Patent Publication Number: US-2022229325-A1

Title: Reduced border displays

Description:
FIELD 
     The invention generally relates to techniques for bezel reduction for LCD displays, in particular flexible LCD displays, and to techniques for implementing curved LCD displays. 
     BACKGROUND 
     A display typically comprises an active area, on which information may be displayed, surrounded by an inactive border or bezel that is not usable for information display. There is a general trend, and market pull, for displays with reduced borders/bezels and for curved displays. However, this imposes manufacturing, yield, and reliability challenges. 
     SUMMARY 
     Reduced Border Displays 
     In one aspect there is therefore provided an LCD (Liquid Crystal Display) display, comprising an active display area, a backlight to illuminate the active display area, and an LCD display stack. The LCD display stack may comprise a substrate, a liquid crystal layer over the substrate, and liquid crystal cover layer. The substrate, the liquid crystal layer, and the liquid crystal cover layer define a liquid crystal cell. In implementations the LCD display stack has an edge seal extending between the substrate and the liquid cover layer. 
     In implementations the LCD display stack extends over the active display area and beyond the active display area to bend around an edge of the backlight, such that the edge seal lies beyond the active display area. 
     That is, in implementations the liquid crystal cell, i.e. a region of the LCD display stack in which there is liquid crystal (LC) material between the substrate and the cover layer, and/or the edge seal, curve around the edge of the backlight. 
     Counterintuitively, as described in more detail later, it has been found advantageous to bend the complete LCD display stack around the edge of the backlight, rather than reducing the numbers of layers to a minimum i.e. to just the substrate. 
     In some implementations the LCD cell bends around an edge of the backlight. This allows the cover layer and substrate to move laterally (in a surface of the display) with respect to one another, because there is LC material between these layers. For similar reasons, in some implementations the edge seal lies behind the backlight. 
     As described later, in some implementations the LCD display stack may be bent through 180 degrees and e.g. fastened to a rear of the backlight or to a rear of a backlight support/tray. In some other implementations the LCD display stack may be bent through an angle of less than 180 degrees, e.g. 130-170 degrees, to reduce stress within the stack. Nonetheless in such implementations some of the display stack still lies behind the backlight. 
     Locating the edge seal behind the backlight also facilitates pulling the display stack around a tight radius and securely retaining the stack, because this facilitates robust attachment of the display stack. Thus in implementations the LCD display stack is attached to a rear of the backlight (or another rear face of the display) by an adhesive layer and the edge seal and adhesive layer overlap laterally. 
     Some implementations of the display may incorporate integrated gate drive (IGD) circuitry. In broad terms this is circuitry, e.g. memory or shift register circuitry, which facilitates addressing pixels of the display with a reduced number of lines (electrical connections). For example such IGD circuitry may be located on the substrate adjacent an edge of the active area of the display and may have a plurality of row or column lines (electrode connections) leading to pixels of the display for driving the display. The IGD circuitry may have a smaller number of lines, e.g. one or more serial data connections, to receive data for driving the pixels of the display. Thus such IGD circuitry may substantially reduce a number of external connections needed by external drive/control circuitry, and can also facilitate a coarser spacing of such external connections. 
     Although the general term for such circuitry is integrated gate drive (IGD) circuitry here the term is used broadly to encompass other types of circuitry which may be used in a similar way, e.g. any type of circuitry e.g. on one or more integrated circuit dies, typically positioned adjacent an edge of the active display area. For example integrated gate drive circuitry may sometimes be referred to as GIP (Gate In Panel) circuitry when formed by the GIP method in which gate drive integrated circuits are provided directly on the display panel. 
     In some implementations the IGD circuitry is mounted on the substrate but moved away from the edge of the active display area and around the bend to a region where the substrate, i.e. display stack, is substantially planar, lengthening the connections between the display pixels and the IGD circuitry. For example in some implementations the edge seal, adhesive layer, and IGD circuitry all overlap. This is not essential but reduces the risk of failure of devices, and hence can increase reliability and yield. 
     Thus in some implementations the IGD circuitry is displaced away from the active display area. 
     Electrical connections between the IGD circuitry and the active display area (display pixels) may comprise a stack of electrically conducting layers including at least a first, compliant layer of first metal and a second protective layer of second metal. For example, the electrical connections may have a sandwich structure in which the layer of first metal is sandwiched between layers of second metal. In implementations a compliance of the first metal is greater than a compliance of the second metal. For example, the first metal may comprise aluminium, or gold. In implementations an oxidation resistance of the second metal is greater than an oxidation resistance of the first metal. For example, the second metal may comprise molybdenum. 
