To date, significant progress has been made to advance the performance of organic thin film transistors (OTFTs). These included new materials and structures and innovative fabrication methods to yield properties such as light-weight, mechanical flexibility, and low temperature fabrication. Yet, many OTFTs still suffer from low on-state drain current and electrical instability seen as a hysteresis or a shift in the transistor transfer characteristics, thus hindering wider OTFT applications. This thesis aims to tackle these issues by presenting low-voltage OTFTs based on air-stable dinaphtho[2,3-b:2',3'-f]thieno[3,2-b]thiophene (DNTT) and hydrophobic bi-layer dielectric made of aluminium oxide and octadecyl phosphonic acid (AlOx/C18PA) on PEN substrates. The fabricated transistors are approximately hysteresis-free and exhibit on-state drain current approaching 100 μA at gate-source and drain-source voltages of -2 V. This is a notable advancement compared to the performance of similar devices reported in the literature and indicative of a robust design and fabrication. High on-state drain current was enabled by ultra-thin gate dielectric and interdigitated source/drain contacts leading to high channel width-to-length ratio and small transistor area. The electrical stability was studied in the above transistors, both fresh and aged. AC square pulses with constant bias time of 1 second and varying pulse period were simultaneously applied to gate and drain of the transistor to simulate the recurrent turn-on/turn-off transistor operation. OTFT performance marginally degraded under AC pulses, with the exception of field-effect mobility that improved. Degradation proceeded faster in aged OTFTs stored in dark ambient environment but the on-state drain current stabilised after ~500 pulses. The stabilisation resulted from the rising field-effect mobility compensating the threshold voltage increase. Finally, the inclusion of the above OTFT as a voltage amplifier in a temperature sensor system raised the temperature sensitivity by a factor of ~5, thus laying foundation for future flexible sensors and circuit applications.
|Date of Award||30 Nov 2021|
- University Of Strathclyde
|Sponsors||University of Strathclyde|
|Supervisor||Helena Gleskova (Supervisor) & Ivan Glesk (Supervisor)|