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Copper (II) Phthalocyanine Based Field Effect Transistors as Total Dose Sensors for Determining Ionizing Radiation Dose

Published online by Cambridge University Press:  07 February 2012

Harshil N. Raval  and
V. Ramgopal Rao
Harshil N. Raval
Affiliation:
Centre of Excellence in Nanoelectronics, Department of Electrical Engineering, Indian Institute of Technology Bombay, Powai, Mumbai – 400 076, India.
V. Ramgopal Rao
Affiliation:
Centre of Excellence in Nanoelectronics, Department of Electrical Engineering, Indian Institute of Technology Bombay, Powai, Mumbai – 400 076, India.
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Abstract

Changes in the material properties of copper (II) phthalocyanine (CuPc) thin-films were studied upon exposure to increasing dose of ionizing radiation using photoluminescence spectrum. We observe generation of new energy states below the band gap upon exposure to ionizing radiation. Organic electronic devices – CuPc based resistor and an organic field effect transistor (OFET) – are proposed in this work as total dose sensors for ionizing radiation. We observe an increase in the conductivity of CuPc thin-films with increasing dose of ionizing radiation. To overcome the possibility of changes/degradation in the electrical properties of CuPc thin-films upon interaction with various gases and moisture in the environment, a passivation layer of silicon nitride, deposited by hot-wire CVD process is proposed. Effect of ionizing radiation on the electrical properties of thin-films of CuPc has been studied. We observe a 170% increase in the resistance of the thin-film for a total of 50 Gy radiation dose using Cobalt-60 (60Co) radiation source. Moreover, significant changes in the electrical characteristics of an OFET, with CuPc as an organic semiconductor, have been observed with increasing doses of ionizing radiation. Experiments with an OFET (W/L = 19350 μm / 100 μm and tox = 150 nm) as a sensor resulted in a ∼100X change in the OFF current for a total of 50 Gy dose of ionizing radiation exhibiting a sensitivity of ∼1 nA/Gy. Moreover, implementing a reader circuit, shift in the threshold voltage of the OFET at 1e-7 A drain current displayed a sensitivity of 80 mV/Gy for a total of 50 Gy dose of ionizing radiation. CuPc based organic electronic devices have advantages as sensors because of their low-cost fabrication, large area coverage on flexible substrates, etc.

Keywords

radiation effectsorganicpassivation
Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 1383: Symposium A – Material Challenges in Current and Future Nuclear Technologies , 2012 , mrsf11-1383-a08-15
Copyright
Copyright © Materials Research Society 2012

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References

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