Passive negative inductor and method for manufacturing the same

Abstract

The present disclosure discloses a negative inductor device (300). The negative inductor device comprises a negative inductor (200) including a ferromagnetic material (200) and a conductive material (203) disposed inside the ferromagnetic material. The negative inductor device further comprises a current limiting circuit (301) electrically coupled to the negative inductor and configured to supply a current (303) having a magnitude within a range (307), the range being defined by a first minimum (121a) and a second minimum (121b) of a current-energy curve of the ferromagnetic material.

Description

[Technical Field]

[0001] The present disclosure relates generally to electrical circuits, and more particularly to negative inductors and methods for making negative inductors. [Background technology]

[0002] background An inductor is a passive two-terminal electrical component that stores energy, usually in the form of a magnetic field, when current flows through it. An exemplary implementation of a basic inductor is an insulated wire wound into a coil. When the current flowing through the coil changes, the time-varying magnetic field induces an electromotive force (emf) (voltage) in the coil, as described by Faraday's law of induction. Such inductors are also referred to herein as positive inductors, in contrast to negative inductors.

[0003] Negative inductors, at least in theory, exhibit properties opposite to those of positive inductors. For example, in a positive inductor, the magnetic flux associated with the positive inductor increases with increasing current through the positive inductor. However, in a negative inductor, this phenomenon is reversed; that is, the magnetic flux associated with the negative inductor decreases with increasing current through the negative inductor. Similarly, a positive inductor has a "U" shaped energy versus current curve (U vs. i), which gives the value of its inductance. In contrast, the shape of the energy versus current curve for a negative inductor is an inverted "U."

[0004] The effect of negative inductors is evaluated based on theory supported by active negative inductors such as negative impedance converters (NICs). NICs are active circuits that inject energy into a circuit, as opposed to a normal load that draws energy from the circuit. NICs are achieved by adding or subtracting an excess varying voltage in series with the voltage drop across an equivalent positive impedance. However, having an active negative inductor in a circuit requires extra energy and extra space, which is undesirable.

[0005] Therefore, the need for a negative inductor remains. Summary of the Invention [Problem to be solved by the invention]

[0006] overview An object of some embodiments is to provide a compound material component that can be used as a negative inductor. It is also an object of some embodiments to fabricate a negative inductor using passive elements to obtain a passive negative inductor. Additionally or alternatively, it is an object of some embodiments to provide such a negative inductor that is suitable for inclusion in an integrated circuit. Additionally or alternatively, it is an object of some embodiments to provide a method for manufacturing a negative inductor. [Means for solving the problem]

[0007] Some embodiments are based on the understanding that the properties of ferromagnetic materials can be used to construct negative capacitors. To that end, some embodiments explore the properties of ferromagnetic materials to construct negative inductors. For example, some embodiments are based on the recognition that the current-energy curve of a ferromagnetic material is a "W"-shaped curve. The current-energy curve of a ferromagnetic material contains two local minima: a first local minimum and a second local minimum. Between the two local minima, near zero current, there is an inverted U-shape that resembles the current-energy curve of a negative inductor. Therefore, the inverted U-shape of the current-energy curve of a ferromagnetic material has a negative curvature, resulting in negative inductance. The zone corresponding to the inverted U-shape of the current-energy curve of a ferromagnetic material is referred to as the negative inductance zone.

[0008] Some embodiments are based on the realization that since the negative inductance zone has high energy, the ferromagnetic material will not remain in the negative inductance zone but will end up in one of two local minima. Furthermore, ferromagnetic materials are not electrically conductive, which prevents the realization of an inductor.

[0009] Some embodiments are based on the realization, supported by simulations and experiments, that when a conductive material is inserted into a ferromagnetic material to carry a current, the magnetic field of the current-carrying conductive material interacts with the ferromagnetic material, resulting in a negative inductor characteristic in a negative inductance zone. Such interaction allows for the creation of electrical components that act as negative inductors. To that end, negative inductors can be constructed by placing a conductive material inside a ferromagnetic material.

