High-performance CMOS-cornpatible micromachined edge-suspended coplanar waveguides on low resistivity silicon substrate

This paper reports a novel low-loss CMOS compatible coplanar waveguide (CPW) structure based on the micromachined edge-suspension of the signal line. It is revealed that, at radio or microwave frequencies, the current is highly concentrated along the edges of the signal line. Since the coupling to the low resistivity silicon substrate is dominated by the current carrying part, the substrate coupling and loss can he effectively suppressed by removing the silicon along and underneath the edges of the signal lines. The edge-suspended structure has been implemented by a combination of deep reactive ion etching and anisotropic wet etching. The suspended structure shows much reduced loss (0.5 dBlmm at 39 GHz) and strong mechanical strength that is provided by the silicon underneath the center of the signal line.