WO2004095120A1

WO2004095120A1 - Liquid crystal display device and manufacturing method

Info

Publication number: WO2004095120A1
Application number: PCT/IB2004/050482
Authority: WO
Inventors: Peter J. Slikkerveer; Petrus C. P. Bouten; Fredericus J. Touwslager; Jacob M. J. Den Toonder
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2003-04-23
Filing date: 2004-04-22
Publication date: 2004-11-04

Abstract

LC display cell architecture having overhanging linear structures for spacer structures (13,14) in the substrates (10,11) which structures ensure the forming of separate conductor lines (6,7) aligned with the spacers. The spacer structures can be obtained by exploiting roll to roll based plastic processing technology. The cell is formed by joining the substrates with linear spacers such that the spacers are intersecting.

Description

LIQUID CRYSTAL DISPLAY DEVICE AND MANUFACTURING METHOD

The invention relates to a display device comprising a liquid crystal material between a first substrate provided with row electrodes and a second substrate provided with column electrodes in which overlapping parts of the row and column electrodes define picture elements. The invention particularly relates to the use of flexible (plastic) substrates in such displays. Such so-called "passive display" devices are used in, for example portable apparatuses such as laptop computers, notebook computers and telephones. The invention also relates to a method of manufacturing such a display device.

Passive matrix displays of this type are generally known and are generally based on the (Super) Twisted Nematic Liquid Crystal effect ((S)TN-effect). Especially the (S)TN display device has become the workhorse of the display industry for handheld applications (mobile phones, PDAs etc.).

Commercial passive matrix displays (and also active matrix displays) at present are made by using glass substrates (sheets), so substantially all manufacturing capability for flat panel displays is dedicated to making glass displays and handling ever larger and larger glass plates from which the display substrates are obtained.

On the other hand it is becoming generally accepted that plastic and flexible displays will provide new options for design and usage of displays and that they have some added value. The introduction of plastic and flexible displays however is seriously hampered by the lack of a dedicated processing capability. The plastic and flexible displays are generally processed in former glass-substrate based factories, which need to be adapted to accommodate the different properties of plastic substrates and their handling. Investment in adapting an existing factory to process on flexible, plastic substrates is still significant, while the adapted processing does not use the specific possibilities enabled by the change of glass substrates to plastic films. The alternative of building a new factory dedicated to plastic film displays on the other hand is particularly risky, since it requires high investment, whereas when it uses the processing benefits of the new plastic film manufacturing methods (like roll-to-roll processing) it will have a display manufacturing capability that is (at least partly) incompatible with main stream manufacturing. This will obviate market introduction of such a new type of flexible display.

The invention has as one of its objects to provide a type of display, the manufacturing of which is compatible with said new plastic film manufacturing methods. The invention has as a further objective to provide a method of manufacturing such displays.

To this end a display device according to the invention comprises first linear spacing parts along the row electrodes on the first substrate and second linear spacing parts along the column electrodes on the second substrate, while the spacing between the substrates is determined by the combined height of the first and second linear spacing parts at crossings of said linear spacing parts. In particular the linear spacing parts have a greater width in a plane between the substrates than at the substrates.

A method for method of manufacturing a display device according to the invention comprises the steps of a) providing a first substrate at least at one side of the substrate with substrate extensions having slanting edges, the angle between said edges and the substrate surface being smaller than 90 degrees b) deposition of a transparent conductor on the first substrate c) providing at least one second substrate having substrate extensions with slanting edges, the angle between said edges and the substrate being smaller than 90 degrees d) deposition of a transparent conductor on the second substrate and e) joining the substrates to form display cells.

The use of profiled (overhanging) spacers together with e.g. directional deposition of electrode material results in the direct forming of separate conductor patterns self aligned between the spacing elements. Such a production method for passive matrix liquid crystal displays combines optimal use of plastic display substrates and a minimum investment in a new display factory. The latter may especially be obtained by the production of half fabricates in large quantities at existing locations having capabilities for processing flexible films (e.g. roll-to-roll).

A further advantage of the method according to the invention is the replacing of laborious lithographic processes by self-aligning processes.

