US 2008/0175034 A1Published application

Ferroelectric memory and operating method of same

AssigneeFujitsu Limited

InventorsShingo Hagiwara, Yoshiaki Kaneko, Amane Inoue, Akihito Kumagai, Isao Fukushi

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Abstract

A nonvolatile decision memory unit stores decision data indicating whether data stored in the normal memory cells is true or false. An inversion control circuit sets the inverting signal to a valid level with a predetermined probability. A write circuit writes data having logic which is inverse logic of data to be rewritten to the normal memory cells and writes decision data indicating false to the decision memory unit when the inverting signal indicates a valid level. Since inverse data is rewritten at a predetermined frequency, an imprint is prevented when a read operation is executed repetitively. Moreover, since frequent repeating of reverse polarization of the ferroelectric capacitor due to a rewrite operation is prevented, deterioration of the ferroelectric capacitor due to reverse polarization is minimized. Thus, occurrence of the imprint and deterioration of characteristics in the ferroelectric capacitor is prevented, and the reliability of the ferroelectric memory is improved.

Claims16

Dependent claims

A ferroelectric memory, comprising:

a plurality of normal memory cells each having a ferroelectric capacitor and storing data written via an external terminal;
a nonvolatile decision memory unit storing decision data indicating whether data stored in said normal memory cells is true or false;
an operation control circuit controlling a write operation, a read operation, and a rewrite operation on said normal memory cells and said decision memory unit, the rewrite operation being executed in a latter half of the read operation;
an inversion control circuit outputting an inverting signal and setting the inverting signal to a valid level with a predetermined probability larger than 0 and smaller than 1 at least during said rewrite operation;
a write circuit writing, at least during said rewrite operation, data having logic which is an inverse of logic of data to be rewritten to said normal memory cells and writing decision data indicating false to said decision memory unit when said inverting signal indicates a valid level, and writing data having logic to be rewritten to said normal memory cells and writing decision data indicating true to said decision memory unit when said inverting signal does not indicate a valid level;
and
a data restoration circuit inverting and outputting, during a read operation, logic of data read from said normal memory cells when decision data indicating false is read from said decision memory unit, and outputting data read from said normal memory cells when decision data indicating true is read from said decision memory unit.

4 more elements

An operating method of a ferroelectric memory which comprises a plurality of normal memory cells each having a ferroelectric capacitor and storing data written via an external terminal and a nonvolatile decision memory unit storing decision data indicating whether data stored in said normal memory cells is true or false, the method comprising:

setting an inverting signal to a valid level with a predetermined probability larger than 0 and smaller than 1 at least during a rewrite operation executed in a latter half of a read operation;
writing, at least during said rewrite operation, data having logic which is an inverse of logic of data to be rewritten to said normal memory cells and writing decision data indicating false to said decision memory unit when said inverting signal indicates a valid level;
writing data having logic to be rewritten to said normal memory cells and writing decision data indicating true to said decision memory unit when said inverting signal does not indicate a valid level;
and
inverting and outputting, during a read operation, logic of data read from said normal memory cells when decision data indicating false is read from said decision memory unit, and outputting data read from said normal memory cells when decision data indicating true is read from said decision memory unit.

2 more elements

Dependencies are inferred from the claim text.