Page 340 - Organic Electronics in Sensors and Biotechnology

Organic Electronics in Memories and Sensing Applications 317

FIGURE 8.12 AFM measurement on an annealed P(VDF-TrFE) layer with a
2
thickness of 200 nm. The area size is 2 × 2 μm with, on the left, the
topography (20 nm gray scale range) and, on the right, the phase response
of the same area. (Reproduced with permission from Ref. 81. Copyright 2005,
American Institute of Physics.)
of the fact that ferroelectric switching takes place only when the applied
field exceeds the coercive field, high-quality thin films of P(VDF-TrFE)
were prepared by using specific solvents (cyclohexane) (see Fig. 8.12).
Typical coercive fields are on the order of 50 MV/m. The important find-
ings on ferroelectric switching in P(VDF-TrFE) suggest that the coercive
83
field does not saturate with decreasing film thickness. An overview of
remanent polarization Pr versus ferroelectric layer thickness is shown
in Fig. 8.13. For the ferroelectric characterization, the Sawyer-Tower

80
70
60
P r (mC/m 2 ) 50 1. Ref. 3

2. Ref. 4
40
3. Ref. 5 (140°C)
4. Ref. 5 (128°C)
30 5. Ref. 5 (120°C)
6. Ref. 6
20 7. Ref. 7
8. Present results
10
0 100 200 300 400
d (nm)
FIGURE 8.13 Summary of the remanent polarization of spin-cast P(VDF-TrFE)
capacitors as a function of the ferroelectric layer thickness. The graph
includes reported as well as present results. The lines are drawn as a guide to
the eye. (Reproduced partly with permission from Ref. 81. Copyright 2004,
American Institute of Physics.)