JPH02199861A - Ferroelectric memory - Google Patents

Abstract

PURPOSE:To read out information nondestructively by a method wherein a temperature of a memory cell is raised at a readout operation and a change in a stored charge amount upon a reduction in a spontaneous polarization is read out. CONSTITUTION:This memory is constituted of the following: electrodes 14 and 18 which are composed of tungsten W; a ferroelectric capacitor 15; e.g. high-resistance polycrystalline Si 19 which pierces it vertically; wiring parts 12, 17 composed of the W. When information is read out, a potential difference is applied to the W wiring parts 12 and 17, an electric current is caused to flow to the polycrystalline Si 19, heat is generated and the ferroelectric capacitor is heated. At the heated ferroelectric, its spontaneous polarization DELTAP is reduced by DELTAP with reference to a changed amount DELTAT of a temperature. By this change DELTAP, a permittivity E is changed by DELTAepsilon and also a capacity is changed by DELTAC; accordingly, a capacity electrode potential is changed by a voltage value DELTAV. The changed amount DELTAP of the spontaneous polarization takes a positive value or a negative value according to a direction of a polarization vector; accordingly, the changed amount DELTAV of the capacity electrode potential at a readout operation takes a positive value or a negative value according to the direction of the polarization vector. Thereby, it is possible to nondestructively read out information stored in a form of the polarization vector.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a memory using ferroelectric material.

[Conventional technology]

Regarding conventional ferroelectric memory, eye, varnish, varnish,
C.C. 88 (1988) pp. 130-131
Page (ISSCG8g, 1988. p p, 130-1
31).

[Problem to be solved by the invention]

The conventional technology described above uses a DRAM type memory cell having the structure shown in FIG. 2, that is, a switching MOS transistor and a ferroelectric capacitor. In the case of this conventional memory cell, stored information stored in the form of polarization of a ferroelectric material is read out by the change in the amount of charge when the polarization is returned to its original state. That is, there is a problem in that the information is destroyed when reading the stored information.

An object of the present invention is to provide a memory cell from which stored information can be read out non-destructively.

[Means to solve the problem]

In order to achieve the above object, the present invention utilizes the temperature dependence of ferroelectric spontaneous polarization shown in FIG. 1(b). That is, a method is used in which the temperature of the memory cell is increased during reading, and the change in accumulated charge when the spontaneous polarization decreases is read out.

[Effect]

The present invention is composed of a ferroelectric capacitor and a heating element that penetrates through the capacitor. At the time of reading, a voltage is applied to the heating element to generate heat, thereby heating the strong Mttt body capacitor. Spontaneous polarization of the heated ferroelectric substance decreases, and the capacitor electrode potential changes as the capacitance decreases.

That is, the capacitor potential V is given by equation (1).

V=Q/C...(1) (Here, Q is the M product charge, and C is the capacitance value of the ferroelectric capacitor) Is the value of this ■ strong? It changes as shown in equation (2) due to the decrease ΔC in the dielectric constant due to the decrease in the spontaneous polarization of the R-heavy body.

ΔV=−−ΔC...(2) Here, Δ■ is the amount of change in the capacitor potential.

Since the sign of ΔV is positive or negative depending on the direction of the polarization vector of the ferroelectric material, the direction of the polarization vector can be measured by the change in the sign of the capacitor potential during heating.

Using this method, the direction of the polarization vector can be read out without changing the direction.

That is, non-destructive reading can be achieved.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG.

FIG. 1(a) shows electrodes 14 and 18 using tungsten (W) and, for example, Pb(Zrz-xTit-x)O
A ferroelectric capacitor using a ferroelectric material 15 such as S, and a ferroelectric memory configured with wiring 12° 17 made of, for example, high-resistance polycrystalline Si 19 and its W, which pass through this capacitor up and down. When writing information as shown in FIG. 1, a potential difference is applied between the W wiring (It poles) 14 and 18, and the ferroelectric material 15 sandwiched between the two electrodes is polarized in a desired direction.

At the time of reading, a potential difference is applied between the 5W wirings 12 and 17 to cause current to flow through the polycrystalline 5i 19 to generate heat and heat the ferroelectric capacitor.

As shown in FIG. 1(b), the heated ferroelectric material has a spontaneous component wp which decreases by ΔP with respect to a temperature change amount Δ1.

The dielectric constant C of the ferroelectric capacitor is the dielectric constant ε0 in vacuum.
, spontaneous polarization P, and it field E, it is expressed as follows.

This dielectric constant changes by Δε shown in the following equation due to a spontaneous polarization change ΔP accompanying a temperature change ΔT.

ΔP Δε=□ ・・・(
4) If the S electric rate is carbonized by 8, the capacitance also changes by ΔC as shown in equation (5, 2), so the voltage shown in equation (6).

The capacitor electrode potential changes by the value ΔV.

C=t-8/T-(
5,1)ΔC=Δε・S/T
(5, 2) ΔV=−−ΔC (6) where C is the capacitance s of the ferroelectric capacitor, and T is the area of the capacitor and the thickness of the ferroelectric, respectively.

Since the amount of change ΔP in spontaneous polarization takes a positive or negative value depending on the direction of the polarization vector, the amount of change Δ■ in the capacitor electrode potential during readout takes a positive or negative value depending on the direction of the polarization vector. . Therefore, the direction of polarization can be known.

