JP3214741B2 - Nonlinear optical thin film and method of manufacturing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fine particle-dispersed composite thin film for a nonlinear optical material, and more particularly to a thin film of a nonlinear optical material in which metal fine particles are dispersed and precipitated in a matrix of a ferroelectric material or a highly dielectric material. . This fine particle-dispersed composite thin film is used as a material having a large nonlinear optical effect used in the optical information field, such as an optical switch and an optical wavelength conversion element.

[0002]

2. Description of the Related Art Glass or the like in which semiconductor ultrafine particles are dispersed has a high optical nonlinearity, and is being developed. In addition, it has been reported that glass and colloid solutions in which metal fine particles are dispersed also exhibit relatively large nonlinearity. Among these, quartz glass, multi-component glass, polymer materials, and the like are generally used as a matrix in which fine particles are dispersed.

[0003] Glass containing gold fine particles is conventionally called "gold red glass" and is a material well known as one of red glasses. This glass is produced by containing about 0.01% by weight of gold, once melting, and then performing a heat treatment to develop a color.

The reported value of the third-order nonlinear susceptibility χ ⁽³⁾ of gold-red glass is about 10 ⁻¹¹ esu, and this value is not necessarily large. The reason for the low value is considered to be a low concentration dispersion of about 10 ^{−5 in} volume fraction of gold in the glass. Therefore, increasing the concentration of fine gold particles is considered to be one method for increasing the non-linear susceptibility. However, in the case of manufacturing by a melting method, there is a limit in increasing the concentration due to the limitation of solubility.

[0005] In order to solve this problem, there has been proposed a sputtering method and an ion implantation method, in which high concentration and composition control are relatively easy. 147,199
1 and JP-A-3-294829.
The former is obtained by dispersing Au fine particles in a SiO ₂ glass matrix by sputtering or ion implantation,
The latter is Au, A grown in the form of islands with a SiO ₂ glass thin film.
g and Cu metal fine particles are alternately laminated.
It is considered that such a metal particle-dispersed glass exhibits high nonlinearity due to excitation of surface plasmons of the dispersed metal particles and a quantum size effect, and can obtain a high χ ⁽³⁾ value.

However, in these proposals, 例 え ば⁽³⁾ is at most about 1 × 10 ^-7 esu even in the former proceedings, and it is desired to further improve χ ⁽³⁾ . Also,
In these proposals, the position of resonance absorption was significantly shifted,
Adjusting the excitation wavelength has not been considered. For example, in the former proceedings, FIG. 2, FIG. At 3, the thin film immediately after the film formation is heat-treated and the absorption spectrum is measured. Due to these, the resonance absorption position changes only at most about 30 nm. As a result, the excitation wavelength of the fine gold particles is limited to 520 to 550 nm, which limits the laser used, making it impossible to provide a nonlinear optical material suitable for various light sources.

[0007]

SUMMARY OF THE INVENTION It is a main object of the present invention to provide a novel nonlinear optical thin film which exhibits a high χ ⁽³⁾ value and is capable of greatly changing an excitation wavelength, and a method of manufacturing the same. It is in.

[0008]

This and other objects are achieved by the present invention which is defined below as (1) to (8). (1) A nonlinear optical thin film including at least one kind of metal fine particles in a ferroelectric or high dielectric matrix, wherein the matrix is titanium oxide or a composite oxide containing titanium oxide. (2) The nonlinear optical thin film according to (1), wherein the fine particles have an average particle size of 1 to 100 nm. (3) The nonlinear optical thin film according to (1) or (2), wherein the content of the fine particles is 1 to 80 vol%. (4) The nonlinear optical thin film according to any one of (1) to (3), wherein the dielectric constant is 10 or more. (5) The nonlinear optical thin film according to any one of (1) to (4), wherein the third-order nonlinear susceptibility χ ⁽³⁾ is 10 ⁻⁷ esu or more. (6) After forming a thin film in which at least one kind of metal fine particles is dispersed in a ferroelectric or high dielectric matrix, heat treatment is performed at a predetermined temperature to adjust the resonance absorption wavelength position of the fine particles to a desired wavelength. And a method for producing a nonlinear optical thin film according to any one of (1) to (5). (7) The method for producing a nonlinear optical thin film according to (6), wherein the film is formed by a simultaneous sputtering method. (8) The method for producing a nonlinear optical thin film according to (6) or (7), wherein the heat treatment is performed at a temperature of 100 to 1100 ° C.

