WO2021053273A1

WO2021053273A1 - Transparent thin film electroluminescent device

Info

Publication number: WO2021053273A1
Application number: PCT/FI2020/050601
Authority: WO
Inventors: Paula PÄIVIKE
Original assignee: Beneq Oy
Priority date: 2019-09-19
Filing date: 2020-09-18
Publication date: 2021-03-25

Abstract

The invention relates to a transparent thin film electroluminescent display device (100) having a display area (9''). The device (100) comprises a first transparent thin film electroluminescent display (1) having a first display area (9) comprising a first active area (10) capable of emitting light and with a first passive area (20) outside the first active area (10), and a second transparent thin film electroluminescent display (1') having a second display area (9') comprising a second active area (10') capable of emitting light and with a second passive area (20') outside the second active area (10'). The first and second transparent thin film electroluminescent displays (1, 1') are arranged in superposed manner such that the first active area (10) is superposed at least partly with the second passive area (20') in the stacked device structure of the transparent thin film electroluminescent display device (100).

Description

TRANSPARENT THIN FILM ELECTROLUMINESCENT DEVICE

FIELD OF THE INVENTION

The present invention relates to a transparent thin film electroluminescent device and more particularly to a transparent thin film electroluminescent device according to preamble of claim 1.

BACKGROUND OF THE INVENTION

Electroluminescent displays are known flat panel displays comprising for example a luminescent material layer between two insulator layers and two conductor layers. The mentioned layers form an active layer of the electroluminescent display. The active layer is formed on a substrate, such as glass substrate, and the substrate supports the active layer. During use of the electroluminescent (EL) display a voltage is applied to the conductor layers such that an electric field is generated over the luminescent material. The electric field excites the luminescent material making it luminous. This kind of displays are thus called thin film EL displays (TFEL displays). Transparent electroluminescent displays are one important and separate subtype EL displays. In transparent electroluminescent displays (TASEL), the conductor layers, meaning the electrodes to which the voltage is applied, are provided as transparent electrodes enabling the viewer of the display to access simultaneously both the information shown on the display and information or events which are present or take place behind the display. In TASEL displays the metal conductor material is a transparent electrode material, for example indium tin oxide (ITO), so that the electrodes on both sides of the luminescent material layer are suitably transparent to light.

When the voltage is applied to the conductor layers, the luminescent material layer emits radiation in some emission wavelengths of spectrum of light in a wavelength of visible light. The light emission colour of TASEL displays depends on the physical properties of the material used as a luminescent material layer. Typical luminescent materials are e.g. ZnS:Mn (zinc sulphide doped with manganese) and ZnS:Tb (zinc sulphide doped with terbium) for yellow and green emission colours, respectively.

The conductors in the conductor layer are usually arranged to form a matrix of row and column electrodes for forming picture elements or pixels. This kind of a display is called a matrix display. It is also possible to arrange the electrodes into segments of symbols or shapes. In this case, the segments can be used independently of one another by applying the voltage to each segment independently. This kind of display is called a segmented display.

Each display has a display area defined by the substrate on which the active layer is formed. The display area of the display further comprises an active area in which the electrodes or electrode elements are provided and a passive area outside the active area. Accordingly, the active area is defined as area in which light may be emitted and thus information or symbols or images shown when electrical current flows between two superposed electrodes through the emissive layer. Thus, the active area forms also the viewing area of the display. The passive area is unable to emit light and does not comprise the electrodes or electrode elements. The passive area comprises electrical leads, which are also called electrical traces, extending in the passive area or through the passive area and connected to the electrodes in the active area. Electrical leads are arranged both in the upper conductor layer and in the lower conductor layer. However, the electrical leads in the opposing two conductor layers (that is, in the upper and lower conductor layers) cannot be superposed with each other as otherwise electric current starts flow between superposed electrical leads on top of each other and light is emitted also on the passive area, which would be interpreted as an erroneous operation or false signal from the display by the user

Each electrode in the active area is to be separately connected to separate electrical lead such that operation of each electrode may be controlled separately. Accordingly, large and/or complex displays have very large number of separate electrical leads in the passive area. Therefore, the surface of the passive area becomes large in the display area. The passive area may occupy over 50% or as much as 75% or even more of the display area. This especially problematic with matrix displays which have large number of separate row and column electrodes. The large surface area of the passive area causes the display to become disproportionally large in relation to the active area or viewing area. Thus, the efficient surface area of the display is small. Further, the passive area needs to be covered causing difficulties in installing the display to other structures. Further, locating the active area in the display area becomes difficult especially as the whole display area is transparent. In transparent displays, the passive area of the display area cannot always be covered but remains visible.

BRIEF DESCRIPTION OF THE INVENTION

An object of the present invention is to provide a transparent thin film electroluminescent display device so as to overcome or at least alleviate the prior art disadvantages.

The objects of the invention are achieved by a transparent thin film electroluminescent display device which is characterized by what is stated in the independent claim 1.

The preferred embodiments of the invention are disclosed in the dependent claims.

The present invention is based on an idea of providing a transparent thin film electroluminescent display device having a display area in width direction of the transparent thin film electroluminescent display device. The transparent thin film electroluminescent display device comprises a first transparent thin film electroluminescent display comprising a first substrate forming a first display area and a first functional layer on the first substrate. The first functional layer is arranged to provide the first display area with a first active area capable of emitting light and with a first passive area outside the first active area. The transparent thin film electroluminescent display device further comprises a second transparent thin film electroluminescent display comprising a second substrate forming a second display area and a second functional layer on the second substrate. The second functional layer is arranged to provide the second display area with a second active area capable of emitting light and with a second passive area outside the second active area. Functional layer is also called an "active layer" in the present application. Thus, first functional layer and the first active layer mean the same. Similarly, second functional layer and second active layer mean the same.

In the transparent thin film electroluminescent display device of the present invention, the first and second transparent thin film electroluminescent displays is arranged superposed for forming the transparent thin film electroluminescent display device having a stacked device structure in thickness direction of the transparent thin film electroluminescent display device.

According to the present invention the first and second transparent thin film electroluminescent displays are arranged in superposed manner such that the first active area is superposed at least partly with the second passive area in the stacked device structure of the transparent thin film electroluminescent display device.

The first and second transparent thin film electroluminescent displays form together the transparent thin film electroluminescent display device having the display area. Therefore, the first active area and the second active area are at least partly adjacent to each other in the display area of the transparent thin film electroluminescent display device. Thus, the passive area of the display area of the transparent thin film electroluminescent display device may be decreased as the first active area is superposed with the second passive area in the stacked device structure of the transparent thin film electroluminescent display device. Accordingly, the first active area and the second passive area overlap each other in the stacked device structure.

According to the invention, the first active area of the first active layer comprises one or more first superposed electrodes, and the second active area of the second active layer comprises one or more second superposed electrodes. Electric current may flow between the superposed electrodes at the superposed areas. The superposed areas of the superposed electrodes further define one or more emissive areas in the active areas.

According to the invention, the first passive area of the first active layer comprises one or more first electrical leads connected to the one or more first superposed electrodes, respectively, and the second passive area of the second active layer comprises one or more second electrical leads connected to the second superposed electrodes, respectively. Accordingly, the first and second passive areas are provided for supplying electricity to the first and second superposed electrodes, respectively, with the first and second electrical leads.

According to the invention, the first display area of the first transparent thin film electroluminescent display further comprises a first contact area outside the first active layer. The first contact area is provided with one or more first electrical connectors for providing electrical connection to the first transparent thin film electroluminescent display. Further, the second display area of the second transparent thin film electroluminescent display further comprises a second contact area outside the second active layer. The second contact area is provided with one or more second electrical connectors for providing electrical connection to the second transparent thin film electroluminescent display.

The contact areas and the electrical connectors are provided outside the active layers and on the substrate, thus on the display area of the transparent thin film electroluminescent display. The electrical connectors are further connected the electrical leads of the passive area.

According to the invention, the one or more first electrical leads extend from the one or more first electrical connectors, respectively, through the first passive area to the one or more first superposed electrodes, respectively. Further, the one or more second electrical leads extend from the one or more second electrical connectors, respectively, through the second passive area to the one or more second superposed electrodes, respectively.

