Novel Ultra-Wide Band (10 MHz–26 GHz) Permeability Measurements for Magnetic Films

Abstract

Magnetic materials are the necessary components of the modern rf components. The demand for higher communication speed such as the upcoming 5G network requires higher operation frequency of rf components. For example, the future spectrum band of mobile network will be extended above 24 GHz [1]. Permeability measurements provide a basis for the design and characterization of magnetic materials and the development of RF devices. However, permeability measurement results and commercially available permeameters have been limited to 9GHz or below [2]–[7]. Conventional broadband permeameters use a vector network analyzer (VNA), and a pick-up coil or an electric short [2], [3], or a broadband transmission line [4], [6] for magnetically exciting the materials under test. Inductance changes are measured at zero magnetic field and at saturation magnetic field through a vector network analyzer for extracting the permeability spectrum. The bandwidth of Pick-up coil is limited to several hundred MHz. Transmission-lines [4]–[6] are widely used for broadband permeameters. However, the transmission-line type permeameters are noisy in the frequency range below 100MHz due to the low inductance. In addition, all these broadband permeameters based on vector network analyzers are expensive, and not reliable in measuring thin films or materials with low permeability because of the low signal to noise ratio (SNR). In this article, we demonstrate a new type of permemeter for ultra-wide band permeability measurements with significantly enhanced signal to noise ratio (SNR), and demonstrate the measurements on a 50nm FeGaB film up to 22GHz and an ultra-thin 2nm NiFe film. This permeameter enables the characterization of the complex permeability between 10MHz-26GHz, as well as many other typical magnetic parameters including linewidth, saturation magnetization, effective anisotropy field, Gilbert damping, and inhomogeneous linewidth broadening. In addition, the new permeability measurement system shows $40 \sim 50$ dB higher SNR over the conventional permeameters.