S. Bellone, M. Petrosino, A. Rubino, P. Vacca
Università degli Studi di Salerno
Dip. Ing. Informazione ed Ing. Elettrica
Organic Electronics
•
Effect of ITO treatment on OLEDs performance
•
Realization and Characterization of
Polymeric Memories
Riunione Annuale GE 2006
Ischia, 21-23 giugno 2006
Università degli Studi di Salerno
Effect of ITO treatment on OLEDs performance
Effect of ITO treatment on OLEDs performance
Al
Electron transporter (ALQ3)
Hole transporter (NPD or PF6)
ITO
200 nm
60 nm
70 nm
200 nm
glass
light
The effect of various chemical–physical ITO
surface treatments have been studied.
These treatments remove surface impurity,
decrease surface roughness and increase
ITO work–function.
Small molecules–ITO (NDP) interface and
Polymeric–ITO (PF6) interface have been
considered.
The hole-transporter layers depositing
technique are been
This work is done in
collaboration with Portici ENEA
Research Center
Riunione Annuale GE 2006
• thermic evaporation for small
molecules
• spin coating for polymeric molecules
Ischia, 21-23 giugno 2006
Università degli Studi di Salerno
Effect of ITO treatment on OLEDs performance
OLEDs Energy diagrams
ITO–NPD–Alq3–Al
device
ITO–PF6–Alq3–Al
device
An additional hole barrier is in NPD device
A bigger hole anode barrier is in PF5 device
Riunione Annuale GE 2006
Ischia, 21-23 giugno 2006
Università degli Studi di Salerno
Effect of ITO treatment on OLEDs performance
ITO chemical–physical properties
for various treatments
RMS
roughness
Spikes
Surface
energy
(W/)
(nm)
(nm)
(mJ/m )
Xp
Piranha solution
10,03
4,50
10,70
63,08
0,58
UV ozone–HCl (12%)
11,13
2,60
9,40
46,60
0,51
HCl (12%)
12,31
3,10
14,50
42,36
0,31
Oxygen plasma
10,44
1,80
11,00
38,72
0,65
Annealing 200°C
10,33
2,50
11,90
36,34
0,48
UV ozone
10,00
3,00
24,90
34,40
0,52
HCl (6%)
12,46
12,50
24,70
33,31
0,44
Untreated
10,55
2,40
17,20
32,56
0,49
Treatment
Sheet
resistance
Riunione Annuale GE 2006
2
Polarity
Ischia, 21-23 giugno 2006
Università degli Studi di Salerno
Effect of ITO treatment on OLEDs performance
PF6–OLED Results
2
Current Density (A / cm )
a
a HCl
b UV-HCl
c O2-Plasma
d annealing
e untreated
f UV Ozono
g Piranha
-4
1x10
-5
1x10
b

1


d


-6

1x10
e
-7
1x10
f
 






     
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0.0
4.0
a HCl
b UV-HCl
c O2-plasma
d annealing
e untreated
f piranha
g UV ozone
c
8.0
12.0
Voltage (V)
Luminance (cd/m^2)
-3
1x10
0.1
f
0.01
b
g
e

16.0
a
c
d
g
20.0
1E-3
12
14
16
18
20
Voltage (V)
• The best result is obtained with HCl–UV treatment with an increase of 60 in
luminance
• The device’s improvement is due to a better adhesion between polymer and
substrate during spinning gotten by
• increment of the apolar ITO surface energy because the solvent used is apolar
• decrement of ITO surface roughness
Riunione Annuale GE 2006
Ischia, 21-23 giugno 2006
Università degli Studi di Salerno
Effect of ITO treatment on OLEDs performance
NPD–OLED Results
0.1
1E-3
1E-4
a HCl
b UV-HCl
c O-Plasma
d annealing
e untreated
a HCL
b UV-HCl
c O2-Plasma
d annealing
e untreated
2
Luminance [cd/m ]
-2
Current density [A cm ]
0.01
1000
1E-5
c
a
100
a
c
b
10
d
1E-6
e
d
b
e
1E-7
0.01
0.1
1
10
Voltage (V)
4
5
6
7
8
9
10
11
12
13
14
Voltage [V]
• The best result is obtained with HCl treatment with an increase of 100 in luminance
• The device’s improvement is due to a better adhesion between evaporated organic
moleculs and substrate during Joule–deposition gotten by
• increment of the apolar ITO surface energy because NPD is an apolar molecule
• increment of ITO surface roughness
Riunione Annuale GE 2006
Ischia, 21-23 giugno 2006
Università degli Studi di Salerno
Polymeric Memories
Realization and Characterization of
Polymeric Memories
Al
200 nm
Polymeric Active Layer
150 nm
Al on glass
or
doped–Si
This research work is done in
collaboration with
Dip. Ing. Chimica ed Alimentare
Università di Salerno
Riunione Annuale GE 2006
New ad hoc polymers are used to
realize organic memory cells.
Organic layer is deposited using
spin–coating technique.
The goal is to realize organic
memory using low-cost
technologies.
To study transport and dynamic
phenomena dummy device have been
realized on p-type and n-type Si
substrate.
Ischia, 21-23 giugno 2006
Università degli Studi di Salerno
Polymeric Memories
Electric Bistability (I)
N-Si / O2-Polymer / Al device
0,0
300,0µ
cycles
(1)
(2)
(3)
(4)
0,0
cycles
(1)
(2)
(3)
(4)
0,0
150,0µ
Current
Current (A)
200,0µ
0,0
[A]
250,0µ
100,0µ
0,0
0,0
50,0µ
0,0
0,0
0,0
-8
-6
-4
-2
0
2
4
Voltage (V)
6
0
2
4
6
Voltage [V]
The molecules show two states with different electrical conductivity
This electrical bistability is imputable to conformational bistability
To return from high conductivity state to low conductivity state, conformational
switching is forced by high reverse electric field
Riunione Annuale GE 2006
Ischia, 21-23 giugno 2006
Università degli Studi di Salerno
Polymeric Memories
Electric Bistability (II)
Al / N-Polymer / Al device
erase
4
(1)
(2)
(3)
(4)
(5)
(6)
(7)
(8)
1E-5
1E-7
2
0
read
-2
write
-4
1E-6
1E-9
Current [A]
| Current | [A]
Voltage [V]
cycles
1E-3
1E-11
1E-7
High
1E-8
Low
1E-9
1E-13
-4
-3
-2
-1
0
1
2
3
Voltage [V]
Read voltage
– 1.5 V
Write voltage
–4V
Erase voltage
+4V
Riunione Annuale GE 2006
4
0
25
50
75
100
125
150
175
200
Time [s]
One order of difference in current
between high conductive state and
low conductive one is obtained
Ischia, 21-23 giugno 2006
225