Ceramic core inductor component

Abstract

A ceramic core inductor component comprising: a ceramic core including a ceramic body portion disposed between first and second ceramic spacers, the ceramic core having a dielectric constant of less than 8; a conductive coil disposed around the ceramic body portion; and a first terminal disposed on a first surface of the first ceramic spacer and a second terminal disposed on a second surface of the second ceramic spacer, a first end portion of the conductive coil being electrically connected to the first terminal and a second end portion of the conductive coil being electrically connected to the second terminal.

Description

The present disclosure relates generally to non-magnetic inductor components, and more particularly to ceramic core inductor components for radio frequency (RF) applications configurable for mounting on a printed circuit board.BACKGROUNDCeramic core inductor components are typically integrated into smaller and smaller electrical circuits and host devices for use in certain radio frequency (RF) applications where reduced size and power are of greatest importance. Such applications include, but are not limited to, portable communication devices, laptops, military and commercial aircraft, and spacecraft. For these and other applications, ceramic core inductors generally have better performance than ferrite core inductors. The better performance is largely attributable to the low permeability of the ceramic core. Ceramic core inductors store energy more efficiently, have a higher Q factor (Q), a higher self-resonant frequency (SRF), and better temperature stability than ferrite core inductors. Nevertheless, there is a constant need for further performance improvements in ceramic core inductor components.BRIEF DESCRIPTION OF THE DRAWINGSThe objects, features and advantages of the present disclosure will become more apparent upon consideration of the following detailed description and the appended claims taken in conjunction with the accompanying drawings. The drawings show only representative embodiments and implementations and are not to be considered as limiting the application of the teachings of the disclosure or the invention, the scope of which is defined by the appended claims. FIG. 1 is a perspective view of a representative ceramic core inductor component. FIG. 2 is a side view of the component of the inductor of FIG. 1. FIG. 3 is a partial cross-sectional side view of the inductor component of FIG. 2. FIG. 4 is a bottom view of the component of the inductor of FIG. 2. FIG. 5 is a representative ceramic core blank. FIG. 6 is an end view of the ceramic core blank of FIG. 5. Figure 7 is an alternative ceramic core blank. FIG. 8 is a side view of the ceramic core blank of FIG. 7 including electrical terminals formed on spacers. FIG. 9 is a bottom view of the ceramic core blank of FIG. 8. FIG. 10 shows comparative Q-factor-to-frequency plots for 1 micro-Henry (μH) ceramic core inductor components of the prior art and the present disclosure. FIG. 11 shows comparative inductance-to-frequency plots for the 1 μH ceramic core inductor components of FIG. 10. FIG. 12 shows comparative Q-factor-to-frequency plots for 470 nano-Henry (nH) ceramic core inductor components of the prior art and the present disclosure. FIG. 13 shows comparative inductance-to-frequency plots for the 470 nH ceramic core inductor components of FIG. 12. FIG. 14 shows comparative Q-factor-to-frequency plots for 12 nano-Henry (nH) ceramic core inductor components of the prior art and the present disclosure. FIG. 15 shows comparative inductance-to-frequency plots for the 12 nH ceramic core inductor components of FIG. 14.Those skilled in the art will understand that the drawings are illustrated for simplicity and clarity and may therefore not be drawn to scale and have no known features, that the order of occurrence of acts or steps may vary from the described representative order, that some or all of these acts or steps may be performed simultaneously unless otherwise stated, and that the terms and expressions used herein have a meaning that is understood by those skilled in the art unless expressly assigned a different meaning.DETAILED DESCRIPTIONThe disclosure generally relates to ceramic core inductor components for radio frequency (RF) applications that have improved performance. The ceramic core inductor components described herein are suitable for use in filters, low noise amplifiers (LNAs), power supplies, oscillators, impedance matching circuits, servos and other regulators, as well as a variety of other electrical circuits. Such circuits are found in space and terrestrial communication systems, radar systems, and automotive, medical, industrial and entertainment electronics, among many other systems and applications.The ceramic core inductor components described herein generally include a conductive coil wound around a ceramic core. In FIGS. 1-3, a representative inductor component 100 includes a ceramic core 110 that carries a conductive coil 120 wound around a body portion of the ceramic core between first and second spacers of ceramic. The conductive coil includes end portions electrically connected to corresponding electrical terminals (also referred to herein as "terminals") integrated with the ceramic core. These and other aspects of ceramic core inductor components are further described herein.The ceramic core inductor components described herein have a