Dielectric materials

This application is a continuation in part of co-pending U.S. patent application Ser. No. 12/778,189, entitled “DIELECTRIC MATERIALS FOR POWER TRANSFER SYSTEM” filed 12 May 2010, which is hereby incorporated by reference herein in its entirety.

This application is related to co-pending U.S. patent application Ser. No. 13/075,911, entitled “DIELECTRIC MATERIALS” filed contemporaneously herewith, which application is hereby incorporated by reference.

The invention relates generally to dielectric materials, and, in particular, to rare-earth-element-based titanate systems.

A dielectric material is an insulating material that does not conduct electrons easily and thus has the ability to store electrical energy when a potential difference exists across it. Common dielectric materials include glass, mica, mineral oil, paper, paraffin, polystyrene, plastics, phenolics, epoxies, aramids, and porcelain. In electronic circuits, dielectric materials may be employed as capacitors. High dielectric constant materials may be used in radar or microwave applications and for circuit miniaturization as the speed of propagation of signal is related to the dielectric constant of the medium through which it passes. If the loss tangent for a material of a given frequency signal is very low, the electrical loss related to the hysteresis decreases resulting in an efficient signal transmission.

There is a need for a dielectric material that has one or more desirable characteristics, such as, a high dielectric constant, a low loss tangent, the ability to withstand a wide range of temperatures, the ability to operate in wide range of frequencies, voltages, atmospheric conditions, and pressures, and the capability for use in the manufacture of composite structures that can be used alone or in combination with other materials.

Briefly, in one embodiment, a material is provided. The material comprises Ca 1-x-y Ba x Sr y Ti 1-z Cr z O 3-δ A p , wherein A is nitrogen, fluorine, or combinations thereof; x and y can vary between the value of zero and one such that 0<x<1 and 0<y<1; z can vary between the value of zero and 0.01 such that 0≦z≦0.01; and δ and p can vary between the value of zero and one such that 0≦δ≦1 and 0≦p≦1, with a proviso that z and p are not simultaneously zero.

In one embodiment, a dielectric component is provided. The dielectric component comprises a material comprising Ca 1-x-y Ba x Sr y Ti 1-z Cr z O 3-δ A p , wherein A is nitrogen, fluorine, or combinations thereof; x and y can vary between the value of zero and one such that 0<x<1 and 0<y<1; z can vary between the value of zero and 0.01 such that 0≦z≦0.01; and δ and p can vary between the value of zero and 1 such that 0≦δ≦1 and 0≦p≦1, with a proviso that z and p are not simultaneously zero.

In another embodiment, a system is provided. The system comprises a dielectric component. The dielectric component comprises a material comprising Ca 1-x-y Ba x Sr y Ti 1-z Cr z O 3-δ A p , wherein A is nitrogen, fluorine, or combinations thereof; x and y can vary between the value of zero and one such that 0<x<1 and 0<y<1; z can vary between the value of zero and 0.01 such that 0≦z≦0.01; and δ and p can vary between the value of zero and 1 such that 0≦δ≦1 and 0≦p≦1, with a proviso that z and p are not simultaneously zero.

In one embodiment, a material is provided. The material comprises α[Ca 1-x-y Ba x Sr y (Ca 1-z Cu z )Cu 2-p La 2p/3 Ti 4-q M q O 12-δ ]+(1−α)[Ba r Sr 1-r TiO 3 ], wherein M is aluminum, chromium, zirconium, or combinations thereof; x can vary between the value of zero and 0.1 such that 0≦x≦0; y, z, and r can vary between the value of zero and 1 such that 0≦y≦1, 0≦z≦1, and 0≦r≦1; p and q can vary between the value of zero and 0.1 such that 0≦p≦0.1 and 0≦q≦0.1; δ can vary between the value of zero and 0.05 such that 0≦δ≦0.05; and α can vary between the value of 0.5 and 1 such that 0.5≦α≦1, with a proviso that when x=y=0 and z=α=1, p and q are greater than zero; and when x=y=z=0, p and q are not simultaneously zero.

In one embodiment, a dielectric component is provided. The dielectric component comprises a material comprising α[Ca 1-x-y Ba x Sr y (Ca 1-z Cu z )Cu 2-p La 2p/3 Ti 4-q M q O 12-δ ]+(1−α)[Ba r Sr 1-r TiO 3 ], wherein M is aluminum, chromium, zirconium, or combinations thereof; x can vary between the value of zero and 0.1 such that 0≦x≦0; y, z, and r can vary between the value of zero and 1 such that 0≦y=1, 0≦z≦1, and 0≦r≦1; p and q can vary between the value of zero and 0.1 such that 0≦p≦0.1 and 0≦q≦0.1; δ can vary between the value of zero and 0.05 such that 0≦δ≦0.05; and α can vary between the value of 0.5 and 1 such that 0.5≦α≦1, with a proviso that when x=y=0 and z=α=1, p and q are greater than zero; and when x=y=z=0, p and q are not simultaneously zero.

