Multilevel resistance in ZnO nanowire memristors enabled by hydrogen annealing treatment

Abstract

In non-volatile memory technology, various attempts to overcome both technology and physical limits have led to development of neuromorphic devices like memristors. Moreover, multilevel resistance and the potential for enhanced memory capability has attracted much attention. Here, we report memristive characteristics and multilevel resistance in a hydrogen annealed ZnO nanowire device. We find that the memristive behavior including negative differential resistance arises from trapped electrons in an amorphous ZnO interfacial layer at the injection electrode that is formed following hydrogen annealing. Furthermore, we demonstrate that it is possible to control electrons trapping and detrapping by the controlled application of voltage pulses to establish a multilevel memory. These results could pave the way for multifunctional memory device technology such as the artificial neuromorphic system.

Recent Developments and Perspectives for Memristive Devices Based on Metal Oxide Nanowires

“…Among all single crystal NWs, isolated single crystalline ZnO NWs are the most extensively studied nanostructures that exhibited resistive switching properties . Even if resistive switching was previously observed in ZnO thin films grown by different techniques, resistive switching in single crystalline ZnO nanowires with wurtzite structure grown by VLS technique was reported for the first time in 2011 by Chiang et al In this case, the Ti/ZnO NW/Ti devices exhibited two well defined resistance states with high performances in terms of HRS/LRS ratio that was reported to be as high as 7.7 × 10 5 with an endurance of 100 cycles.…”

“…[171][172][173][174][175][176][177][178][179] Even if resistive switching was previously observed in ZnO thin films grown by different techniques, [180][181][182] resistive switching in single crystalline ZnO nanowires with wurtzite structure grown by VLS technique was reported for the first time in 2011 by Chiang et al [171] In this case, the Ti/ZnO NW/Ti devices exhibited two well defined resistance states with high performances in terms of HRS/LRS ratio that was reported to be as high as 7.7 × 10 5 with an endurance of 100 cycles. [171][172][173][174][175][176][177][178][179] Even if resistive switching was previously observed in ZnO thin films grown by different techniques, [180][181][182] resistive switching in single crystalline ZnO nanowires with wurtzite structure grown by VLS technique was reported for the first time in 2011 by Chiang et al [171] In this case, the Ti/ZnO NW/Ti devices exhibited two well defined resistance states with high performances in terms of HRS/LRS ratio that was reported to be as high as 7.7 × 10 5 with an endurance of 100 cycles.…”

“…[167] The initial amount of oxygen vacancies and defects resulting from the synthesis can strongly impact the switching parameters and performances, thus the growth conditions play a crucial role for the realization of NW-based resistive switching devices. [177] These aspects will be further discussed in Section 7.1. By using this approach, few works reported an increase of the device performances of single crystalline NWs by surface treatments that can modify the amount of oxygen vacancies in the NW, [173,175,176] or can introduce an amorphous layer at the metal-oxide/electrode interface.…”

“…The authors showed that Ar plasma treatments resulted in lower threshold voltages and increased conductance, while higher threshold voltages were observed after oxygen plasma treatments. [176] Another approach based on hydrogen annealing treatment of ZnO nanowires was proposed by Lee et al [177] After the growth process, ZnO NWs were annealed at 350 °C for 30 min in a H 2 /Ar mixture ambient. The effects of plasma were further discussed by Lai et al in their works [175,176] where authors suggested that a low cost Ar plasma treatment (100 W at 100 Pa, for 60/240 s) can enhance repeatability and decrease SET and RESET voltages in single isolated ZnO NWs grown by VLS method.…”

“…However, the concentration of defects in NWs can be modified by proper treatments even after the growth process. By using this approach, few works reported an increase of the device performances of single crystalline NWs by surface treatments that can modify the amount of oxygen vacancies in the NW, or can introduce an amorphous layer at the metal–oxide/electrode interface . These aspects will be further discussed in Section .…”