Accordingly, the passive area is utilized for providing electrical current for the superposed electrodes. Further, the passive area extends between the active area and the contact area.

In one embodiment, the first active area of the first transparent thin film electroluminescent display is superposed with the second passive area of the second transparent thin film electroluminescent display in the stacked device structure, and the second active area of the second transparent thin film electroluminescent display is superposed with the first passive area of the first transparent thin film electroluminescent display in the stacked device structure.

Thus, the first and second passive area may be at least partly covered with the second and first active areas, respectively, in the display area of the transparent thin film electroluminescent display device. This decreases efficiently the passive area of the display area.

In an alternative embodiment, the first active area of the first transparent thin film electroluminescent display is superposed with the second passive area of the second transparent thin film electroluminescent display in the stacked device structure, and the second active area of the second transparent thin film electroluminescent display is superposed with the first passive area of the first transparent thin film electroluminescent display in the stacked device structure such that first active area and the second active area are arranged non-overlapping in the stacked device structure of the transparent thin film electroluminescent display device.

Accordingly, in this embodiment the first and second active areas are arranged adjacent to each other, or fully adjacent to each other in the display area of the transparent thin film electroluminescent display device. Thus, the first and second active area are not superposed in the stacked device structure.

In one embodiment, the first active area of the first transparent thin film electroluminescent display is arranged partly superposed with the second active area of the second transparent thin film electroluminescent display such that the first and second active areas are arranged partly overlapped in the stacked device structure of the transparent thin film electroluminescent display device.

Thus, the first and second active area may emit light and show information in the overlapped or superposed area or areas of the display area. Thus, brightness of the light emitted may be increased on the overlapping areas, or two different colours may be shown in the overlapping areas or two different information maybe shown simultaneously or alternately.

In one embodiment, the first active area of the first transparent thin film electroluminescent display is partly superposed with the second passive area of the second transparent thin film electroluminescent display in the stacked device structure and partly superposed with the second active area of the second transparent thin film electroluminescent display in the stacked device structure.

Accordingly, the first active area may be superposed with both the second active area and the second passive area. Thus, achieving above mentioned benefits of the two overlapping active areas as well as efficient use of the device area also in the second passive areas.

In another embodiment, the first active area of the first transparent thin film electroluminescent display is partly superposed with the second passive area of the second transparent thin film electroluminescent display in the stacked device structure and partly superposed with the second active area of the second transparent thin film electroluminescent display in the stacked device structure, and the second active area of the second transparent thin film electroluminescent display is partly superposed with the first passive area of the first transparent thin film electroluminescent display in the stacked device structure and partly superposed with the first active area of the first transparent thin film electroluminescent display in the stacked device structure.

Accordingly, the first active area and the second active may be superposed with each other and with the second and the first passive areas, respectively. Thus, achieving above mentioned benefits of the two overlapping active areas as well as efficient use of the device area also in the first and second passive areas.

In one embodiment, 50% or less of the first active area of the first transparent thin film electroluminescent display is superposed with the second active area of the second transparent thin film electroluminescent display and 50% or more of the first active area of the first transparent thin film electroluminescent display is superposed with the second passive area of the second transparent thin film electroluminescent display in the stacked device structure.

Thus, at least 50% of the surface area of the first active area is overlapping with the second passive area for providing efficient use of the display area of the transparent thin film electroluminescent display device. In another embodiment, 50% or less of the first active area of the first transparent thin film electroluminescent display is superposed with the second active area of the second transparent thin film electroluminescent display and 50% or more of the first active area of the first transparent thin film electroluminescent display is superposed with the second passive area of the second transparent thin film electroluminescent display in the stacked device structure. Further, 50% or less of the second active area of the second transparent thin film electroluminescent display is superposed with the first active area of the first transparent thin film electroluminescent display and 50% or more of the second active area of the second transparent thin film electroluminescent display is superposed with the first passive area of the first transparent thin film electroluminescent display in the stacked device structure.

Thus, at least 50% of the surface area of the first and second active areas is overlapping with the second and first passive areas, respectively, for providing efficient use of the display area of the transparent thin film electroluminescent display device.

In one embodiment, the first contact area of the first transparent thin film electroluminescent display is superposed with the second passive area of the second transparent thin film electroluminescent display or with the second contact area of the second transparent thin film electroluminescent display.

Thus, the first contact area is not superposed with the second active area and thus deterioration of the viewing area of the display device may be avoided.

In another embodiment, the first contact area of the first transparent thin film electroluminescent display is superposed partly with the second passive area and partly with the second contact area with the second transparent thin film electroluminescent display.

Thus, the first contact area may be superposed with both the second contact area and the second passive area.

In a further embodiment, the first contact area of the first transparent thin film electroluminescent display is superposed with the second passive area of the second transparent thin film electroluminescent display, and the second contact area of the second transparent thin film electroluminescent display is superposed with the first passive area of the first transparent thin film electroluminescent display.

Therefore, the first and second passive areas may be utilized for superposing the second and first contact area respectively for efficient use of the display area.

In one embodiment, the first contact area is provided to a first edge area of the first display area on the first substrate.

Alternatively, the first contact area is provided to a first edge area of the first display area on the first substrate, and the second contact area is provided to a second edge area of the second display area on the second substrate.

Providing the first and/or second contact area to the edge area, meaning on the substrate in vicinity of the edge of the substrate or such that edge area extends on the substrate surface, on same surface as the active layer, from the edge of the substrate enables easy electrical connection to the transparent thin film electroluminescent display.

In one embodiment, the first and second transparent thin film electroluminescent displays are arranged in superposed manner such that the first contact area is outside the second display area in the stacked device structure of the transparent thin film electroluminescent display device such that the first contact area and the second substrate are arranged non-overlapping in the stacked device structure of the transparent thin film electroluminescent display device.

Accordingly, the first contact extends outside second transparent thin film electroluminescent display and the second substrate. Thus, the first contact area is not under or above the second transparent thin film electroluminescent display and the second substrate, but adjacent to the second transparent thin film electroluminescent display and the second substrate. The first electrical connectors are therefore exposed for providing simple and easy electrical connection.

In another embodiment, the first edge area of the first display area provided with the first contact area is arranged outside the second substrate in the stacked device structure of the transparent thin film electroluminescent display device.

In this embodiment, the same is achieved such that the first edge area exposed and extends outside second transparent thin film electroluminescent display and the second substrate.

In a further alternative embodiment, the first contact area is outside the second display area in the stacked device structure of the transparent thin film electroluminescent display device such that the first contact area and the second substrate are arranged non-overlapping in the stacked device structure of the transparent thin film electroluminescent display device. Further, the second contact area is outside the first display area in the stacked device structure of the transparent thin film electroluminescent display device such that the second contact area and the first substrate are arranged non-overlapping in the stacked device structure of the transparent thin film electroluminescent display device.

Accordingly, the same is achieved for the first and second contact areas.

In a yet alternative embodiment, the first edge area of the first display area provided with the first contact area is arranged outside the second substrate in the stacked device structure of the transparent thin film electroluminescent display device. Further, the second edge area of the second display area provided with the second contact area is arranged outside the first substrate in the stacked device structure of the transparent thin film electroluminescent display device.

Also this embodiment achieves the same for the first and second contact areas.

In one embodiment, the first and second transparent thin film electroluminescent displays are matrix display. The first active area of the first transparent thin film electroluminescent display comprises two or more first column electrodes extending a first direction and two or more first row electrodes extending in a second direction, and the second active area of the second transparent thin film electroluminescent display comprises two or more second column electrodes extending in the first direction and one or more first row electrodes extending in the second direction, and that the two or more first row electrodes of the first active layer are aligned with the two or more second row electrodes second active area.

Alternatively, the two or more first column electrodes of the first active layer are aligned with the two or more second column electrodes second active area.

Further alternatively, the two or more first row electrodes of the first active layer are aligned with the two or more second row electrodes second active area, and the two or more first column electrodes of the first active layer are aligned with the two or more second column electrodes second active area.

