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Compensation of Mechanical Stress-Induced Drift of Bandgap References With On-Chip Stress Sensor

Today's smart sensor systems rely heavily on bandgap circuit techniques to achieve the required high accuracy. However, all presently known bandgap references show a notable lifetime drift of ~1 mV caused by instable mechanical stress in common plastic encapsulated packages. This paper proposes a versatile digital stress compensation scheme which works for arbitrary packages and silicon technologies. It uses a new mechanical stress sensor to measure the sum of in-plane normal stress components. The mechanical stress drifts of bandgap reference, stress, and temperature sensors were characterized on wafer stripes in a four-point bending fixture. With these results a compensation algorithm was derived. Mechanical stress drifts were provoked by thermal cycling measurements on samples in a quad flat no leads-like plastic encapsulated package after moisture soaking. These measurements show that the mechanical stress related drift of a Brokaw bandgap voltage can be reduced by about one order in magnitude over the whole automotive temperature range. Due to the low process spread of the proposed stress sensor only a single-trim at room temperature on wafer level is necessary.