As described above, by using the present invention, the direction of the polarization vector of a ferroelectric material, that is, the information stored in the form of the polarization vector can be read out in a non-destructive manner.

FIG. 3 is an embodiment showing a method of manufacturing the ferroelectric memory of the first embodiment.

A wiring 12 made of W or the like and having a thickness of 500 nm, for example, is formed on an insulating film 11 of 5iOz or the like (a).

On top of that, an insulating film 13 of 5iOz or the like is formed by chemical vapor deposition (C
VD) etc. to a thickness of about 500 nm (
b).

Furthermore, an electrode 14 made of, for example, W and having a thickness of about 500 nm and also serving as wiring is formed (C).

Then a ferroelectric material, e.g. B a T x OJl
tP b (Z rx-xT i z-x) On,
KNOa, N a NOx.

SbS I,C(NHz)An(SOa)zl 2Hz
O.

(N HzCHzC○OH)s・His Oa, (N
Ha)zs 041(NHz)zcSe Cazs r
(CzHsCOOH)a etc. is deposited by sputtering method to form capacitor insulation modification 15 to a thickness of about 20 nm to 1 μm (d).The above film thickness may not exhibit dew dielectric properties if fermented too much. Therefore, about 20 nm is considered to be the limit for thinning the film. 1. Form an electrode 18 made of, for example, W, with a thickness of about 500 nm, which also serves as wiring, on the ferroelectric film 15. (e) 1. Next, by CVD method or the like, Thickness 50
An insulating film 16 of about 0 nm, for example 5 iOz, is formed (f).

Next, 5iOz16, W2B, dielectric 15°W 14,
After forming the S i Ox 131C hole 31 (g),
An insulating film 111 of 5 iOz or the like is deposited on the entire surface using, for example, chemical vapor deposition, and an insulating layer 111 is formed on the side wall of the hole 31 by anisotropic dry etching. Form a wiring 17 using, for example, W with a thickness of 500 nm (j) 1 filled with a high-resistance polycrystal 5i19 (
j).

In this embodiment, 5 iOz was used as the insulating film, but there is no problem in using other insulating films as long as there are no problems with insulation or manufacturing. Furthermore, in this embodiment, W is used as the wiring and electrode material, but AQ.

Mo, (:u, pt, Au, Ag, Ti, TiN.

Of course, various low resistance materials such as WS it, Mo S it, superconducting wiring material, etc. can be used.

FIGS. 4(a) and 4(b) show a planar layout of a memory cell according to an embodiment of the present invention. Reference numeral 41 indicates two wiring layers, which are vertically overlapped.

The lower wiring 41 is the first wiring for feeding power to the heating element, and the upper wiring 41 is the upper pole wiring of the ferroelectric capacitor. 42 also has two wiring layers stacked one above the other. The lower wiring 42 serves as the lower electrode of the ferroelectric capacitor, and the upper wiring 42 serves as a second wiring for feeding power to the heating element. 43 is a hole formed between the first wiring layer for power feeding and the second wiring layer for power feeding;
The cross-sectional structure of the figure has the same structure as that of FIG.

Since one memory cell can be formed at each intersection of vertically and horizontally formed wiring, a highly integrated memory with a simple layout can be manufactured.

〔Effect of the invention〕

According to the present invention, stored information can be read out non-destructively and a highly integrated memory can be provided.

[Brief explanation of the drawing]

FIG. 1(a) is a sectional view of one embodiment of the invention, FIG. 1(b)
is a characteristic diagram showing the relationship between spontaneous polarization and temperature of a ferroelectric material, the second
The figure shows a circuit diagram of a conventional memory cell using a ferroelectric material, FIGS. ) and (b) are plan layout diagrams of a memory cell according to an embodiment of the present invention. 11-8iO2, 12-W, 13-8iOx, 14-W
, 15-P b (Z rl-xT i t-x)O
a, 16...5iOz, 17...W118...W
, 19... Polycrystalline Si, 111... 5iOz, 21
... Switching MOS transistor, 22... Ferroelectric capacitor, 23... Bit line, 24... Word line, 25... Pulse type common plate, 31...
Hole, 41...1st. 3rd wiring layer, 42... 2nd. Fourth wiring layer, 43...buried polycrystalline Si for resistance. 〃 1 Diagram (it) rOz //1 S゛θ2 Ding G Rinku Ayu Akira Diagram Page Diagram Abusive Diagram

Claims (1)

[Claims] 1. A ferroelectric capacitor constituted by two intersecting electrodes and a ferroelectric material formed between them, and an insulating periphery extending approximately perpendicularly through the center of the ferroelectric capacitor. A ferroelectric memory characterized by having a conductive material. 2. The ferroelectric memory according to claim 1, further comprising at least one wiring for supplying voltage to the conductor above and below the ferroelectric capacitor. 3. The ferroelectric memory according to claim 2, wherein the upper and lower wirings for supplying voltage to the conductor cross each other. 4. The method is characterized by changing the absolute value |P| of the spontaneous polarization of the ferroelectric material by heating the ferroelectric capacitor, and examining the polarity of the polarization by measuring the polarity P/|P| at that time. How to read ferroelectric memory.