This thesis presents the development of low-voltage organic thin-film transistors with high transconductance. This was achieved by employing ultra-thin bi-layer gate dielectric consisting of aluminium oxide (AlOx) and a self-assembled monolayer of octadecyl phosphonic acid (C18PA) and by increasing the channel width of the transistors through the implementation of the multi-finger source/drain contacts. The transistors based on dinaphtho[2,3-b:2â²,3â²-f]thieno[3,2-b]thiophene (DNTT) exhibited low turn-on voltage and a.c. transconductance around 30 to 60 ÂµS. Transistor amplifiers based on such transistors exhibited voltage gain approaching 10 V/V and a gain of about 2 V/V when the supply voltage was limited to 5 V. Next, a series of [n]phenacenes ([n] = 5, 6, or 7) was used for the first time in combination with the thin AlOx/C18PA dielectric bi-layer. Regardless of the substrate and the source-drain contact geometry, the field-effect mobility of such transistors was found to inc rease with increasing length of the conjugated [n]phenacene core, leading to the best performance for phenacene with the largest average field-effect mobility of 0.27 cm2/Vâ
s for transistors on glass and 0.092 cm2/Vâ
s for transistors on flexible PEN. The highest transconductance of 12.2 ÂµS was achieved for phenacene transistors on glass, which was lower than that achieved for DNTT transistors. In addition, nearly hysteresis-free behaviour, improved charge carrier injection/extraction properties, and reduced threshold voltage were achieved. Finally, a semi-empirical transistor model was developed in Matlab. The model was validated using d.c. and a.c. measurements obtained on DNTT transistors with high transconductance. Four fitting parameters were extracted by optimising a fitting function using genetic algorithm. The model reproduces the d.c. transistor measurements with high accuracy. The error between the measured and simulated peak-to-peak a.c.transconductance values ran ged from 1.7% to 11.6%.
|Date of Award||6 Feb 2020|
- University Of Strathclyde
|Sponsors||University of Strathclyde|
|Supervisor||Helena Gleskova (Supervisor) & John Soraghan (Supervisor)|