High isolation X-band MEMS capacitive switches

This paper presents the design and optimization of the X-band microelectromechanical system (MEMS) capacitive switch using an electrical model and a mechanical model. The electrical model can accurately extract the resistance, capacitance and inductance of the switch. Based on the electrical model, a single-bridge switch and double-bridge switch with serpentine folded suspensions are proposed to achieve higher isolation compared to a typical MEMS capacitive switch at X-band frequencies. The measurement results show an isolation of 16.5-28 dB for single-bridge switch and 25-35 dB for double-bridge switch, both at 10-13 GHz. The mechanical performance is measured using an optoelectronic laser interferometric system. Due to the low effective spring constant of the serpentine folded suspensions, only 20.4 V of pull-down voltage is required. An improved fabrication process using surface and bulk micromachining techniques is also described.