     Also or instead, the electrical connections between the IGD circuitry and the active display area (display pixels) may fan out into multiple connections over the bend (and then fan back into a single connection). 
     Both these approaches can improve the flexibility of the connections. 
     In implementations one or more encapsulation layers encapsulate the liquid crystal cell, e.g. below the substrate and above the cover layer, extending over the active display area. However, one or both of these may extend over the active display area and beyond the active display area to bend around an edge of the backlight. This can simplify manufacture and improve protection of the LC cell. Also or instead the LCD display stack may be embedded in an encapsulation material such as epoxy where the LCD display stack bends around the edge of the backlight, and optionally up to or beyond where the edge seal begins. 
     Typically the backlight is attached to the display stack by a thin strip of adhesive around the edge of the backlight. However, this obscures light from the backlight and can thus require a small non-active border for the active display area. Some implementations may omit the strip of adhesive along the edge of the backlight adjacent the bend. However, this can result in a bright line along the edge of the active display area due to light leakage. Light may also leak from the bend in the display stack. 
     Thus in some implementations the LCD display stack has a light-blocking layer which is substantially continuous over a region of the LCD display stack where the LCD display stack bends around an edge of the backlight, to inhibit light from the backlight leaking out. This light-blocking layer may be formed from the same layer of material used to form colour filters in a colour LCD display, e.g. a resist layer, coloured black (i.e. light absorbing). 
     In some implementations a backlight tray is provided to hold the backlight. In some implementations the backlight tray may be integrally formed with the backlight. 
     In some implementations the LCD display stack bends around and abuts a curved edge of the backlight tray, and may be adhesively bonded to this curved edge. This can help to impart stability and robustness to the display. 
     In some implementations the backlight tray is configured to absorb light from the backlight at the edge of the backlight tray, e.g. by incorporating a light absorbing (black) material, which inhibits the appearance of a bright edge to the display. Also or instead, the backlight tray may be refractive index matched to the backlight and/or an interface between the backlight tray and the backlight may include a refractive index material. Both these techniques can reduce stray light emissions from the display. This is especially so where the display stack/LC cell blocks light from passing through the stack in the bend region, e.g. because it includes a light-blocking layer. 
     In some implementations the backlight is an edge-lit backlight and includes a light guide to distribute light from an edge of the light guide over the active display area. Then the light guide and backlight tray may integrally formed e.g. from polymer such as PMMA. 
     In some implementations a radius of the bend decreases around the bend from the active display area towards a rear of the display. For example the display stack may curve gently around to the rear of the display, and then bend sharply e.g. to attached to the rear of the backlight (or another rear face of the display). Then an edge of the backlight or, where present, of a backlight tray, may conform to the bend. That is an edge of the backlight or backlight tray may be shaped to define the shape of the display stack around bend (whilst still functioning as a backlight). This can help to control the shape of the edge of the display, whilst also increasing robustness and manufacturability. 
     In some implementations the LCD display is rectangular and the LCD display stack bends around at least two adjacent lateral edges of the backlight/rectangle. The LCD display stack may be necked or notched at the corners, i.e. at one or more corners defined by the at least two adjacent lateral edges of the rectangle. 
     Zero Border Displays 
     In one aspect there is therefore provided a zero-bezel LCD display, i.e. configured to provide a flat display area with all display edges borderless such that displayed information is able to extend over all (i.e. each) of the display edges. The LCD (Liquid Crystal Display) display may comprise a flexible active matrix LCD display stack. The display stack may comprise a flexible substrate bearing active matrix circuitry comprising an array of TFTs (thin film transistors) for controlling pixels of the display. The display stack may further comprise a liquid crystal layer over the substrate. The display stack may further comprise a liquid crystal cover layer. The flexible substrate, the liquid crystal layer, and the liquid crystal cover layer may define a liquid crystal cell. The flexible active matrix LCD display stack may define an active display area. The LCD display may further comprise a backlight behind the flexible active matrix LCD display stack to illuminate the active display area. In implementations, the flexible substrate of the flexible active matrix LCD display stack (including the substrate) is notched at each corner of the flat display area and is folded around (i.e. bends around) each of the edges of the flat display area such that the active display area extends around each of the edges of the flat display area of the zero-bezel LCD display. 
     In this way, an “infinity” display may be created in which the displayed information extends around each of the edges of the display. 
     In implementations the display area is rectangular (which here includes square), with four orthogonal display edges. The backlight may thus also be rectangular. 
