Preliminary characterization of the response of an organic thin film transistor to ionizing radiation
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Organic thin film transistors (OTFTs) were investigated as novel radiation detectors. OTFTs were fabricated on glass and PET substrates, with a pentacene semiconductor, and PMMA or Parylene-C dielectric. Kilovoltage (100, 180 kVp) and megavoltage (6, 18 MV) photon beams were used to irradiate OTFTs to 400 Gy. One OTFT was irradiated to 1000 Gy to observe its longevity. Irradiated devices showed a positive shift in the threshold voltage and a degradation in mobility. Initial sensitivity of devices was greater for kilovoltage-irradiated devices than megavoltage-irradiated devices, but converged after ~200 Gy to a value of ~1 mV/Gy and continued to decrease slowly at higher doses. After 1000 Gy, one device remained functional. Directional and dose rate dependence measurements were inconclusive and require further investigation. Monte Carlo simulations found less than 5% intrinsic energy dependence for photon spectra from Co-60 to 15 MV.