JPH046274B2 - - Google Patents

Description

[Detailed Description of the Invention] <Technical Field> The present invention relates to a thin film EL device that emits EL (electroluminescence) light in response to the application of an electric field, and particularly relates to a thin film EL device that emits EL (electroluminescence) light in response to the application of an electric field. Multilayer thin film sandwiched between dielectric layers
This invention relates to improving interlayer adhesion in EL devices.

<Prior art> A double insulation structure thin film consisting of a light-emitting layer made of ZnS or ZnSe doped with Mn, etc. as a light-emitting center, and both sides of the light-emitting layer covered with a dielectric layer such as an oxide film or a nitride film.
EL elements emit light with high brightness and have a long life, so they are already used in a wide range of applications, such as flat display panels for information display. However, the commonly used ones have Mn as a luminescence center in the ZnS matrix.
ZnS doped with: Mn is used as the emissive layer, _{Y2O3 and}
The EL is limited to a yellow-orange luminescent color in which a dielectric layer such as Si ₃ N ₄ is layered on both sides of the luminescent layer.
The reality is that thin-film EL devices that emit light in multiple colors have not yet reached the level of practical use. On the other hand, with the recent development of information processing technology, multicolor display is becoming an indispensable element.

For example, when rare earth fluoride is used as a luminescent center for the purpose of obtaining multicolor EL luminescence,
It is well known that TbF ₃ , SmF ₃ , TmF ₃ or PrF ₃ can produce green, red, blue, and white EL emissions, respectively, but it is especially important to
When ZnS:TbF ₃ is used, it is seen as promising as a green EL light-emitting device because a value close to practical brightness can be obtained. In the case of a thin film EL device whose light emitting layer is ZnS:Mn, Mr atoms are substituted at Zn lattice positions. On the other hand, in a thin film EL device using ZnS:TbF ₃ as a light-emitting layer, TbF ₃ is in a molecular and particulate state, and in the extreme, in a mixed state. For this reason,
The adhesion between the ZnS:TbF ₃ light-emitting layer and the dielectric layer is
The higher the TbF ₃ concentration, the weaker it becomes, causing a problem of peeling at the junction between the dielectric layer and the light emitting layer. This phenomenon is thought to be due to the following causes. For example, assuming a ZnS film with a TbF ₃ concentration of 1.6 mol%,
Assuming that ₃ TbF molecules are distributed at equal intervals, TbF ₃
There are only three pairs of Zn and S in the shortest molecular spacing ((1.6/100) ^1/3 = 1/4). all sides
There are extremely few Zn and S pairs surrounded by Zn and S pairs on the closest-packed plane of the TbF ₃ molecules. FIG. 3 is an explanatory diagram schematically showing this situation. A ₁ is the luminescent center of TbF ₃ , A ₂ is the Zn-S pair in contact with TbF ₃ , A ₃
represents a Zn-S pair not in contact with TbF ₃ . Zn
It is thought that as a result of a large number of pairs of Zn and S that are not surrounded by pairs of Zn and S, the adhesion strength is significantly reduced. By the way, the optimal TbF ₃ concentration in the film for luminance needs to be about 2 mol %, and for this reason, increasing the luminance and producing a highly reliable device with strong adhesion are in conflict with each other. This problem is not limited to the case where TbF ₃ is used as the luminescent center.
The same problem occurs when other fluorides and chlorides are used.

<Summary of the Invention> In view of the above problems, an object of the present invention is to provide an element structure for obtaining reliability of a thin film EL element.

In general, the light emitting mechanism of a thin film EL device with a double insulation structure is that electrons are accelerated by an induced electric field in the light emitting layer caused by the application of an external voltage, and the resulting hot electrons collide with the light emitting center to emit light. By exciting the center, electromagnetic spectrum is emitted as EL emission. The electric field strength in the light emitting layer is not uniform, and the electric field is stronger near the interface with the dielectric layer. The stronger the electric field, the higher the energy of the electrons, and the more efficiently the luminescent center is excited. However, the non-uniformity of the electric field strength is noticeable only when the external voltage is low, that is, in the low luminance region of the emission luminance vs. applied voltage characteristic. Non-uniformity does not occur in a high brightness region (saturated brightness) which is a practical problem. Therefore, there is little reduction in brightness due to lowering the luminescent center concentration near the interface. From the above, by lowering the concentration of luminescent centers in the luminescent layer near the interface between the luminescent layer and the dielectric layer, it is possible to prevent device reliability from deteriorating due to interlayer peeling without significantly reducing luminance. becomes.