In another embodiment, a system is provided. The system comprises a dielectric component. The dielectric component comprises a material comprising α[Ca 1-x-y Ba x Sr y (Ca 1-z Cu z )Cu 2-p La 2p/3 Ti 4-q M q O 12-δ ]+(1−α)[Ba r Sr 1-r TiO 3 ], wherein M is aluminum, chromium, zirconium, or combinations thereof; x can vary between the value of zero and 0.1 such that 0≦x≦0; y, z, and r can vary between the value of zero and 1 such that 0≦y≦1, 0≦z≦1, and 0≦r≦1; p and q can vary between the value of zero and 0.1 such that 0≦p≦0.1 and 0≦q≦0.1; δ can vary between the value of zero and 0.05 such that 0≦δ≦0.05; and α can vary between the value of 0.5 and 1 such that 0.5≦α≦1, with a proviso that when x=y=0 and z=α=1, p and q are greater than zero; and when x=y=z=0, p and q are not simultaneously zero.

These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:

FIG. 1 illustrates an example system including a dielectric component employing dielectric materials according to an embodiment of the invention;

FIG. 2-121 illustrate dielectric properties of some of exemplary materials according to an embodiment of the invention.

Embodiments of the present invention include materials that have different compositions and may be used as dielectric materials.

In the following specification and the claims that follow, the singular forms “a”, “an” and “the” include plural referents unless the context clearly dictates otherwise.

Materials having low dielectric loss tangent along with high dielectric constant are desired for various electrical applications. Therefore, materials that have both high dielectric constant and low dielectric loss tangent at the frequency of operation of intended applications are desirable.

In one embodiment, it is desirable to use dielectric materials whose dielectric properties such as dielectric constant and loss tangent are substantially stable over a certain frequency range of the desired applications. The term “substantially stable” herein means that the change in values does not lead to more than about 10% of the performance variation of the power transfer system. Thus, the required value and width of the frequency ranges may vary depending on the applications for which the material is used. In one embodiment, the desired frequency range is from about 100 Hz to about 100 MHz. In some embodiments, the desired frequency range is from about 1 kHz to about 100 kHz. In another embodiment, the desired frequency range is from about 100 kHz to about 1 MHz. In one more embodiment, the desired frequency range is from about 1 MHz to about 5 MHz.

The dielectric materials that have the desired dielectric properties can be employed in multiple applications. Non limiting examples include varactor diode replacement, tunable capacitors with low losses, tunable filters, phase shifters, multiplexers, voltage control oscillators, tunable matching network for power amplifiers, low noise amplifiers, general impedance matching network.

FIG. 1 illustrates an exemplary system 10 employing dielectric materials according to an embodiment of the invention. In this example, a contactless power transfer system includes a first coil 12 coupled to a power source 14 and configured to produce a magnetic field (not shown). A second coil 16 is configured to receive power from the first coil 12 and distribute to a load 20 . A dielectric component in the form of a field focusing element 18 , including a dielectric material according to an embodiment of the present invention is disposed between the first coil 12 and the second coil 16 for focusing the magnetic field from power source 14 . In another embodiment, the field focusing element may be used to focus electric fields and/or electro-magnetic fields.

Materials such as, but not limited to, barium strontium titanate and calcium copper titanate are examples of materials exhibiting high dielectric constants. Barium strontium titanate—(Ba, Sr)TiO 3 —and calcium copper titanate—CaCu 3 Ti 4 O 12 —have different crystal structures and exhibit different temperature dependent characteristics. For example, (Ba, Sr)TiO 3 belongs to a perovskite family and is a ferroelectric material. CaCu 3 Ti 4 O 12 is not a ferroelectric material and has a body centered cubic (b.c.c) structure. The factors influencing the dielectric properties such as dielectric constant and dielectric loss tangent in the (Ba, Sr)TiO 3 and CaCu 3 Ti 4 O 12 systems may also be different. For example, it is believed that the generation and ordering of dipoles is a reason for the Ferro electricity and the high dielectric constant in the (Ba, Sr)TiO 3 system, while the CaCu 3 Ti 4 O 12 system is thought to have the effects arising from barrier layer capacitance by having insulating grain boundaries and semi conducting grains.

In one embodiment, the dielectric material is used as a bulk material. The term “bulk material” as used herein indicates any material that has a three dimensional structure with all of the sides greater than about 1 mm In one embodiment, the dielectric materials are used as coatings. The coating can be in a thin film form or in a thick film form. As used herein a “thin film” has a thickness less than about 100 microns, while a thick film can have thickness from about a hundred microns to about a millimeter.

In one embodiment, a combination of materials can be used for getting different desirable dielectric properties such as, for example, high dielectric constant low loss tangent values, constant dielectric constant over a varied frequency range, and constant dielectric constant over a varied voltages. For example, a mixture of two or more materials having high dielectric constant or two or more materials having high permeability can be used as a dielectric material for a particular application. In another example, a mixture of two or more materials, each having different desirable properties at a particular frequency or voltage range may be used as a dielectric material.