     In implementations the notch at each corner may be defined by a concave contour or curve in the flexible substrate (and optionally the rest of the display stack) at the corner. When configured as a zero-bezel LCD display this contour may define a concave contour at each corner of the active display area. In implementations the notch at each corner may be defined by a straight line across the corner when configured as a zero-bezel LCD display. 
     In implementations the notches in the flexible substrate at the corners of the flat display area define a contour, e.g. a concave contour, which cuts off each corner of the flat display area. An edge of the active display area at each corner may then define a convex curve on the flat display area which is displaced away from the concave contour at a point of closest approach of the concave contour and convex curve. The active display area may be defined e.g. by the display stack or part thereof e.g. the array of TFTs. 
     This may facilitate manufacture and increase yield as there is a single point of closest approach of the curves, which have opposite senses, which can facilitate tolerancing and manufacture control, thus also facilitating bringing the two curves close to one another. 
     In implementations the LCD display stack extends over the active display area and beyond the active display area to bend around an edge of the backlight. The flexible active matrix LCD display stack may have an edge seal extending between the substrate and the liquid cover layer. The edge seal may lie beyond the active display area. That is, in implementations the liquid crystal cell, i.e. a region of the LCD display stack in which there is liquid crystal (LC) material between the substrate and the cover layer, and/or the edge seal, curve around the edge of the backlight. 
     Counterintuitively, as described in more detail later, in some implementations it has been found advantageous to bend the complete LCD display stack around the edge of the backlight, rather than reducing the numbers of layers to a minimum i.e. to just the substrate. 
     In some implementations the LCD cell bends around an edge of the backlight. This allows the cover layer and substrate to move laterally (in a surface of the display) with respect to one another, because there is LC material between these layers. For similar reasons, in some implementations the edge seal lies behind the backlight. 
     As described later, in some implementations the LCD display stack may be bent through 180 degrees and e.g. fastened to a rear of the backlight or to a rear of a backlight support/tray. In some other implementations the LCD display stack may be bent through an angle of less than 180 degrees, e.g. 130-170 degrees, to reduce stress within the stack. Nonetheless in such implementations some of the display stack still lies behind the backlight. 
     Locating the edge seal behind the backlight also facilitates pulling the display stack around a tight radius and securely retaining the stack, because this facilitates robust attachment of the display stack. Thus in implementations the LCD display stack is attached to a rear of the backlight (or another rear face of the display) by an adhesive layer and the edge seal and adhesive layer overlap laterally. 
     Some implementations of the display may incorporate integrated gate drive (IGD) circuitry. In broad terms this is circuitry, e.g. memory or shift register circuitry, which facilitates addressing pixels of the display with a reduced number of lines (electrical connections). For example such IGD circuitry may be located on the substrate adjacent an edge of the active area of the display and may have a plurality of row or column lines (electrode connections) leading to pixels of the display for driving the display. The IGD circuitry may have a smaller number of lines, e.g. one or more serial data connections, to receive data for driving the pixels of the display. Thus such IGD circuitry may substantially reduce a number of external connections needed by external drive/control circuitry, and can also facilitate a coarser spacing of such external connections. 
     Although the general term for such circuitry is integrated gate drive (IGD) circuitry here the term is used broadly to encompass other types of circuitry which may be used in a similar way, e.g. any type of circuitry e.g. on one or more integrated circuit dies, typically positioned adjacent an edge of the active display area. For example integrated gate drive circuitry may sometimes be referred to as GIP (Gate In Panel) circuitry when formed by the GIP method in which gate drive integrated circuits are provided directly on the display panel. 
     In some implementations the IGD circuitry is mounted on the substrate but moved away from the edge of the active display area and around the bend to a region where the substrate, i.e. display stack, is substantially planar, lengthening the connections between the display pixels and the IGD circuitry. For example in some implementations the edge seal, adhesive layer, and IGD circuitry all overlap. This is not essential but reduces the risk of failure of devices, and hence can increase reliability and yield. 
     Thus in some implementations the IGD circuitry is displaced away from the active display area. For example the flexible substrate may extend laterally beyond the flexible active matrix LCD display stack to define one or more tabs at each of two, e.g. orthogonal, edges of the flat, e.g. rectangular display area. Then the IGD circuitry may be mounted on each of the one or more tabs. In implementations each of the one or more tabs is connected to a region of the flexible substrate in (beneath) the active display area via a necked region in which a lateral width of the tab diminishes. 
