JPH03187190A - Thin film el device and manufacture thereof - Google Patents

Abstract

PURPOSE:To obtain a thin film EL device with small change in an emission spectrum by adjusting crystal orientation of an electroluminescence EL light emitting layer to be used. CONSTITUTION:A transparent electrode 2 is formed in a stripe on a glass substrate by photo etching, a first insulating layer 3 is formed on it, and then light emitting layers 4, 5 are formed by electron beam deposition method. The light emitting layer 4 is a thin zinc sulfide film containing 0.4 atomic % of manganese while the light emitting layer 5 is a thin strontium sulfide containing 0.08 atomic % of cerium. At this time a structure is provided wherein a thin strontium sulfide film with crystal orientation oriented in [100] and a thin zinc sulfide film with crystal orientation oriented in [111] of a zincblende structure and/or [001] of a wurtzite structure are laminated. Thus a thin film EL device with small change in an emission spectrum for magnitude of voltage to be applied can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a thin film EL (electroluminescence) device, and particularly to a thin film EL device that can be used in a multicolor flat display.

[Prior Art] Thin-film EL devices generally have excellent features such as being thin, all-solid-state, and capable of high-contrast, high-quality display.As shown in FIG. It has a structure in which a first insulating layer 3, an EL light emitting layer 4, a second insulating layer 5, and a second electrode 6 are laminated on the electrode, and between the first electrode 2 and the second electrode 6. Light is emitted by applying a voltage. The material for the light-emitting layer of this thin-film EL device is known to be zinc sulfide with manganese added.Thin-film EL devices using this material emit yellow-orange light and are used in measuring instruments, various volatile information devices, etc. has been done.

By the way, in recent years, there has been a strong desire for the emergence of thin film EL devices that can display multiple colors or full colors in order to display more information. A method has been proposed in which a color filter is placed on top of a thin film EL element that emits light with a certain amount of light. For this reason, thin film EL elements that exhibit a wide range of light emission are being studied. Such thin film EL
It is known that, for example, a thin film made of zinc sulfide to which manganese is added is laminated on a thin film made of a material made of strontium sulfide with cerium and chlorine elements added as an element, and this laminate is used as an EL light emitting layer. However, in this thin film EL element, there is a problem that the emission spectrum changes greatly depending on the level of the applied voltage, and the emission color cannot be sufficiently controlled, and gradation display is difficult.

[Problems to be Solved by the Invention] An object of the present invention is to provide a thin film EL device that emits light with a wide range of emission spectra, and whose emission spectrum changes little depending on the level of applied voltage. be.

[Means for Solving the Problems] The present inventors have conducted intensive studies to solve the above problems, and have found that a thin film EL element with small change in emission spectrum can be created by adjusting the crystal orientation of the EL light emitting layer used. The present inventors have discovered that this can be obtained and have completed the present invention. That is, the present invention provides a structure in which a strontium sulfide thin film with a crystal orientation of [100] and a zinc sulfide thin film with a zinc blende structure of [111] and/or wurtzite structure of [001) are laminated. A thin film EL device and a method for manufacturing the same, characterized in that the strontium sulfide thin film and the zinc sulfide thin film have a light emitting layer containing a rare earth element and/or a transition metal.

The present invention will be explained in more detail below.

By providing the thin film EL element of the present invention with the above-mentioned light emitting layer, the change in the emission spectrum becomes small. The reason for this is that in the crystal lattice of strontium sulfide and zinc sulfide, the (100) plane of strontium sulfide and the (111) plane of the zinc blende structure or the (00) plane of the wurtzite structure of zinc sulfide.
01) This is thought to be due to the fact that when the planes are stacked, the lattice misfit becomes the smallest and an interface with good matching is formed. As an example of a light-emitting layer of a thin-film EL element, a structure in which a strontium sulfide thin film containing cerium and a zinc sulfide thin film containing manganese are laminated is given.The light emission starting electric field of the strontium sulfide thin film containing cerium constituting these light-emitting layers is about 0. 6 MV/ctn, and the luminescence starting electric field of zinc sulfide containing manganese is approximately 1.4 MV/cm. Therefore, the luminescence of the zinc sulfide thin film in the luminescent layer that is not laminated in the crystal orientation is higher than that of the strontium sulfide thin film. Light emission starts from a fairly high voltage, and as a result, the emission spectrum changes greatly depending on the level of the applied voltage. On the other hand, in the thin film EL device of the present invention, the light emitting layer of the strontium sulfide thin film starts to emit light in an electric field of about 0.6 MY/cIll, and at the same time as the light emission, electrons are injected into the zinc sulfide thin film from a well-matched interface. Then, the zinc sulfide thin film also begins to emit light, resulting in small changes in the emission spectrum.

