FR2715262A1 - Light emitting element with thin layers. - Google Patents

Abstract

The invention relates to the manufacture of electroluminescence elements. To obtain excellent visibility over a wide viewing angle in a thin film light emitting element, an intermediate insulating layer (7A) is interposed between a glass substrate (1) and a transparent electrode (2), and this intermediate insulating layer has a refractive index which varies continuously from the refractive index of the glass substrate to that of the transparent electrode, and it has an average optical thickness which is greater than 0.25 times the central wavelength of an emission spectrum. Application to display panels.

Description

I

  Light emitting element with thin layers.

  The present invention relates to an intermediate insulation layer of a thin-film light-emitting element, and particularly relates to an intermediate insulation layer for preventing light reflection.

  emitted for a light emitting layer.

  A thin-film electroluminescence display device of the double-insulated type (hereinafter referred to as a thin film emitter element), in which a light-emitting layer of a fluorescent substance comprising Mn-1 As a light emitting center, is interposed between a transparent electrode and a back electrode, with the interposition of insulation layers, has attracted considerable interest as a thin viewing panel, because it is possible to obtain a light emission with greater brightness, better resolution and more

  is great viewing ability.

  FIG. 8 is a perspective view showing a transmitting element

  of thin-layer light of the double-insulation type belonging to the prior art.

  A thin film emitter element is formed by a glass substrate 1, an intermediate insulation layer 7, a plurality of transparent electrodes 2, a first insulation layer 3 made of Al 2 O 3, SiO 2 silica or Si 3 N 4 silicon nitride, a light emitting layer 4, a second insulating layer formed by the same material as the first insulating layer, and a plurality of Al rear electrodes disposed parallel to the transparent electrodes 3 and in an orthogonal orientation. The thickness of each layer is set at a value of 20 to 1000 nm. The transparent electrodes 2, the first insulating layer 3 and the second insulating layer 5 are formed generally by the sputtering method, and the light-emitting layer is formed by the sputtering method, and the layer light emitter is formed by the sputtering process or the

  electron beam vapor deposition method.

  The light-emitting layer of such a thin-film light-emitting element is ZnS zinc sulfide as a base material, to which a small amount of Mn or TbOF is added as a light-emitting center. The light-emitting layer is deposited while maintaining at an optimum value the concentration of its light emitting center (Mn manganese: 0.4 to 0.6% by mass of zinc sulphide ZnS). After this operation, it is subjected to a heat treatment at a high temperature of about 550 ° C. to improve the crystalline characteristics of the light-emitting layer and to increase the dispersion of the light-emitting center. In such a thin-film light-emitting element, part of the light that is produced in the light-emitting layer 4 directed towards the glass substrate 1 is transmitted partly through the transparent electrode 2 and the layer intermediate insulation 7, passing through the first insulation layer 3, and in part is reflected at respective interfaces of the transparent electrode 2, the intermediate insulation layer 7 and the substrate

glass 1.

  To improve the visibility of the thin film emitter element, it is necessary to minimize the reflection factors and to increase the transmission factor for various angles of incidence at the aforementioned interfaces. The reflectance as described below is given in

  function of the refractive index.

  Fig. 9 is a graphical representation showing the refractive index of the intermediate insulation layer in the light emitting element

  thin film of the prior art.

  The refractive index of the intermediate insulation layer is determined to be an intermediate value between those of the glass substrate and the transparent electrode, so that the refractive index changes in step with each other. The refractive index of the intermediate insulation layer is equal to the square root of the product of the refractive indices of the glass substrate and the transparent electrode. The optical thickness of the intermediate insulation layer, which is the product of the refractive index by the thickness of the intermediate insulation layer, was set at one quarter of the central wavelength

of the light emitted.

  With the refractive index determined above, the reflection factor is minimized and becomes zero only when light from the light emitting layer falls perpendicular to the glass substrate (equal angle of incidence). at O). But in this case, there is almost no problem of visibility, since the element emitting light-film light is generally observed in a direction almost perpendicular to the light-emitting layer for which the reflection factor for light coming from

io from the outside becomes weak.

  In contrast, for incident light that is not normal to the glass substrate (angle of incidence> O), reflection factors for light from the light-emitting layer increase at the interfaces. In this case, the reflection factor for the light from the outside also increases as the thin film light emitting element is observed in the direction of the emitted light. This poses a problem consisting of a strong

reduced visibility.

