JP2002298753A - Manufacturing method for thin film light emitting element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light emitting element of a lightweight construction and equipped with an enhanced color purity consisting of a zinc oxide thin film capable of exerting a high brightness and high light emission efficiency without requiring a heating process at any high temperature. SOLUTION: A precursor film consisting of zinc oxide particulates is formed on a base board and irradiated with active beams having a higher energy than the band gap of the particulates and having an energy density controlled so as to be small when the film is thin and large when film is thick within the range 5-500 mJ/cm<2> .

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a zinc oxide light emitting device useful for color display of a display of a television or a personal computer, a display of a device control panel, or a light source for artificial cultivation of plants such as vegetables and seaweed. And a method for producing the same.

[0002]

2. Description of the Related Art In recent years, a cathode ray tube (CRT), a plasma display (PDP), a vacuum fluorescent display (VFD), a photodiode light emitting device (LED), and an electroluminescent display (E
L) and the like, the demands for higher performance and higher functionality of color display devices are increasing, and research on phosphors and light emitting elements for realizing the same is becoming active.
A new color display device for a field emission display device (FED) and the like, and a color display device provided with a color filter for improving color purity have already been developed (Japanese Patent Application Laid-Open No. Hei 2 (1994)).
-46403). In connection with this, research on a method of manufacturing a light emitting element having high performance and high function at low cost has been actively conducted.

On the other hand, in the field of artificial cultivation of vegetables,
Advances in hydroponic cultivation systems and artificial lighting have enabled planned production and pesticide-free cultivation. As a result, there is a need for a light source for artificial cultivation with high luminance, high luminous efficiency, and long life.

[0004] Of these, low-voltage FEDs, in particular, have high image quality, can make panels thinner, and can be expected to consume less power. Therefore, they are used as displays for next-generation televisions and personal computers. Attention,
Research and development are underway to achieve this. But,
For this purpose, the development of a phosphor exhibiting high luminance and high luminous efficiency by irradiation with an electron beam at a low excitation voltage and having excellent stability is a prerequisite problem.

FIG. 2 is a cross-sectional view schematically showing a low-voltage FED, in which the distance between the electron beam generating element 1 and the phosphor surface 2, 2 ', 2 "is only a few mm. Therefore, when the phosphor is decomposed by irradiation of a high-density electron beam, not only the phosphor itself is deteriorated, but also the electron beam generating element 1 is adversely affected, and the life of the low-voltage FED is shortened. And in order to ensure stability and durability so as not to cause such a situation, as a phosphor material,
Zinc sulfide, which is widely used in CRTs at present, is inappropriate, and as an alternative, a stable oxide-based phosphor such as zinc oxide has attracted attention.

As described above, the zinc oxide phosphor emits blue-green light, that is, green light containing a blue component when irradiated with an electron beam or ultraviolet light, and its powder exhibits high luminous efficiency when irradiated with a low-speed electron beam. There are some disadvantages in using it as a phosphor for a voltage-type FED.

[0007] For example, when a phosphor powder is mixed with a binder and coated on a substrate to form a film, the binder cannot be completely removed. However, there is a disadvantage that the light emitting element is decomposed or evaporates to shorten the life of the light emitting element. Also, when performing fine patterning of the phosphor to obtain a display with high resolution, the conventional phosphor powder has a particle size of about several μm to 10 μm, and it is difficult to miniaturize the phosphor powder. I couldn't. Furthermore, since the phosphor powder has such a large particle size and is difficult to be densely filled, there is a disadvantage that it is difficult to reduce the electric resistance. Note that reducing the electric resistance is a necessary condition for achieving high luminous efficiency of the low-potential type FED phosphor.

In a low-voltage FED, the penetration depth of electrons is about 1 μm even at an acceleration voltage of about 5 kV.
Since the phosphor emits light near the surface, if the phosphor thin film having a thickness corresponding to the thickness of the light emitting layer is formed directly on the substrate, all the above-mentioned disadvantages of the phosphor powder should be overcome. is there.

Therefore, as a method for forming a zinc oxide luminescent thin film, a spray drying method ["Journal of Applied
Physics (J. Appl. Phys.) ", 84th
Vol., Pp. 2287-2294 (1998)] and the sputtering method [“Physica Status Solidi A”
(A)) ", Vol. 65, pp. K131-K134 (1981)], but it was not possible to obtain a phosphor thin film exhibiting high luminance and high luminous efficiency that can be practically used.

