image: (a) Concept: Cloud-enabled human-machine interface enhances HMII application scenarios. (b) Rigorous criteria requirements for interactive devices in HMII contexts. (c) Structural design of the interactive device with an interdigitated configuration. (d) Operating principle of the p-channel metal-oxide-semiconductor field-effect transistor where gate voltage is analogous to a valve in a faucet, regulating the transport of holes by forming a conductive channel. (e) Dynamic gate mechanosensitive process of FSTI involves a mechanosensitive valve for ion transport, including “ox” and “int” are oxidation and intercalation, respectively.
Credit: ©Science China Press
The work proposes a self-powered transistor-like iontronics (STI) device based on an MXene/Bi 2D heterojunction as a compact tactile interface for HMII. Conventional HMII platforms often rely on complex multi-sensor arrays with heavy wiring, signal crosstalk and latency. Here, the authors instead design a single flexible, all-solid-state device that combines sensing, encoding and low-power readout in one structure. The free-standing STI (FSTI) device employs interdigitated MXene@Zn (source) and MXene@Bi (drain) electrodes, a PVDF-HFP-GO solid polymer electrolyte with high ionic conductivity, and a cellulose nanofiber isolation layer. The MXene/Bi heterostructure enlarges MXene interlayer spacing and suppresses restacking, providing abundant active sites and fast Zn2+ diffusion.
Mechanistically, the device mimics a p-channel MOSFET: without pressure, the CNF layer blocks ion channels, and the device is “off”. Under pressure, electrode-electrolyte contact increases, ion channels form, Zn is oxidized at the source and intercalated at the drain, and the resulting ion migration drives an external electronic current. A fixed intrinsic potential difference of ~1.1 V determined by electrolyte concentration, while external pressure modulates the internal resistance via the number of ion channels, tuning the open-circuit voltage. Electrochemical impedance spectroscopy confirms that pressure lowers charge-transfer resistance and enhances Warburg diffusion. Voltage-mode readout yields extremely low power consumption compared with current-mode measurement.
Optimized devices achieve an output up to 1.1 V and 2.3 μA, linear sensitivity (R2 = 0.995), fast response/recovery (66.59/44.18 ms), broad frequency tolerance (up to 2.22 Hz), and outstanding durability over 50,000 loading cycles. Demonstrations include self-powered monitoring of radial pulse, object weight and surface tension, as well as robotic joint motion, with wireless Bluetooth transmission and direct LED driving. Finally, the authors integrate a single FSTI on the wrist with a neural-network model on Arduino to decode five hand gestures with 95.83% accuracy and to provide tactile feedback for a robotic hand, enabling delicate manipulation (e.g., grasping tofu without damage). The work establishes a promising iontronics paradigm for compact, intelligent HMII interfaces.