Biomedical Engineering Reference
In-Depth Information
a
b
a
a
a
′
Au
Gate
Biotin-streptavidin
Cr
Length of the
Au
nanogap
Cr
a
Si body
P
-type
substrate
source
Drain
Buried oxide
Buried oxide
SOI wafer
After blomolecule immobilization
Fig. 5.9
(
a
) 3D schematic and (
b
) cross-sectional structure of a DMFET (Copyright 2007 Nature
Publishing Group)
Fig. 5.10
Shows the sequential V
T
shift according to the biomolecule binding steps. As mentioned
previously, V
T
was shifted in the positive direction in an n-channel DMFET after the formation of
the nanogap, which occurred because the dielectric constant of the dielectric layer was reduced.
However, the positively shifted V
T
returned to a negative value because the dielectric constant was
increased from 1 to a higher number (k>1for biomolecules). As shown in Fig.
5.10
,theV
T
shift
after the binding of streptavidin and biotin was 0.73 V (Copyright 2007 Nature Publishing Group)
The subsequent research on DMFETs concentrated on the charge effect related
to the V
T
shift [
38
]. To maximize the V
T
shift caused by trapped charges or
intrinsic charges, a newly designed DMFET with a very thin gate oxide (4 nm) was
fabricated. Two types of devices, an n-channel DMFET and a p-channel DMFET,
were fabricated at the same time to verify the charge polarity effect according to
