STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[001] The invention described herein was made in the performance of work under a NASA contract and by an employee of the United States Government and is subject to the provisions of Public Law 96-517 (35 U.S.C §202) and may be manufactured and used by or for the Government for governmental purposes without the payment of any royalties thereon or therefore. In accordance with 35 U.S.C, §202, the contractor elected not to retain title.

BACKGROUND OF THE INVENTION (!) Field of the Invention.

[002] The present invention relates to the field of capacitors and more particularly to the field of solid state ultracapacitors.

(2) Description of the related art

[003] Electrical, electronic, and electromechanical (ERE) parts are used many products. Better energy storage and delivery devices are currently needed. For example, space vehicles use rechargeable batteries that utilize silver zinc or lithium- ion electrochemical processes. These current state-of-the-art rechargeable batteries cannot he rapidly charged, contain harmful chemicals, and wear out early. A solid- state ultracapacitor is an RER part that offers significant advantages over current electrochemical, and electrolytic devices.

[004] Ultracapacitor behavior has been reported in a numher of oxides, including reduced barium titanate (BaTK½ 40) and ferroelectric ceramics. BaTitb 40 is a ceramic material in the perovskite family that possesses a high dielectric constant.

Individual coating of ferroelectric BaTii¾ 40 grains with a silica (Si0 ₂ 48) shell, followed by spark plasma sintering (SPS) in reducing conditions, has been shown to lead to stable oltracapacitof behavior. The permittivity values nave been reported to be -10 ^s m eleetroceramics, It has also been shown that treating oxid ed BaTiC¼ 40 at high temperatures in reducing forming gas atmosphere (75-96% nitrogen, >½, and 4~ 25% hydrogen, ¾) produces an N-type semiconducting material. The outer coating, which remains an insulating shell, combines wife feis semiconducting internal layer, resulting in millions of nanocapaeitors in parallel The combination of a

semiconducting grain with an insulating boundary leads to the IBLC effect

[005] These so-called giant ultracapadtor properties are not easily controlled. American Piezo Ceramics International reports a relative dielectric constant of 1,530 and a dielectric dissipation factor (DF) of 0.5 for single-crystal BaTiOa. High permittivity values such as 10,000 are reported in polyerystallirse ferroelectric BaTiC . Reduced BaTK¾ 40 of grain sizes between 70 nni and 300 nm have yielded colossal permittivity values on the order of -10 ⁵ The instant invention was developed by evaluating shell-coated BaTiGj 40 processed under reducing conditions to produce the IBLC effect.

[006] BACKGROUND

LIST OF ACRONYMS AND SYMBOLS

ALB atomic layer deposition

AI2O3 alumina

BaTiO. fearimn titanate dissipation factor

EDLC electrochemical double-layer capacitor electrical, electronic, and electromechanical equivalent series resistance hydrogen high-energy, solid-state capacitor (module)

Internal barrier layer capacitor L€ inductance, capacitance, and resistance

N2 nitrogen

SCFH standard cubic feet per hour

SEM scanning electron microscope

Si silicon

SiGz silica

STEM EDS scanning transmission electros xni croseopy -energy dispersive spectroscopy

Ti titanium electrode surface area

G-jjtsj total, capacitance

& distance between plates

E energy e electron f frequency ί current imaginary unit

Joules/cubic centimeter

J/ce

i ^s power i maximum power

Q stored charge r time tan δ loss tangent delta

V voltage

Fo vacancy sits

Vf final voltage

Vo initial voltage

X reactance

impedance

e& vacuum permittivity

effective permittivity

dielectric permittivity

[007] Conventional Capacitors

[008] A capacitor 6 ^' is an electrical component consisting of two conducting electrodes 4, 20 separated by m insulating dielectric material, typically air 24. When voltage is applied across the capacitor 6, opposite charges accumulate on the surface of each electrode, developing a static electric field. This field causes atoms In the insulator 24 to polarize, producing an internal electric field. Capacitors 6 are able to store energy in this overall electric field. This is illustrated In Figure 1,

[009] Capacitance (C) is a measure of the ability to store charge, and it is the ratio of the stored charge (Q) to the applied voltage (V);

[011 ] A specific material polarises in response to an electric field. The vacuum permittivity (sa) is a constant due to free space vacuum and is 8.854187... x 10 ^"i2 F/m, The relative permittivity multiplied by the vacuum permittivity is usually called the effective permittivity (se//)

[013] Capacitive loads oppose the change of voltage. Impedance (Z) is a measure of the effect of capacitive loads. When reactance (X) is zero, the load Is purely resistive; when resistance (R.) is zero, the load is purely reactive, ideal capacitors 6 consist entirely of reactance, having infinite resistance;

[014] Z - R r jX (3) [015]

[017] Loads are modeled as either & series or parallel combination of a resistive and a reactive load,. The parallel resistance is typically larger Aars the series resistance. To measure small reactive values, such as high-valued capacitors 6, it is preferable to use the series model because the series resistance is more significant than the parallel resi tance. When measuring large reactive values such as high- valued inductors or low-valued capacitors 6, it is preferable to use the parallel model. Table 1 shows the capacitance ranges and which model should be used.

Table I. Model for corresponding ca cit nce ranges.

