Organic dunnfilmtransistors run at low operating voltage

Organic molecular monolayers are better suited for gate dielectrics than inorganic oxides

Organic dunfilm transistors having a gate insulation from an amorphous, molecular monolayer could provide thanks to a low threshold voltage of 0.7 V in the art portable electronic devices for more prolonged battery life. The leakage current through these monolayers is remarkably small, so dunne gate insulation is possible. While so far the operating voltage of organic transistors was around 20 V, it could now be significantly less than 2 V.

Organic Dunnfilmtransistors can control, for example, displays or sensors, are not the problem with the high operating voltage, which is usually about 20 V. The cause of the problem is the low gate capacity of the transistor due to the thick gate dielectric, this is customary from inorganic oxides, nitrides or insulating polymers. An at least 100 nm thick gate insulation ensures as small leakage trreams as possible, this drum from the tunnel effect and therefore take exponentially with the layer thickness. However, the gate capacity must not be arbitrarily small because a tiny charge fluctuation should not lead to signal dissipation.

Cross section through the organic Dunnfilmtransistor with an effective channel length of the 5000 nm, its threshold voltage amounts to 0.7 V, which is unusually low for transistors of this type.

How researchers of the company Infineon in Erlangen together with colleagues of the University of Stuttgart and the Massachusetts Institute of Technology in the edition of 21. October 2004 of the magazine Nature on page 963 reported in Volume 431, a novel manufacturing process with a 2.5 nm thick gate dielectric from an organic molecular monolayer could help. The relative dielectric constant of this monolayer is 2.5; Another advantage is a particularly high electrical breakthrough field strength.

For the channel of the transistor, especially the polymer Pentazen is suitable, this organic semiconductor is characterized by a particularly high charge bearing mobility – each high the charge carrier mobility, the faster a transistor can switch. So converted Dunnfilmtransistors come out with an operating voltage under 2 V. The leakage current through the gate dielectric is even tend to be smaller than comparable mosfets of silicon with quartz as gate oxide.

The low operating voltage is not only contrary to the developers of portable gates, it could also help reduce leakage streams of silicon’s fine nanotransistors and thus reduce the power consumption of microprocessors. Here, however, the semiconductor industry rather rather on gate dielectrics with high relative dielectric dielectric constant and ensures in this way – despite quite thick gate insulation – for sufficiently high gate capacity.