Biology Reference
In-Depth Information
estimatedthatduetoitslowmobility,amorphoussiliconTFTwould
notworkatmorethan10
4
or 10
5
Hz, which rules it out for the use
of addressing logic circuits in future high density arrays [15]. Poly-
Si TFT, however, has a mobility of over 100 cm
2
V
−
1
s
−
1
and can
adequately cover the desired frequency range.
For the measurement circuit, the amorphous silicon TFT has not
been considered suitable for analog circuit or high frequency digital
circuit,duetoitslowmobilityandtransconductance,whilethepoly-
SiTFThasbeendevelopedintoalargevarietyofanalogcircuitswith
moderateperformance.ThesuitabilityofthethreeFETtechnologies
for biosensorarray applications issummarized in Table 6.1.
Overall, polysilicon TFTs can provide all the key components, so
theapplicationtotheproposedintegratedbiosensorarraysiswithin
the capabilities of the technology. Furthermore, it seems to provide
the proper balance between the performance and cost for future
biosensor array applications, although its current development is
hinderedbythelackofcommercialfoundriesforresearchpurposes.
Table 6.1. Advantages and disadvantages of CMOS, poly-Si TFT, and amor-
phousTFTtechnologiesforthedevelopmentofthedifferentcomponentsin
biosensor arrays
Application in biosensor arrays
Addressing
Measurement
Transducer
switches
Driving logic
circuit
CMOS FET
Pros
High internal
High speed,
High speed
High electronic
gain, smaller size
high on-off
performance,
current ratio
compactin size
Cons
Expensiveto have
None
None
None
largerextended
gateor electrodes
Poly-Si TFT
Pros
High internal gain
High on-off
Moderate
Moderate
ratio
speed
performance
Cons
Deviceuniformity
None
None
None
Amorphous
Pros
Low cost, low
Moderate
None
None
TFT
temperature
on-off ratio
manufacturing
Cons
Very low gain,
None
Low speed
Low electronic
deviceuniformity
performance