[0010] In one embodiment, the conductive material is disposed inside the ferromagnetic material such that the majority of the conductive material is within the ferromagnetic material and two opposing ends of the conductive material protrude beyond the surface or exterior of the ferromagnetic material. The two ends of the conductive material form terminals of a negative inductor for electrical connection to another device or circuit. In an alternative embodiment, the conductive material is disposed inside the ferromagnetic material such that the entire conductive material is completely surrounded by the ferromagnetic material. In such an embodiment, terminals are formed separately from a different material than the conductive material and electrically connected to both ends of the conductive material to enable electrical connection.

[0011] Furthermore, some embodiments recognize that to operate in the negative inductance zone, the negative inductor must be supplied with a current whose magnitude is within a range defined by a first local minimum and a second local minimum of the current-energy curve of the ferromagnetic material. To supply a current whose magnitude is within a range defined by the first local minimum and the second local minimum of the current-energy curve of the ferromagnetic material, the negative inductor is connected to a current limiting circuit. The negative inductor, together with the current limiting circuit, constitutes a negative inductor device.

[0012] The current limiting circuit is configured to supply a current i having a magnitude within a range defined by a first minimum and a second minimum of a current-energy curve of the ferromagnetic material. For example, a current i1 corresponding to the first minimum and a current i2 corresponding to the second minimum define a current magnitude range (i1-i2). The current limiting circuit supplies a current i having a magnitude within the range (i1-i2).

[0013] According to certain embodiments, the extent of the negative inductance zone depends on the type of ferromagnetic material and / or the mutual arrangement of the conductive material within the ferromagnetic material. For example, in some embodiments, the ferromagnetic material is slab-shaped, and the conductive material is a spirally twisted wire. The cross section of the wire includes one or a combination of circular, semicircular, rectangular, and semirectangular shapes. The slab-shaped ferromagnetic material surrounds the spiral-shaped conductive material so that the geometric center of the slab-shaped ferromagnetic material coincides with the geometric center of the spiral-shaped conductive material. Such shapes and arrangements of the ferromagnetic material and the conductive material have the advantage that the inductance of the negative inductor is increased, for example, by using a spiral-shaped conductive material. Because the negative inductor is constructed using passive elements such as ferromagnetic materials and conductive materials, it is called a passive negative inductor.

[0014] In some embodiments, the types of ferromagnetic and conductive materials are selected, either mutually or independently, based on the application of the negative inductor. Conductive materials used in different embodiments include copper, aluminum, steel, iron, etc. Ferromagnetic materials used in different embodiments include, for example, various ferromagnetic oxides, cobalt, magnetite, dysprosium, nickel, gadolinium, awalite, permalloy, etc.

[0015] Some embodiments recognize that it is advantageous to connect a negative inductor in parallel or series with a positive inductor. For example, a negative inductor may be connected in parallel with a positive inductor for inductor amplification. In addition, negative inductors may be used in different circuits, such as microwave circuits, monolithic microwave integrated circuits (MMICs), radio frequency integrated circuits (RFICs), power electronic circuits, etc. For example, in RFICs, implementing inductors consumes significant chip area. Therefore, it is desirable to create inductors that consume less chip area. According to embodiments, a negative inductor may be used to amplify the value of a positive inductor in an RFIC by consuming less chip area. In addition, in some embodiments, a negative inductor may be used as a non-Foster element in various devices and components, such as non-Foster wideband antennas and non-Foster artificial magnetic conductors, to eliminate the narrowband resonance behavior inherent in such devices.

[0016] Additionally, some embodiments provide a method for fabricating a negative inductor. The method includes providing a substrate. The substrate may include, but is not limited to, silicon (Si), silicon carbide (SiC), diamond, gallium nitride (GaN), etc. For purposes of illustration, a Si substrate is considered. The Si substrate may be cleaned according to the piranha cleaning method and / or the Radio Corporation of America (RCA) cleaning method. Further, a ferromagnetic oxide is deposited on the cleaned Si substrate using a deposition method such as pulsed laser deposition.

[0017] After the ferromagnetic oxide deposition, the sample may be annealed in an oxygen environment. Metal spirals are then formed on the surface of the ferromagnetic oxide using, for example, photolithography and a lift-off process. Another layer of ferromagnetic oxide is then deposited, completely submerging the metal spirals within the ferromagnetic oxide. Another layer of ferromagnetic oxide is then deposited using pulsed laser deposition.

