MEMS fabrications of broadband epsilon negative (ENG) metamaterial electronic circuit for 0.22 THz sheet beam TWT application

In the course of the DARPA HiFIVE (High Frequency Integrated Vacuum Electronics) program, we have investigated various MEMS techniques for micro-fabrication of electronic circuits built in a 0.22 THz traveling wave tube (TWT) amplifier. The so-called “Barnett-Shin” circuit is a TE-mode waveguide structure of ultra wideband epsilon negative (ENG) metamaterial, comprised of a half-period staggered double grating array. Our prior modeling analyses of the device with a 20 keV and 250 mA sheet beam demonstrated ≥ 12 dB/cm growth rate and the saturated conversion efficiency of 3-5.5% (150-275 W) over 25 % (~ 60 GHz) dynamic bandwidth. Four different MEMS techniques are being developed for circuit fabrication: UV LIGA with (1) KMPR and (2) SU8, (3) high precision CNC nano-machining, and (4) silicon-molded electro-deposition. In the early stages of the program, we performed proof-of-concept experiments at Ka-band, which demonstrated 25 % band response of the ENG metamaterial circuit, and numerically analyzed the potential deleterious effects of deviation of critical dimensions due to fabrication errors on signal response of the fabricated circuits. Currently, the MEMS fabricated 0.22 THz circuits are being investigated by 3D optical microscope and scanning electron microscope (SEM). Also, a scalar network S-parameter analyzing system has been prepared for characterization of the micro-fabricated circuits.