A new technique and a test structure for evaluating Vth distribution of flash memory cells

A new technique for evaluating Vth distribution in a large flash memory array using a simple test structure were studied. This new test technique can evaluate the Vth distribution by measuring I-V characteristics of all cells in an array which has no peripheral circuits. This technique identify the lowest Vth from the subthreshold characteristic and the median Vth from the linear characteristic of the array. A new test structure was designed for this technique and it can be put on the scribe line.