Oxide TFT with Sog Gate Insulator

Abstract

Oxide TFT (thin film transistor) shows higher mobility and less leakage current than amorphous silicon TFT. In this presentation, we investigated solution processed gate insulator for the oxide TFT. The solution process does not require the use of expensive vacuum equipment, and also has advantages of simple process, high productivity and low cost. Less defects and trap centers are required for the gate insulator and the conventional material is SiO2 for which vacuum equipments are used to deposit it. Since the gate insulator is deposited on the active layer for the top gate structure, active layer can be deteriorated by plasma ion bombardment during deposition of the gate insulator. Plasma damage exerted on the active layer during the deposition of the gate insulator have an adverse effect on the TFT characteristics. On the other hand, solution process does not use plasma, therefore, it can remove plasma damage on the active layer. And also, solution process is inexpensive and highly productive process. In this experiments, we used spin on glass material for the solution process of the gate insulator. We investigated the effect of dilution of the SOG with IPA (isopropyl alcohol). It was coated on a p-type Si wafer by spin coating with 3500 rpm. For the diluted solution, we coated several times for the desired thickness of the gate insulator. Hard bake was done for 20 min at 170℃ after soft-bake for 20 min at 85℃. Final cure was done for 1 hour at 420℃ in nitrogen ambient. Figure 1 shows the current densities of the SOG insulator for the various dilutions of SOG solution. The leakage currents were reduced for the diluted solution. Figure 1