The Improvement of Polycrystalline Silicon TFTs Fabricated by Employing Periodic Metal Pads

Polysilicon films with regular-sized and large grains were fabricated by employing periodic metal (Cr–Al) pads as the heat sinks and with underlying silicon oxynitride (SiON) as the heat absorption layer. The poly-Si could grow to regular hexagonal grains after excimer laser annealing (ELA). The thin-film transistors (TFTs) fabricated by this method show uniform characteristics that are suitable for large-area applications. The TFT achieves a field-effect mobility of 270
$hboxcm^2/hboxV cdot hboxs$
and an on–off current ratio exceeding
$hbox10^8$
. It is found that the TFT with the smaller channel width and length results in a better subthreshold swing because it contains fewer grain boundaries and, thus, fewer defects. After comparing the performance of TFTs using either double-metal Cr–Al or single-metal Al photonic-crystal pads, it is found that the Cr could efficiently impede the diffusion of Al into Si during ELA.