A technique for measuring threshold mismatch in DRAM sense amplifier devices

The magnitude of the threshold difference between cross-coupled FET pairs of a DRAM (dynamic random-access memory) sense amplifier directly detracts from the amount of signal developed. A static testing technique is described that quickly and accurately measures the threshold difference between every N-channel device pair in an entire sense amplifier bank on an array-like test structure. The static measurement results are correlated with a dynamic sense amplifier signal margin test. High volume data provided by the technique are useful for characterizing and correcting process- or mas-induced threshold mismatch, in order to maximize signal margin and minimize retention-time losses in VLSI DRAMs.<
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