Defect-creation effects on abnormal on-current under drain bias illumination stress in a-IGZO thin-film transistors

Abstract

On-current ION and field effect mobility μFE changed abnormally by drain bias illumination stress (DBIS) in amorphous InGaZnO thin-film transistors. First, ION dropped to 35% of its initial value and μFE decreased from 11.8 cm2/(V∙s) to 3.0 cm2/(V∙s) because of acceptor-like tail states ATAIL, which were generated by rupture of weak oxygen bonds near the drain region. The ATAIL trap electrons, and therefore have negative charge, which causes scattering of charged carriers and decrease in μFE. As DBIS time elapsed, ionized oxygen vacancies (VO2+) were generated near the drain region, so ION was re-elevated to 1.57 times as high as its dropped value (i.e., to 55% of its initial value); μFE increased from 3.0 cm2/(V∙s) to 6.9 cm2/(V∙s) (i.e., to 59% of its origin value);. These compensation effects happened when ATAIL and VO2+ occurred in the same place, so generation of VO2+ near drain region was the main cause of the re-elevation.