Patent Publication Number: US-2016233173-A1

Title: Thermally-conductive electromagnetic interference (emi) absorbers with silicon carbide

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This patent application claims the benefit of and priority to U.S. Provisional Patent Application No. 62/112,758 filed Feb. 6, 2015. The entire disclosure of the above application is incorporated herein by reference. 
    
    
     FIELD 
     The present disclosure generally relates to thermally-conductive electromagnetic interference (EMI) absorbers that include silicon carbide. 
     BACKGROUND 
     This section provides background information related to the present disclosure which is not necessarily prior art. 
     Electrical components, such as semiconductors, transistors, etc., typically have pre-designed temperatures at which the electrical components optimally operate. Ideally, the pre-designed temperatures approximate the temperature of the surrounding air. But the operation of electrical components generates heat which, if not removed, will cause the electrical component to operate at temperatures significantly higher than its normal or desirable operating temperature. Such excessive temperatures may adversely affect the operating characteristics of the electrical component and the operation of the associated device. 
     To avoid or at least reduce the adverse operating characteristics from the heat generation, the heat should be removed, for example, by conducting the heat from the operating electrical component to a heat sink. The heat sink may then be cooled by conventional convection and/or radiation techniques. During conduction, heat may pass from the operating electrical component to the heat sink either by direct surface contact between the electrical component and heat sink and/or by contact of the electrical component and heat sink surfaces through an intermediate medium or thermal interface material (TIM). The thermal interface material may be used to fill the gap between thermal transfer surfaces, in order to increase thermal transfer efficiency as compared to having the gap filled with air, which is a relatively poor thermal conductor. 
     In addition to generating heat, the operation of electronic devices generates electromagnetic radiation within the electronic circuitry of the equipment. Such radiation may result in electromagnetic interference (EMI) or radio frequency interference (RFI), which can interfere with the operation of other electronic devices within a certain proximity. Without adequate shielding, EMI/RFI interference may cause degradation or complete loss of important signals, thereby rendering the electronic equipment inefficient or inoperable. 
     A common solution to ameliorate the effects of EMI/RFI is through the use of shields capable of absorbing and/or reflecting and/or redirecting EMI energy. These shields are typically employed to localize EMI/RFI within its source, and to insulate other devices proximal to the EMI/RFI source. 
     The term “EMI” as used herein should be considered to generally include and refer to EMI emissions and RFI emissions, and the term “electromagnetic” should be considered to generally include and refer to electromagnetic and radio frequency from external sources and internal sources. Accordingly, the term shielding (as used herein) broadly includes and refers to mitigating (or limiting) EMI and/or RFI, such as by absorbing, reflecting, blocking, and/or redirecting the energy or some combination thereof so that it no longer interferes, for example, for government compliance and/or for internal functionality of the electronic component system. 
     SUMMARY 
     This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features. 
     According to various aspects, exemplary embodiments are disclosed of thermally-conductive EMI absorbers. In an exemplary embodiment, a thermally-conductive EMI absorber generally includes thermally-conductive particles, EMI absorbing particles, and silicon carbide. The silicon carbide is present in an amount sufficient to synergistically enhance thermal conductivity and/or EMI absorption. By way of example, a thermally-conductive EMI absorbing composite may comprise a polymer matrix including alumina, carbonyl iron powder, and silicon carbide. The thermally-conductive EMI absorber may have a thermal conductivity of greater than 2 Watts per meter per Kelvin. 
     Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
    
    
     
       DRAWINGS 
       The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure. 
         FIG. 1  is a line graph illustrating attenuation or absorption (in decibels per centimeter (dB/cm)) versus frequency (in Gigahertz (GHz)) for two different thermally-conductive EMI absorbers with silicon carbide according to exemplary embodiments, and also showing a thermally-conductive EMI absorber that does not include any silicon carbide for comparison purposes. 
     
    
    
     DETAILED DESCRIPTION 
     Example embodiments will now be described more fully with reference to the accompanying drawings. 