In a preferred embodiment at least part of the substrate and substrate extensions are made hydrophilic before depositing a conductive polymer. These and other aspects of the invention are apparent from and will be elucidated with reference to the embodiments described hereinafter. In the drawings:

Figure 1 shows a schematic embodiment of passive display device according to the present invention,

Figure 2 shows an unfolded view of a display device according to the invention, Figure 3 shows a plan view of a display device according to the invention,

Figure 4 shows a cross-sectional view along line IV -IV in Figure 3, Figure 5 shows another view of part of a display device according to the invention,

Figures 6 - 11 show cross-sectional views during manufacture of parts of the display devices according to the invention, while

Figure 12 shows cross-sectional views of further display devices according to the invention and

Figures 13, 14 also show cross-sectional views during manufacture of parts of the display devices according to the invention. The Figures are diagrammatic and not drawn to scale. Corresponding elements are generally denoted by the same reference numerals.

Figure 1 is an electric equivalent circuit diagram of a part of a display device 1 to which the invention is applicable. It comprises a matrix of picture elements 8 defined by the areas of crossings of row or selection electrodes 7 and column or data electrodes 6. The row electrodes, in one mode of driving, are consecutively selected by means of a row driver 4, while the column electrodes are provided with data via a data register 5. To this end, incoming data 2 are first processed, if necessary, in a processor 3. Mutual synchronization between the row driver 4 and the data register 5 occurs via drivelines 9.

The selection electrodes 7 and data electrodes 6 are provided on substrates 10 and 11 respectively, which substrates in this example are plastic foils. Between the substrates 10 and 11 an electro-optical material, such as a liquid crystal layer 12 is present. Further layers such as orientation layers, polarizers, etcetera have not been shown in Figure 1 for clarity reasons.

Figures 2 and 3 show how display substrates 10, 11 are folded together while crossing electrodes 6, 7 in the matrix display after folding define picture elements. Between the electrodes 6, 7 aligning spacer structures 13, 14 are provided which together form the cell spacers where they overlap (see reference numerals 13 in Figure 3), basically at each corner of a picture element.

Figure 4 shows a cross-sectional view along line IV -IV in Figure 3. On the

(plastic) substrate 10 electrodes 6 are provided between linear spacing parts 13, which have a greater width in a plane between the substrates 10, 11 than at the substrate 10. In a similar way (not shown) electrodes 7 of Figures 2, 3 are provided between linear spacing parts 14, which have a greater width in a plane between the substrates 10, 11 than at the substrate 11.

Due to the kind of processing to be discussed further on electrode material 6', 7' may be present on the spacing parts 13, 14. Figure 5 shows another view of part of a display device in which spacer parts

13 enclosing electrodes on a substrate 10 are provided on the substrate 10; the spacer parts

13 have a greater width again in a plane above the substrate 10 than at the substrate 10. Figure 6 show a way of manufacturing a display according to the invention which comprises the steps of: 1 ) Providing a mould 20 with a receded spacer structure, which may be specific for each display design and in this case has the recession inverted with respect to the form to be replicated into the plastic substrate of the display (Figure 6(a)).

2) Replicating the mould into the plastic substrate 10 (Figure 6(b)). The resulting spacer parts (with overhang) are located all around the intended location of the electrode pattern (see Figures 4, 5 , 6(c)). Replicating can be achieved by injection moulding, thermal embossing or embossing in a liquid resin and (photo) curing, where the latter two can be made in a polymer film using a roll-to-roll process. The many techniques available, such as e.g. lithography and controlled lacquer deposition make it possible to use for the spacers 13

(or part of the substrate provided with spacers) other material than the substrate material, as illustrated by the dashed line in Figure 6. To this end the substrate may contain a moldable surface layer of e.g. polymeric material, like a glassy or rubber-like polymer.

Although the spacer patterns are fixed to the mould by their resemblance with swallowtails connections, these patterns can be released by using the elasticity of the polymer substrate and an appropriate choice and a correct temperature regime. The height of the spacer patterns is preferentially chosen to be half that of the cell to be formed and the spacers are created on both substrates of said cell.

3) Depositing (transparent) conductors e.g. by P(lasma) V(apour) D(eposition) or sputtering. After forming the overhanging spacer structures a (transparent) electrode is applied by vacuum deposition on the structured substrates. As transparent conductor an oxide (like ITO), a metal (like MxO, Ag, MxO stacks) or polymeric conductors like PEDOT can be chosen. The combination of a directional deposition and overhanging spacers results in the direct forming of separate conductor patterns 6, 7 self aligned between the spacer parts 13, 14 and conductor patterns 6', 7' on the spacer parts 13, 14 (Figures 4, 6(d)). 4) If necessary an alignment layer 21 can be provided in (the same, continuous process such as a roll-to roll process. For cholesteric LCD's a homeotropic alignment can be obtained with a thin Si02 layer, a very thin Polyimide layer or even with a surface modification of the conductor pattern. Since these alignment layers will be very thin, there will not cause problems when making electrical contact with the electrode patterns beneath. A final step is to assemble two substrates to a display device and fill the display device with liquid crystal material.

