Patent Description:
The subject matter described herein relates generally to laminated magnetic cores. More particularly, the subject matter described herein relates to laminated magnetic cores, methods of fabricating laminated magnetic cores, and electric devices using laminated magnetic cores.

In general, electrically conducting magnetic materials exhibit superior magnetic properties compared to their non-electrical conducting counterparts; however, substantial eddy current losses at high operating frequencies (e.g., the typical <NUM>-<NUM> frequencies used in DC-DC converters, battery chargers, and handheld devices, and higher frequencies (<NUM>-<NUM>) that may be utilized in future power systems-on-chip (PwrSOC) with integrated magnetics) where the skin depths of the materials are smaller than the thickness of the magnetic material limit the use of these materials. By creating stacks of micron or sub-micron thick layers of thin magnetic alloy sheets ('laminations') with interlamination layers of extremely low conductivity, the eddy current losses within the volume of the laminated alloys can be suppressed even at MHz frequencies; such conventionally insulated laminations are ideal for the realization of magnetic materials for high operating frequencies.

Conventionally insulated laminations can present fabrication issues. In view of these issues, there exists a need for improved laminated magnetic cores, methods of fabricating laminated magnetic cores, and electric devices using laminated magnetic cores.

<CIT> describes an amorphous alloy, on which a polymer layer is deposited. On this high-resistivity layer, a further amorphous alloy layer can be deposited thereon.

This document describes laminated structures comprising interlamination layers with balanced electrical conductivities, typically ranging between four to six orders of magnitude lower than the metallic magnetic material. The laminated structures can be useful for, e.g., (<NUM>) uncompromised high frequency performance at (<NUM>) significantly lower fabrication complexity. This is achieved when the conductivities of the interlamination layers are sufficiently high to enable subsequent electrodeposition of metal (e.g., the next lamination layer), and yet sufficiently low that the eddy current losses within the fabricated laminated alloys are sufficiently suppressed for a particular application of interest. For example, suppression of eddy current losses to levels significantly lower than other losses in the magnetic system or electrical system in which the magnetic system is embedded may only be of marginal benefit. Examples of such other losses include the hysteresis losses of the magnetic layers, i.e., the losses due to the magnetization process intrinsic to the magnetic material, or losses in an overall electrical system in which the magnetic system is a part, such as the switching loss in an electrical power converter. Thus, interlamination layer electrical conductivities that are larger than zero may be permissible.

The laminated structures and methods of fabrication can be useful for, e.g., the commercialization of miniaturized inductive components (such as inductors and transformers) operating at high frequencies (e.g., exceeding <NUM>). By using the laminated magnetic cores of which saturation flux densities are higher than that of the commercially-available ferrite cores, the form factors of related end-products (e.g. switch-based DC-to-DC power converters, circuit isolators, handheld electronic devices, LED lights) could be significantly reduced.

The subject matter of the present invention is defined by the appended claims.

<FIG> illustrate an example laminated magnetic core <NUM>. <FIG> shows that laminated magnetic core <NUM> includes magnetic layers <NUM> and <NUM> and interlamination layers <NUM> and <NUM> disposed between the magnetic layers in an alternating fashion. Interlamination layers <NUM> and <NUM> are formed of a partially conducting material. The partially conducting material has a conductivity greater than or equal to <NUM>-<NUM> S/cm and less than or equal to <NUM><NUM> S/cm. In some examples, the partially conducting material has a conductivity between <NUM>/cm and <NUM>/cm.

In some examples, magnetic layers <NUM> and <NUM> are formed of a soft magnetic alloy, e.g., Ni, Fe, NiFe, NiFeCo, or similar materials, and interlamination layers <NUM> and <NUM> are formed of a material of significantly smaller electrical conductivity such as conductive polymers, e.g., polypyrrole. In some examples, magnetic layers <NUM> and <NUM> each have a thickness less than or equal to <NUM> and greater than or equal to <NUM>, and interlamination layers <NUM> and <NUM> each have a thickness less than or equal to <NUM> and greater than or equal to <NUM>.

<FIG> shows the suppressed eddy currents that conduct within laminated magnetic core <NUM>. <FIG> also illustrates the magnetic fields and an appropriate thickness of the magnetic layers relative to the skin depth of the magnetic material. The appropriate thickness of each individual layer is a function of multiple physical and technical parameters, such as the conductivity of the lamination layer or the interlamination layer or both, the magnetic permeability of a ferromagnetic material in the magnetic layers, and the range of frequency at which an electric device is configured to operate.

