High transconductance organic electrochemical transistors

Abstract

The development of transistors with high gain is essential for applications ranging from switching elements and drivers to transducers for chemical and biological sensing. Organic transistors have become well-established based on their distinct advantages, including ease of fabrication, synthetic freedom for chemical functionalization, and the ability to take on unique form factors. These devices, however, are largely viewed as belonging to the low-end of the performance spectrum. Here we present organic electrochemical transistors with a transconductance in the mS range, outperforming transistors from both traditional and emerging semiconductors. The transconductance of these devices remains fairly constant from DC up to a frequency of the order of 1 kHz, a value determined by the process of ion transport between the electrolyte and the channel. These devices, which continue to work even after being crumpled, are predicted to be highly relevant as transducers in biosensing applications.

Figure 1. Active material and structure of the transistor.

(a) Chemical structure of PEDOT and PSS. A hole, indicated as a positive polaron on the PEDOT chain, is compensated by a sulphonate ion on the PSS chain. (b) Schematic of an OECT cross-section and the wiring diagram for device operation. (c) Optical micrograph of an individual transistor. Scale bar, 10 μm.

Figure 2. Steady-state characteristics.

(a) Output characteristics for V_G varying from 0 (top curve) to +0.5 V (bottom curve) with a step of +0.1 V. (b) Transfer curve for V_D=−0.6 V, and the associated transconductance.

Figure 3. Frequency dependence of the transconductance.

The device was biased with V_D=−0.6 V and V_G=0.3 V, and an additional 100 mV peak-to-peak gate voltage oscillation was applied to measure the small-signal transconductance (open squares). The solid line shows the ionic charge injected in the channel.

Figure 4. Resistance to mechanical deformation.

(a) An array of devices removed from the sacrificial glass substrate (active area shown as boxed region). (b) The array aggressively crumpled. (c) The array un-crumpled back to a flat sheet. Scale bar, 1 cm. (d) Output characteristics and (e) transfer characteristics for the same device as-prepared (black), after peeling (red) and after crumpling (blue). (f) Transconductance and time response for devices after peeling (red), and after crumpling (blue), normalized to the performance of each device as-prepared (Error bars represent standard deviation of normalized values for N=16 devices, on three different substrates).