JPS6362135A - Fluorescent display board and its manufacturing method - Google Patents

Abstract

PURPOSE:To form a phosphor display plate with high take-out efficiency of light and is capable of high brightness emission, by forming a rough surface on an interface formed between a substrate and a thin film phosphor and on a surface of the thin film phosphor. CONSTITUTION:Rough recessed and projected parts are formed on an interface (q) 7 of a thin film phosphor 3 formed on a glass substrate 1 made of quartz glass, and phosphor crystal grains 2 are made to grow thereon at angles corresponding to the interface so that the whole surface is densely covered. Surface roughness of the interface (q) 7 is made several mum to several tens mum. Due to this rough interface (q), mutual orientation degrees formed among phosphor crystal grains 2 become small so that rough recessed and projected parts are formed on the surface of the thin film phosphor 3, that is, an interface (p) 6. Light emitted inside the thin film phosphor due to electron beams radiated from the vacuum 4 side is scattered in radiation states and one part of the light enters the glass substrate 1. Because the interfaces (p) and (q) are minute and rough surfaces, the rays of light are repeatedly reflected between an interface (r) and the interface (p) or (q), and they are gradually scattered so that the light to be ejected outside is not kept remain inside the film but all ejected into the side of the vacuum 4 or atmosphere 5.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a phosphor display plate used in display devices, light sources, etc., and a method for manufacturing the same.

BACKGROUND OF THE INVENTION FIG. 2 is a partial sectional view of a phosphor display panel conventionally used in cathode ray tubes and the like. Reference numeral 10 denotes a glass substrate, on the surface of which is coated a phosphor powder layer 11 that emits light upon collision with an electron beam, and on the surface of which a thin aluminum film 12 is provided. The phosphor powder layer is usually 2-3 particle layers.

Further, in a phosphor display plate used in a phosphor display tube or the like, an electrically conductive layer is provided on the surface of a glass substrate, and a phosphor powder layer is further provided on the surface. The phosphor powder is a crystalline substance and comes in various shapes, but it is applied to the glass substrate in such a way that a part of the crystalline substance is in point contact with the glass substrate.

In all of the above conventional examples, phosphor powder is applied to the surface of a glass substrate, and the glass substrate and phosphor powder are in point contact, resulting in extremely poor heat conduction.

Therefore, if an attempt is made to increase the energy density of the electron beam to raise the emission temperature, the temperature of the phosphor increases, and the emission efficiency decreases due to so-called temperature quenching, resulting in a limit to the emission brightness. For example, ZnS of TV phosphor: Ag is 10
At 0° C., the luminous efficiency decreases to about % compared to room temperature. Also, regarding Zn○ used in fluorescent display tubes etc.
The luminous efficiency at 100° C. is about % of that at room temperature. normal C
The power density of an electron beam such as RT is about several mW/ci, so there is no problem of temperature rise, but for projection tubes etc., the power density is about several W/crA.
This results in a serious decrease in luminous efficiency due to an increase in the temperature of the phosphor. Furthermore, line light source devices for electrophotographic optical printers using low-speed electron beam excited phosphors (ZnO:Zn) require extremely high brightness, so the power density of the electron beam is on the order of several tens of W/cl. , and a similar problem occurred.

Therefore, as a means to avoid the temperature increase caused by electron beam irradiation, attempts have been made to form a thin film phosphor on a glass substrate. By forming a thin film phosphor, thermal conductivity with the substrate glass is extremely good compared to conventional phosphors in the form of a powder layer, and the above-mentioned problem of temperature quenching can be avoided.

Problems to be Solved by the Invention However, by making the phosphor a thin film, there is a problem in that the light extraction efficiency is significantly reduced. FIG. 3 is a schematic diagram showing how light is extracted when the phosphor is a powder layer (a) and when the phosphor is a thin film (b).

