A LIQUID CRYSTAL DISPLAY DEVICE AND METHOD OF FABRICATION

Abstract: A liquid crystal display device (10) includes a liquid crystal material (15) such as PSCT disposed between first (12) and second glass substrates (14), and means for applying an electric field to the liquid crystal material so as to effect switching of the liquid crystal material. The liquid crystal material (15) is of the type which exhibits at least three stable states in dependence upon an electric field applied, and which maintains its state (exhibits memory) when the electric field is removed. This display device (10) also includes a colour filter (24) comprising at least two different colours. Liquid crystal display device (10) provides an extremely energy efficient, colour liquid crystal display device having grey scale capability. The energy demand of the device is so low, it is envisaged it will be incorporated into consumer items such as palmtop computers, advertising materials, packaging, handheld computer games, etc.

Description: A LIQUID CRYSTAL DISPLAY DEVICE AND METHOD OF FABRICATION Technical Field This invention relates to a liquid crystal display (LCD) device and its method of fabrication, and more particularly to a reflective type liquid crystal display device which has a low energy consumption. Background Art Liquid crystal materials change their optical properties when subjected to an electric field. This phenomenon has been used, with great success, in a number of display devices of the type found for example in portable (lap top) computers, hand-held (notebook and palmtop) organisers, clocks, watches and increasingly flat screen television displays and desktop monitors. Liquid crystal displays have proven to be very successful and are now widespread. They comprise a liquid crystal material interposed between two transparent sheets of glass. Transparent conductors, which are typically Indium Tin Oxide (ITO), are deposited on the glass so as to provide a means of addressing individual portions of the display known as pixels. These may be arranged in an array of n rows and m columns. The aforementioned type of liquid crystal displays fall into two main categories: the first is where light is reflected off the surface of a liquid crystal display device; the second is where the liquid crystal display device is placed between a viewer and an illumination source. The former operates in a reflective mode; the latter operates in a transmissive mode. Liquid crystal display (LCD) devices which operate in the transmissive mode typically use more energy than reflective mode devices because of the power consumed by the illumination source. This energy requirement has limited the number of applications in which transmissive mode liquid crystal displays have been used. In so called lap top and notebook computers the most common form of LCDs are backlit and colour displays based on either active matrix or supertwist technology. Being used in portable products, the energy consumption of these displays is of increasing concern. A typical supertwist or active matrix 800 x 600 (Super Video Graphics Adapter, or SVGA) LCD module consumes in the region of 3 W, of which approximately 2.5 W are consumed by the backlight. While this level of power consumption can be tolerated in relatively large devices, such as lap top computers, it has proved to be unacceptable to smaller portable devices, such as notebook or palm top computers. The latter devices have tended to use monochrome LCDs which operate without a backlight. Removing the backlight reduces the power consumption of a SVGA LCD module to less than 0.5 W. While this is a great improvement, it still represents a significant level of power consumption. In order to remove the need for a backlight, much effort is being devoted to the development of reflective colour LCDs. For example, Seiko-Epson have described a colour LCD device in their paper entitled: "Full-Colour Reflective LCD Using Internal Reflectors Inverted Scattering (IRIS) Mode", by T. Sonehara et al, published in SID 97 Digest at page 1023. The effect described in the paper uses a polymer dispersed liquid crystal which does not have memory. Therefore the liquid crystal needs to be constantly refreshed in order to maintain the displayed image even if the image is not changing, and this is not very energy efficient A further example of a device operating in reflective mode is described in United States Patent US-A-5493430 (Kent Display Systems). This device comprises a layer of liquid crystal material having two stable states disposed between first and second substrates. A colour imparting layer having one or more colours is disposed adjacent a surface of one of the substrates. The focal conic state of a liquid crystal material occurs when liquid crystal helices are randomly distributed. In the aforementioned