The inventors studied different ways of improving the desirable dielectric properties of the dielectric materials belonging to the (Ba, Sr)TiO 3 and CaCu 3 Ti 4 O 12 systems. The different methods investigated for the property enhancements include, but are not limited to, cation doping, anion doping, grain boundary doping, density increment, composite formations, and changing the sintering conditions, sintering atmospheres, and structural and microstructural aspects.

Accordingly, in one embodiment, a material system represented by Ca 1-x-y Ba x Sr y Ti 1-z Cr z O 3-δ A p is provided, wherein A is nitrogen, fluorine, or combinations thereof; 0<x<1; 0<y<1; 0≦z≦0.01; 0≦δ≦1; and 0≦p≦1, with a proviso that z and p are not simultaneously zero. This material system will be henceforward referred to as “BST material system” for simplicity. As used herein in the BST material system, the representation Ca 1-x-y Ba x Sr y Ti 1-z Cr z O 3-δ A p is a theoretical formula including the mixtures and compounds that are in the specified ratio to be denoted by this formula, and does not necessarily mean that a single compound exists in a form that can be identified by standard characterization techniques. In short, a material specified by the above formula may actually exist as multiple phases which, taken collectively, has an overall composition as specified by the formula.

As used herein and elsewhere in this application, the term ‘greater than zero’ denotes that the intended component is intentionally added, rather than an incidental amount that may be present as an impurity. Further, end points of the ranges include incidental variations above and below the stated number, as appropriate for normal measurement and process variations.

In one embodiment, a material system with the formula α[Ca 1-x-y Ba x Sr y (Ca 1-z Cu z )Cu 2-p La 2p/3 Ti 4-q M q O 12-δ ]+(1−α)[Ba r Sr 1-r TiO 3 ] is provided, wherein M is aluminum, chromium, zirconium, or combinations thereof, and 0≦x≦0.1, 0≦y≦1, 0≦z≦1, 0≦p≦0.1, 0≦δ≦0.05, 0≦r≦1, and 0.5≦α≦1, with a proviso that when x=y=0 and z=α=1, p and q are greater than zero; and when x=y=z=0, p and q are not simultaneously zero. The first part of this material system is is denoted herein as “CCT material system”. The second part is a variation of BST material system. Therefore the material system with the representation α[Ca 1-x-y Ba x Sr y (Ca 1-z Cu z )Cu 2-p La 2p/3 Ti 4-q M q O 12-δ ]+(1−α)[Ba r Sr 1-r TiO 3 ] will be henceforward referred to as “CCTBST material system” for simplicity.

As used herein in the CCTBST material system, the representation Ca 1-x-y Ba x Sr y (Ca 1-z Cu z )Cu 2-p La 2p/3 Ti 4-q M q O 12-δ and α[Ca 1-x-y Ba x Sr y (Ca 1-z Cu z )Cu 2-p La 2p/3 Ti 4-q M q O 12-δ ]+(1−α)[Ba r Sr 1-r TiO 3 ] are theoretical formulae including the mixtures and compounds that are in the specified ratio to be denoted by these formulae, and do not necessarily mean that a single compound exists in a form that can be identified by standard characterization techniques. In short, a material specified by the above formulae may actually exist as multiple phases which, taken collectively, have an overall composition as specified by the formulae.

In general, the cation dopants were found to increase resistance of the grain boundary by absorbing the oxygen vacancies and thereby decrease both the dielectric constant and loss tangent. By doping at cation site, the doped cation gets reduced by absorbing electron density at the grain boundary, thereby decreasing conduction of the grain boundary, thus leading to the decrease in dielectric constant and loss.

In general, by doping at the anion site, the cation of the lattice gets reduced by absorbing the electron density thereby creating insulating planar defects in the grains. The insulating planar defects can reduce the electrical resistivity of internal barrier of the grains and thereby decrease the dielectric loss.

In the BST material system, the barium and strontium levels were varied and studied for their effects on favorable dielectric properties. Thus, in one embodiment, a BST material system is provided such that 0.9≦(x+y)≦1. Therefore, in this embodiment, the calcium doping is comparatively less as seen in the example Ba 0.55 Sr 0.4 Ca 0.05 Ti 1-z Cr z O 3-δ A p . In a further embodiment, 0.3≦x and (x+y)=1. Therefore, in this embodiment the BST material system does not contain calcium or any other dopants in the barium or strontium sites. Example of the above BST material system includes, but is not limited to, Ba 0.3 Sr 0.7 Ti 1-z Cr z O 3-δ A p .

In one embodiment of the BST material system, the titanium is partially replaced by chromium, which may help to decrease the loss tangent. In one embodiment, the chromium is substituted for less than about 2 atomic % of titanium in the BST material system. In a subsequent embodiment, the chromium substitution is in the range of about 0.01 atomic % to about 1 atomic %. Thus, in this embodiment, the quantity z in the formula above varies between about 0.0001 and about 0.01. In a further embodiment, the chromium substitution is in the range of about 0.2 atomic % to about 1 atomic % of titanium with the z value varying between about 0.002 and about 0.01.