[0009]

In the thin film of the present invention, as a result of the three-dimensional confinement of metal fine particles, for example, non-linearity appears due to surface plasmon excitation and quantum size effect of the metal fine particles. As a result, a nonlinear optical material having optical bistability and optical relaxation time on the order of ps is realized, and can be applied to an optical switch or an optical wavelength conversion element such as THG. At this time, a larger χ ⁽³⁾ value is realized as compared with the related art, and the value is 10 ⁻⁶ esu or more. This is considered to be the result of some interaction as a result of the metal fine particles being dispersed in the matrix having a high dielectric constant.

Further, when the thin film immediately after film formation is heat-treated,
As the heat treatment temperature becomes higher, the position of the plasma resonance absorption peak shifts to a longer wavelength. And the change width is 100
nm.

[0011]

[Specific Configuration] Hereinafter, a specific configuration of the present invention will be described in detail.

The fine particle-dispersed composite thin film of the present invention contains fine particles of metal. As a metal to be used, Au (resonance absorption peak position: about 520 nm), Ag (about 370 nm), Cu
(About 630 nm), but various single metals and alloys can be used, and there is no particular limitation.
In any of them, the plasma resonance absorption position is shifted by the heat treatment according to the present invention.

The average particle size of such fine particles is 1 to 100.
nm, preferably 2 to 30 nm. The quantum size effect is realized with such an average particle size. The content of the fine particles is preferably 1 to 80 vol%, particularly preferably 5 to 60 vol% of the whole. If the content is too small, the usefulness as a nonlinear optical material is diminished. If the content is too large, the bulk properties are increased and the optical nonlinearity is reduced. The average particle size of the fine crystal particles can be determined from a transmission electron microscope (TEM) image or from the X-ray diffraction spectrum according to Scherrer's formula. The content may be determined from chemical analysis or ESCA.

The matrix of the fine particle-dispersed composite thin film of the present invention is a ferroelectric material or a highly dielectric material. Ferroelectric materials have a bulk polycrystalline dielectric constant of 15 at room temperature.
The high dielectric material has a dielectric constant of about 10 or more and less than 150 at room temperature in the high dielectric material. It is considered that the dielectric constant changes due to the heat treatment after film formation described below, and as a result, the resonance absorption position shifts significantly.

As such a ferroelectric material, a perovskite compound is preferable. As perovskite compounds, A ¹⁺ B ⁵⁺ O ₃ , A ²⁺ B ⁴⁺ O ₃ , A ³⁺ B ³⁺ O
₃ , A _X BO ₃ , A (B ′ _0.67 B ″ _0.33 ) O ₃ , A
(B ′ _0.33 B ″ _0.67 ) O ₃ , A (B _0.5 ⁺³ B _0.5 ⁺⁵ ) O
₃ , A (B _{0.5 2} ⁺ B _0.5 ⁶⁺ ) O ₃ , A (B _{0.5 1} ⁺ B _0.5
⁷⁺ ) O ₃ , A ³⁺ (B _0.5 ²⁺ B _0.5 ⁴⁺ ) O ₃ , A (B _0.25 ¹⁺ B
_{^{0.75 5+) O 3, A (}} B 0. 5 3+ B 0.5 4+) O 2.75, A (B
_0.5 ²⁺ B _0.5 ⁵⁺⁾ O _2.75 mag be either. For example, BaTiO ₃ , PbTiO ₃ , KTaO ₃ , NaT
aO ₃ , SrTiO ₃ , CdTiO ₃ , KNbO ₃ , L
iNbO ₃ , LiTaO ₃ , PZT (PbZrO ₃ -P
bTiO ₃ ), PLZT (PbZrO ₃ -PbTiO)
₃ : La ₂ O ₃ ).

