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 characteristicswith alarge memory window are demonstrated in a thin-film transistor (TFT)composed of an indium-gallium-zinc oxide (IGZO) channel and a lithium-cobaltoxide (LiCoO x ) ion-supplying layer inthe gate oxide. While the device with a thicker (5 nm) tunneling oxideshowing a threshold voltage shift (Delta V (T)) of about 5 V by electron charging upon positive gate voltage (V (GS)) sweep to +25 V, the device with a 2 nm-thicktunneling oxide exhibits a large memory window with Delta V (T) > 20 V by Li-ion migration from LiCoO x to IGZO channel, which can be controlledas multilevel states with respect to the V (GS) amplitude. Incorporation of Li ions into the IGZO channel actingas p-type dopants reduces carrier concentration in the channel andconsequently increases V (T). The increased V (T) and the consequently reduced drain currentare not instantly restored back by applying negative V (GS), featuring WORM memory characteristics. Although thedevice undergoes partial retention loss, the retention remains upto about 90% after 100 min of retention time. These results verifyWORM memory operations in the IGZO TFTs through gate voltage-drivenLi-ion incorporation into the IGZO channel to modify its conductivestates instead of using a typical electrical charging route.