In some examples, the skin depth and the conductivities of the layers can be used as follows: <MAT> where f is the operating frequency in Hz, µ is the layer permeability in H/m, σm is the conductivity of the material of interest in S/m, and δ is the skin depth in m. Typical conductivities of metallic magnetic materials might be on the order of <NUM><NUM> S/cm, while typical conductivities of conventional insulating materials for interlamination layers might be as low as the order of <NUM>-<NUM> S/cm, and conductivities of partially insulating interlamination layers might range from <NUM>-<NUM> S/cm up to conductivities approaching that of metallic magnetic materials.

The advantages of laminated magnetic core <NUM> compared to conventional laminations with conventionally insulating interlamination layers can include (<NUM>) uncompromised high frequency performance (<NUM>) at reduced fabrication complexity.

The conductivity of interlamination layers <NUM> and <NUM> is balanced so that it is (<NUM>) sufficiently high for a subsequent electrodeposition of the desired magnetic material on the interlamination layer, yet (<NUM>) sufficiently low compared to the magnetic material to suppress the interlamination conduction to a proper level; hence, the fabrication of the laminated alloys is simplified to sequential electrodeposition of magnetic layers and partially-conducting interlamination layers. The total eddy current losses within such laminated materials can be suppressed to a desired level, e.g., the level of the hysteresis losses of the magnetic layers, i.e., the losses due to the magnetization process intrinsic to the magnetic material. Laminated magnetic core <NUM> provides a simple, cost-effective and environment-friendly fabrication approach toward the batch-scale realization of laminated magnetic alloys with nearly uncompromised performances.

<FIG> is a diagram illustrating an example method <NUM> for fabricating a laminated magnetic core. Method <NUM> is based on a sequential multilayer electrodeposition of desired magnetic alloy and properly-chosen conductive polymer (e.g. polypyrrole). Using conductive polymer as interlamination layer material is beneficial in at least two aspects.

First, polymers with extremely wide ranging conductivities (e.g. <NUM>-<NUM>-<NUM><NUM> S/cm) can be synthesized by using appropriate monomers and dopants. Second, the gradual post-deposition conductivity degradation of the polymers stored in ambient conditions, which is widely observed in common conductive polymer systems and unfavorable for most applications, may be beneficial from the perspective of retaining superior performance of the laminated magnetic alloys for an extended period of time. In some examples, this effect is accelerated by subsequent, post-electrodeposition polymer degradation processes such as sample heating at elevated temperatures, or solvent rinsing.

Method <NUM> includes preparation of a seed layer (<NUM>). Method <NUM> includes anodic electropolymerization of a desired conductive polymer followed by cathodic electrodeposition of a desired metal (such as a magnetic material), or vice versa (<NUM>). In some examples, a magnetic layer is deposited over the seed layer, e.g., as shown in <FIG>; in some other examples, an interlamination layer is deposited over the seed layer. Method <NUM> includes repeatedly adding layers in an alternating fashion to fabricate multilayers with designed individual layer thicknesses (<NUM>). Method <NUM> optionally includes a sample rinse and dry (<NUM>). Method <NUM> optionally includes polymer degradation processes such as heating, or solvent treatment (sample rinsing, immersion) (<NUM>). Method (<NUM>) optionally includes the application of a magnetic field during electrodeposition of the magnetic material to preferentially improve the magnetic properties of the magnetic material.

The seed layer, on which the laminated magnetic alloys are synthesized, is prepared on an arbitrary substrate. The seed layer can be metal (e.g. gold, silver, nickel, copper, aluminum, zinc, iron) as well as non-metal (e.g. indium tin oxide (ITO), graphite, graphene, carbonized SU-<NUM> epoxy, highly doped silicon), as long as its conductivity is sufficient to perform step <NUM>. The seed layer can be prepared by various means including both physical deposition (e.g. sputtering, evaporation) and chemical deposition (e.g. electroless deposition).

The electropolymerization of a conductive polymer is performed in an aqueous bath where a proper amount of the monomers of the desired polymers and salts are dissolved. Various monomers (e.g. <NUM>,<NUM>-ethylenedioxythiophene (EDOT), aniline, and pyrrole) can be used to synthesize respective polymers (e.g., poly(<NUM>,<NUM>-ethylenedioxythiophene) (PEDOT), polyaniline, and polypyrrole). Note that the choice of both monomers and salts is appropriate for method <NUM> when the conductivity of the deposited polymer is balanced so that the interlamination layer conductivities are sufficiently high to enable the electrodeposition of magnetic layers, and yet sufficiently low to suppress the interlamination conduction within the laminated structure (or, alternatively, can be made low by post-deposition treatment).