[0010] In addition, all of the known methods for forming a zinc oxide light-emitting thin film require heat treatment at a high temperature. Therefore, the zinc oxide light-emitting thin film itself formed on a transparent conductive layer or a color filter can be formed by a transparent conductive film. Deterioration of the layer and the color filter has the disadvantage that the emission luminance, emission efficiency, color purity and the like are reduced. There is also a disadvantage that the method cannot be applied to a substrate made of a material having low heat resistance such as a polymer material substrate.

[0011]

SUMMARY OF THE INVENTION In view of such circumstances, the present invention requires no heat treatment at a high temperature,
An object of the present invention is to provide a light-emitting element which is made of a zinc oxide thin film having high luminance and high luminous efficiency, and has reduced weight and improved color purity.

[0012]

The present inventors first irradiate a transition metal chalcogenide-containing gel thin film with an actinic ray having energy higher than its band gap and change the energy density of the actinic ray at this time. Optical,
Although a semiconductor thin film with controlled electrical properties was successfully manufactured (Japanese Patent No. 3032827), if this method was used for manufacturing a zinc oxide luminescent thin film, a high-temperature heat treatment could be performed without performing a high-temperature heat treatment. The inventors have found that a zinc oxide thin film light-emitting device exhibiting luminance and high luminous efficiency can be obtained, and based on this finding, have accomplished the present invention.

That is, according to the present invention, after a precursor film composed of zinc oxide fine particles is formed on a substrate, it has an energy higher than the band gap of the zinc oxide fine particles, and has an energy of 5 to 500 mJ / cm ² . Provided is a method for manufacturing a thin-film light emitting device, characterized in that an active ray having an energy density controlled so as to be small when the film thickness is small and to be large when the film thickness is large is provided within the range. Is what you do.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The substrate used in the method of the present invention can be arbitrarily selected from materials conventionally used as a substrate for a zinc oxide light emitting thin film or materials conventionally used as a panel substrate for a light emitting device. Can be. Examples of such a substrate include a glass substrate such as quartz glass, a single crystal substrate such as silicon and sapphire, and a ceramic substrate. Furthermore, a substrate or a panel substrate which has been conventionally difficult to use in terms of heat resistance can also be used. As such, for example, a substrate or panel substrate made of a polymer material having an advantage of light weight,
A color filter, a transparent conductive layer, or a panel substrate on which both are formed are used.

Next, the zinc oxide fine particles used in the method of the present invention include gel particles and microcrystals having a particle size in the range of 0.5 to 500 nm. However, in the case of gel particles, the above particle diameter means the primary particle diameter. In order to produce a zinc oxide luminescent thin film according to the method of the present invention, first, a zinc oxide-containing gel particle having a particle size of 0.5 to 500 nm containing zinc oxide is formed on a desired substrate by using, for example, a sol-gel method. Form a body membrane. This precursor film is prepared by coating a coating solution prepared using a zinc salt, a zinc alkoxide, an organic zinc complex or the like on a substrate by a spin coating method or a dip coating method.
The film thickness is usually 5 to 1000 nm, preferably 10 to 30
After coating in a range of 0 nm, 50 to 350
It is preferably formed by heating at about ° C and drying.

At this time, by applying the actinic ray irradiation to the drying treatment of the precursor film, the precursor can be prepared while keeping the substrate heating temperature from room temperature to a low temperature of about 100 ° C. If the desired coating thickness cannot be obtained by one coating and drying treatment, the coating and drying treatment can be repeated a plurality of times. When a film thicker than 300 nm is desired, the precursor film preparation step and the actinic ray irradiation step may be repeated a plurality of times.

Next, the precursor film thus formed has an energy higher than its band gap,
When the thickness of the precursor film is small in the range of 5 to 500 mJ / cm ² , the energy density is small, and when the thickness is large, irradiation with an active ray controlled to increase the energy density is performed. It is possible to selectively and efficiently generate a luminescent center that expresses blue-green luminescence of zinc oxide, and to manufacture a zinc oxide luminescent thin film with high luminance and high luminous efficiency. At this time, as a light source of illumination light having energy higher than the band gap of the precursor film, for example,
Excimer lasers such as ArF, KrF, XeF, and XeCl, He-Cd lasers, high-pressure mercury lamps, low-pressure mercury lamps, and the like are used. Further, X-rays, electron beams, and the like can be used as the active rays.