In one embodiment, 0<z≦0.01 and (x+y)=1 in a BST material system. Therefore, in this embodiment, there is a certain level of chromium substitution at the titanium sites. An example for this system includes Ba 0.3 Sr 0.7 Ti 0.99 Cr 0.01 O 3-δ A p . In one embodiment, in a BST material system, z>0, and δ and p are both equal to 0. In this embodiment, the BST material system comprises cation substitutions, but not anion substitutions. Examples of the above BST material systems include, but are not limited to, Ba 0.3 Sr 0.7 Cr 0.002 Ti 0.998 O 3 , Ba 0.3 Sr 0.7 Ti 0.995 Cr 0.005 O 3 , and Ba 0.4 Sr 0.6 Ti 0.998 Cr 0.002 O 3 .

In a BST material system, when titanium is substituted with a trivalent cation, such as chromium in the above example, the oxygen level can also stoichiometrically change. For instance in the system Ba 0.3 Sr 0.7 Cr 0.002 Ti 0.998 O 3 , the number of oxygen atoms can be 2.999, instead of 3, to accommodate substitution of 0.002 atoms of chromium. In one embodiment, in the BST material system, the barium or strontium is partially replaced by calcium and titanium is partially replaced by chromium. Examples of the above BST material systems include, but are not limited to, Ba 0.55 Sr 0.4 Ca 0.5 Cr 0.002 Ti 0.908 O 3 .

Table 1 below represents some examples of the BST material systems and their dielectric properties with the varying levels of barium and strontium and with some cation dopants.

In one embodiment of the power transfer system with a BST material system, the oxygen is partially replaced through anion doping. Nitrogen and fluorine are two examples of anion dopants used to substitute for oxygen. Oxygen in the BST material system may be substituted by nitrogen and fluorine individually or in a combination. In one embodiment, oxygen is substituted by nitrogen or fluorine such that 0≦δ≦1; and 0≦p≦1 in the BST material system. Therefore, in one embodiment, the anion substitution is such that about 25% or less of oxygen in the BST material system is substituted by anion. In one embodiment, depending on the process conditions, the nitrogen is in an oxidation state of −3 while substituting for oxygen in the BST material system. In one embodiment, the oxygen is substituted by an anion such that 0≦δ≦1 and 0≦p≦0.8. In one embodiment, the substitution replaces less than about 10 atomic % of oxygen in the BST material system. In one embodiment, the oxygen is substituted by anion such that 0<δ≦0.5 and 0<p≦0.4 and in a further embodiment, the substitution is such that 0.1≦δ≦0.5 and 0.1≦p≦0.4.

In one embodiment of the BST material system, oxygen is substituted by another anion such that z=0, and 0.1≦δ≦0.5 and 0.1≦p≦0.4. Thus in this embodiment, the anion substitutions are conducted in the absence of titanium substitution. A non-limiting example for this system can be represented by Ba 0.3 Sr 0.7 TiO 2.8 N 0.13 . This material shows an extremely low dielectric loss of about 0.0001 with a suitable dielectric constant of about 506 at the frequency of about 2.5 MHz.

In one embodiment, the oxygen is substituted by fluorine such that 0<δ≦1; and 0<p≦0.4. In a further embodiment, the oxygen is substituted by fluorine such that 0.1≦δ≦1; and 0.1≦p≦0.4. In one embodiment, depending on the process conditions, the fluorine is in an oxidation state of −1 while substituting for oxygen in the BST material system. In another embodiment, the oxygen is substituted by both nitrogen and fluorine such that 0.1≦δ≦0.5 and 0.05≦p≦0.3.

In one example, the inventors incorporated fluorine into the BST material system by varying the starting materials for preparation of BST material system and noted a decrease in the loss tangent as a result. A Ba 0.4 Sr 0.6 TiO 3 material was prepared by using BaF 2 and SrF 2 as the source of barium and strontium respectively. By starting with the fluoride sources for barium and strontium, it is expected that some of the fluorine will be substituted for oxygen, thus changing the dielectric values of the BST materials system. The Ba 0.4 Sr 0.6 TiO 3 prepared by using BaF 2 and SrF 2 showed a dielectric loss factor less than about 0.01 over the entire frequency range from 100 Hz to 10 MHz with a minimum of 0.0001 at 1.4 MHz. The material also showed a uniform dielectric constant of about 415 over the entire frequency range mentioned above. The material may be advantageously used for applications that require frequency independent operation.

