JPS58175293A - Electric field light emitting element - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electroluminescent device having a novel structure.

Thin-film electroluminescent devices have been actively developed since the late 1960s because they enable small, lightweight, and high-definition flat panel displays to be realized. In particular, AC electroluminescent elements with a double insulation structure in which a thin film phosphor is sandwiched between two insulating thin films have high practical value due to their high brightness and long life characteristics.

In other words, an electroluminescent device with a double insulation structure in which a ZnS:Mn luminescent layer with a thickness of about 0.6 μm is sandwiched between Y2O3 insulating layers with a thickness of 0.2 μm has a 5kHz
It emits light with a brightness of 150 degrees FFT or more when driven with a high frequency voltage of 1ζ, and exhibits high stability in that the brightness does not decrease even after continuous operation for more than 20,000 hours.

However, the electroluminescent device with this double insulation structure has an excitation voltage of 2. Since the voltage is as high as 0 V or more, the drive circuit becomes complicated, and miniaturization requires an internal cone and the cost is high.

Therefore, in such an electroluminescent device, it is desirable to lower the driving voltage as much as possible.

The present invention was made to realize this desire.
The object of the present invention is to provide a high-luminance, stable electroluminescent device that can be operated at a low voltage.

As an attempt to reduce the excitation voltage of AC-driven thin film electroluminescent devices, there have been two methods: (1) using a material with a high dielectric constant for the insulating layer and relatively increasing the voltage ratio applied to the fluorescent film layer; (2) Two methods have been developed: (2) improvements in the light-emitting layer material and device configuration.

For method (1), the conventional typical insulating material Y2O is used.
As an alternative to 3, 8 m2 os, Ta2 os.

BaTiO3 and PbTiO3 were considered. PbT
The device using the iO3 insulating thin film has a light emission threshold voltage of 70 to 70% compared to the device using the Y2O3 thin film.
A brightness of 300 feet Trumpet is obtained at 8OV.

For method (2), the light emitting layer material is changed from ZnS to Zn5.
Attempts were made to replace it with a or znSxS61-x.

This method has the disadvantage that the saturated brightness is reduced.

As a method to improve the device configuration, an insulating layer is provided only between the emissive layer and the metal electrode.
Attempts have been made to create a Zn8:Mn)-transparent conductive film structure and to further reduce the thickness of the light-emitting layer and the insulating layer, thereby making it possible to lower the excitation voltage at soV'i. As for the brightness, approximately 30 foot lamberts are obtained. However, in an electroluminescent device having such a structure, the thickness of the insulating layer and the luminescent layer is 0.25 μm and 0.1-02 μm, respectively.
Since it is as thin as 1.5 m, it tends to easily cause dielectric breakdown and become unstable. The thinner the film thickness of the phosphor (k) is, the lower the threshold voltage for light emission will be in principle.
When the thickness is less than 4 μm, the crystallinity of the fluorescent film deteriorates, and the luminous efficiency decreases rapidly.

In view of the above, the inventors studied the device structure in order to realize an electroluminescent device that emits light at low voltage and has high brightness and stability. As a result, it was found that an AC electroluminescent device having the structure of conductor crystal substrate-ZnS fluorescent film-insulating film-transparent film electrode has stable characteristics at low voltage and before high brightness. The semiconductor substrate functions as an electrode and also serves as a support substrate for a ZnS fluorescent film or the like. Since the substrate is a single crystal, unlike the case of stacking a conventional vapor-deposited polycrystalline insulating film 1jcZns film, ZnS is
When deposited, a ZnS layer is produced epitaxially. As a result, even if the ZnS film Fi is thin, its crystallinity is good, resulting in a fluorescent film with good luminous efficiency. Therefore, although the fluorescent film is thin, the device has high brightness and is stable. Furthermore, the conventional low voltage light emitting device, metal electrode-insulating layer-Z
nS: In the Mn film-transparent conductive film structure, ZnS fluorescent film and transparent conductive film, generally In2 doped with Sn.
O3 films easily diffuse into each other at their interfaces,
As a result, the efficiency of forming a fluorescent film decreases. On the other hand, such a phenomenon does not occur in the single crystal semiconductor of the present invention, and the efficiency of the fluorescent film does not decrease. In addition, since single crystal semiconductors have a black body color, they have a light absorption effect between light emitting regions.

Contrast is also better compared to conventional products.

The present invention will be specifically explained below with reference to Examples.