device, the focal conic state of the liquid crystal material is arranged to be weakly scattering (optically transparent), so that the colour(s) of the colour imparting layer are visible. The planar texture of a liquid crystal material is defined by the liquid crystal helices being aligned parallel to (in this device) the first and second substrates. The planar texture of the liquid crystal material in the device described in US-A-5493430 is arranged to reflect a particular colour selected by the pitch of the material. For this device, the pitch of the liquid crystal material is selected to reflect a colour which is complementary to the colour of light reflected from a colour imparting layer. For example, a blue background may be combined with a liquid crystal material that reflects yellow portions of the spectrum. The result is a white colour reflected on a blue background. A disadvantage of this display device is that it does not provide a full colour display. Energy consumption of liquid crystal devices can be reduced further by incorporating memory into liquid crystal materials. The liquid crystal effect known as memory is the characteristic that when switched to a particular state, the liquid crystal materials remain in that state even when the electric field is removed. At the present time four types of liquid crystal materials are known to provide displays with memory. These displays are: polymer stabilised cholesteric texture (PSCT) displays, surface stabilised cholesteric texture displays, ferroelectric liquid crystal displays, and smectic-A displays. PSCT technology is described in US Patent US-A-5 ,437,811 (Kent State University) and is able to provide multistable states, (i.e. grey levels) with memory, but is used to provide a reflective monochrome display. In this context, monochrome means a single colour, e.g. red, green, yellow or blue display. In order to provide a multicolour display it has been proposed that a stack of two or more PSCT displays is formed, each display being of a different primary colour so that a spectrum of colours is achieved by varying the amount of grey scale voltage applied to each panel. A disadvantage of this approach is the cost of the additional displays, the occurrence of parallax between the adjacent displays in the stack and the losses resulting from the ambient light having to pass through three displays and not just one. Details of surface stabilised cholesteric texture displays may be found on pages 706 to 709 of the proceedings of the Society for Information Display International Symposium (Vol. XXVIII), held in 1995. FeiToelectric LCDs are bistable devices. That is, they have only two stable states at zero volts and are therefore not able to provide multistable states (i.e. grey levels) with memory. Another disadvantage of ferroelectric LCDs in this context, is that their electro- optic effect relies on the use of polarisers which tend to absorb more than 50% of the light, therefore producing a rather dark display. Smectic-A technology was reported in 1985 in the Proceedings of the SID 1985 meeting in Orlando, USA, and is capable of providing a large area, monochrome display that switches between optically clear and scattering states. However, the power consumption of this display is rather high since it is based on an electro-optic effect that draws current and requires in excess of 100 Volts to switch between states. An aim of the present invention is to overcome the aforementioned deficiencies by providing an energy efficient, colour liquid crystal display (LCD) device having grey scale capability and memory. Disclosure of Invention According to the present invention there is provided a liquid crystal display device comprising: a liquid crystal material disposed between first and second substrates and electrodes for applying an electric field to portions of the liquid crystal material, the liquid crystal material being of the type which can be switched to appear optically transparent in a visible portion of the electro-magnetic spectrum, and which exhibits at least three stable states in dependence upon an applied electric field, and the liquid crystal material being of a type which maintains its switched state when the electric field is removed; and a colour filter disposed between the first and second substrates, said colour filter comprising at least two different colours. Therefore the invention provides a single full colour liquid crystal display that has memory (and therefore a low power consumption) and one or more grey levels. The first and second substrates are preferably glass or other optically transparent material such as PET. Preferably the colour filter comprises three different colours. Preferably a reflector is disposed between the colour filter and the second substrate so as to reflect more light back to a viewer. Most