Development and Application of a High-Resolution Thin-Film Probe

This paper documents the development, characterization, and application of a high-resolution thin-film magnetic-field probe. Probe diameter ranged from 5 mum to 100 mum. The 100 mum probe exhibits a 250 mum improvement in spatial resolution compared to a conventional loop probe, measured at a height of 250 mum over differential traces with a 118 mum spacing. Electric field rejection was improved using shielding and using a 180 degree hybrid junction to separate common-mode (electric field) and differential-mode (primarily magnetic field) coupling. A network analyzer with narrow band filtering was used to detect the relatively weak signal from the probe and to allow detection of phase information. An application of the probe is demonstrated where the probe is used to identify the magnitude and phase of magnetic fields produced by currents in very closely-spaced IC package pins.