SU-8 Micromachining of Millimeter and Submillimeter-wave Waveguide Circuits

There is an increasing interest in the millimeter and submillimeter wave frequency range for various applications such as compact range radar, biological detection and terahertz imaging for example. The Department of Defense has given the U.S. National Ground Intelligent Center has as part of its mission the validation of radar signatures for hostile vehicles and helicopters. One method of obtaining this information is to scale up the frequency and reproduce scale models of targets so that the radar signature of the hostile target is accurately obtained in a controlled environment and cost effective method. In the field of molecular spectroscopy there has been a discovery of THz absorption within the anthrax surrogate, bacillius subtillus. This presents a potential application for the study and identification of biological warfare agents. Terahertz imaging systems are progressing such that imaging tools are being developed with the capability to detect weapons under clothing.;The range of frequencies for these applications extends from 300 GHz to 3 THz corresponding to a wavelength of 1 mm to 100 microm. Typically below this frequency range transmission line structures such as microstrip and coplanar waveguide are widely utilized, with acceptable amounts of loss. As the frequency increases above 100 GHz these transmission-line structures become very lossy. As a result, rectangular waveguides are used as a suitable replacement for the lossy media because of their low-loss characteristic. However, waveguide dimensions become smaller with increasing frequency therefore escalating the complexity and cost of fabrication with conventional machining techniques.;This research proposes using SU-8 photoresist and lithography techniques to develop an SU-8 micromachining process to overcome the limitation of conventional machining in fabrication of millimeter and submillimeter waveguide components. This will be demonstrated with the design and fabrication of waveguide circuits in the 220--325 GHz frequency range (WR 3.4).