preferably the colour filter is positioned substantially adjacent the first substrate. This reduces parallax. The colour filter may, however, be disposed between arrays of electrodes formed on the substrates. In this case, the colour filter is preferably positioned substantially adjacent the array of electrodes associated with the first substrate. By placing the colour filter as close to an array of electrodes disposed on the substrate as possible, good registration is achieved between colour regions of the colour filter and each respective electrode. Preferably the reflective colour display exhibits memory and provides a plurality of grey levels. At least sixteen grey levels have been found to be suitable. The liquid crystal display device advantageously consumes energy at the rate of between 0 W and 0.5 Watts. The power consumption of the device depends on how many pixels require switching, and how often the image is to be refreshed. As the display device has memory, if the image remains unchanged, no energy is consumed by the display device. The type of liquid crystal incorporated in the liquid crystal display device is preferably a Stabilised Cholesteric Texture (SCT) liquid crystal, such as a Polymer Stabilised Cholesteric Texture (PSCT) or a Surface Stabilised Cholesteric Texture liquid crystal. Most preferably the composition of the SCT liquid crystal is arranged so that its planar texture reflects light in the infra-red region of the spectrum, thereby appearing optically clear. When combined with a reflective electrode, this will lead to light being specularly reflected beyond the eye of a viewer, therefore one or more pixels will appear black to the viewer. This may be achieved with SCT liquid crystal material by arranging the pitch of the SCT liquid crystal to be greater than, or substantially equal to, 0.5μm, and most preferably greater than or equal to 0.75 μm. Alternatively, the composition of the SCT liquid crystal may be arranged so that its planar texture reflects light in another non- visible portion of the electromagnetic spectrum, for example in the ultra-violet region of the spectrum. Preferably the liquid crystal material is arranged so that its focal conic state is strongly scattering, so that in use, the colours of the colour filter are visible to the viewer. In order to achieve a strongly scattering focal conic state, the thickness of the layer of liquid crystal material is preferably approximately 6 micrometres. The composition of the liquid crystal material and the dimensions of the display cell may be changed so that a range of states is exhibited. These states range from the planar to the focal conic, with intermediate states giving grey-scale capability to the display device. For example, in a display device having a red colour filter, when the liquid crystal material is in the planar state it is optically clear, and therefore the display appears black. However, when the liquid crystal material is in the focal conic state, light is scattered by the liquid crystal material and the display appears to be red. Intermediate shades of red are visible upon varying the voltage applied to one or more pixels. The fact that the liquid crystal material is not used for imparting colour to the SCT display, but for giving the display device grey-scale capability, is felt to be particularly inventive as this is the first reported use of this technique. This goes against the prior art teaching, wherein colour filters are not required for display devices utilising cholesteric texture liquid crystal materials. In liquid crystal display devices known in the prior art, the pitch of the cholesteric texture liquid material is selected so that it reflects light in the visible range of the spectrum. Examples of liquid crystals suitable for the aforementioned are disclosed in United States Patent US-A-5,437,811 (Kent State University). Moreover the liquid crystal materials described exhibit multiple levels of states so that grey scales may be produced. Hence additional energy is saved using such stabilised liquid crystals. Alternatively the liquid crystal used may be of a smectic-A type liquid crystal material. Drive means are provided for driving the display device and may include electronic microprocessors, hereinafter termed processing means. Processing means may include devices which switch off an address energising waveform to a pixel whose state remains unchanged during first and subsequent time frames. Such processing means are therefore specifically adapted for use with liquid crystal material which exhibit memory and therefore further reduce the energy demand of the display. A number of data compression techniques exist. In moving pictures a protocol called MPEG enables static portions of an image to be left unaltered between two image frames. This technique reduces the amount