[0018] Accordingly, one embodiment discloses a negative inductor device, comprising: a negative inductor including a ferromagnetic material and a conductive material disposed inside the ferromagnetic material, and a current limiting circuit electrically coupled to the negative inductor and configured to supply a current within a range defined by a first minimum and a second minimum of a current-energy curve of the ferromagnetic material.

[0019] Accordingly, another embodiment discloses a negative inductor device including a ferromagnetic material and a conductive material, the conductive material partially surrounding the ferromagnetic material such that both ends of the conductive material protrude from the ferromagnetic material, and the both ends of the conductive material protruding from the ferromagnetic material correspond to terminals of the negative inductor.

[0020] Accordingly, yet another embodiment discloses a method for fabricating a negative inductor, the method including depositing a first layer of ferromagnetic material on a substrate, forming a metal spiral on a surface of the first layer of ferromagnetic material, and depositing a second layer of ferromagnetic material on the first layer of ferromagnetic material and the metal spiral. [Brief explanation of the drawings]

[0021] [Figure 1A] FIG. 1 is a schematic diagram illustrating current-flux characteristics of a negative inductor according to some embodiments of the present disclosure. [Figure 1B] FIG. 1 is a schematic diagram illustrating current-energy characteristics of a negative inductor according to some embodiments of the present disclosure. [Figure 1C] 1 illustrates the energy landscape of a ferromagnetic material according to some embodiments of the present disclosure. [Figure 2] 1 illustrates a negative inductor according to some embodiments of the present disclosure. [Figure 3A] 1 shows a schematic diagram of a negative inductor device according to some embodiments of the present disclosure. [Figure 3B]1 illustrates a range of current magnitudes defined by a first minimum and a second minimum of a current-energy curve of a ferromagnetic material, according to some embodiments of the present disclosure. [Figure 3C] 1 shows a diagram of an electrical circuit for implementation of a current limiting circuit according to some embodiments of the present disclosure. [Figure 4A] 10A-10C show schematic diagrams of negative inductors according to some other embodiments of the present disclosure. [Figure 4B] 4B shows a different perspective view of the negative inductor of FIG. 4A according to some other embodiments of the present disclosure. [Figure 5A] 10A-10C show diagrams of electrical circuits including negative and positive inductors connected in parallel, according to some other embodiments of the present disclosure. [Figure 5B] 10A-10C show diagrams of electrical circuits including negative and positive inductors connected in series, according to some other embodiments of the present disclosure. [Figure 6] 10A-10C show schematic diagrams of methods for manufacturing negative inductors according to some other embodiments of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0022] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] The presently disclosed embodiments will now be described in detail with reference to the accompanying drawings, in which the drawings are not necessarily to scale, with emphasis instead generally being placed upon illustrating the principles of the disclosed embodiments. Detailed Description

[0023] In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the present disclosure. However, it will be apparent to those skilled in the art that the present disclosure may be practiced without these specific details. In other instances, devices and methods are shown only in block diagram form in order to avoid obscuring the present disclosure.

[0024] As used in this specification and claims, the words "for example," "for example," "e.g.," "etc.", and the verbs "comprise," "have," "include," and other verb forms thereof, when used in conjunction with a list of one or more components or other items, should each be construed as open-ended, meaning that the list should not be viewed as excluding other additional components or items. The phrase "based on" means based at least in part on. Furthermore, it should be understood that the phraseology and terminology used herein are for purposes of description and should not be considered limiting. Any headings used within this description are for convenience only and have no legal or limiting effect.

[0025] It is an object of some embodiments to provide a compound material component that can be used as a negative inductor. Additionally, it is an object of some embodiments to fabricate the negative inductor using passive elements, resulting in a passive negative inductor. Additionally or alternatively, it is an object of some embodiments to provide such a negative inductor that is suitable for inclusion in an integrated circuit.

[0026] A negative inductor exhibits the opposite characteristics to a positive inductor (or a normal inductor). For example, in a positive inductor, the magnetic flux associated with the positive inductor increases with increasing current through the positive inductor. However, in a negative inductor, this phenomenon is reversed, as will be explained later in Figure 1A.

