不同绝缘层上生长的并五苯薄膜及其OTFT器件性能的研究

分别以SiO₂和PMMA为绝缘层材料制备了底栅顶接触结构的OTFT器件，得到以PMMA为绝缘层的器件具有更好的性能，其场效应迁移率为0.207 cm2·Vs-1,开关电流比为4.93×103,阈值电压为-4.3 V;而以SiO₂为绝缘层的器件，其场效应迁移率仅为0.039 cm2·Vs-1,开关电流比为5.98×102,阈值电压为-5.4 V。为分析器件性能差异的原因，测得了SiO₂和PMMA薄膜表面的AFM图谱及其上沉积并五苯薄膜后的AFM和XRD图谱。通过AFM图谱发现PMMA表面较SiO₂表面粗糙度小，其表面粗糙度的均方根值为0.216 nm，而二氧化硅薄膜表面粗糙度的均方根值为1.579 nm;且发现在PMMA上生长的并五苯薄膜的成膜质量优于在SiO₂,具有较大的晶粒尺寸和较少的晶粒间界。通过XRD图谱发现在PMMA上生长的并五苯薄膜具有明显的衍射峰，进一步证明了在PMMA上生长的并五苯薄膜具有更好的结晶状况，将更有利于载流子的传输。

The Properties of OTFTs and Pentacene Films Deposited onto Different Insulator Layers

The authors fabricated OTFT devices with different insulator materials. The OTFTs with PMMA as the dielectric layer exhibit better properties, including a mobility of 0.207 cm2·V-1·s-1, an on/off current ratio of 4.93×103, and a threshold voltage of 4.3 V. However, the OTFTs based on oxidized silicon dielectric layer perform not so well, with a mobility of 0.039 cm2·V-1·s-1, an on/off current ratio of 5.98×102, and a threshold voltage of 5.4 V. In order to explain the difference in performances, we compared the surface roughness of the oxidized silicon film with that of the PMMA film according to the results of atomic force microscopy, and found that the former had a roughness mean square (RMS) of 1.579 nm and the latter was more smooth with an RMS of 0.216 nm. The quality of the pentacene films deposited onto oxidized silicon and PMMA was also studied by atomic force microscopy and X-ray diffraction. From the results of AFM, the authors found that the pentacene film deposited on PMMA had high thin film quality with larger grain size and less crystal grain boundaries. From the results of XRD, the authors found that the pentacene film deposited on PMMA had clear diffraction peak, showing 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 dielectric layer.