Ultra-thin gate dielectrics

Organic thin-film transistors (TFTs) often have relatively thick gate dielectrics with a capacitance per unit area of typically less than 100 nF/cm2. As a consequence, organic TFTs often require relatively large gate-source voltages of about 10 V or more.

For certain applications, such as mobile devices that rely on small batteries, significantly lower operating voltages are desirable.

One possibility to reduce the operating voltage of organic TFTs is to use a thinner gate dielectric that provides a larger capacitance per unit area. A particularly promising approach is the combination of an oxygen-plasma-grown metal oxide (e.g., aluminum oxide) and a high-quality alkylphosphonic acid self-assembled monolayer (SAM).

These hybrid oxide/SAM gate dielectrics can be obtained at process temperatures of no more than about 100 °C and can therefore be employed not only on glass substrates, but also on commercially available flexible plastic substrates, such as polyethylene naphthalate (PEN) or polyethylene terephthalate (PET).

The oxide/SAM dielectrics have a total thickness of about 5 to 6 nm and a gate capacitance per unit area of about 500 to 800 nF/cm2, so that the TFTs can be operated with gate-source and drain-source voltages of about 2 to 3 V.

Despite their extremely small thickness and relatively low process temperature, these gate dielectrics have leakage current densities of less than 10-5 A/cm2 at gate fields of around 5 MV/cm.







Flexible organic transistors and circuits with extreme bending stability
T. Sekitani, U. Zschieschang, H. Klauk, T. Someya
Nature Materials, vol. 9, no. 12, pp. 1015-1022, December 2010

Ultralow-power organic complementary circuits
H. Klauk, U. Zschieschang, J. Pflaum, M. Halik
Nature, vol. 445, no. 7129, pp. 745-748, February 2007
 
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