JP2854166B2 - Ferroelectric memory - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ferroelectric memory using a ferroelectric capacitor.

[0002]

2. Description of the Related Art In recent years, a ferroelectric capacitor used as a memory to hold a binary charge has been used.

[0003]

However, in this type of conventional ferroelectric memory, a single ferroelectric capacitor can hold a binary charge amount. Requires a plurality of ferroelectric capacitors corresponding to the number.

[0004]

According to the present invention, apparently, a large number of electrodes are provided on the front surface and the back surface of one ferroelectric, respectively, and one electrode is selectively selected from the electrodes on the front surface and the back surface, respectively. And using it as a ferroelectric memory, it is possible to hold a selectively selected number of charges.

For example, as a ferroelectric memory of the present invention, two electrodes A,
B, C, and D are provided adjacent to each other, and one electrode is selected on each of the front surface and the back surface from among the electrodes.
If each of D, BC, and BD can be specified one by one, three or more different polarization states can be obtained according to the electrode positions AC, AD, BC, and BD.

[0006]

According to the ferroelectric memory of the present invention having the above-described structure, a single ferroelectric capacitor can hold a plurality of charges, so that a plurality of values can be stored with a simple structure. A ferroelectric memory can be provided as a memory element.

Therefore, the amount of information per unit cell can be increased to three values or more. For example,
The information amount per unit cell increases from two values to four or more values, and the information amount per unit area can be dramatically increased without changing the cell area.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram showing an embodiment of the ferroelectric memory of the present invention, and FIG. 2 is a characteristic diagram of electric field versus polarization in the circuit diagram of FIG.

A ferroelectric capacitor 50 shown in FIG. 1 has a plurality of electrodes 6 adjacent to the front and back surfaces of one ferroelectric material, respectively.
1, 62, 63, 64, and the electrodes 62,
64 is connected to the reference potential lines 30 and 31, while the FETs 40 and 41 are connected to the electrodes 61 and 63 on the surface, respectively.
The reference potential lines 30, 31 are at a normal reference potential and are preferably grounded, but the lines 30, 31 can carry non-zero voltage pulses applied thereto. The electrodes 61 and 63 on the surface of the capacitor 50 are coupled to the bit lines 20 and 21 via the sources and drains of the field effect transistors (FETs) 40 and 41.

The FETs 40 and 41 of FIG. 1 are N-channel devices, so that the drain electrodes D of the FETs 40 and 41 are coupled to the bit lines 20 and 21, whereas the source electrode S of the FET 26 is the surface electrode 61 of the capacitor 50. , 63. The gate electrode G is coupled to a separately controlled word line 10. In the present invention, it is not always necessary to use an N-channel FET, and other switching devices can be used.

In the ferroelectric memory 50 shown in FIG.
In FIG. 2, the electric field-polarization characteristic when using the electrode 62 is a curve passing C = P (0) in the case of BD, and when using the electrodes 63 and 64, E = P (1) in the DB of FIG. When electrodes 61 and 64 are used, G = FH in FIG.
When the electrodes 63 and 62 are used, the curve passes through I = P (3) when the electrodes 63 and 62 are used.

Therefore, the FETs 40 and 41 are turned ON, O
FF and set of electrodes 61, 62; 63, 64; 61, 6
4, 63, 62; P (0), P (2), P (3), P (1)
Can be obtained.

As described in detail in the above embodiment, in the ferroelectric memory of the present invention, an appropriate pulse electric field is applied to each electrode of one ferroelectric material provided with a plurality of adjacent electrodes. As a result, two or more polarization inversion states are generated for one ferroelectric substance, and thereby, the storage capacity per cell can be increased.

[0014]

By using one ferroelectric substance, the characteristics of each portion sandwiched between the electrodes can be made substantially the same. For example, when the same voltage is applied, the same polarization state is applied to each portion. And the control of the write operation and the read operation of the memory can be easily performed. Further, since there is no need to manufacture a plurality of ferroelectrics, the manufacturing process can be simplified. Further, three or more different polarization states are possible as a whole in the polarization state of each part of one ferroelectric substance, so that a memory can be configured with a compact cell area, and furthermore, memory control by multi-valued memory. Also becomes possible.

[Brief description of the drawings]

FIG. 1 is an electric circuit diagram showing one embodiment of a ferroelectric memory of the present invention.

FIG. 2 is a characteristic diagram of electric field and polarization in the electric circuit diagram of FIG.

[Explanation of symbols]

 10 WL 20 BL 21 BL 30 DL Reference potential line 31 DL Reference potential line 40 FET 41 FET 50 Ferroelectric 61 Top electrode 62 Back electrode 63 Front electrode 64 Back electrode

Claims (1)

(57) [Claims] 1. A first ferroelectric material comprising: one ferroelectric; and at least two electrodes provided on one surface of the ferroelectric.
An electrode group, a second electrode group including at least two electrodes provided on the other surface side of the ferroelectric so as to face the first electrode group, and an electrode selected from the first electrode group. Means for applying a voltage to an electrode selected from the second electrode group to cause the ferroelectric to generate three or more different polarization states.