Solid State Ultracapacitor

Abstract

An ink of the formula: 60-80% by weight BaTiO.sub.3 particles coated with SiO.sub.2; 5-50% by weight high dielectric constant glass; 0.1-5% by weight surfactant; 5-25% by weight solvent; and 5-25% weight organic vehicle. Also a method of manufacturing a capacitor comprising the steps of: heating particles of BaTiO.sub.3 for a special heating cycle, under a mixture of 70-96% by volume N.sub.2 and 4-30% by volume H.sub.2 gas; depositing a film of SiO.sub.2 over the particles; mechanically separating the particles; incorporating them into the above described ink formulation; depositing the ink on a substrate; and heating at 850-900° C. for less than 5 minutes and allowing the ink and substrate to cool to ambient in N.sub.2 atmosphere. Also a dielectric made by: heating particles of BaTiO.sub.3 for a special heating cycle, under a mixture of 70-96% by volume N.sub.2 and 4-30% by volume H.sub.2 gas; depositing a film of SiO.sub.2 over the particles; mechanically separating the particles; forming them into a layer; and heating at 850-900° C. for less than 5 minutes and allowing the layer to cool to ambient in N.sub.2 atmosphere.

Claims

1. A method of manufacturing a capacitor comprising the steps of: a) obtaining BaTiO.sub.3 particles; said particles having an average grain diameter of 100-700 nm; b) treating said particles in a first furnace under a mixture of 70-96% by volume N.sub.2 and 4-30% by volume H.sub.2 gas for 60-90 minutes at 850-900° C. c) coating said treated particles with a 3-20 nm thick film of SiO.sub.2 or a 3-10 nm thick film of Al.sub.2O.sub.3 whereby said coated treated particles become agglomerated; d) separating said coated, treated particles to break up said agglomeration into individual particles; e) incorporating said separated, coated, treated particles into an ink comprising: i) 60-80% by weight separated, coated, treated particles; ii) 5-50% by weight high dielectric constant glass; said high dielectric constant glass being 0.5-10μ in size iii) 0.1-5% by weight surfactant; iv) 5-25% by weight solvent; and v) 5-25% weight organic vehicle; f) depositing an electrode on a substrate; said electrode having a resistance between 1 mΩ and 10 Ω; g) sintering said substrate and electrode; h) depositing a layer of said ink on said substrate and electrode by a deposition process so that said layer is continuous and has consistent thickness; i) removing solvent from said layer by drying for 15-30 minutes at 120-150° in air; j) repeating steps h) and i) until desired thickness is obtained; k) removing organic binder by exposing said substrate, electrode and ink to the following heating cycle: i) gradually increasing temperature to 280-350° over 45-90 minutes with a heating rate not exceeding 10-15° per minute ii) curing at 280-350° for 4-72 hours. iii) allowing said substrate, electrode and ink to cool to ambient temperature; l) sintering said at least one layer on said substrate by heating in a second furnace, at 850-900° C. for less than 5 minutes and allowing it to cool to ambient under N.sub.2 atmosphere; said N.sub.2 containing less than 25 ppm O.sub.2; a thickness of said at least one layer being sufficient to produce a sintered layer 10-35μ thick; and m) depositing a top electrode on said at least one layer; said top electrode having a resistance between 1 mΩ and 10Ω

2. A method as claimed in claim 1 in which said coating process is atomic layer deposition.

3. A method as claimed in claim 1 in which said deposition process is aerosol jet deposition or silk screening or inkjet printing.

4. A method as claimed in claim 1 in which said separating machine is a three roll mill or a high shear mixer.

5. A method as claimed in claim 1 in which said high dielectric constant glass is lead-germinate glass or zinc borate glass.

6. A method as claimed in claim 1 in which said surfactant is a phosphate ester.

7. A method as claimed in claim 1 in which said solvent is ester alcohol, terpineol or butyl carbitol.

8. A method as claimed in claim 1 in which said substrate is 0.038-0.040 inch thick Al.sub.2O.sub.3, said Al.sub.2O.sub.3 being at least 96% pure; aluminum nitride (AlN); zirconia; beryllium oxide (BeO) or uncured ceramic.

9. A method as claimed in claim 8 in which said uncured ceramic is a mixture of ceramic particles, a binder, a surfactant and a solvent.

10. A method as claimed is claim 9 in which said solvent is 2,2,4-trimethyl-1,3-pentandiol monoisobutyrate, terpineol (C.sub.10H.sub.18O) or butyl carbitol.

11. A method as claimed is claim 9 in which said surfactant is a phosphate ester

12. A method as claimed in claim 1 in which said organic vehicle is ethyl cellulose.

13. A method as claimed in claim 1 in which said first furnace is a multizone belt furnace.

14. A method as claimed in claim 1 in which said first furnace is a fluidized bed vertical tube furnace.

15. A method as claimed in claim 1 in which said second furnace is a multizone belt furnace.

16. A method as claimed in claim 1 in which during sintering, time under 600° C. is 30 minutes maximum; time under 800° C. is 20 minutes maximum; and total time is 60-90 minutes.

17. A method as claimed in claim 14 in which, during sintering, the heating rate is 45-55° C./minute from 300-500° C.; and the cooling rate is 45-55° C./minute from 700-300° C.

