Metals, superconductors, and certain other types of materials are characterized by low resistances and can sometimes be difficult to measure in a Hall effect measurement system. This is because below about 1 Ω, the voltage across the sample becomes too small to measure reliably. In theory, it may seem practical to simply increase the current in an attempt to increase the sample voltage, but this is rarely a viable option. Doing so may cause self-heating and could damage your sample. While current reversal and measurement averaging can combat these effects, it can take a very long time to achieve the desired resolution. So this method can be both inefficient and unreliable.
But if you have a Lake Shore 8400 Series HMS system, there’s a better solution: using the 84033 measurement option to perform low resistance measurements. This option, which can be added to the system at any time, extends the low resistance measurement capabilities of DC field Hall measurements, allowing you to measure low resistance samples or materials with a certain level of confidence. However, the question is, just how low of a resistance noise floor is possible with this measurement?
To answer this, we have started writing a series of application notes to document what’s possible when analyzing certain materials. The first of these notes, written by Dr. Jeffrey Lindemuth, explores the measurement of Hall voltage in metals, specifically, a thin film molybdenum sample (upcoming app notes will focus on the measurement of various other materials). In this particular application, we compared the low resistance mode to the standard resistance mode and high resistance mode over a range of resistance values and determined that, under the right test conditions, one can reduce the resistance noise floor of DC measurements from 100 nV to 3 nV (from 1 µΩ to 0.03 µΩ at 100 mA).