Biology Reference
In-Depth Information
sensor array needs to work at frequencies of 10 4 Hz. Moreover, if
an ac method such as EIS is used as the characterization technique,
all the sensor elements need to be measured in a single period. The
frequency requirement will then be the basic addressing frequency
multipliedbythehighestfrequencyusedinEIS,whichraisesthebar
to around 10 7 Hz in practice.
Other factors that need to be taken into consideration include
temperature variations induced by the power consumption of the
circuit, lifetime in solution which is determined by the passivation
material, and overall chip size and packaging for practical handling.
ThosefactorsarelessimportantintermsoftheuseofFETandneed
to bereviewed for each application.
6.5.3 Development of Biosensor Arrays Based on FETs
Due to their advantages over conventional optical arrays, electronic
biosensor transducers and arrays have attracted intensive research
interest in recent years. The vast majority of those efforts, however,
are focused on the use of FETs as transducers and only a few
groups have successfully prototyped their array devices [46-54].
Theobviousreasonforthisisthehighcostofmaskmakingandchip
fabrication. Among them, the CMOS process dominates due to the
easy access to commercial CMOS foundries.
A configurable electrochemical sensor microarray system-on-a-
chip fabricated in a standard CMOS process has been presented
in the literature [48, 49]. The array had 5 × 10 elements, each
occupyinganareaof160 μ m × 120 μ mandcontainingadifferential
electrochemicaltransducerwithaprogrammablesensor.Thesensor
hadadigitallyconfigurabletopologycapableofperformingdifferent
electroanalytical measurements including voltammetry and field-
effect sensing.
Inanotherreport, aDNAsensorarray of16 × 8sensorelements
with pitch size of 250 μ m has been fabricated using a 0.5
μ m
CMOS process [50, 51, 55]. The DNA hybridization is measured
throughthechangeofinterfacialcapacitanceandthenconvertedtoa
digitaloutputsignalbytheintegratedelectronics.Thechipwaspost-
processedwithagoldlayertofacilitatetheattachmentofprobeDNA
 
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