JPS63234285A - Edge dielectric breakdown protection for acel thin film display - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Matrix AC Electroluminescence (ACEL)
Thin film displays typically consist of a first dielectric layer on a glass substrate with etched transparent (e.g., indium-tin-oxide, or ITo) electrodes or conductors, a phosphor (e.g., Z
nS:Mn) layer and a second dielectric layer. (Here, "conductor" and "
6 sequential dielectric/phosphor/dielectric thin film layers are subsequently deposited to form the heart of the electroluminescent display. Aluminum metal electrodes are finally deposited and etched into parallel stripes orthogonal to the transparent conductor stripes to complete the thin film structure of the ACEL display.

For matrix displays, the front and rear electrographic structures are sets of parallel lines, with the front transparent set (columns) orthogonal to the rear set (rows).

Dielectric selection plays an important role in the functionality and reliability of ACELm film displays. Good dielectric constant and dielectric breakdown strength are required.

A number of fabrication techniques for ACEL displays have been reported, including electron beam, sputtering, thermal evaporation, atomic layer epitaxy, or a combination of these methods.

The goal of producing large thin-film electroluminescent panels capable of displaying full pages of text or high-resolution graphics has been intensely pursued over the past few years. ,M
Miller et al.), “A Large-Area Electro-1%m Display with Full Video Matrix”
inescent Display with Mat
rix Addressing for Full Vi
deo) J, SID 86 Digast, pp
, 167-170 (1986); M, 1. Abdalla et al. (M, 1. Abdalla et al.)'Yield analysis for electroluminescent panel development (Yiefd A
Analysis for Electrolumine
scentPanelDevelopment)
J, 5PIE Vol, 256, Adv.
nces 1nDisplay Technology
y V, pp, 83-88 (1985);
L, E, Tannas et al.
), rACTFEL display (ACTFEL
Djplays) J, SID 82Dig
est, pp. +22-123 (1982).

The most important parameter to evaluate a material is the charge density it can hold without dielectric breakdown. The charge density at breakdown is given by the product of the electrostatic permittivity and the breakdown electric field: Qba=εE tra This quantity is thickness dependent. For films in the range of about 200-400 nm, the charge density at breakdown should exceed about 3 microcoulombs/square centimeter. For example, when the charge density reaches about 1.2 micron/cm2, light is emitted.

The display resolution, ie the number of lines that can be charged during row addressing, is inversely proportional to the duty cycle, which is 0.2% for a 512 line display.

60) (In g, the time allowed to charge all 512 rows is 16 ms, so the time allocated to one column is 0.2% of 16 ms or 32 microseconds. Flicker. To avoid this, the refresh rate must be at least 60 Hg.

Below L kHz, brightness depends linearly on frequency.

At higher frequencies the brightness is limited by the phosphor decay time.

The stability of the electrical and optical properties of the device is also an area of practical concern.

One major difficulty in manufacturing ACEL displays is the precise thickness control required in depositing complex EL stacks. High speed manufacturing particularly requires this. Film thickness variations appear as drive voltage variations across the panel. For practical applications, the film thickness should be maintained within about ±2%.

Non-uniformity in operation can also occur if the ITO sheet resistance is too high for the display size and resolution. The magnitude of this problem increases rapidly with display size.

To avoid premature dielectric breakdown, all layers should be as clean as possible with a minimum density of defects caused by particles or pinholes. The integrity of the electrode system has a decisive impact on yield.

The electrode deposition operation should yield smooth rows and columns with no shorts or opens.

Prior to this discovery, IT techniques were used to improve membrane coverage, reduce electric field concentration, and prevent dielectric breakdown at row edges.
Rounded or beveled edges have been used on Offi. However, this method is inadequate for edge breakdown protection. The present invention solves this problem.

The present invention is therefore a novel ACNMiC8M mini left luminescent display that uses protective dielectric stripes along the edges of transparent electrodes (i.e. conductors).

