Monolithic 3D-Integrated All-Solid Ion-Gated Carbon Nanotube Transistors With Tunable Ionic Conductance for Multi-Timescale Reservoir Computing.

Ion-gated transistors inherently exhibit time-dependent behavior governed by ionic motion associated with electric double-layer formation; however, their practical implementation has been limited by insufficient control over ionic dynamics and poor compatibility with scalable thin-film integration. Here, we present carbon nanotube (CNT) solid-ion-gated transistors (sIGTs) that allow the wide-range engineering of ionic dynamics while remaining fully compatible with wafer-scale thin-film processing. Tunable ionic conductance is achieved by ionic content engineering in the film and thickness scaling into the sub-micron regime, enabling ionic time constants from microseconds to milliseconds. CNT sIGTs demonstrate robust DC operation at low ionic content with an optimized polymer matrix and wafer-scale fabrication on flexible substrates. Frequency-dependent gate modulation governed by ionic conductance is systematically investigated through electrical impedance spectroscopy and small-signal analysis, including a comparison of the -3 dB cutoff frequency and the transit frequency. This analysis provides direct insight into the relationship between ionic conductance and frequency-dependent device response, exhibiting consistent trends across both two-terminal and three-terminal device configurations. Monolithic three-dimensional integration of two-tier CNT sIGTs with engineered dynamic responses is demonstrated as a compact dual-timescale physical reservoir for neuromorphic computing that enables classification of time-varying inputs using a single readout layer.