High-frequency heterojunction bipolar transistor device design and technology

This paper identifies and reviews those aspects of new materials and device technological advances that have pushed HBT circuits towards a 100 GHz operating frequency. The operating principles of the HBT are initially discussed in relation to their differences from homojunction bipolar transistors. The advantages and disadvantages of the various materials systems available to HBTs, how the particular material properties relate to the device performance and a brief outline of growth technologies are then presented. Those device parameters contributing to the frequency performance figures-of-merit are identified and the resulting design approaches discussed. Current device fabrication technology is then reviewed, with the latest results and the most important design aspects for high-frequency operation identified. This is then followed by examples of achievements in both digital and analogue circuit applications. Finally, an attempt is made to identify those device and materials aspects that are likely to contribute to a further improvement in the frequency performance of HBTs