Transcript Das Bristee sol 2014 sm

Crystallization of Perylene Diimides
for Organic Field Effect Transistors
Bristee Das
October 3, 2014
Outline of Presentation
1. Overview of Organic Field Effect Transistors
2. Background on N1100 semiconductor
1. Goal of project
2. Experimental Design
3. Results
4. Future work
What are OFETs?
• The field effect transistor is a major component of modern electronics and
circuitry that functions as an on-off switch to control and amplify electric
signal
• In recent decades, increased interest in organic field effect transistors
(OFETs), which contain organic small molecule or polymer-based
semiconductors, has developed due to their inexpensiveness, mechanical
flexibility, and easy processability
How do OFETs work?
• OFETs consist of source, drain, and gate electrodes. The organic
semiconductor acts as a bridge between the source and drain, and an
insulating dielectric layer keeps it spaced from the gate.
• When a gate bias is applied between the gate and semiconductor, charges
accumulate at the semiconductor-dielectric interface that balances layer of
charge of opposite polarity on gate electrode
• Applying a bias across the source and drain creates a lateral electric field
that allows these accumulated charges to move. Further adjustment of the
gate voltage modulates the conductivity of the channel.
Image: Y-L Loo, AIChE Journal, 2007, 113
Background on N1100
• In particular, the perylene alkyldiimide (PDIR) family is known for having
“one of the highest n-type mobilities known”2
N1100 Single
crystal mobility =
up to 6 cm2/V.s
2C.
Piliego, F. Cordella, D. Jarzab, S. Lu, Z. Chen, A. Facchetti, M.A. Loi, Appl. Phys. A, 2009, 95
Image: K. Willa, R. Hausemann, T. Mathis, A. Facchetti, Z. Chen, B. Batlogg, Journal of Applied Physics, 2013, 113
Goals of Summer Project
• Learn how to fabricate thin film transistors
• Utilize various post-deposition annealing techniques on a variety of
substrate surfaces to gain a better understanding of the effects of
surface modifications, solvent vapor annealing treatments, and
thermal annealing treatments on crystallization kinetics in thin films
and how to control the crystallization process
General Experimental Design
• Surface treatments included OTS treatment of SiO2 and PFBT
treatment of gold for bottom contact, bottom gate geometry
devices
• N1100 was evaporated to a thickness of 45 nm
• As evaporated films are amorphous
• Conducted ex-situ and in-situ thermal and solvent vapor
annealing of N1100 thin films using:





Toluene
THF
DCM
Hexanes
Chlorobenzene
Experimental design: ex-situ SV annealing
Solvent
Stands for
substrates
Glass
Cover
Ex-situ SVA Morphology
DCM
Toluene
Hexanes
Chlorobenzene
Results: Summary of ex-situ testing
Ex-situ
Treatment
Method
Thermal
annealing,
130c, 1 hr
Mobility
(cm2/Vs)
0.856 +/- 0.195
Threshold
Voltage (V)
-7.15 +/- 15.4
Toluene
1.73E-06 +/1.29E-06
12.8 +/- 25.2
Hexanes
3.66E-03 +/3.80E-04
-2.943
+/- 1.73
DCM
5.01E-02 +/3.08E-03
13.0E +/- 0.879
THF
1.29E-04
+/- 7.29E-06
-6.472E+01
+/4.93
Chlorobenzene
2.69E-03 +/1.47E-03
1.50E+01 +/4.51
Experimental design: in-situ SV annealing
Exhaust
N2
Results: in-situ Toluene SVA
N1100 In-situ Thermal Annealing 120C
Conclusions
•
Ex-situ treatments
– Performance of TA devices was better than that of SVA devices
– For various SVA devices, DCM gave the largest mobility, Hexanes and
Chlorobenzene treatment gave the largest on/off ratio
•
In-situ treatments
– THF fastest – mobility plateau’d out after 30 min
– Chlorobenzene slowest – took around 840 min to plateau
– Need to retest DCM with video capture
•
Generally, thermal annealing yields better performance compared to
SVA for both ex-situ and in-situ treatment
Future Work
• Continue in-situ SVA with accompanying video for remaining solvents
• Further analysis and comparison of in-situ and ex-situ data for each
solvent
• Perform AFM to obtain a better understanding of how morphology is
changing with solvent choice
• Attempt simultaneous in-situ thermal and solvent-vapor annealing to
see the effects on the crystallization process
Acknowledgements