fig4

Figure 4. Structural reconfiguration of flexible a-IGZO synaptic transistors. (A) Floating-gate stack engineering: (i) Schematics of IGZO synaptic transistors incorporating IGZO and ITO floating gates, respectively. (ii) Transfer characteristics of the two devices measured under a gate double sweep from -15 to 15 V. (iii) Retention characteristics of the programmed and erased states for devices with IGZO and ITO floating gates. Adapted from Ref.^[28] under the CC BY 4.0 license. Copyright 2025, The Authors; (B) 1D Nanochannel architecture: (i) 3D schematic of an IGZO/In₂O₃ NW heterojunction phototransistor stimulated by a UV light pulse. (ii) Transient current responses at various pulse frequencies and the corresponding extracted SRDP. Adapted with permission from^[89]. Copyright 2024, Elsevier; (C) Vertical 3D integration: (i) Cross-sectional schematic and TEM image of a vertical-channel synapse TFT, minimizing device footprint via HfO₂ spacer engineering. Adapted with permission^[91]. Copyright 2025, American Chemical Society. (ii) Schematic of high-performance IGZO CAA transistors featuring in situ engineered vertical indium gradients. (iii) Comparison of vertical In:Ga atomic ratios at deposition pressures of 30 mTorr. Adapted with permission^[92]. Copyright 2026, American Chemical Society; (D) Multi-terminal collaborative architecture: (i) Illustration of a hetero-synapse excited by electric inputs from two presynaptic terminals and the corresponding electrochemical ion modulation of the channel layer under dual-terminal gating. (ii) Postsynaptic currents (EPSCs) excited by five presynaptic spikes separately or simultaneously applied to G1 and G2 terminals. (iii) Architecture of the neural network based on the hetero-synaptic transistor for MNIST image recognition. (iv) Comparison of classification accuracy between networks based on the dual-gate hetero-synaptic transistor and the single-gate homo-synaptic transistor. Adapted with permission^[105]. Copyright 2022, The Royal Society of Chemistry. a-IGZO: Amorphous indium gallium zinc oxide; ITO: indium tin oxide; NW: nanowire; UV: ultraviolet; SRDP: spike-rate-dependent plasticity; TEM: transmission electron microscopy; TFT: thin-film transistor; CAA: channel-all-around; EPSCs: excitatory postsynaptic currents; MNIST: Modified National Institute of Standards and Technology; PL: protection layer; CH: channel; TL: tunneling layer; FG: floating gate; PAD: pad (contact pad); GI: gate insulator; ACT: active layer.