  The object of the present invention is to provide a thin film light emitting element having excellent visibility over a wide angle of view, by optimizing the refractive index and the optical thickness of the film layer. intermediate insulation, so as to have a reflection factor

  reduced even for light with a non-zero angle of incidence.

  The above object is achieved with a thin-film light emitting element according to the first embodiment, which element comprises: (1) a glass substrate, (2) an intermediate insulation layer, (3) an electrode transparent, (4) the first insulation layer, (5) a light emitting layer, (6) the second insulation layer, and (7) a back electrode and, in this element, the intermediate insulation layer the transparent electrode, the first insulating layer, the light emitting layer, the second insulating layer and the trailing electrode are laminated one by one on the glass substrate, and the glass substrate consists of glass soda base; the intermediate insulation layer has a refractive index having a specific value between the refractive indices of the glass substrate and the transparent electrode and has an optical thickness, produces the refractive index by the thickness of the intermediate insulation layer, equivalent to an intermediate value representing 0.25 to 0.5 times the central wavelength of an emission spectrum; a voltage is applied between the transparent electrode and the rear electrode; the first and second insulation layers consist of a mineral insulating material; the light emitting layer comprises a mineral light-emitting material, and is excited to emit light by electrons propagating from interfaces between the first insulating layer and between the

second layer of insulation.

  Further, the object is also achieved with a thin-film light emitting element according to the second embodiment, said element comprising: (1) a glass substrate, (2) an intermediate insulation layer, (3) a transparent electrode, (4) the first insulation layer, (5) a light emitting layer, (6) the second insulation layer, and (7) a back electrode, and in this element, the intermediate insulation, the transparent electrode, the first insulation layer, the light emitting layer, the second insulation layer and the rear electrode are laminated one by one on the glass substrate, the glass substrate consists of glass made from soda; the refractive index of the intermediate insulation layer has a value that varies continuously between that of the glass substrate at a boundary of the glass substrate and that of the glass electrode at the boundary of the transparent electrode and has an average optical thickness, produces the refractive index by the thickness of the intermediate insulation layer remaining equal to 0.25 times a central wavelength of an emission spectrum or more; a voltage is applied between the transparent electrode and the rear electrode; the first and second insulation layers comprise a mineral insulating material; the light emitting layer comprises a mineral light emitting material and is excited to emit light by electrons propagating from interfaces between the first layer

  insulation and the second insulation layer.

  The optimization of a refractive index and an optical thickness results in a reduced reflection factor of the light in a wide range of angles of incidence which is due to a phase difference in a phenomenon.

  interference from incident light and reflected light.

  Other features and advantages of the invention will be better

  understood from the following detailed description of the modes of

  realization, given as non-limiting examples. The rest of the description is

  Referring to the accompanying drawings, in which: Figure 1 is a perspective view of an embodiment of a thin-film emitter element according to the present invention; FIG. 2 is a graphical representation showing the dependence of the reflection coefficient on the angle of incidence, with the optical thickness nd as a parameter; Fig. 3 is a configuration diagram of a radio frequency sputtering apparatus which is used for manufacturing the embodiment of the thin film emitter element according to the present invention; FIG. 4 is a graphical representation showing a refractive index of the intermediate insulation layer of one embodiment of the thin film emitter element according to the invention; FIG. 5 is a graphical representation showing the dependence of the reflection factor on the average optical thickness (product of the average refractive index by the layer thickness of the intermediate insulation layer), another embodiment of the thin film emitter element according to the present invention; Fig. 6 is a graphical representation showing the variation of the refractive index as a function of the gaseous oxygen content of the sputtering gas to form the insulation layer of this embodiment; Fig. 7 is a graphical representation showing the variation of the spectral transmittance of the intermediate layer as a function of wavelength, in another embodiment of the present invention; Fig. 8 is a perspective view showing a thin-film emitter element of the conventional double insulated type; and FIG. 9 is a graphical representation showing the refractive index of the intermediate insulation layer of the layered light emitting element.

thin classic.

  First Embodiment FIG. 1 is a perspective view of a transmitter element of FIG.

  thin-film light as an embodiment of the present invention.