18. A composition of matter comprising: a) 60-80% by weight BaTiO.sub.3 particles coated with a 3-20 nm film of SiO.sub.2 or a 3-10 nm thick film of Al.sub.2O.sub.3; said BaTiO.sub.3 particles having an average grain diameter of 100-700 nm; said BaTiO.sub.3 having doubly ionized oxygen anion vacancies. b) 5-50% by weight high dielectric constant glass; said high dielectric constant glass being 1-10μ in size c) 0.1-5% by weight surfactant; d) 5-25% by weight solvent; and e) 5-25% weight organic vehicle;

19. A composition of matter as claimed in claim 16 in which said high dielectric constant glass is lead-germinate glass or zinc borate glass.

20. A composition of matter as claimed in claim 16 in which said surfactant is a phosphate ester.

21. A composition of matter as claimed in claim 16 in which said solvent is ester alcohol, terpineol or butyl carbitol.

22. A composition of matter as claimed in claim 16 in which said organic vehicle is ethyl cellulose.

23. A dielectric made by the process of: a) obtaining BaTiO.sub.3 particles; said particles having an average grain diameter of 100-700 nm; b) treating said particles in a first furnace under a mixture of 70-96% by volume N.sub.2 and 4-30% by volume H.sub.2 gas for 60-90 minutes at 850-900° C. c) coating said treated particles with a 3-20 nm thick film of SiO.sub.2 or a 3-10 nm thick film of Al.sub.2O.sub.3 whereby said coated treated particles become agglomerated; d) separating said coated, treated particles to break up said agglomeration into individual particles; e) forming said particles into a layer of sufficient thickness to produce a sintered layer 10-35μ thick; and f) sintering said layer by heating in a second furnace, at 850-900° C. for less than 5 minutes and allowing it to cool to ambient under N.sub.2 atmosphere; said N.sub.2 containing less than 25 ppm O.sub.2. A method as claimed in claim 1 in which said coating process is atomic layer deposition.

24. A dielectric as claimed in claim 23 in which said separating machine is a three roll mill or a high shear mixer.

25. A dielectric as claimed in claim 23 in which said first furnace is a fluidized bed vertical tube furnace.

26. A dielectric as claimed in claim 23 in which said second furnace is a multizone belt furnace.

27. A dielectric as claimed in claim 23 in which during sintering, time under 600° C. is 30 minutes maximum; time under 800° C. is 20 minutes maximum; and total time is 60-90 minutes.

28. A dielectric as claimed in claim 27 in which, during sintering, the heating rate is 45-55° C./minute from 300-500° C.; and the cooling rate is 45-55° C./minute from 700-300° C.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0113] The patent or application file contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawing(s) will be provided by the Office upon request and payment of the necessary fee.

[0114] FIG. 1 Schematic of a conventional capacitor

[0115] FIG. 2A Schematic of an EDLC

[0116] FIG. 2B Enlargement of area marked with a B on FIG. 2A

[0117] FIG. 3 Ragone chart of energy storage devices

[0118] FIG. 4A Internal barrier layer capacitor

[0119] FIG. 4B Enlargement of area identified on FIG. 4A

[0120] FIG. 4C Internal barrier layer capacitor effect

[0121] FIG. 5A BaTiO.sub.3 particle with 10 nm of Al.sub.2O.sub.3 coating.

[0122] FIG. 5B BaTiO.sub.3 particle with SiO.sub.2 coating

[0123] FIG. 6 The BaTiO.sub.3 crystal structure. The green, red, and blue atoms are titanium, oxygen, and barium, respectively

[0124] FIG. 7 Dielectric Test Fixture 1645-1B in front of Agilent E4980A precision LRC meter.

[0125] FIG. 8A Top view of ultracapacitor cell

[0126] FIG. 8B Side view of ultracapacitor cell

[0127] FIG. 8C Layer view of ultracapacitor cell

[0128] FIG. 9 Eight-zone belt furnace temperature settings. Zones 1-8 are the individual heated zones; PV=present temperature value; FV=future, or desired temperature value for the profile; and SV=set temperature value for the individual heater zone controller.

[0129] FIG. 10 Belt furnace temperature profile

[0130] FIG. 11A SEM image of uncoated, untreated BaTiO.sub.3

[0131] FIG. 11B SEM image of BaTiO.sub.3 coated with Al.sub.2O.sub.3 but untreated.

[0132] FIG. 11C SEM image of BaTiO.sub.3 coated with Al.sub.2O.sub.3 and treated at 750° C. for 30 hr.

[0133] FIG. 12A Optical microscopy photographs of (a) uncoated BaTiO.sub.3 pellets (untreated)

[0134] FIG. 12B Optical microscopy photographs of coated, BaTiO.sub.3 pellets (untreated)

[0135] FIG. 12C Optical microscopy photographs of Al.sub.2O.sub.3 coated BaTiO.sub.3 pellets (untreated)

[0136] FIG. 13A Optical microscopy photographs of uncoated, BaTiO.sub.3 pellets treated at 900° C. for 1 hr.

[0137] FIG. 13B Optical microscopy photograph of SiO.sub.2 coated BaTiO.sub.3 pellets treated at 900° C. for 1 hr.

