Characterisation, Measurement & Analysis
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Capacitive MEMs Switch Characterisation App Note

Capacitive MEMS Switch Characterisation

Description: One of the participants in the Zygo Dynamic MEMS Workshop, the Tyndall Institute  in Cork, Ireland provided some novel devices that were measured during the workshop.

Recommended Product: Zygo NewView 7000

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

Research at Tyndall has developed a low-voltage capacitive shunt microswitch for use at radio frequencies, using a low-temperature, CMOS compatible fabrication process. The switch requires an operating voltage of 10-15 V, which represents a substantial improvement on many current devices that require a voltage of up to 70 V. RF performance is also promising: the switches have shown an insertion loss of -0.2 dB at 30 GHz and an isolation of -19.3 dB at 30 GHz.

How it works: Two versions are shown below, with 200x200 microns and 100x100 microns plates, the CPW (coplanar waveguide) Radio-frequency capacitive shunt switches consists of a grounded metallic membrane supported a few microns over a passivated CPW (coplanar waveguide) transmission line. In the up-state of the membrane, the switch capacitance is low and does not affect transmission of a radio-frequency signal along the line. Superimposition of a DC actuation voltage onto the RF signal causes the membrane to become attracted downwards due to the electrostatic force between the membrane and transmission line, at some value of the voltage called pull-in voltage the membrane snaps down and the switch is closed.


workshop1
Measurements of the SIMSWITCH (100x100 microns) using a Zygo NewView 6300 scanning white light interferometer



Zygo NewView 6000 measurement of SIMSWITCH
These images show an alternative SIMSWITCH (200x200 microns) design measured on a Zygo NewView 6300 showing movement from open to closed after a voltage has been applied to activate it.



Micromachined Beams

Micromachined Beams: these devices have been developed as a part of materials characterisation and process development project. Micromachined beams are commonly used as a test structures for material and process characterisation. Based on the pull-in voltage and resonance frequency measurements the material/mechanical properties can be extracted. Fixed-fixed beams and their modifications can be used as micromachined mechanical resonators.


Zygo NewView 6000 measurement of RF MEMS Switch
Shown is a beam fixed from both sides (other beams used were fixed only from one side), the detail of this structure can be clearly seen i.e. thickness and anchor region.


Measurement of the mechanical resonance frequency for the beam fixed on both sides gave a value of 263kHz very close to the theoretical prediction of 251.9KHz.


Click here to see the beam being dynamically measured using the NewView 6300 (WMV file 1.2Mb)