JPH02170306A - Ferromagnetic ferroelectric oxide and manufacture of thin film thereof - Google Patents

Abstract

PURPOSE:To improve ferroelectric ferromagnetic characteristic and stability by constituting with ternary oxide with main constituent of iron oxide - bishmuth oxide - perovskite type. CONSTITUTION:It has been empirically confirmed that arrangement of non- stoichiometric composition is better as preferable composition arrangement than arrangement of stoichio-metric composition of perovskite phase stoichiometry xBiFeO3-(1-x)ABO3 with x=0-1. Namely the composition is changed from the composition of xBiFeO3-(1-x)ABO3 with x=0-1 to a ternary system of iron oxide Fe2O3 - bismuth oxide Bi2O3 - perovskite type ferroelectric ferromagnetic oxide ABO3. This improves the ferroelectric ferromagnetic characteristic and stability.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a ferromagnetic ferroelectric oxide capable of forming a multifunctional thin film and a method for manufacturing the thin film.

[Conventional technology]

In recent years, equipment in many fields, both consumer and industrial, has
With the development of semiconductor device technology such as VLSI, they are becoming more intelligent and smart, and these latest devices are equipped with sensors and transducers with advanced performance.

Actuators have become essential elements along with high-density semiconductor memory and high-density logic operation elements. Sensors are designed to handle situations like this.

Research into new functional devices such as transducers and actuators is becoming more active, and research into new functional materials to improve the performance and diversification of these functional devices is also active.

There was a time when ferromagnetic and ferroelectric materials were studied out of interest in physical properties, unrelated to the consumer and industrial equipment and needs mentioned above. At this time, ABO, a perovskite structure in which a magnetic ion such as iron is substituted at the A or B site (Smolensky et al.: Tekl+n1chsskoy
Fiz 281958), chromium oxide (Cr, O3
) (Rado: Phys Rev Lett, 6
1961).

γ ferrite (y-Fe, O3) (Rado et
al PhysRev, B121977), Ni borasite (Ni, Bt Ox x I) (Ascher
at al: J, ^pp1. Phys 37-1
966) has attracted attention as a material exhibiting ferromagnetism and ferroelectricity, and studies have been conducted on the potential applications of these materials. (V, E, Wood at al: Ma
Gnetoelectric Phenomena in
Crystals ads A, J, Freeman
et a1 However, the reality is that these materials cannot be put to practical use because the volume fraction in which they exhibit ferromagnetism and ferroelectricity is extremely small, and the temperature range in which they exhibit ferromagnetism and ferroelectricity is too low. there were.

On the other hand, this inventor x -BiFeO,-(1-
x) Focusing on the oxide system with the composition ABO3, x = O~1, 1! We are continuing to conduct research.

The progress is as follows:1 For example, IEEJ Magnetics Research Group Material MAG-86-73 (1986) P49-P58゜Journal of Applied Magnetics, Japan Vol. 10. Na2 (19
86) P323-P326. IEEJ Magnetics Study Group Material NAG-88-15 (1988) P35
It is described on page 44 etc.

The conventional composition described in these documents is a so-called stoichiometric composition that can be expressed as xBiFao, -(1-x)ABO, and is a conventional ferromagnetic composition that exhibits large ferromagnetism and ferroelectricity at room temperature. It turned out to be a revolutionary material not found in ferroelectrics.

[Problem to be solved by the invention]

However, although the stoichiometric composition having the perovskite 1IIIt structure is an innovative material that has large ferromagnetism and ferroelectricity at room temperature as described above, there is still room for further improvement in terms of properties and stability. It wasn't like there wasn't one.

In other words, 1) Magnetic properties of ferromagnetic materials 1) Ferroelectric properties of ferroelectric materials that have not reached their respective best levels will be considered as room for improvement, and research will be conducted with the aim of improving the ferroelectric properties of ferromagnetic materials to come even one step closer. That's true! It is righteous.

From this perspective, this invention was created as a result of changing the perspective from the conventional framework of stoichiometric composition to non-stoichiometric composition.

The aim is to provide ferromagnetism and ferroelectricity with better performance than ever before.

[Means and effects for solving the problem] As a result of repeated composition experiments, the inventor found that the preferred composition was xBiFeo.
, -(1-x)ABO, x=O~1 It was experimentally confirmed that it is better to prepare the composition to have a non-stoichiometric composition rather than a stoichiometric one. That is, xBiFao3-(1-x)ABO,x=
From the composition o ~ 1, Fe, O, -Bi2O, -AB
O, ternary system, or Fe2O.

The idea is to change the composition to a quaternary system of -[3i, O, -TMOx -ABO, (TM: iron element) to improve the ferroelectric and ferromagnetic properties as well as the stability.

