JPH0481318B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a thin film EL device that generates EL (electroluminescence) light upon application of an alternating current electric field.

[Prior art]

As a conventional thin film EL element, for example, there is one described in Patent Application No. 19128 of 1982.

FIG. 4 is a cross-sectional view of the above thin film EL element.

In Fig. 4, In ₂ O ₃ and
Front electrode 2 made of transparent conductive film such as SnO ₂ , Y ₂ O ₃
The first dielectric film 3 is made of Si ₃ N ₄ or the like, and contains a trace amount of Mn.
A light emitting film 4 made of ZnS and a second dielectric film 5 made of the same material as the first dielectric film 3 are sequentially laminated by electron beam evaporation or sputtering,
A transparent multilayer film 100 is formed by these 2 to 5.

The film thickness of each part above is 5000Å for the dielectric film.
The thickness of the luminescent film is approximately 6000 Å.

Further, the mass film thickness on the second dielectric film 5 is 50~
An island absorber film 6 made of a 300 Å Mo film is formed by electron beam evaporation or sputtering.

Note that this island-like absorber film 6 can be replaced with another metal film or semiconductor film having an island-like structure, such as Ta, Cr, Si, or the like.

Furthermore, a transparent dielectric film 7 such as Al ₂ O ₃ having a film thickness of about 500 Å is formed on the island-like absorber film 6 , and a metal film 8 such as Al is deposited thereon by vapor deposition or sputtering. Then, stack them one by one. These 6 to 8 form a blackened back electrode 200 that has a high light absorption effect.

The front electrode 2 and the blackened back electrode 200 are patterned into appropriate shapes by conventional photolithography.

In the above device, an AC voltage is applied between the front electrode 2 and the blackened back electrode 200, and the luminescent film 4
When the electric field within reaches 1 to 2×10 ⁶ V/cm, the portion sandwiched between the two electrodes emits light to display the patterned shape.

In the device shown in FIG. 4, since the blackened back electrode 200 is used as described above, the external light that has entered through the transparent multilayer film 100 is absorbed by the island-like absorber film 6 and the transparent dielectric film 7. Therefore, the contrast in a bright environment is significantly improved compared to an element using a high-reflectance metal such as Al for the back electrode.

[Problem that the invention seeks to solve]

Thin film EL using blackened back electrode as above
The visibility of the device can be greatly improved compared to devices using ordinary metal electrodes.

However, in the thin film EL device as mentioned above,
Since the configuration was such that only the back electrode with the shape necessary for display was left and other unnecessary electrode parts were removed, when viewed from the glass substrate 1, the part where the back electrode remained and the back There was a problem in that the background color was different from the part from which the electrode was removed, and as a result, the back electrode stood out during non-display, making the display pattern visible.

In order to solve the above problem, the present inventors have created a non-display area, that is, a part on the back side where the blackened back electrode 200 is not provided with the same material and structure as the blackened back electrode 200, as shown in FIG. We have developed a thin film EL device with a blackened background film 300 formed thereon.

In the thin film EL element shown in FIG. 5, a blackened background film 300 having the same quality and structure as the blackened back electrode 200 is disposed in the non-display part on the back side, so that the background seen from the glass substrate 1 The color becomes completely uniform, so that the problem of the back electrode appearing exposed due to external light during non-display is solved.

However, in the thin film EL element shown in FIG. 5, the blackened back film 300 is uniformly arranged over the entire surface of the part where the blackened back electrode 200 is not provided on the back side, so that a large number of pixels are When the pixels are turned on at the same time, there is a problem in that non-selected pixels are turned on due to capacitive coupling between the non-display portions of the front electrode 2 that occurs via the blackened back film 300.

The above problem will be explained in detail below based on FIGS. 6 and 7.

FIG. 6 is a top view of an example of the thin film EL device shown in FIG. 5, and shows the thin film EL device viewed from the back side.

In FIG. 6, 2A1 to 2An are n front electrodes formed in a stripe shape, and the portion sandwiched between the n front electrodes and the blackened back electrode 200 is the display portion, that is, the pixel e ₁ 〜e _o .

Note that the first dielectric film 3, the light emitting film 4, the second dielectric film 5, etc. are not shown.

Further, c ₁ to _{c o} are capacitances formed by the lead portions (non-light emitting portions) of the front electrodes 2A1 to 2An and the blackened back film 300, respectively.

In the above thin film EL element, for example, the pixel e ₂ ~
When e _o is selected and displayed by emitting light, and e ₁ is not displayed, no voltage is originally applied to the non-display pixel e ₁ , but the capacitance c ₂
A voltage is applied to the pixel _e1 due to the capacitive coupling between ~ _co and _c1 .

FIG. 7 is an equivalent circuit showing the above relationship.

As shown in FIG. 7, the pixel _e1 has a capacitance in which _c2 to _c0 are connected in parallel, and _c1 is connected in series.

When the thin film EL element described above is driven with a voltage E, a voltage E ₁ as expressed by the following equation (1) is applied to e ₁ .

Note that in equation (1), ω is the angular frequency.

In equation (1), as the number of pixels increases, the routing of the lead portion of the front electrode becomes more complicated, and as a result, the lead portion becomes longer, so Σc _i tends to increase.

Furthermore, if the lead part becomes long, the voltage drop in this part may cause uneven brightness for each pixel, so in order to prevent this, the width of the lead part must be expanded, which further increases the Σc _i becomes larger.

For example, in a thin film EL element where the number of pixels n is about 100, the value is about c _i 2e _i .

Assuming n=100 and substituting into equation (1), 1/jω _o 〓 ⁱ⁼²
Since c _i can be ignored, E ₁ = 2E/3, and even though it is in the non-display state, the pixel e ₁ has approximately 67% of the drive voltage.
% voltage will be applied.

