Design and fabrication of low actuation voltage K-band MEMS switches for RF applications

The micromechanical switch is without doubt the paradigm RF MEMS device. However, a major drawback is that these switches are usually electrostatic in nature and commonly driven by bias voltages in the 40--100 V range. The focus of this investigation was the development of a low actuation voltage RF MEMS switch in the K/Ka-band frequency region. The switch structure is composed of four multi-meander folded suspensions attached to actuation pads over the ground planes of FGCPW lines, resulting in a compact design and low spring design. This allowed for the development of capacitive switches with actuation voltages as low as 6 V (one of the lowest values to date) with switching speeds of approximately 50 musec. Furthermore, top electrodes were added over the actuation pads in order to mitigate the effect of stiction due to the low restoring force of the low-actuation devices. Pull-up and pull-down voltage measurements indicated values as low as 1.9 V for actuation over a gap of 2 mum. A low-temperature modular surface micromachining process (with polyimide as the sacrificial layer) for the fabrication the RF MEMS switches was developed. RF characterization of the MEMS switch demonstrated negligible insertion loss (approximately 0.16 dB at 40 GHz) across the frequency range and an isolation of approximately 20 dB at 40 GHz. Furthermore, the low actuation switch design decouples the RF and DC actuation areas, resulting in improved power handling capabilities. Measurements with RF power up to 6.6W at 10GHz resulted in no self-actuation (switch off) or catastrophic failure (switch on) of the device. Furthermore, hot switching was demonstrated using a top electrode for power levels up to 0.8W at 30GHz. These power handling characteristics are the best known to date for MEMS switches. Finally, single-pole single-throw (SPST) and single-pole double-throw (SPDT) switching circuits were demonstrated. The measured SPST results indicated insertion losses less than 1 dB and isolations of better than 25 dB at both 17 and 35 GHz. X- and K-band SPDT circuits performed extremely well with insertion losses below 1 dB and isolations of 43.3 dB and 50 dB at 7 and 20 GHz respectively.