[0138] FIG. 13C Optical microscopy photographs of Al.sub.2O.sub.3 coated BaTiO.sub.3 pellets treated at 900° C. for 1 hr.

[0139] FIG. 14A Optical microscopy photographs of uncoated, BaTiO.sub.3 pellets treated at 1,100° C. for 1 hr.

[0140] FIG. 14B Optical microscopy photographs of SiO.sub.2 coated BaTiO.sub.3 pellets treated at 1,100° C. for 1 hr.

[0141] FIG. 14C Optical microscopy photographs of Al.sub.2O.sub.3 coated BaTiO.sub.3 pellets treated at 1,100° C. for 1 hr.

[0142] FIG. 15A Plots of permittivity of samples treated at 900° C. for 15 hr. and 1,100° C. for 1 hr. compared to the untreated powders

[0143] FIG. 15B Plots of DF of samples treated at 900° C. for 15 hr. and 1,100° C. for 1 hr. compared to the untreated powders

[0144] FIG. 15C Plots of ESR of samples treated at 900° C. for 15 hr. and 1,100° C. for 1 hr. compared to the untreated powders

[0145] FIG. 16A Plots of permittivity of samples treated at 900° C. for 1 hr. compared to the untreated powders

[0146] FIG. 16B Plots of DF of samples treated at 900° C. for 1 hr. compared to the untreated powders

[0147] FIG. 16C Plots of ESR of samples treated at 900° C. for 1 hr. compared to the untreated powders

[0148] FIG. 17 Ultracapacitor test cell made from SiO.sub.2-coated BaTiO.sub.3 deposited by screen printing

[0149] FIG. 18A Plots of permittivity of powdered samples treated at 900° C. for 1 hr. before and after furnace sintering

[0150] FIG. 18B Plots of DF of powdered samples treated at 900° C. for 1 hr. before and after furnace sintering

[0151] FIG. 18C Plots of ESR of powdered samples treated at 900° C. for 1 hr. before and after furnace sintering

[0152] FIG. 19A SEM image at a magnification of 500 showing the level of densification of SiO.sub.2-coated BaTiO.sub.3 test cell with 184 nF of capacitance processed at 900° C. for 1 hour.

[0153] FIG. 19B SEM image at a magnification of 3,000 showing the level of densification of SiO.sub.2-coated BaTiO.sub.3 test cell with 184 nF of capacitance processed at 900° C. for 1 hour.

[0154] FIG. 19C SEM image at a magnification of 5,000 showing the level of densification of SiO.sub.2-coated BaTiO.sub.3 test cell with 184 nF of capacitance processed at 900° C. for 1 hour.

[0155] FIG. 19D SEM image at a magnification of 10,000 showing the level of densification of SiO.sub.2-coated BaTiO.sub.3 test cell with 184 nF of capacitance processed at 900° C. for 1 hour.

[0156] FIG. 20 Voltage versus time used for the direct current (DC) discharge test method.

[0157] FIG. 21A Plots of capacitance of the capacitor test cells, made from the dielectric material treated at 900° C. for 1 hr., before and after furnace sintering

[0158] FIG. 21B Plots of DF of the capacitor test cells, made from the dielectric material treated at 900° C. for 1 hr., before and after furnace sintering

[0159] FIG. 21C ESR of the capacitor test cells, made from the dielectric material treated at 900° C. for 1 hr., before and after furnace sintering

[0160] FIG. 22 Nine, multilayered ultracapacitor cells in parallel printed on a substrate board. Cells can be printed serially or in parallel to get the desired voltage or capacitance. This is known as a slice.

[0161] FIG. 22A is a cross section of a multilayer capacitor cell, nine of which are used in a slice.

[0162] FIG. 23 Ultracapacitor module where multilayered capacitor boards (or slices) are stacked in a housing with active or passive cooling to increase energy storage.

[0163] FIGS. 24A-24D show frequency dependence of Cp˜D and ∈.sub.r for 2 different samples at room temperature from 0.1 Hz to 1 MHz.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0164] While the present invention is described herein with reference to illustrative embodiments for particular applications, it should be understood that the invention is not limited thereto. Those having ordinary skill in the art and access to the teachings provided herein will recognize additional modifications, applications, and embodiments within the scope thereof and additional fields in which the present invention would be of significant utility.

[0165] The instant invention is a method of manufacturing an IBLC capacitor 38. Particles of BaTiO.sub.3 40 (see FIGS. 4, 5 and 6) having an average grain diameter of 100-700 nm are first heated in a furnace under a mixture of 70-96% by volume N.sub.2 4-30% by volume H.sub.2 gas for 60-90 minutes at 850-900° C.

[0166] BaTiO.sub.3 has doubly ionized oxygen anion vacancies—see FIG. 6. The first furnace may be a multizone belt furnace or a fluidized bed vertical tube furnace. The second furnace may be a multizone belt furnace.