Capacitance i <1G nF 10 kO Parallel

[018] At low frequencies, a capacitor 6 is an open circuit, as no current flows in the dielectric. A DC voltage applied across a capacitor 6 causes positive charge to accumulate on one side and negative charge to accumulate on the other side; the electric field due to the accumulated charge is the source of the opposition to the current When the potential associated with the charge exactly balances the applied voltage, the current goes to zero. Driven by an AC supply, a capacitor 6 will only accum ulate a limited amount of charge before the potential difference changes polarity and the charge dissipates. The higher the frequency, the less charge will accumulate, and the smaller the opposition to the current

[01 ] ^' The two primary attributes of a capacitor 6 for ibis Invention are its energy density and power density. The energy (E) stored in a capacitor 6 is directly proportional to its capacitance:

[021] To determine power, capacitors 6 are represented in series with an external load resistance ( ), as shown in Figure 1. The internal components of the capacitor 6 itself contribute to the resistance as the equivalent series resistance (Ei Maximum power (/ ) far a capacitor 6 occurs at matched impedance (R = ESR) 7Ί (6)

[023] ESR is an AC resistance dependent on frequency. In nonelectroiytic capacitors 6 smb. as electroceramics, the resistance of the leads and electrodes and losses in ihe dielectric cause the ESR, For a capacitor 6 _t the ESR typically falls between 0.001 and 0.1 Q and is desired to be low. A high ESR causes increased heat dissipation and results in accelerated aging under high temperature and large ripple current conditions. Additionally, capacitors 6 exhibiting high ESR. have a high current leakage, consuming and wasting power in the idle state, making them bad energy storage devices:

[024] P - ^ x ESR. (7)

g [025] Electrical potential ener y is dissipated in dielectric materials m the form of teat. The DF is a measure of loss rate of energy and is proportional to the ES . Dissipation factor is also known as loss tangent delta (tan S), and it is represented as a percentage. This parameter depends on th dielectric material and the frequency of the electrical signals. In high dielectric constant cerami c , DF can be 1%

-2%:

[027] Electrical characteristics of uliraeapaeitors today lie between those of aluminum-electrolytic capacitors and fuel cells. The electrochemical double-layer capacitor 1.0 (EDLC) (Figure 2 A and B) uses high surface area electrodes 4, 20, resulting m ultracapacitor behavior. EDLCs 10 are constructed, from two carbon- based electrodes 4, 20, an electrolyte 22, am! a separator 26. Ions within the electrolyte solution 22 accumulate at the surface of the electrodes 4, 20 and the separator 26 creates a dowble-layer of charge. EDLCs 10 generally operate with stable performance characteristics for many charge-discharge cycles, sometimes as many as 10 ⁶ cycles. On the other hand, electrochemical batteries are generally limited to only about lO ³ cycles, Because of their cycling stability, EDLCs 10 are well suited for applications that involve nonuser-serviceable locations. Examples include deep sea and mountain environments. However, EDLCs 10 cannot be used in aerospace environments without hermetically sealed containers, which increase mass and volume. Currently, electrolytic ultraeapacitors are used primarily in conjunction wish batteries in terrestrial environments to capture sndden bursts of energy (e.g., regenerative braking systems). However, electrolytic ultracapacitors do not possess the energy density necessary to replace batteries.

[028] Dielectric tan δ of ceramic capacitors is dependent upon specific characteristics of the dielectric formulation, level of impurities, as well as microstructural factors such as grain size, morphology, porosity and density.

[029] Electrochemical Double-Layer Capacitor [030] Conventional capacitors have relatively high power densities bui low energy densities when compared to electrochemical batteries. Stated another way, a battery may store more energy but cannot deliver it as quickly as a capacitor can. Current ultracapgeitors exploit high surface area electrodes and thin dielectrics to increase both capacitance and energy. Additionally, ultraeapacrtors have advantages over electrochemical batteries and fuel cells, including higher power density, shorte charging times, longer cycle life and longer shelf life. The Ragone chart in Figure 3 compares the po wer and energy densities of different types of current energy storage devices.

[031] Internal Barrier Layer Capacitor

[032] A solid-state uitracapacitor would overcome the limits of both the electrochemical batteries presently being used and of currently available

electrochemical ultracapacitors.

[033] Solid-state ultracapacitors provide a robust energy storage device with higher reliability, less weight and less volume than electrochemical batteries and electrolytic ultracapaeitors, They arc recyclable energy storage devices that offer higher power and a greater number of charge/discharge cycles than current rechargeable batteries, They also offer greater breakdown voltage than current electrolytic ultracapacitors. The instant invention Is a high-energy, solid-state capacitor (HESSC&p) module to replace batteries and current state-of-the-art uifracapac!tors. Table 2 presents the primary parameters for aerospace batteries, terrestrial electrolytic ultracapacitors, and the target values for the IIESSCap.

Table 2. Uiifacapacit r baitery comparison.

[034] The HESSCap module achieves high permittivity via the IBLC effect, shown h Figures 4A _S B and C, individual ferroelectric grams are coated by a dielectric shell, followed by sintering at high temperatures under reducing forming gas atmosphere (96% Nj and 4% ¾), The forming gas penetrates the shell and reads with the inner grain, making each grain seraieorsductive. The coating serves as an insulator, resulting Irs millions of nanocapacitors in parallel:

[035] (9)

[03 ] The two main parameters for the internal barrier layer to increase the overall dielectric permittivity of oxides are (1) the inner grain conductivity and {2} the insulating grain boundary. The former is related to the amount of charged defects intentionally formed during the sintering step under reducing conditions. The IBLC model can he applied to any materi l where extended dielectric interfaces of very small thickness separate (semiconducting parts: in ceramics, insulating gram boundaries surround conducting grains: in thi films and multilayers, surfaces and isiergrowth. planes can induce dielectric barriers between conducting layers.

However, the exact nature of the conduction mechanism within the grains and of the charge accumulation at the grain boundaries is not well understood,

[037] In Appi. Phys. Lett., Vol 94, No. 7, 3 pp., doi: 10,1063/13076125, February 2009, Chung, U.-C.; Eiissalde, C; Mornet, S,; et l. (hereafter Chung) disclose controlling the internal barrier in low loss BaTiC supercapaeitars,

[038] At page 4, Chung discloses "standard BaTiGs particles of 500 run diameter" that "have been individually coated with a homogeneous amorphous silica shell of 5 urn thickness using a method derived from the Stbber process." However, the instant invention uulk.es a proprietary gas-phase chemical process rather than the Stdber process. At page 4, Chung also discloses sintering in a "reducing atmosphere at a final temperature of 1100 °C under vacuum".

