Millimeter-wave Fermi tapered slot antennas on micromachined silicon substrates

This paper presents 90 GHz Fermi-type tapered slot antennas (TSA) on a micromachined 100 μm thick silicon substrate (ε_r=11.7) and for comparison purposes, 90 GHz Fermi-type TSA on 150 μm thick quartz substrate (ε_r=3.78). A 100 μm thick wafer is chosen because it is compatible with 90-100 GHz low-noise amplifier circuits on GaAs-InP substrates. The effective thickness of the substrate was reduced by selectively micromachining holes in the silicon wafer using deep reactive ion etching (deep RIE). The radiation patterns of the micromachined antennas were significantly better than the nonmicromachined version and had similar radiation patterns to the quartz design. The etched hole diameter was changed from 300 to 750 μm with minor effect on the radiation patterns. This shows that the predominant reason for the improved patterns lies in the reduced effective dielectric constant and not in substrate-mode suppression effects. This type of antenna is well suited for millimeter-wave imaging arrays