  The components and elements which are the same as in the prior art shown in FIG. 8, are designated by the same reference numerals. Only one intermediate insulation layer 7A has a difference with respect to the thin-film emitter element of the prior art. The perpendicular reflection factor, R0, of a glass surface in contact with air is given by the following formula: R0 = (n1 - 1) 2 / (n1 +1) 2 where n1 is refractive index of glass. With a glass substrate consisting of NA40 (manufactured by HOYA Co.), its refractive index of 1.573 gives a reflection factor R0 equal to 4.97%. The reflection factor R60 for an angle of incidence of 60 is 20.1%. On the other hand, with sodium-based glass (n1 = 1.51), R0 is equal to 0.14%. The reflection factor R60 for an angle of incidence of 60 is 18%. As a result, the soda glass is a bit better for a thin film emitter element having a large viewing angle. Soda glass is used for a glass substrate. The reflection factor R is expressed by the following formula, denoting by no the refractive index of a transparent electrode, by n the refractive index of an intermediate insulation layer, by n1 the index of refraction of a glass substrate, by the thickness of the intermediate insulation layer, by 0 the angle of incidence of the light, and by X the central wavelength of the emitted light: R = [ r1 + r2 exp (-2i 5)] 2 (1) in which r1, r2 and are respectively given by the following formulas: r1 = (no 0-n) / (no 0 + n) (2) r2 = (n -nl) / (n + nl) (3) δ = 2.nd.cos 0 / X (4) Table 1 gives the relations between the reflection coefficients as a function of the angles of incidence with the optical thickness as a parameter . Reflection coefficients are calculated from the phase difference of light using formula (1) in which formulas (2), (3) and (4) are replaced

  by no = 2, or, n1 = 2.51 and n = 1.74.

  Optical thickness 72.5 100 145 205 290 nd (nm) Angle of incidence 0 0.707 0.468 0 0.5 1

0.779 0.592 0.209 0.345 0.913

() 45 0.850 0.592 0.444 0 0.605

0 60 0.924 0.857 0.707 0.444 0

  ; 1 Z1; 1; 1 t% 1 These calculations of the reflection coefficients are normalized so that the reflection factor is equal to 1 for light having a length

  central wave equal to 580 nm emitted without intermediate insulation layer.

  Table I shows that the reflection coefficient of the intermediate insulation layer is reduced over a wide angle of incidence range for optical thicknesses between 145 nm and 290 nm. These thicknesses are equivalent to values between 0.25 times and 0.5 times the central wavelength. The above mentioned results can be applied to the central wavelength lights of 540 nm, 650 nm and 470 nm emitted by ZnS: Tb,

ZnS: Sm and ZnS: Tm.

  FIG. 2 is a graphical representation showing the dependence of the reflection coefficient on the angle of incidence, with

  the optical thickness nd as a parameter.

  Optical thicknesses are chosen at (1) 72.5 nm, (2) 100 nm, (3)

nm, (4) 205 nm and (5) 290 nm.

  We find that the reflection factor becomes low in a range

  extended angle of incidence, at an optical thickness of 205 nm.

  The embodiment of the thin film emitter element according to the present invention is prepared by the following method. Fig. 3 is a configuration diagram of a radio frequency sputtering apparatus that is used to fabricate the embodiment of the thin film emitter element according to the present invention. A radiofrequency (RF) power supply 13, a target 12, a soda-based glass substrate 11 and a gas inlet tube 14 were installed in a chamber 15. The gas inlet tube was passed through 14 a sputtering gas, which

  contained argon, oxygen, and nitrogen in predetermined ratios.

  A SiAION target was used. SiAION is any insulating material comprising the atomic elements Si, Al, N and O. Circulating a mixture of gases consisting of argon, oxygen and nitrogen in proportions of 10: 0.1: 0.05 was applied. an RF voltage for cathodically spraying the SiAION target. SiAION intermediate insulation layer 7A having a refractive index of 1.73 was

  thus formed on the soda glass substrate 11.

  Six optical thicknesses of (1) 72.5 nm, (2) 100 nm, (3) were prepared

  145 nm, (4) 205 nm, (5) 290 nm and (6) 400 nm.

  The transparent electrode 2 was further formed in a thickness of nm on the intermediate insulation layer 7A, using an ITO target (indium oxide containing 10% by weight of tin oxide). The refractive index

  of the transparent electrode was about 2.

  On the transparent electrode 2, aluminum oxide Al 2 O 3 and tantalum oxide Ta 2 O 5 layers, with a total thickness of 350 nm, were furthermore formed by the sputtering method, as for the first time.

insulation layer.

  Immediately after this, the ZnS: Mn light emitting layer with a thickness of 700 nm was formed by the chemical deposition method.

  organometallic vapor phase (MOCVD).

