JPS61271780A - Thin film el 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 [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. This invention relates to improving the adhesion between the eyebrows in a thin film EL element having a multilayer structure sandwiched between dielectric layers.

<Prior art> A thin-film EL device with a double insulation structure, in which a light-emitting layer doped with ZnS or Zn5e, etc., as a light-emitting center, and a light-emitting layer doped with oxide or nitride on both sides, has a high Because it emits light with brightness and has a long life, it is already used in a wide range of applications such as flat display panels for information display.However, the most popular ones are ZnS doped with Mn as a luminescent center: Mn is used as a luminescent layer, and Y2
The technology is limited to yellow-orange light emitting devices in which O3, Si8N4, etc. are used as dielectric layers on both sides of the light emitting layer, and thin film EL elements that emit multicolor EL light have not yet reached the level of practical use. The reality is that there is not.

On the other hand, with the recent development of information processing technology, multicolor display is becoming an indispensable element.

For the purpose of obtaining multicolor EL emission, when rare earth fluorides are used as luminescent centers, for example, TbF3, Sm
It is well known that green, red, blue, and white EL emission can be obtained using FB, TmFB, or PrF3, respectively (although it is known that the luminance is close to practical luminance, especially when the luminescent layer is made of ZnS:TbF3). It is considered promising as a green EL light-emitting device because it can obtain a high value.The light-emitting layer is made of ZnS.
:Mn, MAL atoms are substituted at Zn lattice positions. On the other hand, Z n S'
In a thin film EL device using TbFa as a light emitting layer, TbF
3 is in a molecular and particulate state, and in the extreme, it is in a mixed state. Therefore, Z n S : T b F a
The adhesion between the light-emitting layer and the dielectric layer is weak when the TbF3 concentration is high (indeed, it is weak), which causes 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, Z with a TbF3 concentration of 1.6'mol%
Assuming an nS film, assuming that TbF3 molecules are distributed at equal intervals, there are only three pairs of Zn and S in the shortest molecular spacing of TbF3 ((1・6/1oo)'J=
1/4). Z surrounded by pairs of Zn and S on all sides
There are extremely few pairs of n and S on the closest-packed plane of the TbF3 molecule.

FIG. 3 is an explanatory diagram schematically showing this situation.

A represents the luminescence center of TbF, A represents the Zn-3 pair in contact with TbF3, and A3 represents the Zn-8 pair not in contact with TbF3. It is thought that as a result of the formation of many pairs of Zn and S that are not surrounded by pairs of Zn and S, the adhesion force is significantly reduced. By the way, TbF in the optimal film for luminance
The concentration needs to be about 2 mo1%, and therefore, there is a conflict between increasing luminance and producing a highly reliable device with strong adhesion. This problem occurs not only when TbF3 is used as the luminescent center, but also when other fluorides or 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.

Generally, 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 and excite the light emitting center. As a result, the 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 is, the higher the energy of the electrons is, and the more efficient the excitation of the luminescence center is. However, the non-uniformity of the electric field strength is noticeable only in the low luminance region when the external voltage is low, that is, in the luminance luminance-applied voltage characteristic. Non-uniformity does not occur in the 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. By lowering the concentration of luminescent centers in the luminescent layer, it is possible to prevent a decrease in reliability of the device due to peeling between films without causing a significant decrease in luminance.

<Embodiment> FIG. 1 is a block diagram of a thin film EL device showing an embodiment of the present invention. In2O3 on glass substrate 1.

Transparent electrodes 2 made of SnO□ or the like are arranged in a strip shape, and a lower dielectric layer 3 made of 5tBN4 is deposited thereon by sputtering. Laminated on the lower dielectric layer 8 is a light-emitting layer made of ZnS:TbF3 obtained by electron beam evaporation of sintered pellets doped with FbF3 in a ZnS base material.

This light emitting layer has Tb located on the side in contact with the lower dielectric layer 3.
It has a two-layer structure, consisting of a low concentration region 4 with a small amount of F3 doping and a high concentration region 5 superimposed thereon doped with TbF3 at a concentration optimal for EL emission. The TbF3 concentration in the low concentration region 4 is set to 0.1 to 1.0 mol%, and the TbF3 concentration in the high concentration region 5 is set to an appropriate value around 2 mol%. The thickness of the low concentration region 4 is set to about 10 to 100 Å, preferably 50 to 500 Å, and the thickness of the entire light emitting layer is set to about 2000 to 10,000 Å. The concentration of TbF3 doped in the light emitting layer is determined by using ZnS containing TbF3 as a sintered pellet serving as a target in the electron beam evaporation process and controlling the TbF3 content in this sintered pellet. Y2 on the light emitting layer
An upper dielectric layer 7 made of O3 is coated by sputtering, electron beam evaporation, or the like. , upper dielectric layer 7
On the top, 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 travel from one interface of the light emitting layer to the other interface in the light emitting layer according to the polarity of the induced alternating current electric field, causing TbF3 to emit light. Collision with the center causes EL light emission of the excitation spectrum. The EL light is emitted mainly from the high-concentration region 5 doped with TbF3 to a value close to the optimum value of the light emission characteristics, and high-intensity near-green light 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 TbF3 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 doped with a small amount of TbF3 is inserted in the junction interface region between the light emitting layer and the lower dielectric layer 8 made of amorphous SiB N4, which depends on Waals force and has weaker adhesion than an oxide film. Suppresses the decline in adhesion.

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 junction interface region between the light emitting layer and the lower dielectric layer 3, and a similar low concentration region 6 is inserted in the junction interface region between the light emitting layer and the upper dielectric layer 7.
is inserted to more noticeably prevent 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 5i8N4, 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.

In the above embodiment, a thin film EL element having a light emitting layer of ZnS''TbFa has been described, but the base material of the light emitting layer may be Zn5e, CdSe, etc., and other impurities may be used as the light emitting center. Rare earth fluorides and chlorides may also be used. By selecting the type of luminescent center, a corresponding EL luminescent color can be obtained, making it possible to diversify luminescent displays and also provide 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. Can be done.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a thin film EL device showing one embodiment of the present invention. FIG. 2 is a block diagram of a thin film EL transducer showing another embodiment of the present invention. FIG. 3 is a schematic illustration showing the atomic arrangement of the ZnS:FbF light emitting layer. 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. Agent Patent attorney Aihiko Fuku (and 2 others) Figure 2

Claims (1)

[Claims] 1. A thin film EL device characterized in that a region with a low concentration of the impurity is provided near the junction interface of a light emitting layer doped with a fluoride or chloride impurity as a light emitting center.