Micromachined elevated CPWs for high-performance microwave circuits

In this paper, micromachined elevated coplanar waveguides (ECPWs) based on CMOS-grade silicon with a thin film interface are presented. The respective signal lines for the ECPWs are 10 νm elevated into the air with supporting conductors so as to obtain low attenuation characteristics. For the designed ECPWs, it has been shown that a low loss transmission line is obtainable compared to the conventional CPW and a very low effective dielectric constant close to 2 could be realized by confining most of the electromagnetic fields in the lossless air layer. The overlapped configuration with an elevated signal line placed partially above the planar ground planes on the thin film interface yielded the best attenuation performance, i.e., about 0.29 dB mm^-1 at 20 GHz. In addition, a Chebyshev low-pass filter (LPF) with 0.5 dB ripple is designed on the basis of the high-Z₀ and low-Z₀ ECPWs, and fabricated using the surface micromaching technique. The measured data show good agreement with the predicted values. It is expected that the suggested ECPWs can be applied to high-performance microwave/millimeterwave circuits by employing low-cost silicon surface micromachining technology.