  In addition, the second layer of spray insulation was formed

  cathodic, in the same material as for the first layer of insulation.

  The luminance in a direction perpendicular to a pixel of a thin-film emitting element thus prepared, etched at 60 Hz, was 350 cd / m 2. The luminance was so great that the slightest difference in visibility of the light-emitting light-emitting elements (1) was recognized

  (6), when one observed these elements exactly of face (angle of incidence of 0).

  In contrast, ambient light reflection was observed on the glass substrate at an angle of incidence greater than 0. The reflection of ambient light became considerable, particularly for

  angle of incidence greater than 30.

  When the aforementioned optical thickness was between 145 and 290 nm, the element had a boone visibility even for light having a wide range of angles of incidence. In particular, in the case of the optical thickness

  205 nm, a good result was obtained in agreement with the theoretical calculation.

  For the above-mentioned 205 nm optical thickness of the intermediate insulation layer, the reflection factor of the emitted light becomes minimal at an angle of incidence close to 45. The reflection factor for the ambient light can also be made minimal for an angle of incidence close to 45. This makes it possible to incorporate an outer insulation layer on the surface of the glass substrate opposite to the intermediate insulation layer. The refractive index of the outer insulation layer is chosen between those of the glass substrate and the intermediate insulation layer, and the thickness of the

  outer insulation layer so that its optical thickness is equal to 205 nm.

  The optical thickness of the intermediate insulation layer is determined from the viewing angle in the application of the thin film emitter element. For example, a relatively low optical thickness can be adopted to meet the requirement of a narrow angle of view required for personal computers. Contrary to this, when a large viewing angle is required, as in some display devices, one can

  adopt a relatively large optical thickness.

  SiAION is used for the aforementioned intermediate insulation layer, but it is also possible to use insulators such as aluminum oxide A1203 whose refractive indices are close to 1.74 with the possibility of weak

  differences in refractive indices.

  Second Embodiment FIG. 6 is a graphical representation showing the variation of the refractive index versus the gaseous oxygen content of the sputtering gas to form the insulation layer of this embodiment. In another embodiment of the invention, the intermediate insulation layer is formed by passing from 0 to 0.3 the concentration during the deposition of oxygen gas, maintaining respectively 10 and 0.05 the concentrations of argon gas and nitrogen gas [Ar: 02: N2 = (10: 0: 0.05) to (10: 0.3: 0.05)]. It is found that the refractive index varies continuously

  value close to 1.51 of the glass substrate at the value of 2.00 of the ITO.

  FIG. 4 is a graphical representation showing an example of the refractive index of the refractive layer of the insulation layer

  intermediate of this embodiment.

  The refractive index of the intermediate insulation layer varies continuously from that of the ITO to that of the glass substrate. FIG. 5 is a graphical representation showing the variation of the reflection factor as a function of the average optical thickness (product of the average refractive index and the layer thickness) in the insulation layer

  intermediate of this embodiment.

  It is found that the continuous variation of the reflection factor is significantly reduced for average optical thicknesses equivalent to a quarter or more of the central wavelength. The higher the average optical thickness, the greater the effect. It is more preferable than the refractive index

varies in a linear fashion.

  Fig. 7 is a graphical representation showing the variation of the spectral transmittance of the intermediate insulation layer, based on

  of the wavelength, in this embodiment.

  The mixing ratios in the argon, oxygen and nitrogen sputtering gas are varied in various ways in accordance with the following conditions: (a) 10: 0.005: 0, (b) 10: 0 : 0.02, (c) 10:

  0: 0.1, (d) 10: 0.2: 0.05, and (e) 10: 0: 0.05.

  The spectral transmission characteristics are found to be flat when the mixing ratio of the sputtering gas corresponds to (d) or (e). These ratios are within a range that allows the continuous mode reflectance factor to be changed from the 2.00 value of the ITO to the 1.51 value of the glass substrate. The transparency for the light becomes bad in the cases (a), (b) and (c), because of the poor spectral transmission in the field

short wavelengths.

  The analysis by secondary ion mass spectrometry reveals that the above-mentioned intermediate insulating layer, the refractive index of which is continuously changed using SiAION, also prevents the diffusion of alkali metals from the glass. soda base serving as a glass substrate, and that it also has an effect greater than that of an oxide layer

  A1203 aluminum oxide or SiO2 silicon oxide.

