Write-Once-Read-Many-Times Memory Characteristics with a Large Memory Window Operating at a Low Voltage by Li-Ion Incorporation from the LiCoO_x 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 (LiCoO x ) ion-supplying layer in the gate oxide. While the device with a thicker (5 nm) tunneling oxide showing a threshold voltage shift (ΔV T) of about 5 V by electron charging upon positive gate voltage (V GS) sweep to +25 V, the device with a 2 nm-thick tunneling oxide exhibits a large memory window with ΔV T > 20 V by Li-ion migration from LiCoO x to IGZO channel, which can be controlled as multilevel states with respect to the V GS amplitude. Incorporation of Li ions into the IGZO channel acting as p-type dopants reduces carrier concentration in the channel and consequently increases V T. The increased V T and the consequently reduced drain current are not instantly restored back by applying negative V GS, 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.