In the method of the present invention, in order to achieve high luminance and high luminous efficiency of the zinc oxide luminescent thin film, it is necessary to control the energy density of the irradiated active ray within a predetermined range. However, even if the same energy density of the active ray is irradiated for the same time, depending on the thickness of the precursor film,
Since the brightness and luminous efficiency of the obtained zinc oxide thin film are different, the energy density of the active ray is controlled to be small when the thickness of the precursor film is small, and to be increased when the film thickness is large. It is necessary to. In addition, not only the film thickness but also the substrate heating temperature at the time of irradiation and, in the case of using a pulsed laser beam, the frequency of the laser beam may be affected. The irradiation time depends on other conditions, but is usually in the range of 1 second to 10 minutes, and the substrate temperature is from room temperature to 30 minutes.
Temperatures in the range of 0 ° C are used. Further, the frequency when using the pulsed laser light is selected in the range of 0.5 to 50 Hz, and under this condition, until a desired light emitting element is obtained.
Repeat pulse irradiation. Thus, a zinc oxide luminescent thin film having high luminance and high luminous efficiency can be manufactured.

Further, in the method of the present invention, the zinc oxide light emitting thin film itself is coated on a substrate on which a transparent conductive layer or a color filter or both are formed.
The light-emitting element can be formed without giving any adverse effect to the transparent conductive layer or the color filter, and a light-emitting element with high luminance and high luminous efficiency and a light-emitting element with improved color purity due to the effect of the color filter can be manufactured. . When forming the zinc oxide or zinc light emitting thin film on a transparent conductive layer or a color filter, irradiating a short-time pulse laser such as an excimer laser is preferable to using continuous light such as a mercury lamp. preferable.

Further, in the method of the present invention, by forming the zinc oxide light emitting thin film on a substrate made of a polymer material, for example, polymethyl methacrylate, a light emitting element using a conventional glass panel substrate can be obtained. In comparison, a light-emitting element with reduced weight can be manufactured.

In the case of polymethyl methacrylate, the drying temperature of the precursor and the heating temperature of the substrate during irradiation with active rays are set to 140 ° C.
Below, it is necessary to manufacture at preferably 100 ° C. or less. Therefore, drying of the precursor can also be performed by irradiation with active rays at a substrate temperature from room temperature to 100 ° C. Also in this case, it is more preferable to irradiate a short-time pulse laser such as an excimer laser than to use a continuous light such as a mercury lamp.

Further, by utilizing the method of the present invention, an arbitrary patterned zinc oxide luminescent thin film can be produced. In this case, the precursor film formed in the same manner as described above is irradiated with a patterned actinic ray having an energy higher than the band gap of the precursor film in the same manner as described above, thereby electronically exciting the precursor film. By scanning with irradiation of actinic rays, it is possible to obtain a zinc oxide thin film having a blue-green emission characteristic only in a desired portion.

By using the method of the present invention, a zinc oxide luminescent thin film can be manufactured even on a substrate having a large surface area and a complicated shape. For example, a precursor film is formed on such a substrate by a technique such as a sol-gel method using a dip coating method, or a spray pyrolysis method, and in the same active ray irradiation process as described above, the active ray irradiation is further performed. And focus adjustment of the active line so that the active line is focused on the substrate.

[0024]

Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

Example 1 A coating solution composed of a 2-methoxyethanol solution containing zinc acetate and monoethanolamine at a concentration of 0.6 mol / liter each was prepared. After applying the above coating solution on a quartz glass substrate by spin coating,
Drying was performed at 0 ° C. By repeating the operation of the coating process and the drying process three times, a film thickness of about 120
nm of the precursor film was obtained. This precursor film also contained trace amounts of residual organic components such as acetate, but was composed of zinc oxide fine particles having a particle size of about 10 nm and a band gap of about 3.3 e.
V. Next, a KrF excimer laser beam (energy: 5.0 eV, pulse width: 22 ns) was applied to the precursor film at a substrate heating temperature of 200 ° C. in the air at an energy density of 100, 130, and 150 mJ / cm ² , Irradiation was performed 5 times (frequency: 1 Hz). The obtained zinc oxide thin film showed strong blue-green light emission by electron beam irradiation. The light emission luminance and light emission efficiency depend on the KrF excimer laser density, and the film irradiated at 130 mJ / cm ² has the highest performance, and 100 mJ / cm ² and 150 mJ / cm ^2.
Approximately 2 times and 4 times respectively compared to the irradiation film of mJ / cm ²
It was twice the performance. Further, the light emission luminance and the light emission efficiency were improved twice as compared with a thin film (Comparative Example 1 described later) manufactured by a heat treatment in a reducing atmosphere containing hydrogen gas.