dielectric constant (κ) selected to reduce parasitic losses (e.g., parasitic capacitance), thereby improving the performance of the inductor. The improved performance is characterized by a higher quality factor (Q) and a higher natural resonant frequency (SRF) than in comparable inductors with a ceramic core according to the prior art. The Q factor is a ratio of inductive reactance to a resistance of the inductor, XL / RL, where the inductive reactance is a function of inductance L and parasitic capacitance. The higher SRF is due to the lower parasitic capacitance.Dielectric constant is a material property taken into account in the design of capacitors and not inductors. However, the inventors herein have recognized that the natural resonant frequency (SRF) of ceramic core inductors has a reverse relationship to the dielectric constant (κ) of the ceramic core and that appropriate selection of the ceramic core based on the κ value may improve the performance of the inductor.Representative ceramic core inductor components described herein and having a κ value of 8 or less have an improved Q factor (Q) and SRF, as compared to prior art ceramic core inductors having higher κ values. Representative ceramic cored inductors and ceramic compositions therefor are described herein.In FIGS. 5-6, a representative ceramic core blank 122 includes a body portion 112 between first and second flanges 114 and 116 that extend radially beyond a periphery 113 of the body portion. Each flange or portion thereof includes a mounting surface that forms a spacer for mounting on a main mounting surface 102. In FIG. 5, spacers 124 and 126 each include a corresponding end surface 115 and 117 on which the electrical terminals may be placed as described below. Alternatively, the terminals may be disposed on a portion of the ceramic core away from the spacers 124 and 126.The body portion and the radial flanges may both have a polygonal cross-section, for example a square cross-section as shown in FIG. 6. In other implementations, both the body portion and the flanges may have a circular cross-section, and one or more planar surfaces for surface mounting or for electrical connections as described herein may be provided on each flange. Alternatively, the body portion may have a circular cross-section and the flanges may have a polygonal cross-section. In still other implementations, the ceramic core blank does not have flanges extending radially outward from the body portion.In FIG. 7, an alternative ceramic core blank 128 includes a body portion 112 disposed between first and second flanges and including respective spacers 124 and 126 having respective mounting surfaces 115 and 117. The alternative ceramic core blank 128 comprises a quadrilateral polygonal cross section and the spacers extend over a peripheral portion 113 from at least one side of the body portion.The ceramic cores of FIGS. 5-9 may include other shapes and configurations and may be formed by isostatic or mechanical pressing or by casting, among other known and future ceramic operations, before being fired.The constituents of the composition of the ceramic core generally depend on the required performance characteristics of the component of the inductor. The ceramic core may comprise one or more of the following elements: calcium strontium tungstate, magnesium silicate, magnesium aluminate, magnesium aluminum silicate, calcium silicate, zinc silicate, aluminum silicate or silicon dioxide or a combination of two or more thereof, alone or in combination with other elements or compounds. Each of the above elements or compounds has a dielectric constant (κ) of 8 or less. Aluminum silicate, magnesium aluminum silicate and silicon dioxide each have a dielectric constant of 6 or less. Magnesium aluminum silicate and silica have a dielectric constant of 5 or less.In a particular implementation, the ceramic core comprises, by weight, greater than five percent (5%) of each of the following: magnesium aluminum silicate, magnesium silicate, and magnesium aluminate. In a more specific implementation, the ceramic core comprises, by weight, greater than fifteen percent (15%) magnesium aluminum silicate, greater than five percent (5%) magnesium aluminate, and greater than ten percent (10%) magnesium silicate, wherein the ceramic core has a dielectric constant of 6 or less. In these and other implementations, the ceramic core may optionally include other ingredients, for example fillers or additives.In an alternative implementation, the ceramic core comprises by weight each of the following elements: between 41-54% silica; between 27-38% alumina; between 10-17% magnesia, wherein the ceramic core has a dielectric constant of 5 or less. Other components of this alternative composition may include as much as 12% tin oxide, as much as 7% titanium oxide, and as much as 2% lanthanum oxide, among other additives. These or other additives to the composition of the ceramic core can easily increase the dielectric constant, possibly to more than 5.The conductive coil includes end portions electrically connected to corresponding electrical terminals integrated with the ceramic core. The terminals may be configured as metalized or other conductive pads located on corresponding spacers or on other portions of the ceramic core depending on how the component is electrically integrated (e.g., mounted) into the host device. In FIGS. 8-9, the first and second terminals 130 and 132 are formed on the end