The patent badge is an abbreviated version of the USPTO patent document. The patent badge does contain a link to the full patent document.
The patent badge is an abbreviated version of the USPTO patent document. The patent badge covers the following: Patent number, Date patent was issued, Date patent was filed, Title of the patent, Applicant, Inventor, Assignee, Attorney firm, Primary examiner, Assistant examiner, CPCs, and Abstract. The patent badge does contain a link to the full patent document (in Adobe Acrobat format, aka pdf). To download or print any patent click here.
Patent No.:
Date of Patent:
Jun. 05, 2007
Filed:
Feb. 22, 2006
Tetsuji Takeguchi, Kawasaki, JP;
Tetsuji Takeguchi, Kawasaki, JP;
Fujitsu Limited, Kawasaki, JP;
Abstract
A nonvolatile semiconductor memory device includes a control circuit configured to perform a first block erase operation that erases nonvolatile memory cells together in a lump such that threshold voltages of the memory cells are set lower than a first erase verify voltage, to check whether a threshold voltage of each of the nonvolatile memory cells is lower than a first erase-degree-check voltage after the first block erase operation, to perform a first write-back operation in response to a check result indicating that the threshold voltage is lower than the first erase-degree-check voltage, thereby raising the threshold voltage above a voltage higher than the first erase-degree-check voltage, and to perform a second block erase operation that erases the nonvolatile memory cells together in a lump after the first write-back operation such that the threshold voltages of the memory cells are set lower than a second erase verify voltage.