This enables forming a uniform combined active area for the transparent thin film electroluminescent display device. Thus the combined active area is formed from the first and second active areas such that the two or more first row electrodes of the first active layer are aligned with the two or more second row electrodes second active area, and/or the two or more first column electrodes of the first active layer are aligned with the two or more second column electrodes second active area.

In one embodiment, the first and second transparent thin film electroluminescent displays are segment displays. The first active area of the first transparent thin film electroluminescent display comprises one or more first superposed segment electrodes. Further, the second active area of the second transparent thin film electroluminescent display comprises one or more second superposed segment electrodes.

This enables forming different segment combinations utilizing the first and second transparent thin film electroluminescent displays.

In an alternative embodiment, the first transparent thin film electroluminescent displays is a segment display, and the first active area of the first transparent thin film electroluminescent display comprises one or more first superposed segment electrodes. Further the second transparent thin film electroluminescent display is a matrix displays, and the second active area of the second transparent thin film electroluminescent display comprises two or more second column electrodes extending in the first direction and one or more first row electrodes extending in the second direction.

This enables efficiently combining a segment display features and matrix display features to one transparent thin film electroluminescent display device.

In one embodiment, the first and second transparent thin film electroluminescent displays are arranged superposed such that the first active layer of the first transparent thin film electroluminescent display is arranged towards the second active layer of the second transparent thin film electroluminescent display.

Accordingly, the first and second active layers are close to each other minimizing viewing distortions from various viewing angles other than perpendicular to the display area. Further, the active layers are protected between the first and second substrate.

In one embodiment, the transparent thin film electroluminescent display device comprises a first adhesive layer provide between the first and second transparent thin film electroluminescent displays in the stacked device structure for attaching the first and second transparent thin film electroluminescent displays together.

In another embodiment, the transparent thin film electroluminescent display device comprises a first adhesive layer provide between the first active layer of the first transparent thin film electroluminescent display and the second active layer of the second transparent thin film electroluminescent display in the stacked device structure for attaching the first and second transparent thin film electroluminescent displays together.

Thus, providing only the first adhesive layer between the first and second active layers enables forming short distance between the active layers.

The adhesive layers are provided from transparent adhesive material enabling the transparency of the transparent thin film electroluminescent displays device.

In one embodiment, the transparent thin film electroluminescent display device comprises an intermediate substrate layer arranged between the between the first active layer of the first transparent thin film electroluminescent display and the second active layer of the second transparent thin film electroluminescent display in the stacked device structure. The transparent thin film electroluminescent display device comprises a second adhesive layer provide between the first active layer of the first transparent thin film electroluminescent display and the intermediate substrate layer, and a third adhesive layer provide between the second active layer of the second transparent thin film electroluminescent display and the intermediate substrate layer for attaching the first and second transparent thin film electroluminescent displays together.

The intermediate substrate layer provides rigidity and structural strength to the transparent thin film electroluminescent display device.

It should be noted that also more than two transparent thin film electroluminescent displays may be superposed or superposed in overlapping manner according to the principles of the present invention.

An advantage of the invention is that arranging two or more transparent thin film electroluminescent displays in the superposed manner such that the active area of one transparent thin film electroluminescent display is superposed at least partly with the passive area of another transparent thin film electroluminescent display enables efficient use to the display area in the transparent thin film electroluminescent display device. Further, the passive or free area outside the viewing area may be minimized. This enables providing more compact display devices or larger display devices by combining two or more transparent thin film electroluminescent displays.

BRIEF DESCRIPTION OF THE DRAWINGS The invention is described in detail by means of specific embodiments with reference to the enclosed drawings, in which

Figure 1 shows schematically one transparent thin film electroluminescent display;

Figures 2 and 3 show schematically the stacked structure of one transparent thin film electroluminescent display;

Figure 4 shows schematically active area and passive area in a stacked structure of one transparent thin film electroluminescent display;

Figures 5, 6, and 7 show schematically structures of one transparent thin film electroluminescent matrix display;

Figures 8 and 9 show schematically separately a first and second transparent thin film electroluminescent displays;

Figure 10 shows schematically the first and second transparent thin film electroluminescent displays of figures 8 and 9 arranged in superposed manner according to the present invention;

Figure 11 shows schematically a contact portion of one transparent thin film electroluminescent display;

Figures 12 and 13 show schematically another embodiment of first and second transparent thin film electroluminescent matrix displays;

Figure 14 shows schematically the first and second transparent thin film electroluminescent displays of figures 12 and 13 arranged in superposed manner according to the present invention;

Figures 15 and 16 show schematically another embodiment of first and second transparent thin film electroluminescent matrix displays;

Figure 17 and 18 show schematically the first and second transparent thin film electroluminescent displays of figures 15 and 16 arranged in superposed manner according to the present invention;

Figure 19, 20 show schematically the first and second transparent thin film electroluminescent displays of figures 15 and 16 arranged alternatively in superposed manner according to the present invention;

Figures 21 and 22 show schematically another embodiment of first and second transparent thin film electroluminescent segment displays;

Figure 23 shows schematically the first and second transparent thin film electroluminescent displays of figures 19 and 20 arranged in superposed manner according to the present invention;

Figures 24 to 27 show schematically arrangements for superposing first and second transparent thin film electroluminescent displays.

DETAILED DESCRIPTION OF THE INVENTION

Figure 1 shows a first transparent thin film electroluminescent display 1 having a first substrate 2. The first substrate comprises side edges 3, 4, 5, 6 and defines a first display area 9. The first substrate may be glass or plastic or some other transparent material. The first display area 9 comprises a first active area 10 which forms the viewing area of the first transparent thin film electroluminescent display 1.

The first active area 10 is provided with one or more first emissive areas 14 arranged to emit light for showing information, symbols or images. The first emissive areas 14 are provided by superposed first electrodes, first upper and lower electrodes. The first emissive areas 14 are formed by the two superposed electrodes in the areas where the first upper and lower electrodes are overlapped in thickness direction of the first transparent thin film electroluminescent display 1. Thus, the first active area 10 is defined to be area in which there are first superposed electrodes.

In the context of this application thickness direction is considered to mean direction perpendicular or normal to the substrate surfaces or thin film surfaces or the surface of the display 1, 1’ or display device.

The first display area 9 further comprises a first passive area 20. The first passive area does not comprise first emissive areas 14 and thus the first passive area 20 is unable to emit light and show information. The first passive area 20 may be considered as first free area in the first display area 9. In the first passive, there are no superposed electrodes. However, the first passive area 20 comprises first electrical leads 15, 16, first upper and lower electrical leads 15, 16, connected to the first superposed electrodes, the first upper and lower electrodes, respectively, for providing electricity to the first superposed electrodes. First upper electrical leads are marked with label 15, and first lower electrical leads are marked with label 16.

The display area 9 of the first transparent thin film electroluminescent display 1 further comprise a first contact area 30. The first contact area 30 comprises first electrical connectors, one for each of the first superposed electrodes in the active area 10, or one for each first upper electrode and one or for each first lower electrode. The first electrical connectors are connected respectively to the first electrical leads 15, 16, meaning the first upper and lower electrical leads 15, 16.

The first contact area 30 is provided to a first edge area of the first display area 9 or to the first edge area of the first substrate 2, as shown in figure 1. Accordingly, the first contact area 30 to is provided on first the substrate 2 in vicinity of one or more edges 4, 5 such that contact area 30 extends on the substrate surface.

A voltage source 17 is further connected to the electrical connectors provided to first passive area 20. Thus, electrical connection to the first superposed electrodes is provided.

Figure 2 shows a schematic structure of first transparent thin film electroluminescent display 1. The first transparent thin film electroluminescent display 1 has a layered structure comprising the necessary components for light emission when connected to proper electronics and voltage source 17. Structure of the first transparent thin film electroluminescent display 1 comprises a planar substrate 2 having a first surface 22 and a second surface 21. A first functional layer 40 is provided on the first surface 22 of the substrate 2. The first functional layer 40 comprises the necessary material layers for emitting light. The first functional layer 40 comprises at least one luminescent material layer for emitting light.