In particular, the present invention provides a first dielectric layer disposed on a glass substrate comprising parallel stripes of etched transparent conductor;
Consisting of a multilayer stack comprising a phosphor layer and a second dielectric layer1. The present invention is directed to an AC thin film electroluminescent display device, characterized in that the multilayer stack further includes a dielectric protective stripe disposed along at least the edge of the transparent conductor.

The present invention is also directed to a method of protecting an AC thin film electroluminescent display device against premature dielectric breakdown at the edges of transparent conductors.

This protection is achieved by depositing stripes of dielectric along the edges of the transparent conductor.

The present invention is directed to protecting electroluminescent thin film displays, particularly AC powered electroluminescent (ACEL) displays, from premature edge breakdown and to protected display devices. .

FIG. 1 illustrates a typical ACEL stack. Substrate 10 is typically glass.

As shown, the first layer on the substrate typically has about 300
The transparent electrode (or conductor) layer 12 is a 0 angstrom thick ITO film.

Adjacent to the ITO layer is a first dielectric layer 14, which is made of a material selected from, for example, Y, O, , 5i3Na and/or Al2O3. A phosphor layer 16 is sandwiched between a first dielectric layer 14 and a second dielectric layer 18. The phosphor layer is typically about 5000 angstroms thick and is made of a material such as ZnS:Mn.

A metal electrode 20, such as aluminum, completes the ACEL stack.

The typical ACEL stack shown in FIG. 1, for example, requires an electric field higher than about 10' volts/cm to generate light. Sharp steps in the etched transparent electrode have been found to be the source of field enhancement.

This field enhancement is believed to be due to the fact that the stack is thinner at the edges of the transparent conductor as shown in FIG. It has been found that regions along the edges of the transparent conductor begin to glow first when a voltage higher than the threshold is applied.

In view of Figure 2, the electric field (El) at the edge is defined by the following formula: ■ E, = □, whereas the electric field (E2) in the vixel is defined by the following formula: where V/d, is greater than V/d*.

Increasing the electric field through the display to achieve the desired brightness level can result in premature breakdown at the edges. The transparent conductor array is thus permanently interrupted at the location where dielectric breakdown occurs. Therefore, a loss of the entire column or a portion thereof occurs, resulting in a reduction in the quality and overall appearance of the display.

It has been found that the probability of such breakdown occurring can be substantially reduced or completely eliminated by depositing dielectric stripes along the edges of the transparent conductor.

One preferred example of such an edge-protected dielectric stripe is illustrated in FIG.

Advantageously, edge protection stripes need only be placed at the edges of the transparent conductor that require such protection. For example, it is not necessary to fill the gaps between the transparent electrodes, as shown in FIG. However, even if this does occur, it is not detrimental to the edge protection provided thereby.

Furthermore, it has been found that the dielectric stripes can be made of sufficient width and thickness to reduce the value of the electric field at the edges of the transparent conductor.

In an ACEL display device of the type illustrated in FIG. 1, a "sufficient thickness" for the edge protection dielectric stripes has been determined to be about 200 to 1000 Angstroms, preferably about 500 Angstroms. The width of the stripes only needs to cover the edges of the transparent conductor.

In the illustrated embodiment, this was approximately 7 microns wide. In other cases, larger or smaller widths are required. In most cases, the stripe thickness is such that the electric field at the edges is preferably between 20 and 50
The zero width, which should be sufficient to reduce the percentage, generally does not affect the desired result as long as the edges are covered.

For other (?) ACEL display devices, the thickness of the edge protection dielectric stripes will be different from the values applicable to the device of FIG. However, in view of the present disclosure, one skilled in the art will readily be able to determine an appropriate "sufficient thickness" for a particular application.

In addition, preferred dielectric materials of the present invention, namely A1□0.
has the above-mentioned "sufficient thickness" value when used in an ACEL display device of the type shown in FIG. requires some adjustment. Again, those skilled in the art will be able to readily determine these values based on the present disclosure.

