Biology Reference
In-Depth Information
column connections, which typically amounts to over 2000 external
connections.However,thelogiccircuitsdrivingtheTFTmatrixhave
tobemadebyconventionalsinglecrystalsiliconmicrochips,since
α
-
Si TFTs cannot provide logic drivers with the necessary speed, due
to the low electron mobility (
<
1cm
2
V
−
1
s
−
1
).
Monolithic integration of logic drivers on the active matrix array
plate has the great advantage of reducing the number of electrical
connections between the array and the rest of the system, which
is of particular relevance when compact construction is a premium
to overcome space limitations. Polycrystalline silicon TFTs have a
much higher mobility (
100 cm
2
V
−
1
s
−
1
) than
>
α
-Si TFTs and
can therefore be used to provide the drive logic as well as the
pixel transistors. Complete integration reduces the total number of
external connections to
∼
20 for power, clock, and input data signal
lines [15].
The above properties make poly-Si TFTs a very interesting
technology for the development of low-cost disposable biosensors,
with a large number of parallel channels. A microarray of 100,000
channels,withintegratedlogicdrivers,wouldrequireonlyafewtens
of electrical connections to the rest of the system. These could be
provided by edge connectors thereby enabling easy insertion and
removal of the sensor array from the system and, therefore, single
use of acomplex microarray.
6.3 Field-Effect DNA Sensing
Similarly to the working principle of ISFETs, the sensitivity of
FET devices to the charge on its gate electrode can be utilized to
develop sensors for the detection of charged biological species. In
general, biologically sensitive FETs (BioFETs) can be constructed
from MOSFET structures by functionalizing the gate electrode with
different biological recognition elements. A change in the charge
density of a biolayer immobilized on an electrode induces a change
in the electrode surface charge density,
σ
0
, which in turn alters
the surface potential,
ϕ
0
, that is, the open circuit potential (OCP).
A change in the surface potential may be generated by a catalytic
reactionproduct,surfacepolarizationeffects,orthechangeindipole