     Disclosed herein are exemplary embodiments of thermally-conductive EMI absorbers that include silicon carbide. As disclosed herein, the inventors have discovered that silicon carbide (SiC) works synergistically with the thermally-conductive materials (e.g., Alumina (Al 2 O 3 ), ceramics, etc.) and EMI absorbing materials (e.g., carbonyl iron powder (CIP), etc.) to enhance both thermal conductivity and EMI absorption (e.g., as shown in  FIG. 1 , etc.). The resulting thermally-conductive EMI absorbers have high thermal conductivity (e.g., greater than 2 Watts per meter per Kelvin (W/m-K), etc.) and high EMI absorption or attenuation (e.g., at least 9 decibels per centimeter (dB/cm) at a frequency of at least 5 GHz, at least 17 dB/cm at a frequency of at least 15 GHz, etc.). By way of example only, exemplary embodiments are disclosed herein of thermally-conductive EMI absorbers that may include silicon carbide (e.g., 21 to 27 volume percent (vol %), etc.), carbonyl iron (e.g., 8 to 38 vol %, etc.), and alumina (e.g., 6 to 44 vol %, etc.). 
     The art has not shown an instance where silicon carbide has acted synergistically to provide improved thermal conductivity and high EMI absorption. The following three examples show the synergistic effect that the silicon carbide has on the thermal conductivity and EMI absorption. From a practical point of view, a need in the art has been satisfied. Through the presence of the synergy that the silicon carbide has on the alumina and carbonyl iron powder in these examples, the inventors have created a thermally-conductive EMI absorbing composition having better thermal conductivities with less alumina and/or better absorption with less carbonyl iron powder than the conventional absorbers. 
     The following three example formulations are meant to illustrate the general principles and properties of certain embodiments, and are not intended to limit the scope of the claims. The volume percents of each formulation may be varied in other exemplary embodiments to improve or optimize certain properties of the produce. In these example formulations, the silicon carbide had a mean particle size of about 30 microns with particle sizes ranging from about 16 microns to about 49 microns. The silicon carbide particles were mostly spherical in shape. The range of particle sizes of one alumina particle was from about 1 micron to about 9 microns. The range of particle sizes of the other or second alumina particle was from about 26 microns to about 65 microns. The range of particle sizes for the carbonyl iron particles was from about 1 micron to about 6 microns. The silicon carbide, alumina, and carbonyl iron particles were all mostly spherical in shape. 
     A first example formulation of a thermally-conductive EMI absorber includes 37 volume percent of carbonyl iron powder, 26 volume percent of silicon carbide, 7 volume percent of alumina, 27.7 volume percent of silicone matrix, 2.2 volume percent of dispersant, and 0.1 volume percent of cross-linker. In this first example, the dispersant was Isopropyl triisostearoyl titanate, and the crosslinker was Methylhydrogensiloxane-Dimethylsiloxane copolymer, hydride terminated. This first example formulation had a thermal conductivity of 3 W/m-K. 
     A second example formulation of a thermally-conductive EMI absorber includes 9 volume percent of carbonyl iron powder, 22 volume percent of silicon carbide, 43 volume percent of alumina, 24.4 volume percent of silicone matrix, 1.5 volume percent of dispersant, and 0.1 volume percent of cross-linker. In this second example, the dispersant was Isopropyl triisostearoyl titanate, and the crosslinker was Methylhydrogensiloxane-Dimethylsiloxane copolymer, hydride terminated. This second example formulation had a thermal conductivity of 4 W/m-K. 
     A third example formulation of a thermally-conductive EMI absorber includes 10 volume percent of carbonyl iron powder, 27 volume percent of silicon carbide, 34 volume percent of alumina, 27.1 volume percent of silicone matrix, 1.8 volume percent of dispersant, and 0.1 volume percent of cross-linker. In this third example, the dispersant was Isopropyl triisostearoyl titanate, and the crosslinker was Methylhydrogensiloxane-Dimethylsiloxane copolymer, hydride terminated. This third example formulation had a thermal conductivity of 3.5 W/m-K. 
