A mechano-gated ionic diode enables low-power synaptic tactile spiking

Ionic diodes, which enable unidirectional ion transport, hold great promise for adaptive and energy-efficient ionotronic systems. However, conventional designs often rely on high ion concentrations, which promote ion pairing and clustering, thereby reducing mobility and impeding the formation of stable ion depletion layers (IDLs). Here, we report a mechano-gated ionic diode with balanced ionic conductivity between cationic and anionic polymer layers, achieved through copolymer engineering. This conductivity matching enables the formation of well-defined IDLs, yielding a record-high rectification ratio of 23.5 and pressure-sensitive piezo-ionic behavior. The device transduces mechanical stimuli into discrete ionic spikes via threshold-gated current modulation, consuming only 0.41 nanojoules per spike at rest and 1.49 nanojoules under pressure, achieving up to a 24-fold enhancement in signal-to-noise ratio. When integrated into a tactile interface, the diode exhibits synaptic-like plasticity and activity-dependent signal encoding. These findings establish a material-driven strategy for real-time, low-power ionic sensing and neuromorphic functionality.