High-Density Channel-All-Around Vertical Organic Electrochemical Transistors for Reservoir Computing

Miniaturizing organic electrochemical transistors (OECTs) without compromising ionic access, materials compatibility or mechanical compliance remains a challenge for wearable electronics. Here we report a channel-all-around vertical OECT (CAA VOECT) fabricated through a self-aligned process in which the organic semiconductor is deposited after electrode formation. This geometry defines the channel length by the thickness of the insulating layer while maintaining circumferential electrolyte access to the semiconductor. CAA VOECTs with sub-100 nm channel lengths deliver normalized on-state currents above 5 × 10⁴ A cm⁻². A 10 × 10 array reaches an integration density of 4.76 × 10⁵ devices cm⁻², with a coefficient of variation of 3.3% in maximum transconductance, and the architecture supports complementary logic. Devices fabricated on parylene retain on/off current ratios above 10⁶ after 5000 bending cycles. The history-dependent ionic dynamics of the devices further enable physical reservoir computing, yielding 100% classification accuracy for a five-letter task and 89% for the MNIST dataset. The CAA architecture, self-aligned fabrication and flexible substrates establish a route towards dense, mechanically compliant OECT systems for wearable electronics.