what is BiCMOS

BiCMOS is a technology that integrates bipolar and CMOS together to
take advantage of the high input impedance of CMOS and the low output
impedance and high gain of bipolar. A typical example of a BiCMOS circuit
is a two-stage amplifier, which uses MOS transistors in the first stage
and bipolar transistors in the second. However, BiCMOS as a fabrication
process is not nearly as mature as either Bipolar or CMOS. It is very difficult
to fine-tune both the bipolar and MOS components without adding
extra fabrication steps and, consequently, increasing the cost.