In the display area the electrodes in the matrix display will cross each other and aligning spacer structures 13, 14 together form the cell spacers (see Figure 3), basically at each corner of a picture element. In some cases (for example at large pixel size) and possibly in some other areas of the display it may be advantageous to have additional spacers. These can be made for instance by embossing a number of patterns 22 (e.g. pillars) in the area between the spacer structures 13, 14 on one of the display substrates, which have the full cell height (see Figure 7). If the height of the spacer patterns 22 equals the total height of the spacer structures 13, 14 alignment problems are prevented when assembling the cell. In the method as described the conductive material of the electrodes 6, 7 is deposited after the spacer structures 13, 14 are formed. As a consequence the tops of the spacer structures 13, 14 are covered with a conductive layer. These layers form a conductive grid. Although not necessarily problematic for the display performance, it may be preferred to prevent the forming of this conductive grid. This can be obtained by breaking the grid up in separate sections for example by placing spacing elements 23 at a second level in the length direction of the spacer structures 13 whereby these spacing elements 23 roughly align to the middle of the spacer structures 14 of the second substrate 11 (see Figure 8) It can also be obtained by etching away the conductive electrode layer 6 at the top of the spacer structures 13. This method uses the height difference between the spacer structures 13 and the electrodes. A leveling resist 25 is applied and developed homogeneously from the top (see Figure 9 (a)). This will expose the tops of the spacer structures 13 first (see Figure 9 (b)). Then the electrode layer 6 at the tops is etched (see Figure 9 (c)) after which the rest of the resist can be stripped.

Figure 10 (a) shows how a contact between electrodes at different substrates 10, 11 of the display can be obtained by introducing a sloped ramp showing a reverse slope angle from one level to the next level. This technique can also be used to make contact with the grid of electrodes at the tops of the spacers e. g. to bring them at a well defined potential. Contact between the electrodes at the top substrate and the bottom substrate makes possible a single contact ledge 26 for outside contacting. In this latter case it is advantageous to provide a compressive pressure between the contacts of the two electrode layers (see Figure 10 (b)), which might be obtained from reaction shrinkage of a glue line close to these contacts. Apart from the examples shown in Figure 7, 8 and 10, there is a range of extra features that can be obtained by using more than two levels or using different shapes during the replicating (embossing) of the moulds. As an example it is possible to make crossing electrode patterns like the ones sketched in Figure 11. Although this adds complexity to the mould manufacturing, the further replication process is not influenced. When embossing in a roll-to-roll process, it can be advantageous to make the patterns of the top and bottom substrate side by side which means that a processed film will contain on one area (side) all bottom substrates and on another area (side) all top substrates. After step 3) in the process the roll of processed substrate film is then sliced (separated in two separate films comprising the lower substrates and top substrates respectively). This method of processing greatly simplified logistic and ensures that both display substrates have followed exactly the same processing. This is important for compatibility of top and bottom substrates, especially when a plastic is used as a substrate material.

Figure 12 shows some possible embodiments of devices according to the invention. In the embodiment of Figure 12 (a) the substrate 10 extends beyond the display area and allows for placing a driver IC 27 (e.g. by Chip on plastic -techniques). Particularly when a polymer like PET (polyethylene terephthalate) or PEN (polyethylene naphthalate) is used which both have a low thermal expansion coefficient this is a very practical option. The display area is closed by a cell rim 28. In the double cell display of Figure 12 (b) the middle substrate 10 is processed according to the invention on both sides, so it has spacing parts 13 and electrodes 6 on both sides. When the substrate extends and allows for electrical connections (via's or through holes), a single chip on plastic can drive the complete double cell. Such a double cell can be used for cell compensated S(uper) T(wisted) N(ematic) displays, where only one cell is addressed, of more likely to stacked CTLC displays (Cholesteric LC's) where the stacking will provide an option for making compact stacked CTLC color displays.

