|
Specific forced currents are required for different materials and feature sizes to ensure the best measurement precision and to minimize Joule heating. The determination of the optimum forced current depends on several parameters: sheet resistance, doping level, feature aspect ratio, and arm length/width of the van der Pauw (VDP) structure. A test of several different materials, resistivities, and feature sizes shows that the optimum forced current in the bridge and the VDP structures can be determined by simple empirical equations. The affect of Joule heating in a 0.2 micrometers structure was also evaluated. When supplied a forced current above the critical current density, the initial voltage reading is 9% larger than the initial voltage reading with the optimum forced current. There was no obvious Joule heating effect below the critical current density. In the extreme case an optimum forced current applied to a 0.22 micrometers structure for as long as 10 minutes produced a voltage rise exponentially to only 0.2% of the normalized voltage measured at the beginning.
|
