Fabrication of a Scanning Single Electron Transistor

1
Fabrication of a Scanning Single Electron
Transistor
Y.Kervennic, L. Gurevich, L. Canali, G. Schmid
and L. Kouwenhoven
Department of Applied Physics and Delft Institute
of Microelectronics and Submicron-technology,
Delft University of Technology, P.O. Box 5046,
2600 GA Delft, The Netherlands. Inst. Fur
Anorganische Chemie, Essen University, Germany
From scanning gate to scanning SET
The scanning Single Electron Transistor
consists of a Single Electron Transistor
fabricated at the end of a scanning probe. It is
aimed at imaging the electric potential landscape
of a surface and can be applied to a wide variety
of samples with a resolution much better than
single electron charge. Precedent
approach in the fabrication have been based on
classical e-beam litography and evaporation which
limits the spatial resolution to approximatively
100 nm. We describe a new fabrication
technique which should improve spatial resolution
by at least one order of magnitude. Starting from
a cantilever with two metal electrodes evaporated
on both sides, one can reduce their separation by
controlled electrodeposition and trap a cluster
in the gap to form the island of a SET.
The sample acts as a second gate on the island.
Changes in the current flowing through the SET
are directly related to changes in the potential
of the sample surface. The on-probe gate is used
to tune the SET oscillations.
Electroplating small gaps
To reduce the distance between the two
micro-fabricated metal electrodes we apply a new
technique that makes the fabrication of nanometer
size gaps possible. This technique is based on
electrochemistry.We deposit gold from a gold
cyanid solution and control in-situ the evolution
of the conduction of the gap.
The conductance after making contact shows a
step-like behavior which is interpreted as a
deposition atom by atom until full contact is
made (flat part). Before bridging the gap, a
tunneling regime is visible and can be used for
scaling the distance.
Trapping clusters
Results
Using electroplating, very small gaps can be made
which are suited for trapping metal clusters.
Clusters solved in water solution can be driven
into the gap by current-biasing the two
electrodes.They then remain captured thanks to
Van der Waals forces. We are currently using 20
nm clusters since they show a reasonable gate
effect.
Cantilever are fabricated using RIE and FIB, and
covered with a platinum layer