Dielectric Membranes Supported Millimeter-Wave Passive Circuits

In the last years a lot of studies were focused on micromachining for high-performance microwave and millimeter-wave circuits. A substantial improvement in circuits’ characteristics has been achieved by integration of antennas, components and transmission lines on thin dielectric and semiconductor membranes. Several types of membranes have been developed during the past few years. It is the purpose of this presentation to compare the membranes’ quality and the performances of the circuits manufactured on each type of membrane. The following types of membranes have been successfully manufactured: three-layer (SiO2/Si3N4/SiO2) dielectric membranes on high-resistivity <100> and <111> silicon wafers by means of wet anisotropic and, respectively, isotropic substrate removal; polyimide membranes on semi-insulator GaAs wafers. Comparative results will be presented, including AFM and SEM photos, details about average and maximum roughness of the top and bottom side of the membranes. Lumped elements: meander and S-line inductors, interdigitated capacitors (with 8 and 16 fingers) have been successfully manufactured on these membranes. Experimental comparative microwave measurements on S11 and S21 parameters are presented for the circuits manufactured on three-layer and polyimide membrane as well as for the same circuits on bulk substrate in order to notice the differences and to choose the optimum choice. A substantial improvement of microwave performances has been noticed for the micromachined structures. This work has been supported by the Commission of the European Communities under COPERNICUS Grant No. 977131