Eletrochemical gating of aligned single walled carbon nanotube network field effect transistors

Abstract

Electrochemical gating of individual multiwalled and single-walled carbon nanotubes (SWNT) has recently gained much attention due to its high gating efficiency and its potential application as ionic sensors. However, nanotube networks, which have demonstrated effective gas sensing operation, could have higher application possibilities due to their relative ease of fabrication. Here, we report on electrochemical gating of aligned SWNT network field-effect transistors. The SWNTs were prepared by chemical vapor deposition and dispersed in iso-propanol. Interdigitated Cr/Au electrodes were fabricated on highly doped Si substrates with 100 nm thermal oxide. A drop of SWNT solution was placed on the electrodes and 10 Vpp, 5 MHz ac bias was applied between the source and drain electrodes for 10 min to align the SWNTs between the contacts. This produced aligned SWNT network with 3 m-2 density. Using the substrate-backgate, p-type field-effect transistor operation was demonstrated with minimal leakage currents. We used 10 mM NaCl as the electrochemical gating solution and the electrolyte potential was modified using Ag electrodes. At positive gate voltages the current transport through the device was suppressed. As the applied electrolyte gate voltage increased in the negative direction the current through the device was also increased. When -0.9 V was applied to the electrolyte gate, the source-drain current at -0.8 V bias voltage increased from -0.4 A to -50 A giving an on-off current ratio greater than 100. The threshold voltage shifted from -0.85 V to -0.1 V as the source-drain voltage increased from 0.2 V to 0.8 V. This may be due to the ions in the electrolyte actively regulating hole conduction by donating or removing charge from the SWNTs. Also since transport between interconnected nanotubes within the device takes place by means of tunneling, the ions may act to change the potential height of the tunnel barrier between SWNTs by changing the population of ions along the interface between adjacent SWNTs. We will present electrochemical gating of aligned SWNT networks with differing SWNT density and electrolyte concentrations.