| Using Schottky varactor diodes on GaAs, sampling circuits with bandwidths of 725 GHz have been fabricated and measured. The sampling circuits are integrated with nonlinear transmission lines, which are traveling-wave structures that generate the subpicosecond electrical pulses necessary to strobe the sampling circuits. This bandwidth was obtained by combining a number of technologies had been developed: varactor diodes with RC cutoff frequencies above 4 THz, coplanar waveguide transmission lines with the center conductor elevated off the substrate, and ways of minimizing all parasitics. Other applications of these technologies include a 100 Gbit/sec mux/demux circuit and 200 GHz traveling wave amplifiers.;By applying what had been learned from the varactor diodes, a novel device structure, a Schottky-collector resonant tunneling diode (RTD), was developed in the AlAs/GaAs system. By changing the collector from an ohmic to a Schottky contact, the scaling laws that are used for other devices are now applicable to the RTD. With 0.1 m Schottky fingers, a maximum frequency of oscillation of 900 GHz was attained, more than twice that of a conventional RTD. By applying this technique to AlAs/InGaAs on InP, RTDs with fmax above 2 THz have been tested. The long range goal of the project is to build oscillator arrays for generating power above 1 THz. |
