GB2247977A

GB2247977A - Display assemblies

Info

Publication number: GB2247977A
Application number: GB9118016A
Authority: GB
Inventors: Neil Anthony Fox
Original assignee: Smiths Group PLC
Current assignee: Smiths Group PLC
Priority date: 1990-09-12
Filing date: 1991-08-21
Publication date: 1992-03-18
Also published as: DE4128631A1; IL99269A0; NL9101417A; GB9118016D0; GB9019975D0; FR2666676A1; JPH04234730A

Abstract

A display assembly has a liquid crystal display (2) formed by two soda glass plates (25 and 10) separated by a liquid crystal material (24). The assembly also includes a cold cathode fluorescent lamp (1) formed by two glass plates (10 and 11) separated by a gas-discharge volume (5) and supported by an array of pillars (12). One of the plates (10) of the lamp (1) provides one of the plates of the display (2) so that the display is integral with the lamp and is illuminated on energization of the lamp. The plates 25 and 10 support respective electrodes (26 and 21), one of the plates having a filter layer (28) with regions of different colour transmission properties that are aligned with individual electrodes (21) on the other plate. In another embodiment a second liquid crystal display is added with one of its glass plates forming the other plate of the gas discharge volume. <IMAGE>

Description

1 - 1 DISPLAY ASSEMBLIES This invention relates to display assemblies.

The invention is more particularly concerned with flat panel display assemblies of the kind having a matrix display or the like and a backlight.

Conventional flat panel displays of this kind usually have a flat liquid crystal display behind which is located a backlight such as formed by several fluorescent tubular lamps, a reflector and diffuser. More recently, it has been proposed to utilize flat panel discharge lamps for nack illumination. Examples of such lamps are described in:WO 90/09676, JP-A-5846568, EP-A-0283014, GB-A-2217905, WO 87/04562, JP-A-57180067, JPA-59127357, GB 9115185 and GB 9105626. These flat panel lamps have the advantages of providing a more even illumination than tubular lamps and of being more robust and compact.

In many applications, it is desirable that the overall thickness of the display, that is, including its backlight, is as small as possible without reducing the robustness of the display. The amount by which the thickness of the display can be reduced, however, is limited by the thickness of the two glass plates forming the backlight and the two glass plates forming the - 2 display. Any gap between the front plate of the backlight and the rear plate of the display can lead to multiple reflections which can reduce legibility and the level of illumination. Even if the front surface of the backlight is bonded to the rear surface of the display, this does not completely avoid these problems because it is very difficult to remove completely all air bubbles between the two surfaces. Any mismatch in refractive indices of the glass plates or the bonding material will also cause reflection at the boundary. The bond can also provide a site for weakness. Furthermore, because the glass plates forming the display and the backlight must each be strong enough to prevent damage during assembly, the overall thickness of the two plates wnen bonded together is greater than necessary.

It is an object of the present invention to provide a display assembly that can be used to avoid these disadvantages.

According to the present invention there is provided a display assembly comprising a liquid crystal display of the kind having two glass plates separated by a liquid crystal material, each glass plate supporting a respective electrode layer, and a planar fluorescent lamp formed by two glass plates separated by a gas discharge volume, one of the glass plates of the lamp providing one of the glass plates of the liquid crystal display such that the liquid crystal display is formed integrally with the lamp and such that energization of the lamp causes illumination of the liquid crystal display.

Preferably, the fluorescent lamp is a cold cathode lamp and the liquid crystal display a dichroic display. The lamp may have an array of pillars between the two plates of the lamp which support the plates. The glass plates may be of soda glass. The assembly may include a filter layer of regions of different colour transmission properties, the filter layer being supported by the other plate of the display, and the regions of the filter layer being aligned with individual electrodes of one of the electrode layers. The other of the glass plates of the lamp may support a reflector on its external surface and may support a polarizer between the other plate and the reflector.

