Patent ID: 7515467

Claim:
A method of storing data in a memory cell having a first charge trap and a second charge trap, each of the first and second charge traps being operable to store data with at least three possible values, the method comprising the steps of: (a) programming the first charge trap by using a first programming voltage; (b) reading the first charge trap to obtain a first read current and deciding whether the first read current has been reduced to or below a first value, corresponding to data to be stored in the first charge trap; (c) programming the second charge trap by using a second programming voltage lower than the first programming voltage; (d) reading the second charge trap to obtain a second read current and deciding whether the second read current has been reduced to or below a second value, corresponding to data to be stored in the second charge trap, the second value being higher than the first value; (e) repeating said steps (a), (b), (c), and (d) until an affirmative decision is obtained in at least one of said steps (b) and (d); (f) if an affirmative decision is obtained in said step (b) while a negative decision is still obtained in said step (d), repeating said steps (c) and (d) until an affirmative decision is obtained in said step (d); and (g) if an affirmative decision is obtained in said step (d) while a negative decision is still obtained in said step (b), repeating said steps (a) and (b) until an affirmative decision is obtained in said step (b).