A bio-inspired electronic synapse using solution processable organic small molecule

Author(s): Jing-Yu Mao ¹ ^, ² ^, ³ ^, ⁴ , Li Zhou ¹ ^, ² ^, ³ ^, ⁴ , Yi Ren ¹ ^, ² ^, ³ ^, ⁴ , Jia-Qin Yang ¹ ^, ² ^, ³ ^, ⁴ , Chih-Li Chang ⁵ ^, ⁶ ^, ⁷ ^, ⁸ , Heng-Chuan Lin ⁵ ^, ⁶ ^, ⁷ ^, ⁸ , Ho-Hsiu Chou ⁵ ^, ⁶ ^, ⁷ ^, ⁸ , Shi-Rui Zhang ¹ ^, ² ^, ³ ^, ⁴ , Ye Zhou ¹ ^, ² ^, ³ ^, ⁴ , Su-Ting Han ¹ ^, ² ^, ³ ^, ⁴

Publication date (Electronic): 2019

Journal: Journal of Materials Chemistry C

Publisher: Royal Society of Chemistry (RSC)

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Abstract

A trap-mediated solution-processed small molecule based artificial synaptic device is presented. This work reveals great potential for a small molecule based artificial synapse to serve in neuromorphic computing.

Abstract

Mimicking biological synapses with resistive random switching memory (RRAM) can lay a concrete foundation for the future of artificial intelligence. RRAMs based on low-cost and solution-processed organic materials provide a competitive approach. Here, we report an artificial synaptic device with a solution-processed small molecule (bis-4-( N-carbazolyl)phenyl)phenylphosphine oxide (BCPO) based RRAM. The BCPO-based RRAM exhibits reproducible resistive switching behavior, a long retention time as well as good thermal tolerance with a sufficient on/off current ratio. In situ Kelvin probe force microscopy (KPFM), conductive atomic force microscopy (C-AFM) and density function theory (DFT) calculations demonstrate that both the redox state and the trap-filled space charge limited current (SCLC) determine the resistive switching of a BCPO-based RRAM. Furthermore, the fabricated device was employed to emulate a biological synapse in which several synaptic functions, including spike-rate-dependent plasticity (SRDP), a transition from short-term plasticity (STP) to long-term plasticity (LTP) and spike-time-dependent plasticity (STDP), were realized. To the best of our knowledge, this is the first successful demonstration of solution-processed small molecules in artificial synaptic devices. The BCPO layer is solution-processed at low temperature which is compatible with a flexible substrate and printable electronics. We believe this electronic synapse will have a wide range of applications in future neuromorphic computing.

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Nanoscale memristor device as synapse in neuromorphic systems.

Sung Hyun Jo, Ting Hao Chang, Idongesit Ebong … (2010)

A memristor is a two-terminal electronic device whose conductance can be precisely modulated by charge or flux through it. Here we experimentally demonstrate a nanoscale silicon-based memristor device and show that a hybrid system composed of complementary metal-oxide semiconductor neurons and memristor synapses can support important synaptic functions such as spike timing dependent plasticity. Using memristors as synapses in neuromorphic circuits can potentially offer both high connectivity and high density required for efficient computing.

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Short-term plasticity and long-term potentiation mimicked in single inorganic synapses.

Takeo Ohno, Tsuyoshi Hasegawa, Tohru Tsuruoka … (2011)

Memory is believed to occur in the human brain as a result of two types of synaptic plasticity: short-term plasticity (STP) and long-term potentiation (LTP; refs 1-4). In neuromorphic engineering, emulation of known neural behaviour has proven to be difficult to implement in software because of the highly complex interconnected nature of thought processes. Here we report the discovery of a Ag(2)S inorganic synapse, which emulates the synaptic functions of both STP and LTP characteristics through the use of input pulse repetition time. The structure known as an atomic switch, operating at critical voltages, stores information as STP with a spontaneous decay of conductance level in response to intermittent input stimuli, whereas frequent stimulation results in a transition to LTP. The Ag(2)S inorganic synapse has interesting characteristics with analogies to an individual biological synapse, and achieves dynamic memorization in a single device without the need of external preprogramming. A psychological model related to the process of memorizing and forgetting is also demonstrated using the inorganic synapses. Our Ag(2)S element indicates a breakthrough in mimicking synaptic behaviour essential for the further creation of artificial neural systems that emulate characteristics of human memory.

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Memristors with diffusive dynamics as synaptic emulators for neuromorphic computing

Zhongrui Wang, Saumil Joshi, Sergey Savel'ev … (2016)

Calcium ions play a vital role in enabling synaptic plasticity in biological systems. The dynamic behaviour of these ions has now been emulated in a metal atom diffusion-based memristor.