[0167] Next a 3-10 nm film of SiO.sub.2 48 or Al.sub.2O.sub.3 44 is deposited over each individual particle 40. The resulting grains 32 (see FIGS. 5A and 5B) are agglomerated so they must be mechanically separated. The grains are then incorporated into an ink of the following formulation: [0168] i. 60-80% by weight separated grains 32; [0169] ii. 5-50% by weight high dielectric constant glass; the high dielectric constant glass being 1-10μ in size [0170] iii. 0.1-5% by weight surfactant; [0171] iv. 5-25% by weight solvent; and [0172] v. 5-25% weight organic vehicle.

[0173] The solvent may be ester alcohol, terpineol or butyl carbitol, and the organic vehicle may be ethyl cellulose. The high dielectric constant glass may be lead-germinate or zinc borate glass. Preferably, the surfactant is a phosphate ester.

[0174] Next a layer of the dielectric ink 24a is deposited on a substrate 62 with a pre-sintered and deposited electrode 60 in place. The electrode can be silver, silver palladium, or any material with a resistance between 1 milliohm and 10 ohms. Finally, the dielectric ink 24a is sintered onto the substrate 62 by heating in a second furnace at 850-900° C. for less than 5 minutes and allowing the ink 24a and substrate 62 to cool to ambient. This heating and cooling cycle is carried out under N.sub.2 atmosphere, which contains less than 25 ppm 02. Preferably, during sintering, the time under 600° C. is kept to 30 minutes maximum; time under 800° C. is 20 minutes maximum; and total time is 60-90 minutes. Also, preferably, the heating rate is 45-55° C./minute from 300-500° C.; and the cooling rate is 45-55° C./minute from 700-300° C. Once the dielectric is sintered, a top electrode 74 is added that can be silver, silver palladium or any material with a resistance between 1 milliohm and 10 ohms.

[0175] The substrate 62 is preferably 0.025-0.040 inch thick Al.sub.2O.sub.3 in which the Al.sub.2O.sub.3 is at least 96% pure. Alternatively, the substrate could be aluminum nitride (AlN) zirconia, beryllium oxide (BeO) or uncured ceramic. Uncured ceramic is a mixture of ceramic particles, a binder, a surfactant and a solvent.

[0176] Preferably, the thickness of the deposited dielectric ink 24a is sufficient to produce a sintered layer 10-35 μm thick.

[0177] The process of the instant invention results in an internal barrier layer ultracapacitor (IBLC) 38, which can be used as a battery replacement because it has the following advantages: longer life, lower mass-to-weight ratio, rapid charging, on-demand pulse power, improved standby time without maintenance, and environmental friendliness.

[0178] This invention is also an ink of the formula shown above.

Experimental I

[0179] Test pellets were fabricated utilizing BaTiO.sub.3 particles 40 of 730 and 500 nm particle sizes. Some of the test pellets were made with BaTiO.sub.3 particles 40 that were coated with SiO.sub.2 48, and test pellets were fabricated utilizing BaTiO.sub.3 particles 40 (500 nm) that were coated with Al.sub.2O.sub.3 44. The SiO.sub.2 coating 48 thickness was 5 nm, and the Al.sub.2O.sub.3 44 thickness was 10 nm.

[0180] BaTiO.sub.3 particles 40 were coated using an atomic layer deposition (ALD) process.

[0181] Some un-sintered particles were pressed into pellets without the addition of binder using a potassium bromide dye. A tube furnace was used to heat the pellets under an atmosphere of 96% N.sub.2 and 4% H.sub.2. In such an atmosphere, BaTiO.sub.3 40 is slightly reduced. Quartz boats were each populated with pellets of Al.sub.2O.sub.3-coated, SiO.sub.2-coated, and uncoated BaTiO.sub.3 40. After processing the pellets were left to cool to room temperature inside the tube furnace. Resulting pellets were 4-8 mm thick with masses of 1.5-2.5 g.

[0182] Capacitors can also be made by 3D additive manufacturing. To perform 3D additive manufacturing, the particles are first converted into an ink. Two additive manufacturing techniques can be used for dielectric 78 deposition, such as aerosol jet deposition and screen printing. They require unfused particles in order to deposit properly. In order to screen print the particles, they are separated using a three-roll mill or similar machine.

[0183] The aerosol jet process begins with a mist generator that atomizes a source material. Particles in the resulting aerosol stream are condensed. The aerosol stream is then aerodynamically focused using a flow guidance deposition head, which creates an annular flow of sheath gas to collimate the aerosol. The co-axial flow exits the flow guidance head through a nozzle directed at the substrate, which serves to focus the material stream to as small as a tenth of the size of the nozzle orifice (typically 100 μm).

[0184] The aerosol jet process allows for a large viscosity range of processible inks (typically 0.7-2,500 cP), a flexible distance between substrate and nozzle (typically 1 to 5 mm) as well as a tightly focused aerosol stream for variable line width. This allows the production of fine pitch (typically below 50 μm) electronic devices. Machines for performing this process are available from Optomec, Inc., New Mexico; under the brand name Aerosol Jet®.

[0185] Screen printing is the process of using a mesh-based stencil to apply ink onto a substrate, whether it be T-shirts, posters, stickers, vinyl, wood, or other material.

[0186] Some areas of the mesh are made impermeable and the mesh placed over the substrate. A blade or squeegee is used to move ink across the screen to fill the open mesh apertures with ink. A reverse stroke then causes the screen to touch the substrate momentarily along a line of contact. This causes the ink to wet the substrate and be pulled out of the mesh apertures as the screen springs back after the blade has passed.