In one embodiment, the BST material system is doped with both cations and anions. Thus, in one embodiment, titanium is partially replaced by chromium and oxygen is partially replaced by anions such that z, δ and p are all greater than zero. In a further embodiment, 0<z≦0.01, 0<δ≦0.5, and 0<p≦0.4. Examples of these systems include Ba 0.3 Sr 0.7 Ti 0.995 Cr 0.005 O 2.8 N 0.13 and Ba 0.4 Sr 0.6 Ti 0.995 Cr 0.005 O 2.8 N 0.13 . The material represented by Ba 0.4 Sr 0.6 Ti 0.995 Cr 0.005 O 2.8 N 0.13 demonstrates a loss tangent of about 0.003 with a dielectric constant of about 819 at the frequency of about 3.13 MHz. In a further embodiment, 0<(x+y)<1 and z, δ, and p are all greater than zero such that calcium dopant is present in the barium or strontium site, chromium partially substitutes titanium, and nitrogen and/or fluorine partially substitutes oxygen. Table 2 provides dielectric values of some of the anion-doped materials in the BST material system with and without cation dopants.

As presented earlier, in one embodiment, a CCTBST material system is provided with a combination of CCT material system and BST material system such that α[Ca 1-x-y Ba x Sr y (Ca 1-z Cu z )Cu 2-p La 2p/3 Ti 4-q M q O 12-δ ]+(1−α)[Ba r Sr 1-r TiO 3 ], wherein M is aluminum, chromium, zirconium, or combinations thereof, and 0≦x≦0.1, 0≦y≦1, 0≦z≦1, 0≦p≦0.1, 0≦q≦0.1, 0≦δ≦0.05, 0≦r≦1, and 0.5≦α≦1, with a proviso that when x=y=0 and z=α=1, p and q are greater than zero; and when x=y=z=0, p and q are not simultaneously zero. Thus, in one embodiment comprising CCTBST material system to be used in the field-focusing element 18 , x and y are both equal to zero and z=1, and the copper is partially replaced by other suitable cations such as, for example, lanthanum. Further, the titanium is partially replaced by aluminum, chromium, zirconium, or any of their combinations. In one embodiment, any or all of the above mentioned replacements coexist. When x=y=0, the CCTBST material system will not have barium and strontium substitution in the calcium place. When α=1, the CCTBST material system becomes CCT material system. When z=1, the number of copper atom present, including lanthanum substitution, in the CCTBST material system is about 3. Thus the proviso that of when x=y=0 and z=α=1, p and q are greater than zero denotes a CaCu 3 Ti 4 O 12 system with substitution in copper and titanium sites. The lanthanum substitution at the copper site of CaCu 3 Ti 4 O 12 may vary such that 0<p≦0.1. Similarly titanium can be substituted by aluminum, chromium, zirconium, or any combination such that 0<q≦0.1. Depending on the valence states of titanium site substitutions, the oxygen may be stoichiometric or non-stoichiometric. Therefore, in the above system δ varies such that 0≦δ≦0.05. Examples include CaCu 2.9 La 0.067 Ti 3.99 Zr 0.01 O 12-δ and CaCu 3 Ti 3.92 Cr 0.02 Al 0.06 O 12-δ . Table 3 lists some of the properties of the substituted CaCu 3 Ti 4 O 12 material.

In one embodiment, when x=y=z=0 and α=1, the CCTBST material system approaches substituted Ca 2 Cu 2 Ti 4 O 12 . The substitution can be at the copper site, at the titanium site or the combination of copper and titanium substitutions. In one embodiment, Ca 2 Cu 2 Ti 4 O 12 is a material in the CCT material system of the field-focusing element 18 with about 33.3 mole % of CaCu 3 Ti 4 O 12 and about 66.7 mole % of CaTiO 3 . This material, in the doped form exhibits some good dielectric properties. Examples for the substituted Ca 2 Cu 2 Ti 4 O 12 with good dielectric properties include Ca 2 Cu 2 Ti 3.94 Al 0.06 O 12-δ and Ca 2 Cu 2 Ti 3.98 Cr 0.02 O 12-δ . Further examples along with their dielectric properties can be seen from the Table 4.

In one embodiment, in the power transfer system comprising a CCTBST material system, x>0. In a related embodiment, y>0. In one further embodiment, x>0 and y>0. In an exemplary embodiment, x>0 and y>0 along with z=α=1 and p=q=0. Thus, in the above embodiments, calcium is partially replaced by barium and/or strontium and the CCTBST material system approaches CCT material system. One example of a CCT material system prepared with barium and strontium dopants and demonstrating very good dielectric properties is Ba 0.01 Sr 0.2 Ca 0.79 Cu 3 Ti 4 O 12 . This material has a substantially uniform dielectric constant and loss tangent values over a wide range of frequency ranges, which makes this material useful for an application that will work over a variable range of frequencies. The dielectric constant for the material Ba 0.01 Sr 0.2 Ca 0.79 Cu 3 Ti 4 O 12 lies in the range of about 4500-5000 and the loss tangent is in the range of about 0.06 to 0.08 for the entire frequency range from about 1 kHz to about 100 k Hz. The material is suitable for contactless power transmission at any frequency lying in the range of about 1 kHz to 100 kHz. Another example for the CCT materials with x>0 and y>0 along with z=α=1 and p=q=0, exhibiting good dielectric properties include Ba 0.01 Sr 0.1 Ca 0.89 Cu 3 Ti 4 O 12 .

