Spacial Resolution Enhancement for Integrated Magnetic Probe by Two-Step Removal of Si-Substrate Beneath the Coil

This paper presents an enhancement of high spacial resolution magnetic probe for the applications of measuring magnetic fields emitted from cryptography micro-electronic devices. The on-chip sensing system includes a magnetic pick-up coil, three-stage low-noise amplifier, mixer, and low-pass filter. Noise problems are reduced by the proposal of using the down-conversion mixer. A two-step removal of Si-substrate (Si-SUBS) areas is also proposed by applying a focused-ion-beam process to avoid eddy currents that reduces the coil sensitivity. Four probe chips are fabricated in a 0.18 um CMOS five-metal layer process with different coil sizes and with/without Si-SUBS removals. Experimental results on a thin wire and micro-strip line show the proposed system achieves high spacial resolution and sensitivity for near-field magnetic scanning.