Aug 10, 2011
Tracking down leakage currents in nanodevices
One of the problems that can occur when fabricating nanodevices is the appearance of undesired leakage currents – electrical currents between two terminals in a nanostructure that should be electrically isolated. These leakage currents can limit the measurement range of the structure or even render the device completely useless. It is highly desirable to eliminate such leakage currents and the first step is to learn more about them, particularly the position at which the leak occurs.
To shed light on this question, researchers at ETH Zuerich have used low-temperature scanning gate microscopy to examine a nanostructure fabricated by local anodic oxidation. A metallic tip is scanned over the structure and by keeping the tip voltage fixed, it is possible to move the electrical potential induced by the tip to any position on the structure. No current flows from the tip to the sample.
Using this technique, the team can resolve the position at which leakage currents occur and answer important questions such as: do leakage currents occur homogenously along the whole boundary of two neighboring terminals? Where on such boundaries are leakage currents most likely to occur? Do leakage currents occur most likely at the smallest parts of the nanostructure?
The group has found that in a nanostructure fabricated by local anodic oxidation, leakage currents are most likely to occur at crossings between oxide lines and explain this phenomenon based on the details of the fabrication process. With this knowledge, the researchers can suggest ways of improving the fabrication process. In the future, this may allow developers to build nanostructures that minimize leakage and maximize tunability.
More information can be found in the journal Nanotechnology.
About the author
The research was performed in the nanophysics group of Prof. Klaus Ensslin at ETH Zuerich (Zuerich, Switzerland). Prof. Klaus Ensslin guided the project together with Prof. Thomas Ihn (ETH Zuerich, Zuerich, Switzerland). Magdalena Huefner was conducting her PhD research on scanning probe methods in the group of Prof. Ensslin when the study took place. She is now working as a postdoctoral fellow in the group of Prof. Jenny Hoffman (Harvard University, Cambridge, US). Bruno Kueng and Stephan Schnez (now ABB) are pursuing their PhD in the group of Prof. Ensslin at the ETH Zuerich. The sample wafer was grown by Matthias Reinwald in the group of Prof. Werner Wegscheider (formally Universitaet Regensburg, Germany, now ETH Zuerich, Switzerland).