Substrate 2 in the context of the present application is the material providing the main, rigid structure of the display. Such substrate materials may comprise glass, for example soda lime glass, borosilicate glass, or any other material with sufficient transparency. In some embodiments, substrates other than glass materials may be used, such as polymer substrates which may provide greater mechanical durability or flexibility than glass. The photopic transmission of suitable substrates is preferably greater than 60% for providing transparency. In some embodiments, the photopic transmission of a substrate may be greater than 80% or even greater than 90%. Substrate thickness may be in the range of 0.05mm - 5mm or more. In some embodiments, the thickness of the substrate may be in the range of 0.3 mm - 3mm or 0.7mm - 1.2mm, and a suitable thickness is for example about 1.1mm.

Figure 3 shows schematically one embodiment of the first functional layer 40 in more detail. The structure of the first functional layer 40 comprises at least one luminescent layer 42 capable of emitting light. The material of the luminescent material layer 42 may be for example material comprising zinc sulphide (ZnS), such as ZnS:Mn (zinc sulphide doped with manganese) and ZnS:Tb (zinc sulphide doped with terbium) for yellow and green emission colours, respectively. The material of the luminescent material layer 42 may also be some other material having luminescent properties. The thickness of the luminescent material layer may be in the range 30 to 250 nm, preferably in the range 50 to 200 nm and most preferably in the range 100 to 180 nm.

The first functional layer 40 further comprises an upper insulator layer

43 and a lower insulator layer 44. The upper and lower insulator layer 43, 44 are provided on opposite surface of the luminescent material layer 42. Accordingly, the luminescent material layer 42 is provided between the upper and lower insulator layers 43, 44. The material of the insulator layer may be for example A1203, Ti02, Hf02, Zr02, Si02 or combinations and mixtures of these materials, or other materials, in particular oxide materials. The thicknesses of the insulator layers 43,

44 may be in the range 30 to 500 nm, more preferably in the range 50 to 200 nm. The upper and lower insulator layer 43, 44 may be similar or they may be different in thickness or in material.

The first functional layer 40 further comprises an upper conductor layer or upper electrode layer 45 and a lower conductor layer or a lower electrode layer 46. The upper electrode layer 45 is provided on the surface of the upper insulator layer 43 on opposite side in relation to the luminescent layer 42. The lower electrode layer 46 is provided on the surface of the lower insulator layer 44 on opposite side in relation to the luminescent layer 42. Accordingly, the insulator layers 43, 44 and the luminescent material layer 42 are provided between the upper and lower electrode layers 45, 46. The material of the electrode layers 45, 46 may be for example indium tin oxide (ITO), ZnO:Al, Sn02 or any other conductive material with sufficient transparency. The thickness of the electrode layers 45, 46 may be in the range 30 to 250 nm, preferably in the range 50 to 200 nm and most preferably in the range 100 to 200 nm.

It should be noted that the first functional layer 40 may also comprise other additional layers, such as a reflector layer(s), passivation layer(s) or barrier layer(s), in addition to the electrode layers 45, 46, insulator layers 43, 44 and the luminescent layer 42.

The term "transparent" in the present application means a structure that passes light in the visible spectrum so that the photopic transmission of the structure is above 30%, more preferably above 40% and most preferably above 50%. Thus, the transparency of first transparent thin film electroluminescent display 1 may be defined by means of the concept photopic transmission in the visible light range. This can be measured using a double beam spectrometer, which produces a transmission spectrum with the transmission percentage as a function of the light wavelength. Photopic transmission values, as above, presented in this application are defined to be perpendicular to the display surface plane.

In this application visible light is defined such that it is the portion of the electromagnetic spectrum to which the human eye is sensitive, causing the sense of sight or vision. The spectrum of the visible light has a wavelength of approximately 380nm - 760nm. Human eye interprets different wavelengths of visible spectrum of light as different colours. For example, light with wavelength of 580nm is seen as yellow, light with wavelength of 545nm is seen as green, and light with wavelength of 690nm is seen as red colour.

As shown in figure 3, voltage from a voltage source 17 is applied to the electrode layers 45, 46 such that an electric field is generated over the luminescent material layer 42. The electric field also is generated over the insulator layers 43, 44. The electric field excites the luminescent material of the luminescent material layer 42 making it luminous and emitting visible light.

A preferred manufacturing method for the first transparent thin film electroluminescent display 1 layer 40 is Atomic Layer Deposition (ALD). The luminescent material layer 42 and insulator layers 43, 44, and thin films of barrier and passivation layers may be provided using ALD. ALD is a generally known coating method in which one or more surfaces of a substrate or other such surface are subjected to alternating surface reactions of at least a first and second gaseous precursors. One ALD cycle is completed when the surface to be coated is subjected once to both the first and second precursors. By repeating the cycle, material layers of different thicknesses can be achieved.

However, also other methods may be used in manufacturing one or more of thin film layers of the active layer 40, such as evaporation methods, vapour deposition methods or various sputtering techniques. One manufacturing method for patterning of thin films and particularly for patterning transparent electrode layers are commonly known, including lithography and printing methods.

In the present invention, the transparent thin film electroluminescent display device 100 comprises the first and second transparent thin film electroluminescent displays 1, G. The first transparent thin film electroluminescent display 1 comprises the first substrate 2 and the first functional layer 40 capable of emitting spectrum of light in a wavelength of visible light, as shown in figures 2 and 3. The device 100 further comprises the second transparent thin film electroluminescent display 1’ comprising a second substrate 2’ and a second functional layer 40’. The first and second transparent thin film electroluminescent displays 1, G are arranged in superposed, stacked or overlapping manner such that the first and second active layers 40, 40’ are superposed and spaced apart from each other for forming the transparent thin film electroluminescent display device 100 with a stacked device structure.

Figure 4 shows the first transparent thin film electroluminescent display 1 and the active layer 40 thereof with the first active area 10 and first passive area 20. The upper and lower conductor layers 45, 46 are patterned layers and comprise first superposed electrodes in the first active area 10 for forming the emissive areas 14. The upper and lower conductor layers 45, 46 are further patterned to comprise the first upper and lower electrical leads 15, 16 in the first passive area 20. The first upper and lower electrical leads 15, 16 are not superposed with each other in the first passive area 20. In other words, upper conductor layer 45 is patterned to comprise first upper electrical leads 15, and lower conductor layer 46 is patterned to comprise first lower electrical leads 16. Superposing a first upper electrical lead 15 and a first lower electrical lead 16 would lead into an erroneous light emission.

Figures 5 and 6 show cross sectional views of the layered structure of the active layer 40 of a first matrix display 1 along two different directions. As shown in figures 5 and 6, in the matrix display the upper conductor layer 45 and the lower conductor layer 46 are patterned so as to have first elongated electrodes 45a, 45b, 45c, 46a, 46b, 46c, respectively. The elongated electrodes 45a, 45b, 45c, 46a, 46b, 46c of the upper and lower conductor layers 45, 46 extend in different directions, for example, transversely or perpendicularly relative to each other. The first elongated electrodes 45a, 45b, 45c, 46a, 46b, 46c serve as electrodes for supplying voltage and/or current, in the thickness direction of the first display 1, through the luminescent material layer, meaning emissive layer, 42 and between the upper and the lower conductor layers 45, 46. The emissive layer 42 is configured emit light in the emissive areas upon electrical current flowing through the emissive layer 42 between the upper and the lower conductor layers 45, 46.

The first elongated electrodes 45a, 45b, 45c, 46a, 46b, 46c form the first superposed electrodes of the first display 1.

The first elongated electrodes 45a, 45b, 45c, 46a, 46b, 46c define the emissive areas 14 at the locations where the first elongated electrodes 45a, 45b, 45c, 46a, 46b, 46c of the upper and the lower conductor layers 45, 46 intersect, as shown in figure 17. The display 1 of figures 5, 6, 7 thereby forms a matrix type display with emissive pixels formed at those intersections 14.

