JPH11236220A - Ferroelectric thin film and thin film element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To significantly improve the insulation resistance and residual polarization of a ferroelectric thin film so that it can be suitably used for a ferroelectric nonvolatile memory element or the like by adding a niobium element to Bi4 Ti3 O12 which constitutes the thin film. SOLUTION: Niobium element is added to a ferroelectric thin film comprising Bi4 Ti3 O12 . The added amt. of the niobium element is 0.2 to 2.5 mol.%, preferably 0.2 to 2.0 mol.%. This ferroelectric thin film can be formed, for example, on a single crystal semiconductor substrate. A ferroelectric element is formed by using this ferroelectric thin film. The ferroelectric thin film can be formed by a sputtering method, laser ablation method, sol-gel method, CVD method or the like on a substrate such as glass, magnesium oxide, or single crystal semiconductor substrate such as silicon and gallium arsenide. For example, Bi2 O3 , TiO2 and NbO5 are mixed in a specified ratio, pulverized and sintered to obtain a sintered body, which is then used as a target for sputtering.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ferroelectric thin film and a ferroelectric thin film device using the same, and is particularly suitable for use in a ferroelectric nonvolatile memory device.

[0002]

2. Description of the Related Art Ferroelectric crystals are self-polarizing, have a high dielectric constant,
It has various functions such as a pyroelectric effect and an electro-optical effect, and is used for various devices. In recent years, with the possibility of forming a high-quality ferroelectric thin film, application to DRAM capacitors and development of non-volatile memories using the ferroelectric properties of the ferroelectric capacitors have been performed. ing. Among the many ferroelectric materials, Pb having a perovskite structure _{(Zr 1-x Ti x)} O 3 (PZT), Bi 4
Ti ₃ O ₁₂ and SrBi ₂ Ta ₂ O ₉ (SBT) have been studied.

[0003]

Among the above-mentioned ferroelectric materials, Bi ₄ Ti ₃ O ₁₂ has a ferroelectric property with two kinds of metal elements, Bi and Ti, as compared with other PZT and SBT. Spontaneous polarization Pr = 50 μC / cm ² in a-axis direction, coercive electric field Ec = 50 kV / cm, Pr = 4 μC / cm in c-axis direction
cm ² and a coercive electric field of 4 kV / cm, which are excellent (SE.
Cumminsand L. E. FIG. Cross: J. Ap
pl. Phys. vol. 39 (1968) 226
8) There is a problem that the insulation resistance is lower than that of PZT and SBT.

In view of such circumstances, an object of the present invention is to provide a Bi ₄ Ti ₃ O ₁₂ based ferroelectric thin film having an improved insulation resistance and a ferroelectric thin film element using the same.

[0005]

As a result of various studies to solve the above problems, the low insulation resistance of Bi ₄ Ti ₃ O ₁₂ is due to the low insulation resistance of the material itself and the low Bi resistance. It has been found that the formation of a semiconductor by evaporation and the disorder of the surface morphology due to the Bi layer structure can be improved by adding a niobium element, and the charge compensation and the suppression of grain growth due to the evaporation of Bi occur. The present invention has been completed.

The present invention is directed to a ferroelectric thin film characterized in that a niobium element is added to Bi ₄ Ti ₃ O ₁₂ .

Here, the addition amount of the niobium element is, for example,
It is in the range of 0.2 to 2.5, preferably 0.5 to 2.0 mol%.

Further, the ferroelectric thin film can be formed, for example, on a single crystal semiconductor substrate.

Further, a ferroelectric thin film element can be formed by using a ferroelectric thin film formed by adding a niobium element to Bi ₄ Ti ₃ O ₁₂ and formed on a single crystal semiconductor substrate.

[0010] The ferroelectric thin film of the present invention can be prepared by sputtering, laser ablation, sol-gel, or CVD.
By a predetermined method such as a method, for example, a thin film is formed on a surface of a substrate such as glass or magnesium oxide or a single crystal semiconductor substrate such as silicon or gallium arsenide.

The material for forming the ferroelectric thin film of the present invention is B
A material containing individual elements of i, Ti, and Nb may be used at a predetermined ratio, or a mixed material containing each element at a predetermined ratio.

For example, in the case of the sputtering method, for example, Bi ₂ O ₃ , TiO ₂ , NbO ₅ and Nb ₂ O ₅ are mixed and pulverized at a predetermined ratio to form a sintered body, which is sputtered with a target. Good. Further, each sintered body of each material may be used as a target.

The ferroelectric thin film of the present invention thus formed has a remarkably improved insulation resistance value and a remanent polarization value by adding a niobium element to Bi ₄ Ti ₃ O _12. is there.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described based on embodiments, but the present invention is not limited to these embodiments.

(Examples 1 to 3) Bi_TwoO_Three, TiO_Two, N
b_TwoO_FiveBi powder_FourTi_ThreeO₁₂Against
0.5, 1.0 and 2.0 mol% Nb_TwoO_FiveAddition of
And mix the mixture with ZrO_TwoWith the ball
Into water and pulverize with a ball mill.
Calcium in air for 2 hours at ° C. Then, 7% by weight of PO
Granulating with a polyvinyl alcohol (PVA) solution,
1 ton / cm^Two Pressure to form a 18mm diameter disc
Molded and fired in air at 950-1100 ° C for 2 hours
Was. This was polished to obtain the ceramics of Examples 1 to 3.
And subjected to various tests.