of data which needs to be transmitted once an initial frame of data has been received. Thus only changes in between two adjacent frames need to be transmitted rather than a complete frame. The processing means may be adapted to incorporate data compression steps rather than readdressing each pixel at each frame. Pixels whose colour and intensity remain unaltered are therefore not addressed using the preferred processing means. This saves energy and increases speed of operation of the display device. According to another aspect of the invention there is provided a method of fabricating a liquid crystal device (10), the method including the steps of: a) forming a first array of electrodes on a first substrate; b) arranging a colour filter adjacent the first array of electrodes; c) forming a second array of electrodes on a second substrate; d) forming a display cell with the first and second substrates, the display cell having spacers to space the substrates, characterised in that liquid crystal material of the type which has memory and whose planar texture is arranged to reflect non-visible radiation, is introduced into the display cell. According to a further aspect of the invention there is provided a method of fabricating a liquid crystal device (10), the method including the steps of: a) forming a colour filter on a first substrate; b) forming a first array of electrodes adjacent the colour filter; c) forming a second array of electrodes on a second substrate; d) forming a display cell with the first and second substrates, the display cell having spacers to space the substrates, characterised in that liquid crystal material of the type which has memory and whose planar texture is arranged to reflect non-visible radiation, is introduced into the display cell. The display cells may then be connected to drive means. The first array of electrodes is preferably formed by: a) depositing a layer of insulating material on a surface of the first substrate, b) depositing a layer of conductive material on the insulating layer, and c) etching at least a portion of the conductive material to form the electrode array. The layer of insulating material may be silicon dioxide, or other suitable material. The conductive material is preferably indium tin oxide (ITO). The second array of electrodes is preferably formed by: a) depositing a first layer of insulating material on a surface of the second substrate, b) depositing a second layer of material on a surface of the first layer of insulating material, b) depositing a layer of conductive material adjacent the second layer, and c) etching at least a portion of the conductive material to form the electrode array. The first insulating layer preferably includes silicon dioxide. The second layer of material preferably includes chromium, and the conductive layer is preferably formed from aluminium. A further layer of insulating material may be deposited on the first and/or second array of electrodes, and the surrounding surfaces. This insulating layer prevents electrical currents passing between the first and second electrode arrays. A layer of alignment material may be deposited on the insulating layer. The alignment layer may be buffed in order to align the liquid crystal material. Detailed Description of Preferred Embodiments A number of embodiments of the invention will now be described, by way of examples only, and with reference to the following Figures in which: Figure la shows a cross-sectional view of a liquid crystal display device according to a first embodiment of the invention; Figure lb shows a cross-sectional view of a liquid crystal display device according to a second embodiment of the display device; Figure 2a shows a cross-sectional view of part of an array of electrodes, showing column electrodes formed on a first substrate; Figure 2b shows a perspective view of column electrodes formed on a first substrate; Figure 3 a shows a cross-sectional view of a row of electrodes formed on a second substrate; Figure 3b shows a perspective view of a row of electrodes formed on a second substrate; and Figures 4a and 4b show cross-sectional views of first and second portions of a display cell which is incorporated into an LCD device. Referring to Figure la, liquid crystal display device 10 according to a first embodiment of the invention comprises a rear substrate 12 and a front substrate 14. An eye 16 is positioned adjacent the front substrate 14 to illustrate from which side a viewer sees the device 10. An Indium Tin Oxide (ITO) layer, in the form of a plurality of parallel electrodes, for example arranged in rows 18, is deposited on an inside surface of rear glass substrate 12. Another ITO layer, for example in the form of columns 20, is deposited on an inside surface of front glass substrate 14. The rows 18 and columns 20 together define an array of