First, regarding case a, the example in FIG. 3 shows a case where the phosphor powder layer 21 and the glass substrate 22 are not in contact at all. In this case, the phosphor emits light from the electron beam irradiated from the vacuum 20 side, and the light emitted from the light emitting point 23 diverges in all solid angle directions.
), the interface a (27) between the vacuum 20 and the glass substrate 22
) All of the light that reaches the glass substrate enters the glass substrate without being totally reflected, and is transmitted to the atmosphere 25 through the interface. Therefore, if the reflected components at the interfaces a' and b are ignored, the original light is emitted to the atmosphere 26 or vacuum 20 by a factor of 100. In reality, the phosphor particles and the glass substrate 22 are in optical contact over 20-30% of the surface area of the glass substrate 22. Of the light that has entered the glass substrate 22 through this, light rays at an angle that is too large for the ratio of the contact ratio nq of the glass substrate 22 to the refractive index na of the atmosphere 26 = 1 are already totally reflected at the interface. However, as the light is reflected several times between the interface a and the interface where the phosphor particles are in contact, it is gradually scattered and emitted to the outside.

However, when a smooth thin film phosphor 26 is formed on a smooth substrate as in case b, among the light radially diverged from the light emitting point 32, the refractive index np of the thin film phosphor 26 and the vacuum All the light rays having an angle determined by the ratio of the refractive index nv=1 of 20 are totally reflected at the interface C and interface d or interface e, and are confined within the thin film phosphor 26 or the glass substrate 22. In Figure 3, θ3. θ4 is the critical angle at the interfaces d and e, respectively, θ2 is the angle that the light beam making the critical angle at the interface e makes with the vertical axis in the thin film phosphor 26, and θ2=θ1. 33 and 34 are examples of light trails that are totally reflected and confined between interface C and interface d or interface e. Assuming that there is no scattering, the light extraction efficiency is only 13% in the case of Zn○, 9% in the case of ZnS, and the remainder reaches the side edges of the ends. In reality, scattering occurs due to minute irregularities on the surface of the substrate glass and the surface of the thin film phosphor.
In the case of nS sputtered film, the light extraction efficiency is approximately 25%.
That's about it.

As described above, by making the phosphor thin, there is a problem in that the light extraction efficiency is significantly reduced.

Means for Solving the Problems In the present invention, a rough substrate surface is provided, and a thin film phosphor made of an aggregate of phosphor crystal grains is formed on the rough substrate surface so that the surface is as uneven as possible. Make it a structure.

The light generated within the working phosphor is scattered by the rough substrate/thin-film phosphor interface and the uneven surface of the thin-film phosphor, and is emitted to the outside without being trapped within the substrate or the thin-film phosphor. released. Therefore, a light extraction efficiency comparable to that of a phosphor powder layer can be obtained.

Embodiment FIG. 1 shows a sectional view of a phosphor display plate according to an embodiment of the present invention. A thin film phosphor 3 is formed on a glass substrate 1 made of quartz glass. At the interface q(7) between the glass substrate 1 and the thin film phosphor 3, rough unevenness is formed as shown in the figure, and phosphor crystal grains 2 grow on the surface at an angle corresponding to the surface, making the entire surface dense. A thin film phosphor 3 is formed completely covering the area. The surface roughness of the interface q is from several μm to several tens of μm. The phosphor of this example is Zn○ belonging to a hexagonal crystal system, and each phosphor crystal grain 2 is a columnar crystal with a grain size and height of several μm.

Reflecting the rough interface q, the mutual orientation of the phosphor crystal grains 2 is low, and rough irregularities are formed on the surface of the thin film phosphor 3 (interface p(6)).

In the phosphor display panel having the above configuration, the light emitted inside the thin film phosphor by the electron beam irradiated from the vacuum 4 side is irradiated and a part of it enters the glass substrate 1. . Among them, the critical angle valve is released into the atmosphere 6, but the critical angle is θ. The light that enters at a deeper angle is totally reflected at the interface r and reaches the interface q side again. However, in this configuration, since the interfaces p and q are finely rough surfaces, as the light rays are repeatedly reflected between the interface r and the interface p or q, they are gradually scattered and emitted to the outside. That is, the light trail is similar to that of a conventional powder layer phosphor display panel. All light is emitted to the vacuum 4 or atmosphere 5 side without being confined within the film.