Comparative Example 1 A ceramic of Comparative Example 1 was obtained by operating in the same manner as in the above-mentioned Example using only the powder of Bi ₄ Ti ₃ O ₁₂ , and subjected to various tests together with the ceramics of Examples 1 to 3. did.

Test Example 1 The ceramics of Examples 1 to 3 and Comparative Example 1 were measured for the temperature characteristics of the dielectric constant, and the results shown in FIG. 1 were obtained. From these results, it was found that the dielectric properties of Examples 1 to 3 were much lower than those of Comparative Example 1 although the dielectric properties were close to each other.

Further, when the insulation resistance of the ceramics of Examples 1 to 3 and Comparative Example 1 was measured, the results shown in FIG. 2 were obtained. From these results, it was confirmed that the ceramics of Examples 1 to 3 containing the niobium element had significantly improved insulation resistance as compared with the ceramics of Comparative Example 1 containing no niobium element.

(Examples 4 and 5) As in Examples 1 to ₃ , 1.0 mol% of Nb ₂ O _{5 with} respect to Bi ₄ Ti ₃ O _{12 was used} .
Was calcined in the same manner, pulverized, granulated to a particle size of less than 106 μm, and pressed against a copper plate with a spoon to prepare a target.

Next, as shown in FIG. 3, a platinum thin film 2 was formed by sputtering platinum (Pt) using a glass substrate as the substrate 1. Thereafter, 1.0 mol of the Bi ₄ Ti ₃ O ₁₂ obtained as described above was applied thereto.
The ceramic was sputtered using a target made of a ceramic containing 1% of Nb ₂ O ₅ to form a ceramic thin film 3. Furthermore, on top of this, gold (A
u), sputtering gold electrodes 4 were formed at four locations to produce an MFM capacitor of Example 4.

Further, the substrate 1 is changed from a glass substrate to MgO (1).
00) MFM of Example 5 in the same manner except that a substrate was used.
(Metal-Ferroelectric-Metal: Metal-Ferroel
(Electric-Metal) capacitors were produced.

(Comparative Example 2) 1 for Bi ₄ Ti ₃ O ₁₂
An MFM capacitor was produced in the same manner as in Example 4, except that a ceramic containing no niobium element was used instead of the ceramic containing 0 mol% of Nb ₂ O ₅ .

Test Example 2 Using the MFM capacitors of Examples 4 and 5, and Comparative Example 1, the leakage current was measured. The result is shown in FIG. FIG. 4A shows the result of measurement at a different temperature for Example 4, and FIG.
FIG. 4C shows a comparison between Example 4 and Example 5. FIG. From this result, it was found that the MFM capacitors of Examples 4 and 5 had significantly reduced leakage current as compared with that of Comparative Example 2.

In Examples 4 and 5 and Comparative Example 2, M
With respect to the FM capacitor, the fatigue measurement, that is, the switching cycle was repeated, the remanent polarization at that time was measured, and the hysteresis loop after the initial and switching was repeated 10 ⁹ was measured. 5 to 7 show the respective hysteresis loop and fatigue measurement results.

[0025] From this result, MFM capacitors of Examples 4 and 5 show the fatigue resistance, shows almost the same hysteresis loop after the 10 ⁹ cycle, proved to be significantly better than that of Comparative Example 2 Was.

[0026]

As described above, according to the present invention,
By adding a predetermined amount of niobium to the _{Bi 4 Ti 3 O 12, Bi} 4 Ti 3 O 12 system ferroelectric thin film than can be obtained ferroelectric thin film having improved insulation resistance, various such pyroelectric It is suitable for use in ferroelectric thin film elements.

[Brief description of the drawings]

FIG. 1 is a diagram showing a temperature characteristic of a dielectric constant.

FIG. 2 is a diagram comparing insulation resistance.

FIG. 3 is a diagram schematically illustrating an MFM capacitor created in an example.

FIG. 4 is a diagram comparing leak currents.

FIG. 5 is a diagram showing a hysteresis loop and fatigue measurement results.

FIG. 6 is a diagram showing a hysteresis loop and fatigue measurement results.

FIG. 7 is a diagram showing a hysteresis loop and fatigue measurement results.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Suki Ueno 2-3-6 Shirite, Tsurumi-ku, Yokohama-shi, Kanagawa Pref.

Claims (6)

[Claims] 1. A ferroelectric thin film obtained by adding a niobium element to Bi ₄ Ti ₃ O ₁₂ . 2. The ferroelectric thin film according to claim 1, wherein the amount of the niobium element is in the range of 0.2 to 2.5 mol%. 3. The ferroelectric thin film according to claim 2, wherein the amount of the niobium element is in the range of 0.5 to 2.0 mol%. 4. The ferroelectric thin film according to claim 1, wherein said ferroelectric thin film is formed on a single crystal semiconductor substrate. 5. A ferroelectric thin film device comprising Bi ₄ Ti ₃ O ₁₂ to which a niobium element is added and formed using a ferroelectric thin film formed on a single crystal semiconductor substrate. 6. The ferroelectric thin film element according to claim 5, wherein the amount of the niobium element is in the range of 0.5 to 2.0 mol%.