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Structure. Vacuum level. N. N. H. H. N. N. = 3.4eV. = 4.8eV. Luminescence. Intensity (a.u.). PVD of metal layer on CORNING 7059 substrate. 0.7 eV. LUMO. Photolitographic definition of contacts. H 2 TPP. 2.0 eV. Energy (eV). E F. HOMO. 0.7 eV. 50 m m. -9. 10. - PowerPoint PPT Presentation
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Why porphyrin?
• Low-cost technology
• High-selective gas sensors
• Light emitting devices
• deposition technique• plastic substrate
Electronic nose
Multi-colour display
Organic Transistors: design, fabrication and characterization
S. Salvatori, C. Calcavento,
M. C. Rossi, G. Conte
M. Berliocchi, M. Manenti, A.
Bolognesi, F. Brunetti, P. Lugli, A. Di
Carlo, R.Paolesse, C. Di Natale, A. D’
Amico
A. Sassella,
A. Borghesi
2003PAIS-2001 “TRANS”
d
Contact geometry for test-structures
H2TPP deposition by spray casting or OMBE
Photolitographic definition of contacts
PVD of metal layer on CORNING 7059
substrate 10 m0 50
5
10 m
0
5
0
10m0
5
10 m
Film morphology
OMBE deposition
Band diagram
LUMO
Vacuum level
EF
= 4.8eV = 3.4eV
2.0 eV
0.7 eV
HOMO 0.7 eV
Structure
H2TPP
N N
N N
H
H
Energy (eV)
Inte
nsi
ty (
a.u.
) Luminescence
0.2
0.3
0.4
0.5
0.6
1.6 2 2.4 2.8 3.2
Energy (eV)
Op
tica
l Den
sity Absorption
1.4 1.6 1.8 2 2.2
Spray-deposited films show charge carrier transport which reflects a thermal activated Hopping between homogeneously-dispersed molecules on the surface
50 m
1000/T (K
10-14
10-13
10-12
10-11
5 10 15 20 25-1
)
G (
A V
-1) EA 0.78 eV
EA 2.2 meV
10-14
10-13
10-12
10-11
10-10
10-9
10 100
340 K350 K
325 K
300 K250 K50 K
I=G(T) V
Voltage (V)
Cu
rren
t (A
)
0 100
4 103
8 103
1.2 104
600 800 1000 1200 1400 1600
X 30
Raman shift (cm-1)
Inte
nsi
ty (
a.u
.)
ConclusionsCharge carrier transport properties of metal-free tetra-phenyl-porphyrin samples have been investigated in vacuum condition (5x10-3 Pa) in the 40-340 K temperature range.
We have used two dimensional drift diffusion simulations to calculate the electrical properties of bottom contact pentacene based organic thin film transistor, taking into account field-dependent mobility and interface or bulk trap states.
For the first time a thin film transistor based on a porphyrin (octamethylporhyrin (OMP)) has been realized.
Metal Semiconductor Metal
EF
Va
70 nm
150 nm
(Cr)(Cr)
Multifingers on glass
Drain and Source (Au)
Gate
Insulating layer
Active layer
Si--
Drain and Source contacts:
Multifingers: Cr/Au
Spacing:12 mm
W/L=140
Vth= 0V
Thin Film Transistor structure
0 10 20 30 40-100,0p
-50,0p
0,0
50,0p
100,0p
150,0p
200,0p
250,0p
300,0p
Vg=+20
Vg=-40
-Vds (V)-40 -30 -20 -10 0 10 20
50,0p
100,0p
150,0p
200,0p
250,0p
300,0p
- Id
s (A
)
Vgs (V)
Output Characteristic Transfer Characteristic OMP
We simulate organic devices using an industry standard device simulation tool, namely ISETCADTM, a package able to resolve the standard drift-diffusion equations coupled with Poisson’s equation in two and three dimensions.
ISETCADTM is not capable to handle charge transport in organic material, so we have implemented a new model based on the following properties:
•Organic/Inorganic Band Alignment
•Density of States (equal to molecule density)
•Monte Carlo extracted Field dependent Mobility (see panel above)
•Trap states at the interface between organic material and silicon oxide (see panel below).
Pentacene TFT:Simulation Model and Experimental Device
Geometric Characteristics Measured and simulatedoutput characteristic
Measured transfer characteristic @ Vds=-30 V
All measurements were carried out in vacuum atmosphere at room temperature with Agilent Semiconductor Analyzer 4155C.
Experimental Thin Film Transistor
Vacuum Level
LOMO
HOMO
2.6 eV
2.4 eV
Pentacene Band Structure
From square root of IDSS is possible to calculate pentacene mobility using the expression:
Square root of saturation corrent
)(1
)(1
)()( 0
RGJqt
p
RGJqt
n
NNnpq
pqDqJ
nqDqJ
p
n
ADr
ppp
nnn
Drift Diffusion Equation
We apply this model to the simulation of pentacene organic thin film transistor. In particular we simulate a device with a channel length of 12 m and oxide thickness of 250 nm. The same device was realized and measured from our group.
Source/DrainMetal
0.1 eV
OMP TFT:Experimental Device
Temperature dependence of the dark current of film on Cr multifinger. The bias was 100 V.