As illustrated in FIG. 3, when the edge protection stripes of the present invention are added to the ACEL electrode edges, the following equation is satisfied: Thus, the edge breakdown that occurs under normal ACEL display driving conditions possibility can be completely removed.

The present invention will be described with reference to the following examples which will further aid in understanding the invention, but which should not be considered as limiting the invention. All percentages reported herein are by weight unless otherwise specified. All temperatures are expressed in degrees Celsius.

L- A transparent conductor was etched into parallel stripes approximately 180 microns wide. An edge protection layer was then deposited through a photomask using conventional lift-off photolithography techniques.

The photomask was suitably aligned to cover about 166 microns of the transparent electrode, leaving about 7 microns on each side of the transparent electrode to be covered by an edge protection dielectric layer.

The edge protection dielectric layer used in this case was AlzOs.
, which was deposited by electron beam techniques to a thickness of approximately 500 angstroms. The substrate was kept at room temperature during film deposition. After depositing the edge protection dielectric stripes,
The photomask was removed by dissolving it in acetone.

Subsequently, other layers were deposited: a first dielectric layer, a phosphor layer, a second dielectric layer, and a back electrode to complete the thin film electroluminescent stack.

The invention has been described in detail, including its preferred embodiments. However, those skilled in the art may make modifications and/or improvements to the present invention in light of the disclosure of the present invention, which are still within the scope and spirit of the present invention as indicated in the claims. It is.

4. No. 1. Figure 1 illustrates the basic structure of an AC driven thin film electroluminescent stack.

FIG. 2 illustrates the field strength at the edges of the transparent electrode.

FIG. 3 illustrates the effect on field strength at the transparent electrode edge when using the supplemental edge protection of the present invention (note: it has been removed).

FIG, 1 driFIG, 2 Procedural amendment (method 2 % formula % Indication of case 1988 Japanese Patent Application No. 319151 Title of invention Relationship with the ACEL thin film display edge insulation breakdown correction case Patent application Person name GTE Products Corporation Telephone number: 273-6436.

Name (6781) Patent attorney Motoki Kurauchi
Hiroshi □1m Date of notice of order March 29, 1985 Inventor's column Specification drawings of the application to be amended 1 copy Contents of amendment
As per attached sheet

Claims (1)

[Claims] 1. A first dielectric layer, a phosphor layer, disposed on a glass substrate comprising parallel stripes of etched transparent conductors;
and a second dielectric layer, the multilayer stack further comprising a protective stripe of dielectric disposed along at least the edge of the transparent conductor. 2. The dielectric protective stripe is at least partially
An AC thin film electroluminescent display device as claimed in claim 1, which fills the spaces between parallel stripes of etched transparent conductors. 3. Dielectric protective stripes are Y_2O_3, Si_3
A of claim 2 selected from the group consisting of N_4, Al_2O_3, or any combination thereof.
C thin film electroluminescent display device. 4. The AC thin film electroluminescent display device according to claim 3, wherein the dielectric protective stripe is Al_2O_3. 5. The thickness of the dielectric protection stripe is about 200~100mm
5. The AC thin film electroluminescent display device of claim 4, wherein the AC thin film electroluminescent display device is 0 angstrom. 6. The AC electroluminescent display device of claim 5, wherein the dielectric protective stripe has a thickness of about 500 Angstroms. 7. Protecting AC thin film electroluminescent display devices against premature dielectric breakdown at the edges of transparent electrodes, characterized by depositing a protective stripe of dielectric material of sufficient thickness along the edges of the transparent electrodes. Method. 8. Dielectric protective stripes are Y_2O_3, Si_3
8. The method of claim 7, wherein the material is selected from the group consisting of N_4, Al_2O_3, or any combination thereof. 9. The method according to claim 8, wherein the dielectric of the protective stripe is Al_2O_3. 10. The thickness of the protective dielectric stripe is about 500 to about 10
10. The method of claim 9, wherein the thickness is 0.00 angstroms. 11. The method of claim 10, wherein the protective dielectric stripe has a thickness of about 500 Angstroms.