Electroluminescent matrix display described herein operates by the principles of passive matrix display technology where rows (or alternatively, columns) are addressed one by one, and columns (or alternatively, rows) are excited with electrical pulses to make pixels produce light or remain dark on a row (or alternatively, column). Each of the rows (or alternatively, columns) are sweeped so fast that the human vision perceives a two-dimensional image presented on the matrix display. Owing to the pulsed nature of the excitation, displays described herein are also called Alternating current (AC) thin film electroluminescent displays.

In other embodiments, upper and lower conductor layers 45, 46 may be patterned in another way so as to have conductor patterns different from the first elongated electrodes 45a, 45b, 45c, 46a, 46b, 46c.

In figure 7, a second display G is also shown with features denoted with an apostrophe " '

In the context of the present application, emissive areas 14 are defined to exist at locations where there are electrodes 45a, 45b, 45c, 46a, 46b, 46c present in both upper and lower first conductor layers 45, 46, meaning directly opposite to each other.

Figures 8 and 9 show two similar transparent thin film electroluminescent displays 1, G. The first transparent thin film electroluminescent display 1 and the second transparent thin film electroluminescent display G correspond generally the transparent thin film electroluminescent display 1 of figure 1 and are provided as matrix displays. Thus, the first and second transparent thin film electroluminescent displays 1, G comprise the active area 10, 10’, the passive area 20, 20’ and the contact area 30, 30’.

According to the present invention, a transparent thin film electroluminescent display device 100 is provided the arranging the first and second transparent thin film electroluminescent displays 1, 1’ superposed such that the device 100 comprises the stacked device structure in thickness direction of the transparent thin film electroluminescent display device 100.

As shown in figure 10, the first active area 10 of the first transparent thin film electroluminescent display 1 is superposed with the second passive area 20’ of the second transparent thin film electroluminescent display 1’ in the stacked device structure. Further, the second active area 10’ of the second transparent thin film electroluminescent display is superposed with the first passive area 20 of the first transparent thin film electroluminescent display 1 in the stacked device structure.

Therefore, the viewing area or the combined active area of the display device 100 comprises the first and second active areas 10, 10’ which are arranged adjacent to each other in width direction or lateral direction of the stacked device structure, or in the surface direction of the display device and the first and second transparent thin film electroluminescent displays 1, 1’.

In this embodiment, the first and second transparent thin film electroluminescent displays 1, 1’ are similar in shape and dimensions. Thus, stacked device structure of the device 100 enables doubling the surface area of the active area in relation to only one transparent thin film electroluminescent display and decreasing the surface area of the passive area.

In the embodiment of figure 10, the first contact area 30 of the first transparent thin film electroluminescent display 1 is superposed with the second passive area 20’ of the second transparent thin film electroluminescent display 1’, and the second contact area 30’ of the second transparent thin film electroluminescent display 1’ is superposed with the first passive area 20 of the first transparent thin film electroluminescent display 1.

Further, the first contact area 30 is outside the second active layer 40’ in lateral direction of the display device 100, meaning that they are not superposed in the stacked device structure. The second contact area 30’ is outside the first active layer 40 in lateral direction of the display device 100, meaning that they are not superposed in the stacked device structure.

The first and second displays 1, 1’ are matrix displays. Further, the two or more first row electrodes 46a, 46b, 46c of the first active area 10 are aligned with the two or more second row electrodes 46’a, 46’b, 46’c second active area 10’. Thus, a continuous combined active area 10, 10’ or viewing area may be formed.

Alternatively, the two or more first column electrodes 45a, 45b, 45c of the first active layer 10 may be aligned with the two or more second column electrodes 45’a, 45’b, 45’c second active area 10.

Further, the two or more first row electrodes 46a, 46b, 46c of the first active layer 10 may be aligned with the two or more second row electrodes 46’a, 46’b, 46’c second active area 10’, and that the two or more first column electrodes 45a, 45b, 45c of the first active layer 10 may be aligned with the two or more second column electrodes 45’a, 45’b, 45’c second active area 10’. Figure 11 shows schematically the first and second contact area 30, 30’. The contact areas 30, 30’ are provided on the first surface 21, 21’ of the substrate 2, 2’ and to the edge area of the first surface 21, 21’. Thus, there is no active layer 40, 40’ in the contact area 30, 30’. The contact area 30, 30’ comprises the electrical contacts 32, 32’ connected to the conductor leads 15, 16, 15’, 16’ provided to the passive areas 20, 20’.

In the embodiment of figures 9 to 14, the first and second contact are provided on two adjacent edges of the substrate 2, 2’. Thus, the first and second upper electrical leads 15, 15’ are connected to the contact area 30, 30’ in a first side edge 4 and the first and second lower electrical leads 16, 16’ are connected to the contact area 30, 30’ in a second side edge 6, as shown in figures 8 and 9. Again, first upper conductor layer 45 is patterned to comprise first upper electrical leads 15, and first lower conductor layer 46 is patterned to comprise first lower electrical leads 16. Similarly, second upper conductor layer 45’ is patterned to comprise second upper electrical leads 15’, and second lower conductor layer 46’ is patterned to comprise second lower electrical leads 16’.

Usually there is a need for keeping the contact area 30, 30’ exposed in the stacked device structure such that the first contact area 30 is outside the second display area 9’ in the stacked device structure of the transparent thin film electroluminescent display device 100 such that the first contact area 30 and the second substrate 2’ are arranged non-overlapping in the stacked device structure of the transparent thin film electroluminescent display device 100. Similarly, the second contact area 30’ is outside the first display area 9 in the stacked device structure of the transparent thin film electroluminescent display device 100 such that the second contact area 30’ and the first substrate 2 are arranged non overlapping in the stacked device structure of the transparent thin film electroluminescent display device 100.

Figures 12 and 13 show an embodiment in which a first corner 80 is removed from the first transparent thin film electroluminescent display 1, from the first passive area 20 and from the first substrate 2 thereof such that a first oblique side edge 7 is formed. The first corner 80 is removed from opposite the first contact area 30. Similarly, a second corner 80’ is removed from the second transparent thin film electroluminescent display 1’, from the second passive area 20’ and from the second substrate 2’ thereof such that a second oblique side edge 7’ is formed. The second corner 80’ is removed from opposite the second contact area 30’. Otherwise, the first and second transparent thin film electroluminescent displays 1, V correspond the first and second transparent thin film electroluminescent displays 1, G of figures 8 and 9.

Figure 14 shows the first and second transparent thin film electroluminescent displays 1, superposed such that the transparent thin film electroluminescent display device 100 is formed. The first contact area 30 is located in area of the second corner 80’ such that first contact area 30 is exposed and not superposed with the second transparent thin film electroluminescent display . Similarly, the second contact area 30’ is located in area of the first corner 80 which is removed such that second contact area 30’ is exposed and not superposed with the first transparent thin film electroluminescent display 1.

According to the above disclosed, the first and second contact area 30, 30’ may be arranged such that they are located outside the second and first transparent thin film electroluminescent displays 1, 1’, respectively, or outside the first and second substrates 2, 2’, respectively. The first and second contact area 30, 30’ may be arranged such that they are located outside the second and first transparent thin film electroluminescent displays 1, 1’, respectively, by providing suitable shape or dimensions for the first and second substrates 2, 2’. The shape or dimensions of the first and second substrates 2, 2’ may be similar or different. Further, first and second contact area 30, 30’ may be arranged such that they are located outside the second and first transparent thin film electroluminescent displays 1, G, respectively, by arranging the first and second transparent thin film electroluminescent displays 1, G, respectively, displaced relative to each other in the superposed structure, as shown in figures 19 and 20. Otherwise, the first and second active area 10, 10’ and the first and second passive area 20, 20’ and arranged similarly as in figure 10.

Figures 15 and 16 show alternative embodiments of the first and second transparent thin film electroluminescent displays 1, 1’. Figure 15 shows the first transparent thin film electroluminescent display 1 having the first active area 10, the first passive area 20 and the first passive area 30 along the first side edge 4 of the first substrate 2. Figure 16 shows the second transparent thin film electroluminescent display 1 having the first active area 10, the first passive area 20 and the first passive area 30 along the first side edge 4 of the first substrate 2.

