated by the shorted capacitor to a safe or predetermined value.
In specific embodiments of the invention, applied to the new method of capacitor construction and conventional ceramic capacitors design, the electrically insulating dielectric layer between opposite polarity electrode layers, is broken into at least two intermediate insulating layers, where each intermediate insulating layer has an isolated floating electrode, such that a short or failure of one intermediate insulating layer doesn't create a short circuit through the whole insulating dielectric structure. The breaking up of a single electrically insulating layer into multiple intermediate layers provides a form of self healing for the capacitor so long as the remaining electrically insulating dielectric layer(s) is capable of carrying the full voltage applied across it. The advantage of this specific embodiment is applicable to capacitors operating at high voltages and will allow the thickness of the dielectric layers to decreased, reducing size, manufacturing cost and improve the reliability of the capacitor.
In yet another embodiment the isolated floating electrode in an axial capacitor is broken into segments, all of which are located on the same capacitor layer, between the electrodes. This separates the dielectric into many different sections such that a short circuit to one floating electrode leaves the remaining floating electrodes unaffected.
In other embodiments the floating electrically isolated electrode is often high resistance 1 to 1000 ohm aluminum 10's of angstroms thick. During normal operation of the capacitor occasionally weak sections of the dielectric layer may arc or short to the floating electrode. The energy of the dielectric short circuit converts the very thin aluminum in the area of the arc into an electrical insulator which then acts to isolate the failed section of dielectric from the undamaged parts of the capacitor. This clearing action is a form of self repair, commonly referred to as a "self-healing capacitor".
Further, in other specific embodiments of the invention, applied to the new method of capacitor construction where an electrically insulating dielectric layer is composed of a ceramic dielectric powder, typically smaller than 1 micron in size, bound together into a void free solid matrix with a polymer compound, where the electrically insulating dielectric material is first formed into tapes with an electrode structure formed on one side by suitable means, then the tapes are stacked, where a number, if not all the electrodes, are connected to one of at least two common electrodes located on different sides of the capacitor, where each common electrode is electrically isolated from each other and comprise one part of the capacitor electrical circuit.
In yet another specific embodiment the ceramic polymer tapes with electrodes are wound into an axial capacitor structure.
In other specific embodiments of the invention, applied to the new method of capacitor construction, where an electrically insulating dielectric layer is composed of a ceramic dielectric powder, typically smaller than 1 micron in size, bound together into a void free solid matrix with a polymer compound, where the electrically insulating dielectric material is directly deposited by a method that produces an insulating layer with the required mechanical and electrical properties on top of a proceeding layer followed with an electrode structure directly deposited by a method that produces a conductive layer with the required mechanical and electrical properties. The process is repeated forming a layered structure comprising of alternating electrically insulating dielectric layers followed by an electrode layer where a number if not all the electrodes are connected to one of at least two common electrodes located on different sides of the capacitor, where each common electrode is electrically isolated from each other and comprise one part of the capacitor electrical circuit.
Other specific embodiments of the invention, applied to the new method of capacitor construction, where an electrically insulating dielectric layer is composed of any amount of ceramic dielectric powder, typically smaller than 1 micron in size, bound together into a void free solid matrix with a polymer compound using special electrode construction as required to meet the requirements of the intended application.
In another specific embodiment of the invention, the axial capacitor layers are wound on a hollow structure. The hollow structure allows the passage of a coolant, such as air to pass through the middle of the capacitor, cooling the inner layers. The additional cooling of the inner layers allows the capacitor to dissipate greater amounts of heat, allowing the operation at higher power levels.
In yet another specific embodiment of the invention, the axial capacitor layers are wound on a thermally conductive solid structure. The thermally conductive structure allows the removal of heat from the middle of the capacitor, cooling the inner layers. The additional cooling of the inner layers allows the capacitor to dissipate greater amounts of heat, allowing the operation at higher power levels.

BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 depicts prior art capacitor electrode structures;
FIG. 2, 3, 4 represents prior art arrangement of capacitor structures;
FIG. 5 represents various capacitor electrode configurations of the present invention;
FIG. 6 provides a number of cross-section views of capacitor structures represented by the present invention;
FIG. 7 represents how electrodes are formed on a carrier film or substrate;
FIG. 8 represents another method of electrode structure formed on a carrier film or substrate;
FIG. 9 provides yet another method of electrode structure formed on a carrier film or substrate;
FIG. 10 depicts an axial capacitor construction of the present invention;
FIG. 11 represents a ceramic polymer composition;
FIG. 12 represents the ceramic polymer dielectric constant as a function of percent ceramic;
FIG. 13 represents the ceramic polymer breakdown voltage as a function of percent ceramic;

DETAILED DESCRIPTION OF THE INVENTION
The preferred embodiment of the invention is a ceramic polymer capacitor design that is lower cost to manufacture and smaller in size to an equivalent plastic film capacitor. The insulating dielectric of the preferred embodiment is comprised of a suitable ceramic powder, often comprised of two different size ceramic particles both typically 1 micron in diameter or less, where the smaller particles are no more than 1/2 the size of the larger ones. This ceramic powder is then combined with a suitable polymer compound that includes a compatible solvent and other selected additives to adjust the viscosity and impart desired properties to the mixture. The polymer compound may be a suitable resin dissolved in a solvent; alternately it is activated for curing during a later process stage.
The mixture is then processed to remove any residue gasses, moisture or other undesired substance.
The resulting ceramic polymer mixture is then applied using a suitable process to a substrate. The solvent is adequately removed to leave the ceramic polymer mixture with properties that are compatible with the next step in the capacitor process. In the preferred embodiment the substrate is a thin plastic film which has the desired electrode structure already applied.
The thin polymer substrate with the ceramic polymer dielectric is then either wound in a round or oval cylindrical form if the desired capacitor is to be axial or alternately layered onto a substrate to be cut later into a rectangular or other desired shape. In the preferred embodiment the capacitor structure is completed;
then heated in combination with DC voltage with pressure to enhance the dielectric properties and compresses voids. This forms the final structure and if necessary completing the curing process of the polymer compound. Following the final fabrication process the capacitor has DC voltage applied to the electrodes and is electrically processed following a predetermined process under appropriate environmental conditions, compatible with the type and voltage of capacitor being manufactured.
The DC voltage is used to break down and isolate from the capacitor, any weak areas of the ceramic polymer dielectric. Following this the capacitor is subjected to an AC
voltage, of suitable frequency and voltage to remove any remaining weak ceramic polymer sections. This completes the capacitor fabrication process.

The resulting ceramic polymer dielectric, made in this preferred embodiment has a polymer content typically but not limited to 8% by volume, is often selected to have elastic properties and adheres well to the ceramic particles with high corona resistance. During dielectric failure the polymer compound in conjunction with the ceramic powder should not evolve high volumes of free gas but chemically react into an electrically insulating, inert solid with volume similar to the original ceramic polymer mixture.

The dimensions in all FIGURES are greatly exaggerated and not in any way to scale for purposes of clarity, where in actual practice the ceramic polymer dielectrics are typically only a few l Os of microns thick with the electrodes often a few 10s of angstroms.
Figure 5 represents the most common but not all electrode structures that are formed on the polymer carrier which the ceramic polymer dielectric compound is applied to.
Many different types of carrier substrates are compatible with the fabrication of ceramic polymer layers. Polymer (often referred to as plastic) films are used in the preferred embodiment but in other embodiments the ceramic polymer dielectric layer is formed on a pre-existing capacitor electrode structure or even a preceding ceramic polymer dielectric layer. In yet other embodiments the ceramic polymer dielectric carrier structure is removed during assembly and is not part of the capacitor structure.
In figure 5, 500 represents an internal, electrically isolated from the outside, electrode which is commonly used in a self healing capacitor. It is often used in conjunction with electrode 503 forming a structure such as that found in figure 6D. In figure 5, 502 has 1 to 1000 ohm resistive surfaces often a few 10s angstroms thick, generally fabricated from aluminum but may be any electrically conductive material that when subjected to the energy of an internal short circuit, turns into an electrical insulator. 501 represents the carrier film that has a break down voltage no less than the working voltage of the capacitor as it is subjected to voltage during, and often after, a capacitor internal short clearing process. Further the thickness must be adequate to withstand the stress of forming the ceramic polymer coating on its surface. Electrode 503 is used often in conjunction with electrode 500 to form a structure as that found in figure 6D. Reference 504 are the left capacitor conductive electrode and 506 form the opposite or right capacitor electrodes.
