Low-Loss and High-Frequency Interconnection Technology on Membrane Supported by Porous Silicon Post

Abstract

A coplanar waveguide (CPW) has been fabricated on a 40 pm-thick porous silicon layer and the measured maximum available gain is -0.59 dB/mm at 40 GHz. The coplanar waveguide is then released in the air by etching the porous silicon layer under the signal line, which is supported at each end by porous silicon posts. The porous silicon post is surrounded by silicon sidewalls and a dielectric layer to protect it from the etchant. The porous silicon layer can be etched in 0.25 wt% NaOH solution with the rate of more than 2.5 mum/min but metal patterns are not attacked significantly by the etchant when there is no protection mask for them. A 5-mm-long coplanar waveguide has a maximum available gain of -1.32dB at 40GHz and a return loss of less than -16 dB up to 40 GHz. A maximum available gain of -0.2 dB/mm at 40 GHz is obtained when the gap between the membrane and silicon substrate is 100 mum. Because of its low-loss characteristic, the coplanar waveguide can be used for RF interconnection and multichip module package applications.