Therefore, when applying a voltage considerably higher than the emission start voltage (threshold voltage) and lighting at high brightness, for example when using under strong external light,
The pixel _e1 is turned on even though it is in a non-display state.

The present invention aims to solve the problems of the prior art as described above.

[Means to solve the problem]

In order to achieve the above object, in the present invention, a back film having the same quality and structure as the back electrode is formed on a portion of the back side of the transparent film where the back electrode is not provided, and a plurality of back films are formed. It is configured to be divided into individual parts.

By configuring as described above, the background color can be made uniform, so it is possible to prevent the back electrode from standing out due to external light, and it is also possible to prevent pixels that are not displayed due to capacitive coupling. Since the voltage applied to the display can be reduced or eliminated, there is no fear that non-display pixels will turn on.

[Embodiments of the invention]

FIG. 1 is a top view of a first embodiment of the present invention, showing a thin film EL element viewed from the back side.

In FIG. 1, the fourth layer is placed on a transparent multilayer film 100 (not shown) formed on a glass substrate 1.
A blackened back electrode similar to that shown in the figure is formed, and the blackened back electrode 200 and the blackened back film 400 are separated using photolithography.

Further, the blackened back film 400 is not formed into an integral structure, but is divided by slits s ₁ to s _o-1 parallel to the direction in which the lead portions of the front electrodes 2B1 to 2Bn are drawn out.

Note that this slit preferably has a width of about 100 μm, for example.

Moreover, this slit is connected to the front electrode 2B, respectively.
It should be located between the 1st and 2nd lead parts.

Next, the effect will be explained.

Front electrode 2B1 to 2Bn and blackened back electrode 20
Let the electrostatic capacitance _of the pixel formed at the _portion sandwiched _between Let the capacities be c ₁₁ , c ₁₂ , ...c _1o .

Consider the case where e ₁₂ to _{e 1o} excluding e ₁₁ are selected and displayed, as in the case of FIG. 6 above.

In the case of the device shown in FIG. 1, since the blackened back film 400 is divided by the slits, there is no series connection between c ₁₁ and c _1i in other parts.

Therefore, even if e ₁₂ ~e _1o is selected, e ₁₁
No partial pressure due to capacitive coupling is applied to the electrodes, and there is no possibility of light emission.

Next, FIG. 2 is a diagram showing a second embodiment of the present invention, and the same reference numerals as in FIG. 1 indicate the same parts.

In the embodiment shown in FIG. 1, the slit is provided so that the partial pressure applied to the non-display pixel becomes 0, but if it is sufficient to reduce the applied partial pressure to some extent, As shown in Figure 2, the number of slits can be reduced.

That is, in FIG. 2, a slit is provided for every two front electrodes, and the blackened back film 500 is
It is divided into pieces.

In the device shown in Figure 2, for example, if e ₁₁ is in the non-display state and e ₁₂ to _{e 1o} are in the display state, only the neighboring e ₁₂ causes a partial pressure on e ₁₁ due to capacitive coupling. It is.

When EV is applied to e ₁₂ , the partial pressure E ₁₁ applied to e ₁₁ is expressed by the following equation (2).

E ₁₁ =1/jωe ₁₁ /1/jωe ₁₁ +1/jωc ₁₁ +1/jωc _1
2 E...(2) As above, if c _1i 2e _1i , E ₁₁ = E/2
It can be seen that this is reduced compared to 2E/3 in the example shown in FIG.

Next, FIG. 3 is a diagram showing a third embodiment of the present invention, and the same reference numerals as in FIG. 1 indicate the same parts.

The lead part of the front electrode of an actual thin film EL element is
It is not a straight line, but is usually bent or curved.

The embodiment shown in FIG. 3 shows an example that is effective in such a case.

In FIG. 3, the blackened back electrode 600 is divided vertically and horizontally by grid-like slits s.

Therefore, it is only the neighboring pixels that cause a partial pressure in one pixel due to capacitive coupling, and it can be seen that in this case as well, there is a clear effect of reducing the partial pressure due to capacitive coupling.

Note that it is also easy to change the reduction rate by changing the dimensions of the grid.

〔Effect of the invention〕

As explained above, in the present invention, a back film having the same quality and structure as the back electrode is formed on the part of the back side where the back electrode is not provided, and the back film is divided into a plurality of parts. , the background color can be made exactly the same, eliminating the risk that the back electrode will stand out due to external light, and capacitive coupling between the back film and the lead part of the front electrode will create a partial voltage on non-display pixels. An excellent effect can be obtained in that there is no fear that the lamp will turn on due to the application of the voltage.

[Brief explanation of the drawing]

FIGS. 1 to 3 are illustrations of embodiments of the present invention, respectively.
Figure 4 is a sectional view of an example of a conventional thin film EL element, Figure 5 is a sectional view of an example of a thin film EL element improved from the thin film EL element of Figure 4, and Figure 6 is a cross sectional view of an example of the thin film EL element of Figure 5. The top view and FIG. 7 are equivalent circuit diagrams. Explanation of symbols: 1...Glass substrate, 2...Front electrode, 3...First dielectric film, 4...Light emitting film, 5...
Second dielectric film, 6... Island-shaped absorber film, 7... Transparent dielectric film, 8... Metal film, 100... Transparent multilayer film, 200... Blackened back electrode, 300, 40
0,500,600...Blackened back film, 2B1~
2Bn...Front electrode.

Claims (1)

[Claims] 1. In a thin film EL element in which a transparent film including at least a light emitting film is provided between a transparent front electrode disposed on the display side and a back electrode disposed on the back side,
A thin film characterized in that a back film having the same quality and structure as the back electrode is formed on a part of the back side of the transparent film where the back electrode is not provided, and the back film is divided into a plurality of pieces. EL element.