Third Day Poster Session, 17 June 2010 - NanoTR-VI

Poster Session, Thursday, June 17
Theme F686 - N1123
Electrical and photosensing properties of pentacene organic thin film transistor
Fahrettin Yakuphanoglu
Abstract— The electrical and ultraviolet light responsive properties of the pentacene thin-film transistor with 240 nm poly-4-
vinylphenol (PVP) dielectric layer thin film transistor have been investigated. The electrical parameters, saturation mobility,
threshold voltage, gate voltage swing and an ON/OFF current ratio were determined to be 710 -1 cm 2 /V s, 10.0 V, 2.6 V/dec and
3.8x10 2 , respectively. The transistor was characterized in respect of UV illuminations to investigate its potential for possible use as
a UV detector. The performance of the transistor is indicates a UV photosensitivity in the off-state with a ratio of photocurrent to
dark current of 5.74x10 2 . The obtained results indicate that the organic pentacene thin film transistor can be used as a UV
photodetector.
Organic thin-film transistors (OTFTs) have been extensively
investigated due to their low-cost, low-temperature process,
and compatibility with flexible substrate. Organic thin film
transistors (OTFTs) have many unique advantages, such as
light weight, flexibility, and solution processability. From
these reasons, nowadays, many research groups have
developed OTFTs. Especially, solution processes included
spin coating, screen printing, ink jet, and nanoimprint
lithography can be easily used in coating processes to form
circuits for disposable electronics on a plastic substrate.
According to the reported investigation of active channel
pentacene is a very promising candidate for organic
electronics. Several groups have recently demonstrated
pentacene TFTs and their applications. However, to satisfy the
high performance of OTFT, it is very important to select a
gate insulator material. That is, an insulator gate field-effect
transistor, the role of the insulator is at least as important as
that of the semiconductor. The insulator layer, especially the
insulator-semiconductor interface, has a significant effect on
the performance of OTFTs, because OTFTs operate in
accumulation region and the modulated charge lies within the
area (about 10 nm thick) close to the interface [8]. Therefore,
many research groups have made much effort to be study on
relationship between organic semiconductor and dielectric
layer.
In present study, pentacene thin-film transistor was
fabricated with 240 nm poly-4-vinylphenol (PVP) dielectric
layer. The electrical and photosensing properties of organic
pentacene thin-film transistor fabricated on polyethersulphone
(PES) substrate have been investigated. The transistor
fabricated on PES showed p-type OTFT characteristics. For
photosensing characterization, the output characteristics of the
pentacene thin film transistor were measured under various
illumination conditions. The Electrical characteristics and
photoresponse properties of the transistor were performed
under dark and UV light illuminations by semiconductor
parameter analyzer (Keithley 4200) using a white lamp (200
W) and UV lamp with 366 nm.
Fig.1a shows the drain current-drain voltage characteristics of
pentacene transistor under various gate voltages. The output
characteristics exhibit clear current saturation and pinch off
behavior.
The drain current increases at negative voltages,
indicating that the electrons are generated by the negative gate
voltages due to p-type FET characteristics with good gate
controllability.
-a-
-b-
Fig.1. Output characteristics of pentacene thin film
transistor a) under dark conditions b) under UV illuminations
Fig1b shows the I ds -V ds plots of the transistor under UV
illuminations (366 nm) for various voltages. The drain current
under these illuminations increases due to photogeneration of
electron–hole pairs in the active layer of the transistor. This
suggests that the organic pentacene thin film transistor can be
used as a UV photodetector.
This work was supported by the Management Unit of
Scientific Research Projects of Firat University (FÜBAP)
(Project Number: 1947). Authors wish to thank FÜBAP.
*Corresponding author: fyhan@hotmail.com
6th Nanoscience and Nanotechnology Conference, zmir, 2010 615