A thin film microtransformer with the size of 3.14 x 3.88 mm2 was fabricated by using photolithography technology to support high-frequency switching regulators. The microtransformer was composed of sputtered amorphous magnetic layers, electroplated copper windings with 20 pm width and insulator layers. A coupling factor between the primary and secondard windings of the microtransformer was 0.97 for f= 3 MHz. The input-output voltage ratio of 0.95 at 15 MHz was obtained at no-load. The observation of the domain images under high frequency excitation indicated the magnetic anisotropy of films of the microtransformer with circular spiral coils was induced by a rotating magnetic field annealing so as to increase the output voltage.
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