Role of oxide barrier in a NbOx layer with noninert electrodes for high-yield threshold switching characteristics

Abstract

This study shows how the threshold switching (TS) characteristics of a NbOx layer with noninert W electrodes can be improved by introducing an oxide barrier. The ∼10-nm-thick NbOx layer exhibits TS, which is known to originate from NbO2, after electroforming. However, an unwanted formation of a Nb2O5 layer at the top electrode (TE) interface has been observed, which deteriorates the TS, given the switching capability of Nb2O5. Therefore, a thin oxide layer was introduced to overcome the issue and enhance the TS behavior. Furthermore, the role of the oxide barrier is investigated systematically considering its location and unique properties. This study reveals that depositing a barrier at the bottom electrode interface makes the formation of NbO2 difficult, resulting in poor TS behavior, while placing the barrier at the TE interface could mitigate the Nb2O5 creation, promoting TS. Finally, the effect of incorporating various oxide types has been investigated, showing different switching behavior. Through examining the temperature dependence of the TS obtained from the W/NbOx/W and W/ZrO2/NbOx/W stacks, it was found that the suppression of Nb2O5 at the top interface is indirectly shown as a strengthened Schottky barrier from an electrical measurement perspective. As a result, excellent cell-to-cell uniformity of the TS is achieved in the ZrO2/NbOx stack, which not only prevents the formation of Nb2O5 but also stabilizes NbO2 in the NbOx layer.