Thus, the first contact area 30 is provided only to the first side edge 4 of the first substrate 2. The second contact area 30’ is provided only to the first side edge 4’ of the second substrate 2’.

Figures 17 and 18 show the first and second transparent thin film electroluminescent displays 1, V of figures 15 and 16 superposed in the transparent thin film electroluminescent display device 100 such that the first and second active layer 40, 40’ are towards each other. The first active area 10 and the first passive area 20 are adjacent to each other in the lateral direction of the first transparent thin film electroluminescent display 1. The second active area 10’ and the second passive area 20’ are adjacent to each other in the lateral direction of the second transparent thin film electroluminescent display .

As shown in figure 17, the first active area 10 of the first transparent thin film electroluminescent display 1 is superposed with the second passive area 20’ of the second transparent thin film electroluminescent display 1’ in the stacked device structure. Further, the second active area 10’ of the second transparent thin film electroluminescent display 1’ is superposed with the first passive area 20 of the first transparent thin film electroluminescent display 1 in the stacked device structure.

Therefore, the viewing area or the combined active area of the display device 100 comprises the first and second active areas 10, 10’ which are arranged adjacent to each other in width direction or lateral direction of the stacked device structure, or in the surface direction of the display device and the first and second transparent thin film electroluminescent displays 1, 1’. As may be seen, the first and second passive area 20, 20’ are efficiently utilized in the display device 100.

In the embodiment of figure 17, the first contact area 30 of the first transparent thin film electroluminescent display 1 is superposed with the second passive area 20’ of the second transparent thin film electroluminescent display 1’, and the second contact area 30’ of the second transparent thin film electroluminescent display 1’ is superposed with the first passive area 20 of the first transparent thin film electroluminescent display 1.

As shown in figure 18, the first and second transparent thin film electroluminescent displays 1, 1’, and the first and second substrates 2, 2’ thereof are superposed in aligned manner such that the side edges 3, 4, 5, 6, 3’, 4’, 5’, 6’ are aligned relative to each other.

Figures 19 and 20 show an alternative embodiment in which the first and second transparent thin film electroluminescent displays 1, 1’ of figures 15 and 16 superposed in the transparent thin film electroluminescent display device 100 such that the first and second active layer 40, 40’ are towards each other. In this embodiment, the first and second transparent thin film electroluminescent displays 1, 1’, and the first and second substrates 2, 2’ thereof are superposed in displaced manner such that the side edges 3, 4, 5, 6, 3', 4’, 5’, 6’ are displaced relative to each other.

Accordingly, in the embodiment of figures 19 and 20, the first and second contact area 30, 30’ are arranged such that they are located outside the second and first transparent thin film electroluminescent displays 1, , respectively, or outside the first and second substrates 2, 2’, respectively, due to the displacement of the second and first transparent thin film electroluminescent displays 1, 1’, respectively, or outside the first and second substrates 2, 2’. Thus, the first contact area 30 is not superposed with the second transparent thin film electroluminescent displays 1’ and the second substrates 2’. The first contact area 30 is arranged non-overlapping with the second transparent thin film electroluminescent displays 1’ and the second substrates 2, 2’. Further, the second contact area 30’ is not superposed with the first transparent thin film electroluminescent displays 1 and the first substrate 2. The second contact area 30’ is arranged non-overlapping with the first transparent thin film electroluminescent displays 1 and the first substrates 2.

In the embodiment, the figures 19 and 20, the first active area 10 of the first transparent thin film electroluminescent display 1 is partly superposed with the second passive area 20’ of the second transparent thin film electroluminescent display 1’ in the stacked device structure and partly superposed with the second active area 10’ of the second transparent thin film electroluminescent display 1’ in the stacked device structure. Further, the second active area 10’ of the second transparent thin film electroluminescent display 1’ is partly superposed with the first passive area 20 of the first transparent thin film electroluminescent display 1 in the stacked device structure and partly superposed with the first active area 10 of the first transparent thin film electroluminescent display 1 in the stacked device structure.

Accordingly, the first active area 10 of the first transparent thin film electroluminescent display 1 is arranged partly superposed with the second active area 10’ of the second transparent thin film electroluminescent display 1’ such that the first and second active areas 10, 10’ are arranged partly overlapped in the stacked device structure of the transparent thin film electroluminescent display device 100.

In the superposed areas of the first active area 10 and the second active area 10’ the emitted light may be brighter due to the two superposed emissive areas. Further, each superposed active area may be arranged to emit light of different color such that two or more different colors may be provided to the in the superposed areas first active area 10 and the second active area 10’.

Figures 21 and 22 show a further embodiment in which the first and second transparent thin film electroluminescent displays 1, are segment displays. The first active area 10 of the first transparent thin film electroluminescent display 1 comprises one or more first superposed segment electrodes in the first upper and lower conductor layers 45, 46 of the first active layer 40. The second active area 10’ of the second transparent thin film electroluminescent display 1’ comprises one or more second superposed segment electrodes in the second upper and lower conductor layers 45’, 46’ of the second active layer 40’. The first and second superposed segment electrodes provide the first and second emissive areas 14, 14’ in the first and second active areas 10, 10’, respectively.

Figure 23 shows the first and second segment displays 1, 1’ superposed in the display device 100. As shown in figure 23, the first active area 10 of the first transparent thin film electroluminescent display 1 is superposed with the second passive area 20’ of the second transparent thin film electroluminescent display 1’ in the stacked device structure. Further, the second active area 10’ of the second transparent thin film electroluminescent display 1’ is superposed with the first passive area 20 of the first transparent thin film electroluminescent display 1 in the stacked device structure.

In the embodiment of figure 23, the first contact area 30 of the first transparent thin film electroluminescent display 1 is superposed with the second passive area 20’ of the second transparent thin film electroluminescent display 1’, and the second contact area 30’ of the second transparent thin film electroluminescent display 1’ is superposed with the first passive area 20 of the first transparent thin film electroluminescent display 1.

Alternatively, the second and first transparent thin film electroluminescent displays 1, G or the first and second substrates 2, 2’ may be arranged superposed in displaced manner similarly as in figures 19 and 20. Thus, the first and second contact area 30, 30’ may be arranged such that they are located outside the second and first transparent thin film electroluminescent displays 1, 1’, respectively, or outside the first and second substrates 2, 2’, respectively, due to the displacement of the second and first transparent thin film electroluminescent displays 1, 1’, respectively, or outside the first and second substrates 2, 2’. Thus, the first contact area 30 is not superposed with the second transparent thin film electroluminescent displays and the second substrates 2’. The first contact area 30 is arranged non-overlapping with the second transparent thin film electroluminescent displays G and the second substrates 2, 2’ . Further, the second contact area 30’ is not superposed with the first transparent thin film electroluminescent displays 1 and the first substrate 2. The second contact area 30’ is arranged non-overlapping with the first transparent thin film electroluminescent displays 1 and the first substrates 2.

Figures 25 and 26 show one embodiment of the present invention. Figure 25 shows an exploded view of the superposed or stacked structure of the display device 100 and the figure 26 shows the superposed or stacked structure as it is in the display device 100. The display device 100 comprises a first display 1 comprising a first planar or flat substrate or substrate layer 2 and a first active layer 40. The display device 100 also comprises a second display 1’ comprising a second planar or flat substrate or substrate layer 2’ and a second active layer 40’ provided. In the stacked or superposed structure of the display device 100, the first surface the first and second active layers 40, 40’ are arranged towards each other. The first and second displays 1, 1’ are attached or bonded together with a first adhesive layer 50. The first adhesive layer 50 is provided between the first and second displays 1, 1’. More particularly the first adhesive layer 50 is provided between the first and second active layers 40, 40’ such that the first adhesive layer 50 separates the first and second active layers 40, 40’ from each other.

The superposed structure of the display device 100 of figures 25 and 26 provides thin and light as well as highly transparent structure. In this superposed structure parallax shift is minimized.

