Advanced processing techniques for GaAs monolithic integrated circuits

This paper reports on the fabrication of an X-band GaAs microstrip amplifier as a test vehicle to establish a monolithic process capability. A variety of components are integrated on this circuit, including overlay and interdigital capacitors, via holes, air bridges and transmission lines. A novel geometry for overlay capacitors will be presented that has greatly improved yield and breakdown voltage over previous designs. Due to skin depth consideration, thick (∼ 2 µm) metallization layers are required on these circuits to obtain low microwave loss at X-band. Several liftoff techniques compatible with submicron device fabrication have been developed. These include a chlorobenzene (C6H5Cl) treatment of the photoresist and the use of a photoresist/aluminum layer to achieve negative sloped sidewalls. Both techniques have been used to define high yield 2 µm structures in GaAs.