We present the fabrication and high frequency characterization of a capacitive nanoelectromechanical system (NEMS) switch using a dense array of horizontally aligned single-wall carbon nanotubes (CNTs). The nanotubes are directly grown onto metal layers with prepatterned catalysts with horizontal alignment in the gas flow direction. Subsequent wetting-induced compaction by isopropanol increases the nanotube density by one order of magnitude. The actuation voltage of 6 V is low for a NEMS device, and corresponds to CNT arrays with an equivalent Young’s modulus of 4.5–8.5 GPa, and resistivity of under 0.0077 Ω⋅cm. The high frequency characterization shows an isolation of −10 dB at 5 GHz.
Abstract. We show that thin horizontal arrays of single wall carbon nanotubes (SWNTs) suspended above the channel of silicon MOSFETs can be used as vibrating gate electrodes. This new class of nano-electromechanical system (NEMS) combines the unique mechanical and electronic properties of SWNTs with an integrated siliconbased motion detection. Its electrical response exhibits a clear signature of the mechanical resonance of SWNTs arrays showing that these thin horizontal arrays behave as a cohesive, rigid and elastic body membrane with a Young modulus in the order of 1-10 GPa and ultra-low mass. The resonant frequency can be tuned by the gate voltage and its dependence is well understood within the continuum mechanics framework.
A self-limiting dielectrophoresis technique, aimed at deterministically assembling individual or bundles of single-walled carbon nanotubes (SWCNTs) and multiwalled carbon nanotubes (MWCNTs), is experimentally investigated. A limiting resistor is used to control the electric field after the deposition of a single carbon nanotube. The role of some key parameters such as voltage and duration of the deposition with and without the limiting resistor is studied.
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.
Fig. \ : Top View of (a) Design # \ and (b) Design #2 (e) Cross Section View of the device. (d) 3-D view (e) Simplified fabrication process flow. (e) (d) ••• .AI 2 0 3 /F e • S ilicon _ Si0 2 (1 urn) _ TIN (100 nm) -(10nm/0.5nm) PROCESS, DESIGN AND FABRICATIONIn this section we present a CNT MEM brush varactor realized with a dense array of CNTs vertically grown on adjacent metal lines. The dense CNT array forms a CNT vertical membrane which can be actuated electrostatically by applying a bias voltage between the two vertical electrodes. Fig. I shows the top view, cross-section view, 3D-view and the detailed process flow of the CNT brush varactor. Two different designs were investigated. Design #1 (Fig. la) is a coplanar transmission line configuration. Design #2 (Fig. Ib)is an interleaved electrode structure. To avoid the tubes from collapsing due to their high aspect ratio the tubes on each electrode are grown in a concentric fashion.A silicon wafer (0.1-0.5 Ohm em) with I urn of thermal oxide was used as substrate. 100 nm of TiN was deposited by PVD. The TiN layer was patterned by optical photolithography and IC plasma etching. The catalyst layer (AlzOiFe) for the CNT growth was patterned by optical photolithography and lift-off technique.Abstract: This paper explores the design and fabrication of Micro-Electro-Mechanical capacitors based on vertical carbon nanotube arrays. The devices are realized in vertically single-clamped parallel plate configurations using a dense array of vertically grown MWCNTs on metal lines. The capacitance tuning is performed by electrostatic actuation. From the pull-in voltage value, based on novel analytical model of single-clamped vertical CNT membranes, we extract an equivalent Young modulus of the CNT array ranging in the 10's of MPa. S-parameter measurements combined with an equivalent circuit model enable the demonstration of a capacitors with values of 50-200fF with a tuning range of the order of 19% . INTRODU CTIONToday, tunable micro-electro-mechanical (MEM) capacitors and switches are novel components under research for applications in RF circuits [1, 2] because conventional semiconductor switches and varactors suffer from poor characteristics at radio-frequency. One would expect that MEMS could offer versatile solutions for varactors with higher quality factors, larger power handling ability and low power consumption necessary for tunable networks [I] [2]. Typically, polysilicon or metals have been used as structural materials in MEMS. Carbon nanotubes (CNT) are stiff light materials with high aspect ratio and have been envisioned as an excellent candidate to build electromechanical systems [3] [4]. However, until now there are very limited demonstrations of CNT devices for RF MEMS, the majority being based on individual CNTs for resonators and relays. In this paper, we investigate the potential of using dense array of vertical CNT, as vertical thin film material for building tunable RF MEM capacitors. We report some basic characteristics of vertical electro-mechanical C...
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