Electroforming-free threshold switching of NbO x -based selector devices by controlling conducting phases in the NbO x layer for the application to crossbar array architectures

Kitae Park; Jiyeon Ryu; Dwipak Prasad Sahu; Hyun-Mi Kim; Tae-Sik Yoon

doi:10.1039/d2ra02930h

Electroforming-free threshold switching of NbO _x -based selector devices by controlling conducting phases in the NbO _x layer for the application to crossbar array architectures

RSC Adv. 2022 Jun 23;12(29):18547-18558. doi: 10.1039/d2ra02930h. eCollection 2022 Jun 22.

Authors

Kitae Park¹, Jiyeon Ryu¹, Dwipak Prasad Sahu², Hyun-Mi Kim³, Tae-Sik Yoon^{1

2}

Affiliations

¹ Graduate School of Semiconductor Materials and Devices Engineering, Ulsan National Institute of Science and Technology Ulsan 44919 Republic of Korea tsyoon@unist.ac.kr.
² Department of Materials Science and Engineering, Ulsan National Institute of Science and Technology Ulsan 44919 Republic of Korea.
³ Korea Electronics Technology Institute Gyeonggi-do 13509 Republic of Korea.

Abstract

Bipolar threshold switching characteristics, featuring volatile transition between the high-resistance state (HRS) at lower voltage than threshold voltage (V _th) and the low-resistance state (LRS) at higher voltage irrespective of the voltage polarity, are investigated in the Nb(O)/NbO _x /Nb(O) devices with respect to deposition and post-annealing conditions of NbO _x layers. The device with NbO _x deposited by reactive sputtering with 12% of O₂ gas mixed in Ar shows threshold switching behaviors after electroforming operation at around +4 V of forming voltage (V _f). On the other hand, electroforming-free threshold switching is achieved from the device with NbO _x deposited in the reduced fraction of 7% of O₂ gas and subsequently annealed at 250 °C in vacuum, thanks to the increase of the amount of conducting phases within the NbO _x layer. Threshold switching is thought to be driven by the formation of a temporally percolated filament composed of conducting NbO and NbO₂ phases in the NbO _x layer, which were formed as a result of the interaction with Nb electrodes such as oxygen ion migration either by annealing or electrical biasing. The presence of a substantial amount of oxygen in the Nb electrodes up to ∼40 at%, named Nb(O) herein, would alleviate excessive migration of oxygen and consequent overgrowth of the filament during operation, thus enabling reliable threshold switching. These results demonstrate a viable route to realize electroforming-free threshold switching in the Nb(O)/NbO _x /Nb(O) devices by controlling the contents of conducting phases in the NbO _x layer for the application to selector devices in high-density crossbar memory and synapse array architectures.