Example 2 As shown in FIG. 1, a coating solution prepared in the same manner as in Example 1 was used to form a transparent conductive layer 6, a green color filter 7, a blue color filter 7 'and a black matrix 8. It was applied on the panel substrate 9 by spin coating. At a substrate heating temperature of 100 ° C., KrF excimer laser light is emitted at an energy density of 30 mJ / cm ² ,
It was irradiated five times (frequency: 1 Hz) and dried. By repeating this coating and drying operations three times, a precursor film having a thickness of about 110 nm was obtained. This precursor film is
A small amount of residual organic components was also contained, but the particle size was about 20 nm.
And a band gap of about 3.3.
eV. Next, a KrF excimer laser beam (energy: 5.0 eV, pulse width: 22 ns) is applied to the precursor film at a substrate heating temperature of 100 ° C. in the air.
Was irradiated 5 times (frequency: 1 Hz) at an energy density of 90 mJ / cm ² . In the obtained light-emitting element 5, green light was emitted at a portion transmitted through a green color filter by electron beam irradiation, and blue light was emitted at a portion transmitted through a blue color filter. Further, the light emission luminance and the light emission efficiency have been dramatically improved as compared with a light emitting element manufactured by a heat treatment in a reducing atmosphere containing hydrogen gas.

Example 3 A coating solution prepared in the same manner as in Example 1 was applied to a polymethyl methacrylate substrate by spin coating. At room temperature (20 ° C.), KrF excimer laser light was irradiated at an energy density of 10 mJ / cm ² 20 times (frequency: 10 Hz) and dried. By repeating the operation of the coating process and the drying process three times, a film thickness of about 1
A 10 nm precursor film was obtained. This precursor film also contained a trace amount of residual organic components, but was composed of zinc oxide fine particles having a particle size of about 20 nm, and had a band gap of about 3.3 eV. Next, a KrF excimer laser beam (energy: 5.0 e) is applied to the precursor film in air at room temperature.
V, a pulse width of 22 ns) at an energy density of 80 mJ / cm ² five times (frequency: 1 Hz). The obtained light-emitting element emitted blue-green light when irradiated with ultraviolet light having a wavelength of 320 nm. Since a normal heating process using an electric furnace requires a heating temperature of 600 ° C. or more, a conventional technique requires forming a zinc oxide luminescent thin film on a polymethyl methacrylate substrate having a thermal deformation temperature of about 140 ° C. Could not.

Example 4 A precursor film having a thickness of about 120 nm was obtained on a quartz glass substrate in the same manner as in Example 1. In the obtained precursor film,
At a substrate heating temperature of 200 ° C. in the air, Kr
F excimer laser light was irradiated five times (frequency: 1 Hz) at a predetermined energy density to obtain a zinc oxide thin film having a thickness of about 100 nm. Further, by repeating the preparation of the precursor film and the irradiation of the KrF excimer laser beam four or ten times, a zinc oxide thin film having a thickness of about 400 nm and 1000 nm was obtained. The energy density of the KrF excimer laser light was changed as shown in Tables 1 and 2 according to the number of laser irradiation steps. The obtained zinc oxide thin film emits strong blue-green light upon irradiation with an electron beam, and the emission luminance and emission efficiency are shown in Tables 1 and 2. By performing laser irradiation at an optimum energy density according to the number of laser irradiation steps, that is, the thickness of the precursor film, the emission luminance and the emission efficiency could be improved.