FIGS. 1 and 3 show the relationship between the conventional composition system and the composition system according to the present invention. The conventional composition lies on straight lines AA' and BB' as shown in FIGS. 1 and 3. In contrast, the composition of the present invention is shifted from this gland to the side with more iron oxide. In this way, by shifting the composition from the stoichiometric composition and realizing an amorphous structure, ferromagnetism and ferroelectricity coexist, and moreover, it is possible to achieve stability that could not be obtained with a stoichiometric composition. Now I can have sex.

〔Example〕

(First Example) First, a sample was prepared using a sputtering device. A stainless steel petri dish with a diameter of 12 cm was placed on the cathode plate, and Bi was placed in it.
□03. a-Fe203. PBTiO, and PbO
A target filled with mixed powder was used.

It should be noted that PbO was added to PbTi0. It was added in an excess of 5% to 10%. The sputtering gas was a 4:1 mixed gas of Ar and 02, and the combined pressure was kept constant at 4 x 10-''Torr.When the sputtering gas pressure exceeded 0.ITorr, the sputtering rate was improved, but many samples Murakami: Corning 7059 is used for the substrate, which results in a powdery product with poor condition.
Glass and Si-wafer (100) surfaces were used, and the substrate temperature was 370°C to 400°C.

Sputtering was performed for 1 to 6 hours at a high frequency input power of 3001+1.

All of the thin films obtained in this way were amber in color and transparent with a glossy surface.
Heat treatment was performed at a temperature of ~800°C for 1-2 hours.

While fixing the manufacturing process as described above, the target composition is set to i20. , a-Fe20. , PbT
i0. The three elements were varied as shown in FIG. 1, and the magnetic properties and rtI'lt properties were measured for each element. The magnetic properties were measured using a VSM (vibrating sample magnetometer), and the dielectric properties were measured by depositing an aluminum electrode on the sample surface and measuring the hysteresis curve for each. Ferromagnetism and ferroelectricity were determined by the magnitude of spontaneous magnetization 4πMs and spontaneous polarization Ps. evaluated. Table 1 shows the characteristic results and optimum heat treatment temperature for each composition. If the heat treatment temperature is further increased from this optimum temperature, crystallization occurs throughout the film, and at the same time microcracks appear, the withstand voltage in the film thickness direction decreases, and measurement of dielectric properties becomes almost impossible. In Table 1, the dielectric stability indicates that the remanence polarization Ps measured from the second time onwards has poor reproducibility.

There is reproducibility, but there is fluctuation during measurement Δ, reproducibility is good,
Those with little fluctuation are marked with 0. As is clear from these tables, the conventional composition Nα11~ shown in Figure 1
It can be seen that compared to Nα17 and &21, this example has better magnetic properties and increased dielectric stability. Sample 111a50,2゜3.4,5,6,7,8,9,1
The composition of the region surrounded by Nα51.0 and Nα51.
The area outside the side consisting of 10°9 has a composition with extremely little PbTi0i, and the magnitude of the spontaneous polarization is equal to the ferromagnetic value v
It becomes so small that it cannot be called an i-electric body. Also, Na 6~
The area outside the side consisting of 9 becomes close to the conventional composition and the improvement effect is lost. Outside the side consisting of 44, 5.6, Nα5
The outside of the side consisting of 0, 2, 3.4.

The same applies to the outside of the side consisting of Nα50.51. Furthermore, the effect of heat treatment is remarkable for both compositions.
This is the same as the conventional example (Nα11 to Nα17 and Na20). That is, in the as-blown state without heat treatment, almost no hysteresis curve is detected for both ferromagnetism and ferroelectricity, whereas in the composition range according to this example, hysteresis curves of 700°C
X-ray analysis of the heat-treated films shows that they are both shown in Figure 2 (a) (
As shown in b), the halo pattern has 12 DI and is amorphous, but both hysteresis was observed for ferromagnetism and ferroelectricity.

If the heat treatment temperature is increased to, for example, 770° C. to 800° C., the magnetization will rapidly decrease at the same time as crystallization occurs. In addition, opacity occurs on the film surface along with crystals,
The vI voltage and voltage drop all at once, and the dielectric properties can no longer be determined. In addition, the sample NαF (Table 1) also has PbTi0. 4 πMs Ps Heat treatment temperature (K
G) (μd(cut (”C) 0.5 2.0 001 6900.819
001 690 0.5 14 002 690 1, s 1.5 006 7002.5 1
4 007 700 4 0.7 013 680 4 06 011 (i801 0.7
003 680 0.7 15 002 680 0.08 0.12 0.10 At the heat treatment temperature at which stability and shape retention can be measured, the dielectric constant εr
, tan δ is εr~20. regardless of the composition. tanδ
It was about 0.02.