surfaces (shown in FIGS. 5 and 7 ) of the first and second spacers. FIGS. 2-4 illustrate various views of the electrical terminals 130 and 132. Each electrical terminal may optionally wrap around and cover a lateral wall portion of the corresponding spacer to increase the contact area between the terminals and the ceramic core, as shown in FIGS. 2-3 and 8-9. In FIGS. 8-9, the terminals 130 and 132 at the end surfaces of the spacers represent mounting surfaces. Configured in this manner, the ceramic core inductor component may be electrically and mechanically integrated with a host device (e.g., a printed circuit board) by reflow or wave soldering or other electrical and mechanical operation.In other implementations, the electrical terminals may be disposed on a surface of the ceramic core other than the mounting surface. Configured, the mounting surface of the ceramic core inductor component may be mechanically attached to the host device (e.g., by a bonding material), and the electrical terminals located on different portions of the ceramic core may be electrically integrated with the host device by a wire bond, solder, or other conductive connection means.In one implementation, the electrical terminals include a conductive base layer that is coated with one or more conductive outer layers. The base layer may comprise silver or another highly conductive metal or alloy. In one implementation, the base layer includes a silver frit (Ag) ("silver frit") applied to selected portions of the ceramic core (e.g., the surfaces of the spacers). Alternatively, other conductive tracks can also be used. The base layer may be dip coated or deposited on the ceramic core in another known or future operation.An outermost conductive layer may be formed directly on the base layer or on an intermediate conductive layer. The composition of the outermost conductive layer may be selected to improve the solderableness (e.g., improved wetting) and oxidation protection, among other properties of the terminal. In one implementation, the outermost conductive layer is made of tin (Sn) or a tin-based alloy (e.g., SnPb). Alternatively, other conductor materials may be used. The conductive outermost layer may be deposited on the base layer or on the intermediate layer in a galvanic operation, among other known or future methods.In some implementations, an intermediate conductive layer is located between the base layer and the outermost conductive layer to protect the base layer. The intermediate layer can have a higher melting temperature than the base layer, for example. In one implementation, the intermediate layer comprises copper (Cu). Alternatively, the intermediate layer can also consist of nickel (Ni) or another conductor or an alloy. The conductive intermediate layer may be deposited on the base layer in a galvanic operation, among other known or future methods.In other implementations, the electrical terminals comprise a silver-platinum-palladium alloy (AgPtPd) deposited on selected portions of the ceramic core. Alternatively, other platinum group metals or alloys may be used. Representative low melting point solders developed for terminals of surface-mountable components and including such alloys include Sn62-type solders, among others. The electrical terminals may be deposited on the ceramic core by dipping or other known or future operation.The conductive coil may comprise a solid wire or a hollow core wire. In one implementation, the conductive coil is formed from a solid copper wire, among other good conductors. In another implementation, the conductive coil includes a copper-free (e.g., aluminum) inner core coated with copper or silver. The wire may optionally comprise a non-conductive outer sheath, for example enamel, for electrical insulation. The wire may be wound around the ceramic core after the formation of the terminal in a coil operation. The end portions of the conductive coil may be connected to the corresponding terminals by a spot or other welding operation, by soldering, wire bonding, or other electrical operation. In some implementations, the end portions of the conductive coil are flattened prior to electrical integration. In FIG. 4, each end portion 121 and 123 of the conductive coil 120 is electrically integrated with the corresponding terminals 130 and 132 located on the end surface of the corresponding spacer.The ceramic core inductor components described herein may be configured for surface mounting or other integration into the host device. In FIG. 2, the first and second spacers are arranged such that an axis of the conductive coil is aligned parallel to the mounting surface 102 of the host when the ceramic core inductor component 100 is mounted on the mounting surface. The first and second spacers 124 and 126 are sized such that the conductive coil is spaced from the mounting surface when the ceramic core inductor component is mounted on the mounting surface.In some implementations, the ceramic core inductor component includes a non-conductive handle to enable automated assembly and other component handling operations. The non-conductive handle covers at least a portion of the inductor component. In FIGS. 2-4, the ceramic core inductor components 100 include a non-conductive handle 136 located on a portion of the ceramic core opposite the spacers. In other implementations, the non-conductive handle covers all portions of the inductor component except for the electrical terminals. The non-conductive