rf mems capacitive switch

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Published on Tyndall (http://www.tyndall.ie)

Home >RF MEMS Capacitive Switch

RF MEMS Capacitive Switch

(SIMSWITCH)

SEM images of RF MEMS capacitie switches fabricated in Tyndall using post-CMOS surfacemicromachining process and 3D switch models from FEM software CoventorWare.SEM images of RF MEMS capacitie switches fabricated in Tyndall using post-CMOS surfacemicromachining process and 3D switch models from FEM software CoventorWare.

Capacitive MEMS switches are micron-scale devices that employ the movement of amechanical component to place a variable capacitance in the path of a radio-frequencytransmission line, thereby either blocking or enabling transmission of an RF signal along that

line.

These surface micromachined devices have the potential to offer substantial advantages overmore conventional semiconductor switches, such as high isolation, low loss and low powerconsumption. They will find applications in areas such as telecommunications, aerospaceand defence, automotive and high-performance instrumentation systems. Although thistechnology is currently the subject of intensive worldwide research, no commerciallyavailable switch yet exists. This is largely due to the high operating voltages required bymany MEMS switches, reliability concerns associated with the structures, and the high costand complexity of packaging.

Research at Tyndall has developed a low-voltage capacitive shunt microswitch for use atradio frequencies, using a low-temperature, CMOS compatible fabrication process. Theswitch requires an operating voltage of 10-15 V, which represents a substantial improvementon many current devices that require a voltage of up to 70 V. RF performance is also

MEMS Capacitive Switch http://www.tyndall.ie/print/1662

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promising: the switches have shown an insertion loss of -0.2 dB at 30 GHz and an isolationof -19.3 dB at 30 GHz.. A very high degree of reliability has also been achieved by replacingthe usual silicon nitride intermetal dielectric with silicon oxide. To date, measured lifetime hasexceeded five billion switching cycles without significant performance degradation or failure.

Switch Operation

Switch consists of a metalic electrode (membrane)

suspended above a metalic coplanar waveguide (CPW) that

is passivated with the dielectric (oxide). When the voltage is

applied between the suspended electrode and the signal line

the electrode collapses on the CPW due to electrostatic

attraction. When the voltage is removed, themechanical restoring force causes it to return tothe up position. In the up-position thecapacitance between the electrode and the signalline is low (1-100 fF), allowing the RF signal to pass to the output port unimpeded. In thedown-position the capacitance is high (1-10 pF) and the RF signal is coupled to the ground.

Contact:

Further information: Dr. Conor OMahony

Funding: Advanced Technical Research Programme (Enterprise Ireland)

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rf mems capacitive switch

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