Micromachined Membrane Filters for Microwave and ( ) Millimeter - Wave Applications Invited Article

Recent developments in micromachining techniques at the University of Michigan have resulted in novel high-performance low-loss filters for microwave and millimeter-wave applications. The idea is based on suspending the filters on thin dielectric membranes to eliminate dielectric loss and dispersion problems, resulting in a pure TEM mode of propagation and conductor-loss-limited performance. The dielectric membrane and the surrounding cavities are built using chemical etching in Silicon and GaAs wafers. The filters are therefore compatible with low-cost IC fabrication techniques and can be combined with planar diodes and transistors to result in active filter networks. Several state-of-the-art filters have been realized including 15-GHz and 20-GHz bandpass interdigital suspended stripline filters, lowpass and bandpass microshield filters at 30 GHz and 90 GHz, microstrip 94-GHz bandpass filters, and a 250-GHz bandpass filter with 1.0–1.5-dB insertion loss. This article reviews the associated fabrication techniques, the different types of transmission lines achieved using this technology, and the measured performance from 15 to 350 GHz. The study concludes with a detailed description of the future work in this area. Q 1997 John Wiley & Sons, Inc. Int J Microwa©e Millimeter-Wa©e CAE 7: 149–166, 1997.