BiCMOS for High Performance Analog and Digital Circuits

As a result of its high packing density, low power dissipation and ease of design, CMOS has in recent years emerged as the standard technology for VLSI circuits. Compared to CMOS, bipolar technology offers better analog features, e.g. offset voltage as well as unique speed advantages. ECL processors, for example, operate at clock rates over 100MHz whereas CMOS processors operate typically at 30MHz. Thus bipolar and CMOS devices form an ideal combination. The only drawback is the higher cost of their fabrication on the same chip. BiCMOS processes are more costly than CMOS processes due to additional masks, processing steps and reduced yield. However, this cost factor is less severe today than in earlier years because of the convergence of bipolar and CMOS technologies. This report describes BiCMOS techniques for high-speed/ high-density circuits for digital as well as analog functions. First the features of MOS and bipolar devices are compared. The different aspects of designing a BiCMOS process are described next. Finally the advantages of the BiCMOS technology for systems applications are demonstrated.