JP2692646B2 - Capacitor using bismuth-based layered ferroelectric and its manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a capacitor using a bismuth-based layered ferroelectric substance and a manufacturing method thereof.

[0002]

2. Description of the Related Art A bismuth-based layered ferroelectric substance has a structure in which a pseudo-perovskite structure is sandwiched between bismuth oxide layers, and is a material expected to be applied to a nonvolatile memory. Its ferroelectricity is B of the pseudo-perovskite part sandwiched between bismuth oxide layers.
Although it originates from the displacement of site ions, it is known that the anisotropy with respect to the crystal axis is strong, and the ferroelectricity in the a-axis direction is larger than that in the c-axis direction.

Conventionally, as a capacitor structure using such a material, for example, International Patent W
O 93/12542 (International
Patent Publication Number
Some of them are also shown in WO 93/12542). The basic structure thereof was a structure in which a ferroelectric thin film 2 was laminated on an insulating substrate 3 with an upper electrode 5 and a lower electrode 6 sandwiched therebetween, as shown in FIG.

[0004]

In the bismuth layered ferroelectric substance, the remanent polarization has anisotropy with respect to the crystal axis, and the maximum remanent polarization is obtained in the a-axis direction, and the remanent polarization in the c-axis direction is very small. I know that. However, when thinning this material, a c-axis oriented film is easily obtained by a conventional growth method such as a physical vapor deposition (PVD) method such as a sputtering method or an evaporation method or a chemical vapor deposition (CVD) method. It was difficult to align the maximum polarization axis direction with the direction perpendicular to the substrate surface. Therefore, the conventional element structure, which is a structure in which an electric field is applied in the direction perpendicular to the substrate surface, cannot effectively utilize remanent polarization,
There is a problem that it is difficult to miniaturize the element and reduce the voltage.

Further, in general, when forming a bismuth layered ferroelectric thin film, a high temperature of 700 C or higher is required and the film is exposed to an oxidizing atmosphere. Therefore, in the laminated structure of the lower electrode, the ferroelectric and the upper electrode, the ferroelectric film is formed. At times, a reaction between the lower electrode and the ferroelectric substance and a conduction failure due to oxidation of the lower electrode occurred, making it difficult to manufacture an element having good characteristics.

An object of the present invention is to provide a structure and manufacturing method of a capacitor which eliminates the above-mentioned conventional drawbacks.

[0007]

The present invention relates to a capacitor having a c-axis oriented bismuth-based layered ferroelectric substance and an electrode on an insulating substrate, and at least a part of the ferroelectric substance in a direction parallel to the substrate surface. A pair of electrodes including a first electrode and a second electrode for generating an electric field are provided in contact with the ferroelectric substance. At this time, the electrode is c
It is preferable that the axially oriented bismuth-based layered ferroelectric substance is provided at a position where the maximum electric field is applied in the maximum polarization direction, because the voltage can be further lowered.

The method of manufacturing a bismuth-based layered ferroelectric capacitor according to the present invention comprises a first step of forming and patterning a c-axis oriented bismuth-based layered ferroelectric on a substrate, and a pair of the ferroelectrics. And a second step of forming the electrode. Here, if the maximum polarization direction of the ferroelectric substance is detected after forming the ferroelectric substance or after patterning, a pair of electrodes capable of applying an electric field in the detected maximum polarization direction is patterned. It can also be formed on the ferroelectric surface.

[0009]

FIG. 1 shows a capacitor structure according to the present invention. By applying an electric field parallel to the substrate surface to the c-axis oriented bismuth layered ferroelectric on the insulating substrate using a pair of electrodes, the residual in the a-axis direction limited in the plane parallel to the substrate surface. The polarization can be effectively used. That is, the required charges can be obtained with a small electrode area, so that the element can be miniaturized. Further, by manufacturing the electrode after forming the ferroelectric film, the reaction between the ferroelectric film and the electrode and the oxidation of the electrode at high temperature can be suppressed, and the reliability of the element can be improved. Furthermore, when the maximum polarization axis direction is aligned mainly in one direction in the plane parallel to the substrate surface, the effective charge density is further increased, so that the polarization reversal of the capacitor can be performed with a smaller electric field and the voltage can be further lowered. Is possible.

[0010]

【Example】

(Example 1) Bismuth tantalate strontate (SrBi ₂ Ta ₂ O ₉ , hereinafter referred to as SBT) was used as the bismuth layered ferroelectric, a surface-oxidized silicon substrate was used as the insulating substrate, and W was used as the electrode material. FIG. 2 shows an embodiment in which RF magnetron sputtering is used as the film method. The capacitor manufacturing procedure was as follows.
When a 1 μm-thick SBT was produced on the surface-oxidized silicon substrate by the RF magnetron sputtering method, a c-axis oriented SBT thin film was formed at a substrate temperature of 700 C or higher. Then, apply this SBT thin film to the bottom surface of 0.5 μm × 5 μm,
After etching to a convex structure having a height of 1 μm, W was deposited to a thickness of 0.3 μm by the CVD method. After that, W was removed by etching, leaving 1 μm × 5 μm side surface of the SBT convex structure and a lead electrode connected thereto. At this time 1 μm
The two extraction electrodes on the surface of × 5 μm are connected to the extraction electrodes from the same side surface of the other element, and have a structure in which a plurality of capacitors are connected in parallel. The hysteresis characteristics obtained with the capacitor having this structure are shown in FIG.
For comparison, the characteristics of the conventional structure in which the ferroelectric substance is sandwiched between the upper and lower Pt electrodes are also shown. When electrodes are stacked on the top and bottom (dashed line), the remanent polarization value is 1.4 μC / cm ²
However, when an electric field parallel to the substrate was applied (solid line), it was 10.5 μC / cm ² , and the remanent polarization value was remarkably increased, showing that the device density can be increased. .