The strontium sulfide thin film and the zinc sulfide thin film constituting the light emitting layer of the thin film EL device of the present invention each contain a rare earth element and/or a transition metal, but these are not particularly limited as long as they are optically active. Among these, it is preferable to use manganese as the transition metal and cerium, praseodymium, europium, thulium, or the like as the rare earth element because the brightness of the resulting thin film EL device will be good. In addition, although the content varies depending on the element, good brightness is usually obtained by setting the content to 0.03 to 3.0 at% for rare earth elements and 0.2 to 1.0 at% for transition metals. be able to. Among these, particularly rare earth elements include cerium 0.03 to 0.25 at%, praseodymium 0.0 to 0.2 at%, and europium 0°O to 0.05 at%.
By containing 0.0 to 0.2 atomic % of thulium, even better brightness can be obtained, which is preferable.

Further, the thickness of the thin film constituting the light-emitting layer is not particularly limited, but the total thickness is 0.5 to 3.0 in consideration of drive voltage and brightness.
It is preferable to set it to 0 μm.

The light-emitting layer of the thin-film EL device of the present invention is obtained by a method that can improve the orientation of the thin film constituting the light-emitting layer. The light-emitting layer has a structure in which zinc sulfide thin films oriented in this direction are laminated, for example, by electron beam evaporation using strontium sulfide containing rare earth element sulfide and/or transition metal sulfide as a deposition source at a substrate temperature of 300 to 700°C. The zinc sulfide thin film can be obtained through a process of forming a strontium sulfide thin film by performing a method and a process of forming a zinc sulfide thin film by performing an electron beam evaporation method at a substrate temperature of 200 to 250°C. Here, the rare earth elements and/or transition metals contained in the zinc sulfide thin film may be mixed alone or may be co-deposited. Further, a wurtzite-type zinc sulfide thin film oriented in [0011] can be formed by a method such as a CVD method or an ALE method. As mentioned above, it is preferable that rare earth elements and transition metals be present in the form of sulfides in the evaporation source used when forming the strontium sulfide thin film, since the crystal orientation can be easily controlled.

[Examples] Hereinafter, the present invention will be illustrated by Examples, but the present invention is not limited thereto.

Example 1, Comparative example 1 A thin film EL device having the structure shown in FIG. 1 was manufactured.

First, a striped transparent electrode 2 was formed on a glass substrate 1 by photoetching, and a first insulating layer 3 was formed thereon. The first insulating layer 3 contains 0.03 silicon oxide
0.17 #m of silicon nitride was laminated by RF sputtering method.

Next, light emitting layers 4 and 5 were formed by electron beam evaporation. The light emitting layer 4 is a zinc sulfide thin film containing 0.4 atomic % of manganese, and its thickness is about 0.7 pm. Also, the fifth
The figure shows the X-ray diffraction pattern of the light-emitting layer 4, and it was confirmed from the figure that the light-emitting layer 4 was oriented in [111] with a zincblende structure.

The light-emitting layer 5 laminated on the light-emitting layer 4 contains cerium of 0.0.
The light-emitting layer 5 was formed to a thickness of about 1.21 m by electron beam evaporation using pellets shown below as a evaporation source.

Pellet 1 (Example 1) 0.08 at% of cerium sulfide in strontium sulfide
Added Pellet 2 (Comparative Example 1) Strontium sulfide with cerium chloride added in an amount of 0.08 at. As below,
During the deposition, the atmosphere was controlled by introducing hydrogen sulfide, and the deposition rate was set at 5 people/second.

The X-ray diffraction pattern of the light emitting layer 5 formed as described above was measured. The results are shown in FIG. 4. From the same figure, the peaks of the X-ray diffraction pattern of the light emitting layer 5 formed from the pellet 1 have a particularly high (200) peak intensity, and a strong orientation in the [100] direction. On the other hand, it was confirmed that the luminescent WI5 formed from pellet 2 had weak [100] conformation.

Thereafter, a second insulating layer 6 was formed on the light emitting layer 5 by RF sputtering. The second insulating layer 6 was formed by laminating silicon nitride with a thickness of 0.15 μm and aluminum oxide with a thickness of 0.05 pm. Further, metal aluminum was formed as a back electrode 7 on the second insulating layer 6 with a thickness of 0.1 x m so as to be perpendicular to the transparent electrode.

A back glass was attached to the thin film EL device produced by the above method as a moisture-proof measure, and silicone oil containing silica gel was injected into the space from the injection port, and the injection port was sealed. Characteristics of the device were measured. The characteristics were measured using transparent electrode 2 and back type electrode 6.
An alternating current pulse with a frequency of 50 Hz and a pulse width of 30 μsec was applied between the two. Figure 2 shows the brightness-voltage characteristics.
FIG. 3 shows the dependence of the emission spectrum when changing the voltage. The thin film EL device fabricated in Example 1 has a brightness-voltage characteristic that is relatively close to a straight line, and regarding the emission spectrum, the balance between the emission of the strontium sulfide thin film at 450 to 550 nm and the emission from the zinc sulfide thin film at 550 to 640 r++g is determined by the voltage. It remained almost constant even if the value changed. On the other hand, the thin film EL device fabricated in Comparative Example 1 has many inflection points in its brightness-voltage characteristics, and the emission spectrum shows the onset of light emission from the strontium sulfide thin film at low voltages of 450 to 550 tv, and a sharp rise from around 200 V. 55
Emissions from the zinc sulfide thin film of 0 to 640 nw were observed, and it was therefore confirmed that the balance of the luminescent color changes considerably depending on the voltage.

