Electrically active polymers Transistors

Electrically conducting polymers can be used as the active element in metal-insulator-semiconductor field-effect transistors (MISFET). MISFETs are generally produced by spin-coating a solution of a polymer onto the surface of oxidized silicon onto which metal electrodes have previously been deposited to form source and drain contacts (Fig. 21) [765]. 

In this chapter, the application of this technique to the thin film processing of electroactive polymers is discussed. The fabrication of controlled molecular assemblies of electroactive polymers provides a unique opportunity to investigate the structure-property and structure-function relationships of multilayer thin films containing electrically conductive, optically nonlinear and redox active polymers. These assemblies can also be coupled to appropriate solid supports for application in such molecular electronic devices as ultrathin electrodes and transistors, opticd waveguides and switches, and chemical and biochemical microelectronic sensors. 

Y. Hong, J.-Y. Nahm, and J. Kanicki, Opto-electrical properties of 200 dpi four amorphous silicon thin-film transistors active-matrix organic polymer light-emitting display, Appl. Phys. Lett., 83, 3233-3235, 2003. 

In conducting polymers, the extra carriers added upon doping are able to drift under an applied electrical field. In semiconducting polymers, no carriers are available except those thermally excited across the gap. However, negative (positive) carriers can be injected into the material by metallic contacts when the barrier between the metal work function and the LUMO (HOMO) molecular levels is overcome. Then, the injected carriers can move inside the semiconductor if a bias field is applied. Injection of carriers and their transport is a fundamental issue for all electronic devices and transistors in particular. In the following, main transport properties of organic semiconductors (both small molecules and polymers-based) used as active materials in transistors will be reviewed. 

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