Out-of-plane spiral-coil inductor self-assembled by locally controlled bimorph actuation

A method to manufacture 3D microcoils based on locally controlled bimorph actuation is reported. A simple and batch-compatible method for producing out-of-plane spiral structures is developed to create inductors whose inductances are tuned independently of their base dimensions. A 500-nm-thick Cr layer used as the stress layer is patterned on a planar Cu coil to induce plastic deformation of the coil in the vertical direction uniformly, defining the final 3D coil shape. The Cr pattern, as well as the temperature of post-fabrication annealing, is varied to achieve different levels of vertical deformation and inductance of the coils. A maximum vertical expansion of 721 μm is demonstrated to yield a 12 inductance change. The Q factor of 17 and the self-resonance at ~1.2~GHz are obtained.