[0027] 1A shows a schematic diagram 100 illustrating the current-flux characteristics of a negative inductor, according to some embodiments of the present disclosure. A current-flux curve 101 is plotted between the current 103 through the negative inductor and the magnetic flux 105 associated with the negative inductor. The current-flux curve 101 implies that the magnetic flux associated with the negative inductor decreases with increasing current through the negative inductor.

[0028] Furthermore, some embodiments are based on the understanding that the current-energy curve of a positive inductor is a U-shaped curve, whereas the current-energy curve of a negative inductor is an inverted U-shaped curve.

[0029] 1B shows a schematic diagram 107 illustrating the current-energy characteristics (or current-energy curve) of a negative inductor according to some embodiments of the present disclosure. The negative inductor current-energy curve 109 is plotted between the current 111 through the negative inductor and the energy 113 of the negative inductor. The shape of the negative inductor current-energy curve 109 is an inverted U.

[0030] Some embodiments are based on the understanding that the properties of ferromagnetic materials can be employed to construct negative capacitors that exhibit the properties described above in Figures 1A and 1B. To that end, some embodiments aim to explore the properties of ferromagnetic materials to construct negative inductors.

[0031] 1C illustrates an energy landscape 127 of a ferromagnetic material according to some embodiments of the present disclosure. The current-energy curve 115 of the ferromagnetic material is plotted between the current 117 through the ferromagnetic material and the energy 119 of the ferromagnetic material. The current-energy curve 115 includes two local minima: a first local minimum 121a and a second local minimum 121b. Between the two local minima 121a and 121b, near zero current, there is an inverted U-shape 123 that resembles the current-energy curve 109 of a negative inductor. Thus, the inverted U-shape 123 of the current-energy curve 115 of the ferromagnetic material has a negative curvature, resulting in negative inductance. The zone 125 corresponding to the inverted U-shape 123 of the current-energy curve 115 is referred to as the negative inductance zone.

[0032] According to an embodiment, the negative inductance behavior can be understood from the Landau mean field theory, according to which the Gibbs free energy of a ferromagnetic material is given by the following equation:

number

[0033] where a and c are material-based parameters. As long as the temperature is below the Curie temperature (typically >10,000°C), the material-based parameter "a" is negative, resulting in a negative inductance.

[0034] Some embodiments are based on the realization that since the negative inductance zone 125 has high energy, the ferromagnetic material does not remain within the negative inductance zone 125 but falls into one of two local minima 121 a and 121 b. Furthermore, the ferromagnetic material is not electrically conductive, which prevents the realization of an inductor.

[0035] Some embodiments are based on the realization, supported by simulations and experiments, that when a conductive material is inserted into a ferromagnetic material to carry a current, the magnetic field of the current-carrying conductive material interacts with the ferromagnetic material to result in a negative inductor characteristic in the negative inductance zone 125. Such an interaction allows for the creation of an electrical component that acts as a negative inductor. To that end, a negative inductor can be constructed by placing a conductive material inside a ferromagnetic material. Such a negative inductor is shown in FIG. 2.

[0036] FIG. 2 illustrates a negative inductor 200 according to some embodiments of the present disclosure. The negative inductor 200 includes a ferromagnetic material 201 and a conductive material 203 disposed inside the ferromagnetic material 201. In one embodiment, the conductive material 203 is partially enclosed within the ferromagnetic material 201 such that a majority of the conductive material 203 is within the ferromagnetic material 201, and two opposing ends of the conductive material 203, i.e., a first end 205a and a second end 205b, protrude beyond the surface or exterior of the ferromagnetic material 201. The first end 205a and the second end 205b of the conductive material 203 form terminals of the negative inductor 200 for electrical connection with another device or circuit. Accordingly, the first end 205a is referred to as the first terminal 205a, and the second end 205b is referred to as the second terminal 205b.

[0037] In an alternative embodiment, the conductive material 203 is disposed inside the ferromagnetic material 201 such that the entire conductive material 203 is completely surrounded by the ferromagnetic material 203. In such an embodiment, to enable electrical connection, the first terminal 205a and the second terminal 205b are separately formed from a material different from the conductive material 203 and are electrically connected to opposite ends of the conductive material 203, respectively.