  As mentioned above, the intermediate layer has a continuous change in the refractive index and is able to reduce the reflection factor if the optical thickness is equivalent to a quarter or more of the center wavelength of the spectrum. 'program. That is why such a layer-thicker intermediate layer also has the effect of reducing the reflection factor irrespective of the central wavelength, thereby effectively applying the layer to a light-emitting element. colorful to

thin layers.

  According to the first embodiment of the invention, there is provided an intermediate insulation layer having a specific value of refractive index which is between those of the glass substrate and a transparent electrode having an optical thickness. , produces the refractive index by the thickness of the layer, equivalent to 0.25 to 0.5 times the central wavelength of an emitted light. In the second embodiment of the invention, it is provided that the intermediate insulation layer has a refractive index value which varies continuously from that of the glass substrate to that of the transparent electrode, with a average optical thickness equivalent to 0.25 times, or more,

  the central wavelength of the emitted light.

  These intermediate layers provide significantly reduced reflectance factors for incident lights at widely distributed angles, allowing thin-film light emitting elements to

  give excellent visibility for large angles of view.

  Further, the cathode sputtering in the second embodiment is the SiAION RF thin-film emitter element, by the use of argon gas, oxygen gas and nitrogen gas, with a continuous change in the oxygen concentration. This cathodic sputtering forms a continuously variable intermediate insulation layer of the refractive index, which easily gives a thin-film emitting element of excellent visibility. Further, a cathode sputtering with a given ratio of argon gas, oxygen gas and nitrogen gas in advance gives an intermediate layer for a thin film emitter element having excellent transparency and capable of preventing any sodium diffusion out of a glass substrate. The intermediate insulation layer can also be formed for example in

12 2715262

  changing the mixing ratios of gases consisting of argon, oxygen and

  nitrogen from 10: 0: 0.5 to 10: 0.2: 0.05.

Claims (6)

  A thin film emitter element comprising (1) a glass substrate, (2) an intermediate insulation layer, (3) a transparent electrode, (4) a first insulation layer, (5) a layer light emitter, (6) a second insulation layer, and (7) a back electrode, the intermediate insulation layer, the transparent electrode, the first insulation layer, the light emitting layer, the second layer the insulation and the rear electrode being laminated in this order and one by one on the glass substrate, characterized in that: the substrate comprises soda-based glass; the intermediate insulation layer has a specific refractive index between the refractive indices of the glass substrate and the transparent electrode, and an optical thickness, which is the product of the refractive index by the thickness of the intermediate insulation layer, equivalent to an intermediate value between 0.25 and 0.5 times the central wavelength of a transmission spectrum; a voltage is applied between the transparent electrode and the rear electrode; the first and second insulating layers consist of a mineral insulating material, the light emitting layer comprises a mineral light-emitting material and is excited to emit light by electrons propagating from interfaces between the first insulation layer and between the second layer of insulation.   A thin film emitter element comprising (1) a glass substrate, (2) an intermediate insulation layer, (3) a transparent electrode, (4) a first insulation layer, (5) a layer light emitter, (6) a second insulation layer, and (7) a back electrode, the intermediate insulation layer, the transparent electrode, the first insulation layer, the light emitting layer, the second layer of insulation and the back electrode being laminated, in this order and one by one, on the glass substrate, characterized 14 2715262   in that the glass substrate comprises soda-based glass; the intermediate insulation layer has a specific refractive index between the refractive indices of the glass substrate and the transparent electrode, and an optical thickness, which is the product of the refractive index by the thickness of the layer, equivalent to 0, 25 times, or more, the central wavelength of an emission spectrum; a voltage is applied between the transparent electrode and the rear electrode; the first and second insulation layers consist of a mineral insulating material; the light emitting layer comprises a mineral light-emitting material and is excited to emit light by electrons propagating from interfaces between the first insulating layer and between the second layer of insulation.   Thin film light emitting element according to Claim 2, characterized in that the intermediate insulation layer includes SiAION.   Thin film emitter element according to Claim 3, characterized in that the intermediate insulation layer is   formed by a high frequency sputtering method.   Thin film light emitting element according to Claim 4, characterized in that the intermediate insulation layer is   formed using gases consisting of argon, oxygen and nitrogen.   Thin-film light-emitting element according to Claim 5, characterized in that the intermediate insulation layer is formed by changing, during its formation, the mixing ratios of the gases.   consisting of argon, oxygen and nitrogen of 10: 0: 0.05 to 10: 0.2: 0.05.