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Nonvolatile semiconductor memory and read method

  • US 6,222,763 B1
  • Filed: 02/03/2000
  • Issued: 04/24/2001
  • Est. Priority Date: 12/20/1996
  • Status: Expired due to Term
First Claim
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1. A nonvolatile semiconductor memory device comprising:

  • a plurality of data lines;

    a plurality of source lines;

    a plurality of memory cells each of which has a threshold voltage corresponding to data of at least two bits, and each of which is coupled to a corresponding data line of said plurality of data lines and which is coupled to a corresponding source line of said plurality of source lines;

    wherein each of said plurality of memory cells is programmed with data by using a tunnel effect in a program mode, and wherein a threshold voltage of each of said plurality of memory cells is distributed in one of at least four threshold voltage distributions; and

    a word driver circuit applying a read voltage to one or more selected memory cells a plurality of times in a read mode, wherein said read voltage has at least three voltage levels, wherein, in said read mode, each of source lines coupled to said selected memory cells is coupled so as to be applied with a predetermined potential; and

    wherein a first read voltage is first applied to said selected memory cells, and then at least two other read voltages at levels higher than said first read voltage are successively applied to said selected memory cells in order to successively read data starting with data corresponding to a lowest threshold voltage distribution and ending with data corresponding to a highest threshold voltage distribution.

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