Contact-electrification-activated artificial afferents at femtojoule energy

Abstract

Low power electronics endowed with artificial intelligence and biological afferent characters are beneficial to neuromorphic sensory network. Highly distributed synaptic sensory neurons are more readily driven by portable, distributed, and ubiquitous power sources. Here, we report a contact-electrification-activated artificial afferent at femtojoule energy. Upon the contact-electrification effect, the induced triboelectric signals activate the ion-gel-gated MoS₂ postsynaptic transistor, endowing the artificial afferent with the adaptive capacity to carry out spatiotemporal recognition/sensation on external stimuli (e.g., displacements, pressures and touch patterns). The decay time of the synaptic device is in the range of sensory memory stage. The energy dissipation of the artificial afferents is significantly reduced to 11.9 fJ per spike. Furthermore, the artificial afferents are demonstrated to be capable of recognizing the spatiotemporal information of touch patterns. This work is of great significance for the construction of next-generation neuromorphic sensory network, self-powered biomimetic electronics and intelligent interactive equipment.

Fig. 1. Biological afferent nerve system and CE-activated artificial afferents.

a The basic procedure of the postsynaptic current activated by external stimulation in the biological afferent nerve system. The external stimulation initiates an action potential in the sensory neuron. The action potential propagates along with the nerve fiber and leads to a potential change in the adjacent nerve cell (i.e., activating postsynaptic current). b Schematic illustration of the CE-activated artificial afferent. It includes a self-activation component, a synaptic transistor, and a functional circuit. c Cross-sectional view of the CE-activated MoS₂ synaptic transistor and illustration for each component. d Circuit diagram of the CE-activated artificial afferents.

Fig. 2. Typical synaptic characteristics of the CE-activated artificial afferent.

a Schematic illustration of an EPSC activated by a single CS action. b The transferred charges of the CE-activated MoS₂ synaptic transistor within a cycle of contact-separation. c The EPSC responses under one CS action (D = 20 μm). d The decay phenomenon fitting of the EPSC with the exponential decay model (Supplementary Note 3). e The EPSCs under different CS action distances. Inset: D increases from 20 to 120 μm. f The EPSC responses under different CS action durations (D = 50 μm). Inset: Illustration of the increase in duration. g The energy dissipation vs. distance. h Comparison of the energy dissipation per spike for different types of artificial synapses. The dissipation is 11.9 fJ in the CE-activated artificial afferent (red star).

Fig. 3. The basic synaptic plasticity of CE-activated artificial afferents.

Schematic illustration of EPSCs activated by (a) paired CS actions and (b) multiple CS actions. c The typical EPSC responses under paired CS actions (interspike interval, △T_pre = 1 s). A₁ and A₂ represent the amplitudes of the first and second EPSCs, respectively. d A series of EPSC responses activated by paired CS actions with different interspike intervals, with D = 50 μm. The interspike interval decreases from 4 s to 1 s. Inset: the PPF index (defined as the ratio of A₂/A₁) vs. the interspike interval. e, The EPSC responses under 60 CS actions. Inset: an illustration of 60 CS actions (left) and the first (A₁, middle) and last (A₆₀, right) current peak of the EPSCs. f The current gain (defined as the ratio of A_n /A₁) vs. action number. g Real-time EPSC responses to multiple CS actions; the number of actions (n) increases from 2 to 40. Inset: the EPSC responses under n = 4 (left) and n = 10 (right).

Fig. 4. The advanced spatiotemporal synaptic characteristics of CE-activated artificial afferents.

a Schematic illustration of EPSCs activated by dual-TENGs. b Schematic illustration of CE-activated artificial afferents in dual-TENG mode. c EPSCs activated by single and paired CS actions with spatiotemporal information. d The recorded second EPSCs vs. ΔT_pre2-pre1 (interval time between the first and second CS actions). e The recorded EPSC responses to TENG-1 and TENG-2 simultaneously. f The extracted frequencies of the TENG-1 and TENG-2 activations after Fourier transform. The frequencies of the two activation components are clearly extracted from Fig. 4e and Supplementary Fig. 23.

Fig. 5. Demonstration of the dynamic logic of the CE-activated artificial afferent.

a Schematic illustration diagram, (b) a simplified circuit diagram, and (c) a photo of the artificial afferent for dynamic logic demonstration. d Red LEDs triggered by CS action from TENG-1 (top) and green LEDs triggered by CS action from TENG-2 (bottom).