Tunable MEMS capacitors using vertical carbon nanotube arrays grown on metal lines.

In this work, tunable MEMS capacitors are realized using a vertically grown carbon nanotube array. The vertical CNT array forms an effective CNT membrane, which can be electrostatically actuated like the conventional metal plates used in MEMS capacitors. The CNT membrane is grown on titanium nitride metal lines, with a Al/Fe bi-layer as buffer layer and catalyst material respectively, using chemical vapor deposition process. Two different anchor configurations are investigated. A maximum capacitance of 400 fF and maximum tunability of 5.8% is extracted from the S-parameter measurements. Using the tunable MEMS vertical array capacitor a voltage controlled oscillator (VCO) is demonstrated showing promise for integrating CNTs for communications applications.

Determination of the effective Young's modulus of vertically aligned carbon nanotube arrays: a simple nanotube-based varactor.

The electromechanical properties of arrays of vertically aligned multiwalled carbon nanotubes were studied in a parallel plate capacitor geometry. The electrostatic actuation was visualized using both optical microscopy and scanning electron microscopy, and highly reproducible behaviour was achieved for actuation voltages below the pull-in voltage. The walls of vertically aligned carbon nanotubes behave as solid cohesive units. The effective Young's modulus for the carbon nanotube arrays was determined by comparing the actuation results with the results of electrostatic simulations and was found to be exceptionally low, of the order of 1-10 MPa. The capacitance change and Q-factor were determined by measuring the frequency dependence of the radio-frequency transmission. Capacitance changes of over 20% and Q-factors in the range 100-10 were achieved for a frequency range of 0.2-1.5 GHz.