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Fabrication of Thick Silicon Dioxide Air-Bridge for RF Application Using Micromachining Technology

This paper proposes a 10 µm thick oxide air-bridge structure which can be used as a substrate for RF circuits. The structure was fabricated by anodic reaction, multi-step thermal oxidation and micromachining technology using tetramethylammonium hydroxide (TMAH) etching. This structure is mechanically stable because of thick oxide layer up to 10 µm and is expected to solve the problem of high dielectric loss of silicon substrate in RF region. The properties of the transmission line formed on the oxidized porous silicon (OPS) air-bridge were investigated and compared with those of the transmission line formed on the OPS layers. The insertion loss of coplanar waveguide (CPW) on OPS air-bridge is (about -2 dB) lower than that of CPW on OPS layers. Therefore, this technology is very promising for extending the use of complementary metal oxide (CMOS) circuitry to higher RF frequencies.