[0038] Furthermore, some embodiments recognize that to operate in the negative inductance zone 125, the negative inductor 200 must be supplied with a current whose magnitude is within the range defined by the first local minimum 121 a and the second local minimum 121 b. To supply a current whose magnitude is within the range defined by the first local minimum 121 a and the second local minimum 121 b, the negative inductor 200 is coupled with a current limiting circuit 301. The negative inductor 200, together with the current limiting circuit 301, constitutes a negative inductor device.

[0039] 3A shows a schematic diagram of a negative inductor apparatus 300 according to some embodiments of the present disclosure. The negative inductor apparatus 300 includes a negative inductor 200 and a current limiting circuit 301. The negative inductor 200 is electrically connected to the current limiting circuit 301. For example, the current limiting circuit 301 is connected to the negative inductor 200 via a first terminal 205a and a second terminal 205b. The current limiting circuit 301 provides a current “i” 303 having a magnitude within a range defined by a first local minimum 121a and a second local minimum 121b.

[0040] For example, with reference to Figure 3B, current "i1" 305a corresponding to first local minimum 121a and current "i2" 305b corresponding to second local minimum 121b define a range (i1-i2) of magnitude of current 307. Current limiting circuit 301 provides current "i" 303 having a magnitude within range 307. An exemplary implementation of current limiting circuit 301 is described below in Figure 3C.

[0041] FIG. 3C shows an electrical circuit diagram for an implementation of current limiting circuit 301 according to some embodiments of the present disclosure.

[0042] The current limiting circuit 301 includes bipolar transistors 309 and 311, a reference source 313, and a resistor 315. The bipolar transistors 309 and 311 form a current mirror circuit. According to an embodiment, the reference source 313 outputs a reference value that defines the magnitude of the current flowing through the bipolar transistor 311 and the negative inductor 200. The reference source 313 outputs the reference value based on a range 307. The reference source 313 may output the reference value as a fixed value or may output a variable reference value that defines the magnitude of the current within the range 307. Furthermore, the current flowing through the bipolar transistor 309 is based on the current flowing through the bipolar transistor 311.

[0043] The circuit configuration of the current limiting circuit 301 shown in Fig. 3C is an example, and the current limiting circuit 301 of the present disclosure is not limited to the circuit configuration shown in Fig. 3C. The current limiting circuit 301 may have a different circuit configuration.

[0044] According to the embodiment, the extent of the negative inductance zone 125 depends on the type of ferromagnetic material 201 and / or the mutual arrangement of the conductive material 203 within the ferromagnetic material 201. For example, in some embodiments, the ferromagnetic material 201 has a first shape, the conductive material 203 has a second shape, and the first shape of the ferromagnetic material surrounds the second shape of the conductive material such that the geometric center of the first shape coincides with the geometric center of the second shape. The first and second shapes may be symmetrical or asymmetrical. Such embodiments are described below in FIGS. 4A and 4B.

[0045] 4A shows a schematic diagram of a negative inductor 400 according to some other embodiments of the present disclosure. FIG. 4B shows a different perspective view 410 of the negative inductor 400 according to some other embodiments of the present disclosure. The negative inductor 400 includes a ferromagnetic material 401 and a conductive material 403. The ferromagnetic material 401 is slab-shaped, and the conductive material 403 is a wire twisted into a spiral. The cross section of the wire includes one or a combination of a circular, semicircular, rectangular, and half-rectangular shape. The slab-shaped ferromagnetic material 401 has a geometric center F of the slab-shaped ferromagnetic material 401. c is the geometric center C of the spiral-shaped conductive material 403 c The spiral-shaped conductive material 403 is surrounded by the ferromagnetic material 401 so as to coincide with the spiral-shaped conductive material 403. Such a shape and arrangement of the ferromagnetic material 401 and the conductive material 403 has an advantage that, for example, by using the spiral-shaped conductive material 403, the inductance of the negative inductor 400 is increased.

[0046] The negative inductor 400 (or the negative inductor 200) is constructed using passive elements such as a ferromagnetic material 401 and a conductive material 403. Therefore, the negative inductor 400 (or the negative inductor 200) is called a passive negative inductor.

