Possibility of terahertz amplification by active transmission lines loaded with resonant tunneling diode pairs

Active transmission lines loaded with resonant tunneling diode (RTD) pairs were investigated as possible THz amplifiers. The RTD pair consists of two RTDs connected serially and is biased by voltages of the same absolute value with opposite signs. The RTD pair has unique current-voltage characteristics at the intermediate node; the true negative resistance appears in the low-voltage region. The linearity of this region is good owing to the symmetry of the circuit. Moreover, the RTD pair circuit can be stabilized more easily than that of a single RTD. On the basis of these advantages, the RTD pair transmission lines are a promising candidate for THz amplifiers. RF signal amplification was demonstrated by circuit simulation. The cutoff frequency was also demonstrated to increase with decreasing unit cell size, and it exceeds 1 THz with RTDs of 1 μm² emitter area.