High frequency magnetic near field measurement on LSI chip using planar multi-layer shielded loop coil

Magnetic near-field measurements of circuitry are gathering increasing interest as an effective technique for detecting noise emission current sources. Against this background, we developed planar thick-film multi-layer shielded loop coils with loop apertures of 20 mum x 1000 mum and 600 mum x 600 mum. The shielded-loop structure's main feature is the cancellation of voltage induced by the electric field. A 60-mum wide microstrip line was used as the device under test (DUT). In a spatial resolution test conducted at 1 GHz, we obtained optimum spatial resolution of 90 mum at the 6 dB degrading point for a rectangular coil with a 20 mum x 1000 mum aperture. This resolution level is 2.8 times better than that we obtained with our previous product comprising a low temperature co-fired ceramic (LTCC) board, because with the new coils we were able to successfully reduce the mean distance between the loop and the DUT. In measuring nonuniform magnetic field distribution near the 1.58 mm-wide microstrip line and the internal chip of a large-scale integrated (LSI) circuit, we found the new model could measure a finer distribution than our previous probe.