Terahertz Resonant-Tunneling Diode With Series-Fed Patch Array Antenna

Resonant-tunneling diodes (RTDs) are promising electronic sources for terahertz (THz) waves. A recently proposed slot-based RTD simplifies the fabrication process by removing the metal–insulator–metal capacitor, which is used for dc separation, and introducing an etch stopper layer for simple air bridge formation. The simplified RTD structure, however, exhibits an unexpected large tilt angle in the main lobe of its radiation pattern due to the coupling between the slot antenna and the bias pads. Here, we present a series-fed patch array design that exploits the biasing structure and directs leakage surface waves to the broadside direction. The simulation result shows that the main lobe is along the broadside, with a maximum directivity over 12 dBi and a 3-dB bandwidth around 20%. The radiation efficiency is improved from 22% to 28% at 275 GHz. An experimental validation with a bullet lens indicates that the RTD device with a series-fed patch array antenna has a narrower beamwidth and a sidelobe level much lower compared with the original RTD. With such improved radiation performance, this simple RTD device becomes a potential source for the development of future array-level designs and flat lens systems.