Polymer-based microelectrochemical

Figure 1. A conducting polymer-based microelectrochemical transistor. P3MeT connects two wires of a microfabricated array. Electrodes 1 and 2 are source and drain, respectively. At left, Vq is such that the polymer is neutral... 

The characteristics of the polymer-based microelectrochemical transistors are as follows. The current between source and drain. Ip, is a function of the potential between source and drain, Vp, at various fixed gate potentials, Vq. When the Vg using poly(3-methylthiophene) or PP is held at negative potentials where the polymer... 

In this article we report the synthesis and electrochemical properties of the polymer derived from oxidation of X, poly(I), and the characteristics of a microelectrochemical transistor based on the polymer. Poly(I), which is formed by electrochemical oxidation of X, Equation 1, consists of a conducting polymer backbone, polythiophene. 

The poly(I)-based transistor is the first illustration of a microelectrochemical transistor based on a combination of a conducting and a conventional redox polymer as the active material. The transistor "turns on" at VG corresponding to oxidation of the polythiophene backbone. The resistivity of poly(I) declines by a factor of 105 upon changing VG from 0.4 V to 0.8 V vs. Ag+/Ag. When Vg is moved close to the one-electron reduction potential of V2+/+, the conventional redox conductivity gives a small degree of "turn on". A sharp Iq-Vq characteristic results, with an Ip(peak) at Vq = E° (V2+/+). Though the microelectrochemical devices based on conventional redox conduction have both slow switching speed and a... 

The redox behavior of PVFc (VFc ) has been utilized in the construction of a microelectrochemical diode along with a redox-active viologen-based V,A -dibenzyl-4,4 -bipyridinium-based polymer (BPQ ). The polymers were coated upon microelectrodes and current was found to pass when the negative lead was attached to the (BPQ ) electrode and the positive lead was connected to the (VFc ) electrode. Thus, as the applied potential approached the difference in redox potentials of the two polymers, current flowed as shown in Equation (5a), and is favorable by p 0.9V. However, current does not flow if the applied potential is in the opposite sense as seen in Equation (5b), as it is disfavored by 0.9 V. The switching time of this diode, which is controlled by the time required to oxidize or reduce the polymers, was long in comparison with that of the solid-state diodes. ... 

Not long ago,this group first described microelectrochemical devices, which are based on microfabricated arrays of electrodes, connected by electroactive materials. Because the active components of these devices are chemical in nature, many of these devices are chemically sensitive,and comprise a potentially useful class of chemical sensors. Devices showing sensitivity to pH, 02r 2 f and Na" have been demonstrated. These devices are, typically, operated in fluid solution electrolytes. If this class of devices is to be useful as gas sensors, systems which are not dependent on liquid electrolytes need to be developed. We have recently reported solid state microelectrochemical transistors, which replace conventional liquid electrolytes with polymer electrolytes based on polyethyleneoxide (PEG) and polyvinylalcohol (PVA). In this report, we discuss additional progress toward solid-state devices by employing a new polymer ion conductor based on the polyphosphazene comb-polymer, MEEP (shown below). By taking advantage of polymer ion conductors we have developed microelectrochemical devices, where all of the components of the device are confined to a chip. 

Figure 5 shows an example from a new class of solid-state microelectrochemical transistors, which are based on redox-active molecules dissolved in the polymer. The redox-active material is N,N,N, N -tetramethyl-p-phenylenediamine (TMPD) which is sublimed into the MEEP/LiCF3S03 film. Here, the MEEP/LiCF3S03 acts as both polymer host and electrolyte. The transistor characteristic of this device is also shown in Figure 5. Below 0.0 V vs. Ag, the device is off, Iq = 0, since all the TMPD is neutral. As TMPD is oxidized, the device turns on, with a maximum Iq near /2 TMPD" /. We have...

Figure 5. Schematic and transistor characteristic of a new class of microelectrochemical device,which is based on a redox-active material dissolved in a polymer ion conductor. Here, TMPD is sublimed into and saturates the MEEP/LiCF3S03 film. The drain voltage, V j, is 25 mV.

Sulfur-ojqrgen interactions have been proposed as a possible cause for the considerable stability of polyalkojQfthiophenes, based on ex situ investigations of a large selection of substituted thiophenes and their polymers [843]. The amplification of chemical and electrical signals has been applied in a microelectrochemical transistor based on poly(3-methylthiophene) [844]. 

In the near future, further development in new soft microelectrochemical devices based on conjugated polymer actuators will require their complete conception, operation, and interfacing systems all integrated on a single substrate to allow easy and independent operation. This still poses a real challenge that remains to be overcome. Also, it would be of great interest to develop microactuators with linear actuation to further extend the tool box of CP microactuator devices. 

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