Both electrodes 504 and 506 are designed such that electrical connection may be made to them from outside the capacitor. In figure 5, 505 is the carrier substrate film and does not have to be any thicker than that necessary to support the ceramic polymer forming process.
Electrode 503 may be used to form a capacitor structure similar to figure 6C
if first a ceramic polymer layer of suitable material and thickness is formed on the electrode surface, then an electrically isolated conductive layer is formed on top, over lapping both the right and left electrode areas. Next another suitable ceramic polymer layer would have to be formed on top. The carrier substrates are then stacked on top of each other to form an alternating capacitor structure.
In figure 5, 507 is carrier substrate where 509 is the electrically insulating layer and 508 the electrode, often aluminum, typically a few l Os of angstroms thick with the ability to form an outside electrical connection. Carrier substrate reference 507 is subjected to low voltage stress and only is thick enough to survive the formation of the ceramic polymer layer on top of it. In figure 5 reference 515 is identical to 507 except reversed, 516 represent the electrodes that facilitate the forming of an external electrical connection to the capacitor plate and 517 the electrically insulating substrate layer, subjected to low voltage stress and mechanical stress from the formation of the ceramic polymer layer on its surface. Electrodes 507 and 515 in figure 5 are often used to form capacitor structures like those in figures 6A & C. The conductive surfaces 508 & 517 are often made to be low resistance aluminum 0.01 to 10 ohms, when 507 & 515 are used in a capacitor structure represented by figure 6C.
Figure 5 electrode 520 offers the capability of self healing and is the simplest capacitor construction. Item 524 is a floating electrode with no outside electrical connection, often high resistance 1 to 1000 ohms a few l Os of angstroms of aluminum and when subjected to the energy of an arc converts into an electrically insulating material, extinguishing the arc. 521 is the carrier substrate, often a polymer film that is of adequate thickness to withstand the full working voltage of the capacitor and the mechanical stress of forming a ceramic polymer layer on top. Electrode 524 is often used to make a self healing capacitor structure such as that in figure 6E.
Figure 5, 510 represents a base substrate that if often used when a rectangular capacitor structure is desired. Item 511 is the left electrode connection, 513 the right and 512 is the substrate itself, which is often but not limited to ceramic. Substrate 510 is present in capacitor structures shown by figures 6, A through E.
Figure 6 represents various capacitor cross sections used by a number of embodiments of the invention. All figures 6A, B, C, D and E use the preferred embodiment ceramic polymer dielectric and fabrication steps for assembly of the finished capacitor structure. Figure 6A is formed by applying a layer of ceramic polymer to the top side of figure 5 reference 507 & 515 electrodes. They are placed in alternating layers such that the right electrodes of one polarity are separated by at least one ceramic polymer layer from the left polarity electrodes, which form the other half of the capacitor. Reference 600 & 605 are the substrates for the capacitor, which are often ceramic if a hard durable material is required for a printed circuit board surface mount capacitor. Item 603 are the left electrodes, 602 the right ones and 601 the ceramic polymer dielectric. The end electrical connections 603 & 606 make electrical contact to each of the electrical electrodes 602 & 603 respectively; formed by any of the methods commonly used in the manufacture of plastic film capacitors. To make the structure self healing electrodes 603 & 602 are high resistance 1 to 1000 ohms often a few 10s angstroms of aluminum.

Figure 6B is similar to A except only one carrier film is used with the left and right conductive electrodes on opposite side and making a simpler design where the ceramic polymer is often applied to one side and the layers stacked together until the desired capacitance value is achieved. Though Figure 6B is simpler in construction the carrier substrate has to withstand the full working voltage of the capacitor, which is not a requirement in figure 6A.
This is not a problem for low voltage capacitors but becomes less economical for high voltage capacitors which preferably use figure 6A, C or D for lower cost and the smallest size. In figure 6 B, 620 & 625 are the end substrates, 621 the ceramic polymer, 622 the carrier film with opposite polarity electrodes, 623 &
624 are the end electrical connections made using any compatible process used by the manufacture of plastic film capacitors. To make the structure self healing, electrodes on the carrier film reference 622 must be high resistance often 1 to 1000 ohms a few l Os angstroms of aluminum.
