Ferromagnetic RF MEMS – Materials and Possible Applications
Research Institute of Electrical Communication, Tohoku University
2-1-1 Katahira, Aoba-ku Sendai 980-8577, Japan
Huge applications of soft magnetic films can be expected as integrated passives in the latest IT devices, including CMOS compatible RF integrated inductors and transformers, transmission line devices, electromagnetic noise countermeasure, sensors, etc.
Possibility of these applications largely depends on the frequency profile of complex permeability, _r=_r’ -j_r”, of the thin film candidate materials. Therefore we began with development of a new 1MHz-9GHz permeameter consisting of a side-open TEM cell, a shielded-loop type planar pickup coil, a solenoid coil, a network analyzer and a host computer. Experimental data on CoNbZr, CoZrO, CoAlPdO, electroplated NiZn(Co) ferrite, etc. will be shown in the presentation. A novel film-patterning technique to enhance the effective anisotropy field will also be discussed.
The permeability evaluation was followed by the microfabrication of two types of RF integrated magnetic thin-film inductors on high resistivity Si wafer (_>500_cm): The sandwich type one-port spiral inductor and a simple on-top type two-port spiral inductor. This application needs high _r’ and negligibly small _r”. Performance in a 100MHz-5GHz range will be discussed. Extensive design will be discussed based on simulation work
Another possible application is integrated electromagnetic noise countermeasure which needs low _r’ and high _r” in an RF range. Possible configuration is to integrate the magnetic film on to a RF transmission line. The ideal role of magnetic film is not to raise insertion losses in the pass-band and to give as large attenuation as possible at the stop-band. Experimental and simulation results suggest that this application should be possible up over 10GHz.
Masahiro Yamaguchi obtained B.Sc, M.Sc. and Dr.Sc. degrees in electrical and communication engineering from Tohoku University, Japan. He has been working in Tohoku University as research associate (1984-1991), associate professor (1991-2003) and full professor (From April 2003). He was a visiting associate professor at University of Wisconsin-Madison during October-December 1995. His interests include materials, microfabrication processes, device applications and related high frequency measurements of thin-film micromagnetic devices. His industrial partners have commercialized thin film permeameters (1MHz-9GHz), and magnetic near field probes for IEC standard (SC47/WG9). He initiated International Symposium on High Frequency Micromagnetic Devices and Materials.