Miniaturized thin-film magnetic field probe with high spatial resolution for LSI chip measurement

It is important to obtain the absolute value of current flowing through each power line on a large-scale integrated (LSI) circuit by measurement because this current on an LSI chip is regarded as conductive noise. We have developed a thin-film magnetic field probe that has spatial resolution high enough to obtain the absolute value of high-frequency power current on an LSI chip. Spatial resolution was enhanced by miniaturizing the shielded loop coil, the detection part of the probe. The outer size of the new coil is 50×22 μm. In taking measurements with the new probe over a 60 μm wide microstrip line used as a device under test (DUT), we obtained a 6 dB decrease point of 40 μm, which indicates the spatial resolution of the probe. This value is comparable to the typical width of power lines on an LSI chip, around 50 μm and is less than half that of our conventional probes, around 90 μm. In measurements with the new probe over an LSI chip, we obtained such a fine magnetic near-field distribution that the magnetic fields generated from the lines on the chip were separated. On-chip decoupling was also confirmed by using the new probe. The new probe enables direct verification of a circuit design for suppressing electromagnetic interference (EMI), while conventional coarse mapping of the magnetic near-field cannot be used to evaluate such conductive noise.