Coulomb Blockade at Room Temperature in Selforganized Arrays of Platinum Clusters

 

Franz Kreupl (1), Johann Vancea (2), Lothar Risch (1), Horst Hoffmann (2)

 

(1) Infineon Technologies, Corporate Research CPR1, D-81730 Munich, Germany

(2) Institut für Angew. und Exp. Physik, Universität Regensburg, D-93040 Regensburg, Germany

 

franz.kreupl@infineon.com

 

 

Among the most promising candidates for future electron devices are the Single-Electron-Transistor and its derivatives, which make use of the Coulomb blockade effect occurring in structures with small feature sizes. In order to make these devices work at room temperature, structures with dimensions between 5 and 2 nm has to be created and has to be coupled with tunnel barriers having even smaller dimensions. Hitherto no lithographic and structuring methods are known to solve this "tiny" problem.

In this talk we present an approach for creating such small structures by utilizing the selforganization of platinum clusters during thin film growth of platinum on oxides. By appropriate deposition parameters we can grow 2-dimensional arrays of Pt-clusters on both thin Al2O3- and SiO2-films. The Pt-clusters are 2-4 nm in diameter and separated from each other by about 1 nm.

Electron transport through individual Pt-clusters has been studied with an UHV-STM in-situ after their preparation in a UHV-deposition chamber. Together with the STM-tip and the 1-2 nm thick Al2O3-film on top of a conductive Au-substrate, the Pt-cluster establishes a doubletunnel-junction arrangement showing Coulomb blockade at room temperature with offset voltages between 0.3 1 Volt.

In addition, we studied electron transport through 2-dimensional arrays of Pt-clusters, which have been deposited between two nanostructured contact Au-electrodes on top of a 100 nm thick SiO2-gateoxide. The electrodes have been made by e-beam lithography and lift-off technique and the distance between them was varied from 20 to 120 nm. Electron transport measurements in these arrays also revealed Coulomb blockade at room temperature with offset voltages ranging between 0.2 to 1 Volt. By capacitively coupling a "gate"-voltage by a third electrode to the array, we could change the current flowing through the array, which we attribute to a field effect where current oscillations are superimposed.

In conclusion we have demonstrated a selforganizing process for creating 2-5 nm small, metallic structures, which are separated from each other by about 1 nm and which exhibit Coulomb blockade at room temperature.