PG-CAS: Patterned-Ground Co-planar Capacitive Asymmetry Sensing for mm-range EM Side-channel Attack Probe Detection

Electromagnetic (EM) side-channel analysis (SCA) attack, which breaks cryptographic implementations, has become a major concern in the design of circuits and systems. This paper presents the design and analysis of the EM side-channel attack detection system utilizing patterned-ground co-planar capacitive asymmetry sensing (PG-CAS) for approaching probe, targeting to improve sensitivity, detection range, and power consumption compared to LC oscillator utilizing inductive sensing. The PG-CAS consists of a grid of four metal plates of the same size at the top metal layer and a patterned ground plane at a lower metal. As an EM probe approaches, electric field lines between the plates and plate-ground get distorted, thereby breaking the symmetry of the inter-plate and the plate-ground capacitance system and this change in capacitance is sensed. The PG-CAS circuit consists of two LC oscillators, mixer, low pass filter (LPF), resistive feedback amplifier (RFA) and a digital logic. By down-converting sensing signal to low-frequency using mixer, LPF, RFA and digital logic, the detection range is significantly improved. At a distance of 1 mm between the sensing metal plates and the approaching EM probe, system-level simulation results using TSMC 65nm technology and Ansys Maxwell show a > 10% change in the output frequency from the baseline frequency, leading to a > 10x improvement in the detection range and a similar to 3x improvement in power consumption over existing inductive sensing methods.