Silicon Gate CMOS Linear Technology

Since most linear design is accomplished with bipolar junction transistors, an examination of CMOS and Bipolar Junction Technology (BJT) and the merits of each will best explain the advantages of each technology. Then, a comparison of metal and silicon gate CMOS technology will further identify silicon gate CMOS transistors’ unique role. CMOS technology is “simpler” than BJT technology in that the BJT’s three dimensional parameters like base depth, base thickness and base and collector doping do not need to be considered.

Since the three-dimensional bipolar parameters are more difficult to control, CMOS technology leads to a better controlled process with less variation in crucial device parameters. In addition, recent advances in processing techniques and equipment are more applicable to CMOS ICs. This means it is likely CMOS technology will advance more quickly than BJT technology.

Finally, as the number of chips required per function and the chip count per device goes down, the need for monolithic analog and digital circuitry will increase. CMOS linear devices use the same fabrication process as CMOS digital devices which makes integration of analog and digital devices simple. Bipolar junction transistor technology needs to combine with CMOS technology which makes fabrication cumbersome, complex and expensive.

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