Modulation\non Transconductance and Switching Speed\nof Vertical Organic Electrochemical Transistors via Structure Engineering

Vertical\norganic electrochemical transistors (vOECTs) have received\nwidespread attention in bioelectronics, wearable, and neuromorphic\nelectronics due to their high transconductance (<i>g</i><sub>m</sub>), low driving voltage, and biocompatibility. As key\nparameters of vOECTs, <i>g</i><sub>m</sub> and switching\nspeed (or transient time, τ) are vital for achieving satisfying\nperformance in various practical applications. Here we employ vOECTs\nwith varying top electrode widths for effective <i>g</i><sub>m</sub> and switching speed modulation. It is found that both <i>g</i><sub>m</sub> and τ increase linearly (from 60.0 to\n105.8 mS and from 1.15 to 1.60 ms, respectively) with the increasing\ntop electrode width (from 40 to 120 μm). This result indicates\nthat it is challenging to simultaneously obtain both high <i>g</i><sub>m</sub> and short τ. Consequently, grid-like\ntop electrodes are employed, which are composed of small electrodes\narranged with certain intervals, where ions can be injected from the\ngap of electrodes instead of the side of a single large electrode,\nleading to both high <i>g</i><sub>m</sub> (202 mS) and short\nτ (0.797 ms). In addition, the grid-like electrode-based vOECTs\nsuccessfully achieve electrocardiogram (ECG) and electrooculogram\n(EOG) monitoring with high signal quality. This work provides an ingenious\ndesign of the top electrodes in vOECTs and promotes further optimization\nof device performance, increasing <i>g</i><sub>m</sub> while\nenabling high-frequency operation.