Modulation on Transconductance and Switching Speed of Vertical Organic Electrochemical Transistors via Structure Engineering

Vertical organic electrochemical transistors (vOECTs) have received widespread attention in bioelectronics, wearable, and neuromorphic electronics due to their high transconductance (g_m), low driving voltage, and biocompatibility. As key parameters of vOECTs, g_m and switching speed (or transient time, τ) are vital for achieving satisfying performance in various practical applications. Here we employ vOECTs with varying top electrode widths for effective g_m and switching speed modulation. It is found that both g_m and τ increase linearly (from 60.0 to 105.8 mS and from 1.15 to 1.60 ms, respectively) with the increasing top electrode width (from 40 to 120 μm). This result indicates that it is challenging to simultaneously obtain both high g_m and short τ. Consequently, grid-like top electrodes are employed, which are composed of small electrodes arranged with certain intervals, where ions can be injected from the gap of electrodes instead of the side of a single large electrode, leading to both high g_m (202 mS) and short τ (0.797 ms). In addition, the grid-like electrode-based vOECTs successfully achieve electrocardiogram (ECG) and electrooculogram (EOG) monitoring with high signal quality. This work provides an ingenious design of the top electrodes in vOECTs and promotes further optimization of device performance, increasing g_m while enabling high-frequency operation.