Micromachined Coreless Single-Layer Transformer Without Crossovers

This letter presents the design and characterization of a novel micromachined fractal-shaped microtransformer for VHF and UHF frequency ranges. To eliminate the loss in magnetic core materials at high frequency and to achieve high coupling and quality factor, the microtransformer is designed to be coreless (air core). The novel design with a single metal layer and no crossover interconnections facilitates the standard metal multiuser microelectromechanical systems (metalMUMPsR^®) fabrication process, as well as eliminates the interconnection resistance and electromagnetic interference due to vias and crossovers. A primary inductance of 7.14 nH and a transformer quality factor of 5.92 were achieved at 500 MHz. The coupling coefficient of the transformer at 1 GHz is 0.77, and the efficiency of the transformer at 250 MHz with matched load is 71%.