Fabrication of new micromachined transmission line with dielectric posts for millimeter-wave applications

This paper describes a new GaAs-based surface-micromachined microstrip line supported by dielectric posts and with an air gap between the signal line and the ground metal. This new type of dielectric post and air-gapped microstripline (DAML) structure was developed using surface micromachining techniques to provide an easy means of air-bridge connection between the signal lines and to achieve low losses in the millimeter-wave frequency band with a wide impedance range. Each DAML is fabricated with a length of 5 mm. By elevating the signal lines from the substrate using micromachining technology, the substrate dielectric loss can be reduced. Compared with conventional microstrip transmission lines, which show over 10 dB cm^-1 loss, the loss of a DAML can be reduced to 1.1 dB cm^-1 at 50 GHz.