1. Field of Invention
The present invention relates to methods of forming an insulating layer and forming a device, and more generally to methods of forming a hydrophobic silicon dioxide (SiO2) layer and forming an organic thin film transistor (OTFT) including the hydrophobic SiO2 layer.
2. Description of Related Art
OTFTs have recently attracted much attention for their applications in radio-frequency identification (RFID) tags, large-area sensors and active matrix flat panel display (AMPD) backplane driving circuits.
Generally, a SiO2 layer is one of the most widely used gate insulating layers in OTFTs. When an OTFT is formed on a flexible substrate, the process temperature of the SiO2 gate insulating layer must be lowered for compatibility, otherwise the flexible substrate may be damaged. However, the SiO2 gate insulating layer formed at low temperature usually includes a significant amount of hydroxyl (OH) groups, which makes the surface of the SiO2 gate insulating layer more polar and hydrophilic. This OH-terminated SiO2 surface may cause poor crystalline growth of an organic semiconductor active layer (e.g. pentacene), and thus the performance of the OTFT is affected.
It is known that the OTFT performance can be greatly improved by modifying the SiO2 surface with a hydrophobic self-assembled monolayer (SAM), such as hexamethyldisilazane (HMDS) or octadecyltrichlorosilane (OTS). HMDS or OTS can form a hydrophobic methyl SAM (CH3-SAM) on the SiO2 surface, so as to reduce the SiO2 surface energy and improve the crystalline growth quality of the organic semiconductor active layer (e.g. pentacene). However, due to the surface modification treatment, the process becomes more complicated and time-consuming and the cost is increased.