TH-CD-201-12: Preliminary Evaluation of Organic Field Effect Transistors as Radiation Detectors.

PURPOSE: To fabricate organic field effect transistors (OFETs) and evaluate their performance before and after exposure to ionizing radiation. To determine if OFETs have potential to function as radiation dosimeters.

METHODS: OFETs were fabricated on both Si/SiO2 wafers and flexible polymer substrates using standard processing techniques. Pentacene was used as the organic semiconductor material and the devices were fabricated in a bottom gate configuration. Devices were irradiated using an orthovoltage treatment unit (120 kVp x-rays). Threshold voltage values were measured with the devices in saturation mode and quantified as a function of cumulative dose. Current-voltage characteristics of the devices were measured using a Keithley 2614 SourceMeter SMU Instrument. The devices were connected to the reader but unpowered during irradiations.

RESULTS: Devices fabricated on Si/SiO2 wafers demonstrated excellent linearity (R(2) > 0.997) with threshold voltages that ranged between 15 and 36 V. Devices fabricated on a flexible polymer substrate had substantially smaller threshold voltages (∼ 4 - 8 V) and slightly worse linearity (R(2) > 0.98). The devices demonstrated excellent stability in I-V characteristics over a large number (>2000) cycles.

CONCLUSION: OFETs have demonstrated excellent potential in radiation dosimetry applications. A key advantage of these devices is their composition, which can be substantially more tissue-equivalent at low photon energies relative to many other types of radiation detector. In addition, fabrication of organic electronics can employ techniques that are faster, simpler and cheaper than conventional silicon-based devices. These results support further development of organic electronic devices for radiation detection purposes. Funding Support, Disclosures, and Conflict of Interest: This work was funded by the Natural Sciences and Engineering Research Council of Canada.