A fully integrated MEMS tera hertz interaction circuit with multi wafer packaging

This paper presents a fully integrated MEMS THz interaction circuit implemented by multiple bonding of bulk micromachined silicon wafers. A metal to metal eutectic bonding scheme was optimized for attaching four wafers and a parylene was adopted as etch stop during silicon penetration process without any charging effect and poor step coverage on entire wafer. `Silicon sidewall smoothing´ process was performed to diminish scallops for avoiding VNA response distortions resulting from the change of actual electrical length of the circuit lines. The optimized bonding metal combination was experimented to increase bonding strength and additional surface treatment with argon plasma was successfully implemented before bonding. The yield after fabrication of the circuits achieved 90 % and the VNA characteristics of the fabricated THz circuits identically showed similar values to each other, agreeing well with the HFSS simulation results. The measured S₁₁ response was -30 dB levels at 98 GHz.