[039] At page 4, Chung further states that the density of the pressed pellets was 9?%- At page 5, Chung states that "the room temperature dielectric pmniitivity is in the range of the so called giant dielectri c materials (e~ 2.105 at f- 10 ⁴ Hz) meaning that our core shell particles are indeed leading to IBLC ceramics (Fig. 2a)J ^f

[040] At page 5 Chung reports that the dielectric losses of the material are on the order 5% at 10 ⁴ Hz "instead of 100% in the existing literature". The BaTiC¾ particle size and thickness of the si l ica shell of Chung are i dentical to the particle size and coating thicknesses for StOi for the instant invention. However, Chung does not disclose a capacitor fabricated utilizing the disclosed IBLC ceramic material, Also, Chung does not disclose the proprietary coating process (page 8) utilized in this invention. Further, the Chung sintering temperature (1100° C) is somewhat higher than the 850-900° C temperature utilized to fabricate the capacitors in accordance with the Instant invention.

[041 ] Reynolds et al. U.S. Patent Publication No. 2014/0022694 (hereafter Reynolds), discloses a method for manufacturing multi-layer ceramic capacitors. At paragraph [0058], Reynolds diseloses a method including forming a bottom electrode on a substrate utilizing "thick film methods m&h as screen printing or tape casting" or "thin-film techniques Including hat not limited to sputtering, evaporation, ion plating, post laser deposition, atomic layer deposition, chemical vapor deposition, plasma- enhanced chemical vapor deposition, electroplating and eleetroless plating."

[042] At paragraph [0060], Reynolds states thai the ceramic dielectric is deposited following deposition of the bottom electrode which "can be by thick film techniques such as screen printing or tape casting," Reynolds states that thin-film techniques can also be utilized to deposit the ceramic dielectric. At paragraph [0060], Reynolds discloses a post-deposition heat treatment of the ceramic dielectrics such as "a high temperature firing in vacuum or in a reducing environment to remove the organic and volatile compounds of the inks and binders nsed, for example, in the screen printing process a d also to form the desired crystal and gram structures for high-k materials such as doped barium titanates that must be converted to their perovskite phase."

[043] At paragraph [0061], Reynolds states that the ceramic is then coated with a thin film "such as silicon nitride {S3N _S ), silicone dioxide (Si<¾) _s aluminum oxide (Ab<¾), etc." Reynolds states that the films "will probably have thicknesses > to 5 urn" but "they can be even thinner." Suitable deposition techniques "Include sol- gel deposition, sputtering, evaporation, ion plating, pulse laser deposition, atomic layer deposition, plasma-enhanced chemical vapor deposition, 'electrografting' and especially chemical vapor deposition,"

[044] At paragraph [0061], Reynolds also states that "atmospheric CVD is again preferred because thermal CVD is able to penetrate into very small spaces, even between the gaps of the individual high-k grams. In this way, an internal barrier-layer type capacitor dielectric is formed with a large capacitance but with reduced leakage and increased dielectric breakdown strength."

[045] At paragraph [0062], Reynolds states that the substrates can be introduced into a multi-zone furnace having a first high temperature e

incorporating a reducing ambient The stack is men allowed to cool, and a second

II layer of metal electrode material is deposited, and a second layer of Mgh-k ceramic is then deposited onto the second metal electrode (paragraphs [0063]-[0064]),

[046] However, in the instant invention the particles used to formulate the dielectric ink are coated with a proprietary gas-phase chemical process. In contrast, Reynolds states that an internal barrier-type capacitor dielectric can be formed by utilizing a CVD process to coat particles (e.g. barium titanate 40) after the particles are deposited using an ink and screen printing technique. This results in only an upper layer of particle coating whereas inner particles are not coated,

[047] Development of a capacitor for replacing batteries which can provide longer life, lower mass-to-weight ratio,, rapid charging, on-demand pulse power, improved standby time without maintenance,, and environmental friendliness represents a great improvement in the field of electronics and satisfies a long felt need of engineers and manufacturers,

SVMMAEY OF THE INVENTION

[048] The present invention is a novel method for forming solid state uitracapacitors, utilizing internal harrier layer capacitor (!BLC) material, 1BLC materials generally Include electrically conductive grains that are coated by an insulating material. Ferroelectric gi-ains may be coated by a dielectric shell, followed by sintering at high temperatures in a reducing forming gas atmosphere (96% N2 and 4% ¾}. The forming gas penetrates the shell and reacts with the inner grain, making each grain semi-conductive. The coating serves as an insulator, resulting in millions of nanoeapadtors in parallel 0 5] The instant invention is a method of manufacturing a capacitor.

Particies of BaTiCb having an average grain diameter of 100-700 nrn are first heated in a furnace under a mixture of 70-96% by volume N2 4-30% by volume l¾ gas for 60-90 minutes at 900°C [050] The first furnace may be a multizone belt furnace or a fluidized bed vertical tube furnace. The second furnace ma be a multizone belt furnace.

[051 ] Next a 3-20 n film of SiOz or AI2O5 is deposited over the particles. The resulting material is agglomerated so the coated particles must be mechanically separated. The particles are then incorporated into an ink of the follo wing formulation: i. 60?80% by weight separated, coated, treated ceramic particles; ii. 5-50% by weight high dielectric constant glass; the high dielectric constant glass being 0 -1 um in size ill 0.1.-5% by weight surfactant; iv. 5-25% by weight solvent; and v. 5-25% weight organic vehicle,

[052] Next a layer of the dielectric ink is deposited on a substrate with a pre- sintered and deposited electrode in place. Methods of depositing electrodes on a substrate are well known in the field of capacitor manufacture, The electrode can be silver, silver palladium, or any material with a resistance between 1 roilliohm and 10 ohms. Finally, the dielectric ink is sintered onto the substrate by heating in a second furnace at 850-900 °C for 60-90 minutes and allowing the ink and substrate to cool to ambient This heating and cooling cycle is carried out imder N2 atmosphere, which con tens less than 25ppni 0 ₂ , Preferably, during sintering, the time under 600 °C is kept to 30 minutes maximum; time uuder 800 °C is 20 minutes maximum; and total time is 60-90 minutes, Also, preferably, the heating rate is 45-55 "C/mraute 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 is added that can be silver, silver palladium or any material with a resistance between 1 milliohm and 10 ohms.