       FIG. 1  is an exemplary line graph illustrating attenuation or absorption (dB/cm) versus frequency (GHz) for the first and second formulations described above. For comparison purposes,  FIG. 1  also shows attenuation or absorption (dB/cm) versus frequency (GHz) for a conventional thermally-conductive EMI absorber (labeled control in  FIG. 1 ) that does not include any silicon carbide. The results shown in  FIG. 1  are provided only for purposes of illustration and not for purposes of limitation. 
     The conventional absorber (control) included 43 volume percent of by volume of carbonyl iron powder, 0 volume percent of by volume of silicon carbide,  22  volume percent of by volume alumina, 33.1 volume percent of silicone matrix, 1.7 volume percent of dispersant, and 0.2 volume percent of cross-linker. For the control, the dispersant was Isopropyl triisostearoyl titanate, and the crosslinker was Methylhydrogensiloxane-Dimethylsiloxane copolymer, hydride terminated. The control had a thermal conductivity of 2 W/m-K. 
     As compared to the three sample formulations, the conventional absorber had the lowest thermal conductivity of 2 W/m-K. By comparison, the first formulation had a higher thermal conductivity of 3 W/m-K despite having less alumina of only 7% by volume. Thus, this shows the synergistic effect that the silicon carbide had on the thermal conductivity. 
     A shown in  FIG. 1 , the attenuation of the second formulation was better than the conventional absorber or control. This was despite the second formulation having only 9% by volume of carbonyl iron powder, as compared to the conventional absorber&#39;s 43% by volume of carbonyl iron powder. The second formulation also had a thermal conductivity of 4 W/m-K, which was double the thermal conductivity of the conventional absorber. 
       FIG. 1  also shows that the attenuation of the first formulation was better or higher than (e.g., about a threefold increase (3×), etc.) the conventional absorber. The first formulation also had a thermal conductivity of 3 W/m-K, which is higher than the conventional absorber&#39;s thermal conductivity of 2 W/m-K. 
     For EMI absorption or attenuation, each of first, second, and third sample formulations included carbonyl iron powder in the amounts of 37 vol %, 9 vol %, and 10 vol %, respectively. Advantageously, carbonyl iron powder offers better performance for frequencies of interest ranging from about 5 GHz to about 15 GHz. Other exemplary embodiments may include one or more other EMI absorbers instead of or in addition to carbonyl iron powder. For example, other exemplary embodiments may include one or more of the following EMI absorbers: carbonyl iron (e.g., carbonyl iron powder, etc.), iron silicide, iron particles, iron oxides, iron alloys, iron-chrome compounds, SENDUST (an alloy containing 85% iron, 9.5% silicon and 5.5% aluminum), permalloy (an alloy containing about 20% iron and 80% nickel), ferrites, magnetic alloys, magnetic powders, magnetic flakes, magnetic particles, nickel-based alloys and powders, chrome alloys, combinations thereof, etc. The EMI absorbers may comprise one or more of granules, spheroids, microspheres, ellipsoids, irregular spheroids, strands, flakes, particles, powder, and/or a combination of any or all of these shapes. In some exemplary embodiments, the EMI absorber may comprise magnetic material, such as a magnetic material with a magnetic relative permeability greater than 2 at 1.0 Megahertz. For example, the EMI absorber may have a relative magnetic permeability greater than about 3.0 at approximately 1.0 Gigahertz, and greater than about 1.5 at 10 Gigahertz. Alternative embodiments may include EMI absorbers configured differently and in different sizes. These specific numerical values provided in this paragraph (as are all numerical values disclosed herein) are for purposes of illustration only and not for purposes of limitation. 
