The organic field effect transistors (OFET), the key building block of device of organic electronics, have long been suffering low current output and high operating voltage, compared to inorganic FETs. This relatively poor performance results from both the conventional design of OFET and the low mobility of organic semiconductors.

As shown in Figure 1, conventional design of OFETs has a lateral structure. The space between the source and the drain needs to be minimized in order to reduce voltage need and to increase current output of the OFETs. However, such a requirement is often limited by the fabrication techniques. Moreover, conventional design requires the gate to be located between the source and the drain, which limits the cross-sectional area for current flow and therefore limiting current output.

The above limitations of conventional OFETs might be overcome by a novel design, the vertical organic field effect transistor (VOFET). Invented by the Yang Yang Laboratory at UCLA, and licensed to ORFID Corp., VOFET has a vertical structure, where gate-source-drain are arranged layer-by-layer (Fig. 2). The device consists of two major cells. The first is an active cell (drain/organic/source) vertically stacked on top of a capacitor cell (source/dielectric/gate). These two cells share (are joined by) a common-source electrode.

This unique design allows a very short channel length (less than 0.1 µm) between the source and drain and an extremely large cross-sectional area, allowing low operating voltages (less than 5 V) and high current outputs (up to 10 mA). Also, such layered VOFETs are suitable for low-cost fabrication techniques, such as roll-to-roll printing.

See the following video for demonstration:

(Image and video source: www.orfid.com)