Variable Microelectronic Inductors

A thin-film microelectronic inductor is proposed. It is suitable for use in the frequency range from 5 to 20 MHz. The inductor is in the shape of a square spiral and is surrounded by patterned permalloy thin films. The pattern allows these films to be driven in their easy axes of magnetization by the high-frequency signal current. In the presence of a small dc magnetic field applied in the hard direction and equal to the anisotropy field, the resulting permeability is very high, and thus the inductance of the pattern is greatly increased. Since the inductance is a function of the dc magnetic field applied in the hard direction, variable inductors and tunable planar resonant circuits are readily implemented using the proposed device. The design considerations of the device are described, and the significance of the theoretical results is discussed. Experimental work is being carried out to verify the above results.