A contactless THz transmission measurement gives you the sheet resistance of a thin-film conductor directly — at a resolution no other contactless method reaches over large areas, and through insulating overlayers that stop a four-point probe.
Contactless techniques average over a footprint far larger than the defects you are looking for. Contact techniques resolve better but touch the film — and stop at the first insulating layer.
| Method | Contact | Typical footprint | Buried layers |
|---|---|---|---|
| Four-point probe | Yes — invasive | mm-scale probe spacing | No |
| Eddy-current | No | mm-scale coil | Yes |
| Microwave / open resonator | No | sub-mm to mm | Yes |
| THz near-field transmission | No | down to 3 µm | Yes |
Footprint figures are order-of-magnitude for the method class, not vendor specifications — the point is the gap in scale, which is two to three orders of magnitude. The THz figure is the max. spatial resolution of the TeraSpike TD-800-X in HR configuration.
The probe tip sits in the near field of the layer, so the resolution is set by the tip geometry rather than by the THz wavelength. That is what breaks the diffraction limit.
A broadband single-cycle pulse is generated by femtosecond excitation and sent as a plane wave through the sample from the substrate side. Because the pulse is broadband, one acquisition carries the full spectral response.
The TeraSpike microprobe records the transmitted field in the near field of the conducting layer. The photo-switch gap — 1.5 µm on the HR probe — sets the spatial resolution, not the wavelength.
Comparing the transmitted waveform against a reference on bare substrate yields the complex transmission. A thin-film inversion converts it to sheet conductivity, pixel by pixel.
Each pixel is a full time-domain waveform, so the result is a spatially resolved image of the layer rather than an average over a probe footprint.
Cracks and slits far narrower than the spatial resolution still register, because they interrupt the current path the THz field drives.
At up to 5 ms per pixel, full-wafer and large-area maps stay practical — including flat, curved and rough surfaces.
No parasitic sensitivity to carrier-lifetime variation, and optical scattering does not disturb the measurement.
Anything with a measurable sheet conductance in the 1–2000 Ω/□ window — transparent conductors through to thin-film metals.
In devices: flexible and curved touch sensors, displays, OLEDs, thin-film solar cells, smart windows, EM shielding and flexible electronics.
If you want the measurement in-house, this is the chain — probe, scanner, analysis.
Measurement images published with the kind permission of the sample owners.
Most projects start with us measuring a sample, because that answers the feasibility question before anyone specifies a system.
We run the measurement, deliver the maps and the raw waveforms, and tell you what the data does and does not support. Also available as a research study or a technology-development project.
Tell us your layer stack, the resistance window and the area you need to cover. We will name the probe, the scanner configuration and the realistic throughput — or say when the method does not fit.