     Electrical connections between the IGD circuitry and the active display area (display pixels) may comprise a stack of electrically conducting layers including at least a first, compliant layer of first metal and a second protective layer of second metal. For example the electrical connections may have a sandwich structure in which the layer of first metal is sandwiched between layers of second metal. In implementations a compliance of the first metal is greater than a compliance of the second metal. For example the first metal may comprise aluminium, or gold. In implementations an oxidation resistance of the second metal is greater than an oxidation resistance of the first metal. For example, the second metal may comprise molybdenum. 
     Also or instead, the electrical connections between the IGD circuitry and the active display area (display pixels) may fan out into multiple connections over the bend (and then fan back into a single connection). 
     Both these approaches can improve the flexibility of the connections. 
     In implementations one or more encapsulation layers encapsulate the liquid crystal cell, e.g. below the substrate and above the cover layer, extending over the active display area. However, one or both of these may extend over the active display area and beyond the active display area to bend around an edge of the backlight. This can simplify manufacture and improve protection of the LC cell. Also or instead the LCD display stack may be embedded in an encapsulation material such as epoxy where the LCD display stack bends around the edge of the backlight, and optionally up to or beyond where the edge seal begins. 
     Typically, the backlight is attached to the display stack by a thin strip of adhesive around the edge of the backlight. However, this obscures light from the backlight and can thus require a small non-active border for the active display area. Some implementations may omit the strip of adhesive along the edge of the backlight adjacent the bend. However this can result in a bright line along the edge of the active display area due to light leakage. Light may also leak from the bend in the display stack. 
     Thus in some implementations the LCD display stack has a light-blocking layer which is substantially continuous over a region of the LCD display stack where the LCD display stack bends around an edge of the backlight, to inhibit light from the backlight leaking out. This light-blocking layer may be formed from the same layer of material used to form colour filters in a colour LCD display, e.g. a resist layer, coloured black (i.e. light absorbing). 
     In some implementations a backlight tray is provided to hold the backlight. In some implementations the backlight tray may be integrally formed with the backlight. 
     In some implementations, the LCD display stack bends around and abuts a curved edge of the backlight tray, and may be adhesively bonded to this curved edge. This can help to impart stability and robustness to the display. 
     In some implementations the backlight tray is configured to absorb light from the backlight at the edge of the backlight tray, e.g. by incorporating a light absorbing (black) material, which inhibits the appearance of a bright edge to the display. Also or instead the backlight tray may be refractive index matched to the backlight and/or an interface between the backlight tray and the backlight may include a refractive index material. Both these techniques can reduce stray light emissions from the display. This is especially so where the display stack/LC cell blocks light from passing through the stack in the bend region, e.g. because it includes a light-blocking layer. 
     In some implementations the backlight is an edge-lit backlight and includes a light guide to distribute light from an edge of the light guide over the active display area. Then the light guide and backlight tray may integrally formed e.g. from polymer such as PMMA. 
     In some implementations a radius of the bend decreases around the bend from the active display area towards a rear of the display. For example the display stack may curve gently around to the rear of the display, and then bend sharply e.g. to attached to the rear of the backlight (or another rear face of the display). Then an edge of the backlight or, where present, of a backlight tray, may conform to the bend. That is an edge of the backlight or backlight tray may be shaped to define the shape of the display stack around bend (whilst still functioning as a backlight). This can help to control the shape of the edge of the display, whilst also increasing robustness and manufacturability. 
     The approaches described herein may be used with direct lit or edge lit backlighting. 
     “Zero Border Displays” implementations described above may be combined with the “Reduced Border Displays” described above. 
     Curved Displays 
     In one aspect there is therefore provided a flexible LCD (Liquid Crystal Display) display to provide a curved display area. The curved display area has display edges and may be curved about one, two or more axes. The flexible LCD display may comprise a flexible active matrix LCD display stack. The flexible active matrix LCD display stack may comprise a flexible substrate bearing active matrix circuitry comprising an array of TFTs (thin film transistors) for controlling pixels of the display. The flexible active matrix LCD display stack may further comprise a liquid crystal layer over the substrate, and a liquid crystal cover layer. The flexible substrate, the liquid crystal layer, and the liquid crystal cover layer may define a liquid crystal cell. The flexible active matrix LCD display stack may have an edge seal extending between the substrate and the liquid cover layer. The flexible active matrix LCD display stack may define an active display area. 
     The flexible LCD display may further comprise drive circuitry, e.g. IGD (integrated gate drive) circuitry, for driving the active matrix circuitry. The flexible substrate may extend laterally beyond the flexible active matrix LCD display stack to define one or more tabs at each of two adjacent, e.g. orthogonal, edges of the curved display area, and the drive circuitry may be mounted on each of the one or more tabs. Each of the one or more tabs may be connected to a region of the flexible substrate in (i.e. beneath) the active display area via a necked region in which a lateral width of the tab diminishes. 
