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. 2022 Dec 19;15(24):9087.
doi: 10.3390/ma15249087.

Non-Volatile Memory and Synaptic Characteristics of TiN/CeOx/Pt RRAM Devices

Hoesung Ha  1 , Juyeong Pyo  1 , Yunseok Lee  1 , Sungjun Kim  1
Affiliations

Non-Volatile Memory and Synaptic Characteristics of TiN/CeOx/Pt RRAM Devices

Hoesung Ha et al. Materials (Basel). .

Abstract

In this study, we investigate the synaptic characteristics and the non-volatile memory characteristics of TiN/CeOx/Pt RRAM devices for a neuromorphic system. The thickness and chemical properties of the CeOx are confirmed through TEM, EDS, and XPS analysis. A lot of oxygen vacancies (ions) in CeOx film enhance resistive switching. The stable bipolar resistive switching characteristics, endurance cycling (>100 cycles), and non-volatile properties in the retention test (>10,000 s) are assessed through DC sweep. The filamentary switching model and Schottky emission-based conduction model are presented for TiN/CeOx/Pt RRAM devices in the LRS and HRS. The compliance current (1~5 mA) and reset stop voltage (−1.3~−2.2 V) are used in the set and reset processes, respectively, to implement multi-level cell (MLC) in DC sweep mode. Based on neural activity, a neuromorphic system is performed by electrical stimulation. Accordingly, the pulse responses achieve longer endurance cycling (>10,000 cycles), MLC (potentiation and depression), spike-timing dependent plasticity (STDP), and excitatory postsynaptic current (EPSC) to mimic synapse using TiN/CeOx/Pt RRAM devices.

Keywords: cerium oxide; memristor; neuromorphic system; resistive switching.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
(a) Schematic of TiN/CeOx/Pt RRAM cells, (b) cross-sectional TEM image with EDS mapping that consists of Ti (red), N (purple), Ce (green), O (yellow), Pt (sky blue), and (c) Ce 3d and (d) O 1s XPS spectra of CeOx film.
Figure 2
Figure 2
I-V curves of (a) forming process and (b) bipolar resistive switching including set and reset processes. (c) Retention and (d) endurance test by DC sweep. (e) Endurance test by pulse mode.
Figure 3
Figure 3
(a–c) Schematic diagram of the filament evolution for (a) initial state, (b) forming, (c) reset, and (d) set. ln(I) versus V1/2 for Schottky emission of (e) LRS and (f) HRS.
Figure 4
Figure 4
(a) I-V curves by controlling compliance current (1 mA, 2 mA, 3 mA, 4 mA, and 5 mA) and (b) MLC set process by increasing compliance current. (c) I-V curves by reset stop voltage (−1.3 V, −1.6 V, −1.9 V, and −2.2 V) and (d) MLC reset process by fine control of reset voltage.
Figure 5
Figure 5
(a) Pulse schematic. (b) Potentiation and depression in cycles.
Figure 6
Figure 6
(a) Pulse schemes of pre-spike (black line) and post-spike (red line). (b) Pre-spike occurs before post-spike by Δt, causing the overlapped pulse for potentiation. (c) Pulse schemes of pre-spike (black line) and post-spike (red line). (d) Pre-spike occurs after post-spike by Δt, causing the overlapped pulse for depression. (e) Synaptic weight change as a function of spike time for STDP emulation.
Figure 7
Figure 7
EPSC characteristics in (a) positive voltage and (b) negative voltage.
See this image and copyright information in PMC

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