Figures 26 and 27 show another embodiment of the present invention. Figure 26 shows an exploded view of the superposed or stacked structure of the display device 100 and the figure 27 shows the superposed or stacked structure as it is in the display device 100. The display device 100 comprises the first display 1 comprising a first planar or flat substrate or substrate layer 2 and the first active layer 40 provided on first substrate 2. The display device 100 also comprises a second display 1’ comprising the second planar or flat substrate or substrate layer 2’ and the second active layer 40’ provided on the second substrate 2’. In the stacked or superposed structure of the display device 100, the first and second active layers 40, 40’ are towards each other. The display device 100 further comprises an intermediate substrate layer 3. The intermediate substrate layer 3 is provided between the first and second displays 1, 1’. More particularly the intermediate substrate layer 3 is provided between the first and second active layers 40, 40’ such that the intermediate substrate layer 3 separates the first and second active layers 40, 40’ from each other. In the embodiment of figures 26 and 27, the display device 100 further comprises a second adhesive layer 51 provided between the first display 1 and the intermediate substrate layer 3 for attaching the intermediate substrate layer 3 to the first display 1. More particularly, the second adhesive layer 51 is provided between the first active layer 40 and the intermediate substrate layer 3 for attaching the intermediate substrate layer 3 to the first display 1. The display device 100 further comprises a third adhesive layer 51’ provided between the second display 1’ and the intermediate substrate layer 3 for attaching the intermediate substrate layer 3 to the second display G. More particularly, the third adhesive layer 51’ is provided between the second active layer 40’ and the intermediate substrate layer 3 for attaching the intermediate substrate layer 3 to the second display G. Thus, the first and second displays 1, 1’ are attached or bonded together with the second and third adhesive layers 51, 51’. The second and third adhesive layers 51, 51’ and the intermediate substrate layer 3 are provided between the first and second displays 1, 1’. More particularly the second and third adhesive layers 51, 51’ and the intermediate substrate layer 3 are provided between the first and second active layers 40, 40’ such that the second and third adhesive layers 51, 51’ and the intermediate substrate layer 3 separate the first and second active layers 40, 40’ from each other.

The invention has been described above with reference to the examples shown in the figures. However, the invention is in no way restricted to the above examples but may vary within the scope of the claims.

Claims

1. A transparent thin film electroluminescent display device (100) having a display area (9") in width direction of the transparent thin film electroluminescent display device (100), the transparent thin film electroluminescent display device comprising:

- a first transparent thin film electroluminescent display (1) comprising a first substrate (2) forming a first display area (9) and a first active layer (40) on the first substrate (2), the first active layer (40) being arranged to provide the first display area (9) with a first active area (10) capable of emitting light and with a first passive area (20) outside the first active area (10); and

- a second transparent thin film electroluminescent display ( ) comprising a second substrate (2’) forming a second display area (9’) and a second active layer (40’) on the second substrate (2’), the second active layer (40’) being arranged to provide the second display area (9’) with a second active area (10’) capable of emitting light and with a second passive area (20’) outside the second active area (10’), the first and second transparent thin film electroluminescent displays (1, 1’) being arranged superposed for forming the transparent thin film electroluminescent display device (100) having a stacked device structure in thickness direction of the transparent thin film electroluminescent display device (100), c h a r a c t e r i z e d in that

- the first and second transparent thin film electroluminescent displays (1, 1’) are arranged in superposed manner such that the first active area (10) is superposed at least partly with the second passive area (20’) in the stacked device structure of the transparent thin film electroluminescent display device (100),

- the first active area (10) of the first active layer (40) comprises one or more first superposed electrodes (45a, 45b, 45c, 46a, 46b, 46c), and the second active area (10’) of the second active layer (40’) comprises one or more second superposed electrodes (45’a, 45’b, 45’c, 46’a, 46’b, 46’c),

- the first passive area (20) of the first active layer (40) comprises one or more first electrical leads (15, 16) connected to the one or more first superposed electrodes (45a, 45b, 45c, 46a, 46b, 46c), respectively, and the second passive area (20’) of the second active layer (40’) comprises one or more second electrical leads

(15’, 16’) connected to the second superposed electrodes (45’a, 45’b, 45’c, 46’a, 46’b, 46’c), respectively,

- the first display area (9) of the first transparent thin film electroluminescent display (1) further comprises a first contact area (30) outside the first active layer (40), the first contact area (30) being provided with one or more first electrical connectors (32) for providing electrical connection to the first transparent thin film electroluminescent display (1), and the second display area (9’) of the second transparent thin film electroluminescent display (G) further comprises a second contact area (30’) outside the second active layer (40’), the second contact area (30’) being provided with one or more second electrical connectors (32’) for providing electrical connection to the second transparent thin film electroluminescent display (1), and

- the one or more first electrical leads (15, 16) extend from the one or more first electrical connectors (32), respectively, through the first passive area (20) to the one or more first superposed electrodes (45a, 45b, 45c, 46a, 46b, 46c), respectively, and the one or more second electrical leads (15’, 16’) extend from the one or more second electrical connectors (32’), respectively, through the second passive area (20’) to the one or more second superposed electrodes (45’a, 45’b, 45’c, 46’a, 46’b, 46’c), respectively.

2. A transparent thin film electroluminescent display device according to claim 1, c h a r a c t e r i z e d in that:

- the first active area (10) of the first transparent thin film electroluminescent display (1) is superposed with the second passive area (20’) of the second transparent thin film electroluminescent display (1’) in the stacked device structure, and the second active area (10’) of the second transparent thin film electroluminescent display (1’) is superposed with the first passive area (20) of the first transparent thin film electroluminescent display (1) in the stacked device structure; or

- the first active area (10) of the first transparent thin film electroluminescent display (1) is superposed with the second passive area (20’) of the second transparent thin film electroluminescent display (1’) in the stacked device structure, and the second active area (10’) of the second transparent thin film electroluminescent display (1’) is superposed with the first passive area (20) of the first transparent thin film electroluminescent display (1) in the stacked device structure such that first active area (10) and the second active area (10’) are arranged non-overlapping in the stacked device structure of the transparent thin film electroluminescent display device (100).

3. A transparent thin film electroluminescent display device according to claim 1, c h a r a c t e r i z e d in that the first active area (10) of the first transparent thin film electroluminescent display (1) is arranged partly superposed with the second active area (10’) of the second transparent thin film electroluminescent display ( ) such that the first and second active areas (10, 10’) are arranged partly overlapped in the stacked device structure of the transparent thin film electroluminescent display device (100).

4. A transparent thin film electroluminescent display device according to claim 1 or 3, c h a r a c t e r i z e d in that:

- the first active area (10) of the first transparent thin film electroluminescent display (1) is partly superposed with the second passive area (20’) of the second transparent thin film electroluminescent display (1’) in the stacked device structure and partly superposed with the second active area (10’) of the second transparent thin film electroluminescent display (1’) in the stacked device structure; or

- the first active area (10) of the first transparent thin film electroluminescent display (1) is partly superposed with the second passive area (20’) of the second transparent thin film electroluminescent display (1’) in the stacked device structure and partly superposed with the second active area (10’) of the second transparent thin film electroluminescent display (1’) in the stacked device structure, and the second active area (10’) of the second transparent thin film electroluminescent display (1’) is partly superposed with the first passive area (20) of the first transparent thin film electroluminescent display (1) in the stacked device structure and partly superposed with the first active area (10) of the first transparent thin film electroluminescent display (1) in the stacked device structure.

5. A transparent thin film electroluminescent display device according to claim 3 or 4, c h a r a c t e r i z e d in that:

- 50% or less of the first active area (10) of the first transparent thin film electroluminescent display (1) is superposed with the second active area (10’) of the second transparent thin film electroluminescent display (1’) and 50% or more of the first active area (10) of the first transparent thin film electroluminescent display (1) is superposed with the second passive area (20’) of the second transparent thin film electroluminescent display (G) in the stacked device structure; or

- 50% or less of the first active area (10) of the first transparent thin film electroluminescent display (1) is superposed with the second active area (10’) of the second transparent thin film electroluminescent display (1’) and 50% or more of the first active area (10) of the first transparent thin film electroluminescent display (1) is superposed with the second passive area (20’) of the second transparent thin film electroluminescent display (1’) in the stacked device structure; and

- 50% or less of the second active area (20) of the second transparent thin film electroluminescent display (1’) is superposed with the first active area (10) of the first transparent thin film electroluminescent display (1) and 50% or more of the second active area (10’) of the second transparent thin film electroluminescent display (1’) is superposed with the first passive area (20) of the first transparent thin film electroluminescent display (1) in the stacked device structure.

