Preliminary characterization of the response of an organic field effect transistor to ionizing radiation

Organic thin film transistors (OTFT) were investigated as a novel radiation detector. The OTFTs were fabricated on a flexible PET substrate with a PMMA dielectric layer and a pentacene semiconductor. OTFTs were irradiated up to 400 Gy using kilovoltage (100 and 180 kVp) and megavoltage (6 and 18 MV) photon beams. One OTFT was irradiated to 1000 Gy using 6 MV to observe the longevity of the device. Irradiating the devices caused a positive threshold voltage shift in each device. The magnitude of the threshold voltage shift per unit dose decreased with accumulated dose until it stabilized after approximately 200 Gy. The sensitivity ranged from 2 to 10 mV/Gy at low accumulated dose and decreased to 0.5-1.5 mV/Gy after 200 Gy of accumulated dose across the various OTFTs. After 400 Gy all of the devices were still functional with a loss in mobility of about 15, 14, 12 and 9% for beam qualities of 100 kV, 180 kV, 6 MV, and 18 MV, respectively. After 1000 Gy using 6 MV the OTFT was still functional with a sensitivity of 0.8 ± 0.1 mV/Gy after 300 Gy. This study showed that an OTFT on a flexible substrate shows a measureable response to photon irradiation of various qualities.