The examples presented herein depict the different CCT material systems with their approximate measured dielectric constant and loss tangent values. While some particular examples are presented herein, the variations in the dopant combinations and levels will be appreciated by one skilled in the art.

In one embodiment of the CCTBST material system, when 0.5≦α<1, the dielectric material comprises (1−α)[Ba r Sr 1-r TiO 3 ], along with the CCT material system. The CCTBST material of this form can be mixtures or coexistence of the CCT and BST material systems with the above mentioned formula limitations, but some of the materials of this system were found to be increasing favorable dielectric properties that are not predicted by rule of mixtures. One example of this dielectric material is (0.6CaCu 3 Ti 4 O 12 +0.4SrTiO 3 ). Individually while CaCu 3 Ti 4 O 12 has a dielectric value >6000 at the frequency range of about 10 kHz to about 35 kHz, the loss tangent value is around 0.1. The dielectric constant and loss tangent values of SrTiO 3 at this frequency range are about 70 and 0.26 respectively. However, the combination (0.6CaCu 3 Ti 4 O 12 +0.4SrTiO 3 ) has a dielectric constant value greater than about 7000 and the loss tangent value less than about 0.09 at the frequency range from about 10 kHz to about 35 kHz. Another example of this dielectric material is (0.6CaCu 3 Ti 3.94 Al 0.06 O 11.97 +0.4SrTiO 3 ). This combination has a dielectric constant value greater than about 9000 and the loss tangent value less than about 0.09 at the frequency range from about 1 kHz to about 10 kHz. One more example of this material system includes (0.6CaCu 3 Ti 3.98 Cr 0.02 O 12-δ +0.4SrTiO 3 ).

The inventors further conducted experiments on the dielectric materials by treating the materials in different atmospheres such as an oxygen-rich atmosphere, a nitrogen atmosphere, a chromium atmosphere, or a reducing atmosphere such as a hydrogen atmosphere, for example. An oxygen-rich atmosphere, for example, is able to effect changes in the dielectric properties of CCT, BST, and therefore CCTBST family materials. It is observed that in the CCT family materials, sintering in the oxygen atmosphere compensates the oxygen vacancies in the materials, thus leading to lower dielectric constant and lower loss tangent. In the BST material system, sintering in the oxygen atmosphere increases the density of materials and thus increases the dielectric constant. Sintering in nitrogen atmosphere is expected to take out some of the oxygen from the materials, thus turning the material oxygen deficient, increasing the oxygen vacancies and electron densities, and leading to high dielectric constant and increased loss tangent. Sintering in chromium atmosphere is expected to accommodate a small level of chromium in the material as a substitution or in the interstitials, thus changing the material dielectric properties. For example, a sintered sample of CaCu 3 Ti 4 O 12 in Cr atmosphere has yielded higher dielectric constant and lower loss tangent of 0.033 as compared to the CaCu 3 Ti 4 O 12 sintered in air. This decrease in loss tangent is believed to be the result of chromium doping. In one embodiment, the amount of chromium incorporated is less than about 0.01 mol % of the material. In a particular embodiment, the amount of chromium incorporated in the material by sintering in chromium atmosphere is in ppm levels.

In one experiment, BST materials were subjected to cold isostatic pressing (CIP) and also were sintered in oxygen atmosphere for obtaining better dielectric values. Examples include, but not limited to, Ba 0.55 Sr 0.4 Ca 0.05 Cr 0.01 Ti 0.99 O 3 sintered in oxygen atmosphere at about 1440° C. for 2 hours that has a dielectric constant value greater than about 1300 and the loss tangent value less than about 0.001 in the frequency of about 4.95 kHz.

In one embodiment, a dielectric component comprising BST or CCTBST material systems described in above paragraphs is presented. In one embodiment, a system comprising a dielectric component that comprises the BST or CCTBST materials system is presented.

In one embodiment, the dielectric materials exist in the bulk material form and are polycrystalline, with grains and grain boundaries. Increased grain boundary conduction in BST or CCTBST material system may increase both dielectric constant and loss tangent. For example, a metallic precipitate at the grain boundary creates electrostatic potential due to the metal and electron interface, thereby increasing grain boundary conduction and, consequently, the dielectric constant and loss tangent.

In one embodiment, any of the materials described above is doped with a bismuth-containing material, such as bismuth oxide. In a further embodiment, bismuth exists in a metallic phase in the grain boundaries of the polycrystalline materials used for field-focusing element. In a related embodiment, bismuth oxide is doped and reduced to become metallic bismuth in the grain boundaries of the dielectric material. In one embodiment, the bismuth oxide is introduced to the grain boundaries by mixing Bi 2 O 3 and TiO 2 with the calcined BST powders before forming the BST materials into the bulk form that is incorporable into a component, and sintering.