The assembly may include a second liquid crystal display having two glass plates separated by a liquid crystal material, each glass plate of the second liquid crystal display supporting a respective electrode layer, and the other of the plates of the lamp providing one of the glass plates of the second liquid crystal display such that the second liquid crystal display is formed integrally with the lamp and such that energization of the 4 lamp causes illumination of both liquid crystal displays.

The assembly may include a sensor responsive to inversion of the assembly to cause a change in information provided by the display assembly.

Display assemblies-in accordance with the present invention willnow be described, by way of example, with reference to the accompanying drawings, in which:

Figure 1 is a sectional view of one form of assembly; Figure 2 is a sectional view of an alternative assembly; and Figures 3 are perspective views and 4 illustrating two further forms of assembly.

With reference first to Figure 1, the display assembly comprises a backlight formed by a flat panel, cold cathode fluorescent lamp 1, and a dichroic liquid crystal display (LCD) 2 above the lamp.

The lamp 1 is of the kind described in WO 90/09676 but may be any other flat panel fluorescent lamp. The lamp 1 comprises two parallel flat plates 10 and 11 of soda lime glass, each of which are machined with a matrix array of rows and columns of supporting pillars in the form of frusto-pyramids 12 on facing surfaces such that the flat tops of corresponding pyramids on each plate contact one another and support the plates against inward deformation. other forms of support between the two plates could be used. The two plates are sealed together around their peripheries and the volume 5 between them filled with a gas discharge mixture at low pressure, a phosphor coating 6 being deposited on the internal surfaces of the two plates. Two electrodes 13 and 14 extend along oppogite sides within the gas-discharge volume 5 inside the lamp such that when the electrode are energized, discharge occurs causing the generation of light from the phosphor coating 6. A polarizer 15 is attached to the outer surface of the lower plate 11; the polarizer may include a retardation film. An aluminium layer 16 is deposited on the lower surface of the polarizer 15 to act as a reflector. The reflecting layer - 6 may either be flat or it may be profiled to increase the proportion of light transmitted through the pillars 12.

The plate 10, in addition to forming the upper, forward plate of the lamp 1 also provides the lower, rear plate of the LCD 2 and is, therefore, the intermediate plate of the assembly. Energization of the lamp 1 causes illumination of the LCD 2.

Directly deposited on the upper surface of the plate 10 is a matrix array of thin f ilm transistors or diode switches 20 which provide on their upper surface a layer of individual electrodes 21. Multiple wires 22 extend to the rows and columns of the switches 20 so that individual ones of the electrodes 21 can be addressed, in the usual way.

The upper surface of the electrodes 21 is coated with a lower aligning layer 23 of a polar organic substance the purpose of which is t(j-,imp,-,. -- a cw-Lst'to the molecules of a conventional liquid crystal material 24 which is drawn into the narrow space between the intermediate plate 10 and an upper plate 25 of the LCD 2. Directly deposited on the lower surface of the upper plate 25 is a thin, semi-transparent layer 26 of indium tin oxide which provides the upper, common electrode of the LCD 2. External electrical connection to the electrode layer 26 is made by a wire 27. On the lower surface of the electrode layer 26 there is screen printed a filter layer 28. The filter layer 28 is of a transparent polyamide or similar material and comprises a matrix array of red, green and blue regions aligned with and of the same size as the individual electrodes 21 of the transistors in the array 20 on the plate 10. In practice, the size of the filter regions 28 and individual electrodes 21 will be considerably smaller than illustrated. Further details of the manufacture of suitable filter layers are given in the article by Kamamori et al. "Multicolor Graphic LCD with Tricolor Layers Formed by Electrodeposition", SID 84 Digest pp 215, 216. Where a monochrome display is desired, the filter layer 28 would be omitted. on the lower surface of the filter layer 28 there is an upper aligning layer 17 identical to the lower aligning layer 23.

