Integration and packaging of GaAs MMIC subsystems using silicon motherboards

A technique has been developed for the integration and packaging of subsystems containing GaAs MMICs (monolithic microwave ICs) or a mix of MMIC, quasi-monolithic, and hybrid components on a single substrate of high-resistivity silicon. This silicon motherboard (SMB) technique differs from the monolithic GaAs-on-silicon approach in that, in this approach, conventional MMICs, FETs dielectric resonators, and other components are attached to a low-loss silicon substrate which contains etched recesses for MMIC chips and devices, vias, and monolithic overlay capacitors, resistors, air bridges, and other typical MMIC components and structures. The silicon acts as the transmission medium, chip carrier, and heat conductor. This integrated structure requires far fewer manual assembly operations than conventional approaches and exhibits fewer discontinuities, thus reducing cost and improving reliability, reproducibility, and performance. As a test vehicle for this technique, a three-stage, 2 W C-band power amplifier was adapted for implementation in an SMB form. The output power and gain of the amplifier closely match the predicted values of 33 dBm and 33 dB, respectively. The measured efficiency is 36%. Subsequent nonlinear analysis indicates that efficiency and output power can be improved by the addition of a third via under the output FETs.<>