Investigation of High Current Tetracene-TFT Using Surface Nitrided SiO2 Gate Insulator Film

Abstract

The use of surface nitrided SiO2 film as gate insulator of tetracene-TFT (Thin Film Transistor) has been proposed. Using Ar/N2 plasma, the nitridation has been carried out on the SiO2 surface to remove carrier trapping sites due to hydroxyl groups. As a result, transistor output characteristics have been drastically improved with extremely high current level using tetracene film as organic semiconductor material. Recently, there has been widely interested in organic-TFT because of its flexibility, ability to have a lot of material designs, applicability to large area devices and so on. However, the surface of conventional gate insulator such as SiO2and other metal oxide films often contain charge trapping sites due to the existence of hydroxyl (-OH) groups and surface defects. The carriers of organic-TFT have to move at the surface layer in the organic film adjacent to the gate insulator. Therefore it is important to control the surface and/or interface of organic film and gate insulator to avoid the carrier scattering at the charge trapping sites. Now, commonly used method to overcome this problem is deposition of SAM (Self-Assembled-Monolayer) film on the gate insulator. As a result, it is reported that electrical characteristics have been drastically improved. But it takes time about at least half a day to deposit the SAM film. In this paper, we have attempted to improve the carrier mobility in the tetracene film as organic semiconductor material, with surface nitride SiO2 film as the gate insulator for a short processing time. Figure1 shows transistor output characteristics with the channel length (L) = 70[um] and channel width (W) = 2000[um], respectively. It is clearly shown the extremely high current have been achieved from the tetracene-TFT on surface nitrided SiO2. On the contrary, no modulation due to gate bias could be achieved on SiO2film without the nitridation. Also, to clarify the difference, the property of tetracene/SiO2 interface of each sample, C-V measurement has been carried out. After the nitridation have been done on the SiO2 surface that had been etched with dil-HF to make hydroxyl groups, the width of C-V hysteresis is decreased. Therefore we can conclude the surface nitridation of SiO2 films with Ar/N2 plasma is effective method to remove charge trapping sites related to hydroxyl groups and improve transistor output characteristics. Figure 1