Transistor Action by Transit Time Phase Shift - a Study for SiGe Based Devices

In the present paper we report on a study on extended frequency operation in Si/SiGe heterojunction bipolar transistor structures. Calculations based on the results from a previous survey show the conditions for which an active behaviour in excess offmax can be obtained High frequency transistors with various shaped base potentials are produced and the unilateral gain is deduced from S-parameter measurements. A first indication of an active behaviour at frequencies above fmax is observed. This preliminary study serves as a guideline for designing structures which enables extended frequency operation.