Page 396 - Organic Electronics in Sensors and Biotechnology

Electrophoretically Deposited Polymers for Organic Electronics 373

300 V
0.2
250 V
Current density (mA/cm 2 ) 0.1 150 V
200 V

100 V

0 50 V
0 5 10 15 20 25 30
Time (min)
FIGURE 10.3 Stability of current density of n-propanol for different applied
voltages. (Reprinted from Ref. 1. Copyright 2007, with permission from
Elsevier.)

deposit formed by EPD. It is considered that the unstable current den-
sity influences the quality of deposition morphology. From the current
density profile in Fig. 10.3, it is reasonable to suggest that the applied
voltage should be less than 100 V in the case of n-propanol. It is observed
that amount of YSZ (Y O -stabilized ZrO ) deposition from the n-
2 3 2
propanol bath increases with increasing applied voltage. However,
the deposit surface morphologies are found to be flat at low voltages,
and they became rougher with increasing applied voltage.
Concentration of Solid in Suspension Predominantly for multicompo-
nent EPD, the volume fraction of the solid in the suspension plays an
important role. In some cases, although each of the particle species
has the same sign of surface charge, they could be deposited at differ-
ent rates depending on the volume fraction of solids in the suspen-
sion. If the volume fraction of solids is high, the powders deposit at
an equal rate. If, however, the volume fraction of solids is low, the
particles can deposit at rates proportional to their individual electro-
phoretic mobility. 36
Conductivity of Substrate The uniformity and conductivity of a sub-
strate electrode are important parameters critical to the quality of the
37
deposition of green films by EPD. Peng and Liu have observed that
low conductivity of the La Sr MnO (LSM) substrate leads to non-
0.9 0.1 3
22
uniform green film and slow deposition. Chen and Liu have
observed that when as-pressed LSM or LSM-YSZ composite pellets
are used as substrates for EPD, the deposition rate of YSZ is slow and