Eddy-Current Measurement vs. Four-Point Probe

Eddy-Current vs. Four-Point Probe Sheet-Resistance Measurement

Surface-Resistance Measurement: Eddy Current vs. Four-Point Probe

The four-point probe is a traditional method for measuring sheet resistance. For many applications, a non-contact eddy-current method can provide practical advantages, especially when contact with the sample surface should be avoided or measurements are needed during production.

Advantages of Eddy-Current Measurement

1. Non-destructive measurement: avoids probe marks that can damage the sample surface.
2. Measurement through an insulating layer: in suitable applications, an insulating layer on the sample does not prevent measurement of the conductive material beneath it.
3. Measurement of moving samples: can be used for real-time measurement on a production line when the system and process are configured for it.
4. Real-time data: provides immediate readings and can reduce measurement time.
5. Lower probe-consumable costs: avoids routine replacement of four-point probe tips.

Measurement Considerations and Limitations

1. Calibration: calibrate appropriately for the material to achieve the required measurement accuracy.
2. Probe-to-sample distance: maintain a stable lift-off distance for repeatable, stable results.
3. Probe selection: different measurement ranges may require different probes to achieve suitable performance.
4. Measurement area: the measured area is larger than that of a four-point probe, which may matter when evaluating small or localized features.

Choosing a Method

Both methods have their own applications. A four-point probe makes electrical contact with the sample and is a well-established option. Eddy-current measurement is non-contact and may be useful when reducing surface damage or contamination risk, measuring a moving sample, or obtaining rapid readings is important.

The suitable method depends on the material, conductive-layer properties, required measurement range, feature size, sample condition, and production setup. Confirm calibration, measurement geometry, and acceptance criteria before comparing results.

Need help selecting a sheet-resistance measurement method?

Contact Fulcrum Technology to discuss your material and process requirements and evaluate whether a non-contact eddy-current system or a four-point probe is suitable.

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