Example 1 Mu S was doped. Two types of electroluminescent devices shown in FIG. 1 were fabricated on a single crystal Si substrate having a resistivity of . First, as shown in FIG.
-IF-HNO3- based solution is etched, and a ZnS phosphor film 2 containing 0.8% manganese is deposited on top of it.
25 pm, a Y203 insulating film 3 of 0.6 pm, and finally an (In , Sn ) 203 (hereinafter referred to as ITO) transparent conductive film 4 to a thickness of 0.2 μm. In addition,
The ZnS film 2 and the Y2O3 film 3 were produced by electron beam evaporation, and the ITO film was produced by snornitering.

On the other hand, the element with the structure shown in FIG.
The thickness is 6 μm, and these two Y2O3 films 5 and 6 are
They were formed above and below the nS film 2. This structure is the same as a conventional electroluminescent device with double insulation structure.

The light emission of the electroluminescent device having the structure shown in FIGS. 1(M) and 1(B) was observed from the ITO transparent conductive film 4 side.

5kHz between ITO transparent conductive film 4 and single crystal 81 substrate 1
An alternating current voltage with a frequency of z was applied to cause each to emit light.

The voltage-luminance characteristics are shown in FIG.

As is clear from the figure, the device with the structure shown in FIG.
The former has higher saturation luminance than the latter. For example, when comparing at 120V,
The device shown in Figure 1 (Figure 1) exhibits 30% higher luminance than the element shown in Figure 1 (B).

In the elements of these two structures, the thickness of the ZnS film and the total thickness of the Y2O3 film are equal.

This improvement in brightness is due to the fact that the luminous efficiency of the ZnS film is superior in the device shown in FIG. This is thought to be due to improved crystallinity, and this was confirmed by X-ray reflection t-que observation. Furthermore, when looking at the threshold voltage for starting light emission, the device shown in FIG. 1 (M) is about 1oV lower than the device shown in FIG. It can be said that this is a suitable structure.

Example 2 In order to produce an electroluminescent device driven at an even lower voltage than in Example 1, strontyl titanate r7', which has a higher dielectric constant than Y2O3, was used as an insulating layer.1. (5rTi03) film was used. The dielectric constant of the Y2O3 film is 11.5r, and that of the Ti03 film is 150, and S r T 103 (7
) If an insulator having a dielectric constant one or more orders of magnitude larger than that of Zn5 (dielectric constant 8) is laminated, most of the voltage applied to the device is applied to the ZnS layer, and the emission threshold voltage decreases.

FIG. 3 shows an electroluminescent device using an 8rTi03 film. Figure 2 (Mu) and (B) are respectively Figure 1 (Mu).
, the structure corresponds to (B), but Y2 is used as an insulator.
Use Te5rTi03 (ST) instead of 03. The ST films 7, 8 and 9 were fabricated by high frequency magnetron sputtering in 80% mr-20% 02 gas using a ceramic of 8rTiO3 as a target.

Other ZnS films 2. The ITO film 4 was produced using the same method as in Example 1. Regarding the film thickness, the Zn8 film 2 is 0.25 μm in the device shown in FIG.
03 film 7 is 0.60t1-"l, element B in the same figure (B)
In ZnSl1g2ka()26 μm, 5r
The T103 films 8 and 9 are divided into two parts each having a length of 026 μm, and these are arranged on both sides of the ZnS film 2. The voltage-luminance characteristics of pixel elements M and B are as shown by curves M and B in FIG. 4, respectively. As is clear from the voltage-luminance characteristics of the device, unlike the case of the Y203 insulating film in Example 10,
The brightness rises rapidly depending on the voltage. The emission starting voltage is 2
0V, which is significantly lower than that using the Y2O3 film. On the other hand, the ZnS film 20 is divided into 5 parts on both sides.
The device B with the rTi03 film 8.9 has a higher emission starting voltage of about 7 V and lower luminance than the device M. 40
When compared with the applied voltage of V, the luminance of element B is about 40% higher than that of element B. Furthermore, in element B, even if a voltage twice the emission starting voltage of 20 V is applied, no breakdown of the element itself is observed, but in element B, when a voltage twice the emission starting voltage is applied, It almost broke down, and then the device either did not emit any heat or had extremely low brightness.

As described above, in an electroluminescent device aiming at low emission voltage, the device with the structure shown in FIG. It can be seen that the brightness and stability are superior to the structure.

