Solution based insulator was applied for low temperature poly silicon thin film transistor (TFT). Solution process has several advantages of low cost, short process time and no plasma damage. Several kinds of solution-based materials were tested for TFTs, including organic insulators. In this paper, we present the aluminum oxide gate insulator based on solution process.

For poly-silicon process, amorphous silicon is deposited by sputtering and crystallized by blue laser diode annealing. After pattering of the poly-silicon, gate insulator of Al₂O₃ was formed by solution process. After gate insulator etching, source/drain metal was deposited and patterned. Low temperature process below 400℃ for all TFT fabrication with low cost has been developed and reported.

The insulator was characterized with the metal-insulator-semiconductor (MIS) structure. 0.8 M Al(NO₃)₃9H₂O solution with DMAC (Di-methyl-acetamide) was coated on the Si-wafer. The surface of silicon wafer was treated with oxygen plasma before coating to improve the adhesion. After spin-coating, it was baked at 150℃ for 5 min. It was annealed finally at 300℃ for 1 h.

To improve the insulator performance, the multi coating was tested. After coating and baking, it was coated again. Figure 1 shows the I-V characteristics for the sample coated for three times. As the number of coating increased, leakage current was reduced and the break down voltage increased.