Fabrication of thick silicon dioxide air-bridge for RF application using micromachining technology

With operating frequencies constantly increasing in communication and integrated circuits, there is a great demand for a low-cost/low-loss substrate medium. Although silicon is a low-cost material and has a high thermal conductivity, it has not been used as a microwave substrate because of its extremely high dielectric loss. The micromachined oxide bridge or membrane was reported to overcome the problem of high dielectric loss of the low-resistivity silicon substrate. However, the resulting structure is relatively fragile because the thickness of oxide bridges supporting the passive elements is too thin in a conventional process. Therefore, for the purpose of solving this problem, we have successfully fabricated thick silicon dioxide bridges using the anodic reaction, oxidation, and surface micromachining process. This process is compatible with the conventional CMOS fabrication process since it is post-processing. Therefore, it is believed that this thick silicon dioxide air-bridge could be used for RF application.