The Transient Response of Organic Electrochemical Transistors

Abstract

A fast response of organic electrochemical transistors (OECTs) to electrical or chemical changes is essential for a widespread acceptance of this technology. However, finding design rules for fast switching OECTs is complicated by the fact that current transient device models are highly simplified and rely on a 1D approximation of the device that neglects details of the ion and hole concentration inside the transistor channel. To improve the understanding of transient processes limiting the speed of OECTs, a 2D drift-diffusion model is presented and experimentally validated. It is shown that switching is strongly influenced by lateral ion currents that are neglected in previous models. A consistent treatment of these currents leads to a dependency of the time constants on the applied drain potential and a complex dependency of the response time constants on the detailed device geometry. In addition to an improved understanding of the transient response of OECTs, the results discussed here highlight the challenges in properly characterizing switching time constants of OECTs, and reinforce the necessity to ensure that switching is measured between two steady-state conditions, and not between transient states.

Downsizing the Channel Length of Vertical Organic Electrochemical Transistors

“…The spin-coated device performs better than the electropolymerized ones in terms of the frequency response; therefore, a temporal response of six identical devices was captured as well, yielding averaged time constants of τ OFF = (36.4 ± 1.8) μs and τ ON = (124.0 ± 1.9) μs for devices with W = 50 μm and d = 400 nm (Figure C). The time constant for turning ON the transistor is significantly slower, showing the same behavior as reported in some other works. − Paudel et al showed that for a planar OECT, lateral current in the channel when switching the transistor off is the limiting factor, as the channel length is usually much larger than the thickness of the semiconductor, rendering turning OFF the slower process of the two. Here, we attribute the opposite behavior partly to the fact that the channel length and semiconductor thickness are similar.…”

“…The time constant for turning ON the transistor is significantly slower, showing the same behavior as reported in some other works. 27−30 Paudel et al 27 showed that for a planar OECT, lateral current in the channel when switching the transistor off is the limiting factor, as the channel length is usually much larger than the thickness of the semiconductor, rendering turning OFF the slower process of the two. Here, we attribute the opposite behavior partly to the fact that the channel length and semiconductor thickness are similar.…”

Layer-by-Layer Assembly Monitored by PEDOT-Polyamine-Based Organic Electrochemical Transistors

“…Results observed in Figure S8 show that the nature of the charge of the polyelectrolyte does not affect the shape of the transient behavior of the devices; that is, there is no effect ascribed to the charge exclusion, showing that the process is governed by the exchange of both type of ions. Moreover, it is important to note that, compared to other recently reported OECTs, the obtained t average of 41 μs (for 1:5 dilution OECTs) is remarkably lower. A detailed comparison with previously reported OECTs is presented in Table S1.…”

Neural-inspired artificial synapses based on low-voltage operated organic electrochemical transistors

“…OECTs generally exhibit a response time of up to a few tens of microseconds. 60,65 OECTs with gel-or solid-state electrolytes show even slower t. This range of response time resembles the electrophysiological signal, establishing OECTs as the most suitable for synaptic application. 66 Another performance parameter for OECTs is the effective formation of EDL and electrochemical ion doping in the channel, leading to G m increment.…”