An anodic potential during the electropolymerization might lead to an undesirable corrosion of the underlying layer (i.e. metallic seed layer or electrodeposited metallic magnetic layers); specific salts (e.g. sodium oxalate, sodium tartrate, sodium saccharin, sodium salicylate) that are co-dissolved in the bath may help creating a passivation layer on the substrate during the first few seconds of the polymerization, which inhibits the substrate corrosion. As an alternative to conducting polymer electrodeposition, other deposition techniques, such as dip, spin, or spray coating, could be used to deposit the desired conducting polymer.

The cathodic electrodeposition of a desired metal is performed on the deposited conductive polymer layer. Various common soft magnetic metal alloys (e.g. Ni alloys such as NiFe, CoNiFe, NiFeMo) can be directly deposited on the polymer layer using appropriately-designed electrolyte baths and deposition conditions; however, for some metals, their relatively high cathodic deposition potential may attract significant amount of the dissolved anion to the polymer network, expanding the volume of the polymer matrix that leads to an undesirable film delamination during the deposition. This issue is resolved in the present invention by pre-electrodeposition of a low deposition potential metal film (e.g. copper, nickel) with a thickness much smaller than the lamination thickness.

<FIG> illustrates an example fabrication environment <NUM> for method <NUM> including a robot arm of an electrodeposition robot that automatically transfers a sample wafer from bath to bath. Both deposition reactions are performed at appropriately-designed, fixed potentials (in relative to a reference electrode) or electrical currents, while the deposition time in the respective bath is controlled to achieve individual layers with desired thicknesses.

Large numbers of laminated magnetic alloys with desired individual layer thicknesses can be created. The lateral extent of the laminated alloys can be defined either by top-down machining (e.g. laser cutting) post deposition, or bottom-up through-mold electrodeposition using an appropriate mold material that is intact throughout the multilayer deposition (e.g. SU-<NUM> or other photoresists). Any polymer degradation processes (such as oxidative degradation processes at elevated temperatures, or solvent-induced degradation processes) that lead to the decrease of the conductivity of the deposited polymer may follow as long as the magnetic properties of the deposited magnetic alloys are not substantially negatively impacted.

<FIG> is a block diagram of an example automated, robot assisted multibath electrodeposition setup. Magnetic and polymeric (i.e. polypyrrole, or PPY) layers are sequentially deposited in the respective baths. After depositing a material, the sample is moved to the water bath to avoid bath cross-contamination. Note that the sample is under positive potential (compared to the counter electrode) to perform anodic polymerization.

<FIG> show an example of fabricated laminated alloys. This material comprises <NUM> layers of <NUM>-thick permalloy (Ni<NUM>Fe<NUM>, a representative soft magnetic metallic alloy) with <NUM> layers of <NUM>-thick polypyrrole interlamination. The deposition bath for the polymer is comprised of pyrrole and sodium salicylate. The conductivity of the polypyrrole measured using <NUM> point probe is approximately <NUM>/cm, which is nearly <NUM> orders of magnitude smaller than the conductivity of the magnetic material, yet still conductive enough to perform multilayer electrodeposition.

<FIG> illustrate example electric devices that can use the laminated magnetic core <NUM>. Various electric devices can use the laminated magnetic core <NUM> and the illustrated devices are presented for purposes of illustration.

<FIG> shows an example inductor <NUM> that includes laminated magnetic core <NUM> and a wire <NUM> coiled around laminated magnetic core <NUM>. Inductors can be made of various sizes and shapes to fit particular applications.

<FIG> shows an example transformer <NUM> that includes laminated magnetic core <NUM>. In this example, laminated magnetic core <NUM> has been fabricated as a rectangle with a rectangular hole to permit wrapping a primary winding <NUM> and a secondary winding <NUM> about laminated magnetic core <NUM>. Transformer <NUM> transfers electrical energy from an input coupled to primary winding <NUM> to a load <NUM> coupled to secondary winding <NUM>.

Claim 1:
A laminated magnetic core (<NUM>) comprising:
a plurality of magnetic layers (<NUM>, <NUM>); and
a plurality of interlamination layers (<NUM>, <NUM>) disposed between the magnetic layers (<NUM>, <NUM>) in an alternating fashion;
a low deposition potential metal film deposited by pre-electrodeposition on each interlamination layer (<NUM>), wherein the low deposition potential metal film has a film thickness much smaller than a lamination thickness,
wherein the interlamination layers (<NUM>, <NUM>) comprise a partially conducting material having a conductivity greater than or equal to <NUM>-<NUM> S/cm and less than or equal to <NUM><NUM> S/cm