     For thermal conductivity, each of the first, second, and third example formulations included alumina in the amounts of 7 vol %, 43 vol %, and 34 vol %, respectively. Advantageously, alumina is relatively low cost and is available in various particle sizes, which allows for nesting or packing of alumina particles to increase volume loading of the alumina for higher thermal conductivity. Other exemplary embodiments may include one or more other thermal conductors or thermally-conductive fillers instead of or in addition to alumina. For example, some exemplary embodiments may include thermally-conductive fillers having a thermal conductivity of at least 1 W/m-K (Watts per meter-Kelvin) or more, such as a copper filler having thermal conductivity up to several hundred W/m-K, etc. Also, for example, other exemplary embodiments may include one or more of the following thermally-conductive fillers: zinc oxide, boron nitride, silicon nitride, alumina, aluminum, aluminum nitride, iron, metallic oxides, graphite, ceramics, combinations thereof (e.g., alumina and zinc oxide, etc.), etc. In addition, exemplary embodiments may also include different grades (e.g., different sizes, different purities, different shapes, etc.) of the same (or different) thermally-conductive fillers. For example, a thermally-conductive EMI absorber may include two different sizes of boron nitride. By varying the types and grades of thermally-conductive fillers, the final characteristics of the thermally-conductive EMI absorber (e.g., thermal conductivity, cost, hardness, etc.) may be varied as desired. In exemplary embodiments disclosed herein, the thermally-conductive EMI absorbers may have a thermal conductivity greater than 2 W/m-K. For example, the example formulations of  FIG. 1  have thermal conductivities of 3 W/m-K, 3.5 W/m-K, and 4 W/m-K. These thermal conductivities are only examples as other embodiments may include a thermal interface material with a thermal conductivity higher than 4 W/m-K, less than 3 W/m-K, between 2 and 4 W/m-K, etc. 
     The first, second, and third example formulations included a silicone matrix (e.g., silicone elastomer, silicone gel, etc.). In other exemplary embodiments, the matrix may comprise other materials, such as other thermoset polymers including polyurethanes, rubber (e.g., SBR, nitrile, butyl, isoprene, EPDM, etc.), etc. By way of additional examples, the matrix material may comprise thermoplastic matrix materials, polyolefins, polyamides, polyesters, polyurethanes, polycarbonates, polystyrene and styrenic copolymers, acrylnitriles, polyvinyl chlorides, polysulfones, acetals, polyarlyates, polypropylenes, surlyns, polyethylene terephthalates, polystyrenes, combinations thereof, etc. The matrix may be selected based on the particular amount of silicon carbide, carbonyl iron powder (or other EMI absorber), and alumina (or other thermally-conductive material) that may be suspended or added to the matrix. The matrix may also be substantially transparent to electromagnetic energy so that the matrix does not impede the absorptive action of the EMI absorbing filler (e.g., carbonyl iron powder, etc.) in the matrix. For example, a matrix exhibiting a relative dielectric constant of less than approximately 4 and a loss tangent of less than approximately 0.1 is sufficiently transparent to EMI. Values outside this range, however, are also contemplated as these specific numerical values provided in this paragraph (as are all numerical values disclosed herein) are for purposes of illustration only and not for purposes of limitation. 
     By way of example only, the following is a description of an exemplary process that may be used for making a thermally-conductive EMI absorber, such as the a thermally-conductive EMI absorber having the first, second, or third example formulation described above. In a first step or operation, a high speed mixer may be used to mix silicone gel parts A and B, along with the dispersant and cross linker until well blended (e.g., mixing for about 2 minutes, etc.). In a second step or operation, carbonyl iron powder may then be slowly added while mixing (e.g., for about 5 minutes, etc.) until the carbonyl iron powder is well mixed and wetted with silicone polymer. In a third step or operation, silicon carbide may next be slowly added while mixing (e.g., for about 5 minutes, etc.) until well blended. In a fourth step or operation, alumina or aluminum oxide having a first or smaller particle size may be slowly added while mixing (e.g., for about 5 minutes, etc.) until well blended. In a fifth step or operation, alumina or aluminum oxide having a second or larger particle size may be slowly added while mixing (e.g., for about 5 minutes, etc.) until well blended. In a sixth step or operation, the mixing may be continued (e.g., for about 5 minutes, etc.) until the mixture is thoroughly smooth. In a seventh step or operation, the mixture may be placed under vacuum (e.g., for about 5 minutes, etc.) to remove air. An eighth step or operation may include setting a gap may between calendering rolls for desired product thickness. In an ninth step or operation, the mixture may be rolled between two release liners in-between the calendering rolls. In a tenth step of operation, the resulting sheets may be cured in an oven, e.g., at 285 degrees Fahrenheit for about 1 to 2 hours depending on thickness. 