     In some implementations the flexible substrate defines a plurality of tabs at a first of the two adjacent edges. This first edge is curved, and the flexible active matrix LCD display stack is curved about an axis which may be parallel to the second of the two adjacent edges. In implementations, for at least the tabs at the first of the two adjacent edges, the necked region includes a compliant structure, e.g. a fold, and has notches at corners where the necked region joins the flexible substrate. In some implementations the flexible active matrix LCD display stack is curved to define a cylindrical display, e.g. with the shape of a circular cylinder or elliptic cylinder. Taken collectively these features facilitate manufacture of a curved e.g. cylindrical display with improved reliability and manufacturing yield. 
     In some implementations the active display area is rectangular, with four orthogonal edges. However, the active display area may have other shapes e.g. a triangular, octagonal, or other polygonal shape. In implementations the above described features allow the active display area to be formed into complex convex and/or concave shapes, optionally with multiple curves e.g. curves about multiple different axes. 
     The flexible active matrix LCD display stack may be curved such that two opposite edges of the active display area (typically straight edges) abut along a line, i.e. a join line, in particular where the active display area is rectangular. The LCD display stack (including the substrate) may be notched at each end of one or both of the two opposite edges (i.e. at the corners) and folded around respectively one or both of the two opposite edges, to reduce an inactive area of a cylindrical display in a strip along the join line. In particular, the LCD display stack may be notched at each end of both the two opposite edges and folded around both of the two opposite edges, such that the active display area abuts along the opposite, e.g. straight, edges (which may be parallel to an axis of the cylinder) to define a substantially continuous active display area extending around a circumference of the cylindrical display. 
     Some implementations of the display may incorporate integrated gate drive (IGD) circuitry. In broad terms this is circuitry, e.g. memory or shift register circuitry, which facilitates addressing pixels of the display with a reduced number of lines (electrical connections). For example such IGD circuitry may be located on the substrate adjacent an edge of the active area of the display and may have a plurality of row or column lines (electrode connections) leading to pixels of the display for driving the display. The IGD circuitry may have a smaller number of lines, e.g. one or more serial data connections, to receive data for driving the pixels of the display. Thus, such IGD circuitry may substantially reduce a number of external connections needed by external drive/control circuitry, and can also facilitate a coarser spacing of such external connections. This in turn can facilitate a curved LCD display. 
     Although the general term for such circuitry is integrated gate drive (IGD) circuitry here the term is used broadly to encompass other types of circuitry which may be used in a similar way, e.g. any type of circuitry e.g. on one or more integrated circuit dies, typically positioned adjacent an edge of the active display area. For example integrated gate drive circuitry may sometimes be referred to as GIP (Gate In Panel) circuitry when formed by the GIP method in which gate drive integrated circuits are provided directly on the display panel. 
     In some implementations the drive circuitry comprises one or more integrated circuits i.e. IGD integrated circuits. The flexible LCD display may further comprise a rigid interconnect structure (i.e. stiffer than the flexible substrate), mounted on each of the tabs bearing the one or more integrated circuits and optionally having an edge connector for making an external electrical connection to the LCD display. In some arrangements e.g. where the curved display is bent around a very tight curve, successive interconnect structures may alternate above and then below adjacent interconnect structures along the curve. In some other arrangements multiple interconnect structures may define a plane and connect to a common interconnect PCB (Printed Circuit Board). In some implementations, rather than being mounted on an interconnect structure the IGD integrated circuits may be mounted directly onto the flexible substrate. 
     In implementations the IGD circuitry is mounted on the substrate but moved away from the edge of the active display area and around the bend to a region where the underlying substrate is substantially planar, lengthening the connections between the display pixels and the IGD circuitry. For example in some implementations the edge seal, adhesive layer, and IGD circuitry all overlap. This reduces the risk of failure of devices, and hence can increase reliability and yield. 
     Electrical connections between the IGD circuitry and the active display area (display pixels) may comprise a stack of electrically conducting layers including at least a first, compliant layer of first metal and a second protective layer of second metal. For example, the electrical connections may have a sandwich structure in which the layer of first metal is sandwiched between layers of second metal. In implementations a compliance of the first metal is greater than a compliance of the second metal. For example, the first metal may comprise aluminium, or gold. In implementations an oxidation resistance of the second metal is greater than an oxidation resistance of the first metal. For example, the second metal may comprise molybdenum. This can improve the flexibility of the connections. 
