Development of W-band backward-wave oscillator

The precise patterning of periodic slow-wave structures can be successfully accomplished by modern photolithography technology on flat substrates in high frequency regime (>100 GHz). When the aspect ratio of the structure between in-plane and out-of-plane dimensions becomes higher than unity, however, controlled MEMS (micro-electromechanical systems) technologies are strongly required to achieve accurate depth profiles of slow-wave beam-wave interaction circuits. Here we report a W-band backward-wave oscillator using microfabrication technologies by which a fully 3-dimensional slow-wave interaction circuit is successfully employed on multi-bonded silicon wafers. The return loss measurement of the circuit appears to be very similar to the simulation, which indicates not only the dimensions but also the surface roughness is under control. A more detailed discussion on the design, fabrication, and RF test result will also be included.