FABRICATION AND MICROWAVE CHARACTERIZATION OF MULTILAYER CIRCUITS FORMMIC APPLICATIONS

A technique to fabricate novel multilayer monolithic microwave integra ted circuit (MMIC) structures using polyimide as insulating dielectric layer is described. The polyimide layer formation, curing and dry etc hing processes are investigated in an attempt to obtain high quality d ielectric layers suitable for MMIC applications. By employing this tec hnique, MMIC design and circuit routings become much easier and conven tional microstrip transmission lines and lumped passive components can be realised with effective use of the substrate material. In the pape r it is shown that a V-shaped MMIC coplanar waveguide (CPW) transmissi on lines with low characteristic impedance and edge offset broadside d irectional couplers can easily be designed using the multilayer techni que. This implementation can avoid the well known current crowding eff ects on the conductor edges. Within the Ku and K band frequency range, circuits have been characterised and show good performances. By using the same technique, miniaturisation of a lumped-distributed CPW ring- resonator bandpass filter can be achieved with built-in shunt capacito rs. Two transmission poles and two transmission zeros could be impleme nted by introducing two discontinuities. The measured results show a 3 dB bandwidth of 3.7 GHz at 13.7 GHz.