Silicon bipolar device structures for digital applications: technology trends and future directions

The double-polysilicon self-aligned bipolar device structure has come a long way since its first inception, but there is still room for further scaling of this structure and continued improvements in performance. An analysis of the current state-of-the-art double-poly structure leads naturally to a discussion of future trends and technologies necessary to continue scaling into the sub-0.25 μm regime. In addition, it has become highly desirable to extend bipolar processes in new directions to take advantage of the opportunities offered by emerging materials technologies, such as bonded silicon-on-insulator films and medium or low temperature Si and SiGe epitaxy. Opportunities also exist for high-performance bipolars in BiCMOS technology and in complementary bipolar processes for low-power, high-speed digital applications. These extensions beyond “conventional” bipolar technology will be discussed in terms of their requirements and the device structures that are evolving to match these needs