<title>Effect of barrier layer thickness on the performance of thin film transistors on glass substrates</title>

Abstract

Top-gated poly-Si thin film transistors (TFTs) were fabricated on Corning COde 1737 glass substrates coated with SiO<SUB>2</SUB> barrier layers of varying thickness. The leakage current, or minimum current in the off state of the transistor, was measured and analyzed to evaluate the influence of barrier layer thickness on the TFT characteristics. Our results indicate that using a thick barrier layer may results in higher TFT leakage currents. Control devices on oxidized silicon have higher leakage currents than TFTs on barrier coated Code 1737 glass. Those on glass substrates show the effect of barrier layer thickness. As the barrier layer thickness increases the leakage current also increase. One possible explanation for this is the nature of the glass substrate. Even a thin SiO<SUB>2</SUB> layer can suppress diffusion of electrically active impurities from the substrate to the device. However, aluminoborosilicate glasses such as Corning Code 1737 are also known to act as sinks for sodium and other process impurities. Thick barrier layers separate the TFT from the gettering effects of the substrate and limit the removal of impurities from the device region.