[0029]

[Table 1]

[0030]

[Table 2]

Comparative Example 1 A precursor film formed in the same manner as in Example 1 was placed in a nitrogen gas containing hydrogen gas (hydrogen gas concentration: 2% by volume) atmosphere in an electric furnace at 600 ° C. for 1 hour. Heat treatment was performed to produce a zinc oxide thin film. Although the obtained thin film was able to confirm blue-green light emission by electron beam irradiation, the light emission luminance and the light emission efficiency were about half as low as the light emission efficiency of the zinc oxide thin film manufactured in Example 1.

Comparative Example 2 A precursor film formed in the same manner as in Example 1 was placed in an atmosphere of nitrogen gas containing hydrogen (the concentration of hydrogen was 2% by volume).
Heat treatment was performed in an electric furnace at 00 ° C. for 1 hour to produce a zinc oxide thin film. The obtained thin film hardly showed blue-green light emission due to electronic excitation, and showed weak orange light emission.

Comparative Example 3 In the same manner as in Example 2, a precursor film was formed on a panel substrate on which a transparent conductive layer, a green color filter, a blue color filter, and a black matrix were formed. As in Comparative Example 1, the precursor film was placed in an atmosphere of nitrogen gas containing hydrogen gas (the concentration of hydrogen gas was 2% by volume) in an atmosphere of 600%.
A heat treatment was performed in an electric furnace at a temperature of 1 ° C. for 1 hour to produce a zinc oxide thin film. In the obtained light emitting device, the light emission luminance and light emission efficiency due to electron beam irradiation could not be measured.

[0034]

According to the present invention, not only a heat-resistant substrate but also a zinc oxide thin-film light-emitting device having high luminance and high luminous efficiency can be used.
It can be easily formed on a transparent conductive layer or a color filter formed on a substrate. Further, this thin-film light emitting element has an advantage that it can be formed on a substrate made of a lightweight material although it has low heat resistance such as a polymer material. Also, conventional phosphors practically used in CRTs are:
Contains multiple elements such as zinc sulfide doped with copper, gold and aluminum. On the other hand, the zinc oxide phosphor that is expected to be put to practical use by the present invention is a simple composition substance consisting of only zinc and oxygen elements, and therefore has the advantage of being an environmentally friendly phosphor excellent in recyclability.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a light-emitting element obtained in Example 2.

FIG. 2 is a cross-sectional view showing a model of the structure of a low-voltage FED.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 electron beam generating element 2 red phosphor 2 ′ green phosphor 2 ″ blue phosphor 3,6 transparent conductive layer 4,9 panel substrate 5 light emitting element 7 green color filter 7 ′ blue color filter 8 black matrix

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Toshihiko 2214-14, Hayashi-cho, Takamatsu-shi, Kagawa Prefecture Within the Shikoku Institute of Industrial Technology Research Institute, Ministry of Economy, Trade and Industry (72) Inventor Yoichiro Nakanishi 3 Johoku, Hamamatsu City, Shizuoka Prefecture No.5-1, Shizuoka University, Research Institute of Electronic Engineering (72) Inventor Yuko Konan 3-5-1, Jokita, Hamamatsu-shi, Shizuoka Prefecture F-Term, Shizuoka University, Research Institute of Electronic Engineering 4F001 CA06 CF01 XA08 XA30 5C028 FF01 FF11 FF14 5C036 EE01 EE14 EF01 EF06 EF08 EG01 EG25 EG28 EG36 EH07 EH08 EH13

Claims (5)

[Claims] After forming a precursor film composed of zinc oxide fine particles on a substrate, the precursor film has an energy higher than the band gap of the zinc oxide fine particles and is 5 to 500 m.
A thin-film light-emitting element characterized by irradiating an active ray having an energy density controlled so as to be small when the film thickness is small and to be large when the film thickness is large within the range of J / cm ^2. Manufacturing method. 2. The method according to claim 1, wherein the zinc oxide fine particles have a particle size of 0.5 to 500 nm.
The method for producing a thin-film light emitting device according to claim 1, having a particle diameter in the range of: 3. The active ray is an excimer laser.
Or the method for producing a thin-film light emitting device according to 2. 4. The substrate according to claim 1, wherein the substrate is a polymer material substrate.
4. The method for producing a thin film light emitting device according to 2 or 3. 5. The method according to claim 1, wherein a color filter or a transparent conductive layer is formed on the substrate.