[0047] Some embodiments recognize that it may be advantageous to connect a negative inductor 400 in parallel or in series with a positive inductor. For example, the negative inductor 400 may be connected in parallel with a positive inductor for inductor amplification, as described below in FIG. 5A.

[0048] 5A shows a diagram 500 of an electric circuit including a negative inductor 400 and a positive inductor 501 connected in parallel, according to some other embodiments of the present disclosure. Some embodiments are based on the understanding that when two positive inductors of inductances L1 and L2 are connected in parallel with each other, the overall inductance L is smaller than the inductance of the individual inductors. L=L1||L2=L1 * L2 / (L1+L2), where L <L1,L2である。

[0049] However, when a negative inductor 400 is connected in parallel with a positive inductor 501, the overall inductance of the parallel connection is greater than the individual inductances. For example, if L2 is negative, then L=(L1 * The inductor 400 is negative (|L2| - L2) / (L1 - L2), where L is positive only if |L2| > L1. Thus, the negative inductor 400 is used for inductor amplification. The first terminal 503a and the second terminal 503b are used to enable electrical connection with other circuits and devices.

[0050] Additionally or alternatively, in some embodiments, the negative inductor 400 and the positive inductor 501 may be connected in series. FIG. 5B shows a diagram 505 of an electrical circuit including the negative inductor 400 and the positive inductor 501 connected in series, according to some other embodiments of the present disclosure. The series connection of the negative inductor 400 and the positive inductor 501 is advantageous because it provides a larger inductance while consuming less chip area. Larger inductors are required for various analog and radio frequency (RF) applications, such as oscillators and power amplifiers. The series connection of the negative inductor 400 and the positive inductor 501 not only saves chip area but also provides an inductance with a high Q factor.

[0051] Additionally, the negative inductor 400 may be used in different circuits, such as microwave circuits, monolithic microwave integrated circuits (MMICs), radio frequency integrated circuits (RFICs), power electronic circuits, etc. For example, in RFICs, the implementation of inductors consumes a significant amount of chip area. Therefore, it is desirable to create inductors that consume less chip area. According to an embodiment, the negative inductor 400 may be used to amplify the value of a positive inductor in an RFIC by consuming less chip area.

[0052] Additionally, in some embodiments, negative inductor 400 can be used as a non-Foster element in various devices and components, such as wideband antennas and artificial magnetic conductors. A non-Foster circuit element is one that does not obey Foster's theorem. Negative inductor 400 can be used as a non-Foster element in wideband antennas to eliminate narrowband resonant behavior inherent in wideband antennas.

[0053] Furthermore, the negative inductor 400 can be used to improve impedance matching between a power amplifier (PA) and an antenna. For example, in a transmitter system, a passive matching network is inserted between the output of the power amplifier (PA) and the antenna to match the output impedance of the PA to the output impedance of the antenna. Passive matching networks typically include one or more capacitors and one or more inductors. Passive matching networks receive power only from their power source (typically the PA) and do not require any external power source. Passive matching networks conform to Foster's reactance theorem and perform well in matching the impedance of the PA to the impedance of the antenna at a single frequency. However, they are not perfect even at a single frequency because real-world inductors and capacitors are not ideal, i.e., they have resistance in addition to reactance. Furthermore, most practical applications require the transmitter to operate over a certain bandwidth, especially when antennas with small physical sizes are utilized. It is often impossible to achieve acceptable or desirable impedance matching over an acceptable or desirable bandwidth using Foster (passive) networks. The impedance matching can be improved by using a non-Foster (or active) network based on the negative inductor 400. The non-Foster network based on the negative inductor 400 can be called a non-Foster impedance matching circuit. The non-Foster network based on the negative inductor 400 cancels the reactance of the antenna, which improves the efficiency and bandwidth of the PA.

[0054] Additionally, in some embodiments, the negative inductor 400 can be used as a non-Foster element in an artificial magnetic conductor. An artificial magnetic conductor (AMC) is a type of metamaterial that emulates a magnetic conductor over a limited bandwidth. AMC ground planes enable conformal antennas in which currents flow parallel to the surface because parallel image currents in the AMC ground plane improve their source. AMCs can have limited bandwidths. Their bandwidths are proportional to the thickness and permeability of the substrate. At VHF-UHF frequencies, the thickness and / or permeability required for reasonable AMC bandwidth are excessively large for antenna ground plane applications.