[0187] Screen printing was utilized to fabricate test cells. The capacitor 38 test cells were sintered using a belt furnace after deposition of each layer. Subsequent testing showed energy densities in the range of 1.0 to 2.0 J/cc.

[0188] Atomic Layer Deposition-Coated Ceramic Barium Titanate Particles 40

[0189] A prior study focused on BaTiO.sub.3 particles 40 of various sizes in both coated and uncoated configurations, with the latter serving as a baseline. Table 3 provides the details on particle diameter, coating material and thickness, purity, and supplier.

TABLE-US-00003 TABLE 3 Materials. Particle Thick- Size Purity ness Material Supplier (nm) (%) Coating (nm) Color BaTiO.sub.3 40 Ferro 730 99.95 Uncoated — White BaTiO.sub.3 40 TPL 500 99.95 SiO.sub.3  5 Light grey BaTiO.sub.3 40 ALD 500 99.95 Al.sub.2O.sub.3 10 White Nano- Solutions BaTiO.sub.3 40 Sakai 140 99.95 uncoated — white

[0190] The BaTiO.sub.3 particles 40 used in this study varied in diameters ranging from 140 nm to 730 nm as their D50, or median particle size. Coating configurations varied from uncoated to 10 nm. The uncoated BaTiO.sub.3 40 sample was a fine powder, while the coated BaTiO.sub.3 40 samples were agglomerated. The clumps are likely caused by hydrophilic interaction or static charge. The clumps were dispersed before processing into ink formulations.

[0191] Atomic layer deposition (ALD) was used to deposit nanothin films over BaTiO.sub.3 nanoparticles. The nanothin film coatings consist of a 10 nm thick layer of alumina (Al.sub.2O.sub.3 44) and 5 nm thick layer of silica (SiO.sub.2 48). FIG. 5A illustrates a BaTiO.sub.3 particle 40 coated with Al.sub.2O.sub.3 44. FIG. 5B illustrates a BaTiO.sub.3 particle 40 coated with SiO.sub.2 48. The number of cycles performed during ALD determines the coating thickness. The coating thickness rate for Al.sub.2O.sub.3 44 was 10 Å per cycle, and for SiO.sub.2 48 was 4 Å per cycle. It is important to note that previous IBLC research using SPS of BaTiO.sub.3 particles 40 were coated by the Stöber process, a method based on a seeded growth process. The Stöber process is known to produce an inconsistent coating.

[0192] High-Temperature and Reduced Forming Gas Sintering

[0193] In reducing atmospheres (75-96% N.sub.2 and 4-25% H.sub.2), BaTiO.sub.3 40 is slightly reduced, forming doubly ionized oxygen (anion) vacancies. This produces the same effect as vacuum sintering, so a reducing atmosphere is the preferred method of processing. To understand vacancy creation, BaTiO.sub.3 40 crystal structure is shown in FIG. 6. The conductivity results from the electron exchange between Ti.sup.+4 and Ti.sup.+3 resulting from oxygen vacancies at the octahedron. The induced free electrons make the reduced perovskite material highly semiconducting as shown in equations (10) and (11). Sintering BaTiO.sub.3-based dielectrics in forming gas decreases the insulation resistance by 10-12 orders of magnitude. FIG. 6 shows the BaTiO.sub.3 crystal structure.

BaTiO.sub.3+xH.sub.2.fwdarw.=BaTiO.sub.3-x[V.sub.0].sub.x+xH.sub.2O  (10)

and

[V.sub.0].fwdarw.[V.sub.0].sup.−+2e  (11)

[0194] A three-zone, Thermo Scientific™ Lindberg/Blue tube furnace was used to process the particles. The furnace was heated to 850-950° C. for at least 60 minutes. The uncoated BaTiO.sub.3 40, serving as a baseline, was always heat treated to evaluate its electrical properties versus those of coated particles. The forming gas was turned on at 1-3 SCFH for 10 min. prior to placing the samples inside. After the desired annealing duration, the forming gas was left flowing until the powder reached a temperature under 300° C. to avoid any reoxidation of the powder. The samples were left to cool to room temperature inside the tube furnace before removal.

[0195] Previous studies show that the reduction of BaTiO.sub.3 40 in H.sub.2 at intermediate temperatures (500° C.) leads to bodies of bright yellow color. Reduced SiO.sub.2-coated material obtained through SPS at a final temperature of 1,110° C. is expected to change from white to a navy blue color. Uncoated BaTiO.sub.3 40 and doped BaTiO.sub.3 specimens that show a remarkable reduction in resistivity has also been characterized with a bluish color. To assess color changes, optical microscopy images of the pellets were taken at ×7 magnification.

[0196] When powdered particles 32 are heated to a high temperature below the melting point, the atoms in the particles diffuse across the particle boundaries, fusing the particles together. Two additive manufacturing techniques used for electrode and dielectric deposition, such as aerosol jet deposition and screen printing, require unfused particles in order to deposit the material properly.

[0197] In order to screen print the particles, they were separated using a three-roll mill.

