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Appendix
• Modes of operation of a field-effect transistor
Alam, Principles of Nanobiosensors, 2013 |
22 |
How does a Ion-sensitive Field Effect Transistor work (accumulation)
φ
Ox
Charge
φ 
C0
n-Si
DNA, Protein, etc.
Qbio = QMOS = C0φ
I =QMOSυ =Qbio µVD
L
The role of charge can be viewed as shifting the flat-band voltage
Alam, Principles of Nanobiosensors, 2013 |
23 |
ISFET in electrolyte ( accumulation)
φ
electrolyte
Metal |
Ox |
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CDL C0
n-Si
Qbio =QL +QR
=CDLφ +C0φ
φ= Qbio (pH) CDL (+saClt0) +C0
QMOS =C0 C QbioC
DL + 0
I =Qυ υ
1MOS
Electrolyte reduces sensitivity
Alam, Principles of Nanobiosensors, 2013 |
24 |
How does an ISFET work (inversion)
φ
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Charge |
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Q1
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Q1 =C0 |
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QT =CO (VG −VT ) +QMOS
=CO (VG +φ −VT )
ID =QTυ
∆ID =QMOSυ
Alam, Principles of Nanobiosensors, 2013 |
25 |