pixels (not shown). A reflective layer 22 is deposited on an inside surface of layer 18. The reflective layer 22 comprises one or more metallic layers which has/have a high reflectivity. Alternatively if the reflective layer is metallic (and therefore electrically conductive) layer 18 may be omitted and reflective layer 22 may act as a reflector and as an electrode. Colour filter (or colour mosaic) 24 is interposed between substrate 14 and the layer of Indium Tin Oxide 20. Colour filter 24 comprises parallel rows of closely spaced bars or columns of red, green and blue stripes. These stripes are in registration with the parallel columns 20 of Indium Tin oxide (ITO). Referring to Figure la, a cross-sectional view of a second embodiment of the invention is shown. A layer of silicon dioxide 30 is deposited on the inside surface of front glass substrate 14. An rTO layer 20 is formed on a surface of layer 30. A plurality of parallel electrodes 21 are formed by etching the ITO layer 20. Colour filter 24 is formed on a surface of electrodes 21. Colour filter 24 comprises parallel rows of red, green and blue stripes. These stripes are in registration with electrodes 21, as in the first embodiment of the invention. A layer of insulating material 60 such as silicon dioxide is deposited on the inside surface of rear glass substrate 12. A layer of chromium 32 is then deposited on the surface of insulating layer 60. A reflective layer of aluminium 22 is formed on the surface of layer 32. A plurality of electrodes are formed by etching the aluminium layer 22. For both the first and second embodiments of the invention, the liquid crystal 15. contained between substrates 12 and 14, is of the stabilised cholesteric texture (SCT) type whose pitch has been adjusted to be greater than, or equal to. 0.5 μm. This order of dimensions in the pitch is so that the liquid crystal material 15 reflects infra-red radiation in the planar texture state, whilst appearing transparent to radiation in the visible waveband. Such liquid crystal material 15 possesses the ability to be switched to several different stable states upon application of an electric field established by a switching voltage, (VI volts) across electrodes 18 and 21. Depending on the state of the liquid crystal 15 it may totally scatter or totally reflect incident radiation, or exist in a plurality (preferably at least sixteen) of states between these two extremes. When the electric field has been removed the liquid crystal material 15 remains in the condition in which it was prior to removal of the electric field. Display device 10 will now be described briefly in operation. A pixel (not shown) having the address row number p and column number q is to be switched to red by a driver (not shown). Row p and column q each receive a voltage which establishes a potential difference of VI volts and therefore an electric field across pixel (pq). Pixel (pq) is adjacent a red stripe of colour filter 24. Applying voltage waveform (VI) across ITO electrodes 18 and 21 produces the planar texture state in the liquid crystal material 15 and thus provides an optically transparent state to a viewer. Applying a second waveform (V2) produces a focal conic texture in the liquid crystal 15 which causes a highly scattering optical state. Waveforms having intermediate voltages VI and V2 provide a series of grey levels, i.e. states in which the level of scattering is lower than that produced by applying V2 but greater than that achieved by applying VI. In common with the SCT electro-optic characteristics each of these states, (i.e. the optically clear, the strongly scattering and the intermediate grey levels) is stable at zero voltage. That is when the device is switched off and not consuming any energy, liquid crystal material remains in its switched state. Thus once switched a pixel in the display device 10 requires no energy. Hence, provided there is no change to the pixel colour, the field can be switched off (in respect of the pixel(s) concerned) and processing means may be provided for determining and achieving this. Such processing means acts to further reduce energy consumption as no energy is spent re-addressing pixels whose state does not change from one frame to the next, and which includes a liquid crystal material which exhibits memory. Also because no polarisers are used the display device 10 is relatively bright. A method of fabricating the display device 10 is now described, the device in this example being a surface stabilised display. The device 10 includes a display cell which is formed from two planar substrate portions, typically made from either sodalime or borosilicate glass. The first portion of the display cell includes column electrodes 21, for example, and a colour filter. The glass substrate 14 is first coated with a layer of silicon dioxide 30, and