Patent ID: 7184336

Claim:
A method for evaluating threshold voltage distribution of memory cells, the method comprising: connecting all sources and drains of the memory cells in a memory array to a fixed voltage and providing a pulse to gates thereof; wherein a peak voltage of the pulse is a first gate voltage and a valley voltage of the pulse is a second gate voltage; measuring the charge pumping current characteristic of a single memory cell versus the first gate voltage when the second gate voltage is a fixed potential; measuring the charge pumping current characteristic of the memory cell versus the second gate voltage when the first gate voltage is a fixed potential; measuring the total charge pumping current characteristic of the memory array versus the first gate voltage when the second gate voltage is a fixed potential; measuring the total charge pumping current characteristic of the memory array versus the second gate voltage when the first gate voltage is a fixed potential; and comparing the charge pumping current characteristics of the memory cell and array versus the first and second gate voltage to determine a minimum and maximum threshold voltage of threshold voltage distribution of the memory cells; wherein the charge pumping current is a total substrate current of the memory array.