US 6,747,894 B2 · Nonvolatile multilevel cell memory

Abstract

First and second memory units store reference values and verification values for generating reference voltages and verification voltages of nonvolatile multilevel memory cells. A reference voltage generator generates the reference voltages and the verification voltages according to the reference values and the verification values stored in the first and second memory units. Since the first and second memory units are rewritable, the reference voltages and the verification voltages can be set after the fabrication of the cell memory in accordance with the characteristics of the memory cells which are dependent on variations of fabrication process. A programming test circuit for obtaining the reference voltages and the verification voltages can also be used to set the reference voltages and the verification voltages after the fabrication of the cell memory. Consequently, it is possible to improve the read margins of data read from the memory cells with an enhancement in fabrication yield.

Claims19

Dependent claims

A nonvolatile multilevel cell memory comprising:

electrically-rewritable nonvolatile multilevel memory cells;
a programming voltage generator for generating a plurality of programming voltages to change threshold voltage in each of said memory cells according to logic of write data;
a first memory unit for storing a plurality of reference values respectively corresponding to a plurality of reference voltages for judging the threshold voltages of said memory cells, at least one of said reference values being rewritable;
and
a reference voltage generator for generating said reference voltages, respectively, according to said reference values stored in said first memory unit, when reading data from said memory cells.

2 more elements

A nonvolatile multilevel cell memory comprising:

electrically-rewritable nonvolatile multilevel memory cells;
a programming voltage generator for generating a plurality of programming voltages to change threshold voltage in each of said memory cells according to logic of write data;
a reference voltage generator for generating a plurality of reference voltages for judging the threshold voltages of said memory cells when reading data from said memory cells;
a verification voltage generator for generating, when writing data to said memory cells, a plurality of verification voltages to verify that the threshold voltages of said memory cells exceed a value corresponding to said data;
and
a programming test circuit for operating in a test mode, for programming each of said memory cells according to the logic of said write data, and for obtaining at least one of said reference voltages and at least one of said verification voltages based on distributions of the threshold voltages of said memory cells programmed, wherein
said reference voltage generator generates at least one of said reference voltages according to a value obtained by said programming test circuit, and
said verification voltage generator generates at least one of said verification voltages according to a value obtained by said programming test circuit.

5 more elements

Dependencies are inferred from the claim text.

Nonvolatile multilevel cell memory

Life of this patent

Nonvolatile multilevel cell memory

Life of this patent

Abstract

Claims19