As the high dielectric material, TiO ₂ , 2
_{MgO · TiO 2, MgO · TiO} 2, MgO · 2Ti
O ₂ , ZnO—TiO ₂ , CaTiO _{3 and the} like are suitable. As these ferroelectric or high-dielectric materials, titanium oxide or a composite oxide (titanate) containing titanium oxide is preferable. In particular, the dielectric constant of a bulk polycrystal at room temperature is about 100 to 300. Titanate perovskite type compounds such as BaTiO ₃ , SrTiO ₃ , Ca
TiO ₃ and PbTiO ₃ are preferred.

In these matrices, a clear peak is not observed in the X-ray diffraction spectrum (XRD) immediately after film formation and after heat treatment, and the matrix is substantially in an amorphous state. However, in observation with a transmission electron microscope (TEM), grains are usually observed after heat treatment. At this time, the average diameter of the grains is 50 to 1000 nm, particularly 100 to 500 nm.
It is.

The thickness of a thin film in which fine particles are dispersed in such a matrix is generally about 0.01 to 5 μm. Further, two or more kinds of fine particle materials and, in some cases, matrix materials can be used.

In order to produce the thin film of the present invention, it is preferable to simultaneously sputter the matrix material and the fine particle material. The method of sputtering may be any,
From the viewpoint of the film forming speed, RF magnetron sputtering is preferable. At this time, the operating pressure is about 10 ⁻³ to 10 ⁻² Torr, and the substrate temperature is about normal temperature to about 300 ° C. Then, by changing the film forming speed and the target area of both, it is possible to easily disperse the fine particles with the above-mentioned content.

Instead of the simultaneous sputtering method, an ion implantation method described in the above-mentioned optoelectronic material symposium preliminaries and an alternately laminated sputtering method described in JP-A-3-294829 can be used.

In such a thin film immediately after film formation, fine particles are dispersed in a matrix. In the present invention, it is preferable to perform a heat treatment on the thin film immediately after the film formation in order to adjust the resonance absorption position. The heat treatment is performed in air or an inert gas atmosphere at a temperature of 100 ° C. or more, particularly 300 ° C. or more,
It may be carried out by holding at a temperature of 00 ° C. or higher, generally 1100 ° C. or lower, particularly 1000 ° C. or lower for about 10 hours or shorter, generally 1 minute or longer, especially 10 minutes or longer. This causes a shift in the resonance absorption position, and the shift width is 100 nm.
Also reach. Therefore, if the relationship between the heat treatment conditions and the absorption position is determined from experiments, a nonlinear optical thin film having a desired resonance absorption peak position can be easily obtained with good reproducibility.

When the dielectric constant ε of such a thin film is measured,
Generally 10 or more, especially 100 or more, further 150
As described above, the number can be set to 200 or more. In order to measure the dielectric constant of such a thin film, a platinum thin film lower electrode is formed on a synthetic quartz glass substrate by a sputtering method, a thin film to be measured is formed thereon, and a platinum thin film is further formed thereon. A pad upper electrode having a diameter of 1 mm is formed, and then heat treatment is performed as necessary. Then, C and Q are measured using an LF impedance analyzer, and ε may be obtained by calculation from this.

