To satisfy the different requirement of TFTs function as peripheral driving circuit and pixel switching device, the modified TFT structure with various thicknesses of gate insulating layers is disclosed. For the peripheral driving circuit, the thinner thickness of the gate-insulating layer is formed, the higher driving ability the TFT performs. However, for the pixel switching device, the thicker thickness of the gate insulating layer is formed, the better reliability the TFT has. The present invention provides a first TFT (peripheral driving circuit) comprising a first gate insulating layer and a second TFT (pixel switching device) comprising a first and second gate insulating layer. Thus, the gate insulating layer of the peripheral driving circuit has a thickness less then that of the pixel switching device.