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The electrical performance of the fabricated switch was evaluated under atmospheric conditions using a model N5244A PNA-X vector network analyzer (VNA) from Agilent Technologies, and 150-μm-pitch ground-signal-ground (GSG) coplanar probes from Cascade Microtech. A short-open-load-through (SOLT) standard on-wafer calibration technique was employed to set up the test system. Figure 10 shows simulated and measured S-parameters. The simulated insertion loss was less than 0.2 dB over all bandwidths from 30 to 40 GHz, with simulated isolation of better than 37.5 dB. The measured insertion loss was less than 0.3 dB, with measured isolation of better than 33 dB.

MEMS Switch Manages Millimeter-Wave Signals, Fig. 10

As Fig. 10 shows, the measured insertion loss and isolation show only small deviations across frequency. The discontinuity induced by the cascaded CPW lines, which have different dimensions at input and output ports, may result in the deviations. Overall, the measured S-parameters agree well with the simulated S-parameters.

The DC characteristics were tested as follows. The 10-Hz, 1.8-V sawtooth waves for the actuation voltage test and the 1-Hz, 8-V square waves for the switching time test were supplied by a model 33220A function/arbitrary waveform generator from Agilent Technologies and a model BA4825 high-speed bipolar power amplifier from NF Corp. Both the drive signal and test signal were observed and compared by the UNI-T UTD2052CEL digital storage oscilloscope from Morton Controls. Figure 11 shows the measurement results of the switching time testing. The actuation time was 29.5 ms for the transition from the “off” to the “on” state, and the releasing time was 0.95 ms for the transition from the “on” to the “off” state.

MEMS Switch Manages Millimeter-Wave Signals, Fig. 11

The speed of operation of the electrothermally actuated switch was slower than switches actuated by electrostatic force. The use of electrothermal actuation is expected to provide a high-force contact, which is important for reducing the contact resistance of the MEMS switches with high restoring force. The actuation time is longer than the release time, since the electrothermal actuator generates movement through an expansion of materials caused by the Joule effect, which has a long actuation time.However, once the voltage was removed, the actuator begun to cool down, and the switch makes the transition from “on” state to “off” state fairly quickly.

The high spring constant of the nickel beams is another important factor that helps the switch reach the “off” state quickly. Although the switching time of the proposed switch is longer than its electrostatic counterparts, it could find several applications where the switching time requirement is less stringent. Examples include redundancy networks, multiband receiver band selection networks, and automated test equipment.

The objective of this research was to design a high-performance MEMS switch for millimeter-wave communication applications. The result of the work is a switch actuated byan electrothermal actuator with better than 0.2-dB insertion loss from 30 to 40 GHz and more than 33-dB isolation at frequencies below 40 GHz. The switch is suitable for use with many microwave components and systems, such as power source and phase shifters.

Yan-Qing Zhu, Engineer

Lei Han, Associate Professor

Jie-Ying Tang, Professor Key Laboraty of MEMS of Ministry of Education, Southeast University, Nanjing 210096, People’s Republic of China, +0086-25-83794642-8823, FAX: +0086-25-83792939.

Acknowledgment

This work is supported by the National Natural Science Foundation of China (grant No. 61106114).

References

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3. Y-H. Jang, Y-S. Lee, Y-K. Kim, and J-M. Kim, “High isolation RF MEMS contact switch in V-and W-bands using two directional motions,” Electronics Letters, Vol. 46, No. 2, 2010, pp. 153-155.

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