The χ ⁽³⁾ value of such a thin film is 10
^-7 esu or more, especially 10 ^-6 esu can be obtained. Such a high χ ⁽³⁾ value is obtained because the metal fine particles dispersed in the matrix have a high concentration, and the matrix material used in the present invention is compared with SiO ₂ usually used in a matrix. Is considered to be due to the high dielectric constant. Note that the χ ⁽³⁾ value is for the next generation of basic industrial technology, 2nd Symposium on Optoelectronic Materials, pp. 139-147, 199
1. The phase-conjugated degenerate four-wave mixing method (DFWM) according to 1.
It can be measured according to. The above χ ⁽³⁾ value is a value when the second harmonic (532 nm) of the Nd: YAG laser (1.06 μm) is used, and is not a value at the plasma resonance absorption peak position. Χ ⁽³⁾ at the plasma resonance absorption peak wavelength is 10 ⁻⁷ esu or more, particularly 10 ⁻⁶ esu.
In the above range, it is even higher.

[0024]

EXAMPLES Hereinafter, the present invention will be described in more detail by showing specific examples of the present invention.

Example 1 Using an RF magnetron sputtering apparatus, an Au chip was mounted on a BaTiO ₃ target, and simultaneous sputtering was performed.
Synthetic quartz glass was used as the substrate. The conditions for forming the thin film were such that the gas pressure was 5 × 10 ⁻³ Torr, the substrate temperature was 150 ° C., and the RF power was 100 W in an argon atmosphere. The Au concentration was controlled by the amount of the chip, and the film thickness was controlled by the sputtering time to produce a thin film.

Next, this thin film was heat-treated at a predetermined temperature, and sample Nos. 1-4, 11-14, 2
1 to 23. Heat treatment conditions and Au dispersion (vol%)
Table 1 shows the film thickness.

[0027]

[Table 1]

Sample Nos. 1-4 and Sample No. 1
1 and 2 are shown in FIGS.
Shown in The plasma resonance absorption peak position was measured from this transmission spectrum. The results are shown in Table 1 and FIG.
From these, it can be seen that the absorption peak position is shifted to 100 nm depending on the heat treatment conditions.

FIG. 4 shows the X-ray diffraction spectra of Sample Nos. 1-4. From these, it can be seen that the matrix is in an amorphous state. Further, according to the TEM image, Au fine particles and a matrix were confirmed.

FIG. 5 shows the relationship between the heat treatment temperature and the average particle size of the Au fine particles. According to FIG. 5, the fine particles are coarsened by the heat treatment, but the coarsening alone cannot explain the shift of the resonance absorption position. Thus, the relationship between the dielectric constant ε at room temperature of the BaTiO ₃ sputtered film at a film thickness of 0.5 μm and the heat treatment temperature was measured. FIG. 6 shows the results. From the results shown in FIG. 6, it is considered that the change in ε of the matrix is correlated with the shift of the absorption position. Actually, when the dielectric constant of each sample was measured according to the above, the value was 15 or more, and the value of the heat-treated sample was 20 to 300.

COMPARATIVE EXAMPLE 1 An Au fine particle-dispersed thin film N having a matrix of SiO ₂ glass was prepared in the same manner as in Example 1 except that BaTiO ₃ was changed to a SiO ₂ target and the RF power was set to 200 W.
o. 31 to 38 were prepared. Table 2 shows the results.

[0032]

[Table 2]

When SiO ₂ is used as a matrix, the peak position of the plasma resonance absorption changes only at most 30 nm or less irrespective of the heat treatment temperature and time, and the excitation wavelength is limited. On the other hand, in the BaTiO ₃ matrix of the present invention, as the heat treatment temperature becomes higher, the absorption peak position shifts to a longer wavelength, and a shift up to 100 nm is possible.
The effects of the present invention are clear.

Example 2 The fine particles dispersed in the fine particle-dispersed thin film No.
41-44 were obtained. Table 3 shows the results. From these results, the effect of the present invention is clear. Ε of each sample is 20
That was all.

[0035]

[Table 3]

Example 3 As in Example 1, the substrate was changed to an Al ₂ O ₃ single crystal substrate, and BaTiO ₃ of Example 1 was replaced with Sr.
A fine particle-dispersed thin film was obtained with the change to the TiO ₃ target. Samples for measuring these characteristics were No. 51,
52, 61 to 63.

