Three-dimensional passive circuit technology for ultra-compact MMICs

A novel passive circuit technology of a three-dimensional (3-D) metal-insulator structure is developed for ultra-compact MMICs. By combining vertical passive elements, such as a wall-like microwire for shielding or coupling, and a pillar-like via connection with multilayer passive circuits, a 3-D passive circuit structure is formed to implement highly dense and more functional MMICs. O₂/He RIE for forming trenches and holes in a thick polyimide insulator, low-current electroplating for forming gold metal sidewalls in the trenches or holes, and ion-milling with a WSiN stopper layer for patterning the gold metal are used to produce such a structure. The complete 3-D structure provides miniature microstrip lines effectively shielded with a vertical metal-wall, a miniature balun with low-loss vertical wall-like microwires, and inverted microstrip lines jointed with pillar-like vias through a thick polyimide layer. This technology stages next-generation ultra-compact MMICs by producing various functional passive circuits in a very small area