a layer of indium tin oxide 20 is deposited over the silicon dioxide layer. The electrodes 21 are formed by etching the indium tin oxide layer so that the required areas of silicon dioxide 30 are revealed, as shown in Figure 2. The electrodes are etched using well-known photolithographic and selective etching techniques. The colour filter 24 is formed by depositing pigmented substances on the electrodes, and selectively removing portions of the substances using photolithographic techniques. Before the colour filter is deposited on the electrodes, a black matrix may be deposited on the ITO electrodes and the exposed areas of silicon dioxide. The black matrix is then etched from the ITO electrodes, leaving a thin coating of the matrix previously exposed areas of silicon dioxide. However, it is sometimes advantageous to place the colour filters underneath the ITO electrodes in order to avoid a drop in voltage across the colour filter. The second portion of the display cell includes row electrodes, for example, and a reflective layer. The second portion of the display device is formed by depositing a thin layer of chromium 32 followed by a layer of aluminium 33. Layer 32 is required as aluminium does not easily adhere to glass. The electrodes of the first portion of the display cell are formed by etching the aluminium layer 33 in order to produce a row electrode pattern, as shown in Figure 3. If the glass used is sodalime, then it is necessary to have an insulating layer of silicon dioxide between the chromium layer and the glass. This prevents the migration of ions from the glass into the liquid crystal material. Both portions of the display cell are then coated with a barrier layer 34 formed from a spin-on-glass of vacuum deposited silicon dioxide. The barrier layer 34 prevents electrical shorts between row and column electrodes. Layer 34 is subsequently coated with a surface alignment layer 36 being formed by spin coating, roller coating, or other suitable printing technique. The surface alignment material used is a polyimide such as AL5417 which is available from Japan Synthetic Rubber. After deposition, the polyimide is dried, cured and then rubbed (buffed) in order to align the liquid crystal material which is to be added at a later stage of fabrication. The first and second portions of the display cell having layers 34 and 36 are illustrated by Figures 4a and 4b, respectively. Both portions of the display cell are now ready to be assembled. An edge seal material, for example XN5AC produced by Mitsui, is now deposited around the periphery of the first portion of the display cell. A small gap is left in the edge seal material in order to form a fill hole. Spacer material is deposited on the surface of the second portion of the display cell by, for example, spraying a mixture of spacer balls and a solvent. The spacer balls used are typically 6 micrometres in diameter, and are available from Nagase. The display cell is then assembled by applying heat and pressure to the two separate portions. Liquid crystal material 15 is then introduced into the display cell by vacuum filling. The liquid crystal material used in this example is a mixture of a nematic liquid crystal mixed with chiral dopant such that the mixture has a cholesteric pitch of greater than, or equal to, 0.5 micrometres. A nematic crystal such as ZLI 2222-100 and chiral dopant CB15 supplied by Merck may be used. After the display cell has been filled, the cell is subjected to external pressure in order to force the glass portions to rest on the spacers. Under applied external pressure, excess liquid crystal material escapes from the display cell via the fill hole. This excess liquid crystal material is removed from the fill hole, and the fill hole is plugged with, for example a UV curable adhesive such as Norland™ 63. The display cell may now be connected to respective drive means via electrical contacts (not shown). The invention has been described by way of example only and it will be appreciated that variation may be made to the embodiments described without departing from the scope of the invention. For example, SCT material may be replaced by Smectic-A material. The invention may be incorporated into many items such as hand-held computer games, wrist-watches, laptop or palmtop computers, pocket calculators, personal organisers and camcorders. It may even be used in advertising. For example, the display device may be incorporated into packaging, or even attached to shopping trolleys (carts) to show advertisements or to convey other information to a customer. In the embodiment where the device is incorporated on shopping trolleys, and RF receiver may permit in-store broadcasts or advertisements to be transmitted simultaneously to all trolleys, thereby bringing to the attention of customers information such as special offers.

