Patent ID: 11972818
Assignee: SANDISK TECHNOLOGIES, INC.
Field: Computer technology (Electrical engineering)
Classification: CPC G | IPC G

Claim 1:
2. The memory apparatus as set forth in claim 1, wherein the memory cells are operable in one of a first read condition in which a word line voltage of the plurality of word lines is discharged and a second read condition in which the word line voltage of the plurality of word lines is coupled up to a residual voltage level, and the control means is further configured to, in the verify level trimming process:
program the memory cells connected to a sample group of the plurality of word lines in at least one sample block;
apply a predetermined refresh read voltage to the selected ones of the plurality of word lines in the at least one sample block for a predetermined period of time at predetermined intervals of time to maintain the memory cells in the second read condition during a refresh read operation;
read the memory cells connected to the sample group of the plurality of word lines in the at least one sample block after a predetermined sample test time and count the quantities of the memory cells having threshold voltages crossing over between the plurality of data states;
determine each of a plurality of measured failure bit count percentages for the memory cells of the at least one sample block equal to each of the quantities of the memory cells having the threshold voltage crossing over between two adjacent ones of the plurality of data states in each of the plurality of crossovers divided by a total failure bit count for all of the memory cells of the at least one sample block;
compare the plurality of measured failure bit count percentages to a plurality of predetermined optimum failure bit count percentages each corresponding with one of the plurality of crossovers; and
select the program verify voltages based on the comparison of the plurality of measured failure bit count percentages to the plurality of predetermined optimum failure bit count percentages.