Write-Once-Read-Many-Times Memory Characteristics with a Large Memory Window Operating at a Low Voltage by Li-Ion Incorporation from the LiCoOx Ion-Supplying Layer into the InGaZnO Channel of a Thin-Film Transistor

Abstract

Write-once-read-many-times (WORM) memory characteristics with a large memory window are demonstrated in a thin-film transistor (TFT) composed of an indium-gallium-zinc oxide (IGZO) channel and a lithium-cobalt oxide (LiCoOx) ion-supplying layer in the gate oxide. While the device with a thicker (5 nm) tunneling oxide showing a threshold voltage shift (ΔVT) of about 5 V by electron charging upon positive gate voltage (VGS) sweep to +25 V, the device with a 2 nm-thick tunneling oxide exhibits a large memory window with ΔVT > 20 V by Li-ion migration from LiCoOx to IGZO channel, which can be controlled as multilevel states with respect to the VGS amplitude. Incorporation of Li ions into the IGZO channel acting as p-type dopants reduces carrier concentration in the channel and consequently increases VT. The increased VT and the consequently reduced drain current are not instantly restored back by applying negative VGS, featuring WORM memory characteristics. Although the device undergoes partial retention loss, the retention remains up to about 90% after 100 min of retention time. These results verify WORM memory operations in the IGZO TFTs through gate voltage-driven Li-ion incorporation into the IGZO channel to modify its conductive states instead of using a typical electrical charging route.