     In some exemplary embodiments, a thermally-conductive EMI absorber may further include an adhesive layer, such as a pressure-sensitive adhesive (PSA), etc. The pressure-sensitive adhesive (PSA) may be generally based on compounds including acrylic, silicone, rubber, and combinations thereof. The adhesive layer can be used to affix the thermally-conductive EMI absorbers to a portion of an EMI shield, such as to a single piece EMI shield, to a cover, lid, frame, or other portion of a multi-piece shield, to a discrete EMI shielding wall, etc. Alternative affixing methods can also be used such as, for example, mechanical fasteners. In other exemplary embodiments, the thermally-conductive EMI absorber may be tacky or self-adherent such that the thermally-conductive EMI absorber may be self-adhered to another surface without any adhesive layer. 
     In some embodiments, a thermally-conductive EMI absorber may be attached to a lid or cover of a EMI shield (e.g., a lid or cover of a single-piece EMI shield, a removable lid or cover of a multi-piece EMI shield, a lid or cover of an EMI shield from Laird Technologies, etc.). The thermally-conductive EMI absorber may be placed, for example, on an inner surface of the cover or lid. Alternatively, the thermally-conductive EMI absorber may be placed, for example, on an outer surface of the cover or lid. The thermally-conductive EMI absorber may be placed on an entire surface of the cover or lid or on less than an entire surface. For example, the thermally-conductive EMI absorber may be placed on a frame or base and a separate thermally-conductive EMI absorber may be placed on a removable lid or cover that is attachable to the frame or base. The thermally-conductive EMI absorber may be applied at virtually any location at which it would be desirable to have a thermally-conductive EMI absorber. 
     In exemplary embodiments, a thermally-conductive EMI absorber may be used to define or provide part of a thermally-conductive heat path from a heat source to a heat dissipating device or component. A thermally-conductive EMI absorber disclosed herein may be used, for example, to help conduct thermal energy (e.g., heat, etc.) away from a heat source of an electronic device (e.g., one or more heat generating components, central processing unit (CPU), die, semiconductor device, etc.). For example, a thermally-conductive EMI absorber may be positioned generally between a heat source and a heat dissipating device or component (e.g., a heat spreader, a heat sink, a heat pipe, a device exterior case or housing, etc.) to establish a thermal joint, interface, pathway, or thermally-conductive heat path along which heat may be transferred (e.g., conducted) from the heat source to the heat dissipating device. During operation, the thermally-conductive EMI absorber may then function to allow transfer (e.g., to conduct heat, etc.) of heat from the heat source along the thermally-conductive path to the heat dissipating device. 
     Example embodiments of thermally-conductive EMI absorbers disclosed herein may be used with a wide range of heat dissipation devices or components (e.g., a heat spreader, a heat sink, a heat pipe, a device exterior case or housing, etc.), heat-generating components, heat sources, heat sinks, and associated devices. By way of example only, exemplary applications include printed circuit boards, high frequency microprocessors, central processing units, graphics processing units, laptop computers, notebook computers, desktop personal computers, computer servers, thermal test stands, etc. Accordingly, aspects of the present disclosure should not be limited to use with any one specific type of heat-generating component, heat source, or associated device. 
     In some exemplary embodiments, the thermally-conductive EMI absorber may be configured to have sufficient conformability, compliability, and/or softness to allow the thermally-conductive EMI absorber to closely conform to a mating surface when placed in contact with the mating surface, including a non-flat, curved, or uneven mating surface. In some exemplary embodiments, the thermally-conductive EMI absorber has sufficient deformability, compliance, conformability, compressibility, and/or flexibility for allowing the thermally-conductive EMI absorber to relatively closely conform to the size and outer shape of an electronic component when placed in contact with the electronic component. 
