The Influence Of Rubbing Alignment Of Active Layer On Organic Field-effect Transistors

Organic field-effect transistor(OFET) has attracted considerable interests in areas of chemistry, physics, materials, and microelectronics, since the first OFET was realized in the 1980 s. Meanwhile, the functional OFET has gradually become the focus of research due to the huge value for commercialization. This thesis adopted OFET as sensing component, and we mainly studied the influence of rubbing process on the electrical characteristics and gas sensing properties of OFET on the basis of the optimization of dielectric thickness. The specific contents are shown as follows:1. Pentacene OFETs consisted of PMMA/PS bilayer dielectric were studied. By using poly(methyl methacrylate)(PMMA) and polystyrene(PS) as the dielectric layer, pentacene as the organic active layer, OFETs based on different thickness of dielectric were investigated. Two groups of OFETs were designed in the experiment, one fixed the thickness of PMMA at 280 nm, the thicknesses of PS were 140 nm, 170 nm, 220 nm and 290 nm, respectively. The other one fixed the thickness of PS at 200 nm, and the thicknesses of PMMA were 140 nm, 180 nm, 220 nm and 250 nm, respectively. The results showed that the OFET with 280 nm PMMA and 220 nm PS exhibited optimal performances with a field-effect mobility of 0.15 cm2/Vs and a current on/off ratio of 2.8?105.2. The influence of rubbing process on the sensing properties of OFET based on single PS dielectric was investigated. A conventional paintbrush made of nylon fibrils was used to rub pentacene layer with parallel, perpendicular or tilted rubbing direction to the source/drain contacts(SD). Firstly, we studied the influence of different orientation on the device electrical characteristics. The results showed that the perpendicular rubbed device got the best performance with a field-effect mobility of 0.17 cm2/Vs and an on-state current of 0.45 μA, which were both 1 fold as much as the nonrubbed device, respectively. Furthermore, the influence of different orientation on the device sensing properties was studied. The results showed that the parallel rubbed device got the best sensing performance with the highest sensitivity(S = 1.3 %) and fastest response time(?70 s) to 2 ppm NO2.3. The influence of rubbing process on the sensing properties of OFET on the basis of the optimization of dielectric thickness was studied. On the basis of preparation of the high performance OFET based on PMMA/PS bilayer dielectric, a nylon fibrils was used to rub pentacene layer with parallel, perpendicular or tilted rubbing direction to the SD. The results showed that the perpendicular rubbed device got the highest performance with a field-effect mobility of 0.46 cm2/Vs and an on-state current of 60.4 μA, which were 2 folds and 1.5 folds as much as the nonrubbed device, respectively. Furthermore, the parallel rubbed device got the best sensing performance with the highest sensitivity(S = 1.1 %) and fastest response time(?50 s) to 2 ppm NO2. Compared with single PS dielectric layer devices, the PMMA/PS bilayer dielectric devices showed better electrical characteristics and gas sensing properties, no matter whether through rubbing process. At last, combining gas-sensing mechanism and charge carrier transport theory, the experimental results that different orientation producing different effect on gas sensing properties of OFETs were analysed.