Monolithic process for co-integration of GaAs MESFET and silicon CMOS devices and circuits

A monolithic process to cointegrate Si CMOS and GaAs MESFET devices and circuits on a silicon chip through epitaxial growth of a GaAs layer on a prefabricated Si wafer is described. By embedding the GaAs layer in Si recesses in selected regions of a Si wafer, the cointegration has been realized in a coplanar structure appropriate for IC processing. On a monolithically integrated wafer, a 2-μm gate length Si CMOS ring oscillator showed a minimum delay of 570 ps/gate, and a 1-μm gate GaAs MESFET BFL ring oscillator had a minimum delay of 68 ps/gate. These results indicate that the individual device speed is not degraded by monolithic integration. Some changes in threshold voltage, however, were observed for Si CMOS devices after the GaAs device fabrication. A composite ring oscillator consisting of a string of Si CMOS inverters and a string of GaAs MESFET inverters connected in a ring has been successfully fabricated