Bounds on Distinguishing Separated Wires Using Magnetic Field Measurements

TL;DR

This paper establishes theoretical limits on the ability of magnetic field measurements, including advanced imaging devices, to distinguish between different wire current configurations at various distances.

Contribution

It provides the first theoretical bounds on the spatial resolution of magnetic field measurements for microelectronics testing, considering emerging imaging technologies and vector field data.

Findings

Derived lower bounds on wire distinguishability based on separation and standoff distance.

Compared performance of single-point sensors versus array measurements.

Highlighted advantages of full vector magnetic field measurements.

Abstract

Magnetic current imaging (MCI) is useful for non-destructive characterization of microelectronics, including both security analysis and failure analysis, because magnetic fields penetrate the materials that comprise these components to enable through-package imaging of chip activity. Of particular interest are new capabilities offered by emerging magnetic field imagers, such as the Quantum Diamond Microscope, which provide simultaneous wide field-of-view, high spatial resolution vector magnetic field imaging capabilities under ambient conditions. While MCI offers several advantages for non-destructive measurement of microelectronics functional activity, there are many limitations of the technique due to rapid falloff of magnetic fields and loss of high frequency spatial information at large sensor standoff distances. To understand spatial resolution as a function of standoff distance, we consider the problem of using magnetic fields to distinguish (1) between a single wire carrying current $I$ and a pair of wires carrying current $I/2$ in the same direction and (2) between no currents and a pair of wires carrying current $I/2$ in opposite directions. In both cases, we compare performance for a single point measurement, representative of typical magnetometers, to performance for an array of measurements found in emerging magnetic imaging devices. Additionally, we examine the advantage provided by measurement of the full vector magnetic field compared to measurement of a single component. We establish and compare for the first time the theoretical lower bounds on separability based on the wire separation and sensor standoff distance of the magnetic field measurements obtained from traditional and new microelectronics reliability tools.