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

On-current I-ON and field effect mobility mu(FE) changed abnormally by drain bias illumination stress (DBIS) in amorphous InGaZnO thin-film transistors. First, I-ON dropped to 35% of its initial value and mu(FE) decreased from 11.8 cm(2)/(V.s) to 3.0 cm(2)/(V.s) because of acceptor-like tail states A(TAIL), which were generated by rupture of weak oxygen bonds near the drain region. The A(TAIL) trap electrons, and therefore have negative charge, which causes scattering of charged carriers and decrease in mu(FE). As DBIS time elapsed, ionized oxygen vacancies (V-O(2+)) were generated near the drain region, so I-ON was re-elevated to 1.57 times as high as its dropped value (i.e., to 55% of its initial value); mu(FE) increased from 3.0 cm(2)/(V.s) to 6.9 cm(2)/(V.s) (i.e., to 59% of its origin value);. These compensation effects happened when A(TAIL) and V-O(2+) occurred in the same place, so generation of V-O(2+) near drain region was the main cause of the re-elevation.