     Also or instead, the electrical connections between the IGD circuitry and the active display area (display pixels) may fan out into multiple connections in the necked region i.e. over the bend, and may then fan back into a single connection. This can also improve the flexibility of the connections. 
     In some implementations the flexible active matrix LCD display stack is curved about an axis. The flexible LCD display may further comprise a backlight behind the flexible active matrix LCD display stack to illuminate the active display area. The backlight may be curved to confirm to the curvature of the flexible active matrix LCD display stack. 
     Counterintuitively, as described in more detail later, in some implementations it has been found advantageous to bend the complete LCD display stack around the edge of the backlight, rather than reducing the numbers of layers to a minimum i.e. to just the substrate. 
     In some implementations the LCD cell bends around an edge of the backlight. This allows the cover layer and substrate to move laterally (in a surface of the display) with respect to one another, because there is LC material between these layers. For similar reasons, in some implementations the edge seal lies behind the backlight. 
     As described later, in some implementations the LCD display stack may be bent through 180 degrees and e.g. fastened to a rear of the backlight or to a rear of a backlight support/tray. In some other implementations the LCD display stack may be bent through an angle of less than 180 degrees, e.g. 130-170 degrees, to reduce stress within the stack. Nonetheless in such implementations some of the display stack still lies behind the backlight. 
     Locating the edge seal behind the backlight also facilitates pulling the display stack around a tight radius and securely retaining the stack, because this facilitates robust attachment of the display stack. Thus, in implementations the LCD display stack is attached to a rear of the backlight (or another rear face of the display) by an adhesive layer and the edge seal and adhesive layer overlap laterally. 
     In implementations one or more encapsulation layers encapsulate the liquid crystal cell, e.g. below the substrate and above the cover layer, extending over the active display area. However, one or both of these may extend over the active display area and beyond the active display area to bend around an edge of the backlight. This can simplify manufacture and improve protection of the LC cell. Also or instead the LCD display stack may be embedded in an encapsulation material such as epoxy where the LCD display stack bends around the edge of the backlight, and optionally up to or beyond where the edge seal begins. 
     Typically, the backlight is attached to the display stack by a thin strip of adhesive around the edge of the backlight. However, this obscures light from the backlight and can thus require a small non-active border for the active display area. Some implementations may omit the strip of adhesive along the edge of the backlight adjacent the bend. However, this can result in a bright line along the edge of the active display area due to light leakage. Light may also leak from the bend in the display stack. 
     Thus in some implementations the LCD display stack has a light-blocking layer which is substantially continuous over a region of the LCD display stack where the LCD display stack bends around an edge of the backlight, to inhibit light from the backlight leaking out. 
     This light-blocking layer may be formed from the same layer of material used to form colour filters in a colour LCD display, e.g. a resist layer, coloured black (i.e. light absorbing). 
     In some implementations a backlight tray is provided to hold the backlight. In some implementations the backlight tray may be integrally formed with the backlight. 
     In some implementations the LCD display stack bends around and abuts a curved edge of the backlight tray, and may be adhesively bonded to this curved edge. This can help to impart stability and robustness to the display. 
     In some implementations the backlight tray is configured to absorb light from the backlight at the edge of the backlight tray, e.g. by incorporating a light absorbing (black) material, which inhibits the appearance of a bright edge to the display. Also or instead, the backlight tray may be refractive index matched to the backlight and/or an interface between the backlight tray and the backlight may include a refractive index material. Both these techniques can reduce stray light emissions from the display. This is especially so where the display stack/LC cell blocks light from passing through the stack in the bend region, e.g. because it includes a light-blocking layer. 
     In some implementations the backlight is an edge-lit backlight and includes a light guide to distribute light from an edge of the light guide over the active display area. Then the light guide and backlight tray may integrally formed e.g. from polymer such as PMMA. 
     In some implementations a radius of the bend decreases around the bend from the active display area towards a rear of the display. For example the display stack may curve gently around to the rear of the display, and then bend sharply e.g. to attached to the rear of the backlight (or another rear face of the display). Then an edge of the backlight or, where present, of a backlight tray, may conform to the bend. That is an edge of the backlight or backlight tray may be shaped to define the shape of the display stack around bend (whilst still functioning as a backlight). This can help to control the shape of the edge of the display, whilst also increasing robustness and manufacturability. 
     In some implementations the LCD display is rectangular and the LCD display stack bends around at least two adjacent lateral edges of the backlight/rectangle. The LCD display stack may be necked or notched at the corners, i.e. at one or more corners defined by the at least two adjacent lateral edges of the rectangle. 
