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. 2021 Aug 16;11(1):16601.
doi: 10.1038/s41598-021-96197-8.

Nonideal resistive and synaptic characteristics in Ag/ZnO/TiN device for neuromorphic system

Jongmin Park  1 , Hojeong Ryu  1 , Sungjun Kim  2
Affiliations

Nonideal resistive and synaptic characteristics in Ag/ZnO/TiN device for neuromorphic system

Jongmin Park et al. Sci Rep. .

Abstract

Ideal resistive switching in resistive random-access memory (RRAM) should be ensured for synaptic devices in neuromorphic systems. We used an Ag/ZnO/TiN RRAM structure to investigate the effects of nonideal resistive switching, such as an unstable high-resistance state (HRS), negative set (N-set), and temporal disconnection, during the set process and the conductance saturation feature for synaptic applications. The device shows an I-V curve based on the positive set in the bipolar resistive switching mode. In 1000 endurance tests, we investigated the changes in the HRS, which displays large fluctuations compared with the stable low-resistance state, and the negative effect on the performance of the device resulting from such an instability. The impact of the N-set, which originates from the negative voltage on the top electrode, was studied through the process of intentional N-set through the repetition of 10 ON/OFF cycles. The Ag/ZnO/TiN device showed saturation characteristics in conductance modulation according to the magnitude of the applied pulse. Therefore, potentiation or depression was performed via consecutive pulses with diverse amplitudes. We also studied the spontaneous conductance decay in the saturation feature required to emulate short-term plasticity.

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Conflict of interest statement

The authors declare no competing interests.

Figures

Figure 1
Figure 1
Material and chemical analyses of the Ag/ZnO/TiN device: (a) STEM image for EDS mapping. EDS mapping image with different elements: (b) Ag, (c) Ti, (d) O, (e) Zn, (f) N. (g) TEM image. (h) EDS line scan.
Figure 2
Figure 2
(a) Typical I–V characteristics of the Ag/ZnO/TiN device. (b) Endurance testing involving 1000 cycles. (c) Cumulative probability of HRS and LRS with a read voltage of 0.1 V.
Figure 3
Figure 3
Schematic for the switching mechanism of the Ag/ZnO/TiN device. (a) Initial state. (b) Forming state. (c) Reset state. (d) Negative-set state.
Figure 4
Figure 4
Nonideal resistive switching. (a) N-set behavior after reset. (b) HRS and LRS distributions after N-set. (c) Temporal disconnection of filament in the HRS. (d) Typical I–V characteristics of Ag/ZnO/Pt device.
Figure 5
Figure 5
Synaptic behaviors of the Ag/ZnO/TiN device. (a) Potentiation and depression characteristics with a set pulse (0.8 V, 500 μs) and a reset pulse (− 0.6 V, 500 μs). (b) Gradual stepwise increase in conductance via an incremental pulse scheme. (c) Conductance modulation by varying the reset pulse voltage. (d) Multiple potentiation and depression curves.
Figure 6
Figure 6
STP and LTP characteristics of the Ag/ZnO/TiN device. (a) Current decay characteristics after one pulse response. (b) Normalized conductance decay for the observation of STP. (c) LTP by multiple pulse inputs with different pulse voltage conditions.
See this image and copyright information in PMC

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