[053] The substrate is preferably 0.025-0.040 inch thick AI2O3 in which the AI2O3 is at least 96% pure. Alternatively, the substrate could be ahirninura nitride (A1N) zirconta, beryllium oxide (BeO) or nncured ceramic. ilncured ceramic is a mixture of ceramic particles, a binder, a surfactant and a solvent. Formulae for nciired ceramic are well known,

[054] Preferably the thickness of the deposited dielectric ink is sufficient to produce a sintered layer 10-35 urn thick,

[055] This invention is also an ink of the following formulation; a. 60-80% by weight BaT Os particles coated with a 3-20 run film of SiCh or AI2G3; the BaTi<¾ particles having an a erage grain diameter of 100-700 nm; the Ba ^' TiOs having doubly ionized oxygen anion vacancies; b. 5-50% by weight high dielectric constant glass; the high dielectric constant glass beirsg 1-1 Ομ in size; c. 0.1-5% by weight sisrfactant; cL 5-25% hy weight solvent; and e, 5-25% weight organic vehicle;

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

[057] The process of the instant invention results in an internal barrier layer ultracapaeitor (IBLC) made from novel dielectric materials as a battery replacement with the following advantages: longer life, lower mass-to- weight ratio, rapid charging, on-demand puke power, improved standby time without maintenance, and environmental friendliness,

[058] Test pellets were fabricated utilizing BaTi<¾ particles of 730 and 500 nm particle sizes. Some of the test pellets were made with BaTiOs particles that were coated with $iO _¾ and test pellets were fabricated utilizing BaTiO¾ particles (500 ran) that were coated with AI2O3. The S5G2 coating thickness was 3 nm, and the AI2O3 thickness was 10 nm.

[059] BaTiOs panicles were coated using an atomic layer deposition (ALD) process. Atomic Layer Deposition (ALD) is a thin film deposition method in which js film is grown on a substrate by exposing its surface to alternate gaseous species (typically referred to as precursors), to contrast to chemical vapor deposition (CVD) ₅ the precursors are never present simultaneously in the reactor, but they are inserted as a series of sequential,, non-overlapping pulses, in each of these pulses the precursor molecules react with the surface in a sclt-Hmiting way, so that the reaction terminates once all the reactive sites on the surface are consumed. Consequently, the maximum amount of material deposited on the surface after a single exposure to all of the precursors (a so-called ALD cycle) is determined by the nature of the precursor- surface interaction. See Puurunen, Riikka, Surface chemistry of atomic layer deposition: A case study for the trimethylaliimin m/water process, Journal of Applied Physics 97, 121301 (2005),

[060] By varying the number of cycles it is possible to grow materials uniformly and with high precision on arbitrarily complex and large substrates. The n-sintered particles were pressed Into pellets without the addition of binder using a potassium bromide dye, and a tube furnace was used to heat the pellets under an atmosphere of 96% N2 and 4% Ha. in such an atmosphere, BaTiCfe is slightly reduced. Quarts boats were each populated with pellets of AkCh-coated, Si€¾- coated, and uneoated BaTiCfe. After processing and the pellets were left to cool to room temperature inside the tube furnace. Resulting pellets were 4-8 mm thick with masses of L5-2.5g.

[061] Capacitors can also be made by 3D additive manufacturirig. To perform 3D additive manufacturing, the particles are first con verted into an ink. 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. In order to deposit the particles, they are separated using a three-roll mill or similar machine. [062] The aerosol jet process begins with a mist generator that atomizes a source material. Particles In the resulting aerosol stream are then condensed, The aerosol stream is then aero ynamically focused using a flow guidance deposition head, which creates an annular flow of sheath gas to coliimate the aerosol The coaxial 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 ΙΟΟμπι),

[063] The aerosol j t process allows for a large viscosity range of proeess!ble inks (typically 0.7-2,500 cF) _s a flexible distance between substrate and nozzle (typically ! 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 um) electronic devices. Machines for performing this process are available from Optomec, Inc.. New Mexico; under the brand name Aerosol Jet®.

[064] 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.

[065] 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 men 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.

[066] Screen printing was utilized to fabricate test ceils. The capacitor test cells were sintered using a belt furnace after each layer deposition. Subsequent testing showed energy densities m the range of 1,0 to 2,0 J/ce.

[067] An appreciation of the other aims and objectives of the present invention and an understanding of it may be achieved by referring to the

accompanying drawings and description of a preferred embodiment. BRIEF DESCRIPTION OF THE DRA WINGS

[068] 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.

[069] Figure 1 Schematic of a conventional capacitor

[070] Figure 2A Schematic of an EDLC

[071] Figure 2B Enlargement of area marked with a B on Figure 2 A

[072] Figure 3 Ragone chart of energy storage devices

[073] Figure 4A Internal barrier layer capacitor

[074] Figure 4B Enlargement of area identified on Figure 4A

[075] Figure 4C Internal barrier layer capacitor effect

[076] Figure 5 A BaTiOs particle with 10 mn of AhC¾ coating.

[077] Figure 5B BaTiCfe particle with SiOs coating

[078] Figure 6 The BaTiO^ crystal structure. The green, red, and bine atoms are titanium, oxygen, and barium, respectively

[079] Figure 7 Dielectric Test Fixture 1 45- IB in front of Agilent E4980A precision L C meter,

[080] Figure 8A Top view of ultracapacitor cell

[081] Fi gnr e SB Side view of ultracapacitor cell

[082] Figure 8C Layer view of ultracapacitor cell [083] Figure 9 Eight-zone belt furnace temperature setiisigs. Zones 1 -8 are the Indi vidual heated zones; PV = present temperature value; FV ¹⁼¹ future, or desired temperature value for the profile; and SV ^:::: set temperature value for the indrvidsml heater zone controller,

[084] Figure 10 Belt furnace temperature profile

[085] Figure 1A SEM image of ncoated, untreated BaTiCb

[086] Figure 1 I B SEM image of BaTii¾ coated with AhGa but untreated,

[0S7] Figure 11.C SEM image of BaTiCb coated with A½G-3 and treated at 750 °C for 30 hr.