[0198] Pellet Electrical Characterization

[0199] Un-sintered BaTiO.sub.3 particles 40 were pressed into pellets without the addition of binder using a potassium bromide die. A literature review revealed that pellets pressed at pressures above 345 MPa (50,000 psi) could not be recovered. Various pressures were tested, revealing that pellets pressed at forces above 1.8 kN (400 lb.) could not be recovered from the potassium bromide die in suitable shape. Because of these findings, the pellets were made by pressing them at 1.3 kN (300 lb.) of force using a TestResources (Shakopee, Minn.) compression and tension machine. The pellets were 4-8 mm thick with masses of 1.5-2.5 g.

[0200] Adsorption of water vapor increases the permittivity by a factor of 2.19 However, the focus of the characterization at this phase of the study was to identify a sample with a large change in permittivity, specifically by a factor of 10.sup.4. Because the focus was large changes in permittivity, no attempt was made to remove water. In addition, thin film electrical characterization is used to obtain the most accurate measurements, and since these samples are sintered, water absorption effects are eliminated.

[0201] Capacitance, DF, and ESR were measured for a frequency range of 20 Hz to 2 MHz using a Dielectric Test Fixture 1645-1B together with an Agilent E4980A precision inductance, capacitance, and resistance (LCR) meter, shown in FIG. 7. The capacitance was initially assumed small, and therefore, measurements were made using the LCR meter's parallel mode. If the values were found to be higher than expected, then the instrument could be reset to use series mode. The dielectric constant of the samples was determined from the instrument's reported capacitance value. No porosity correction was made to the dielectric constant. FIG. 7 shows Agilent E4980A precision LCR meter (top) and Dielectric Test Fixture 1645-1B (bottom).

[0202] Dielectric Ink Formulation

[0203] To perform 3D additive manufacturing, the powders were first converted into an ink. The formulation for this ink is shown in table 4. Glass particulates were used to increase densification, but high quantities of glass particles decrease the permittivity, so the concentration of glass was kept as low as possible to produce a usable ink. Surfactant was used as a wetting agent to allow the ink to spread. A thinner was also used to get the proper ink viscosity. Texanol™ was used as a thinner because it volatilizes at 120° C. The vehicle was an organic binder formulated from a blend of Ashland Chemical ethyl cellulose in Texanol ester solvent. It was used to further enhance the viscosity of the ink. The vehicle was chosen because it volatilizes between 250° C. and 350° C. during sintering.

TABLE-US-00004 TABLE 4 Dielectric ink formulation. Component Concentration (%) BaTiO.sub.3 dielectric 32 72.5 Lead-germinate high K glass 7.5 Surfactant (wetting agent) 0.5 Texanol (solvent) 5 Ethyl cellulose organic vehicle 15

[0204] The dielectric ink 24a formulation was mixed and then ground in a three-roll mill. A three-roll mill is a tool that uses shear force by three horizontally positioned rolls rotating at opposite directions and different speeds relative to each other to mix, refine, disperse, and homogenize viscous materials fed into it. The final ink was a dense, homogenous mixture used for screen printing.

[0205] Three-Dimensional Additive Thin Film Deposition

[0206] The screen printing method was the chosen method of printing a test cell for this study. This technique can produce layers as thin as 5 μm. By producing such a thin dielectric layer, the capacitance equation shows that the energy stored can be increased significantly. The screen printing process began by creating a capacitor design on a woven mesh using photolithography. The ink was forced into the mesh openings by a squeegee and onto the printing surface during the squeegee stroke. The larger the number of intertwined meshes, the thinner the deposition became for a single stroke. The capacitor layers (FIGS. 8A-8C) were printed using a Hary Manufacturing, Inc. (Lebanon, N.J.) 485 precision screen printer. Palladium silver ink that is used in multilayer chip capacitors due to its conductance and resistance to silver migration was used as the electrode 60, 74 material. Al.sub.2O.sub.3 (0.039 in and 96% purity) was used as the substrate 62 on which each layer was deposited. Al.sub.2O.sub.3 was chosen because it has a very low coefficient of expansion and will not impart excessive stress during later sintering steps. As a result, each layer is only able to densify in the z-axis due to clamping to the substrate 62. The ultracapacitor test cells 38 were made using two layers of dielectric ink 24a applied through 325 and 400 mesh screens. FIGS. 8A-8C shows views of the ultracapacitor 38 cell: 8A Top, 8B side, and 8C layers

[0207] The capacitor test cell was sintered using a HAS 1505-0811Z belt furnace from HengLi Eletek Co. (San Diego, Calif.) at 850° C. peak for 10 min and a total cycle time of 1.5 hr. This sintering step was performed after each layer of deposition in order to burn off organic materials and achieve high densification. The temperature settings of the eight-zone belt furnace are shown in FIG. 9, the temperature profile in FIG. 10, and the N.sub.2 flow profile in table 5. Previous work shows that when reduced SiO.sub.2-coated 48 BaTiO.sub.3 40 is post-annealed at 800° C. for 12 hr. in air, it remains blue, while reduced uncoated BaTiO.sub.3 40 turns white. For this reason, the SiO.sub.2 shell 48 is thought to act as an efficient barrier against oxidation. As a further preventative measure, the belt muffle furnace was purged with N.sub.2 to avoid re-oxidation. Densification of the dielectric layer was then evaluated with the scanning electron microscope (SEM). FIG. 9 shows temperature settings for the eight-zone belt furnace. On FIG. 9, zones 1-8 are the individual heated zones; PV stands for present temperature value; FV stands for future, or desired temperature value for the profile; and SV stands for set temperature value for each individual zone heater controller. FIG. 10 shows the belt furnace temperature profile.

