Detecting IC Reuse via Reflow-Exposure Fingerprints in Pre-Stressed Ring Oscillators

Abstract

This work presents an IC-reuse detection methodology based on temperature-exposure fingerprints extracted from pre-stressed ring-oscillator (RO)-based monitors. A set of RO monitors is pre-stressed under controlled conditions, storing a known degradation state. After enrollment, these monitors recover passively as a function of time and temperature. This recovery occurs even when the chip is unpowered, enabling detection of thermal events during off-state periods that conventional aging monitors cannot track. If the device undergoes a thermalexcursion event, e.g., due to a reflow-like soldering/desoldering process during PCB assembly, the pre-stressed monitors exhibit accelerated annealing, detectable during end-user readout. Onchip heaters subject the monitors to controlled thermal annealing, enabling the construction of a recovery model that discriminates between normal IC use and reflow-like thermal exposure. The approach is validated on a 28 nm HKMG RO-array chip using an autonomous PCB characterization platform. In a reflowemulation case study, the method recovers a thermal-exposure tuple of (202 °C, 102 s), matching the (200 °C, 100 s) profile.