In one embodiment, less than about 3 mole % of Bi 2 O 3 .3TiO 2 is present the CCT material system. The CCT material system doped with Bi 2 O 3 .3TiO 2 show very good temperature stability up to about 700° C. along with reasonable voltage tunability as will be further demonstrated in the examples and figures below. Temperature stable dielectric materials are advantageous in preparing devices that work efficiently regardless of temperature variations. Applications of temperature-stable dielectric materials include, but are not limited to, high temperature stable devices including sensors, multilayer ceramic capacitors, and dielectric absorbers. For example, the dielectric materials described above may be used as the robust absorption materials of electromagnetic waves in industries such as aviation so that the airplane is not easily detected by the radar system.

In one embodiment, less than about 3 mole % of Bi 2 O 3 .3TiO 2 is present the BST material system. In one embodiment, the BST material system has a metallic bismuth phase in the grain boundaries. It is found that the dielectric constant of the BST material system increases significantly by having a metallic bismuth phase in the grain boundaries. In some instances, the increment in dielectric constant value of the BST material system by disposing metallic bismuth in the grain boundary was more than about two orders of magnitude. The BST material system with grain boundary bismuth precipitation, the material is temperature stable up to about 200° C. while exhibiting an enhanced voltage tunability showing variations in the dielectric constant at low levels of voltage such as up to about 5 volts.

The voltage tunable characteristic of a dielectric material system is useful in many applications such as, but not limited to, varactor diode replacement, tunable capacitors with low losses, tunable filters, phase shifters, multiplexers, voltage control oscillators, tunable matching network for power amplifiers, low noise amplifiers, thermoelectric effect including power systems, general impedance matching network, wireless communication antennas and inverted F-antenna that is tuned using a ferroelectric capacitor, phased array antennas made using dielectric thick films, ferroelectric varactors for capacitive shunt switching, liquid crystal displays, limiters of electromagnetic waves and more particularly to RF waves, spatial light modulator, thermodynamically stable substrate type materials for electronic semiconductor devices, optical switches using ferroelectric liquid crystal displays, radio frequency phase shift devices or the devices capable of producing a continuous, reciprocal, differential RF phase shift with a single control voltage, tunable radio frequency (RF) microelecromechanical system (MEMS) capacitive switches and electrically tunable delay line.

Examples for the BST materials that had grain boundary doping, and that show desirable dielectric properties, include Ba 0.3 Sr 0.7 Cr 0.002 Ti 0.998 O 3 doped with about 1 mole % Bi 2 O 3 .3TiO 2 . This material showed a dielectric constant of about 7668 with a dielectric loss of about 0.007 at about 1.4 MHz. Another example of a dielectric material with both cation and grain boundary doping is Ba 0.3 Sr 0.7 Cr 0.005 Ti 0.995 O 3 doped with about 1 mole % Bi 2 O 3 .3TiO 2 . This material demonstrates a very high dielectric constant of greater than about 3,470,000 at the frequency of about 100 Hz. However, this material has a high loss tangent value of about 1 that may limit the application of the material in high power transfer application.

In one embodiment, a BST material system having an anion doping is further doped with grain boundary dopants. In one embodiment, oxygen is partially replaced by nitrogen and bismuth was disposed in the grain boundaries. An example of a BST material that had both anion doping and grain boundary doping, and that showed desirable dielectric properties, includes Ba 0.3 Sr 0.7 TiO 2.8 N 0.13 doped with about 1 mole % Bi 2 O 3 .3TiO 2 . The above-mentioned material showed an extremely high dielectric constant of about 1,793,610 at the frequency of about 100 Hz. However, this material had a loss tangent of about 1. This material can be used for low power transfer systems. Further, experimenting on different substitution or methods for bringing down the loss tangent value may result in a more suitable material to be used in other multiple applications including high power transfer applications.

In one embodiment, a BST material system doped with cations, anions, and grain boundary dopants is presented. In one embodiment, titanium is partially replaced by chromium, oxygen is partially replaced by nitrogen, and metallic bismuth is disposed in the grain boundaries. One example of a material having cation, anion, and grain boundary dopants in the BST material system is Ba 0.3 Sr 0.7 Cr 0.005 Ti 0.995 O 2.8 N 0.13 with about 1 mole % of Bi 2 O 3 .3TiO 2 . This material showed an extremely high dielectric constant greater than about 63,000 and dielectric loss tangent of about 0.006 at a frequency of about 150 kHz. Therefore, this material is very suitable in multiple dielectric applications.

