Page 339 - Organic Electronics in Sensors and Biotechnology

316 Cha pte r Ei g h t

10 –4 10 –4
V = –30 V V = –30 V
d
d
10 –5 10 –5
Programming –6 Programming
–6
(A) 10 (V = 200 V) (A) 10 V = –200 V
g
g
–I d 10 –7 1 st Erasing –I d 10 –7 1 st
10 –8 nd (V = –100 V) 10 –8 nd Erasing
g
2 2 V = –200 V
g
10 –9 3 rd 10 –9 3 rd
–40 –20 0 20 40 60 80 –150 –100 –50 0
V (V) V (V)
g
g
(a) (b)
V g Prog. (V) 200 10 –5 V = –10 V
d
–6
100
10
Programming
0
g
–100 (A) 10 –7 1 st V = 60 V
Erasing
–8
(A) 10 –3 –I d 10 –9 2 nd V = –50 V
g
rd
10
3
–5
–I d 10 4 th
10 –7 5 th
0 20 40 60 80 100 –20 –10 0 10 20
Time (μs) V (V)
g
(c) (d)
FIGURE 8.11 Shifts in transfer curves at V = –30 V in the (a) positive and
ds
(b) negative directions for an OFET memory device with a 300 nm thick SiO layer.
2
(c) Reversible switching for on and off current states. (Programming: V = 200 V
gs
and V = 0 V, reading: V = 0 V and V = –30 V, and erasing: V = –100 V and
ds gs ds gs
V = 0 V). (d) Shifts in transfer curves at V = –10 V for an OFET memory device
ds ds
with a 100 nm thick SiO layer, where V = 60 V and V = –50 V were applied for
2 gs gs
1 μs for programming and erasing, respectively. (Reproduced with permission from
Ref. 73. Copyright 2006, Wiley VCH Verlag GmbH & Co.)
on the threshold gate voltage analogous to a floating gate in a flash
memory. Such a bistable state is demonstrated in Fig. 8.11. Resulting
devices have switching speeds on the order of 1 μs, which is the fast-
est among all the devices reported, but at voltage levels still too high
to be useful in practical applications.
FeFETs
FeFETs are field-effect transistors with ferroelectric gate insulators.
These devices make use of the dipole polarization of ferroelectric
capacitors which shows butterflylike hysteresis loops. Memory func-
tionality is obtained by the bistable polarization of the ferroelectric
gate dielectric, which remanently attenuates the charge density in the
semiconductor channel.
For this class of devices, ferroelectric copolymers such as P(VDF-
TrFE) 80, 81 and glassy dipolar polymers such as MXD6 are used. Because
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