TABLE-US-00005 TABLE 5 Furnace N.sub.2 flow profile. Section Nitrogen Flow (LPM) Entrance curtains 40 Preheat 45 Venturi exhaust 100 Cooling gas 20 Exit curtains 20

[0208] Thin Film Electrical Characterization

[0209] The ultracapacitor 38 test cell was measured for parallel capacitance using an LCR meter. Capacitance readings were then used to determine if the device was functional. Samples that showed functionality were also tested via the discharge method. To use the discharge method, the capacitor was discharged through a resistor that was chosen to yield a reasonable time constant. The voltage versus time plot was captured with a DP05104 digital phosphor oscilloscope (Marietta, Ga.). A large region of the discharge curve was chosen, and the values of voltage in the discharge cycle and time required to drop between the two voltages were entered into equation (12) along with the known resistor value. In this equation, t is the time it takes to discharge the capacitor between some initial voltage (V) to some final volt-age (Vf). The capacitance (C) is to be determined, and R is a resistor through which the capacitor is discharged:

[00006]$\begin{array}{cc}t=C*R*\ln \left(\frac{V_f}{V_i}\right).& \left(12\right)\end{array}$

[0210] Analysis

[0211] Pellet Electrical Characterization

[0212] SEM images of the untreated particles 40 (FIGS. 11A and 11B) revealed that particles indicated by the manufacturer to be 500 nm actually varied in diameter from 250 nm up to 1 μm. Treated particles 32 (FIG. 11C) also showed varying particle sizes of the same range. These observations show that the furnace treatment was not causing large scale grain growth. FIGS. 11A-11C show SEM images of BaTiO.sub.3 40: 11A uncoated, 11B coated with Al.sub.2O.sub.3 44, and 11C Al.sub.2O.sub.3 44 coated, treated at 750° C. for 30 hr.

[0213] All three batches of particles 32, 12 were initially white in color, as can be seen in FIGS. 12A-12C. When treated at temperatures below 900° C., they turned to a bright yellow or a neon green color. These particles remained that color under the reducing forming gas atmosphere and changed to white after the first minute of exposure to air. Scraping off the top layer of the treated powder revealed two shades of color: a lighter tone on top and a darker tone underneath. This non-uniform color, shown in FIGS. 13 and 14, indicates that the particles were not being reduced homogeneously. This indicated that proper reduction of the particles had to be done individually in a fluidized bed as opposed to pelletized form and this treatment method was adopted. FIGS. 12A-12C show optical microscopy photographs: 12A uncoated, 12B SiO.sub.2-coated 48, and 12C Al.sub.2O.sub.3 44 coated BaTiO.sub.3 40 pellets (untreated). FIGS. 13A-13B show optical microscopy photographs: 13A uncoated, 13B SiO.sub.2-coated 438, and 13C Al.sub.2O.sub.3 44 coated BaTiO.sub.3 40 pellets treated at 900° C. for 1 hr. FIGS. 14A-14C show optical microscopy photographs: 14A uncoated, 14B SiO.sub.2-coated 48, and 14C Al.sub.2O.sub.3 44 coated BaTiO.sub.3 40 pellets treated at 1,100° C. for 1 hr.

[0214] At temperatures below 900° C., no significant changes were seen in the permittivity. At temperatures above 900° C., the permittivity and DF slightly increased for uncoated BaTiO.sub.3 40 and decreased for coated samples 44, 48. The ESR decreased only for the Al.sub.2O.sub.3 44 coated sample, the greatest decrease occurring with 900° C. treatment. The decrease in ESR seen in FIGS. 15A-15B coincides with the color change seen in FIGS. 14A-14B. This can be interpreted as the material undergoing reduction.

[0215] The synthesis conditions that produced the maximum increase in permittivity for all samples was at 900° C. for 1 hr. Table 6 shows the effect of a short-duration treatment versus a long-duration treatment with constant (900° C.) temperature. The SiO.sub.2-coated sample exhibits the highest permittivity.

TABLE-US-00006 TABLE 6 Synthesis profile effect on dielectric permittivity. At 20 Hz Untreated 1 hr. at 900° C. 15 hr. at 900° C. BaTiO.sub.3 40 Color Permittivity Color Permittivity Color Permittivity Uncoated 40 White 9 White 2,227 White 708 Al.sub.2O.sub.3- White 217 Light 6,886 Navy 182 coated 44 blue blue SiO.sub.2- White 7,638 Grey 19,980 Grey 4,384 coated 48

[0216] The capacitor properties versus frequency of the samples treated at 900° C. for 1 hr. are compared in FIGS. 16A-16B. Low-frequency permittivities are high (maximum: 19,980 at 20 Hz), indicating the dielectric would be good for DC applications. The DF was found to increase with treatment. The decreased ESR for all treated powders indicated that they are becoming semiconducting, one of the desired outcomes for the IBLC effect. SiO.sub.2-coated 48 and Al.sub.2O.sub.3 44 coated BaTiO.sub.3 40 treated at 900° C. for 1 hr. SiO.sub.2-coated 48 and Al.sub.2O.sub.3-coated 44 BaTiO.sub.3 40 treated at 900° C. for 1 hr were chosen as the dielectric for the capacitor test cell because of they had the best capacitance traits.