[0055] The bandwidth limitations of AMC can be overcome by using a negative inductor 400 as a non-Foster element. When a negative inductor 400 is introduced into an AMC, its negative inductance in parallel with the substrate inductance results in a larger net inductance and therefore a larger AMC bandwidth. Furthermore, the negative inductor 400 can be used as a non-Foster element in an AMC to eliminate the narrow-band resonant behavior inherent in AMC.

[0056] In some embodiments, the types of ferromagnetic material 401 and conductive material 403 are selected mutually or independently based on the application of negative inductor 400. Examples of conductive materials used in different embodiments include copper, aluminum, steel, iron, etc. Examples of ferromagnetic materials used in different embodiments include various ferromagnetic oxides, cobalt, magnetite, dysprosium, nickel, gadolinium, awalite, permalloy, etc.

[0057] In one embodiment, negative inductor 400 is formed by immersing spiral conductive material 403 in a ferromagnetic oxide, which is a ferromagnetic material. Similarly, negative inductor 200 is formed by immersing conductive material 203 in a ferromagnetic oxide. A method for fabricating negative inductor 400 (or negative inductor 200) is described in detail in FIG. 6.

[0058] 6 shows a schematic diagram of a method for fabricating a negative inductor 400 according to some other embodiments of the present disclosure. The method includes providing a substrate. The substrate may include, but is not limited to, silicon (Si), silicon carbide (SiC), diamond, gallium nitride (GaN), etc. For purposes of illustration, consider a Si substrate 601. The Si substrate 601 may be cleaned according to a piranha cleaning method and / or a Radio Corporation of America (RCA) cleaning method.

[0059] The method further includes depositing 603 a first layer 605 of ferromagnetic material (e.g., a ferromagnetic oxide) on the cleaned Si substrate 601 using a deposition method, such as pulsed laser deposition (PLD). Alternatively, in some embodiments, MBE (molecular beam epitaxy), MOCVD (metal organic chemical vapor deposition), CVD (chemical vapor deposition), sputtering, or e-beam evaporation may be used to deposit the first layer 605 of ferromagnetic material. After deposition of the ferromagnetic material, the sample 607 may be annealed in an oxygen environment.

[0060] The method further includes forming 609 metal spirals 611 on the surface of the first layer of ferromagnetic material 605 using, for example, photolithography and / or a lift-off process. Photolithography involves the use of light to produce finely patterned thin films of a suitable material on a substrate.

[0061] The method further includes depositing 613 a second layer 615 of ferromagnetic material over the first layer 605 and the metal spirals 611, completely submerging the metal spirals 611 within the ferromagnetic material. The second layer 615 of ferromagnetic material is deposited 613 using a PLD method.

[0062] PLD is a physical vapor deposition technique that allows for non-equilibrium and versatile tuning of complex stoichiometry. PLD combines the properties of both evaporation and sputtering. Thin films may be deposited using PLD. Thin film deposition is achieved by focusing a laser pulse onto a target of the desired stoichiometry, generating a plume containing atomic species of the target material that deposits on the substrate. For example, in PLD, the laser pulse delivers 2-3 J / cm on the target. 2 The laser pulse is guided and focused by high-quality quartz optics, allowing for energy densities in the range of 1000 sq. m / s. The target spot where the laser pulse strikes is rapidly heated and vaporized, and the vapor absorbs more energy from the laser pulse and decomposes into a high-density plasma. The high-density plasma absorbs the remaining energy from the laser pulse and expands to produce a plume perpendicular to the target surface, resulting in deposition onto a substrate positioned directly above the target. The substrate may be rotated during deposition to ensure uniformity and low roughness of the film surface, and the target is rotated and rastered during laser ablation and deposition to ensure uniform ablation of the target.

[0063] The following description provides exemplary embodiments only and is not intended to limit the scope, applicability, or configuration of the present disclosure. Rather, the following description of exemplary embodiments provides those skilled in the art with an enabling description for implementing one or more exemplary embodiments. Contemplated are various changes that may be made in the function and arrangement of elements without departing from the spirit and scope of the disclosed subject matter as set forth in the claims.

