Active solid-state devices (e.g. – transistors – solid-state diode – Miscellaneous
Reexamination Certificate
1999-04-16
2001-02-20
Fahmy, Wael (Department: 2823)
Active solid-state devices (e.g., transistors, solid-state diode
Miscellaneous
C257S421000, C438S003000, C438S022000, C365S145000, C360S318000, C360S328000, C360S123090, C360S125020, C360S125330
Reexamination Certificate
active
06191495
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention is directed, in general, to integrated circuits and, more specifically, to a micromagnetic device including a ferromagnetic core having an anisotropic property and a method of manufacture therefor.
BACKGROUND OF THE INVENTION
A magnetic device includes a magnetic core coupled to conductor windings such that magnetic flux flows in a closed path about the core. Magnetic devices are generally configured in an EE-type structure or a toroidal geometry. In the EE-type magnetic device, a first and second core-portion of the magnetic core surround the conductor windings. In the toroidal magnetic device, a first and second winding-portion of the conductor windings surround the magnetic core.
Micromagnetic devices (e.g., microinductors or microtransformers) are micron-scaled integrated circuit magnetic devices; the electromagnetic properties of the device are provided by the presence of the magnetic core and conductor windings. In the past, micromagnetic devices were only applicable to low-level signal applications (e.g., recording heads). With the advancement in production techniques for integrated circuits, it is now possible to fabricate micromagnetic devices for relatively large signal, power processing and high speed data transmission applications. For instance, micromagnetic devices may be employed in power systems for wireless communications equipment or in data transmission circuits.
While many power semiconductor devices (having ferrite cores, for instance) have been scaled down into integrated circuits, inductive elements at the present time remain discrete and physically large. Of course, there is a strong desire to miniaturize these inductive components as well. By extending thin-film processing techniques employed in power semiconductor devices to ferromagnetic materials, the size of the conventional discrete ferromagnetic-core inductive devices can be reduced significantly. Ferromagnetic materials such as alloys, however, have much higher saturation flux densities than ferrites (e.g., 10-20 kG verses 3 kG), thereby reducing the physical volume of the core for a given inductance and energy requirement. To limit the eddy current losses in the ferromagnetic materials, the materials must be fabricated in inordinately thin films. Processing thin-film ferromagnetic materials with traditional rolling and tape winding techniques proves to be very costly as the desired tape thicknesses drops below 0.001 inches (i.e., 25 &mgr;m). It is thus advantageous to produce such thin films by other integrated circuit deposition techniques such as sputtering or electroplating.
Another germane consideration associated with manufacturing micromagnetic devices is securing the ferromagnetic material to a silicon substrate or the like. More specifically, forming an adequate bond between the ferromagnetic material and an insulator coupled to the substrate is an important consideration. Many factors (such as oxide formation, melting point temperature, interposed contamination, affinity between materials and mechanical stress at the interface) may influence the adhesion of a thin film to a substrate. For instance, one technique readily employed in thin film manufacturing processes is the formation of an oxide-metal bond at the interface between the substrate and the film. The oxide-metal bond may be formed by employing an oxygen-active metal (such as tungsten or chromium) on an oxygen-bearing substrate (such as glass or ceramic) in conjunction with a refractory metal (such as tantalum or tungsten). With regard to contaminants, it is advantageous to remove any impurities interposed on the substrate. Cleaning methods vary in effectiveness and the method selected depends on the ability of the deposition process to dislodge contaminant atoms. As an example, different cleaning techniques may be employed with sputtering or electroplating.
Of course, the ultimate consideration with regard to the adhesion properties depends on the materials employed. While others have attempted to address the adhesion of ferromagnetic materials to an insulator coupled to a substrate [e.g., Measured Performance of a High-Power-Density Microfabricated Transformer in a DC-DC Converter, by Charles R. Sullivan and Seth R. Sanders, IEEE Power Electronics Specialists Conference, p. 287-294 (July 1996), which is incorporated herein by reference], to date, the problem remains unresolved. The development of an adhesive material that simultaneously forms a bond with the insulator and the ferromagnetic material such that thin-film processing can be applied to inductive elements would provide a foundation for the introduction of power processing or data transmission micromagnetic integrated circuits.
Regarding the magnetic properties, current micromagnetic devices are typically isotropic in that their properties are the same when measured in different directions. Although anisotropic properties are generally known in the domain of magnetics, anisotropic properties have not been employed in the design of micromagnetic devices due, in part, to the limitations as addressed above regarding the fabrication of micromagnetic integrated circuits. Micromagnetic devices with the ability to induce a designed magnetic anisotropic property into the core, having a desired direction and characteristic, would be very useful.
Accordingly, what is needed in the art, in addition to a micromagnetic device for use in integrated circuits, is a way to implement the micromagnetic device that exhibits a defined anisotropic property to achieve a desirable magnetic characteristic.
SUMMARY OF THE INVENTION
To address the above-discussed deficiencies of the prior art, the present invention provides, in one aspect, for use with an integrated circuit including a substrate having an insulator coupled to the substrate, a micromagnetic device and method of manufacture therefor. In one embodiment, the micromagnetic device includes an adhesive coupled to the insulator and a ferromagnetic core, coupled to the adhesive that forms a bond between the insulator and the ferromagnetic core, having an anisotropic property.
The present invention introduces the broad concept of a micromagnetic device having an anisotropic ferromagnetic core. The introduction of the defined anisotropy provides a mechanism to more ostensibly delineate the magnetic properties of the micromagnetic device. For instance, the anisotropy may be employed to introduce a high permeability region or a low hysteresis region, or a combination thereof, to tailor the characteristics of the device. It should be understood that the micromagnetic device may be employed to advantage in many applications including, for instance, power processing and data transmission circuits.
In one embodiment of the present invention, the micromagnetic device includes a ferromagnetic core having an easy axis and a hard axis. In a related, but alternate embodiment of the present invention, the easy axis is substantially transverse to the hard axis. These embodiments will hereinafter be described to illustrate that an external magnetic field may be applied during a deposition process thereby allowing the magnetic characteristics of the micromagnetic device to be tailored to meet specific design criteria.
The foregoing has outlined, rather broadly, features of the present invention so that those skilled in the art may better understand the detailed description of the invention that follows. Additional features of the invention will be described hereinafter that form the subject of the claims of the invention. Those skilled in the art should appreciate that they can readily use the disclosed conception and specific embodiment as a basis for designing or modifying other structures for carrying out the same purposes of the present invention. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the invention in its broadest form.
REFERENCES:
patent: 5312674 (1994-05-01), Haertling et al.
patent: 5432734 (19
Kossives Dean P.
Lotfi Ashraf W.
Schneemeyer Lynn F.
Steigerwald Michael L.
Van Dover R. Bruce
Berezny Neal
Fahmy Wael
Lucent Technologies - Inc.
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