Figure 6C is a structure that requires more process steps but has the highest impulse current capability of any design, still having a degree of self healing. The capacitor is assembled by alternating two different carrier films. The first electrode 632 is formed by applying at least one ceramic polymer layer followed by the application of an externally isolated floating electrode 634 of high resistance 1 to 1000 ohms material that forms an electrically insulating material if it is involved in a dielectric short circuit between capacitor layers. The isolated electrode is often formed by different processes, such as but not limited to inkjet printing, spraying, screen printing, evaporation and sputtering. The isolated electrode is followed by at least one additional layer of ceramic polymer. More than one isolated electrode 634 may be used not shown, to further increase the self healing capability, where each isolated electrode is followed by at least one layer of ceramic polymer dielectric compound. The whole process is repeated for opposite electrode structure 633.
The two different electrode layers are laid on top of each other building up the structure until the desired capacitance value is achieved. In figure 6C, 630 & 637 form the capacitor support substrates, 631 is the ceramic polymer dielectric material, 632 & 633 the electrode structures often thick foil 0.01 to 1 ohm resistance for high impulse current capability, 635 & 636 are the electrical connections made to the capacitor electrodes in the same manner as figure 6A.
Figure 6D is another design that has superior self healing capability relative to 6B, though more complex often more expensive to manufacture. Figure 6D is formed by two different carrier films 641 & 644, where each film has at least one layer of ceramic polymer dielectric applied to them before they are laid on top of the previous layer. The structure uses electrodes figure 5, 500 &
503. In figure 6D, 640 & 646 are the substrates the capacitor is assembled on, 641 the external electrodes often but not limited to high resistance 1 to 1000 ohm of aluminum a few 10s angstroms thick, 642 is the ceramic polymer dielectric and 643 & 645 the end electrical connections made to the electrodes in the same manner as in figure 6A. The ceramic polymer dielectric and capacitor electrode carrier films do not carry any electrical voltage and only need to be thick enough to survive the stress of forming the ceramic polymer dielectric layers on top of them.
Figure 6E is a low cost design well suited for low voltage ceramic polymer capacitors, where the carrier film is required to block the working voltage of the capacitor.
The electrodes are often deposited directly on the carrier film as shown in figure 5, 520. They are high resistance 1 to 1000 ohm often aluminum a few 10s of angstrom thick and posses a degree of self healing if a short circuit should occur across the ceramic polymer dielectric. The capacitor is made by forming at least one layer of ceramic polymer dielectric of the desired thickness on top of the carrier film. The films are then stacked until the desired capacitance value is achieved. In figure 6E, 650 & 655 are the substrates that support the capacitor structure, item 651 has both the left &
right electrodes in addition to serving as a carrier film for the ceramic polymer dielectric. End terminations 643 & 645 are the electrical connections formed in the same manner as in figure 6A.
Figure 7 shows the capacitor electrode structure formed on a continuous carrier film. The carrier films in figures 7, 8 and 9 are often a polymer that is used in conventional polymer film capacitor construction. It is similar to that used in the manufacture of plastic film capacitors. The sheet as shown is designed to simultaneously manufacture a number of capacitors using an electrode structure similar to figure 5, 520 and figure 6E. In figure 7, 706 is the top layer of the film, 711 the bottom layer and 720 a cross section of one strip. The ceramic polymer dielectric would be formed on the top surface prior to slitting or cutting the film into sections along reference lines 700. The explanation of each element is as follows, 704 represents the edge margin of the film to be discarded. Item 702 would be the left capacitor plate, 703 the right electrode and both are electrically isolated from each other by area 705 and make electric connection outside of the structure. Lines 701, 707, 710 and 714 represent the fact that the sheet is continuous and only a small segment is shown. Item 713 is the area on the bottom of the sheet that is free of any conductive film. Areas 712, all are hatched, represent areas that are electrically conductive, often high resistance 1 to 1000 ohm aluminum a few 10's of angstroms thick, but have no outside electrical connection as the conductive area is well back from the cut lines.