The upper plate 25 is sealed around its periphery to the intermediatcplate 10, after introduction of the liquid crystal material 24, by means of a glass seal 29.

Above the upper plate 25 there is a retardation film 30 of a stretched polycarbonate that is highly birefringent. This film 30 is optional and, where used, serves to retard the phase of radiation passing through the film. Radiation incident on the film 30 which is 8 - elliptically polarized will, after passing through the film, be more linearly polarized. Located above the retardation film 30 is a polarizer 31.

The construction and operation of the LCD 2 is conventional except in so far as the lower plate of the LCD is provided by the upper plate 10 of the lamp 1.

Conventionally, LCD's are made using aluminosilicate glass or aluminoborosilicate glass because they have very low alkali contents. Alkali ions present in cheaper soda lime glass are thought to induce instability in the material forming the thin film transistor layer and to contaminate the liquid crystal material. It is now, however, believed that cheaper soda lime glass can be used in LCD's, see the article by Uchikoga et al. "Soda Lime Glass as a Substrate for TFT-LM1s, Japan Display 1989, pp 426-428. Another problem which has previously cast doubt on the suitability of soda lime glass in WDIs is its large shrinkage during processes such as chemical vapour deposition. This problem can, however, be avoided L,, the glass to 500 degrees C prior to processing.

The assembly of the present invention has several advantages over previous assemblies, where the LCD is a component separate from the back light. Firstly, by using only three glass plates instead of four, the assembly can be thinner and lighter than previous displays. This is especially important with large area displays, because any increase in weight of the display will make it more prone to deformation; this could have an adverse effect on the performance of the LCD. Secondly, the present construction avoids the need for two glass/air interfaces between the backlight and the LCD. This reduces radiation losses at the interface and avoids multiple reflections between the surfaces. Thirdly, the integral nature of the LCD and the backlight gives a much more robust construction than previous assemblies where the LCD is separate from the backlight. This makes the assembly of the present invention less prone to damage by vibration and mechanical shock. Even where the LCD and backlight of previous assemblies are bonded together, this still results in the total of the two bonded glass plates being thicker than is necessary with the present invention. A bonded boundary also provides a site for mechanical weakness and for radiation losses.

Furthermore, the bonding process of the assembly adds to the number of processing steps and hence to the cost of the assembly.

The fact that the LCD forms a part of the backlight means that there will be good thermal transfer between the backlight and the LCD. This can be an advantage where the assembly is used in cold environments since it can avoid the need to use separate display heaters. The heat generated by the backlight can be sufficient to keep the intermediate wall at about 45 degrees Centigrade. Temperature fluctuation is also reduced which might otherwise adversely effect the display.

Cold-cathode fluorescent lamps, of the kind described above, have a long life compared with heated electrode lamps. The life of Lhe lamp can, therefore, be similar to that of the LCD, in the order of 15k to 20k hours.

The display assembly described above is of the dichroic type although it will be appreciated that various other liquid crystal di-splay.,..-:a used, such as twisted nematic, supertwist displays, ferroelectric displays or polymer dispersed TN displays. These alternatives involve the need for an additional polarizer to polarize radiation from the backlight. This additional polarizer could, for example, be located between the backlight 1 and the LCD 2, such as, between the common electrode 20 and the filter layer 23. Alternatively, the polarizer could be located on the lower surface of the backlight, between the lower plate 11 and the reflector 15. In this way, the polarizer will polarize light reflected by the reflector 15 so that light emergent from the intermediate plate 10 has a significant proportion that is polarized. However, because light must pass through the polarizer in two directions, this reduces the overall level of radiation and the proportion that is polarized.

A display assembly of the present invention could be used in many applications, such as in vehicle instrumentation, in large area flat television screens, or in advertising applications.