In one experiment, BST material system was densified by cold isostatic pressing before sintering. In a further embodiment, the material was also doped with the bismuth oxide in the grain boundary and the bismuth oxide was reduced to metallic bismuth by reducing atmosphere treatment such as 5% hydrogen in nitrogen at about 1200° C. for about 12 hours. In one embodiment, a bismuth doped BST material system is presented. The examples include the materials such as Ba 0.4 Sr 0.6 Cr 0.01 Ti 0.99 O 3 +1 mole % Bi 2 O 3 .3TiO 2 and Ba 0.4 Sr 0.6 Cr 0.01 Ti 0.99 O 3 +1 mole % Bi 2 O 3 .3TiO 2 . The above-mentioned materials demonstrate extremely high dielectric constant of greater than about 11,030,000 at a frequency of about 100 Hz. However, the dielectric loss tangent of the materials has a somewhat high value of about 0.9 at a frequency of about 100 Hz. These materials may be useful in applications where a high dielectric constant is of high importance while the high loss tangent values can be accommodated such as in low power transfer applications, for example.

In some applications, it is desirable to employ dielectric materials whose dielectric properties such as dielectric constant and/or loss tangent are stable over a certain temperature range around room temperature to accommodate the changes in temperature due to, for example, environmental or operational changes. In one embodiment, the dielectric materials are beneficial if their dielectric properties are substantially stable from about −50° C. to about 150° C. “Substantially stable” as used herein indicates that the dielectric properties of the materials do not change more than about 10% of their room temperature values over a given temperature range. In one embodiment, the dielectric materials presented herein are having their dielectric properties substantially stable from about −15° C. to about 120° C. In a further embodiment, the dielectric materials have dielectric properties that are substantially stable from about −20° C. to about 60° C. In one embodiment, the BST and CCTBST materials presented here are ceramic materials stable over a wide temperature range and having dielectric properties that are stable around room temperatures.

In some applications, it is desirable to employ dielectric materials whose dielectric properties such as dielectric constant and/or loss tangent are stable over a certain voltage range to accommodate the applications that may have certain variations in voltages. In one embodiment, the dielectric materials are beneficial if their dielectric properties are substantially stable up to about 200V. “Substantially stable” as used herein indicates that the dielectric properties of the materials do not change more than about 10% over a given voltage range. In one embodiment, the dielectric materials presented herein are having their dielectric properties substantially stable up to about 150V. In a further embodiment, the dielectric materials have dielectric properties that are substantially stable up to about 100V.

In some applications, it is desirable to employ dielectric materials whose dielectric properties such as dielectric constant and/or loss tangent vary with voltage variations to accommodate the applications that may need variable dielectric properties at varied voltages. The variation of dielectric properties may be any function of voltage variations including directly proportional, inversely proportional to voltage variation.

The following examples illustrate methods, materials and results, in accordance with specific embodiments, and as such should not be construed as imposing limitations upon the claims. All components are commercially available from common chemical suppliers.

Preparation of Materials:

A general method of preparation followed for the BST, CCT, and CCTBST material systems identified in different examples are outlined below. However, one skilled in the art would appreciate that small variations in the starting materials; temperatures, times, and atmospheres of preparation, calcination, and sintering; size and shape variations of the prepared powders and bulk materials could be accommodated to the examples presented below.

Preparation of Doped CCT and BST Material Systems

Stoichiometric concentrations of CaCO 3 , CuO and TiO 2 were mixed and ball-milled in dry conditions and calcined at 1000° C. for 24 hours in air. The calcination temperatures and atmospheres were varied for some materials to investigate the effect of temperatures and atmospheres. BaCO 3 , SrCO 3 , Cr 2 O 3 , Al 2 O 3 , La 2 O 3 , ZrO 2 were added in the required mole percents by solid state mixing for doping barium, strontium, chromium, aluminum, lanthanum, and zirconium dopants respectively, whenever required. About 1 mole % of Bi 2 O 3 .3TiO 2 was added for grain boundary doping. Urea was used for nitrogen doping in oxygen sites by solid state mixing and calcining Stoichiometric amounts of BaF 2 , SrF 2 , and/or CaF 2 were used as starting materials for including a fluorine dopant in the oxygen site.

The calcined mixture was added with about 2 wt % polyvinyl acetate (PVA) and mixed thoroughly using an agate mortar. The mixture was further milled using ball milling in isopropanol medium. The powders were pressed into green pellets using hydraulic pressing with a pressure of 4 MPa followed by 6 MPa. For obtaining cold isostatic pressed (CIP) pellets, a CIP machine was used to further densify the hydrostatically pressed pellets. The pellets were then sintered at 1050° C., 1100° C., 1350° C., or 1440° C. for 2, 12, or 24 hours in air, oxygen, chromium, or nitrogen atmosphere, as required. 5% hydrogen in nitrogen atmosphere was used for reducing bismuth oxide to metallic bismuth during sintering. The sintered pellets were coated with silver paste for the purpose of dielectric measurement. The dielectric measurements were carried out using an Agilent 4294A impedance analyzer and verified using a Novocontrol Alpha-K impedance analyzer. XRDs of the calcined and sintered samples were verified. While the general method for the preparation, processing and dielectric value measurements of materials are outlined above, the examples provided below contain the specific details of preparation, processing, measurements, and results of some of the selected materials.