A Water‐Gate Organic Field‐Effect Transistor

Abstract

Organic field-effect transistors (OFETs) promise for printed intelligence embedded into, and coated onto many different items that previously have been considered impossible to make electronically active. It is crucial that this technology is driven at low voltage and power. Also, we need to obtain solid understanding of the charge transport in organic semiconductors. Different materials [1] and architectures have been utilized as the probe to reveal the nature of charge transport along the transistor channel and to achieve low-voltage switching. In transistors operating according to field-effect or electrochemical principles, respectively, vacuum, air, [2] oxides, [3] high-permittivity dielectrics, [4] organic mono-layers, [5] and electrolytes [6] have successfully served as the medium to electronically separate the gate from the transistor channel, of which the latter three allow low-voltage operation. In particular electrolytes have attracted much attention lately since they generate very high electric fields at the organic transistor channel/electrolyte interface already at very low voltages, i.e., below 1 V. One issue with those devices is that electrochemical switching and field-effect modulation of the organic channel often coexist, [7] which result in transistors that are typically slow and that exhibit a great degree of hysteresis. Here, we report OFETs gated via pure water that operates entirely in the field-effect mode of operation. Our findings shed new light on low-voltage operating OFETs, their charge transport characteristics under exposure to water [8] and opens for sensor applications using water-gated OFETs as transducers in aqueous media.[9] Because of the simplicity and readiness of its production, it could also reveal a very helpful tool for rapid testing of new organic semiconductor compounds.Electrolyte (insulator)/semiconductor interfaces have attracted much attention during the last decades, in part driven by an interest to achieve high-performing sensors operating in water, to reach low-voltage operation for OFETs and to study the fundamentals of charge transport in semiconducting solids. In ion-sensitive field-effect transistors (ISFETs), the electrical potential at the electrolyte/insulator interface is translated into a modulation of the transistor output characteristics.[10] Actually, the modulation originates from that the threshold voltage (V T ) is sensitive to the ion concentration. The high electric field that is possible to establish at electrolyte/solid interfaces becomes a powerful tool for probing various features of the transport and accumulation of charges inside solids. Electrostatic field-operated transistors and switches, including for instance silicon, carbon nanotubes, [11] rubrene, [12] or manganites [13] as the active material, have been extensively studied in the past. In all those cases pure field-effect operation, without any parasitic electrochemical reactions of the bulk of the solid, is achieved simply because the materials included in the devices are known ...

Phospholipid film in electrolyte-gated organic field-effect transistors

“…2A Table 1, show an electronic performance comparable to those previously published for a water-gated OFET [14].…”

“…In this range of frequency, the  dependence on V DC can be attributed to the onset of water electrolysis [14]. The capacitance of 0.9 F*cm -2 for the Au/P3HT/H 2 O/Au system and 0.7 F*cm -2 for the PL-OFET, respectively, leads to mobility values of (4.6±0.3)*10 -3 cm 2 V -1 s -1 and(1.5±0.1)*10 -3 cm 2 V -1 s -1 , in line with previous determinations [14].…”

“…A capacitive coupling between the polymeric electrolyte and the OS is generated in this case by the formation of a Helmholtz double layer [12][13] yielding a capacitance of 10 F*cm -2 [10]. A Helmholtz double layer can also be generated in a water-gated OFET [14][15] when pure water is directly interfaced to the OS. These devices have been shown to operate in a mostly capacitive mode thus demonstrating that no significant organic semiconductor degradation occurs under water operation.…”

“…These devices have been shown to operate in a mostly capacitive mode thus demonstrating that no significant organic semiconductor degradation occurs under water operation. Water-gated FETs, like electrochemical ones, can be operated in the sub-volt regime and exhibit a mobility ranging between 10 -3 cm 2 V -1 s -1 [14] and 10 -1 cm 2 V -1 s -1 if a semiconductor/insulator blend is used as active layer [15].…”

On the mode of operation in electrolyte-gated thin film transistors based on different substituted polythiophenes

“…using architectures not appropriate for sensors, indicate that the chemical nature of the semiconducting polymers is crucial since it affects the operation mechanisms. The EGOTFTs typically run either in a field-effect (OFET) [26]or an electrochemical (OECT) mode of operation P3CPT, [11], i.e. current modulation is due either to charge polarization occurring along the aqueous analyte-semiconductor interface or chemical doping occurring within the bulk of the semiconductor channel.…”