[Second Example] In this example, Fe2O5-Bi, O, -AIIO,
ABO of the system.

This relates to a composition in which BaTi0□ is used. The composition shown in the literature (IEEJ Magnetics Study Group material NAG-88-15 (1988) P35) in the ternary system composition diagram (Figure 3), that is, (BiFeO3)l-x(ABO3)
The relationship between the composition when compounded to match x x = 0 to 1 and the composition range of this example is shown. Table 2 shows the characteristic values.

As shown in Figure 3, α-Fe is
, O, , Bi, 03, and B1TiO3 powders were mixed in a ball mill for 16 hours, dehydrated and dried, and then filled into a stainless steel Petri dish with a diameter of +2 am, using this as a target in an RF magnetotroton sputtering device. It sputtered. The sputtering conditions are argon gas pressure: r
a Elementary gas pressure = 4:1. Total gas pressure = 4~6X10S To
rr RF power 3001, substrate temperature 50-500℃
, the substrate was a Si wafer, and the electrode spacing was 5 cm.

The target was placed on the anode, and sputtering was performed for 2 to 6 hours. The film thus created has a film thickness of 0.5 to 2.
．． It exhibits an amber color at 0 μm, and by applying an antireflection film in the near-infrared region, a material with a transparent and smooth surface with a transmittance of 90% or more can be obtained (Figure 4).The substrate temperature during sputtering can be adjusted to Although the film was formed at a temperature varying from room temperature to 400° C., essentially no effect on the properties was observed. After film formation, heat treatment was performed in the atmosphere at 400°C to 800°C for 3 hours. Table 2 shows the values after heat treatment.If heat treatment is not performed, neither ferromagnetism nor ferroelectricity will be observed.Also, if the heat treatment temperature is too high, the film will crystallize and at the same time become cloudy due to the generation of microcracks. It becomes opaque.

The residual magnetization also decreases, and ferroelectricity becomes unmeasurable due to a short between the electrodes.The optimal heat treatment temperature varies depending on the composition, but the tendency is for Fs, 03-Bi, O
, -BaTi0. The larger the mixing ratio of BaTiOi in the system, the higher the temperature shift, and the residual magnetization 4πMs and remanent polarization at the optimum heat treatment temperature (Table 2).
Heat treatment temperature (KG) (μC/(”C)) 9 05 0.5 2.0 0.01 6
209 0.2 0.8 19 0.01
6208 15 0.5 1.3 0.0
2 6208 05 1.5 1.2 0
．． 07 7007 0.5 2.5 1.2
0.12 7005.5 05 4 1.7
0,13 7004.5 1,5 4
0.7 0.12 6803.5 . 2,5 4
0.7 0.10 6804 3
3 0.7 0.07 6804.5 3.
5 2 06 0.03 6805 4
1 07 0.02 6206.7
2.6 0.7 15 0.13 620 Stability 40' 7 2 1 1.4 0.08
680 041 6 2 2 1.3
0.12 680 042 5 2 3
It was confirmed that 1.0 0.10 700 0 becomes smaller. The composition range of this example, i.e.
When heat treatment was performed at the temperatures shown in Table 2 within the shaded area in the figure, all of the samples were in an amorphous state. In addition, for the composition outside the shaded area in FIG. 3, the conventional example (Nα3
2 to 39) have not been obtained. The characteristics were measured in the same manner as in the first example.

(Third Example) This example uses Fe, 0. -Bi, 0. -A [IO, is a composition system in which a fourth component NOx is added, and as Tn+, Ti, V, Cr, Km,
Fa, Cb, Ni.

Cu and Fezo3-BiTMOx-Pb
Ti0. It was prepared as

(Table 3) Sample Na Fe, O, Bi2O, BaTiO34
32,6T A=Ti4.2 44〃 Force=V4.2 45 LI TM-Cr4.246 7
/ TM:Mn 4.247ノ'TM"Ga4.2 48 〃TxiangNi4.2 49 u TMCu 4.24πMs P
s Heat treatment temperature (KG) (μc/ac ('C) 1.5 0,11 750 The method of preparing the sample is the same as in the first example, only the heat treatment temperature may differ depending on the composition. In the third embodiment, both the magnetic and dielectric properties had the conventional composition NQII~
&17. Nα21. Although it is comparable to Nα32 to Nα39, the dielectric stability is improved. The difference in composition between the first to third embodiments and the conventional example is that the latter has a stoichiometric composition, while the former has a non-stoichiometric composition. How this is related to HR stability will not be known until future research results are obtained.However, the transparency of No. 47 (Co) is slightly worse, but the characteristics are similar to those shown in Figure 4. Ta.

