Sheet Resistance Imaging on Ag Thin Films with THz-TDS in Reflection Geometry

We present sheet resistance imaging of silver (Ag) thin films on a similar to 50 mu m-thick dielectric layer on a plane steel substrate. THz imaging avoids damaging these films through contacting and allows for a high spatial resolution. We use a commercial THz time-domain spectroscopy system in reflection geometry. Our measurement data are interpreted by a least squares fit to a simple model of the frequency response of the layer stack based on Fresnel equations and the Drude model. The analysis reveals the thickness of the dielectric and the Ag-layer as well as the dielectric function of the Ag-layer. By raster-scanning the sample, spatially-resolved sheet resistance maps are non-destructively generated.