Studies On The Effects Of Insulator Layers On The Performance Of Organic Thin Film Transistors

The characteristics of insulator layers,such as the morphology of thin films,thickness,will strongly determine the performance of organic thin film transistors(OTFTs).These characteristics can directly influence the growth of organic semiconductor layers and the performance of OTFT devices.In this paper,we carried out our researches on OTFTs from the following three aspects:1.OTFTs based on inorganic dielectric layers.Firstly,we compared the properties of OTFTs based on different inorganic insulator layers fabricated by electron beam evaporation.The OTFTs based on SiO₂ as insulator layer showed the bigger mobility(0.457cm²/vs)than that of OTFTs based on Si₃N₄(0.133 cm²/vs).And then,we compared the performance of devices using silicon nitride gate dielectric by different process of preparing dielectric films.The device with its insulator layer manufactured by RF reactive magnetron sputtering showed a larger on/off current ratio than that deposited by electron beam evaporation due to the decreases of leakage current.2.OTFTs based on organic dielectric layers.Firstly,OTFTs with different insulator materials were fabricated.The OTFTs with PMMA as the dielectric layer exhibit better properties,including a mobility of 0.207 cm²/Vs,an on/off current ratio of 4.93×10³,and a threshold voltage of 4.3V.However, the OTFTs based on oxidized silicon dielectric layer perform not so well,with a mobility of 0.039cm²/Vs,an on/off current ratio of 5.98×10²,and a threshold voltage of 5.4V.In order to explain the difference of the performances,we compared the surface roughness of the oxidized silicon film with that of the PMMA film from the morphology obtained by atomic force microscopy,finding the latter being smoother with an roughness mean square(RMS)of 0.216nm.The film quality of the pentacene films deposited onto oxidized silicon and PMMA were also studied by atomic force microscopy and X-ray diffraction.We found that the pentacene film deposited on PMMA had greater crystallite quality once again.Therefore,OTFTs with PMMA as insulator layers have advantages over those OTFTs with oxidized silicon as dielectric layer.Then,we fabricated OTFTs with different thickness of PMMA insulator layers, the device with thinner insulator layers exhibited better performance.3.OTFTs based on inorganic/organic heterojunctions insulator layers. OTFTs based on inorganic/organic heterojunctions insulator layers as the gate dielectric layers were fabricated,the experimental results demonstrated that heterojunctions insulator layers can improve electric characteristics and decrease working voltage of OTFTs.