Effect of opposite side electrodes in organic field-effect transistor structure

For nanoscale devices, the source and drain electrodes in organic filed effect transistor (OFET) are usually placed on the opposite side of the insulator and gate electrode. While the conventional model to describe FET was extracted from the planar structure with all electrodes laid in the same side. Therefore the effect of the opposite side electrode OFET structure was investigated by using two-dimensional numerical simulation and then comparing to the current-voltage characteristic of fabricated top-contact bottom-gate OFET structures based on pentacene. For this type of structure, a layer of organic semiconductor with a few hundred nanometers thick was employed as active layer and the thickness of this layer has an influence on the saturated current characteristic. The ratio between the saturated drain current and the organic layer thickness becomes approximately constant in some range of the film thickness. In addition the effect of various channel lengths (defined by the distance between edge of source and drain electrodes instead of the heavy doped regions) was examined and the linear dependence part was determined. The effect of insulator thickness dependence can also be demonstrated by modification of electric field from the gate voltage. This model was applied to fabricate the device and verify the effect of electric field from the opposite side of gate electrode.