Example 2 Bismuth strontium niobate (SrBi ₂ Nb ₂ ) as a bismuth layered ferroelectric substance
O ₉ , hereafter SBN, or bismuth titanate (Bi ₄
Ti ₃ O ₁₂ , hereinafter referred to as BIT), a surface-treated silicon substrate as an insulating substrate, W as an electrode material, and RF magnetron sputtering as a film forming method are shown. The procedure for manufacturing the capacitor is the same as that in the first embodiment. Table 1 shows the ferroelectric characteristics obtained with the capacitor having this structure.
Although the absolute value of the remanent polarization is small, the remanent polarization value increased when an electric field parallel to the substrate was applied as in the case of the SBT film, and it was shown that the device density can be increased.

[0012]

[Table 1]

(Embodiment 3) Using the MgO single crystal (100) plane as an insulating substrate, the SBT was carried out in the same manner as in Embodiment 1.
Was deposited to form a capacitor structure similar to that of Example 1. In this case, since the SBT thin film was epitaxially grown on the MgO substrate, the polarization directions were aligned even in the plane parallel to the substrate. To determine the direction of applying the electric field, SB
A dot-shaped electrode group as shown in FIG. 4 was prepared on the surface of the T film, and the residual polarization between the electrodes A and the electrodes B to F was measured by the two-terminal method. An example of the measurement result is shown in FIG. In this case, it was found that the polarization value between the electrodes A and D was the largest and this direction was the maximum polarization axis direction. According to this result, the electrodes were formed so that the voltage was applied in parallel with the directions of the electrodes A-D. FIG. 6 shows the hysteresis characteristic of polarization obtained by the capacitor having this structure. For comparison, the characteristics of the same sample having Pt electrodes formed on the upper and lower portions are shown. When the upper and lower electrodes are stacked (dashed line), almost no hysteresis characteristics are shown, whereas when an electric field parallel to the substrate is applied (solid line), it becomes 13.7 μC / cm ^{2 and the} remanent polarization value increases significantly. I was seen. The remanent polarization value was increased by 30% and the coercive electric field was decreased by 22% as compared with the case where an electric field parallel to the substrate of Example 1 was applied, showing that the device can be made higher in density and lower in voltage. Was done.

The materials used in the above-mentioned examples are two or three.
The present invention is not limited to the materials described in the above embodiments, and can be applied to all materials of c-axis oriented ferroelectric substance whose maximum polarization direction does not match the c-axis. .

[0015]

By using the device structure according to the present invention, it is possible to effectively utilize the remanent polarization of the bismuth layered ferroelectric substance, and as a result, it is possible to increase the device density and reduce the driving voltage. Further, the conduction failure of the lower electrode is reduced, and high reliability can be realized.

[Brief description of the drawings]

FIG. 1 is a diagram showing a capacitor structure according to the present invention.

FIG. 2 is a diagram showing a manufactured capacitor element structure.

FIG. 3 is a diagram showing a hysteresis characteristic of a manufactured capacitor element.

FIG. 4 is a diagram showing a dot-shaped electrode group for determining an electric field application direction.

FIG. 5 is a diagram showing a remanent polarization value between dot-shaped electrodes.

FIG. 6 is a diagram showing a hysteresis characteristic of a capacitor element when a single crystal substrate is used as an insulating substrate.

FIG. 7 is a view showing a conventional thin film capacitor structure.

[Explanation of symbols]

 1 Electrode 2 Bismuth Layered Ferroelectric 3 Insulating Substrate 4 Extraction Electrode 5 Upper Electrode 6 Lower Electrode 7 Dot-shaped Electrode

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location H01L 21/8247 H01L 29/78 371 27/10 451 27/108 29/788 29/792

Claims (4)

(57) [Claims] 1. A capacitor having a c-axis oriented bismuth-based layered ferroelectric substance and an electrode on an insulating substrate, wherein first and first electric fields are generated in at least a part of the ferroelectric substance in a direction parallel to the substrate surface. A capacitor using a bismuth layered ferroelectric, wherein a pair of electrodes composed of two electrodes are provided in contact with the ferroelectric. 2. The bismuth-based layered structure according to claim 1, wherein the pair of electrodes are provided at positions where a maximum electric field is applied in the maximum polarization direction of the c-axis oriented bismuth-based layered ferroelectric substance. Capacitor using ferroelectric material. 3. A first step of forming and patterning a c-axis oriented bismuth-based layered ferroelectric substance on a substrate, and a second step of forming a pair of electrodes on the ferroelectric substance. A method of manufacturing a capacitor using a characteristic bismuth-based layered ferroelectric substance. 4. A ferroelectric material is formed, or after patterning, a maximum polarization direction of the ferroelectric material is detected, and a pair of electrodes capable of applying an electric field in the detected maximum polarization direction is patterned. The method of manufacturing a capacitor using a bismuth-based layered ferroelectric according to claim 3, wherein the capacitor is formed on the surface of the ferroelectric.