Next, this thin film was heat-treated at a predetermined temperature except for Sample No. 63, and the particle size, film thickness, metal fine particle concentration, transmittance, plasma resonance absorption peak position and 吸収⁽³⁾ value were obtained by the above-mentioned methods. Was measured. However, the χ ⁽³⁾ value was measured by the DFWM method using a laser wavelength of 532 nm. Table 4 shows the measurement results.

[0038]

[Table 4]

From Table 4, it can be seen that BaTiO ₃ and SrTiO
The χ ⁽³⁾ value at 532 nm of the fine particle-dispersed thin film having ₃ as a matrix is improved to 10 ⁻⁷ esu or more, and the maximum is 10 ⁻⁶ es.
It turns out that it becomes u or more. Further, the samples of Examples 1 and 2 also showed a value of 10 ⁻⁷ esu or more. At this time, since the used wavelength of 532 nm is not the absorption peak position, χ ⁽³⁾ shows a larger value at the absorption peak position. further,
When the dielectric constant ε of the thin film was measured according to the above, No. 5 was obtained.
1 to 52 and 61 to 63 showed values of 20 to 300.

Comparative Example 2 In the same manner as in Comparative Example 1, an Au fine particle-dispersed thin film having a matrix of SiO ₂ glass was prepared, and this thin film was heat-treated at a predetermined temperature to obtain Sample Nos. 71 to 73. The same measurement as in Example 3 was performed on these sample samples. Table 5 shows the results.

[0041]

[Table 5]

Table 5 shows that when SiO ₂ is used as the matrix, the χ ⁽³⁾ value is 10 ⁻⁸ esu or less.

[0043]

According to the present invention, the χ ⁽³⁾ value is 10 ⁻⁷ esu
A non-linear optical thin film having the above high value and capable of freely changing the absorption peak position to an arbitrary wavelength with a large fluctuation width is realized.

[Brief description of the drawings]

FIG. 1 is a graph showing a transmission spectrum of a nonlinear optical thin film of the present invention.

FIG. 2 is a graph showing a transmission spectrum of the nonlinear optical thin film of the present invention.

FIG. 3 is a graph showing a relationship between a heat treatment temperature of a nonlinear optical thin film of the present invention and a plasma absorption position.

FIG. 4 is a graph showing an X-ray diffraction spectrum of the nonlinear optical thin film of the present invention.

FIG. 5 is a graph showing the relationship between the heat treatment temperature of the nonlinear optical thin film of the present invention and the average particle diameter of the fine particles.

FIG. 6 is a graph showing a relationship between a heat treatment temperature and a dielectric constant of a matrix material constituting a nonlinear optical thin film of the present invention.

Continuation of the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G02F 1/355 501 JICST file (JOIS)

Claims (8)

(57) [Claims] 1. A nonlinear optical thin film comprising at least one kind of metal fine particles in a ferroelectric or high dielectric matrix, wherein said matrix is titanium oxide or a composite oxide containing titanium oxide. 2. The nonlinear optical thin film according to claim 1, wherein said fine particles have an average particle size of 1 to 100 nm. 3. The nonlinear optical thin film according to claim 1, wherein the content of the fine particles is 1 to 80 vol%. 4. The nonlinear optical thin film according to claim 1, which has a dielectric constant of 10 or more. 5. The third-order nonlinear susceptibility χ ⁽³⁾ is 10 ⁻⁷ esu
The nonlinear optical thin film according to any one of claims 1 to 4, which is as described above. 6. A thin film in which at least one kind of metal fine particles is dispersed in a ferroelectric or high dielectric matrix is formed, and then heat-treated at a predetermined temperature to set the resonance absorption wavelength position of the fine particles to a desired wavelength. A method for producing a nonlinear optical thin film according to any one of claims 1 to 5, wherein the method is adjusted to: 7. The method for manufacturing a nonlinear optical thin film according to claim 6, wherein the film is formed by a simultaneous sputtering method. 8. The method according to claim 6, wherein the heat treatment is performed at a temperature of 100 to 1100 ° C.