Biomedical Engineering Reference
In-Depth Information
Fig. 1
Description of the chiral vectors of different nanotubes: zigzag (10,0), chiral (6,4), and
armchair (5,5) nanotubes
Fig. 2
Schematic representations of a CNT fi eld-effect transistor (CNT-FET) and its ambipolar
behavior.
S
source,
D
drain,
G
gate,
V
GS
gate voltage,
I
D
device current,
V
GS
drain voltage
resistance in a nanotube with metallic electrical properties does not change by
applying another potential (
gate
voltage), the current in a semiconducting nanotube
can be tuned by applying external stimulations. This behavior led to the fabrication
of CNT fi eld-effect transistors (CNT-FETs; Martel et al.
2001
; Tans et al.
1998
) .
The basic structure of CNT-FET involves two metal electrodes designated as
source
and
drain
connected by a semiconducting nanotube. A third electrode, the
gate
is
separated from the nanotube by a thin insulator fi lm (Fig.
2
left). At the initial stage,
if no potential is applied between the gate and the source, no current crosses the
device and this describes the
OFF
state. In a p-type CNT-FET, if a negative gate
voltage is applied at a certain threshold, hole current appears in the nanotubes.
Reciprocally, for an n-type transistor, an electron current fl ows when a positive gate
voltage is applied and the voltage exceeds the threshold (Fig.
2
right). Similarly to
complementary metal-oxide-semiconductor (CMOS) technology, the ON/OFF
switching is obtained by sweeping the gate voltage.