The electrode layer on the underside is segmented into isolated areas of a specific size. The purpose is to limit any permanent dielectric short circuit to a small area of the capacitor.
Additionally, this limits the energy released during the dielectric short circuit to a predetermined level and if the fault is not cleared, only a small portion of remaining ceramic polymer is subjected to higher operating voltage. The segmenting of the inner electrode is predominately used only on capacitors with large amounts of stored energy, providing a further level of protection, improving capacitor reliability. The extra protection allows higher voltage stress to be applied to the ceramic polymer without affecting production yield or product reliability, making the capacitor smaller and lowering cost. Item 720 is a cross section of the carrier film where 721 is the left electrode, 722 the right electrode both of which have outside electrical connections. Item 724 is the electrically isolated inner electrode and 723 represents the electrically insulating carrier layer. The carrier layer as shown is a design that would often be used to manufacture an axial style of capacitor. To make a stacked version the top electrodes require horizontal zones along the horizontal cut lines, that are free of conductive film and would appear similar to the bottom layer except the conductive films would be in line with the existing top strips and the end result, when cut into individual electrodes, look similar to figure 5, 520. The electrode films are often high resistance 1 to 1000 ohm aluminum a few 10s of angstroms thick, deposited in any manner that provides an electrically conductive film with the desired properties. Materials other than aluminum may be used but, they should form an electrically insulating material after the dielectric short circuit has cleared.
Figure 8 represents a variation of the carrier film pattern used in the construction of the capacitor structure figure 6D, where the isolated inner electrode is either a separate carrier film of electrode type figure 5, 500 or printed directly on the ceramic polymer layer.
The whole structure is constructed using the method explained and shown in figure 6C. In figure 8, 806 is the top layer, 811 the bottom layer, 800 the slit lines for separation after manufacture.
Area 804 & 814 are the edge keep back zone, discarded during manufacture, 802 & 812 the left electrode, with 803 & 813 the right electrode. Item 820 represents a cross section of the film, 821 &
824 the left electrode, 822 & 825 the right and 823 the dielectric layer that is not subjected to high voltage stress, but must withstand the mechanical stress of forming one or more ceramic polymer layers on top before assembly. Figure 8 represents a continuous film structure often used in the manufacture of an axial capacitor. To use the film for a stacked capacitor design as represented by figure 6C or 6D then horizontal strips free of conductive film would have to be present and would look similar to that shown in figure 7, 712, except shifted to be inline with the vertical slit lines 800. The end result would be an electrode similar to figure 5, 503. The conductive films are often high resistance 1 to 1000 ohm aluminum a few 10s of angstroms thick, deposited in any manner that provides a conductive film of the desired properties. Materials other than aluminum may be used but they should form an electrically insulating material after the dielectric arc has cleared.
Figure 9 represents another variation of carrier film pattern that may be used in the construction of the capacitor structure figure 6B. In figure 9, 906 is the top layer, 911 the bottom layer, 900 the slit lines for separation after manufacture. Item 904 & 914 are the edge keep back zone, discarded during manufacture, 902 the left electrode, with 912 the right electrode located on the bottom layer. Item 920 represents a cross section of the film, 921 the left electrode, 925 the right with 923 the dielectric layer that is subjected to voltage stress equal to that across the ceramic polymer dielectric and must withstand the mechanical stress of forming one or more ceramic polymer layers on top of it before assembly. Figure 9 represents a continuous film structure typically used in the manufacture of an axial capacitor. To use the film for a stacked design as explained and shown in figure 6B, then horizontal strips free of conductive film would have to be present and would look similar to that shown in figure 7 reference 712, except shifted to be inline with the vertical slit lines 900. The end result would be an electrode similar to figure 5, 507, except the upper electrode of the pair 508 would have its electrical connection to the left instead of right. This capacitor structure would find application in capacitors under 550 volts and represents a simple low cost method of manufacture. The electrode electrically conductive films are often high resistance 1 to 1000 ohm aluminum a few 10s of angstroms thick, deposited in any manner that provides a conductive film of the desired properties. Materials other than aluminum may be used but they should form an electrically insulating material after the dielectric arc has cleared.