When the light-emitting layer 5 was formed from the pellet 2 by changing the deposition rate, an improvement in its orientation was observed, and the balance of light emission in the thin-film EL device thus obtained remained almost constant even when the voltage changed. there were.

Further, a color filter having spectral characteristics as shown in FIG. 6 was applied to the thin film EL element produced in Example 1 to obtain a thin film EL panel.

The brightness-voltage characteristics of red, green, and blue of the obtained thin film EL panel are as shown in FIG. 7, and the brightness ratio of red, green, and blue was about 3:6:1 and did not change depending on the voltage. Furthermore, the brightness level was 60.111.20 cd/m2 for each of red, green, and blue when driven at 235V, which was confirmed to be at a practical level. The chromaticity coordinates of this thin film EL panel at 235V are shown in FIG. It can be seen that although the color purity of the three primary colors is inferior to that of CRT, the chromaticity coordinates are also stable and hardly change depending on the voltage. Furthermore, from the above results, it was found that the thin film EL of the present invention is capable of displaying gradations.

Example 2 The same procedure as in Example 1 was used except that the pellet used to deposit the light-emitting layer 5 was strontium sulfide to which 0.08 at.% of cerium sulfide and 0.02 at.% of praseodymium sulfide were added. The EL device shown in FIG. 1 was manufactured by the method.

Using the obtained thin film EL element, a color filter was applied in the same manner as in Example 1 to obtain a thin film EL panel.
The brightness ratio of red, green, and blue for this panel was about 3:6:1 and did not change with voltage.

Further, the chromaticity coordinates of the three primary colors of this panel are shown in FIG. 9, and red and green are CRT, and the chromaticity coordinates are vertical.

In addition to the above, thin-film EL devices were manufactured that included a strontium sulfide thin film containing europium sulfide or thulium sulfide as the light-emitting layer 5, and these emitted light with improved red and blue color purity. Ta.

Note that the thin film EL device of the present invention is not limited to having a light emitting layer of the type shown in FIG. good. Further, the light-emitting layer may be provided by stacking several layers of both layers alternately, and the elements contained in different strontium sulfide thin films and zinc sulfide thin films may be different.

[Effects of the Invention] As described above, it is possible to reduce the change in the emission spectrum of the light emitted by the thin film EL element of the present invention due to applied voltage to a level that causes no practical problems. Furthermore, since the thin film EL element of the present invention is capable of displaying gradation, full color display is possible by combining it with a color filter. Furthermore, since the thin film EL element of the present invention has a quick response, color display is also possible.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing an example of the structure of a thin film EL element. FIG. 2 is a diagram showing the brightness-voltage characteristics of the thin film EL device obtained in Example 1 of the present invention and the thin film EL device obtained in Comparative Example 1. FIG. 3 is a diagram showing the relationship between the emission spectrum and driving voltage of the thin film EL device obtained in Example 1 of the present invention and the thin film EL device obtained in Comparative Example 1. FIG. 4 is a diagram showing X-ray diffraction patterns of strontium sulfide thin films contained in the light emitting layers of the thin film EL device obtained in Example 1 of the present invention and the thin film EL device obtained in Comparative Example 1. FIG. 5 is a diagram showing the Xa diffraction pattern of the zinc sulfide thin film contained in the light emitting layer of the thin film EL device obtained in Example 1 of the present invention and Comparative Example 1. FIG. 6 is a diagram showing the spectral transmission characteristics of the color filter used in Example 2 of the present invention. Figure m7 is a diagram showing the luminance-voltage characteristics of red, green, and blue light emission of the thin film EL panel produced in Example 2 of the present invention. FIG. 8 is a diagram showing the chromaticity coordinates of the thin film EL panel and the CRT produced in Example 2 of the present invention. FIG. 9 is a diagram showing the chromaticity coordinates of the thin film EL panel and the chromaticity coordinate of the CRT obtained in Example 3 of the present invention.

Claims (3)

[Claims] (1) It has a structure in which a strontium sulfide thin film with a crystal orientation of [100] and a zinc sulfide thin film with a zinc blende structure of [111] and/or wurtzite structure of [001] are stacked, A thin film EL device characterized in that the strontium sulfide thin film and the zinc sulfide thin film are provided with a light emitting layer containing a rare earth element and/or a transition metal. (2) Strontium sulfide thin film is cerium 0.03~
0.25 atom% praseodymium 0.0-0.2 atom% europium 0.0-0.05 atom% thulium 0.0
~0.2 at.%, and the zinc sulfide thin film contains 0.2 at.% of manganese.
2. The thin film EL device according to claim 1, wherein the thin film EL device contains 2 to 1.0 at.%. (3) Step of forming a strontium sulfide thin film by performing electron beam evaporation at a substrate temperature of 300 to 700°C using strontium sulfide containing rare earth element sulfide and/or transition metal sulfide as a deposition source, and substrate temperature of 200°C.
2. The method for manufacturing a thin film EL device according to claim 1, wherein the light emitting layer is obtained through a step of forming a zinc sulfide thin film by performing an electron beam evaporation method at ~250°C.