Sub-terahertz slow-wave circuits for coherent radiation sources

In this letter, we propose sub-terahertz (sub-THz) slow-wave circuits for coherent radiation sources through beam-wave interaction mechanism. The circuits are prepared using microfabrication in advanced silicon (Si) technologies. Our approach is to split the circuit into multi levels allowing a low aspect ratio configuration and alleviating the loading effect of deep-reactive-ion etching on silicon wafers. This makes it easier to achieve flat-etched bottom and smooth sidewall profiles in nanoscale accuracy for high frequency operation. The dispersion relation retrieved from the measurement, therefore, corresponds well to the theoretical estimation. In particular, the sub-THz radiation is successfully measured in pulsed operation through the vacuum-sealed integration of the slow-wave circuit with a 15-kV, 90-mA thermionic electron gun. This observation offers a promising opportunity for the development of terahertz radiation sources based on silicon micro- and nanofabrication technologies.