6. A transparent thin film electroluminescent display device according to any of claims 1 - 5, c h a r a c t e r i z e d in that:

- the first contact area (30) of the first transparent thin film electroluminescent display (1) is superposed with the second passive area (20’) of the second transparent thin film electroluminescent display ( ) or with the second contact area (30’) of the second transparent thin film electroluminescent display (1’); or

- the first contact area (30) of the first transparent thin film electroluminescent display (1) is superposed partly with the second passive area (20’) and partly with the second contact area (30’) with the second transparent thin film electroluminescent display (1’); or - the first contact area (30) of the first transparent thin film electroluminescent display (1) is superposed with the second passive area (20’) of the second transparent thin film electroluminescent display (G), and the second contact area (30’) of the second transparent thin film electroluminescent display (G) is superposed with the first passive area (20) of the first transparent thin film electroluminescent display (1). 7. A transparent thin film electroluminescent display device according to any of claims 1 - 6, c h a r a c t e r i z e d in that:

- the first contact area (30) is provided to a first edge area of the first display area (9) on the first substrate (2); or

- the first contact area (30) is provided to on a first edge area of the first display area (9) on the first substrate (2), and the second contact area (30’) is provided to a second edge area of the second display area (9’) on the second substrate (2’).

8. A transparent thin film electroluminescent display device according to any one of claims 1 - 7, c h a r a c t e r i z e d in that the first and second transparent thin film electroluminescent displays (1, 1') are arranged in superposed manner such that:

- the first contact area (30) is outside the second display area (9’) in the stacked device structure of the transparent thin film electroluminescent display device (100) such that the first contact area (30) and the second substrate (2’) are arranged non-overlapping in the stacked device structure of the transparent thin film electroluminescent display device (100); or

- the first edge area of the first display area (9) provided with the first contact area (30) is arranged outside the second substrate (2’) in the stacked device structure of the transparent thin film electroluminescent display device (100); or

- the first contact area (30) is outside the second display area (9’) in the stacked device structure of the transparent thin film electroluminescent display device (100) such that the first contact area (30) and the second substrate (2’) are arranged non-overlapping in the stacked device structure of the transparent thin film electroluminescent display device (100), and the second contact area (30’) is outside the first display area (9) in the stacked device structure of the transparent thin film electroluminescent display device (100) such that the second contact area (30’) and the first substrate (2) are arranged non-overlapping in the stacked device structure of the transparent thin film electroluminescent display device (100); or

- the first edge area of the first display area (9) provided with the first contact area (30) is arranged outside the second substrate (2’) in the stacked device structure of the transparent thin film electroluminescent display device (100), and the second edge area of the second display area (9’) provided with the second contact area (30’) is arranged outside the first substrate (2) in the stacked device structure of the transparent thin film electroluminescent display device

(100).

9. A transparent thin film electroluminescent display device according to any one of claims 1 - 8, c h a r a c t e r i z e d in that the first and second transparent thin film electroluminescent displays (1, 1’) are matrix displays, and that:

- the first active area (10) of the first transparent thin film electroluminescent display (1) comprises two or more first column electrodes (45a, 45b, 45c) extending a first direction and two or more first row electrodes

(46a, 46b, 46c) extending in a second direction, and the second active area (10’) of the second transparent thin film electroluminescent display (1’) comprises two or more second column electrodes (45’a, 45’b, 45’c) extending in the first direction and one or more first row electrodes (46’a, 46’b, 46’c) extending in the second direction, and that the two or more first row electrodes (46a, 46b, 46c) of the first active layer (10) are aligned with the two or more second row electrodes (46’a, 46’b, 46’c) second active area (10’); or

(46a, 46b, 46c) extending in a second direction, and the second active area (10’) of the second transparent thin film electroluminescent display (1’) comprises two or more second column electrodes (45’a, 45’b, 45’c) extending in the first direction and one or more first row electrodes (46’a, 46’b, 46’c) extending in the second direction, and that the two or more first column electrodes (45a, 45b, 45c) of the first active layer (10) are aligned with the two or more second column electrodes (45’a, 45’b, 45’c) second active area (10’); or the first active area (10) of the first transparent thin film electroluminescent display (1) comprises two or more first column electrodes (45a, 45b, 45c) extending a first direction and two or more first row electrodes

(46a, 46b, 46c) extending in a second direction, and the second active area (10’) of the second transparent thin film electroluminescent display (1’) comprises two or more second column electrodes (45’a, 45’b, 45’c) extending in the first direction and one or more first row electrodes (46’a, 46’b, 46’c) extending in the second direction, and that the two or more first row electrodes (46a, 46b, 46c) of the first active layer (10) are aligned with the two or more second row electrodes (46’a, 46’b, 46’c) second active area (10’), and that the two or more first column electrodes (45a, 45b, 45c) of the first active layer (10) are aligned with the two or more second column electrodes (45’a, 45’b, 45’c) second active area (10’).

10. A transparent thin film electroluminescent display device according to any one of claims 1 - 9, c h a r a c t e r i z e d in that:

- the first and second transparent thin film electroluminescent displays (1, 1’) are segment displays, and that the first active area (10) of the first transparent thin film electroluminescent display (1) comprises one or more first superposed segment electrodes (14), and the second active area (10’) of the second transparent thin film electroluminescent display (1’) comprises one or more second superposed segment electrodes (14’); or

- the first transparent thin film electroluminescent displays (1) is a segment display, and the first active area (10) of the first transparent thin film electroluminescent display (1) comprises one or more first superposed segment electrodes (14); and

- the second transparent thin film electroluminescent display (1’) is a matrix displays, and the second active area (10’) of the second transparent thin film electroluminescent display (1’) comprises two or more second column electrodes (45’a, 45’b, 45’c) extending in the first direction and one or more first row electrodes (46’a, 46’b, 46’c) extending in the second direction.

11. A transparent thin film electroluminescent display device according to any one of claims 1 - 10, c h a r a c t e r i z e d in that the first and second transparent thin film electroluminescent displays (1, 1’) are arranged superposed such that the first active layer (40) of the first transparent thin film electroluminescent display (1) is arranged towards the second active layer (40’) of the second transparent thin film electroluminescent display (1’).

12. A transparent thin film electroluminescent display device according to any one of claims 1 - 11, c h a r a c t e r i z e d in that:

- the transparent thin film electroluminescent display device (100) comprises a first adhesive layer (50) provide between the first and second transparent thin film electroluminescent displays (1, 1’) in the stacked device structure for attaching the first and second transparent thin film electroluminescent displays (1, 1’) together; or - the transparent thin film electroluminescent display device (100) comprises a first adhesive layer (50) provide between the first active layer (40) of the first transparent thin film electroluminescent display (1) and the second active layer (40’) of the second transparent thin film electroluminescent display ( ) in the stacked device structure for attaching the first and second transparent thin film electroluminescent displays (1, 1') together.

13. A transparent thin film electroluminescent display device according to of claim 11, c h a r a c t e r i z e d in that: - the transparent thin film electroluminescent display device (100) comprises an intermediate substrate layer (3) arranged between the between the first active layer (40) of the first transparent thin film electroluminescent display (1) and the second active layer (40’) of the second transparent thin film electroluminescent display (1’) in the stacked device structure; and - the transparent thin film electroluminescent display device (100) comprises a second adhesive layer (51) provide between the first active layer (40) of the first transparent thin film electroluminescent display (1) and the intermediate substrate layer (3), and a third adhesive layer (51’) provide between the second active layer (40’) of the second transparent thin film electroluminescent display (1’) and the intermediate substrate layer (3) for attaching the first and second transparent thin film electroluminescent displays (1, 1’) together.