handle may comprise an epoxy, plastic, resin, or other non-conductive material. The non-conductive handle may be applied after the coil is placed around the ceramic core by dipping, spraying or other operation.Representative dimensions for the ceramic core inductor components described herein are set forth in Table I below. The "size" refers to the length and width dimensions of the mounting surface of the component. The sizes disclosed below are typical of surface-mountable components and are not intended to limit the scope of the disclosure. In other implementations, the ceramic cored inductors described herein may be larger or smaller than the sizes depicted below, depending on the electrical and power requirements and integration constraints for the intended application. Table I Table I100504021.000.500.600.8nH1000nH160806031.600.800.801nH3μH201208052.001.251.401.8nH10 μH252010082.502.021.803nH10 μH322512103.062.401.903nH10 μHThe inductance of the ceramic core inductor component is a function of the geometry of the coil (e.g., number of coil turns, length and cross-sectional area of the coil) as well as the magnetic permeability of the ceramic core and the adjacent materials. The range of inductance values for the ceramic core inductor components described herein is therefore generally limited by the size of the component and the nature of the ceramic core and surrounding materials. Typical minimum induction values for the representative sizes of the ceramic core inductor components in Table I are between 0.8 nH and 3 μH. However, the inductance may be greater or smaller depending on the electrical and power requirements and integration constraints for the intended application.Table II shows the measured properties of a prior art 1 μH ceramic core inductor and a 1 μH ceramic core inductor having a dielectric constant of 5 or less according to the present invention. Both inductors have an inductance of 1 μH with a tolerance of 10% or less. The inductor according to the present invention has higher minimum and maximum Q factors and a higher SRF than the inductor according to the prior art. The size represents the length and width dimensions (i.e., 2.5 mm x 2.0 mm) of the components. Table II Table IIPrior Art25209354655 @ 122 MHz395Invention: Invention25209885062 @ 110 MHz405FIG. 10 illustrates plots of the measured Q factor versus frequency for the 1 μH ceramic core inductors shown in Table II. The higher Q factor of the ceramic cored inductor of the invention indicates a higher efficiency (i.e., lower parasitic losses) than the prior art inductor and thus improved performance. FIG. 11 illustrates plots of the measured inductance-to-frequency for the 1 μH ceramic core inductors shown in Table II.Table III shows the measured properties of a prior art 470 nH ceramic core inductor and a 470 nH ceramic core inductor having a dielectric constant of 5 or less according to the present invention. Both inductors have an inductance of 470 nH with a tolerance of 5% or less. The inductor according to the present invention has higher minimum and maximum Q factors and a higher SRF than the inductor according to the prior art. The size represents the length and width dimensions (i.e., 2.5 mm x 2.0 mm) of the components. Table III Table IIIPrior Art25204525766 @ 182 MHz575Invention: Invention25204646370 @ 159 MHz589FIG. 12 illustrates plots of the measured Q factor versus frequency for the 470 nH ceramic core inductors shown in Table III. The higher Q factor of the inductor with ceramic core according to the invention indicates a higher efficiency (for example lower parasitic losses) than the inductor according to the prior art and thus an improved performance. FIG. 13 illustrates plots of measured inductance versus frequency for the 470 nH ceramic core inductors shown in Table III.Table IV shows the measured properties of a prior art 12 nH ceramic core inductor and a 12 nH ceramic core inductor having a dielectric constant of 5 or less according to the present invention. Both inductors have an inductance of 470 nH with a tolerance of 5% or less. The inductor according to the present invention has higher minimum and maximum Q factors and a higher SRF than the inductor according to the prior art. The size represents the length and width dimensions (i.e., 2.5 mm x 2.0 mm) of the components. Table IV Table IVPrior Art2520126789 @ 1000 MHz>1000Invention: Invention252011.682120 @ 1000 MHz>3000FIG. 14 illustrates plots of the measured Q factor versus frequency for the 12 nH ceramic core inductors shown in Table IV. The higher Q factor of the inductor with ceramic core according to the invention indicates a higher efficiency (for example lower parasitic losses) than the inductor according to the prior art and thus an improved performance. FIG. 15 illustrates plots of the measured inductance-to-frequency for the 12 nH ceramic core inductors shown in Table IV.While the disclosure and what is at present considered to be the best mode thereof has been described in a manner that establishes ownership and enables those skilled in the art to make and use it, it will be understood and appreciated that there are many equivalents to the representative embodiments described herein and that numerous modifications and variations may be made thereto without departing from the scope and spirit of the invention, which is not to be limited by the described embodiments, but is to be limited by the appended claims and their equivalents.