For such a full color CTLC display either two dual cells can be used, allowing to use four colors in stead of three for a better cooler gamut or some cells can be filled with other orientation to enhance the display brightness (e.g. right hand and left hand green LC to boost the green colors). Alternatively a cell can be made by stacking two middle substrates 10, 31 with spacing parts 13, 34 and electrodes 6, 36 respectively on both sides and two closing substrates 11, 41 with spacing parts 14, 44 and electrodes 7, 47 respectively, giving the three layers cell of Figure 12 (c). Figures 13 and 14 also show several methods (cross-sectional views) to manufacture display devices according to the invention especially the auto-structuring of the conductive lines. The conductive material in this case can be conductive polymers (for example PEDOT or PANI) or any other conductive materials that are deposited in the fluid phase. In a first method the (display) substrate 10 after replication from a mold, such that it contains overhanging spacing parts 13 as shown in Figure 13 (a), is subjected to a surface modification treatment. This can e.g. be a UV-ozone treatment (which is directional) resulting in hydrophilic regions 32 and hydrophobic regions 33 (in the "shadows" of the overhanging structures, see Figure 13 (b)) and then spincoating of the polymer solution to obtain electrodes 6, 6'. The adherence will be good only in the hydrophilic regions and in the hydrophobic regions the solution will dewet away. Structures (without any electrical interconnection between the electrodes 6, 6') are obtained as shown in Figure 13 (c).

In a second method the display substrate is subjected to an oxygen-plasma treatment without a preferential direction. The surface becomes hydrophilic, see Figure 14 after which the polymer solution is deposited by spraying onto the substrate. The area under the overhanging structures will not be covered due to the shadow (shielding)-effect. A similar result as in figure 13 (c) is obtained. It is also possible to combine the two methods, i.e. combine the UV-ozone treatment with spraying of the polymer solution. The protective scope of the invention is not limited to the embodiments described, while many variations within the scope of the invention are possible. For instance, to improve the release of the spacer structures from the mould, it may be advantageous to prevent straight edges at the electrode pattern, like the ones drawn in the Figures, but have rounded or curved edges at the electrode pattern.

In the embodiments shown also plastic transistors may be realized on the substrate(s)0.

The invention resides in each and every novel characteristic feature and each and every combination of characteristic features. Reference numerals in the claims do not limit their protective scope. Use of the verb "to comprise" and its conjugations does not exclude the presence of elements other than those stated in the claims. Use of the article "a" or "an" preceding an eleent does not exclude the presence of a plurality of such elements.

Claims

CLAIMS:

1. A display device (1) comprising a liquid crystal material (12) between a first substrate (10) provided with row electrodes (6) and a second substrate (11) provided with column electrodes (7) in which overlapping parts of the row and column electrodes define picture elements (8) the display device comprising first linear spacing parts (13) along the - 5 row electrodes on the first substrate and second linear spacing parts (14) along the column electrodes on the second substrate, the spacing between the substrates being determined by the combined height of the first and second linear spacing parts at crossings of said linear spacing parts.

10 2. A display device according to claim 1, at least one of the groups of linear spacing parts being covered with electrode material of the adjacent electrode.

3. A display device according to claim 1 or 2, the linear spacing parts having a greater width in a plane between the substrates than at the substrates.

15

4. A display device according to claim 1 , 2 or 3 the display device comprising further spacing parts (22) on one of the substrates having a height substantially equal to the spacing between the substrates.

20 5. A display device according to claim 2 display device comprising spacing parts having a slanted edge to electrically interconnect the electrode material to an electrode structure on one of the substrates.

6. A display device according to claim 1 or 2, the substrate material being 25 flexible.

7. A display device according to claim 6, the substrate material containing at least a moldable surface layer.

8. A display device according to claim 6, the surface layer containing polymeric material

9. A display device according to claim 6, the electrode material being an organic 5 conductor comprising at least one of polyaniline , poly(3,4-ethylenedioxythiophene) and poly(styrene sulfonate).

10 A method of manufacturing a display device, the method comprising the steps of 10 a) providing a first substrate (10) at least at one side of the substrate with substrate extensions (13) having slanting edges, the angle between said edges and the substrate surface being smaller than 90 degrees b) deposition of a transparent conductor on the first substrate c) providing at least one second substrate (11) having substrate extensions (14) 15 with slanting edges, the angle between said edges and the substrate being smaller than 90 degrees d) deposition of a transparent conductor on the second substrate and e) joining the substrates to form display cells.

20 11. A method according to claim 10 in which the substrate with substrate extensions having slanting edges is manufacture by means of a mold (20).

12. A method according to claim 10 in which at least part of the substrate and substrate extensions are made hydrophilic before depositing a conductive polymer.

25

13. A method according to claim 12 in which at least part of the substrate and substrate extensions are made hydrophilic by means of a UV-ozone treatment or an oxygen- plasma treatment.

30 14. A method according to claim 13 in which the conductive polymer is deposited during the UV-ozone treatment.