What is the four-probe electrode method?

The four-probe electrode method, also known as four-terminal sensing or four-wire sensing, is an electrical impedance measuring technique used to measure resistance in various applications accurately. This method utilizes separate pairs of current-carrying and voltage-sensing electrodes to overcome the limitations of traditional two-terminal sensing.

Two pairs of electrodes are employed in the four-probe method: the force connections (current leads) and the sense connections (voltage leads). The force connections supply the current to the measured impedance, while the sense connections are placed adjacent to the target impedance to measure the voltage drop without including the voltage drop in the force leads or contacts. By separating the current and voltage electrodes, the four-probe method eliminates the effects of lead and contact resistance, enabling more precise measurements, particularly for low resistance values.

The technique is widely used in ohmmeters, impedance analyzers, and various applications such as wiring for strain gauges, resistance thermometers, and sheet resistance measurements of thin films, especially semiconductor thin films [1]. It is also referred to as Kelvin sensing, named after William Thomson, Lord Kelvin, who invented the Kelvin bridge in 1861 for measuring very low resistances using four-terminal sensing.

In addition to measuring resistance, the four-probe method is utilized to calculate sheet resistance, a critical electrical property of thin films. Sheet resistance characterizes the lateral resistance through a thin square of material and is independent of the square's size, allowing for easy comparison between different samples. The four-probe method and geometric correction factors accurately measure sheet resistance.

To summarize, the four-probe electrode method, or four-terminal sensing, is an impedance-measuring technique that uses separate pairs of current-carrying and voltage-sensing electrodes to measure resistance accurately. It is used in various applications, including ohmmeters, impedance analyzers, strain gauges, resistance thermometers, and sheet resistance measurements of thin films.

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