Claims

A ceramic core-inductor component comprising: a ceramic core comprising a ceramic body portion disposed between first and second ceramic spacers, the ceramic core comprising a dielectric constant less than 8; a conductive coil disposed around the ceramic body portion; and a first terminal disposed on a first surface of the first ceramic spacer and a second terminal disposed on a second surface of the second ceramic spacer, wherein a first end portion of the conductive coil is electrically connected to the first terminal and a second end portion of the conductive coil is electrically connected to the second terminal.The ceramic core inductor component of claim 1, which is a surface-mountable device, wherein the first and second terminals each comprise a conductive pad, and each of the first and second ceramic spacers is arranged to align an axis of the conductive coil parallel to a surface when the ceramic core inductor component is mounted on the surface.The ceramic core inductor component of claim 2, further comprising a non-conductive handle attached to the ceramic core and at least partially covering the conductive coil.The ceramic core-inductor component according to any one of claims 1-3, wherein the ceramic core comprises a dielectric constant of 6 or less.The ceramic core inductor component of claim 4, which is a 1 μH inductor having a tolerance of 10% or less, comprising a Q factor greater than 50 and a self resonant frequency greater than 400 MHz.The ceramic core inductor component of claim 4, which is a 470 nH inductance with a tolerance of 5% or less, comprising a Q factor of greater than 60 and a self resonant frequency of greater than 550 MHz.The ceramic core inductor component of claim 4, which is a 12 nH inductance with a tolerance of 5% or less, comprising a Q factor of greater than 80 and a self resonant frequency of greater than 3000 MHz.The ceramic core-inductor component of claim 4, wherein the ceramic core comprises more than five weight percent (5%) each of magnesium aluminum silicate, magnesium silicate, and magnesium aluminate.The ceramic core-inductor component of claim 4, wherein the ceramic core comprises, by weight, greater than fifteen percent (15%) magnesium aluminum silicate, greater than five percent (5%) magnesium aluminate, and greater than ten percent (10%) magnesium silicate.The ceramic core-inductor component of claim 4, wherein the ceramic core comprises, by weight, between 41%-54% silica, between 27%-38% alumina, and between 10%-17% magnesia.The ceramic core inductor component of claim 10, wherein the ceramic core further comprises, by weight, up to 12% tin oxide, up to 7% titanium oxide, and up to 2% lanthanum oxide.The ceramic core inductor component of any one of claims 1 to 3, wherein the ceramic core comprises Calciumstrontiumwolframat magnesium silicate, magnesium aluminate, magnesium aluminum silicate, calcium silicate, zinc silicate, aluminum silicate, or silica, or more thereof.A ceramic core-inductor component subassembly comprising: a ceramic core comprising a body portion disposed between first and second spacers, the ceramic core comprising a dielectric constant of less than 8; a first conductive terminal disposed on an end surface of the first spacer; and a second conductive terminal disposed on an end surface of the second portion of the second spacer.The ceramic core inductor component subassembly of claim 13, wherein the first and second conductive terminals each comprise a base layer on the end surface of the corresponding spacer and an outermost conductive layer covering the base layer.The ceramic core inductor component subassembly of claim 14, wherein the base layer comprises silver and the outermost conductive layer comprises tin.The ceramic core inductor component subassembly of claim 15, wherein the first and second conductive terminals each further comprise an intermediate conductive layer between the base layer and the outermost conductive layer.The ceramic core-inductor component subassembly of claim 16, wherein the conductive interlayer comprises nickel or copper.The ceramic core inductor component subassembly of claim 13, wherein the first and second conductive terminals each comprise a silver-platinum-palladium alloy deposited on the end surface of the respective spacer.The ceramic core-inductor component subassembly of claim 13, wherein the ceramic core is a pressed ceramic and the first and second conductive terminals cover a lateral portion of the corresponding first and second cover portions.The ceramic core-inductor component subassembly of any of claims 13-19, wherein the ceramic core comprises a dielectric constant of 6 or less.The ceramic core-inductor component subassembly of claim 20, wherein the ceramic core comprises, in weight percent, greater than fifteen percent (15%) magnesium aluminum silicate, greater than five percent (5%) magnesium aluminate, and greater than ten percent (10%) magnesium silicate.The ceramic core-inductor component subassembly of any of claims 13 to 19, wherein the ceramic core comprises by weight between 41% and 54% silica, between 27% and 38% alumina, and between 10% and 17% magnesia, wherein the ceramic core comprises a dielectric constant of 6 or less.The ceramic core-inductor component subassembly of claim 22, wherein the ceramic core further comprises up to 12% tin oxide, up to 7% titanium oxide, and up to 2% lanthanum oxide by weight.The ceramic core-inductor component subassembly of claim 22, wherein the ceramic core comprises a dielectric constant of 5 or less.

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