The effect of roughening the surface of the substrate is, firstly, to promote the scattering of light at the interface q, and secondly, by using the optimal film forming method as described below, the effect of roughening the surface of the substrate is to promote the scattering of light at the interface q. By lowering the degree of orientation of each crystal grain of the thin film phosphor, the surface of the thin film phosphor (interface p) can be easily roughened without damaging the crystallinity of the phosphor itself, and light is easily scattered on this surface as well. It is about making it happen. Therefore, in order to maximize the effect of the roughened substrate surface on the roughening of the thin film phosphor surface, the film thickness should not be too thick, and is generally thinner than the maximum surface roughness of the substrate surface. It is effective to keep it to a certain extent.

Next, a method for manufacturing a phosphor display plate according to an embodiment of the present invention will be described. First, the surface of the quartz glass substrate 10 is roughened to a predetermined surface roughness by using sandblasting or sandpaper with a temperature varying from #1°C to #1α°C. The surface roughness is preferably from a few μm to several tens of μm.A phosphor thin film is grown thereon.

If a transparent conductive layer is required, a transparent conductive thin film is first deposited by 2,000 to 3,000 layers, and then a phosphor thin film is grown thereon. The material for the transparent conductive film is low-resistance ZnO, which is doped with an appropriate amount of impurities such as A1 to increase the conductivity.
A membrane is suitable.

In this example, Zn◯:Zn phosphor element was used as the phosphor material. The film forming method used was a gas phase transport method using hydrogen as a carrier gas. In a vacuum open tube, a ZnO thin film was grown on a roughened quartz glass substrate using H2 or wet H2 bubbled in water as a carrier gas. The source used was a disc-shaped sintered reagent ZnO powder.

The basic chemical reaction is Zn0 (solid) + H2 (air) Zn (air) + H20 (
is). That is, Zn gas H20 gas produced by reducing source ZnO in H2 gas at high temperature (~1Q00°C) is transported and Zn
The gas is reoxidized and a Zn○ thin film grows.

At this time, if a physical vapor deposition method such as sputtering is used, the surface of the thin film phosphor will be a film with a uniform thickness that extends over the underlying substrate surface, that is, the interface p and the interface q will be Although the light extraction efficiency cannot be sufficiently increased because the planes are parallel, if the chemical vapor deposition method used in this example is used and appropriate film forming conditions are selected, the particle size and height can be reduced. Columnar Z with several μm
The nO crystal grains can be grown densely with a low degree of orientation.

By the way, even if a ZnO film is simply grown on a smooth substrate surface using the same method, a film with a high degree of orientation is likely to be formed, and the proportion of areas where interface p and interface q are close to parallel increases, resulting in a decrease in light extraction efficiency. It decreases to seven.

If the substrate surface is roughened and a thin film phosphor is grown using chemical vapor deposition as in this example, a thin film phosphor with sufficiently rough surfaces on both interfaces p and q can be obtained. can be produced reliably and with good reproducibility.

Furthermore, by using a chemical vapor deposition method, as typified by the vapor phase transport method of this example, which can create a thin film phosphor with good crystallinity without causing damage to the film during film formation. , it is possible to create a film whose internal luminous efficiency of the phosphor itself is comparable to that of an ordinary powdered phosphor.

In the above examples, the range of conditions for producing a thin film phosphor with high internal luminous efficiency and high light extraction efficiency was approximately as follows. That is, Sono ZnOtD humidity temperature 9
00℃~11oo℃, substrate temperature 550℃~760℃
, particularly preferably about 660°C to 700°C. Gas pressure is 5
Torr ~ 20 Torr, 50 Torr as carrier gas
~600 sccM of wet H2 is used. The H2o partial pressure in the introduced carrier gas is preferably 10 to 10 Torrlj degrees. The deposition time varies depending on the washing conditions, but is about 30 minutes to 2 hours. Source temperature 10QO℃, substrate temperature 700℃,
Gas pressure 8 Torr.