[088] Figure 12A Optical microscopy photographs of (a) uncoated BaTIOs pellets (untreated)

[089] Figure 12B Optical microscopy photographs of coated, BaTiCb pellets Cu s treated)

[090] Figure 12C Optical microscopy photographs of A½03 coated BaTiOj pellets (untreated)

[0 1] Figure 13 A Optical microscopy photographs of unseated, BaTiO? pellets treated at 900 °C for 1 S r,

[092] Figure 13B Optical microscopy photograph of SiG ₂ coated BaTIOs pellets treated at 900 °C for 1 hr,

[093] Figure 13C Optical microscopy photographs of AI2O3 coated BaTlOs pellets treated at 900 °C for 1 hr.

[094] Figure I4A Optical microscopy photographs of uncoated, BaTiOs pellets treated at 1,1.00 °C for 1 hr,

[095] Figure MB Optica! microscopy photographs of SiO?. coated BaTiOs pellets treated at 1,100 °C for 1 hr. [096] Figure 14C Optica! microscopy photographs of AI2O3 coated BaTsi¾ pellets treated at 1 ,100 °C for 1 hr,

[097] Figure ISA Plots of pemittivity of samples treated at 900 °C for 15 hr, and LI 00 °C for 1 hr. compared to the u treated powders

[098] Figure 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

[099] Figure 15C Plots of ES of samples treated at 900 °C for 15 hr. and 1,100 °C for 1 hr, compared to the untreated powders

[0100] Figure 1 A Plots of permittivity of samples treated at 900 °C for 1 hr. compared to the untreated powders

[0101] Figure 16B Plots of DF of samples treated at 900 °C for 1 hr, compared to the untreated powders

[0102] Figure 16C Plots of ESR of samples treated at 900 *C for 1 hr.

compared to the untreated powders

[0103] Figure 17 Ultracapacitor test cell made from SiO?~coated BaTiOs deposited by screen printing

[0104] Figure SA Plots of permittivity of powdered samples treated at 900 ^C C for 1 hr, before and after furnace sintering

[0105] Figure 18B Plots of DF of powdered samples treated at 900 °C for 1 hr. before and after furnace sintering

[0106] Figure ISC Plots of ESR of powdered samples treated at 900 "C for 1 hr. before and after furnace sintering 0! 07] Figure 1 A SEM image at a. magnification of 500 showing the level of densifieation of SiO¾-eoated BaTiQs test cell with 184 tiF of capacitance processed at 900°C for 1 hour. [0108] Figure 19B SEM image at a magnification of 3,000 showing the level of densification of Sii¾~eoated BaTii¾ test cell with 184 nF of capacitance processed at 900°G for 1 hoot.

[0109] Figure 1 C SEM image at a magnification of 5,000 showing the level of densification of SiC¾-coated BaTiO. test cell with 184 nF of capacitance processed at 900°C for 1 hour.

[0110] Figure 1 D SEM image at a magnification of 10,000 showing the level of densification of SiGi-eoated BaTiOs test cell with .184 nF of capacitance processed at 900°C for 1 hour.

[0Π 1] Figure 20 Voltage versus time used for the direct current (DC) discharge test method,

[0112] Figure 21 A Plots of capacitance of the capacitor test cells, made from the dielectric material treated at 900 °C for 1 hi,, before and after furnace sintering

[0113] Figure 21B Plots of DF of the capacitor test cells, mads from the dielectric material treated at 900 °C for 1 hr. ₅ before and after furnace sintering

[01 14] Figure 21 C ESR of the capacitor test cells, made from the dielectric material treated at 900 °C for 1 nr., before and after furnace sintering

[0115] Figure 22 Nine, niultilayered iiltracapaeitor cells in parallel printed on a substrate board. Ceils can be printed serially or in parallel to get the desired voltage or capacitance. This is known as a slice.

[0116] Figure 22A is a cross section of a multilayer capacitor cell, nin of which are used in a slice.

[01.17] Figure 23 Ultracapacitor module where multilayered capacitor boards (or slices) are stacked in a housing wit active or passive cooling to increase energy storage. [01 IS] Figures 24A-24D show frequency dependence of Cp~-D and s _r for 2 different samples at room temperature from 0,1 Hz to 1 MHz.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[011 ] 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,

[0120] The instant invention is a method of manufacturing an iBLC capacitor 38. Particles of BaTsQj 40 (see Figures 4, 5 and 6) having an average grain diameter of 100-700 mn are first heated in a furnace under a mixture of 70-96% by volume N2 4-30% by volume Hi gas for 60-90 minutes at §50-900*0.

[0121] BaTiOs has doubly ionized oxygen anion vacancies - see Figure 6, The first furnace may be a mnltlz ne belt furnace or a Suidked bed vertical tube furnace. The second fiimace may be a rnulfeone belt furnace.

[0122] Next a 3-10 nm film of SiC¾ 48 or A½Cb 44 is deposited over each individual particle 40. 'His resulting grains 32 (see Figures 5 A and 5B) are agglomerated so they must be mechanically separated. The grains are then

Incorporated Into an ink of the following formulation:

1, 60-80% by weight separated grains 32; ii. 5-50% by weight high dielectric constant glass; the high dielectric constant glass being 1-10μ in size

Hi. 0, 1-5% by weight surfactant; iv. 5-25% by weight solvent; and v. 5-25% weight organic vehicle.

