Fast Characterization of Threshold Voltage Fluctuation in MOS Devices

Random microscopic fluctuations in the number and location of dopant atoms can cause a large variation in the threshold voltage (VT) of a MOS device. In this paper, we present a technique for fast characterization of random threshold voltage mismatch in MOS devices. Our VT scatter characterization method measures threshold voltage shift by monitoring the change in gate-to-source voltage VGS for a fixed drain current IDS and drain-to-source voltage VDS . We present circuit schematics to characterize VT scatter by measuring VGS variation for a large set of devices arranged in an individually addressable array. We report experimental results of VT scatter measurement from test chips fabricated in 65-nm silicon-on-insulator and 65-nm bulk CMOS processes. We also measure and report the magnitude of local device current mismatch caused by VT fluctuation.