Claims: Claims A liquid crystal device (10) comprising a liquid crystal material (15) disposed between first (12) and second (14) substrates and electrodes for applying an electric field to portions of the liquid crystal material, the liquid material crystal being of the type which can be switched to appear optically transparent in a visible portion of the electromagnetic spectrum, and which exhibits at least three stable states in dependence upon an applied electric field, the liquid crystal material being of a type which maintains its state when the electric field is removed; and a colour filter (24) disposed between the first and second substrates, said colour filter comprising at least two different colours. 2. A device (10) according to claim 1 wherein the colour filter (24) comprises 3 different colours. 3. A device (10) according to claims 1 or 2 wherein the colour filter (24) is substantially adjacent the first substrate (12). 4. A device (10) according to claim 1 wherein a reflector (22) is disposed between the colour filter (24) and the second substrate (14), so that the display appears brighter when viewed. 5. A device (10) according to claim 1 wherein the liquid crystal material (15) comprises polymer stabilised cholesteric texture liquid crystal material. 6. A device (10) according to claim 1 wherein the liquid crystal material (15) comprises surface stabilised cholesteric texture liquid crystal material. 7. A device (10) according to claim 1 wherein the liquid crystal material (15) comprises a smectic-A liquid crystal. 8. A device (10) according to any of claims 5 to 7 wherein the liquid crystal material (15) is arranged so that its planar texture reflects non-visible radiation. 9. A device (10) according to any of claims 5 to 7 wherein the liquid crystal material (15) is arranged so that its focal conic state is strongly scattering. 10. A device (10) according to claim 8 wherein the pitch of the liquid crystal material (15) is substantially greater than 0.5 micrometres. 11. A device (10) according to claim 1 including a drive means. 12. A device (10) according to claim 11 including processing means for determining a change in the state of a pixel and for switching off an electric field when there is no change in the pixel between consecutive time frames, thereby reducing energy consumption of the device. 13. A hand-held computer game incorporating the device claimed in any of claims 1 to 12. 14. A wrist-watch incorporating the device claimed in any of claims 1 to 12. 15. A lap-top computer incorporating the device claimed in any of claims 1 to 12. 16. A pocket calculator incorporating the device claimed in any of claims 1 to 12. 17. A shopping trolley incorporating the liquid crystal display device claimed in any of claims 1 to 12. 18. A personal organiser incorporating the device claimed in any of claims 1 to 12. 19. A camcorder incorporating the device claimed in any of claims 1 to 12. 20. Packaging incorporating the device claimed in any of claims 1 to 12. 21. An advertising hoarding incorporating the device claimed in any of claims 1 to 12. 22. A method of fabricating a liquid crystal device (10) including the steps of: a) forming a first array of electrodes on a first substrate; b) arranging a colour filter adjacent the first array of electrodes; c) forming a second array of electrodes on a second substrate; d) forming a display cell with the first and second substrates, the display cell having spacers to space the substrates, characterised in that liquid crystal material of the type which has memory and whose planar texture is arranged to reflect non-visible radiation, is introduced into the display cell. 23. A method of fabricating a liquid crystal device (10) including the steps of: a) forming a colour filter on a first substrate; b) forming a first array of electrodes adjacent the colour filter; c) forming a second array of electrodes on a second substrate; d) forming a display cell with the first and second substrates, the display cell having spacers to space the substrates, characterised in that liquid crystal material of the type which has memory and whose planar texture is arranged to reflect non-visible radiation, is introduced into the display cell. 24. A method according to claim 22 or 23 wherein the first array of electrodes is formed by: a) depositing a layer of insulating material on a surface of the first substrate, b) depositing a layer of conductive material on the insulating layer, and c) etching at least a portion of the conductive material to form the electrode array. 25. A method according to claim 22 or 23 wherein the second array of electrodes is formed by: a) depositing a first layer of insulating material on a surface of the second substrate, b) depositing a second layer of material on a surface of the first layer of insulating material, b) depositing a layer of conductive material adjacent the second layer, and c) etching at least a portion of the conductive material to form the electrode array. 26. A method according to claim 24 including the step of depositing a layer of insulating material on at least the first array of electrodes. 27. A method according to claim 25 including the step of depositing a layer of insulating material on at least the second array of electrodes. 28. A method according to claim 26 and claim 27 including the step of depositing a layer of alignment material on the insulating layer. 29. A method according to claim 28 wherein the alignment layer is brushed in order to align the liquid crystal material. 30. A device substantially as herein described with reference to the Figures. 31. A method substantially as herein described with reference to the Figures.

Inventors: MOSLEY ALAN, MOSLEY, ALAN
Applicants: CENTRAL RESEARCH LAB LTD, MOSLEY ALAN, CENTRAL RESEARCH LABORATORIES LIMITED, MOSLEY, ALAN
Application year: 1998
Main classification: G02F1
IPC codes: G02F1