PMMA介质层铟锌氧化物薄膜晶体管的制备与研究

【作者】 冯佳涵；

【导师】 张群；

【作者基本信息】 复旦大学 ， 物理电子学， 2011， 硕士

【摘要】 本文低温制备了以铟锌氧化物(IZO)为沟道层、聚甲基丙烯酸甲酯(PMMA)为介质层的薄膜晶体管。由反应直流磁控溅射法沉积无机IZO沟道层,浸渍提拉法制备有机PMMA介质层,真空热蒸发沉积金属铝电极。整体工艺温度低于90℃,与柔性电子学相兼容。分别对沟道层、介质层单层薄膜的表面形貌、光学性能和电学性能进行了表征。PMMA介质层/IZO沟道层两层薄膜的可见光区平均透射率高于90%(不含基板)。分析了沟道层厚度、溅射氧分压、靶材组分、介质层厚度等因素对铟锌氧化物薄膜晶体管(IZO-TFT)性能的影响,优化实验参数,改善器件性能。探索性地研究了TFT器件稳定性和低温制备透明电极。室温下反应直流磁控溅射In/Zn合金靶材于玻璃基板上沉积IZO沟道层。所制备的IZO薄膜为非晶结构,表面平整,可见光区平均透射率高于85%(不含基板)。包括沟道层厚度、溅射氧分压、靶材组分含量在内的实验参数对IZO-TFT的电学性能有影响。IZO厚度为60～90 nm时制备的器件性能较优。溅射氧分压为5.0×10-2Pa时制备得到饱和迁移率最高的IZO-TFT,数值是7.67cm2V-1s-1,其闽值电压为-14.59 V,开关比2.4×102。靶材中Zn含量的适当增加有利于提高TFT的饱和迁移率,同时关态电流略增。使用浸渍提拉法在IZO沟道层上制备有机PMMA介质层。PMMA薄膜表面十分平整,可见光区平均透射率达到92%(不含基板)。制备了AI-PMMA-A1的MIM结构,测试表明PMMA薄膜的介电性能良好,1 kHz时相对介电常数为3.49。随着PMMA介质层厚度在150～580 nm范围内增加,TFT的饱和迁移率和阈值电压均呈现先增加后减小的现象。调节介质层厚度在360 nm左右制备的IZO-TFT电学特性最优,饱和迁移率1.99 cm2V-1s-1,阈值电压-2.77 V,电流开关比约2.6×104。通过对IZO-TFT施加一定时间的固定栅极偏压,分析老化过程中器件饱和迁移率、阈值电压的偏移情况以判断其电学稳定性。先适当施加较小的栅极偏压进行一定时间的老化有利于提高器件稳定性。探索低温制备适用作电极的透明导电氧化物薄膜。室温下用反应磁控溅射沉积了非晶掺钨氧化铟(IWO)薄膜,调节氧分压与溅射功率以提高其导电性和透光性。掺钨含量1 wt%的IWO薄膜可达最小的薄膜电阻5.75×10-4Ω·cm,可见光区平均透射率高于90%。更多还原

【Abstract】 Indium zinc oxide based thin film transistors (IZO-TFTs) were fabricated at low temperature, where poly(methyl methacrylate) (PMMA) serves as the insulator. The inorganic channel layers were deposited by reactive de magnetron sputtering. The organic dielectric layers were prepared by dipping method and aluminum electrodes by thermal evaporation. The processing temperature all along is below 90℃, which is compatible with the fabrication of flexible electronics. The optical and electrical properties of channel layers and dielectric layers were characterized, respectively. The average transmittance in the visible region of PMMA layer together with IZO layer is more than 90%. The effects of experimental parameters including channel thickness, oxygen partial pressure, target composition and dielectric thickness on the electrical performances of IZO-TFTs were analyzed. Besides, electrical stability of the devices and transparent electrodes prepared at low temperature were investigated.Amorphous IZO channel layers were deposited from an alloy target by reactive dc magnetron sputtering at room temperature. The surfaces are smooth and the average transmittance in the visible region is over 85%. Channel thickness, oxygen partial pressure and target composition affect electrical performances of IZO-TFTs. IZO-TFTs exhibit optimum characteristics with channel thickness of 60～90 nm. The device prepared at oxygen partial pressure of 5.0×10-2 Pa reaches its highest saturation mobility of 7.67 cm2V-1s-1, with the threshold voltage of-14.59 V and on/off current ratio of 2.4×102. The increase of zinc content in the alloy target helps to enhance the mobility of TFT while off current increases simultaneously.The PMMA dielectric layers were prepared by dipping method. The average transmittance of PMMA thin film in the visible region is 92%. Its surface is rather smooth. The MIM capacitor with Al-PMMA-Al structure was fabricated. The dielectric property of PMMA is good and its relative dielectric constant is 3.49 measured at 1 kHz. With the enhancement of dielectric thickness from 150 to 580 nm, the saturation mobility and threshold voltage of devices both increase firstly and decrease afterward. The prepared IZO-TFT exhibits the optimum performance when dielectric thickness is around 360 nm. Its saturation mobility is 1.99 cm2V-1s-1and the threshold voltage is-2.77 V with on/off current ratio of 2.6×104.The electrical stability of IZO-TFT was tested by applying bias stress with gate voltage for some time. The variations of saturation mobility and threshold voltage of the device are studied. A prior aging process with a relatively small gate bias stress is conductive to device stability. Tungsten-doped indium oxide (IWO) films were investigated for the usage of transparent electrodes. The IWO films deposited at room temperature are amorphous and the ones prepared from 1 wt% tungsten-doped target reach a minimum resistivity of 5.75×10-4Ω·cm with the average transmittance of over 90% in the visible region.更多还原