[0064] In the following description, specific details are given for a thorough understanding of the embodiments. However, it will be understood by those skilled in the art that the embodiments may be practiced without these specific details. For example, systems, processes, and other elements in the disclosed subject matter may be shown as components in block diagram form so as not to obscure the embodiments in unnecessary detail. In other instances, well-known processes, structures, and techniques may be shown without unnecessary detail to avoid obscuring the embodiments. Furthermore, like reference numbers and names in the various drawings indicate like elements.

[0065] Also, particular embodiments may be described as a process that is depicted as a flowchart, a flow diagram, a data flow diagram, a structure diagram, or a block diagram. While a flowchart may describe operations as a sequential process, many of the operations can be performed in parallel or simultaneously. Additionally, the order of operations may be rearranged. A process may terminate when its operations are completed, but may have additional steps not discussed or included in the diagram. Moreover, not all operations in any specifically described process may occur in all embodiments. A process may correspond to a method, a function, a procedure, a subroutine, a subprogram, etc. When a process corresponds to a function, the termination of the function may correspond to a return of the function to the calling function or the main function.

[0066] The embodiments of the present disclosure may be embodied as a method, of which an example is provided. The acts performed as part of the method may be ordered in any suitable manner. Thus, embodiments may be constructed in which acts are performed in a different order than illustrated, including simultaneously performing some acts shown as sequential acts in the exemplary embodiment.

[0067] Although the present disclosure has been described with reference to certain preferred embodiments, it is to be understood that various other adaptations and modifications can be made within the spirit and scope of the disclosure. It is therefore the object of the appended claims to cover all such variations and modifications that come within the true spirit and scope of the disclosure.

Claims

1. 1. A negative inductor device, comprising: a negative inductor including a ferromagnetic material and a conductive material disposed inside the ferromagnetic material; a current limiting circuit electrically coupled to the negative inductor and configured to supply a current having a magnitude within a range defined by a first minimum and a second minimum of a current-energy curve of the ferromagnetic material.

2. The negative inductor device of claim 1 , further comprising first and second terminals electrically connected to the first and second ends, respectively, of the conductive material.

3. 2. The negative inductor device of claim 1, wherein the ferromagnetic material has a first shape and the conductive material has a second shape, and the first shape of the ferromagnetic material surrounds the second shape of the conductive material such that a geometric center of the first shape coincides with a geometric center of the second shape.

4. The negative inductor device of claim 3 , wherein each of the first shape and the second shape is a symmetrical shape.

5. The negative inductor device of claim 4 , wherein the first shape is a slab and the second shape is a spiral.

6. 6. The negative inductor device of claim 5, wherein a cross section of the wire comprises one or a combination of a circular, semicircular, rectangular, and half-rectangular shape.

7. A negative inductor, a ferromagnetic material; a conductive material partially enclosed within the ferromagnetic material such that both ends of the conductive material protrude from the ferromagnetic material, the both ends of the conductive material protruding from the ferromagnetic material corresponding to terminals of the negative inductor.

8. A negative inductor, a ferromagnetic material; a conductive material disposed inside the ferromagnetic material.

9. 9. An electric circuit comprising a positive inductor electrically connected in parallel with the negative inductor of claim 8.

10. 9. An electric circuit comprising a positive inductor electrically connected in series with the negative inductor of claim 8.

11. 10. A non-Foster impedance matching circuit including the negative inductor of claim 8 for impedance matching between a power amplifier (PA) and an antenna.

12. An artificial magnetic conductor including the negative inductor according to claim 8, wherein the negative inductor according to claim 8 acts as a non-Foster element.

13. 1. A method for manufacturing a negative inductor, comprising: depositing a first layer of ferromagnetic material on a substrate; forming a metal spiral on a surface of the first layer of ferromagnetic material; and depositing a second layer of ferromagnetic material over the first layer of ferromagnetic material and the metal spiral.

14. The method of claim 13 , wherein the first layer of ferromagnetic material and the second layer of ferromagnetic material are deposited using pulsed laser deposition (PLD).

15. The method of claim 13 , wherein the metal spiral is formed on the surface of the first layer of ferromagnetic material using photolithography.

Images