The carrier gas has a H2o partial pressure of 5X10 Torr.
Z grown on a quartz glass substrate with an average surface roughness of about 107 fl at t N2200 sccM and a deposition time of 30 min.
n○ Thin film phosphor has a normal average particle size of 1 μm and a layer thickness of about 2
A luminous efficiency completely equivalent to that of a 0 pm powdered phosphor layer was obtained. Figure 4 shows a smooth quartz glass substrate with an average surface roughness of approximately 1.
The surface sEM@ of a ZnO phosphor thin film grown under the same conditions on a 0 μm quartz glass substrate is shown. A is a film grown on a smooth surface, and b is a film grown on a rough surface. As mentioned above, in the case of a, the degree of orientation of the crystal grains is high;
A high proportion of the film surface forms a plane parallel to the substrate surface. On the other hand, in the case of glass, the degree of orientation of the crystal grains is low, and the surface is formed with fine irregularities. The light extraction efficiency of b is four times higher than that of a.

Similar effects can also be obtained by using a metal organic chemical vapor deposition method (hereinafter abbreviated as MO-CVD method) as a suitable film forming method. As an organometallic compound containing Zn, high purity dimethylzinc; (CH3)2Zn or diethylzinc (02H6)2Zn is used, and 02 as an oxidizing gas.
(In addition to 02, H2O, N20.CO3°NO2 may also be used). The organometallic compound is carried to the reaction chamber by a carrier gas such as Ar or N2 through a bubbler, and is blown onto the substrate whose surface has been roughened through a plurality of small holes near the substrate. At a substrate temperature of 200°C or higher, as in the previous example,
A thin film phosphor with high internal luminous efficiency and high light extraction efficiency can be obtained.

The phosphor display plate made of the ZnO:Zn thin film phosphor formed as described above can be used, for example, as a line light source for an optical printer. That is, if the phosphor surface of the present invention is separated into dots arranged linearly at regular intervals using means such as photolithography and selectively irradiated with an electron beam, high light extraction efficiency can be achieved. It is possible to realize a phosphor array with a small amount of optical crosstalk to adjacent dots. Because it is a thin film-like phosphor surface, it is possible to avoid temperature consumption and charge-up due to high current density electron beam irradiation, and it is possible to irradiate an electron beam with a beam power density of 20 W/cA or more and generate a high power of 200 mW/ctA or more. You can get the light output.

The present invention is also effective with other phosphor materials, such as television phosphors (ZnS: A, g, Cl, Y
By growing a thin film of 202S (Eu, etc.) on the roughened inner surface of the face plate, it is possible to create a phosphor display surface that can withstand high current density electron beam irradiation, greatly improving the brightness of the projection tube. do.

Effects of the Invention To realize a phosphor display board capable of emitting high-intensity light with high light extraction efficiency by configuring the interface between the substrate and the thin film phosphor and the surface of the thin film phosphor to be rough. Can be done.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a phosphor display plate according to an embodiment of the present invention, FIG. 2 is a sectional view of a phosphor portion conventionally used in cathode ray tubes, etc., and FIG. A cross-sectional view of a phosphor portion schematically showing how light is extracted in the case of a light body, FIG.
FIG. 4 shows the case where the plate surface is smooth, and the same figure shows the case where the glass substrate surface is rough. 1... Glass substrate, 2... Fluorescent crystal grains, 3... Thin film phosphor. Name of patron: Patent attorney Toshio Nakao and one other name
1 Figure 4

Claims (4)

[Claims] (1) A substrate with a roughened surface and an aggregate of phosphor crystal grains deposited on the surface thereof, and at least one crystal plane of the phosphor crystal grains is fixed to the substrate surface. Features a fluorescent display board. (2) The phosphor display plate according to claim 1, wherein the thickness of the thin film phosphor is thinner than the maximum surface roughness of the substrate surface. (3) The phosphor display plate according to claim 1, characterized in that the degree of orientation of the phosphor crystal grains is low. (4) A method for manufacturing a phosphor display plate, which comprises roughening the substrate surface in advance and growing a thin film phosphor on the roughened substrate surface by chemical vapor deposition.