Figures 7, 8 and 9 has demonstrated how three of the electrode structures from figure 5 are be made into a continuous sheet form often used in the manufacture of ceramic polymer axial capacitors. Following similar design philosophy other styles of electrode carrier sheets could be designed. Wider sheets and alternative electrode patterns used in polymer (plastic) film capacitors are often compatible with the manufacture of ceramic polymer capacitors.
Figure 10 represents the design of a round axial style of ceramic polymer capacitor similarly may be manufactured into oval or flat axial styles. A number of different layers make up its construction. Item 956 represents the capacitor body as the layers 950 through 955 are wound on to it. Item 957 is the structure the capacitor is wound on to and in this example a hollow structure is shown. It is not necessary to make the middle of a ceramic polymer axial capacitor hollow and often it is manufactured using a variation of those methods used in the construction of axial polymer (plastic) film capacitors. However, by making the middle of the capacitor hollow, air or a coolant can be circulated through the middle to cool the inner layers, allowing the capacitor to be operated with much higher power dissipation. Lead 958 is one electrical connection and 962 the opposite, both of which are connected to the left and right capacitor electrodes respectively. The external electrical connections 958 & 962 are joined through connections 959 & 961 respectively to the inner electrodes through similar processes to those used by polymer film capacitor manufacture. Item 960 represents the outer insulating and protective layer of the axial capacitor.
Layers 950 through 955 are required in varying numbers by different capacitor structures.
For example to construct an axial capacitor as in figure 6D, layer 950 becomes the left and right electrode (figure 5-503) with a ceramic polymer layer deposited on top.
Layer 951 is a high resistance 1 to 1000 ohm aluminum 10s of angstrom thick, self healing isolated electrode (figure 5-500) with a ceramic polymer layer on top. Layers 952, 953, 954 and 955 are not used. Layers 950 and 951 are then wound together on the capacitor body 956 until the required capacitance value is reached.

The simplest axial capacitor is formed following figure 6E using a single layer 950 which has electrode figure 5-520 deposited on it, with a single ceramic polymer layer on top and layers 951 through 955 unused.

The remaining common capacitor structures represented by figure 6A through 6E
require a varying number of layers but are wound on the capacitor body in a similar manner to the two provided examples. The carrier films with appropriate electrodes often are designed similar to figures 7, 8 and 9. It is easy to see from the various examples that various capacitor structures can be manufactured similar to those used in the manufacture of polymer (plastic) film capacitors.

A common formula for the capacitance between two parallel plates is C = KEoA/d equation 1 where C => the capacitance in Farads K => dielectric constant of the material between the parallel plates so => permittivity of free space which is 8.854 x 10"12 F/m A => area of the plates in m2 d => the separation of the plates in m Polymer (plastic) film capacitors have a very low dielectric constant K of 3 to 14 while commonly used ceramic dielectrics have K values of 50 to 6,000 with less common ceramics exhibiting values as high as 100,000. The ratio of the difference in dielectric constants between ceramic materials to polymer film is 17 to 2000 and for less common ceramics as high as 33,000!
The voltage breakdown of ceramic materials is equal if not higher than that of polymer films however, they suffer from a large number of structure defects that greatly reduce their practical working voltage. Polymer film capacitors do not have as serious structural defect problem and when combined with self healing electrodes they are able to operate close to their break down voltage.
Ceramic capacitors having far higher dielectric constant values are smaller as expected but only 1/4 the size of polymer film capacitors, larger by 3 orders of magnitude than what should be possible!
Examining equation 1 it becomes obvious that if a ceramic material was substituted for the polymer in a plastic film capacitor the capacitance value would be substantially increased. If for example a commonly used ceramic dielectric material, known in the electronics industry as XR7 with a K value of 1200 replaced the polymer with a K of 3, leaving the capacitor size and geometry unchanged, the capacitance would be 400 times that of the original polymer capacitor. With the cost of the ceramic material within the same order of magnitude as that of the polymer film, then the substitution of a ceramic material for the polymer would dramatically reduce the size and cost of the capacitor's manufacture by at least 2 orders of magnitude.

