Biomedical Engineering Reference
In-Depth Information
CNTFETs are useful to monitor chemical environments due to
surface atoms in the CNT conductive channel, and therefore small
changes in the molecular environment will result in measurable
changes in the FET conductance. A charge transfer between
semiconducting CNT channel and metal electrodes in the FET
can be generated by the Schottky barriers caused by the different
work functions between CNTs and metal electrodes. This produces
a conductance current in the CNT channel that can be modulated
by injection or removal of electron carriers from electron donation
or electron withdrawal of chemical species. Adsorbing species
deposited onto CNT channel in the FET device can modulate the
charge mobility and/or conductance by introducing scattering
sites. This effect results in a change in the slope of the electrical FET
transfer characteristics, called
transconductance
.
. [34] measured the conductance of semiconducting
SWCNTs in FET structures and investigated the device response to
alcoholic vapors. The semiconducting SWCNTs were synthesized
by CVD onto heavily doped Si substrate capped with 100-nm thick
SiO
Someya
et al
and the electrode contacts were formed by evaporating Cr-Au
with metal shadow masks. Figure 9.33 shows significant changes at
2
Figure 9.33
(
) Schematic view of the SWCNT-based FET sensor
integrated in SiO
a-Left
) SEM image of the
nanotube FET:A single-walled carbon nanotube bridges
source and drain Cr-Au electrodes with a spacing of
5
/Si substrate. (
b-Left
2
= −20 V)
as a function of time upon exposure to saturated vapors of
various alcohols: methanol, ethanol, 1-propanol, 2-propanol,
1-butanol, tertiary-butanol, 1-pentanol, and 1-octanol.
This figure is reprinted and adapted with permission from
ACS [34]. See also Color Insert.
µ
m. (
Right
) Drain currents (
V
= −100 mV;
V
SD
G
