Fig. 1. (Color online) Schematic of an electrolyte-gated transistor for neuromorphic applications such as synaptic plasticity, spatiotemporal integration, and artificial perceptual systems.

Fig. 2. (Color online) (a) Schematic diagram of neuron structure^[42]. (b) Schematic diagram of ion transport in biological synapses^[43]. (c) Schematic of the biological synapse structure and two types of synaptic plasticity^[42]. (d) Double-pulse facilitation behavior^[44].

Fig. 3. (Color online) Schematic diagrams of (a) a top gate EDLT and (b) a side gate EDLT^[55].

Fig. 4. (Color online) (a) Models of the electrical double layer at a positively charged surface: the inner Helmholtz plane (IHP) and outer Helmholtz plane (OHP)^[56]. (b) Schematic of the MoS₂/PTCDA hybrid heterojunction modulated by electrical or optical spike^[59]. (c) Schematic diagram of the process of potential-induced hysteresis behavior based on Li⁺ embedded in α-MoO₃ nanosheets^[60].

Fig. 5. (Color online) (a) Chemical structures of oligomeric ionic liquids IL₄^TFSI and IL₂^TFSI, and monomeric ionic liquids BMI^TFSI and DEME^TFSI as references^[62]. (b) Graphene-molecule–graphene single-molecule junctions with ionic liquid gate dielectric and a brief scheme of energy level shifts under different gate voltages^[64]. (c) Schematic of In₂O₃ synaptic transistors and repeatability of long-term potentiation and depression^[65]. (d) Full schematics of an ionic liquid gated FET and schematic illustration of the conduction and valence band edges of monolayer MoSe₂^[66]. (e) Schematic structure of MoS₂-EDLT based on DEME-TFSI modulation; transfer characteristic curves; I−V curves at different temperatures^[67].

Fig. 6. (Color online) (a) Ion gel films prepared by spin-coating and drop-casting, respectively. (b) Relationship between membrane thickness and rotational speed, specific capacitance and frequency for ionic gel of different thicknesses^[69]. (c) Schematic structure of 2H-MoTe₂-EDLT. (d) Transfer curves of the bottom gate and the ion gates^[70]. (e) Schematic structure of the ion doped MoS₂ in-surface homogeneous PN junction. (f) Side-gate modulation curves at different bias voltages. (g) Bottom-gate transfer characteristic curves at different side-gate voltages^[71].

Fig. 7. (Color online) (a) Transmission characteristics of P₃HT under polymer electrolyte gate control^[73]. (b) A schematic diagram of the oxide transistor array connected to the test system. (c) The EPSC response and V_th of pain perception are strongly dependent on the projection^[74]. (d) Schematic diagrams for obtaining a InZnO EDL transistor on the graphene coated PET substrate. (e) A schematic diagram for the measurement of PPF^[75]. (f) Schematic diagram of a neuron transistor based on SnO₂ nanowires and an artificial neural network structure^[76].

Fig. 8. (Color online) (a) 3D schematic of the fabricated YSH-based EGFET structure. (b) Retention characteristics and ANN operating accuracy at different yttrium concentrations in YSH^[80]. (c) Schematic illustration of the measurement of synaptic characteristics. (d) Plot of linearity and the asymmetric ratio of 0.32^[81]. (e) Schematic diagram of the device, EPSC triggered by longer spikes and channel current^[82].

Fig. 9. (Color online) (a) Schematic diagram of the PEDOT: PSS organic electrochemical EGTs device. (b) Simulation of IPSC response. (c) Realization of low-pass filtering characteristics^[86]. (d) Chitosan electrolyte-based ITO EGTs and their pulse test protocol for simulating STDP behavior. (e) Simulation of STDP behavior. (f) Simulation of SM and STM. (g) Simulation of memory level LTM^[87]. (h) Schematic diagram of MoS₂ EGTs with multiple signaling modes. (i) LTP and LTD behavior in different signaling modes. (j) Regulation of STDP behavior by ion signal in electrical mode and electrical signals in the ionic signaling mode^[88].

Fig. 10. (Color online) (a) Schematic of PEDOT: PSS EGTs device with 3 × 3 coplanar Au electrodes^[94]. (b) Distribution of EPSC current response for gate triggering at different positions. (c) Polar plots of EPSCs for input pulses with different spatial orientations^[95]. (d) Schematic diagram of a neural system consisting of photodetectors and synaptic devices of EGTs^{[96, 97]}. (e) Realization of the spatial localization function of the human ear^[98]. (f) Results of Pavlov’s learning, time difference between the training spike applied at G1 and G2 (ΔT) as a function of the ΔW_peak^[99].

Fig. 11. (Color online) (a) Schematic diagrams of the human eye structure and the photosensitive principle of the human visual system, structure diagram of In₂O₃ transistor. (b) Electrical enhancement and light depression function of an In₂O₃ transistor. (c) Self-adapted transistor arrays for artificial visual perception^[104]. (d) The schematic diagram of an artificial synaptic opto-electronic transistor under light illumination. (e) Potentiation and depression emulated by an artificial opto-electronic synaptic transistor under various pulse widths^[105]. (f) Schematic of the EGT triggered by voltage pulses and chiral light irradiation^[43].

Fig. 12. (Color online) (a) A schematic picture of the HVVHT. (b) 3D image of SRDP and the Z index^[106]. (c) The 3D device structure of sub-10-nm vertical coplanar-multiterminal flexible transient ITO phototransistor network, threshold properties of VN behavior and the statistics of detailed P_th^[107]. (d) A sensory neuron (top) compared to our NeuTap (bottom)^[108]. (e) Piezoresistor–nociceptor system, the response of nociceptor under variable degrees of forces. (f) Transition of the device to LTM mode after five consecutive light pulses. SNDP test at different numbers of light pulses^[109].