75-GHz fT SiGe-Base Heterojunction Bipolar Transistors

We report the fabrication of silicon heterojunction bipolar transistors which have a record unity-current-gain cutoff frequency (fT) of 75 GHz for a collector-base bias of 1 V, an intrinsic base sheet resistance (Rbi) of 17 kΩ/∧, and an emitter width of 0.9 µm. This performance level, which represents almost a factor of 2 increase in the speed of a Si bipolar transistor, was achieved in a poly-emitter bipolar process by using SiGe for the base material. The germanium was graded in the 45-nm base to create a drift field of approximately 20 kV/cm, resulting in an intrinsic transit time of only 1.9 ps. © 1990 IEEE