Low-Cost Si and Si/Si1−xGex Heterostructure BiCMOS Technologies for Wireless Applications

BiCMOS for analog circuits is finding applications for which the high transconductance, low noise, high output resistance, and additional speed of the bipolar devices yield a performance not easily obtained through a CMOS technology alone. However, for BiCMOS to remain a viable alternative for these applications, costs must be kept low. Our BiCMOS approach, MBiC (Modular BiCMOS), starts with a state-of- the-art CMOS technology and adds a bipolar transistor in a modular fashion while minimizing additional process steps. Using process steps such as high-energy implantation in place of epitaxy over a heavily doped sub-collector, and amorphous-Si refill techniques under the extrinsic base region, we produce Si homo-junction devices with cutoff frequencies of about 30 GHz with only three additional masking levels. Using similar device structures with the same “CMOS first” philosophy, we also fabricated Si/SiGe hetero-junction bipolar transistors with a cut off frequency of 54 GHz.