[0123] The solvent may be ester alcohol tetpineol or butyl csrbitoL and the organic vehicle may be ethyl cellulose, The high dielectric constant glass may he lead-germinate or zinc borate glass. Preferably, the surfactant is a phosphate ester,

[0124] Nex t a layer of fee dielectric ink 24a is deposited on a substrate 62 with a pre-sintered and deposited electrode 60 in place. The electrode cm be silver, silver palladium, or any material with a resistance between 1 milHohm 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 N2 atmosphere, which contains less than 25ppm C¾« 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/minuie 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 miiliohm and 10 ohms,

[0125] The substrate 62 is preferably 0.025-0.040 inch thick AI2O3 in which the AI2O3 is at least 96% pure. Alternatively, the substrate could be aluminum nitride (Afi ) ziroonia, beryllium oxide (BeO) or uneured ceramic. Uncured ceramic is a mixture of ceramic particles, a binder, a surfactant and a solvent,

[0126] Preferably, the thickness of the deposited dielectric ink 24a is sufficient to produce a sintered layer 10-35um thick.

[0127] The process of fee instant invention results in an internal barrier layer ultracapacitor (IBLC) 38, which can be used as a battery replacement because it lias the following advantages: longer life, lower niass-to- eight ratio, rapid charging, on- demand pulse power, improved standby time without maintenance, and environmental friendliness. [0128] This invention is also m ink of the formula sho above, [0129] Experimental 1

[0130] Test pellets were fabricated utilizing BaTiC particles 40 of 730 and 500 nm particle skes. Some of the test pellets were made with BaTiC particles 40 that were coated with S1O2 48, and test pellets were fabricated utilizing BaTiOs particles 40 (50Θ nm) that were coated with AhC¾ 44. The SiCh coating 48 thickness was 5 nm, and the AI2O3 44 thickness was 10 nm,

[ 131] BaTiOj particles 40 were coated using an atomic, layer deposition (AID) process.

[0132] Some im-sintered particles were pressed into pellets without the addition of binder using a potassium bromide dye. A tube furnace wa s used to heat the pellets under an atmosphere of 96% 2 and 4% ¾ s . I such as atmosphere, BaTiC 40 is slightly reduced, Quarte boats were each populated with pellets of AlsOs-coated. SiOr coated, aid uncoated BaTiO^ 40. After processing the pellets were left to cool to room temperature inside the tnhe furnace. Resulting pellets were 4- mm thick with masses of l.5-2.Sg.

[0133] Capacitors c also be made by 3D additive manufacturing. To perform 3D additive manufacturing, the particles are first converted into an ink. Two additive manufacturing techniques cars be used for dielectric 78 deposition, such as aerosol jet deposition and screen printing. They require unfused particles m order to deposit properly, in order to screes! print the particles, they are separated using a three-roll mill or similar machine.

[0134] 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 aerodynamieally focused using a flow guidance deposition head, which creates an annular flow of sheath gas to eollimate 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 a tenth of the size of the n zzle orifice (typically lOOum). [0135] The aerosol jet rocess allows for a large viscosity range of processihle inks (typically 0.7-2,500 eP), a flexible distance betwee substrate and nozzle (typically 1 to 3 mm) as well as a tightly focused aerosol stream for variable me width. This allows the production of fine pitch (typically below 50 μτη) electronic devices. Machines for performing this process are available from Optomec, Inc., New Mexico; under the brand name Aerosol Jet®.

[0136] Screen printing is the process of using a mesh-based stencil to applynk onto a substrate, whether it be T-shirts, posters, stickers, vinyl, wood, or oilier material.

[0137] 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 rnesh 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.

[0138] Screen printing was utilized to fabricate test cells. The capacitor 38 test cells were sintered aslng a belt furnace after deposition of each layer. Subsequent testing showed energy densities in the range of L0 to 2.0 J/cc.

[0139] Atomic Layer Deposition-Coated Ceramic Barium Titanate Particles

40

[0140] A prior study focused on BaTiQs particles 40 of various sizes in both coated and ncoated configurations, with the tetter serving as a baseline. Table 3 provides the details on particle diameter, coating material and thickness, purity, and supplier. Table 3, Materials.

[0141] The BaTiC¾ particles 40 used in this study varied in diameters ranging from 140 nm to 730 nm as their DSQ. or median particle size. Coating configurations varied from imeaated to 10 nm. The uneoated BaTiOa 40 sample was a fine powder, while the coated BaTiQs 40 samples were agglomerated. The ciuraps are likely caused by hydrophilic interaction or static charge. The clumps were dispersed before processing into ink formulations.

[0142] Atomic layer deposition (ALD) was used to deposit nanothin films over BaTiOj nanoparticles. The nanothin film coatings consist of a 10 nm thick layer of alumina (AI2O3 44) and 5 nm thick layer of silica (Si(½ 48), Figure 5A illustrates a BaTiCb particle 40 coated with AI2O3 44. Figure SB illustrates a BaTiOs particle 40 coated with Sit¾ 48. The numher of cycles performed during ALD determines the coating thickness, The coating thickness rate for A < 44 was 10 A per cycle, and for SiOs 48 was 4 A per cycle. It is important to note thai previous IBLC research using SPS of BaTiO? particles 40 were coated by the Stober process, a method based 011 a seeded growth process. The Stober process is known to produce an inconsistent coating.

[ 0143] High-Temperature and Reduced Forming Gas Sintering

[0144] In reducing atmospheres (75-96% N ₂ and 4-25% ¾), BaTi ¾ 40 is slightly reduced, .forming doubly ionized oxygen (anion) vacancies. This prod ces the same effect as vacuum sintering, so a reducing atmosphere is the preferred method of processing. To understand vaca c creation, BaTiCfe 40 crystal structure is shown in Figure 6. The conductivity results from the electron exchange between Τ ⁴ and Ti ⁺³ resulting from oxygen vacancies at the octahedron. The induced free electrons make the reduced perovskite materia, highly semiconducting as shown in equations (10) and (11). Sintering BaTiQs-based dielectrics in forming gas decreases the insulation resistance by 10-12 orders of magnitude, Figure 6 shows the BaTiOs crystal structure.

