Electrical characterization in temperature

The cleanroom of the Solid State Physics laboratory is equipped with an home-developed apparatus designed to perform current-voltage characterization in 2-probe and 4-probe configurations of mm-sized samples at variable temperature.

The setup consists of a vacuum chamber interfaced with a turbo-molecular pump that allows operating pressures down to ~1×10-6 mbar. In these vacuum conditions, the sample under analysis can be brought to either high or cryogenic temperatures without incurring in oxidation or frosting phenomena which might deteriorate the sample and perturb the measurement process.

Through a series of mechanical feedthroughs, it is possible to manually control the positioning of a set of four tungsten-carbide microprobes, for the real-time electrical probing with micrometric spatial accuracy of different points of interest in the sample/device under analysis. The probes are connected through electrical feedthroughs to a high-precision KeithleyTM electrometer for accurate electrical measurements. A long-working-distance microscope interfaced with the chamber though a large optical window allows for the accurate positioning of the microprobes on the sample.

Inside the chamber, a molibdenum resistive heating stage is employed to raise the sample temperature up to ~500 °C. The sample holder is is water-cooled during high-temperature operations to avoid the heating of the whole chamber. Alternatively, the stage can be cooled down to cryogenic temperatures through a pump-driven continuous flux of liquid nitrogen from an external reservoir.The sample temperature is monitored by means of a type K thermocouple.

The whole system (sample heating, electrical measurements) is controlled via PC to allow for fully automatized electrical measurements campaigns at different temperatures.