Tuning Organic Electrochemical Transistor Threshold Voltage using Chemically Doped Polymer Gates

Abstract

Organic electrochemical transistors (OECTs) have shown promise as transducers and amplifiers of minute electronic potentials due to their large transconductances. Tuning the OECT threshold voltage is important to achieve low‐powered devices with amplification properties within the desired operational voltage range. However, traditional design approaches have struggled to decouple channel and materials properties from threshold voltage, thereby compromising on several other OECT performance metrics, such as electrochemical stability, transconductance, and dynamic range. In this work, simple solution‐processing methods are utilized to chemically dope polymer gate electrodes, thereby controlling their work function, which in turn tunes the operation voltage range of the OECTs without perturbing their channel properties. Chemical doping of initially air‐sensitive polymer electrodes further improves their electrochemical stability in ambient conditions. Thus, OECTs that are simultaneously low‐powered and electrochemically resistant to oxidative side reactions under ambient conditions are demonstrated. This approach shows that threshold voltage, which is once interwoven with other OECT properties, can in fact be an independent design parameter, expanding the design space of OECTs.

A guide for the characterization of organic electrochemical transistors and channel materials

“…94 Controlling V T has been of particular interest for OECT-based sensors 104 and logic circuits as it dictates the noise margin and the circuit power consumption. 105 V T has been shown to vary by the gate electrode type and electrochemical potential, 37,105,106 the sidechains of the polymer which affect ion penetration, 107 the type and concentration of ions in the electrolyte, 93,94,104 and device architecture such as dual-liquid gate, 108,109 microfluidic channels 13 or channel aspect ratio. 110 The ON/OFF ratio is defined as the ratio of the maximum channel current when the OECT is turned on (for an enhancement-mode transistor) and the current at OFF state (at V G = 0 V if the material is undoped at this voltage) (Fig.…”

“…[26][27][28] Postprocessing efforts (such as side chains removal, 29 annealing, 30 acid post-treatment, 31 solvent mixtures 32,33 or small molecule additives in the solution 34,35 ) aimed to improve chain aggregation, 25 reduce traps, 36 increase the charge carrier density or introduce chemically doped charges in the film. 37 All these efforts have focused on OECT amplification performance. Besides amplification, the switching speed is also important for biological applications,…”

Tuning Threshold Voltage of Electrolyte-Gated Transistors by Binary Ion Doping

“…Few strategies have been demonstrated to control the V th of the devices such as employing dual-gate electrodes, utilizing an interfacial layer, changing a metal gate electrode, or conducting surface treatment of a semiconductor layer. − However, these methods need complicated structures or lack precise tuning of V th . Recently, Salleo and co-workers reported a solution-processing-based V th tuning method using chemically doped polymer gates . However, V th control methods are still limited and various strategies need to be developed to expand the applicability of electrolyte-gated ionic/electronic devices including electrochemical transistors, biosensors, and neuromorphic devices.…”

“…Recently, Salleo and co-workers reported a solutionprocessing-based V th tuning method using chemically doped polymer gates. 52 However, V th control methods are still limited and various strategies need to be developed to expand the applicability of electrolyte-gated ionic/electronic devices including electrochemical transistors, biosensors, and neuromorphic devices.…”

Solid‐State Homojunction Electrochemical Transistors and Logic Gates on Plastic

“…[13][14][15][16] Numerous studies have sought to develop high-performance OECTs by optimizing the molecular structure of the semiconducting materials and the device architecture. [17][18][19][20][21][22] However, improving the flexibility and mechanical durability of OECTs for use in next-generation bioelectronics remains an engineering challenge. [23][24][25] The metallic materials typically employed as electrodes in conventional OECTs exhibit high electrical conductivity but are rigid and fragile, meaning that they are not suitable as flexible, mechanically robust biocompatible components for wearable and/or implantable devices that require design flexibility and a variety of form factors.…”