BaTiO, + jcH,→ « BaTiO, v _a 1 + χΗ,Ο

[0145] ^{" L Jt ■*} (10)

[0146] and

[0148] A three-zone, Thermo Scientific™ Lmdberg Blue tube furnace was used to process the particles. The furnace was heated to 85Ο~950 ^ΰ Ο for at least 60 minutes. The uncoated BaTiOs 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 tor 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.

[0149] Previous studies show thai the reduction of RaTiCh 40 in ¾ at intermediate temperatures (500 °C) leads to bodies of bright, yellow color. Reduced SiG2-eoaied material obtained through SPS at a final temperature of 1 , 110 °C is expected to change from white to a navy blue color. Unseated BaTi(¾ 40 and doped BaTiOs specimens that show a remarkable reduction in resistivit has also been characterized with a bkish color. To assess color changes, optical microscopy images of the pellets were taken at X7 magnification.

[0150] 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 raamiiacturing 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,

[0151] in order to screen print the particles, they were separated using a three- roil mill,

[0152] Pellet Electrical Characterization

[0153] Un~sintered BaTiCh 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 feat pellets pressed at forces above l .§ 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 TestResourees (Shakopee, M ) compression and tension machine. The pellets were 4-8 mm thick with masses of 1.5— 2,5 g.

[0154] 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 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. [0155] Capacitance, DF, and ESR were sneasnred for a frequency range of 20 Hz to 2 MHz using a Dielectric Test Fixture 1645-1 together with an Agilent E4980A recision inductance, capacitance, and resistance (LC ) meter, shown in Figure Ί, The capacitance was initially assumed small, and therefore, measurements were made using the LCR meter's parallel mode. f 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 mstrarnent's reported capacitance value. No porosity correction was made to the dielectric constant. Figure 7 shows Agilent E498GA precision LCR meter (top) and Dielectric Test Fixture 1645- 1B (bottom).

[0156] Dielectric Ink Formulation

[0157] To perform 3D additive manufacturing, fee powders were first converted into an ink. The formulation for this ink is shown in table 4. Glass particulates were used to increase densificaiion, but high quantities of glass particles decrease the permittivity, so the concentration of glass was kept as 3ow 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 ^a C. The vehicle was an organic binder formulated from a blend of Ashland Chemical ethyl cellulose in TexanoS ester solvent. It was used to farther enhance the viscosity of the ink. The vehicle was chosen because it volatilizes between 250 °C and 350 °C during sintering.

Tabic 4. Dielectric ink formulation.

Com onen Concentration (%)

BaTiQs dielectric 32 72,5

Lsad-gmnisste high K. glass 7 5

Surfeeta (wetting agent) 0.5 Texsno! (solvent) 5

Ethyl cellulose organic ve cle 15

[0158] lie dielectric ink 24a formulation was mixed and then ground in a three-roil mill, A three-roil mill is a tool that uses shear force by three horizontally positioned rolls rotating at opposite directions a id different speeds relative to each other to mix, refine, disperse, and homogenize viscous materials fed into it, The iismi ink was a dense, homogenous mix lure used for screen printing.

[0159] Three-Dirnensiona! Add tive Thin Film Deposition

[0160] 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 μιυ. By producing such a thin dielectric layer, the capacitance equation shows that the energy stored eat! 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 (Figures 8A-8C) were printed using a Hary Manufacturing, Inc. (Lebanon, Mi) 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, Abi¾ (0.039 in and 96% purity) was used as the substrate 62 on which each layer was deposited. AI2G3 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. Figures A-8C shows views of the ultracapacitor 3$ cell: BA Top, SB side, and BC layers

[0161] The capacitor test cell was sintered using a HAS 1505-0811Z belt furnace from HengLl Eletek Co. (San Diego, CA) at §50 ^a C peak for 10 min and a total cycle time of 1.5 hn This sintering step was performed after each layer of deposition in order to burn off organic materials sod achieve high densificatiori. The temperature settings of the eight-zone belt furnace are shown in Figure 9, the temperature profile in Figure 10, and the Ni flow profile in table 5. Previous work shows that when reduced Si02-eoated 48 BaTI03 40 is post-annealed at SOO °C for 12 hr, in air, it remains bine, while reduced uncoated BaTiCb 40 turns white. For this reason, the SiC¼ shell 48 is thought to act as an efficient barrier against oxidation. As a fl hef pr ve tative measure, the belt muffle furnace was purged with r¾ to avoid re-oxidation. Densifi cation of the dielectric layer was then evaluated with the scanning electron microscope (SEM). Figure 9 shows temperature settings for the eight-zone belt furnace. On Figure 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; nd SV stands for set temperature value for each Individual zo e heater controller. Figure 10 shows the belt furnace temperature profile.

Table 5. Furnace M ₂ flow profile,

Sec on Nitrogea Flow (I..PM)

Entra ce curtains 40

Preheat 45

Veaiuri ssdh&uss 100

C ol g gas 20

Exit c riam s 20

[0162] Thin Film Electrical Characterization

[0.163] 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 mat was chosen to yield a reasonable time constant. The voltage versus time plot was captured with a DPG51G4 digital phosphor oscilloscope (Marietta, GA), A large region of the discharge em-ve 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 is a resistor through which the capacitor is discharged:

[0165] ANALYSIS

[0166] Pellet Electrical Characterization

[0167] SEM images of the untreated particles 40 (Figures 11A and 11B) revealed that particles indicated by the manufacturer to he 500 nm actually varied in diameter from 250 nm np to I μτη. Treated particles 32 (Figure 11 ) also showed varying particle sizes of the same range. These observations show that the furnace treatment was not causing large scale grain growth. Figures 11 A~l 1C show SEM images of BaTi(¾ 40; 11A urtcoated, 1 IB coated with A½(¾ 44, and 11C AI2O3 44 coated, treated at 750 ^e C for 30 hr.