We investigated a device using a glass substrate 1o as the substrate as shown in Figure 2 ((j). This structure is the basic structure of a conventional double-insulated thin film electroluminescent device. is observed from the lower glass substrate 10 side, unlike the upper side in the case of element B.
Since the ITO transparent conductive film 4 is provided on the glass substrate 10F, which is made by cutting the glass substrate 10F, the light reflection effect caused by this means that in principle, the brightness of the device B can be approximately twice as high. but,
As shown in the voltage-brightness characteristic curve C in FIG. 4, the brightness is about twice that of element B, but not twice that of element B, and is lower than that. Moreover, like element B, this element C easily breaks down when a voltage of 2ff't, which is the emission starting voltage, is applied. Therefore, it is not very preferable as a low voltage light emitting device.

Figure 3 (B), (1 in the structure shown in (j)
It may be possible to further reduce the thickness of the Zn8 layer 2 in order to make the luminescence starting voltage equal to that of the device, but this would further increase the tendency for the brightness to decrease and break down, making it impractical to lower the voltage. It no longer makes sense. However, as shown in FIG. 3(I)), the present invention shown in FIG.
D) An element with the same structure as the element but with only the Zn8 layer 2 having a thickness of 0.15 μm has lower luminance as shown in the voltage-luminance characteristic curve in Figure 4, but the emission starting voltage is 16 V. Furthermore, even if a voltage twice the emission starting voltage is applied, no blemish occurs and the device is stable.

As explained above in Examples 1 and 2, in order to reduce the voltage of the electroluminescent device, the AC electroluminescent device in which the semiconductor single crystal substrate of the present invention, the Zn8 fluorescent film, and the insulating thin film are laminated in this order, It is superior to an insulating structure in terms of improved brightness, improved stability, and ease of lowering the voltage. This means that
This is thought to be due to the good crystallinity of the ZnS film epitaxially formed on the semiconductor single crystal substrate. Based on this idea, it was confirmed that semiconductor single crystal substrates made of Go, GaAa, G&P, etc., which can also be epitaxially formed with Zn8, are as effective as Si. For example, in GaAs5, the crystallinity of the ZnS film formed is better than that of Si, and when comparing the same film thickness, the emission starting voltage was the same as that of the Si substrate, but the brightness was approximately 16% higher. . Since such a single crystal substrate has a black body color, when an element is formed, it has a light absorption function, so one of the features of the present invention is that the contrast can be improved and L can be increased. .

The material of the insulating film is not essential to the present invention and is not limited to its type. In order to lower the voltage, it is preferable to use an insulator with a high dielectric constant, but Zn has a high dielectric constant.
When the F value is one order of magnitude higher than that of S, it becomes possible to further reduce the voltage by reducing the thickness of the ZnS film. In that case, it becomes necessary to form stable ZnS with good crystallinity.

In this respect, the element of the present invention is made of stable Zn with good crystallinity even if it is thin.
An S film is formed.

1 In addition, although the ZnS phosphor film has been explained only with manganese doping, other luminescent centers, TbF3゜S■F
, PrF3, etc., as long as the crystallinity of the matrix ZnS is good, is not subject to any other restrictions in principle as a ZnS fluorescent film.

As explained above, the AC electroluminescent device of the present invention has a structure particularly effective for producing a low voltage driven light emitting device.
Even if the thickness of the phosphor film is reduced, there is little reduction in brightness due to this, and the light emitting element has high stability and contrast.

[Brief explanation of the drawing]

FIG. 1 (M) is a cross-sectional view of one embodiment of the electroluminescent device according to the present invention, FIG. 1 (II) is a cross-sectional view of a comparative example thereof, and FIG. Figure (B) is a cross-sectional view of the pond example.
. (C) is a cross-sectional view of the comparative example; FIG. 1... Semiconductor single crystal Si substrate, 2...
ZnS fluorescent film, 3... Y2O3 insulating film, to 4.
...170 transparent conductive film, completed...SiT
i03 membrane ◎Tsuru 1 Figure IAI jB) @
tri pillow L (Vr, m illusion

Claims (2)

[Claims] (1) An electroluminescent fluorescent film, an insulating thin film, and a transparent electrode are provided on a semiconductor single crystal substrate, and an alternating current electric field is applied between the semiconductor single crystal substrate and the transparent electrode to form the electroluminescent fluorescent film. An electroluminescent device characterized by emitting light. (2) The semiconductor single crystal substrate is silicon or germanium. The electroluminescent device according to claim 1, characterized in that it is made of gallium arsenide or gallium phosphide.