Enhancing Reliability and 2 mm-Axial Mechanical Bending Endurance by Gate Insulator Improvements in Flexible Polycrystalline Silicon TFTs

Abstract

In this study, the electrical performance and bending stress endurance of flexible low-temperature polycrystalline silicon thin film transistors (LTPS TFTs) are enhanced by increasing the helium concentration (1500 sccm) during gate insulator (GI) manufacture to create a high-quality GI device. Experimental results confirm that the subthreshold swing (S.S.) and mobility of these new &#x201C;high-flow&#x201D; devices are better than those with a lower helium concentration, which we term &#x201C;low-flow&#x201D; devices. The flow of helium gas is increased to achieve a better-quality oxide layer. The energy-dispersive X-ray spectroscopy (EDS) line data show a clear enhancement in oxygen content in the devices under this helium gas process. After mechanical compression and tensile bending stresses of 100000 iterations in the channel width-axis direction, perpendicular to the channel, with bending at <inline-formula> <tex-math notation="LaTeX">${R} = {2}$ </tex-math></inline-formula> mm, the modified GI devices with their more Si-O bond content exhibit less stress damage in the GI layer than do low-flow devices. As a result, this new manufacturing condition can effectively reduce the electrical degradation after negative-bias temperature stress (NBTS), and improve the overall electrical performance.