Sensing of Biomolecules - Bionanoelectronics: Bioinquiring and Bioinspired Devices - page 57

Chapter 2
Sensing of Biomolecules

Abstract This chapter is dedicated to the label-free detection of various
biomolecules using nanodevices such as field-effect transistors having channels
with nanometric dimensions made from various nanomaterials like nanowires,
nanotubes, or graphene; cantilevers, optical waveguides, nanopores, and other
nanosized devices will be described for sensing of biomolecules.

2.1 Nanotransistors Based on Nanotubes, Nanowires,

and Graphene for Biosensing

In the field-effect transistor (FET), the transport of carriers is controlled by an
electrode called gate. The carriers flow along a channel bordered by two contacts
termed drain and source. The gate controls the charge density in the channel by an
electric field and is separated from the channel by an insulator. The FET can be
driven in an on and an off state by tuning the drain and gate voltages and constitute
a genuine switch.
The MOSFET (metal-oxide-semiconductor FET) is the basic configuration for
the majority of nanosized transistors having a gate length smaller than 100 nm,
irrespective of the channel type, which could be made entirely from nanomaterials,
such as nanowires or graphene, or from a heterostructure. The name MOSFET
indicates that the metallic gate is isolated from the channel region by an oxide.
Typically, a MOSFET consists of doped Si channel/active region isolated by a SiO 2
layer from a metallic gate. Other isolator materials are Si 3 N 4 or high-permittivity
dielectrics.
Initially, MOSFETs had a p-channel (PMOS), but the successive n-channel
transistors (NMOS) were faster switches than PMOS. Both MOSFET types are
integrated in a CMOS (complementary MOSFET) transistor, which is a low-power-
consuming device with a similar high switching rate as NMOS.
The MOSFET transistor is the most effective and simplest electronic device,
and therefore, CMOS is an essential element in integrated circuits, allowing an