[0168] All three batches of particles 32, 12 were initially white in color, as can be seen in Figures 12A-12C. When treated at temperatures below 900 °C, they turned to a bright yellow or a neon green color. These particles remained thai color under the reducing forming gas aimosphere 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 Figures 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 k & fiuidteed bed as opposed to pelletized form and this treatment method was adopted. Figures 12A-12C show optical microscopy photographs: I2A uncoated, I2B SiGa-coated 48, and 12C AI2O3 44 coated BaT Oi 40 pellets

(untreated). Figures I3A-13B show optical microscopy photographs: 13A uncoated, 13B Si0 ₂ -coated438 _s and 13C AI2O3 44 coated BaTiC 40 pellets treated at 900 °C for 1 hf. Figures 14A-14C show optical microscopy photographs: 14A uncoated, 14B Ssi¾~coated 48 _s and I4C Αί ₂ 0 ₃ 44 coated BaTiOs 40 pellets treated at 1,100 °C for 1 far.

(0169] At temperatures below 900 , no significant changes were seen in the permittivity. At temperatures above 900 °C, fee permittivity and DF slightly increased for uncoated BaTIOa 40 and decreased for coated samples 44, 48. The ESR decreased only for the AI2O3 44 coated sample, the greatest decrease occurring with 900 °C treatment, The decrease in ESR seen in Figures 15A-15B coincides with the color change seen in Figures I4A-14B, This can be interpreted as the material undergoing reduction.

[0170] The synthesis conditions that produced the maxirnum increase in permittivity for all samples was at 900 ' for 1 hr. Table 6 shows the effect of a short- duration treatment versus a long-duration treatment with constant (900 °C) temperature. The SiOs-coated sample exhibits the highest permittivity.

Table 6, Synthesis profile effect on dielectric permittivity.

[0171 J The capacitor properties versus frequency of the samples treated at 900 °C for 1 hr. are compared in Figures 16Ά-16Β, 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 tes&t&d powders indicated that they are becoming semiconducting, one of die desired outcomes for the IBLC eflect. SiCfe-coated 48 and AI2O3 44 coated BaTiOs 40 treated at 900 °C for 1 hr. SiC¾~coated 48 and AK -coaied 44 BaTiQj 40 treated at 900 °C for llir w ere chosen as the dielectric for the capacitor test ceil because of they had the best capacitance traits..

[0172] Thin Film Electrical Characterization

[0173] Figure 17 shows an ulir&capacitor test cell made with Si ⁽ ¾-coaied 48 BaTiC G.

[0174] SEM images (Figure 1 } of the utiraeapadtor 38 test cells showed a 70%~80% densification. The thickness for samples built using the 325 mesh was an average of 20 ιη, The capacitance obtained through the discharge method using a DC source agreed with fee LC measured capacitance values within ±5%. The voltage versus time plot for the 184.2 nF capacitor is shown in Figure 20.

[0175] Figure 20 shows voltage versus time used for me discharge method,

[0176] Electrical characterization (Figures 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 si 03. This negative capacitance effect is observed in a variety of semiconductor devices.

[0177] Experimental 11 [0178] Several capacitors 38 were made as described . An Agilent (Santa Clara, CA) 4294A impedance analyzer was used to characterise the dieleeSric/electrie properties of these devices over a frequency range from 100 Hz. to 100 MHz using Cp-D arid R~X .function. 301 points were chosen in this range.

[0179] A Sola-iron (West Susses, UK) Si 1260 Impedance/Gain Phase Analyzer was used for the low frequency characterization from 0,1 Hsr. to 10 kHz at room lerxrperatiire. in the experiments, the AC amplitude is a constant of 100 mY, while the DC bias is 0 V. 50 points were chosen in this range,

[01 SO] ^' Hie P-E hysteresis loops were measured using Sawyer-Tower circuit (Radiant Technologies Precision LC unit, Albuquerque, NM). The profile is standard bipolar and frequency is 10 Hz.

[0181] Figures 24A-248 show the two results combined: 1) high frequency using Agilent 4294 A 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 ALB#1 is a out 500 iiF. The capacitance of ALD#2 is about 600 nF.

[0182] CONCLUSIONS

[0183] A materia! and se of processing conditions were selected that gave the optimal properties for fabricating a capacitor 38. The material of choice, SiCfe-eoated 48 BaTiCh 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: pennMvity of 1 _S 980 _S a DF of 215% _s and an ESR of 806 kOhms. A test cell was built with the selected material at a thickness of 13.5 pm, 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 ahout 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 dif&slon. SK¾ ₅ although it did not experience a color change, had the highest initial and after treatment permittivity, Ths color tone difference within a powder batch alter being reduced indicates that a better sealed tubs furnace or other synthesis techniques like the fluidized bed process, are necessary to obtain a homogeneous treatment,

[0184] The following reference numbers are used on Figures 1 -24.

[0185] 4 positive electrode

[0186] 6 air gap capacitor

[0187] 8 resistive load

[0.1.88] 10 electrolytic capacitor

[0189] 12 applied voltage

[0190] 16 current flow

[0191] 20 negative electrode

[0192] 22 electrolyte

[0193] 24 air dielectric

[0194] 24a dielectric ink separator

[0196] 2S current collector

[0197] 32 grain of conductive ceramic

[0198] 36 eapacitive grain boundary

[0199] 38 IBLC capacitor

[0200] 40 Bal ^' iOB particle

[0201] 44 A1203 coating [0202] 48 Si02

[0203] 52 soldered correction to test lead

56 connection soldered to bottom electrode 60 bottom electrode [0206] 62 substrate [0207] 64 bottom contact pad [0208] 66 test lead

[0209] 70 connection soldered to top electrode [0210] 74 top electrode [0211] 76 top contact pad

[0212] 78 dielectric made in accordance with tills invention [0213] 82 multilayer capacitor cell [0214] 84 multilayer capacitor slice [0215] 86 housing [0216] 90 cooling Mock

[0217] 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,

[021 S] 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.