JPS5855636B2 - Thin film EL element - Google Patents

Description

[Detailed description of the invention] The present invention uses EL (Electr) by applying an alternating electric field.

Luminescence) This relates to the structure of a thin film EL element that emits light.

Conventionally, for AC-operated thin film EL elements, a high electric field (about 10'V/(m)) is regularly applied to the light-emitting layer to improve dielectric strength, luminous efficiency, stability of operation, etc.
1 to 2.0 wt excellent Mn (or Cu s A /l
s B r etc.) doped with ZnS.

Three-layer structure ZnS:Mn in which a semiconductor light emitting layer such as Zn5e is sandwiched between dielectric thin films such as Y2O, Ti02, etc.
(or Zn5e:Mn) EL devices have been developed, and improvements in various light-emitting characteristics have been confirmed.

This thin film EL element emits light with high brightness when an alternating current electric field of several KHz is applied, and is characterized by long life.

It was also discovered that the light emission of this thin film EL element has a hysteresis characteristic in which the luminance of the light emitted by the same applied voltage differs in the process of increasing the applied voltage and in the process of decreasing the voltage from the high voltage side. In the process of increasing the applied voltage to a thin film EL element having hysteresis characteristics, when light, electric field, heat, etc. are applied, the thin film EL element has a hysteresis characteristic.
The element is excited to a state of luminescence brightness corresponding to its intensity,
The so-called memory phenomenon, in which the luminance remains high even when light, electric field, heat, etc. are removed and the original state is restored, has opened up a new field of application for display technology.

The basic structure of a ZnS:Mn thin film EL device is shown in the drawing as an example of a thin film EL device.

The structure of the thin film EL element will be specifically explained based on the attached drawings.Ln203 is placed on a glass substrate 1.

Transparent electrode 2 such as SnO2, further layered on top of Y2
O3, Ti02jA1208. Si, N,.

A first dielectric layer 3 made of SiO□ or the like is formed in an overlapping manner by sputtering, electron beam evaporation, or the like.

A ZnS light emitting layer 4 is formed on the first dielectric layer 3 by electron beam evaporation of ZnS:Mn sintered pellets.

At this time, the ZnS:Mn sintered pellets used for vapor deposition are pellets in which Mn, which is an active substance, is set at a concentration depending on the purpose.

A second dielectric layer 5 made of the same material as the first dielectric layer 3 is laminated on the ZnS light emitting layer 4, and A1
A back electrode 6 is formed by vapor deposition.

The transparent electrode 2 and the back electrode 6 are connected to an AC power source 7, and the thin film EL element is driven.

When an AC voltage is applied between the electrodes 2 and 6, the ZnS light emitting layer 4
The above AC voltage is induced between the dielectric layers 3 and 5 on both sides of the ZnS light emitting layer 4. Therefore, the electric field generated in the ZnS light emitting layer 4 excites the electrons into the conductor, accelerates them, and obtains sufficient energy. , directly excites the Mn luminescent center, and emits yellow light when the excited Mn luminescent center returns to the ground state.

That is, when the electrons accelerated by a high electric field excite the electrons of the Mn atoms that have entered the Zn site, which is the luminescence center in the ZnS luminescent layer 4, and fall to the ground state, a strong emission occurs in a wide wavelength range with a peak of approximately 5800 A. Exhibits luminescence.

The thin film EL element having the structure described above can be used as a flat thin display device that takes advantage of the space factor to display characters, symbols, still images, moving images, etc. in computer output display terminal equipment and various other display devices that contain characters and figures. It can be used as a means of displaying images, etc.

Thin-film EL panels as flat flat display devices have a lower operating voltage than conventional cathode ray tubes (CRTs), and are superior in terms of weight and strength compared to plasma display panels (FDPs), which are also flat display devices. It has a wider operating temperature range than liquid crystal display (LCD).
It has many advantages such as fast response speed.

In addition, since it can be used as a pure solid matrix type panel, its operating life is long and its address accuracy makes it extremely effective as an input/output display means for computers, etc.

The present invention provides a thin film EL element in which a dielectric layer is interposed between the light emitting layer and the back electrode as described above, by controlling the film thickness of the dielectric layer. A new and useful technology that makes the phase of the reflected light the same as the phase of the reflected light at the interface between the dielectric layer and the back electrode, prevents the intensity of the reflected light from decreasing due to interference, and effectively guides the light to the outside. The purpose of the present invention is to provide a structure of a thin film EL element.

Hereinafter, one embodiment of the present invention will be described in detail.

In the attached drawing, when the film thickness of the dielectric layer 5 interposed between the back electrode 6 and the light emitting layer 40 is d, and the refractive index is n, reflection from the interface between the light emitting layer 4 and the dielectric layer 5 is Light and back electrode 6
The phase difference ξ between ξ and the reflected light from the interface with the dielectric layer 5 is given by the following equation.

When the following relational expression is satisfied, the reflected light from the two interfaces strengthens each other and heads in the direction in which the light is led out, that is, in the direction of the glass substrate 1.

In a thin film EL device in which the light emitting layer 4 is made of ZnS:Mn and the dielectric layer 5 is made of Y2O3, the peak wavelength of the emission spectrum is around 5800 arrows, as described above, and 580
The refractive index of Y2O3 for light with a wavelength of 0X is 2.
The film thickness of the dielectric layer 5 that satisfies the equation 2) is m=
1450A for m=2, and 2900A for m=2.

Whether the thickness of the dielectric layer 5 is 145 OA or 2900 Å is appropriately selected based on the emission starting voltage, the stability of the thin film EL element, etc.

As explained in detail above, the present invention effectively guides reflected light reflected at the interface of light traveling toward the back electrode to the outside by controlling the film thickness of the dielectric layer disposed between the back electrode and the light emitting layer. This can contribute to increasing the brightness of thin film EL elements.

[Brief explanation of the drawing]

The accompanying drawing is a cross-sectional view schematically showing the structure of a thin film EL element. DESCRIPTION OF SYMBOLS 1... Glass substrate, 3, 5... Dielectric layer, 4... Light emitting layer, 6... Back electrode.

Claims (1)

[Claims] 1. In a thin film EL element in which a thin film light emitting layer is disposed between a transparent electrode and a back electrode, and a dielectric layer is interposed between the thin film light emitting layer and the back electrode, the film thickness of the dielectric layer is The reflected light from the interface between the thin film light emitting layer and the dielectric layer and the reflected light from the interface between the dielectric layer and the back electrode are approximated to a value in which they have the same phase, thereby reducing mutual interference between the reflected lights. A thin film EL device characterized by the following.