     In some exemplary embodiments, the thermally-conductive EMI absorber is conformable even without undergoing a phase change or reflow. In other exemplary embodiments, the thermally-conductive EMI absorber may comprise a phase change material. In some exemplary embodiments, the thermally-conductive EMI absorber may comprise a non-phase change gap filler, gap pad, or putty that is conformable without having to melt or undergo a phase change. 
     The thermally-conductive EMI absorber may be able to adjust for tolerance or gaps by deflecting at low temperatures (e.g., room temperature of 20° C. to 25° C., etc.). By way of example, a thermally-conductive EMI absorbers may have a Young&#39;s modulus of less than or equal to about 300 pound force per square inch (lpf/in 2 ) or 2.1 megapascals (MPa). In exemplary embodiments, a thermally-conductive EMI absorber may have a Young&#39;s modulus that falls within a range from about 200 lbf/in 2  to about 300/in 2  or from about 1.4 MPa to about 2.1 MPa. Also by way of example, a thermally-conductive EMI absorbers may have a Shore 00 Hardness less than or equal to 60. In exemplary embodiments, a thermally-conductive EMI absorber may have a Shore 00 Harness value that falls within a range from about 50 to about 60. 
     In some exemplary embodiments, the thermally-conductive EMI absorber may be conformable and have sufficient compressibility and flexibility for allowing the thermally-conductive EMI absorber to relatively closely conform to the size and outer shape of an electrical component when placed in contact with the electrical component. For example, a thermally-conductive EMI absorber may be along the inner surface of a cover of an EMI shield such that the thermally-conductive EMI absorber is compressed against the electrical component when the EMI shield is installed to a printed circuit board over the electrical component. By engaging the electrical component in this relatively close fitting and encapsulating manner, the thermally-conductive EMI absorber can conduct heat away from the electrical component to the cover in dissipating thermal energy. 
     In some embodiments, a thermally-conductive EMI absorber may be formed as a tape. The tape, for example, can be stored on a roll. In some embodiments, desired application shapes (e.g., rectangle, circle, ellipse, etc.) can be die-cut from the thermally-conductive EMI absorber, thereby yielding thermally-conductive EMI absorbers of any desired two-dimensional shape. Accordingly, the thermally-conductive EMI absorber can be die-cut to produce the desired outlines of an application shape. 
     In operation, a thermally-conductive EMI absorber according to exemplary embodiments disclosed herein may be operable for absorbing a portion of the EMI incident upon the EMI absorber, thereby reducing transmission of EMI therethrough over a range of operational frequencies (e.g., a frequency range from about 2 GHz to at least about 18 GHz, a frequency range from about 5 GHz to at least about 15 GHz etc.). The EMI absorber may remove a portion of the EMI from the environment through power dissipation resulting from loss mechanisms. These loss mechanisms include polarization losses in a dielectric material and conductive, or ohmic, losses in a conductive material having a finite conductivity. 
     By way of background, EMI absorbers function to absorb electromagnetic energy (that is, EMI). EMI absorbers convert electromagnetic energy into another form of energy through a process commonly referred to as a loss. Electrical loss mechanisms include conductivity losses, dielectric losses, and magnetization losses. Conductivity losses refer to a reduction in EMI resulting from the conversion of electromagnetic energy into thermal energy. The electromagnetic energy induces currents that flow within an EMI absorber having a finite conductivity. The finite conductivity results in a portion of the induced current generating heat through a resistance. Dielectric losses refer to a reduction in EMI resulting from the conversion of electromagnetic energy into mechanical displacement of molecules within an absorber having a non-unitary relative dielectric constant. Magnetic losses refer to a reduction in EMI resulting from the conversion of electromagnetic energy into a realignment of magnetic moments within an EMI absorber. 
     Example embodiments are provided so that this disclosure will be thorough, and will fully convey the scope to those who are skilled in the art. Numerous specific details are set forth such as examples of specific components, devices, and methods, to provide a thorough understanding of embodiments of the present disclosure. It will be apparent to those skilled in the art that specific details need not be employed, that example embodiments may be embodied in many different forms, and that neither should be construed to limit the scope of the disclosure. In some example embodiments, well-known processes, well-known device structures, and well-known technologies are not described in detail. In addition, advantages and improvements that may be achieved with one or more exemplary embodiments of the present disclosure are provided for purpose of illustration only and do not limit the scope of the present disclosure, as exemplary embodiments disclosed herein may provide all or none of the above mentioned advantages and improvements and still fall within the scope of the present disclosure. 
