A Natural Silk Fibroin Protein‐Based Transparent Bio‐Memristor

The recent discovery of nanoelectronics memristor devices has opened up a new wave of enthusiasm and optimism in revolutionizing electronic circuit design, marking the beginning of new era for the advancement of neuromorphic, high‐density logic and memory applications. Here a highly non‐linear dynamic response of a bio‐memristor is demonstrated using natural silk cocoon fibroin protein of silkworm, Bombyx mori. A film that is transparent across most of the visible spectrum is obtained with the electronic‐grade silk fibroin aqueous solution of ca. 2% (wt/v). Bipolar memristive switching is demonstrated; the switching mechanism is confirmed to be the filamentary switching as observed by probing local conduction behavior at nanoscale using scanning tunneling microscopy. The memristive transition is elucidated by a physical model based on the carrier trapping or detrapping in silk fibroin films and this appears to be due to oxidation and reduction procedures, as evidenced from cyclic voltammetry measurements. Hence, silk fibroin protein could be used as a biomaterial for bio‐memristor devices for applications in advanced bio‐inspired very large scale integration circuit design as well as in biologically inspired synapse links for energy‐efficient neuromorphic computing.     

Unraveling the Origin and Mechanism of Nanofilament Formation in Polycrystalline SrTiO3 Resistive Switching Memories

Three central themes in the study of the phenomenon of resistive switching are the nature of the conducting phase, why it forms, and how it forms. In this study, the answers to all three questions are provided by performing switching experiments in situ in a transmission electron microscope on thin films of the model system polycrystalline SrTiO₃. On the basis of high‐resolution transmission electron microscopy, electron‐energy‐loss spectroscopy and in situ current–voltage measurements, the conducting phase is identified to be SrTi₁₁O₂₀. This phase is only observed at specific grain boundaries, and a Ruddlesden–Popper phase, Sr₃Ti₂O₇, is typically observed adjacent to the conducting phase. These results allow not only the proposal that filament formation in this system has a thermodynamic origin—it is driven by electrochemical polarization and the local oxygen activity in the film decreasing below a critical value—but also the deduction of a phase diagram for strongly reduced SrTiO₃. Furthermore, why many conducting filaments are nucleated at one electrode but only one filament wins the race to the opposite electrode is also explained. The work thus provides detailed insights into the origin and mechanisms of filament generation and rupture.     

一步掩膜法制备ZnO纳米线忆阻器

本文基于单根ZnO纳米线(NW),采用一步掩膜的方法制备了Au/ZnO NW/Au忆阻器。器件表现出无极性忆阻行为,开关比可达10~5以上。低阻态具有半导体导电特性,推测忆阻行为可能来源于ZnO NW表面氧空位形成的不连续导电丝的通断。一步掩膜法工艺简单,制备过程对器件污染少,因此是制备纳米线器件的有效方法。     

A Highly Transparent Artificial Photonic Nociceptor

A nociceptor is an essential element in the human body, alerting us to potential damage from extremes in temperature, pressure, etc. Realizing nociceptive behavior in an electronics device remains a central issue for researchers, designing neuromorphic devices. This study proposes and demonstrates an all‐oxide‐based highly transparent ultraviolet‐triggered artificial nociceptor, which responds in a very similar way to the human eye. The device shows a high transmittance (>65%) and very low absorbance in the visible region. The current–voltage characteristics show loop opening, which is attributed to the charge trapping/detrapping. Further, the ultraviolet‐stimuli‐induced versatile criteria of a nociceptor such as a threshold, relaxation, allodynia, and hyperalgesia are demonstrated under self‐biased condition, providing an energy‐efficient approach for the neuromorphic device operation. The reported optically controlled features open a new avenue for the development of transparent optoelectronic nociceptors, artificial eyes, and memory storage applications.     

Gate‐Tunable and Multidirection‐Switchable Memristive Phenomena in a Van Der Waals Ferroelectric

Memristive devices have been extensively demonstrated for applications in nonvolatile memory, computer logic, and biological synapses. Precise control of the conducting paths associated with the resistance switching in memristive devices is critical for optimizing their performances including ON/OFF ratios. Here, gate tunability and multidirectional switching can be implemented in memristors for modulating the conducting paths using hexagonal α‐In₂Se₃, a semiconducting van der Waals ferroelectric material. The planar memristor based on in‐plane (IP) polarization of α‐In₂Se₃ exhibits a pronounced switchable photocurrent, as well as gate tunability of the channel conductance, ferroelectric polarization, and resistance‐switching ratio. The integration of vertical α‐In₂Se₃ memristors based on out‐of‐plane (OOP) polarization is demonstrated with a device density of 7.1 × 10⁹ in.^?2 and a resistance‐switching ratio of well over 10³. A multidirectionally operated α‐In₂Se₃ memristor is also proposed, enabling the control of the OOP (or IP) resistance state directly by an IP (or OOP) programming pulse, which has not been achieved in other reported memristors. The remarkable behavior and diverse functionalities of these ferroelectric α‐In₂Se₃ memristors suggest opportunities for future logic circuits and complex neuromorphic computing.     

A New Memristor with 2D Ti3C2Tx MXene Flakes as an Artificial Bio‐Synapse

Two‐dimensional (2D) materials have attracted extensive research interest in academia due to their excellent electrochemical properties and broad application prospects. Among them, 2D transition metal carbides (Ti₃C₂T_x) show semiconductor characteristics and are studied widely. However, there are few academic reports on the use of 2D MXene materials as memristors. In this work, reported is a memristor based on MXene Ti₃C₂T_x flakes. After electroforming, Al/Ti₃C₂T_x/Pt devices exhibit repeatable resistive switching (RS) behavior. More interestingly, the resistance of this device can be continuously modulated under the pulse sequence with 10 ns pulse width, and the pulse width of 10 ns is much lower than that in other reported work. Moreover, on the nanosecond scale, the transition from short‐term plasticity to long‐term plasticity is achieved. These two properties indicate that this device is favorable for ultrafast biological synapse applications and high‐efficiency training of neural networks. Through the exploration of the microstructure, Ti vacancies and partial oxidation are proposed as the origins of the physical mechanism of RS behavior. This work reveals that 2D MXene Ti₃C₂T_x flakes have excellent potential for use in memristor devices, which may open the door for more functions and applications.