Figure 11 is an example of a ceramic polymer compound that may be substituted as the electrically insulating dielectric material in a modified polymer capacitor manufacturing process. In this example the polymer content is about 30%, exaggerated for purposes of clarity and much larger than the preferred embodiment of typically but not limited to less than 10%.
In figure 11, 980 and 986 are the capacitor electrodes, 981, 983 including 987 are regions of mostly polymer, which in this example is present near the electrodes. Item 982 and all other hatched areas are the ceramic dielectric material, of which there are shown two predominate sizes the smaller of which is about 1/4 the size of the larger. Item 988 is an area where the amount of polymer is about 60% by volume and is partially devoid of ceramic particles. Reference 985 is showing areas where the polymer is very thin between the ceramic particles and parallel to the electrodes.
One problem that figure 11 represents is that the ceramic particles often clump together and leave areas, occasionally near the electrodes, devoid of ceramic particles.
The polymer compound under most circumstances has a dielectric value typically 1/1000 that of the ceramic. The isolated areas of only polymer combined with the difference in dielectric constants presents a serious problem most evident when AC is applied across the capacitor electrodes 980 and 986. When AC is applied across the electrodes the ceramic powder appears like a short circuit placing a large portion of the AC voltage across the polymer in areas such as represented in figure 11 by 981, 983, 987. The concentration of voltage is because the polymer and ceramic particles act like two different capacitors in series with each other. From equation 1, the polymer region with 1/1000 the K value will have 1/1000 the capacitance as a ceramic particle of equal size. The result is two capacitors in series, the polymer capacitor having 1/1000 the capacitance of the ceramic one. When a voltage is applied across the two capacitors in series approximately 99.9% of the voltage will appear across the smaller value in this example the polymer one. This implies that the areas that are polymer rich are subjected to a much larger voltage than those which are dense with ceramic particles, breaking down from over voltage long before the ceramic rich ones. This is a highly simplified explanation and its purpose in not mathematical accuracy but to simply explain why a ceramic polymer dielectric with very high concentrations of high K ceramics are not able to reliably sustain voltages equal to those of when either the polymer or ceramic are by themselves.
The voltage concentrates across the polymer sections in areas 981, 983 & 987 and as it is increased the dielectric will start to fail either through heating as the polymer is subjected to very high leakage current breakdown. Either mechanism of failure produces reaction products such as gas, leading to mechanical deformation of the capacitor structure. The damage often propagates until it extends completely through the ceramic polymer dielectric resulting in a short circuit and the expenditure of a large amount of energy, from the capacitor leads, into a very small volume.
Figure 13 represents a graph of the break down voltage, under AC bias as a function of the percentage concentration of ceramic particles in the ceramic polymer dielectric. The graph assumes the worst possible circumstance that areas of polymer exist without ceramic particles present. The breakdown often occurs near the electrodes, shown in figure 11 item 981, 983 and 987. As the concentration of the ceramic rises, the thickness of the polymer between ceramic particles and the electrode interface region decreases, reducing the polymer's ability to withstand the voltage applied across the capacitor without suffering from either local heating or micro breakdowns. In figure 13, item 853 represents the breakdown withstand capability, in percent, of a dielectric layer consisting only of polymer. Item 855 represents the relative breakdown voltage, in percent, for a solid ceramic dielectric layer. Item 854 represents the relative AC voltage blocking ability of the preferred embodiment with a 92% ceramic content, without suffering from localized polymer heating or micro breakdown events. The graph is presented as a representation of the problem and actual results can vary greatly depending on the type of polymer, ceramic particle size and method of fabrication. For the same applied voltage, graph 13 implies that a 90% high K ceramic polymer dielectric may require a much as 10 times the thickness of a pure polymer or ceramic dielectric.
Figure 12 represents a the value of the ceramic polymer dielectric constant as the concentration of ceramic is varied. This graph is only a general representation and actual results may vary greatly depending on the method of fabrication, type of polymer used and ceramic particle size.
Item 850 represents the dielectric constant that results if there was no ceramic powder present and 852 is the value as if there was no polymer. From this graph it is seen that to achieve a high dielectric value the amount of ceramic present has be very high. However, figure 13 shows that as the ceramic content is increased the ceramic polymer dielectric breakdown voltage decreases.
Using the information from figures 11, 12 and 13 methods of enhancing the properties of the ceramic polymer dielectric were developed for the preferred embodiment of the invention to reduce if not eliminate the voltage breakdown problem. This processing allows the use of much thinner ceramic polymer dielectric layers. The preferred embodiment uses various manufacturing processes to shift the dielectric constant in figure 12 along reference line 851 to a value nearly the same as point 852, as if the polymer had been removed from in-between the ceramic particles. The result is a higher dielectric constant and improved AC performance. The preferred embodiment manufacturing process shifts the break down voltage from the point figure 13, 854 along line 856 to a value close to if not to 855. The effect is as if the polymer was removed from between the ceramic particles, increasing the voltage breakdown of the ceramic polymer dielectric. However, this last claim assumes that the polymer has at least similar if not the same voltage break down value as the ceramic else the final value will be closer to the lesser of the two.
The first part of the manufacturing process that has to be controlled is to minimize the amount of polymer, such that only the small voids are filled around the ceramic particles. This is achieved by combining ceramic powders of greatly differing sizes reducing the amount of void space that the polymer has to occupy. This is evident from figure 11, in the areas where the ceramic particles are of differing sizes and very dense, the area around the ceramic particles require only very small amounts of polymer to fill the voids. The actual amount of polymer required is dependent on the size of ceramic particles and method of mixing. Very dense areas of ceramic particles do not suffer from a substantially lowered voltage blocking capability as would be expected with a ceramic polymer dielectric with a much higher percentage of polymer than the minimal amount.

Below is the formula that gives the force between parallel capacitor plates when a voltage is applied between them.
F = (CV)2/(2KsoA) equation 2 where F => the force between the plates in newtons C => is the capacitance of the parallel plates V => the voltage applied between the parallel plates K => dielectric constant of the material between the parallel plates Eo => permittivity of free space which is 8.854 x 10"12 F/m A => area of the plates in m2 Equation 2 is involved through the "Winslow Effect" which is a behavior of an electrorheological fluid. In the preferred embodiment this type of fluid exists when the ceramic particles are in solution with the uncured polymer, with or without solvent present.
Another process used by the preferred embodiment is the application of an electric field across the ceramic polymer dielectric layer before the polymer has cured. The application of a voltage, preferably DC, across the ceramic polymer dielectric layer will produce the "Winslow Effect" which is the behavior of an electrorheological fluid where the ceramic particles will form chains along the electric field lines, forcing the polymer in a direction perpendicular to the ceramic particles. The Winslow Effect will replace any polymer in undesirable areas, such as the electrodes and replace it with ceramic particles. Even further improvement in the dielectric constant of some ceramic dielectric materials will occur if an appropriate voltage is applied across the ceramic polymer solvent mixture immediately after it is applied to the carrier substrate. The voltage will cause the highest dielectric constant orientation of the ceramic particles to align in the direction of the applied electric field, increasing the dielectric constant of the final ceramic polymer dielectric film. In some embodiments an electric field is applied to the carrier film immediately after application of the ceramic polymer solvent mixture in addition to the capacitor after assembly but before the polymer is fully cured.
Another manufacturing process of the preferred embodiment, that increases the voltage blocking capability of the ceramic polymer is to apply AC voltages of very low frequencies such as but not limited to 0.001 Hz, slowly increased in amplitude and frequency to over heat and break down the polymer areas that are weak. The triggering or use of the capacitor's self healing capability will disconnect the defective areas internally from the rest of the capacitor, in a controlled manner.

The recording of the number of healings during the breaking in period will determine whether a the ceramic polymer dielectric layer meets the final product reliability requirement and will identify capacitors of low quality through their high number of defects.
A final process of the preferred embodiment that improves the reliability and product yield during capacitor manufacture is to use a number of isolated floating electrodes, with self healing properties, such as in the capacitor design represented by figure 6C. The use of this technique is common in high voltage polymer film capacitors and is equally applicable to capacitors using ceramic polymer dielectrics.
Although the invention has been described in connection with a preferred embodiment, it should be understood that various modifications, additions and alterations may be made to the invention by one skilled in the art without departing from the spirit and scope of the invention as defined in the appended claims.

Claims

WHAT IS CLAIMED IS:

To be submitted later