THz Bipolar Transistor Circuits: Technical Feasibility, Technology Development, Integrated Circuit Results

We examine the feasibility of developing bipolar transistors with current-gain and power-gain cutoff frequencies of 1-3 THz. High bandwidths are obtained by scaling; the critical limits to such scaling are the requirements that the current density increase in proportion to the square of bandwidth and that the metal-semiconductor contact resistivities vary as the inverse square of device bandwidth. Transistors with 755 GHz f_max and 324 GHz amplifiers have been demonstrated. Contacts with resistivity sufficient for the 64 nm scaling generation (1 THz f_tau2 THz f_max) have been developed.