Semiconductor Device-Based Sensors for Gas, Chemical, and Biomedical Applications

6 Semiconductor Device-Based Sensors for Gas, Chemical, and Biomedical Applications

© 2011 by Taylor & Francis Group, LLC

depletes and the current channel is pinched off. The drain current in the nonsaturated region (below

pinch-off) is

I U U U U

D ref T DS DS

= ⋅ − − ⋅β

1

2

, (1.1)

where β is a parameter depending on the geometry (the channel width to length ratio W/L), the

mobility µ of the electrons in the 2DEG, and the gate insulator capacitance per unit area C

ox

:

U E

e

Q Q Q

C

T ref o sol

AlGaN SS ox B

ox

F

= − + − −

+ +

+Ψ Χ Φ

φ

2 . (1.2)

In the case of an ISFET, the gate voltage is the voltage at the reference electrode U

ref

= U

GS

. The

threshold vol