     “Curved Displays” implementations described above may be combined with the “Reduced Border Displays” described above. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the invention will be described, by way of example, with reference to the accompanying drawings, in which: 
         FIG. 1  shows an example LCD display stacks. 
         FIGS. 2 a  and 2 b    show, respectively, a display assembly for a display, and details of an LCD display curved at two adjacent edges. 
         FIGS. 3 a  and 3 b    show, respectively, a cross-sectional schematic view of a first display with a reduced bezel, and a cross-sectional schematic view of a display with a reduced bezel according to an embodiment. 
         FIGS. 4 a  and 4 b    show, respectively, a close-up view of connections between pixels and IDG circuitry, and a cross-sectional view through a connection structure. 
         FIG. 5  shows an example of a display with a changing bend radius. 
         FIG. 6  shows a flexible active matrix LCD display stack. 
         FIGS. 7 a  and 7 b    show a zero-bezel LCD display, and an example configuration of a corner of an active area of the LCD display. 
         FIGS. 8 a  and 8 b    show, respectively, an example of a fabricated, flat, LCD display with a borderless edge, and an example of a zero-bezel LCD display with all the edges borderless. 
         FIGS. 9 a -9 c    show first, second and third examples of curved LCD displays. 
     
    
    
     In the figures, like elements are indicated by like reference numerals. 
     DETAILED DESCRIPTION OF EMBODIMENTS 
       FIG. 1  illustrates a schematic cross-sectional view of an example LCD (liquid crystal display) display stack  100 . In the example display, stack liquid crystal (LC) material  130  is disposed between a substrate  120  and a liquid crystal (LC) cover layer  135 . The substrate layer  120  may also carry electrical connections, such as row and column and interconnect lines of the display, and control circuitry (not shown), for example thin film transistors (TFTs), for pixels of the display. In some implementations, e.g. for flexible displays, the TFTs may be organic. 
     Each of the substrate  120  and LC cover layer  135  may be provided with a respective encapsulation layer  115 ,  140 . An edge seal  125  is provided between the substrate and LC cover layer  120 ,  135 , in the example shown on each edge of the LC material  130 , to seal and protect the liquid crystal material. 
     A sheet of LCD display stack comprising the substrate, LC cover layer, and LC material may be referred to as an LC cell; as described herein the LCD display stack extends beyond the edges of the LC cell and includes the edge seal. 
     An LCD display stack will typically include one or more polarizing layers. Thus in the structure of  FIG. 1 , a first light polarizing layer  110  is provided below the substrate  120  and a second light polarizing layer  145  is provided above the LC cover layer  135 . In some implementations the or each encapsulation layer may be combined with a respective light polarizing layer. In the later description explicit reference to the polarizing layers is sometimes omitted. 
     A backlight layer  105  is provided below the first light polarizing layer  110 . The backlight layer  105  is generally a separate part to the LCD display stack; a polarizer may be built into the backlight. In implementations the backlight incorporates a light guide, for example fabricated from PMMA. For example this may allow the display to be edge-lit e.g. by one or more LEDs. The backlight may also include a diffuser, e.g. a layer of light-diffusing film, over the light guide i.e. between the light guide and the LCD display stack. The light guide may have a back reflector. 
     The substrate  120  may be a glass substrate or, e.g. in flexible displays, may comprise TAC (Cellulose Triacetate). The LC cover layer  130  may comprise TAC or glass. Where the substrate and/or LC cover layer comprises glass separate encapsulation layers may be omitted. In some applications the LCD display stack may be flexible but the display as a whole may be inflexible. 
     The LCD display stack may include a colour filter layer (not shown); this may reside on the LC cover layer  135  and may be fabricated from coloured resist material. To reduce parallax it is helpful if the colour filter layer is close to the layer of LC material. 
     More details of suitable technology can be found on the Applicant&#39;s web site and in the Applicant&#39;s earlier published patent applications. 
     Merely be way of illustration a total thickness of the LCD display stack may be less than 1 mm, e.g. a few hundred microns. The substrate and LC cover layer may each have a thickness of e.g. ˜40-130 μm; the encapsulation layers may each have a thickness of e.g. ˜10 μm; the light polarization layers may each have a thickness of e.g. ˜50-60 μm. 
       FIG. 2 a    shows a display assembly or panel  200  for a display. The display assembly  200  comprises an LCD display stack  100  having an active e.g. TFT addressable area  150  with pixels for displaying information, and a set of one or more chip-on-film (COF) interconnect structures  210 . Each COF interconnect structure  210  comprises, in this example, one or more driver integrated circuits  212  and connects to the LCD display stack  100  via a connection region  214  and, in use, to a PTB (Printed Wire Board) module (not shown) or PCB (Printed Circuit Board) module (not shown). 
