Semiconductor memory device having a supplemental element...

Details Semiconductor memory device having a supplemental element... Semiconductor memory device having a supplemental element...

2001-09-13

2003-04-08

Tran, M. (Department: 2818)

Static information storage and retrieval

Systems using particular element

Ferroelectric

C365S149000

Reexamination Certificate

active

06545901

ABSTRACT:

CROSS-REFERENCE TO RELATED APPLICATION
The entire disclosure of Japanese patent application No. 2000-280510 filed on Sep. 14, 2000 including specification, claims, drawings, and summary are incorporated herein by reference in its entirety.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to semiconductor memory devices, in particular to a technique for accurately reading data from semiconductor memory devices.
2. Description of the Prior Art
Destruction type ferroelectric memories are known as the nonvolatile random access memory.
FIG. 13
schematically shows part of the circuit constitution of a kind of conventional destruction type ferroelectric memory, a ferroelectric memory
2
of the
1
T
1
C (one-transistor one-capacitor).
The ferroelectric memory
2
comprises a ferroelectric capacitor
4
and a loading capacitor
6
. The ferroelectric capacitor
4
has stored data of “1” or “0” in nonvolatile manner corresponding to the difference in residual polarization arising from hysteresis characteristic of the ferroelectric.
When reading data, a reading-purpose voltage is applied to the plate line PL to detect a voltage Vb
1
produced on the bit line BL. The value of the voltage Vb
1
varies with the value of the residual polarization of the ferroelectric capacitor
4
.
Therefore, whether the data stored in the ferroelectric capacitor
4
has been “1” or “0” can be found by judging whether the voltage Vb
1
is higher or lower than a reference voltage Vref.
Nonvolatile random access memories may be fabricated easily as described above using the destructive type ferroelectric memory.
However, the conventional destructive type ferroelectric memory has the following problems: When data are read from the destructive type ferroelectric memory, data are destroyed and so the data must be written again.
After repeated accesses to the ferroelectric capacitor
4
causes the hysteresis characteristic of the ferroelectric capacitor
4
to deteriorate and the difference in the residual polarization values becomes small between when the data is 1 and when the data is 0. When the difference between the residual polarization values becomes small, difference becomes also small between the voltage Vb
1
produced in the bit line and the reference voltage Vref when a data is read, and so it becomes difficult to judge whether or not the voltage Vb
1
is greater than the reference voltage Vref.
When data contents are held unchanged for a long period of time, distortion occurs in the hysteresis characteristic of the ferroelectric capacitor
4
due to so-called imprint effect and so it is also difficult to judge whether or not the voltage Vb
1
is greater than the reference voltage Vref.
When it becomes difficult to determine whether or not the voltage Vb
1
is greater than the reference voltage Vref as described above, data cannot be read accurately.
SUMMARY OF THE INVENTION
A semiconductor memory device according to the present invention includes:
a memory capacitor for storing information; and
a loading capacitor connected substantially in series with the memory capacitor at least at the time of reading data, to read data that have been stored in the memory capacitor according to the voltage produced at a connection point between the memory capacitor and the loading capacitor due to a reading voltage applied to both ends of the compound capacitor including the memory capacitor and the loading capacitor interconnected substantially in series, characterized in that the capacity of the loading capacitor is arranged to be variable based on a capacitance changing signal so that data are read free from troubles.
A semiconductor memory device according to the present invention includes:
a memory element for storing data; and
a supplemental element substantially electrically associated with the memory element at least at the time of reading data,
to read data stored in the memory element by applying specified electric action to a compound element including the memory element and the supplemental element substantially electrically mutually associated, characterized in that an electric characteristic of the supplemental element is adapted to be variable based on a signal for changing the electric characteristic of the supplemental element so that data are read without any trouble.


REFERENCES:
patent: 6067265 (2000-05-01), Mukumoki et al.
patent: 6094369 (2000-07-01), Ozawa et al.
patent: 6363002 (2002-03-01), Nishimura et al.

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