Patent ID: 7236405
Filing Date: 2007-06-26
Classification: G11C

Abstract:
1. A method for setting erasing pulses by determining the number of or time for applications of the erasing pulses in a block erasing operation where a target block which consists a plurality of memory cells to be erased in a nonvolatile memory is erased by applying the erasing pulses a plurality of times for erasing its block data together, the method comprising, in the process of applying the erasing pulses the plurality of times: an extraction step of extracting at least two pairs (Np a first conversion step of converting the two ratios Re a second conversion step of converting the two accumulated numbers of the erasing pulses Np extracted in the extraction step into common logarithms Log(Np) respectively; an extrapolation step of calculating a common logarithm Log(Nt) through a point [Log(Nt), S(T)] including predetermined target normalized variables S(T) larger than the two normalized variables S(Re a third conversion step of converting the common logarithm Log(Nt) determined in the extrapolation step into an extrapolation erasing pulses number Nt; and a determination step of determining the number of or time for applications of the remaining erasing pulses so that the extrapolation erasing pulse number Nt determined in the third conversion step is a target accumulated number of applications of erasing pulses.