Traditional Von Neumann structure, where memory and computational units are separated, is now facing significant difficulties in terms of power consumption and computing speed in big data era. Therefore, human brain-like computing architecture is now paid attention in research field owing to its high parallelism, fault tolerance and robustness^1-2. In this biological system, synaptic weight which plays crucial role in memory and learning is modulated by ionic species, especially protons transmitted between synapses. Here, we focused on short length peptide Y7C (YYACAYY) thin film which induces proton coupled electron transfer (PCET) due to its Tyrosine-rich structure. The Y7C film has shown an interesting behavior in which electrical conductivity varies with humidity^3-4. By this modulation, bimodal memristor using both of voltage and humidity⁵ input and synaptic transistor which shows dynamic reponses through humidity have been demonstrated, but direct relation between current and proton conduction is still ambiguous. Therefore, we measured transient current flow between Pd and Au electrode and detected proton conduction of Y7C film.

In previous studies, voltage & humidity controlled Y7C bimodal memristor has been reported. However, since the current regulation through humidity showed insufficient response than that through voltage, a definite relationship between moisture and current needs to be defined. To achieve that, thin film of the peptide material dissolved in Trifluoroacetic acid (TFA) 99% solution was spin coated on SiO2/Si substrate. By measuring the transient current of the Y7C film, presence of temporary charge carriers was observed. Also, the electrical impedance spectroscopy (EIS) of peptide layer showed a semicircle and a nonvertical tail, which indicate ionic conduction through the film. Lastly, film characterization of Y7C thin layer unveiled that the corresponding ions are protons as originally targeted. This research has showed principles of peptide thin film’s current increment driven by both of humidity and voltage through electrochemical reaction.

Fig.1. Transient charge flowing through Y7C thin film measured in various atmospheric conditions and electrodes

Acknowledgment

This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (No. 2020R1A2C2004864).

References

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5. Song, Min-Kyu, et al. "Proton-enabled activation of peptide materials for biological bimodal memory." Nature Communications 11.1 (2020): 1-8.