A Near-Field Magnetic Sensing System With High-Spatial Resolution and Application for Security of Cryptographic LSIs

Abstract

This paper presents a high-resolution inductive near-field magnetic sensing system to detect sensitive and suspicious areas of cryptographic large-scale integration (LSI) chips for nondestructive inspection. The proposed system includes a probe chip based on a 0.18- $\mu \text{m}$ five-metal-layer CMOS process technology and a microposition calibration mechanism. The probe chip includes a magnetic pick-up coil followed by a three-stage low-noise amplifier (LNA) to amplify the induced voltage on the coil. The Si-substrate area under the coil is removed by applying a focused-ion-beam (FIB) technique to enhance the quality factor of the coil. A mechanical scanning system with an ability of microposition calibration is proposed to allow high-precision calibration and microscanning operation. High-spatial resolution magnetic scanning experiment is conducted on a microstrip line and on the surface of a cryptographic field programmable gate array (FPGA) running 128-b advanced encryption standard (AES) algorithm. By making a comparison in the scanning performance of a commercial probe, this sensing measurement holds the advantage of higher resolution magnetic maps in multiple frequency bands. Moreover, the proposed system can be used to identify vulnerable areas of cryptographic LSI chips that can cause location-dependent side-channel leakage.