Accurate characterization of random process variations using a robust low-voltage high-sensitivity sensor featuring replica-bias circuit

Abstract

Accurate and fast measurement and characterization of random threshold voltage (Vth) fluctuations is crucial in process optimization and yield learning, particularly for matching critical transistors such as SRAMs, sense amplifiers, differential amplifiers, etc. Traditional methods in which multiplexed devices under test (DUTs) are characterized using accurate current measurements require extensive data analysis [1–3]. A sense-amplifier based measurement method presented in [4] provides limited statistical data since it can measure the mismatch between only two devices. Recently, a digital array based technique is proposed in [5] with limited sensitivity. Finally, a sub-threshold technique presented in [6] provides high sensitivity but lacks on-chip calibration. This paper presents a low voltage, high sensitivity random process variations sensor utilizing an on-chip calibration circuit for improved accuracy. Moreover, the proposed sensor features a replica bias circuit which compensates global process-voltage-temperature (PVT) variations and maintains sensitivity for robust operation.