Analysis and optimization of vertically oriented, through-wafer, laminated magnetic cores in silicon

Abstract

This paper compares two fabrication methods for achieving through-wafer, laminated magnetic cores in silicon, intended for microfabricated magnetic devices where vertically oriented (normal to the wafer) magnetic laminations are required to reduce eddy current losses. Given certain fabrication constraints for each method, a theoretical framework is presented to permit the design of the optimal lamination scheme for a particular application. As an example, the analysis is applied to the optimization of laminations for a miniaturized synchronous permanent magnet motor/generator.

Design and Fabrication of Integrated Power Inductor Based on Silicon Molding Technology

“…Researchers have used through-wafer silicon trenches as electroplating molds for interconnects in three dimensional packaging [19,20]. More recently, using through-wafer silicon trenches for magnetic lamination was studied [13] and a coreless RF inductor based on through-wafer silicon molds was demonstrated [21]. However, using silicon molding technique to construct a power inductor by stack multiple thick metal layers has not been reported.…”

“…To solve this dilemma, either core lamination or magnetic materials with large skin depth or high saturation flux density should be employed for power inductors. Many approaches for laminating power inductor cores have been reported [13][14][15], but most of them suffer from low space lamination efficiency and long processing time. Techniques other than electroplating have also been explored to make magnetic materials that are suitable for high frequency and high power applications [4,[16][17][18].…”

3-D Microtransformers for DC–DC On-Chip Power Conversion

“…An appropriate material for the magnetic core of a power transformer should have a high saturation magnetization, high permeability, high resistivity, low coercivity and high thermal conductivity. Among the above-mentioned properties, resistivity, thermal conductivity and saturation magnetization are intrinsic properties of a material, while the other depend on the external effects, such as the shape and dimension of the core [19], fabrication process [20], operating frequency [10], extra annealing [20], and excitation waveform [21]. All these parameters need to be considered when designing an efficient core.…”

“…Ferrites are popular candidates as a core material for MHz frequency regime applications, mainly due to their high resistivity which is necessary to damp the induced eddy current in the core at high frequencies [22]- [26]. This advantage is paid by the relatively low permeability and high coercivity, which limit the further miniaturization of ferrite cores [4], [10]. Besides, the main disadvantage of ferrites is the relatively lower saturation flux density when compared to other types of core magnetic materials.…”

“…The hysteresis loss can be controlled by choosing the right material composition as well as annealing of the core magnetic material [9]. The eddy current losses can be minimized either by using high resistivity magnetic materials or by splitting the bulk magnetic core into thin layers, which are in the same thickness range of the skin depth in the frequency range of interest [10]. However, both approaches increase the complexity of the magnetic components.…”