Anomalous variations of OFF-state leakage current in poly-Si TFT under static stress

Abstract

In this letter, we study the anomalous variations of the OFF-state leakage current (I-OFF) in n-channel poly-Si thin-film transistors (TFTs) under static stress. The dominant mechanisms for the anomalous I-OFF can be attributed to 1) I-OFF increases due to channel hot electrons trapping at the gate oxide/channel interface and silicon grain boundaries and 2) I-OFF decreases due to hot holes accumulated/trapped near the channel/bottom oxide interface near the source region. Under the stress of high drain bias, serious impact ionization effect will occur to generate hot electrons and hot holes near the drain region. Some of holes will be injected into the gate oxide due to the vertical field (similar to(V_stress - V_ - Dstress) /T-ox) near the drain and the others will be migrated from drain to source along the channel due to lateral electric field (similar toV_Dstress/L-CH).