[0217] Thin Film Electrical Characterization

[0218] FIG. 17 shows an ultracapacitor test cell made with SiO.sub.2-coated 48 BaTiO.sub.3 40.

[0219] SEM images (FIG. 19) of the ultracapacitor 38 test cells showed a 70%-80% densification. The thickness for samples built using the 325 mesh was an average of 20 μm. The capacitance obtained through the discharge method using a DC source agreed with the LCR measured capacitance values within ±5%. The voltage versus time plot for the 184.2 nF capacitor is shown in FIG. 20.

[0220] FIG. 20 shows voltage versus time used for the discharge method.

[0221] Electrical characterization (FIGS. 21A-21C) shows normal capacitor behavior up to 1.3 MHz. Above the latter frequency, the capacitor test cells exhibit a negative capacitance and a DF that spikes up to 3×103. This negative capacitance effect is observed in a variety of semiconductor devices.

Experimental II

[0222] Several capacitors 38 were made as described. An Agilent (Santa Clara, Calif.) 4294A impedance analyzer was used to characterize the dielectric/electric properties of these devices over a frequency range from 100 Hz to 100 MHz using Cp˜D and R˜X function. 301 points were chosen in this range.

[0223] A Solartron (West Sussex, UK) SI 1260 Impedance/Gain Phase Analyzer was used for the low frequency characterization from 0.1 Hz to 10 kHz at room temperature. In the experiments, the AC amplitude is a constant of 100 mV, while the DC bias is 0 V. 50 points were chosen in this range.

[0224] The P-E hysteresis loops were measured using Sawyer-Tower circuit (Radiant Technologies Precision LC unit, Albuquerque, N. Mex.). The profile is standard bipolar and frequency is 10 Hz.

[0225] FIGS. 24A-24B show the two results combined: 1) high frequency using Agilent 4294A impedance analyzer (100 Hz˜1 MHz) (open dot) and 2) Low frequency using Solartron SI 1260 Impedance/Gain Phase Analyzer (0.1 Hz˜10 kHz) (solid line). The capacitance of ALD#1 is about 500 nF. The capacitance of ALD#2 is about 600 nF.

CONCLUSIONS

[0226] A material and set of processing conditions were selected that gave the optimal properties for fabricating a capacitor 38. The material of choice, SiO.sub.2-coated 48 BaTiO.sub.3 40, exhibited the highest dielectric permittivity. This particular sample was treated at 900° C. for 1 hr. The processed material exhibited the following properties at 20 Hz: permittivity of 19,980, a DF of 215%, and an ESR of 806 kOhms. A test cell was built with the selected material at a thickness of 13.5 μm, and it exhibited a capacitance of 125 nF at 1 kHz. The breakdown voltage of this sample was measured to be 450V. The calculated energy density based on a 184 nF capacitor at this breakdown voltage would be about 5 J/cc. Treatment at temperatures below 900° C. does not significantly affect the dielectric properties of the material. The decrease in properties for samples treated above 900° C. may be attributed to an over reduction or to excess inter-diffusion. SiO.sub.2, although it did not experience a color change, had the highest initial and after treatment permittivity. The color tone difference within a powder batch after being reduced indicates that a better sealed tube furnace or other synthesis techniques like the fluidized bed process, are necessary to obtain a homogeneous treatment.

[0227] The following reference numbers are used on FIGS. 1-24. [0228] 4 positive electrode [0229] 6 air gap capacitor [0230] 8 resistive load [0231] 10 electrolytic capacitor [0232] 12 applied voltage [0233] 16 current flow [0234] 20 negative electrode [0235] 22 electrolyte [0236] 24 air dielectric [0237] 24a dielectric ink [0238] 26 separator [0239] 28 current collector [0240] 32 grain of conductive ceramic [0241] 36 capacitive grain boundary [0242] 38 IBLC capacitor [0243] 40 BaTiO.sub.3 particle [0244] 44 Al.sub.2O.sub.3 coating [0245] 48 SiO.sub.2 coating [0246] 52 soldered connection to test lead [0247] 56 connection soldered to bottom electrode [0248] 60 bottom electrode [0249] 62 substrate [0250] 64 bottom contact pad [0251] 66 test lead [0252] 70 connection soldered to top electrode [0253] 74 top electrode [0254] 76 top contact pad [0255] 78 dielectric made in accordance with this invention [0256] 82 multilayer capacitor cell [0257] 84 multilayer capacitor slice [0258] 86 housing [0259] 90 cooling block

[0260] Thus, the present invention has been described herein with reference to a particular embodiment for a particular application. Those having ordinary skill in the art and access to the present teachings will recognize additional modifications, applications and embodiments within the scope thereof

[0261] It is therefore intended by the appended claims to cover any and all such applications, modifications and embodiments within the scope of the present invention.