| Summary: | 碩士 === 大同大學 === 化學工程學系(所) === 95 === The main aim of this thesis is the enhancement on the characteristics of pentacene organic thin film transistor. Three kinds of different chlorosilane treated agents were employed to modify hydrophilic character of dielectric layer, and promoted the electric characteristics of organic thin-film transistor (OTFT).
We investigated the electrical properties of the OTFTs using pentacene fabricated by thermal evaporation in a high vacuum with the three kinds of dielectric surface treating agent: octadecyltrichlorosilane (C18H37SiCl3) (OTS), phenyltrichlorosilane (C6H5SiCl3) (PTS), and phenethyltrichlorosilane (C6H5C2H4SiCl3) (PETS). Studies on properties of pentacene thin film and the performance of the device are affected by self-assembled monolayer (SAM) via the analysis of water contact angle, atom force microscope (AFM), X-ray diffractometer (XRD), field emission gun scanning electron microscopy (SEM), and semiconductor parametric test system (HP 4155C) have been carried out.
Water contact angle of OTS-treated SiO2 surface is 84°, 85°, 86°, and 90°for the OTS concentration of 0.1, 0.5, 1.0, and 1.5 wt%, respectively. Water contact angle of PTS-treated SiO2 surface is 74°,
76°, and 81°for the PTS concentration of 0.5, 1.0, and 2.5 wt%, respectively. Therefore, the analysis result that the water contact angle of SiO2 surface
increases with increasing the concentration of treating agent.
The optimal evaporated temperature of pentacene OTFT with PTS-treated SiO2 was substrate temperature at 120℃ and pentacene evaporation temperature at 435℃. The field-effect mobility, on/off current ratio, threshold voltage, and subthreshold slope of pentacene OTFT were 9.97 ´ 10-2 cm2/Vs, 2.28 × 107, -15.7 V, and 1.05 V/decade, respectively.
Through different concentration of OTS-treated SiO2 used, it is found that the best characteristics of OTFT occurs by 0.1 wt% OTS-treated SiO2. The field-effect mobility, on/off current ratio, threshold voltage, and subthreshold slope of OTFT were 3.57 × 10-1 cm2/Vs, 1.76 × 107, -7.7 V, and 1.01 V/decade, respectively.
For the same reason, PTS and PETS-treated SiO2 can improve the characteristics of OTFT. The field-effect mobility, and on/off current ratio of pentacene OTFT with 2.5 wt% PTS-treated SiO2 were 2.09 ´ 10-1 cm2/Vs, and 3.66 × 106, respectively. The field-effect mobility, and on/off current ratio of pentacene OTFT with 0.3 wt% PETS-treated SiO2 were 2.28 ´ 10-1 cm2/Vs, and 3.99 × 107, respectively. The best performance of device is obtained using OTS as self-assembly monolayer agent. The field-effect mobility, and on/off current ratio of pentacene OTFT with OTS-treated SiO2 were enhanced one to two orders of magnitude, larger than those of untreated device.
Photographs of Atom Force Microscope (AFM) and Scanning Electron Microscopy (SEM) showed that the size of crystals was smaller, and similar. The surface of pentacene was more flatness. Therefore, it lead to the packing of pentacene thin-film being more compact and less trap, hence enhanced OTFT’s electrical property.
The intensity of single crystal phase of pentacene thin film deposited on the surface of 0.1 and 0.5wt% OTS-treated SiO2 exhibits 1642 and 804, respectively. The corresponding field-effect mobility is 3.57 × 10-1 and 1.17 × 10-1 cm2/Vs. Similarly, the intensity of single crystal phase of pentacene thin film deposited on the surface of 0.1, 1.5 and 2.5wt% PTS-treated SiO2 exhibits 1390, 2090, and 4198, respectively. The corresponding field-effect mobility is 1.48 × 10-1, 1.48 × 10-1 and 2.09 × 10-1cm2/Vs. Therefore, XRD shows that the higher the intensity of single crystal / thin film phase, the better the electric properties.
The less amount of water in a air at lower pressure, resulting in the trap was less in the material. It enhanced the characteristics of OTFT. The field-effect mobility and on/off current ratio of pentacene OTFT with 0.1 wt% OTS treated SiO2 are 4.12 ×10-1 cm2/Vs and 3.04 × 107, respectively, at the pressure of 4.6 × 10-2 torr. The field-effect mobility and on/off current ratio of pentacene OTFT with 2.5 wt% PTS treated SiO2 are 2.09 ×10-1 cm2/Vs and 108, respectively, at the pressure of 4.9 × 10-2 torr. The field-effect mobility and on/off current ratio of pentacene OTFT with 0.3 wt% PETS treated SiO2 are 2.65 ×10-1 cm2/Vs and 3.43 × 107, respectively, at the pressure of 19 torr.
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