Interfacing Biomolecules, Cells and Tissues with Nanowire-based Electrical Devices - Applications of Electrochemistry and Nanotechnology in Biology and Medicine - page 71

logues to the effect of applying a voltage with a gate electrode.
The idea for sensing with FETs was introduced several decades
ago, 12 but with planar FET sensors of previous planar devices
which precluded their application due to their limited sensitivity.
Semiconductor nanowires and carbon nanotubes can also be
configured as FETs. These devices overcome limitations of planar
CHEMFETS by the use of their 1D nanoscale morphology, be-
cause the extremely high surface-to-volume ratios associated with
these nanostructures make their electrical properties extremely
sensitive to species adsorbed on their surfaces. 13
The diameter of single wall carbon nanotubes, naturally occur-
ring as hollow cylinders, is in the 1-nm range, the diameter of a
DNA duplex. Because of the tubular structure of the nanotube, all
the current flows at the surface of the channel, in direct contact
with the environment. 14 In the case of nanowire device, an analyte
binding to the surface of the nanowire leads to a change through
the entire cross section of the device versus only a thin region near
the surface of a planar device, resulting in a much greater change
in device conductance for the NW versus a planar FET, 15 increas-
ing the sensitivity to a point that single molecule detection is pos-
sible. 13
Specifically, Si-nanowires configured as FETs exhibit per-
formance characteristics comparable to or better than the best re-
ported in the microelectronics industry for planar silicon devices
16 . Silicon-based nanotechnology is particularly promising since it is
compatible with the conventional silicon microtechnology; silicon has
been without doubt the basic building material for the semiconduc-
tor industry and the workhorse for micro-and nanotechnologies.
SiNWs can be prepared as single crystal structures with diameters
as small as 2-3 nm, 17 with complementary n- and p-type doping.
Their electronic characteristics are well controlled during growth
in contrast to carbon nanotubes and are also achieved with high
reproducibility. 16b The fabrication of SiNW-FET devices is rela-
tively straightforward compared to conventional planar silicon
FET devices, and combines bottom-up assembly of the nanowires
on the device chip together with a single step of photolithography
to make the metal contacts. Furthermore, SiNWs can be assembled
on nearly any type of surface, including those that are typically not
compatible with standard CMOS processing, such as flexible plas-
tic substrates. 18 Lastly, their native oxide surfaces allow to chemi-