     Specific dimensions, specific materials, and/or specific shapes disclosed herein are example in nature and do not limit the scope of the present disclosure. The disclosure herein of particular values and particular ranges of values for given parameters are not exclusive of other values and ranges of values that may be useful in one or more of the examples disclosed herein. Moreover, it is envisioned that any two particular values for a specific parameter stated herein may define the endpoints of a range of values that may be suitable for the given parameter (i.e., the disclosure of a first value and a second value for a given parameter can be interpreted as disclosing that any value between the first and second values could also be employed for the given parameter). For example, if Parameter X is exemplified herein to have value A and also exemplified to have value Z, it is envisioned that parameter X may have a range of values from about A to about Z. Similarly, it is envisioned that disclosure of two or more ranges of values for a parameter (whether such ranges are nested, overlapping or distinct) subsume all possible combination of ranges for the value that might be claimed using endpoints of the disclosed ranges. For example, if parameter X is exemplified herein to have values in the range of 1-10, or 2-9, or 3-8, it is also envisioned that Parameter X may have other ranges of values including 1-9, 1-8, 1-3, 1-2, 2-10, 2-8, 2-3, 3-10, and 3-9. 
     The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting. As used herein, the singular forms “a”, “an” and “the” may be intended to include the plural forms as well, unless the context clearly indicates otherwise. The terms “comprises,” “comprising,” “including,” and “having,” are inclusive and therefore specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. The method steps, processes, and operations described herein are not to be construed as necessarily requiring their performance in the particular order discussed or illustrated, unless specifically identified as an order of performance. It is also to be understood that additional or alternative steps may be employed. 
     When an element or layer is referred to as being “on”, “engaged to”, “connected to” or “coupled to” another element or layer, it may be directly on, engaged, connected or coupled to the other element or layer, or intervening elements or layers may be present. In contrast, when an element is referred to as being “directly on,” “directly engaged to”, “directly connected to” or “directly coupled to” another element or layer, there may be no intervening elements or layers present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., “between” versus “directly between,” “adjacent” versus “directly adjacent,” etc.). As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. 
     The term “about” when applied to values indicates that the calculation or the measurement allows some slight imprecision in the value (with some approach to exactness in the value; approximately or reasonably close to the value; nearly). If, for some reason, the imprecision provided by “about” is not otherwise understood in the art with this ordinary meaning, then “about” as used herein indicates at least variations that may arise from ordinary methods of measuring or using such parameters. For example, the terms “generally”, “about”, and “substantially” may be used herein to mean within manufacturing tolerances. Or for example, the term “about” as used herein when modifying a quantity of an ingredient or reactant of the invention or employed refers to variation in the numerical quantity that can happen through typical measuring and handling procedures used, for example, when making concentrates or solutions in the real world through inadvertent error in these procedures; through differences in the manufacture, source, or purity of the ingredients employed to make the compositions or carry out the methods; and the like. The term “about” also encompasses amounts that differ due to different equilibrium conditions for a composition resulting from a particular initial mixture. Whether or not modified by the term “about”, the claims include equivalents to the quantities. 
     Although the terms first, second, third, etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms may be only used to distinguish one element, component, region, layer or section from another region, layer or section. Terms such as “first,” “second,” and other numerical terms when used herein do not imply a sequence or order unless clearly indicated by the context. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the example embodiments. 
     Spatially relative terms, such as “inner,” “outer,” “beneath”, “below”, “lower”, “above”, “upper” and the like, may be used herein for ease of description to describe one element or feature&#39;s relationship to another element(s) or feature(s) as illustrated in the figures. Spatially relative terms may be intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “below” or “beneath” other elements or features would then be oriented “above” the other elements or features. Thus, the example term “below” can encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly. 
     The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements, intended or stated uses, or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure.