Electrical device with high dielectric constant

[57] ABSTRACT

An electrical device is presented having unusual electrical properties, the physical configuration of the device being generally characterized as having a pair of conductive sheets or plates with a layer of a polymeric association product sandwiched between the plates which in many aspects behaves like a solid electrolyte. The association product comprises constituent materials which are characterized by ionic donor or acceptor sites or interstitial ionic impurities; and in particular, as used in this invention, an association product is a class of materials having molecular weight in excess of about 5,000 and which is characterized by a multiplicity of ionic acceptor and donor sites distributed along or pendant to a molecular chain, such material commonly being characterized by solubility of from 2 to 100 or more grams of the material per liter of water, and having tensile strength in excess of 10 pounds per square inch. The general class of constituent materials may range from low molecular weight liquids to high molecular weight solids. A particular important and attractive application for the device is that of a capacitor, but many other applications are possible.

Claims, 10 Drawing Figures

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DIELECTRIC CONSTANT

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FREQUENCY (hz)

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DC VOLTS BIAS

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ELECTRICAL DEVICE WITH HIGH DIELECTRIC CONSTANT

This is a continuation, of application Ser. No. 226,429, filed Feb. 15, 1972 now abandoned.

SUMMARY OF THE INVENTION

This invention relates to the field of electrical devices having the general configuration of a pair of conductive sheets or plates with a thin layer of organic polymeric insulative or semiconductor material sandwiched between the plates. More particularly, this invention relates to electrical devices of such configuration wherein the polymeric material is an association product, and particularly an association product of polyethylene oxide and a polymeric resin.

Of course, electrical devices having the general configuration of a pair of plates with a layer of insulating or semiconductor material sandwiched therebetween are old and well known as is their application to such uses as capacitors and transducers. However, we have discovered that unusual and unexpected results in electrical and electromechanical properties are obtained by using certain organic polymer association products as the sandwiched layer of material between the conductive plates. The particular association products in the electrical devices of the present invention are characterized by (a) high dielectric constants, sometimes greater than 1,000 often on the order of 50 to 100, usually in excess of 30, and at least more than 10, with or without d.c. bias and (b) a d.c. conductivity of less than 2X10^-10 mho/cm after 500 hours at a stress of 1 volt per mil of dielectric thickness. The layer of polymer in the present invention may be a very thin layer, on the order of only several thousandths of an inch or less, although thicker layers might be used for high voltage level applications. The devices of the present invention are inexpensive to manufacture, easy to handle and of small size. For example, in the case of capacitors, extremely high capacitance values can be achieved in a much smaller and lighter weight device than is the case with capacitors of conventional construction. In addition, the polymeric association product provides a physical and mechanical bond between the conductive plates, thus providing a significant advantage and improvement over electrolytic capacitors which do not have such bonding.

Accordingly, one object of the present invention is to provide novel and improved electrical devices having unusual electrical properties.

Another object of the present invention is to provide novel and improved capacitors and other electrical devices having a pair of conductive sheets with a layer of an organic polymeric association product sandwiched therebetween.

Another object of the present invention is to provide novel and improved capacitors and other electrical devices having a pair of conductive sheets with a layer of a polymeric association product of polyethylene oxide and a polymeric resin sandwiched therebetween.

Still another object of the present invention is to provide novel and improved capacitors and other electrical devices having a pair of conductive sheets with a layer of a polymeric association product of polyethylene oxide and a phenolic resin sandwiched therebetween.

Still another object of the present invention is to provide novel and improved capacitors and other electrical devices having improved electrical properties and being easy and/or inexpensive to manufacture.

Other objects and advantages will be apparent and understood from the following detailed description and drawings.

BRIEF DESCRIPTION OF DRAWINGS:

In the drawings:

FIG. 1 is a diagramatic side elevation view of the general configuration of the present invention.

FIG. 2 is a diagramatic side elevation view of another configuration of the present invention.

FIG. 2A is a diagramtic side elevation view of still another configuration of the present invention.

FIG. 3 is a graph of test results showing negative resistance characteristics.

FIG. 4 is a graph of test results of a pressure transducer specimen.

FIGS. 5 and 6 are graphs of test results of a temperature transducer specimen.

FIG. 7 is a graph of test results of a filter specimen.

FIG. 8 is a graph of test results of an amplifier specimen.

FIG. 9 is a schematic of an audio transducer application of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT:

While the exact mechanism or reason by which the electric devices of the present invention acquire and exhibit their unusual, unexpected and improved electrical properties is not known for certain, it appears that hydrogen bonding and transfer of electrical charge by hydrogen ion or proton mobility in the material of the polymeric association product may be an important factor. As used in this specification and claims, a polymeric association product is a class of polymeric materials which are characterized by a multiplicity of ionic donors (or interstitial impurities which act as ionic donors) and a multiplicity of ionic acceptors. As indicated above, the material is preferably an association product of polyethylene oxide and a polymeric resin, preferably a phenolic compound. It appears that the polyethylene oxide is characterized by a multiplicity of proton acceptor hydrogen bonding sites, and the polymeric resin is characterized by a multiplicity of proton donor hydrogen bonding sites. It further appears that the polymer blend serves as a relatively rigid matrix within which the proton donors or other relatively mobile ions or electrons or mobile polar molecules can travel or be rotated under the influence of an applied electric field. Interstitial impurities in the polymeric association product material may also be a key factor in the demonstration of the unusual, unexpected and improved electrical qualities. While such hydrogen bonding or similar mobility theory may or may not be the correct explanation, it will be understood that the improvements and unusual characteristics of the present invention do not depend on the accuracy of such theories.

FIG. 1 shows the basic general configuration of the electrical devices of the present invention where a pair of conductive plates 10 and 12 has sandwiched therebetween the polymeric association product material 14. The plates 10 and 12 may be any good conductive material such as, for example, aluminum, aluminum

3,883,784 with an oxide coating or copper of thickness (t), and the association product material 14 serves also to bond the plates together. Aluminum sheets with an anodized oxide coating appears to be particularly useful.

The polymeric association product material 14 may be a thin film, on the order of only several thousandths of an inch in thickness, and it may be formed by any convenient method either as an independent sheet or a laminate or coating on one of the conductive sheets. For example, polymeric association product material 14 may be formed by casting, painting, spraying or electrophoretically depositing materials out of solution or dispersion. The material can also be made by blending the constituent elements by hot melt milling and similar means and then melt coating, calendaring or extruding onto one of the metal sheets or into an independent sheet. Also, a porous inert sheet may be saturated with the association product to form the thin film. After formation of the basic configuration as shown in FIG. 1, the device may be further treated by baking, pressing, molding, rolling, quenching, rinsing or forming.

The basic configuration shown in FIG. 1 may be expanded as shown in FIG. 2 by the addition of alternate layers of polymeric association material and conductive sheets.

In accordance with the teachings of the present invention, a wide variety of electrical devices can be formed having the basic configuration of FIG. 1 or an expanded version as in FIG. 2. Examples of such devices that may be formed include capacitors, transducers, filters, amplifiers, laminar bus bar assemblies (which have significant improvement in capacitive characteristics) audio transducers, either pickups or speakers, memory and semiconductor devices. The polymeric association product material has a very high dielectric constant-at least greater than 10, usually in excess of 30, and often on the order of 50 to 100, and sometimes 1,000 or more, depending on the specific composition thereof. This high dielectric constant, along with other characteristics of the material, makes it possible to form these electrical devices with significant improvement over similar existing devices in one or more of the several attributes of performance, cost, ease of handling and reduced size. For example, in the case of capacitors, very high capacitance values can be achieved in devices of much smaller size than with conventional construction. Furthermore, the capacitors can be formed by techniques and with low costs similar to those in forming electrolytic capacitors. Thus, although some capacitors of the present invention may have relatively high d.c. leakage currents and dissipation factors which make them unsuitable for some applications, they are suitable as replacements for electrolytic capacitors in many applications. The bonding of the plates is also desirable in many applications, thus providing an advantage over electrolytics. It will be understood, however, that the capacitors of the present invention may be bidirectional rather than polar devices in the sense of electrolytic capacitors. Furthermore, because of the very thin film of polymeric association product material 14 that can be used, devices which are essentially thin film capacitors can be formed which are also bidirectional. By way of further example. laminar bus bars (such as those shown in U.S. Pat. No. 3,504,103) can be formed for either signal or power distribution in accordance with the present invention. and those bus bars will have significantly im4 proved capacitance characteristics over those now available.

As has been stated above material 14 is an association product preferably of polyethylene oxide and a polymeric resin material, preferably a phenolic compound. The preferred polymeric resins are phenolformaldehyde resol resins and phenolformaldehyde novolak resins. Such association products and the methods of formation thereof are disclosed in U.S. Pat. Nos. 3,125,544; 3,231,377; 3,231,381; 3,231,378; 3,321,382; and 3,309,202, to which reference is hereby made and all of which are hereby incorporated herein by reference with respect to the various and different compositions of such association products and the methods of formation thereof.

Since it appears that the unusual qualities of the present invention are due, at least in part, to hydrogen bonding between the constituents of the association product, any material capable of forming an association product with and hydrogen bonding with the polyethylene oxide may be used. Accordingly, the specific resin may be replaced by (1 ) polar liquids (such as water, formamide, dimethylsulfoxide or glyoxal) or (2) intermediate molecular weight (400-4,000) solids (such as pyromelletic acid, paraphenylene diamine, and methylene dianiline) and (3) high molecular weight (over 4,000) resins such as epoxy resins including, diglycidyl ethers of bisphenol A, epoxidized phenolformaldehyde novolaks (or epoxidized novolaks based on cresol or rescorcinol) and peracetic acid type epoxy resins, styrenemaleic anhydride resins, melamine-formaldehyde and other amino resins, polyester, polyurethane, silicone, polystyrene, polyamide, and polyester resins, and natural and synthetic rubbers. Furthermore, the polyethylene oxide can be replaced by polyacrylic acid, polyvinylpyrollidone, poly (methyl vinyl ether), copolymers of maleic anhydride and methyl vinyl ether, polyfluorosulfonic acid, polyethylene imine, polyacrylamides — especially diacetone acrylamide. Additives, or other materials, such as curing agents monomeric materials, pigments, dyes, fillers, processing aids, solvents, diluents, flow control agents, adhesion promoters, antioxidants and the like, may be included in the blend of polyethylene oxide and other resinuous material. Also, dopants which may be either proton donors or proton acceptors may be added to the association product, either before or after processing. Such dopants include water, formic acid, dimethyl formamide, formaldehyde and formamide. These dopants appear to function by increasing the density of proton donor and acceptor sites. Thus, the dopants influence the electrical properties of the association product.

In the present invention, the preferred material is an association product of (by weight) approximately 60% polyethylene oxide (such as Polyox WSR 301 obtainable from Union Carbide Corporation) and approximately 40% (by weight) phenol-formaldehyde resin (such as BRL1031 obtainable from Union Carbide Corporation). As stated above, additives or dopants may also be present, in which event the weight ratio of polyethylene oxide to phenol resin will be maintained at 6:4.

The following examples were prepared in accordance with the present invention:

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EXAMPLE 1.

Two laminar bus bars (a and b) were constructed in the configuration shown in FIG. 2 with the conductive sheets 10 and 12 being 2½ long, % inch high and 0.006 inch thick (Z) aluminum sheets. The insulating materials 14 between the conductive sheets were sheets of paper saturated with polymeric association product for the respective bus bars (tz) 0.003 inch bleached Kraft, and (b) 0.0023 inch unbleached Kraft which had been saturated with a solution of 60% (solids basis) Union Carbide Corporation Polyox WSR-301 and 40% Union Carbide Corporation BRL1031, phenol-formaldehyde resin. The sheets were saturated and then dried for 10 minutes at 100°C. The assembled specimens were lightly clamped and baked for 15 minutes at 100°C to effect adhesion of the insulators to the conductors, and then electrical measurements were obtained. The 120hz capacitance at 2 volts a.c. and 5 volts d.c. bias was 800nf for (a) and 250nf for (b), thus showing the samples to be suitable for filtering capacitors or noise suppressing bus bars. Test results were:

<td></td><td> Capacitance</td><td> Dissipation Factor</td><td colspan="2"> Leakage Current</td>

<td> a)</td><td> 800nf</td><td> 4.01%</td><td> 220</td><td></td>

<td> b)</td><td> 250nf</td><td> 6.7%</td><td> 70</td><td> μΑ</td>

EXAMPLE 2.

A % X % inch capacitor consisting of two outside 0.018 inch thick tin lead-plated copper ground electrodes and a center electrode separated by a polymeric insulating film was constructed. The polymeric insulator was a 0.007 inch thick film cast from a solution identical to that of Example 1. The insulator was cast using a drying temperature of 77°C and then sandwiched between the plates. Leakage current readings at 120hz were obtained at several applied d.c. bias voltages. So called negative resistance regions as shown in the graph of FIG. 3 were observed between 2 and lOv and between 50 and lOOv. This device therefore qualifies as a low voltage amplifier.

EXAMPLE 3.

A sample of grained aluminum sheet to which had been applied an extremely thin coating (2 X 10 inches) of a polymeric film identical in composition to that of Example 2 was connected to the common connection of a d.c. voltmeter. Rubbing the polymer surface with a probe (which serves as the second conductive layer) yielded voltage readings as high as 1.5v. Rubbing the polymer surface with aluminum strip produced low voltage readings of opposite polarity. In this example, the polymer 14 is open faced on one sheet of metal 12 (see FIG. 2A), and the probe or aluminum strip 16 serves as the second conductive layer. A speed measuring transducer is thus suggested.

EXAMPLE 4.

A sheet of polymeric insulator approximately 0.007 inch thick was prepared by mixing Polyox WSR301 (60%) and phenol-formaldehyde BRL1031° (40%, solids basis) on a two roll mill heated to 280°-320°F. After mixing for some time, the association product banded on the cold roll of the mill and was stripped as a film and allowed to cool to room temperature and then sandwiched between the metal plates. A specimen structurally similar to that of Example 1 was prepared using this film as an insulator. Capacitance readings were taken with the specimen mounted in a jig which was constructed so that a pressure could be applied to in² of the specimen area. The jig was equipped with a force gauge so that the applied pressure could be read. An approximately linear plot of capacitance readings with increasing pressure was obtained and is shown 10 in FIG. 4 wherein the linearity can be noted especially between 50 pounds and 600 pounds of force. The device thus qualifies as a pressure transducer.

EXAMPLE 5.

A specimen structurally similar to that of Example 2 was prepared using an insulating film which had been cast from solution and dried for 6 hours at 75°C. The insulator was composed of (solids basis) 90% Polyox WSR301 and 10% BRP2444, a phenol-formaldehyde resin and obtainable from Union Carbide. 120hz capacitance at 1 volt d.c. bias was 4.2nf, thus showing the device to be suitable for use as a capacitor.

EXAMPLE 6.

A specimen similar in configuration to that of Example 2 and measuring about 2.5 X 0.75 inches was prepared using an insulating film which had been cast from solution and dried for 6 hours at 75°C. The insulator was composed of (solids basis) 60% Polyox WSR301 ³⁰ and 40% Cymel 405 (American Cyanamid), a water soluble melamine-formaldehyde resin, and was 0.006 inch thick. lOOOhz capacitance at 2 volts a.c. and 10 v.d.c. bias was 390n.f. Similar specimens were prepared using each of the following in 40% amounts as ³⁵ substitutes for the Cymel 405 melamine resin of this example: (a) Dow DER331, a diglycidyl ether of bisphenol A obtainable from Dow Chemical Corp, (insulating film thickness 0.0065 inch, lOOOhz capacitance at 2 volts a.c. and 10 v.d.c. bias was 2.7 n.f.); (b) Dow ⁴⁰ D.E.N. 438, an expoxidized phenol-formaldehyde novolac obtainable from Dow Chemical Corp, (insulating film thickness 0.0085 inch, lOOOhz capacitance at 2 volts a.c. and 10 v.d.c. bias was 0.71 n.f.); (c) DuPont 46,971 polyester resin, obtainable from E. J. DuPont ⁴^ de Nemours Company; (d) DuPont 46,97 1 with a urethane crosslinking agent; (e) Dow 331 with a primary aliphatic amine curing agent; and (f) a diallyl phthalate resin. The insulating films used in preparing these specimens (c)—(/) displayed dielectric constants, when ⁵⁰ measured at l.OOOhz 2 volts a.c. and 10 v.d.c. bias, ranging from 6.7 to 2,400 thus indicating usefulness of these devices as capacitors.

EXAMPLE 7.

⁵⁵ A sample was prepared using a cast film identical to the composition of the association product in Example 1. The film was cast and dried at a temperature of 125°C for a period of 4 hours. The sample was formed according to the structure of FIG. 1 with the film be- ⁶⁰ tween plates of solder plated copper measuring 0.75 by

2.5 inches. The structure was formed by dry pressing the plates and film for 5 minutes. The sample was subjected to temperatures between 75°F and 160°F, and changes in capacitance and dielectric constant were ³ noted with the results set forth in graph form in FIGS.

and 6, respectively. Capacitance and dielectric constant are in a logrithmic scale in FIGS. 5 and 6, and it

3,883,784 can be seen that a distinct logrithmic relationship was observed between temperature and capacitance or dielectric constant. Thus, the device of Example 7 qualifies as a temperature transducer.

EXAMPLE 8.

A sample was made using a cast film identical to the composition of the association product of Example 1. The film was cast as in Example 7, and the sample was formed with the structure of FIG. 1 by pressing the film between two 0.75 X 2.5 inch solder plate copper plates for 2 minutes at 300°F. Changes in capacitance with variations in frequency from 200hz to 1,000hz under a 2 volt a.c. field (no d.c. bias) were noted and are shown in graph from in FIG. 7. (frequency being on a logrithmic scale). A reduction in capacitance as a function of increasing frequency was noted, thus qualifying the device as a low pass frequency filter.

EXAMPLE 9.

The sampe of Example 8 was also subjected to variations in d.c. voltages from 0.1 v. to 40v., and a linear relationship of changing capacitance was noted, thus suggesting use of the device in a parametric amplifier application. The results are set forth in graph form in FIG. 8 (the spike in the mid range of the graph apparently being a spurious reading).

EXAMPLE 10.

A sample was prepared by depositing a dimethyl formamide solution of 60% (solid basis) Union Carbide Polyox 3,010 polyethylene oxide and 40% Union Carbide BRL1031 phenol formaldehyde resin onto a 1 X 1 x 0.020 inch aluminum sheet. The solvent was allowed to evaporate at room temperature whereby a flexible coating of about 0.010 inch thickness was formed on the sheet. A transducer was then formed having the structure of FIG. 1 by placing another identical aluminum sheet over the coating. Referring to FIG. 9, an audio frequency signal 17 was amplified by amplifier 18 to about 50 volts and connected in series to an adjustable (0-400 v.d.c.) power supply 20 and then to the transducer 22. The device of this example functioned as an acoustical transducer in that an audio output was obtained from the transducer as a result of the field thus imposed across the transducer 22. Frequency doubling of the audio signal with respect to the signal 17 was noted without the d.c. bias, and the output of the audio signal increased with increased bias voltage.

EXAMPLE 11.

A sample was prepared by forming an anodized surface on an aluminum sheet of ½ X 5 inches. Three layers of film of composition identical to that in Example 1 were then cast on the anodized surface of the sheet, each layer being dried for fa hour at 300°F, the total thickness t of the three layers of film being 4.5 mils. A &amp; X 5 inch sheet of copper was then placed on the open face of the film under light pressure. Capacitance of this sample was measured at 30 x 10^-9 farads at 120hz, thus indicating suitability for use as a capacitor.