An alternative display assembly is shown in Figure 2 which has a single backlight 11 which is identical to that of Figure 1 except that it does not have a reflecting layer on its lower plate 111. Instead, the lower plate 111 forms one plate of a second J-r'T) 211 which is identical with the upper LCD 21. In this way, light from one backlight 11 is used to illuminate both the upper and lower displays. A double-sided display assembly of this kind could be used in various applications. For example, it might be used in an advertising display 130, as shown in Figure 3, where it is mounted vertically and rotated by a motor 131 about a vertical axis. The displays on 11 opposite sides of the assembly could be arranged to display the same, or different messages.

Alternatively, the display assembly could be incorporated into a handheld display terminal 40, such as for a computer. Different information could be displayed on opposite sides 41 and 42 of the assembly. The terminal 40 might, for example, include a sensor, such as a tilt switch 43, responsive to inversion of the terminal which causes a change in the information presented. In this way, the terminal could be arranged to mimic a book with a different page of information on each side that changes each time the terminal is inverted. The sensor could also be responsive to inversion of the terminal in different senses, that is, right to left or left to right, so that the terminal either causes later or earlier pages of information to be displayed.

The display assembly may include other conventional features as a touch-sensitive membrane on top of the polarizer 31 -for the input or selection of data.

Claims

1 A display assembly comprising a liquid crystal display of the kind having two glass plates separated by a liquid crystal material, each glass plate supporting a respective electrode layer, and a planar fluorescent lamp formed by two glass plates separated by a gas-discharge volume, wherein one of the glass plates of the lamp provides one of the glass plates of the liquid crystal display such that the liquid crystal display is formed integrally with the lamp and such that energization of the lamp causes illumination of the liquid crystal display.

A display assembly according to Claim 1, wherein the fluorescent lamp is a cold cathode lamp.

A display assembly according to Claim 1 or 2, wherein the liquid crystal cLisple-,., is a dichroic display.

A display assembly according to any one of the preceding claims, wherein the lamp has an array of pillars between the two plates of the lamp which support the plates.

A display assembly according to any one of the preceding claims, wherein the glass plates are of soda glass.

6.

7.

A display assembly according to any one of the preceding claims, wherein the assembly includes a filter layer of regions of different colour transmission properties, wherein the filter layer is supported by the other plate of the display, and wherein the regions of the filter layer are aligned with individual electrodes of one of the electrode layers.

A display assembly according to any one of the preceding claims, wherein the other of the glass plates of the lamp supports a reflector on its external surface.

A display assembly according to Claim 7, wherein the othei.--- jlass plates supports a polarizer between the other plate and the reflector.

A display assembly according to any one of Claims 1 to 6, including a second liquid crystal display having two glass plates separated by a liquid crystal material, each glass plate of the second liquid crystal display supporting a respective electrode layer, and wherein the other of the plates of the lamp provides one of the glass plates of the second liquid crystal display such that the second liquid crystal display is formed integrally with the lamp and such that energization of the lamp causes illumination of both liquid crystal displays.

10.

11.

12.

A display assembly according to any one of the preceding claims, including a sensor responsive to inversion of the assembly to cause a change in information provided by the display assembly.

A display assembly substantially as hereinbefore described with reference to Figuic I of the accompanying drawings.

A display assembly substantially as hereinbefore described with reference to Figure 1 as modified by Figure 2 of the accompanying drawings.

- 16 13. A display assembly substantially as hereinbefore described with reference to Figure 1 as modified by Figures 2 and 3 of the accompanying drawings.

14.

A display assembly substantially as hereinbefore described with reference to Figure 1 as modified by Figures 2 and 4 of the accompanying drawings.

15.

Any novel feature or combination of features as hereinbefore described.

Published 1992 at The Patent Office. Concept House. Cardiff Road. Newport. Gwent NP9 1RH. Further copies may be obtained from Sales Branch. Unit 6. Nine Mile Point, Cwmfelinfach, Cross Keys. Newport. NPI 7HZ. Printed by Multiplex techniques ltd, St MarY Cray. Kent.