Tunable High-Frequency Thin-Film Inductor through Stress-Induced Magnetic Anisotropy

Thin-film solenoid-type inductors, owning low flux leakage and low parasitic capacitance, is required with high stability and tunability for flexible electronics. The existing solutions for flexible and tunable thin-film solenoid-type inductors is limited with the operations ease, device size and compatibility in flexible electronics. This work demonstrates a general approach to realize thin-film solenoid-type inductors on flexible substrate via stencil lithography. Ultrathin solenoid-type inductors were achieved with the total thickness less than 1 µm, and this ultrathin construction benefited the pliability and deformation uniformity during deformation regulation. The magnetic anisotropy and the permeability of permalloy magnetic core were directly impacted by bending the substrate through the magnetoelastic coupling. Based on this, the applied tensile/compressive strains gave rise to the multi-directional tunability of the thin-film inductors, showing the maximum enhancement over 140% of the inductance value at 800 MHz by bending. With the highly stability over 1,000 bending cycle tests, this method for thin-film solenoid-type inductors with easy-access turnability is expected for the future applications of flexible electronics in RF circuit and wireless communication.