Abstract
This study evaluated the memristive switching characteristics of a biomaterial solid polymer electrolyte (SPE) chitosan-based memristor and confirmed its artificial synaptic behavior with analog switching. Despite the potential advantages of organic memristors for high-end electronics, the unstable multilevel states and poor reliability of organic devices must be overcome. The fabricated Ti/SPE-chitosan/Pt-structured memristor has stable bipolar resistive switching (BRS) behavior due to a cation-based electrochemical reaction between a polymeric electrolyte and metal ions and exhibits excellent endurance in 5 × 102 DC cycles. In addition, we achieved multilevel per cell (MLC) BRS I-V characteristics by adjusting the set compliance current (Icc) for analog switching. The multilevel states demonstrated uniform resistance distributions and nonvolatile retention characteristics over 104 s. These stable MLC properties are explained by the laterally intensified conductive filaments in SPE-chitosan, based on the linear relationship between operating voltage margin (ΔVswitching) and Icc. In addition, the multilevel resistance dependence on Icc suggests the capability of continuous analog resistance switching. Chitosan-based SPE artificial synapses ensure the emulation of short- and long-term plasticity of biological synapses, including excitatory postsynaptic current, inhibitory postsynaptic current, paired-pulse facilitation, and paired-pulse depression. Furthermore, the gradual conductance modulations upon repeated stimulation by 104 electric pulses were evaluated in high stability.
Highlights
The rapid development of electronic technology and information science requires various types of device structures, materials, and computing methods [1,2]
Among various organic-based materials, chitosan electrolytes are promising for solid polymer electrolyte (SPE)-based memristor devices due to the following advantages: chitosan is a cationic biopolymer derived from chitin extracted from shrimp or crab shells, consisting of repeating β(1,4)-linked D-glucosamine (N-deacetylated chitin) and N-acetyl-D-glucosamine units [17,18], (1) chitosan is natively insulating, but its ionic conductivity can be modulated by adding acidic solution, (2) the amine and hydroxyl groups in chitosan are extremely reactive with metal ions, (3) chitin, which is the source material of chitosan, is the second-most abundant polysaccharide in the crust, followed by cellulose, (4) chitosan is a nontoxic and biodegradable polymer, and (5) chitosan powder or flakes are soluble in diluted acetic acid solution
A DC voltage and an electrical synaptic pulse were applied to the Ti-top electrode (TE) with the Pt-bottom electrode (BE) grounded, showing that the devices exhibit typical bipolar resistive switching (RS) (BRS) behavior
Summary
The rapid development of electronic technology and information science requires various types of device structures, materials, and computing methods [1,2]. Among various organic-based materials, chitosan electrolytes are promising for solid polymer electrolyte (SPE)-based memristor devices due to the following advantages: chitosan is a cationic biopolymer derived from chitin extracted from shrimp or crab shells, consisting of repeating β(1,4)-linked D-glucosamine (N-deacetylated chitin) and N-acetyl-D-glucosamine units [17,18], (1) chitosan is natively insulating, but its ionic conductivity can be modulated by adding acidic solution, (2) the amine and hydroxyl groups in chitosan are extremely reactive with metal ions, (3) chitin, which is the source material of chitosan, is the second-most abundant polysaccharide in the crust, followed by cellulose, (4) chitosan is a nontoxic and biodegradable polymer, and (5) chitosan powder or flakes are soluble in diluted acetic acid solution. We evaluated the stable multilevel RS, endurance, retention, and analog switching characteristics of the fabricated memristor devices without an additional doping process on chitosan. We analyzed the RS mechanism of the SPE-chitosan layer and the short- and long-term plasticity of chitosan-based SPE memristors, which are essential for synaptic calculation and information storage
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