(Fourth Example) This example is the same as the first to third examples in terms of composition, except that the film is formed by a sol-gel method. As described in the first to third embodiments, it is known that all samples in which magnetic hysteresis and dielectric hysteresis are simultaneously observed are in a glass state.

One of the typical sol-gel methods is to use a metal alkoxide solution as a raw material and to produce oxides by hydrolyzing and heat-treating this solution. It is known that an amorphous state can be achieved even if

This example focuses on the above points and is an example of manufacturing a thin film ferromagnetic ferroelectric material by the sol-gel method.

The composition is Fe, 03-Bi, 0. - BaTi0.
It is shown below when it is executed.

As starting materials, 8a isoprokoxide (Ba(0·nc, o7)a') and tetraisopropyl titanate (Ti(0·nC, H, L)) were used.

However, the former is metal barium and alcohol (n-C, H,
Mixing both 0 synthesized by direct reaction of 01l),
This solution was then stirred for 1 hour.
,)39H,O).

A mixed solution of bismuth nitrate (Bi(No3)35+(20), alcohol (n-C, H7011), and nitric acid is added dropwise while keeping the same temperature, and stirring is continued.The composition in this example is Fa: Bi: ( Ba+Ti) =
The composition is such that the atomic weight ratio is 5:2:3. During this stirring and mixing, water from the hydrate causes a hydrolysis reaction, resulting in gelation. In this state, a silicon or zirconia substrate is immersed to form a film. In the gel state, it has a yellowish brown color. To remove excess alcohol, heat to 0.150°C or keep at about 80°C and dry under reduced pressure. Thereafter, this produced film was heat-treated at 500°C to 800°C. When considering the heat treatment conditions for this composition and manufacturing method, the X-ray diffraction results are as shown in Figure 5, but depending on the drying method,
As shown in Figures (a) and (b), it can be seen that there is a large difference in the way the magnetic hysteresis curves appear. Drying method■
The diffraction line of the perovskite phase is seen, and this is the 6th phase.
It does not seem to be involved in the magnetic hysteresis at room temperature as shown in Figure (b). Therefore, it is thought that the structure that does not appear as an xi diffraction peak, that is, the amorphous nature is involved. In the drying method, no clear X-ray diffraction peak appeared even after heat treatment at 790°C.

As mentioned above, the composition in this example is B1Fe0x-ABO
, and the composition does not deviate from the stoichiometric composition. The ferromagnetic and ferroelectric properties have been improved compared to the ferromagnetic properties, and the dielectric stability has also been improved.The 0 ferromagnetism shows large values as shown in Figure 6 (a) and (b). The properties also show relatively large values, Ps=O, lμc/aJ.

〔Effect of the invention〕

As mentioned above, Fe2O, -si, o, -ABO, (ABO
, is a perovskite type ferroelectric) system or Fe, O, -
By forming a thin film with Bi, O, -TMOx-ABO3 (TM is a transition metal element) composition by RF sputtering or sol-gel method, and heat-treating it at a temperature that does not damage the glass state, a stable and translucent film is created. A highly ferromagnetic and ferroelectric film can be obtained, and can be used as a new multifunctional thin film for sensors, transducers,
It will be possible to apply it to actuators, optical control function devices, etc.

[Brief explanation of the drawing]

FIG. 1 is a compositional diagram for explaining an example of the present invention, FIGS. 2(a) and 2(b) are X and 1 diffraction measurement diagrams for explaining the same example, and FIG. 3 is a diagram for explaining the same example. Compositional tree for explaining other embodiments of this invention, No. 4
5(a) and 5(b) are X-ray diffraction measurement diagrams of the thin film formed in this example after heat treatment. Figure 6 (a) (b)
is a magnetic hysteresis curve diagram of the same example. R filling wound 10 stone 6 M, explosion 11■

Claims (5)

[Claims] (1) Iron oxide (Fe_2O_3) Bismuth monoxide (Bi
_2O_3)-Perovskite ferroelectric oxide (AB
A ferromagnetic ferroelectric oxide characterized by being composed of a ternary oxide containing O_3) as a main component. (2) The above composition includes transition metal oxides such as Ti, V, and Mn.
, Co, Ni, Cu oxide, or a quaternary or higher multi-component oxide formed by adding one or more oxides. thing. (3) The ferromagnetic ferroelectric oxide according to claim 1 or 2, wherein the ferromagnetic ferroelectric oxide has a glass-like structure. (4) The ferromagnetic ferroelectric oxide according to claim 1, 2 or 3, wherein the ferromagnetic ferroelectric oxide is a thin film. (5) The ferromagnetic ferroelectric oxide of claim 4 is formed into a thin film using a film forming method capable of forming a film in a glass state, such as vacuum evaporation, sputtering, or sol-gel method, and then heat treatment is performed. A method for producing a ferromagnetic ferroelectric oxide thin film.