Analysis of the 0.65 THz High-Frequency Circuits Fabricated by MEMS Technologies

The terahertz (THz) traveling wave tube (TWT) is characterized by low interaction efficiency and insufficient output power. Higher power can be obtained by minimizing insertion loss through advanced processing techniques. The 0.65 THz high-frequency circuits, composed of serpentine waveguide (SWG) slow wave structure (SWS), were designed, fabricated, cold tested, and analyzed in this article. The high-frequency characteristics of the process-adapted SWSs, applicable to both the high-precision computer numerical control (CNC) and deep reactive-ion etching (DRIE) technologies, are analyzed and compared. Then, two high-frequency circuits for high power 0.65 THz TWT are fabricated by those micro-electro-mechanical system (MEMS) technologies. The circuits fabricated by CNC and DRIE techniques exhibit superior equivalent conductivity of $2.4\times 10^{7}$ S/m in cold test. Benefiting from the high precision bonding and DRIE technology feature, the circuit can eliminate the $3\pi $ /2 point cave in the ${S} _{21}$ curve. The particle-in-cell (PIC) simulation results of the 3-D models, reconstructed based on the cold test data, predict that low-loss high-frequency circuits manufactured by advanced manufacturing technologies can achieve 25% output power improvement. Employing the DRIE process, it is possible to not only reduce manufacturing costs and shorten the manufacturing cycle, enabling mass production, but also effectively mitigate $3\pi $ /2 point oscillation, enhancing the stability of the device.