Study On The Effect Of Source And Drain On Bottom Gate Bottom Contact Organic Thin-film Transistors

Organic thin film transistors get attention and development widely in recent years. It has many advantages, such as simple preparation, low cost, solution preparation and flexibility. With the increasing types of organic materials and performance improvement, it can be roughly the same with the traditional polycrystalline silicon transistors in terms of performance. Organic thin film transistors have great application prospects and great potential for development in the smart cards, electronic labels, sensors and especially the applications in display. So it is very worthy of deep research.This paper is mainly based on a new polymer epoxy resin as the gate insulating layer and do research on the effect of source and drain on bottom gate bottom contact organic thin-film transistors.Firstly, we introduced the composition of this new insulator this paper based on. And then use the structure of MIM(metal insulator metal) to test the dielectric constant of the polymer materials. The relative dielectric constant measured is 4. Then optimized for the concentration of photosensitive agent PAG290, baking time, exposure time and single or double layer structure of insulator in insulating characteristics. When the photosensitive agent PAG290 accounted for 2% according to weight percentage, baking for 1 hour at 190 ℃,exposured for 100 seconds with the wavelength of 365 nm, power of 20 W/cm2 of the light, the leakage characteristics is best under unit of electric field intensity.Secondly, this paper adopts gold(Au) as materials of source and drain and based on the new insulating material, compares the performance of organic thin film transistors by wet-etch and lift-off. When using lift-off, the best mobility, on/off ratio and threshold voltage can reach 0.13 cm2/Vs, 9.35 ×104 and-6.17 V respectively; When using wet-etch, the best mobility, on/off ratio and threshold voltage can reach 0.21 cm2/Vs, 2.12 ×105 and-2.35 V respectively. The reason for this difference is contact resistance that was produced by these two different processes. The largest gap between the contact resistance is about 1.5 orders of magnitude. But wet-etch is better than lift-off in performance of devices. So a new type of lift-off is introduced, bilayer photoresist lift-off. It can make up for the bad contact of electrodes and OSC caused by single layer photoresist lift-off.Finally, this paper introduced the problem which was found during experiments when using gold as source and drain through wet-etch. When the length of channel is under 30μm, hysteresis of devices become obvious. And with the decreasing of channel length, the phenomenon is more significant. This is mainly due to the gold is a material of high work function. And when evaporating gold on insulator this paper based on directly, it will cause penetration of some gold into gate insulator. So residual of gold will stay during channels after wet etched. The phenomenon of hysteresis will be caused. Then through the experiment of silver(Ag), this material of relatively low work function as source and drain, the hysteresis was eased. Later the mixed material of silver and gold was used as source and drain. Silver was used as buffer layer to protect gold into insulator and then gold was evaporated as source and drain. This method can also ease hysteresis.