<Example> FIG. 1 is a block diagram of a thin film EL device showing one example of the present invention. In ₂ O ₃ , SnO ₂ on glass substrate 1
A lower dielectric layer 3 made of Si ₃ N ₄ is deposited thereon by a sputtering method. ZnS on the lower dielectric layer 3
ZnS: TbF ₃ obtained by electron beam evaporation of sintered pellets doped with TbF ₃ in the base material
A luminescent layer consisting of is laminated. This light-emitting layer consists of a low-concentration region 4 with a small amount of TbF ₃ doped located on the side in contact with the lower dielectric layer 3 and a high-concentration region 5 doped with TbF ₃ to an optimal concentration for EL emission superimposed thereon. It is composed of a total of two layers. The TbF ₃ concentration in the low concentration region 4 is set to an appropriate value of 0.1 to 1.0 mol%, and the TbF ₃ concentration in the high concentration region 5 is set to an appropriate value of about 2 mol%. The thickness of the low concentration region 4 is set to about 10 to 1000 Å, preferably 50 to 500 Å, and the thickness of the entire light emitting layer is set to about 2000 to 10000 Å. The concentration of TbF ₃ doped in the emissive layer is controlled by controlling the sintered pellets that serve as targets during the electron beam evaporation process.
It is determined by using ZnS containing TbF ₃ and controlling the TbF ₃ content in this sintered pellet.
An upper dielectric layer 7 made of Y ₂ O ₃ is coated on the light emitting layer by sputtering or electron beam evaporation. On the upper dielectric layer 7, Al formed into strips by vapor deposition or the like is arranged as a back electrode 8 in a direction perpendicular to the transparent electrode 2, forming a matrix electrode structure.

When an alternating current electric field is applied to the light emitting layer via the transparent electrode 2 and the back electrode 8, hot electrons in the light emitting layer travel from one interface of the light emitting layer to the other depending on the polarity of the induced alternating current electric field, and the TbF ₃ Upon collision with the luminescent center, EL emission of the excitation spectrum is generated. This EL emission is mainly emitted from the high concentration region 5 where TbF ₃ is doped to a value close to the optimum value of the emission characteristics, and high brightness near green emission is observed through the glass substrate 1. Since the low concentration region 4 is thin, the EL luminance of the high concentration region 5 is hardly lowered, and a high contrast luminescent display can be performed.

As mentioned above, when doping TbF ₃ into the light emitting layer at a high concentration, the adhesion force tends to weaken at the bonding interface with the dielectric layer. A low concentration region 4 with a small amount of TbF ₃ is doped at the junction interface region between the light emitting layer and the lower dielectric layer 3 made of amorphous Si ₃ N ₄ , which depends on Waals force and has weaker adhesion than an oxide film. This suppresses the drop in adhesion when inserted.

FIG. 2 is a configuration diagram of a thin film EL device showing another embodiment of the present invention.

In this embodiment, a low concentration region 4 similar to the above is inserted in the joint interface region between the light emitting layer and the lower dielectric layer 3, and a similar low concentration region 6 is inserted in the joint interface region between the light emitting layer and the upper dielectric layer 7. This significantly prevents a decrease in the adhesion between the light emitting layer and the dielectric layer. The upper low concentration region 6 also has a thickness of about 10 to 1000 Å, preferably 50 to 500 Å, as described above. Further, the upper dielectric layer 7 is also made of Si ₃ N ₄ which has water resistance similar to the lower dielectric layer 3, and can have a structure that is highly effective in preventing moisture from entering the light emitting layer.

Although the above example describes a thin film EL device with a light emitting layer of ZnS: _TbF3 , the base material of the light emitting layer is
ZnSe, CdSe, etc. may be used, and other rare earth fluorides or chlorides may be used as impurities that serve as luminescent centers. By selecting the type of light-emitting center, a corresponding EL light color can be obtained, making it possible to diversify light-emitting displays and providing long-term reliability of the device.

<Effects of the Invention> As detailed above, according to the present invention, it is possible to obtain high-brightness EL light emission compatible with rare earth compounds without reducing the bonding strength at the interface of the light emitting layer, leading to the diversification of displays. be able to.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a thin film EL device showing one embodiment of the present invention. FIG. 2 is a configuration diagram of a thin film EL device showing another embodiment of the present invention. Figure 3 is
FIG. 2 is a schematic explanatory diagram showing the atomic arrangement of a ZnS:FbF light emitting layer. DESCRIPTION OF SYMBOLS 1... Glass substrate, 2... Transparent electrode, 3... Lower dielectric layer, 4, 6... Low concentration region, 5... High concentration region, 7... Upper dielectric layer, 8... Back electrode.

Claims (1)

[Scope of Claims] 1. Exhibits EL light emission in response to the application of an electric field, and has a three-layer structure consisting of a thin film light-emitting layer doped with fluoride or chloride impurities as a light-emitting center and covered with an insulating film. . A thin film EL device, characterized in that the impurity concentration near the bonding interface with at least one of the thin film light emitting layers and the insulating film is formed to be lower than that in the central portion in the thickness direction of the thin film light emitting layer.