RF MEMS Reconfigurable Monolithic Circuits

With great demands of high-performance agile wide-band radio frequency (RF) integrate chips from multiple-mode and multiple-frequency wireless communications, intelligent mobile phones, radar and satellite communications, the reconfigurable networks technology based on RF MEMS has been in active research. In the past years, the reconfigurable filters, reconfigurable matching networks and MEMS electronically steerable antennas have been realized using RF MEMS technologies, and some RF MEMS switches have been put into production. On the basis of domestic MEMS design and manufacturing, this dissertation presents on high-isolation MEMS switches, tunable MEMS filters, millimeter-wave MEMS phase shifters which are typical RF MEMS reconfigurable monolithic circuits.Switches are one of the essential components in RF circuits and systems. The MEMS activities have focused on the reliability after switch performances have been achieved. The structure reliability of MEMS switches was studied in this dissertation. Not only the pull-in voltage and RF performance optimization was studied but also the contact force, restoring force, contact resistance, switching time were researched thoroughly, the dielectric layer between electrostatically actuated electrodes was threw away from the structure of MEMS switches. The synthesis design methods of improving the switches reliability were presented. The simulated resonant frequency of the cantilever switch was greater than50KHz, and the spring constant, restoring force and the isolation was70N/m,182.6μN,-20dB@10GHz respectively, which reach up to the performance of MEMS switches produced by foreign companies. The measured switching time, life-cycle and power handling of switches was llus,3.4×108,1.8W respectively.The isolation characteristic of one MEMS switch unit is not able to meet the applications of channel selecting RF front-ends. Based on the series-shunt circuit configuration, three MEMS switches were innovatively integrated into one chip. Here, total chip size was well compact to1mm×1.2mm similar with single switch unit in size due to making full use of coplanar waveguide space, moreover, the return loss was better than that of one switch unit resulting from the matching design between the equivalent inductance of series switch in the on-state and that of shunt switches in the off-state. The performance of fabricated samples is as follows:the isolation is lower than-40dB at0.1-13.5GHz, the insertion loss is-0.3dB, the return loss is lower than-30dB, and the pull-in voltage is in a range of60volts to80volts, which represent the highest level of domestic MEMS switches with high isolation.In recent years, the tunable MEMS filters have been studied extensively. The compact vialess low loss transation of CPW to microstrip lines, parallel-coupled microstrip lines, MEMS switch units and bias circuit were integrated to a tunable filter at Ku band with15.1mm×3mm in size has been designed and fabricated, and the characteristics are as follows:the center frequency of filters can be shifted from15.05to13.05GHz with the control voltage is from zero to70V. The tuning range of14.2%,3-dB fractional bandwidth of10.2%, insertion loss of-3.6to-4.6dB, the quality factor of63to74and the skirt slopes of over30dB/GHz at both states have been demonstrated. Compared with previous tunable MEMS filters, the present filter implementation has demonstrated the more sharp skirt slopes with the relatively low insertion loss and high Q.Millimeter-wave MEMS phase shifters with advantages of lower loss are currently studied extensively. The cantilever MEMS switches were applied in MEMS phase shifters at Ka-band in the dissertation. The circuit matching of MEMS phase shifters was accomplished by adopting stepped impedance coplanar waveguide (CPW) lines. The two-bits switched-line millimeter-wave MEMS phase shifters have been achieved and taken the lead inland, whose measured data showed that the average insertion loss of-3.4dB at35GHz, phase error in the low phase of under1.6°@0°～67.5°, phase error in the high phase of under9.1°@0°～270°, the pull-voltage of60to80volts, and the total chip size of2.7mm×2.8mm have been accomplished.