Multi-Terminal Memtransistors from Polycrystalline Monolayer MoS2 (1802.07783v1)

Abstract: In the last decade, a 2-terminal passive circuit element called a memristor has been developed for non-volatile resistive random access memory and has more recently shown promise for neuromorphic computing. Compared to flash memory, memristors have higher endurance, multi-bit data storage, and faster read/write times. However, although 2-terminal memristors have demonstrated basic neural functions, synapses in the human brain outnumber neurons by more than a factor of 1000, which implies that multiterminal memristors are needed to perform complex functions such as heterosynaptic plasticity. Previous attempts to move beyond 2-terminal memristors include the 3-terminal Widrow-Hoff memistor and field-effect transistors with nanoionic gates or floating gates, albeit without memristive switching in the transistor. Here, we report the scalable experimental realization of a multi-terminal hybrid memristor and transistor (i.e., memtransistor) using polycrystalline monolayer MoS2. Two-dimensional (2D) MoS2 memtransistors show gate tunability in individual states by 4 orders of magnitude in addition to large switching ratios with high cycling endurance and long-term retention of states. In addition to conventional neural learning behavior of long-term potentiation/depression, 6-terminal MoS2 memtransistors possess gate-tunable heterosynaptic functionality that is not achievable using 2-terminal memristors. For example, the conductance between a pair of two floating electrodes (pre-synaptic and post-synaptic neurons) is varied by 10X by applying voltage pulses to modulatory terminals. In situ scanning probe microscopy, cryogenic charge transport measurements, and device modeling reveal that bias-induced MoS2 defect motion drives resistive switching by dynamically varying Schottky barrier heights.

• The paper demonstrates the integration of memristor and transistor functionalities in a single device using polycrystalline monolayer MoS2 to achieve gate-tunable heterosynaptic plasticity.
• It employs in situ scanning probe microscopy and cryogenic charge transport measurements to reveal defect-driven resistive switching via dynamic modulation of Schottky barriers.
• The research highlights scalable manufacturing via CVD, paving the way for neuromorphic circuit applications inspired by Hebbian learning and complex synaptic behavior.

Multi-Terminal Memtransistors from Polycrystalline Monolayer MoS2

The paper presents a significant advancement in the field of memristive devices by detailing the development and characterization of multi-terminal memtransistors fabricated from polycrystalline monolayer MoS2. The integration of memristors and transistors in a single device structure represents a salient progression toward realizing complex neuromorphic computing systems.

Memristors have garnered attention for their potential use in non-volatile resistive random access memory (RRAM) and more recently as elements within neuromorphic architectures. While traditional 2-terminal memristors have been successful in demonstrating basic neural functions, the complexity of human brain functionality necessitates multi-terminal configurations to emulate sophisticated neural dynamics, such as heterosynaptic plasticity. In this research, polycrystalline monolayer MoS2 serves as the foundational material for constructing memtransistors that operate as hybrid devices with tunable states and robust resistive switching capabilities.

The multi-terminal architecture of the devices is a crucial innovation, achieved by leveraging the unique properties of MoS2. The devices exhibit gate tunability of individual states over four orders of magnitude, a characteristic that significantly enhances switching ratios and stability over extended cycling and retention tests. Notably, the researchers observe that the conductance between pairs of electrodes can be modulated by approximately 10-fold through the application of voltage pulses to auxiliary terminals, demonstrating gate-tunable heterosynaptic functionality not feasible with 2-terminal memristors.

Experimental insights are deepened by in situ scanning probe microscopy techniques and cryogenic charge transport measurements, which collectively point to MoS2 defect motion as the driver behind resistive switching. The dynamic adjustment of Schottky barrier heights underpins this mechanism, facilitated by a methodological approach to model device behavior and defect kinetics.

Furthermore, the integration of multi-terminal memtransistors provides an exploratory platform for implementing Hebbian learning-inspired circuits. The ability to emulate multiple synaptic connections in a neuronal manner is pivotal for advancing neuromorphic computing paradigms. These memtransistors function analogously to synaptic elements in biological systems, with the potential to induce long-term potentiation and depression and to reflect spike-timing dependent plasticity.

The practical implications of this research are profound. The manufacturability of polycrystalline MoS2 films via chemical vapor deposition (CVD) supports the scalability of this technology, coupling economic production with large-area device arrays suitable for integrated circuits. Additionally, the paper underlines the importance of uniform growth and device architecture in ensuring consistent performance metrics across fabricated devices.

For future theoretical and practical developments in AI and computing systems, the insights provided by this paper hold promise for constructing more efficient and robust neuromorphic networks. The research suggests tangible avenues for exploring the physics of defect kinetics in two-dimensional materials, adding to the growing knowledge base required for the successful implementation of bio-realistic computing systems.

As the exploration of memristive phenomena in 2D materials continues, this paper sets a foundational precedent for multi-terminal device architectures capable of answering the intricate demands of modern computing paradigms.