Electrochemical transistors

Figure 11 Electrochemical transistor using a conducting polymer.

Figure 2. (a) Schematic cross section of an organic field-effect transistor (OFET). (b) Schematic cross section of an organic electrochemical transistor (OECT). The applied source-drain voltage Vd and gate voltage Vg are also shown. 

Electrochemical Transistors for Applications in Chemical and Biological Sensing... 

PEDOT PSS-Based Electrochemical Transistors for Ion-to-Electron Transduction and Sensor Signal Amplification... 

In 2002, David Nilsson reported an electrochemical transistor using poly(3,4-ethylenedioxythiophene) doped with poly(styrene sulfonate) (PEDOT PSS) as the active layer [14]. In this system, both the electronically conducting system (PEDOT) and the dopant are polymers and therefore nonvolatile as the oxidation state of the PEDOT is altered. PEDOT is pristinely doped and is therefore in its high conducting state. This allows us to define the drain, source, and gate as well as the transistor channel in PEDOT PSS solely, see Fig. 9.1. As the gate is addressed positively, vs. the source electrode, PEDOT in the channel is reduced to its neutral state. 

In this work, an ionophore-based solvent polymeric membrane is cast on top of the PEDOT PSS channel in order to obtain an ion-selective organic electrochemical transistor (IS-OECT). The polymeric membrane is composed of 2-nitrophenyl octyl ether (o-NPOE, 57.2% ww), poly(vinyl chloride) (PVC, 27.9% ww), V.. V.. V. . V -i( I i i( ycloli( xyl-3-oxapentanedianii(le (ETH 129, 9.6% ww) and potassium tetrakis(4-chlorophenyl)borate (KTpCIPB, 5.4% ww), where ETH 129 is a Ca2+-selective ionophore. The channel region of the transistor that is coated by the Ca2+-selective membrane is immersed in an aqueous solution containing 0.1 M KC1 as a background electrolyte and... 

Fig. 9.6. Schematic description of the Ca2+-selective organic electrochemical transistor. Modulation of the drain current (Ids) by the gate potential (Vg) depends on the ion transport properties of the selective membrane (see Fig 9.7)...

SPICE [32] simulations indicate that the electrochemical transistor can be used favorably to implement a number of useful digital and analogue circuits. Naturally, the slower speed, compared to traditional electronics (by about a factor 108 ), should be taken into consideration. The area of (silicon-based) electronic circuit theory offers numerous solutions to the implementations of circuits. However, depletion-type transistors are less favorable to use in system designs than their enhancement counterparts. For this reason, it is rare to find circuits that use depletion transistors. One has to go back to the electron tube era to find solutions that can be used as templates for circuits suitable for the electrochemical transistor. 

In the design of circuits there are certain basic electrical design rules for the electrochemical transistor that should be kept in mind ... 

The PEDOT PSS-based electrochemical transistor balance at the boundary between amperometric and potentiometric sensor functionality. Its device architecture is simple and robust and these PEDOT PSS sensors can easily be manufactured using standard printing technologies. In addition, its proper ion-to-electron transduction characteristics and the possibility to integrate biologically active substances promise for simple and sensitive sensors in the... 

Fig. 9.18. The classical ring-oscillator circuit top and the associated output characteristics bottom left and an electrochemical transistor ring oscillator printed on a plastic foil bottom right ...

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