In this paper, a novel MEMS-based planar fractal transformer is presented. Space-filling property of Hilbert curve is exploited for the miniaturization of integrated transformers. Compared to traditional spiral transformer, the fractal Hilbert transformer requires only one metal layer and no interconnection vias or cross-overs, thereby reducing micro-fabrication complexity, EMI interference and resistive loss in the cross-overs. The transformer is implemented in a low-cost MetalMUMPs standard process. The transformer is coreless and the silicon underneath the primary and secondary coils is removed to mitigate the parasitic capacitance. The dc resistance of the transformer is 0.78 O, and the primary inductance of 9.3 nH has been obtained at 30 MHz. The quality factor of the transformer at 60 MHz is 1.6 and the total area of the transformer is 0.27 mm2. The obtained inductance density of 35 nH/mm2 is better than other air core transformers thus far in the literature.
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