     More particularly, in implementations the COF interconnect structure  210  may have a stiff substrate mounting the driver integrated circuit(s)  212  and mechanically and electrically connected to the flexible substrate  120  via connection region  214 . The COF interconnect structure  210  may have an edge connector for connecting to further electronic circuitry on the printed board e.g. a MPWB (Module printed wire board) of a device for which the LCD display stack provides a display. 
     The driver integrated circuits provide row and/or column drive signals, e.g. gate and/or source drive signals, to the active area  150 , either directly, or indirectly via IGD circuitry. The number of row/column lines depends on the resolution of the display; for example it may be of order &gt;10 3  for a colour display with red, green, and blue subpixels. 
     The display stack has non-driveable regions  220   a - d  surrounding the active area. Typically there are connections to each lateral side of active area  150 , in regions  220   b,c , and at the bottom, i.e. towards the COF interconnect structures, in region  220   d . No connections may be necessary at the top of the active area, in region  220   a , which may be narrow e.g. a width of the edge seal there e.g. &lt;1 mm. The connections to each lateral side of the active area can create crowding of the connection lines, which is lessened by using IGD circuitry. 
     To reduce the bezel size the display stack may be folded along one or more of lines  230   a,b,c , to move some of the inactive/non-driven areas out of view e.g. around the back of the display/backlight. Depending upon what folds are made, and where, the LCD display stack may be necked or notched  240  at two or more, e.g. all four corners of the active area. 
       FIG. 2 b    shows display assembly or panel  250  in which an innermost point of the neck/notch  240  defines a location of two perpendicular folds so that the display stack may be folded around two adjacent edges of the backlight i.e. around adjoining lateral edges of the LCD display. The active area  150  may have a rounded corner  252  to facilitate this. In implementations the innermost point of the neck/notch  240  lies adjacent the active area  150  of the display. The active area  150  may terminate where the curved edge begins, or may continue around one or both adjacent curved edges of the display. In implementations the active area  150  wraps around at least 75 degrees or 90 degrees of the bend radii of the backlight. In this way, in some implementations a rectangular display may be provided with three or four curved edges, to achieve a zero border display. 
     In the example shown implementations IDG circuitry, e.g. the one or more driver integrated circuits  212 , is provided on a tab  254  at each folded edge and may be located behind the display/backlight (in  FIG. 2 b    these tabs are shown unfolded from behind the backlight). In implementations the display panel  250  has a transparent protective layer  256  over the surface of the display which, in a similar manner, may curve around the edges of the display. 
       FIG. 3 a    shows a cross-sectional schematic view of a first display  300  with a reduced bezel. In the example of  FIG. 3 a    the LCD display stack  100  is bent around behind the display and backlight and reduced to a minimum thickness in a region of the bend  310  i.e. where the substrate is non-planar. Thus around the bend  310  the display stack is reduced to just the substrate  120 , and the interconnects it carries. The edge seal  125  is located at the front of the display where the substrate is planar; the IGD circuitry may be located under the edge seal. 
     This has been fabricated but in practice exhibits some problems. Bending at the edge of the display, e.g. during manufacture, can cause the edge seal to pull apart at location  312 . Also encapsulation can be difficult, and if the LC cover layer  135  is not to be bent the edge seal  125  must be located on the viewable surface which is thus constrained to have some inactive border. 
       FIG. 3 b    shows a cross-sectional schematic view of a display  350  with a reduced bezel according to an alternative approach. Counterintuitively this addresses the aforementioned problems by maintaining the complete liquid crystal cell i.e. at least the substrate  120 , LC material  130 , and LC cover layer  135  around the bend  310  i.e. where the substrate is non-planar. In some implementations the complete LCD display stack (without the light polarizing layers) is maintained around the bend  310 . 
     Thus in the region of the bend the substrate  120  and LC cover layer  135  are separated mostly by the LC material  130  (there may also be spacers at intervals) and can thus slip past one another. This also protects the substrate, which bears the interconnects and potentially other electrical features, in the region of the bend. 
     In implementations the edge seal  125  is located where the liquid crystal cell ends, e.g. behind the display/backlight and/or where the substrate again becomes planar. This facilitates the substrate  120  and LC cover layer  135  moving past one another at the bend. Locating the edge seal here also reduces bending forces on the seal, reducing the risk of the seal pulling apart and increasing reliability, robustness and yield of the manufactured display. 
     In implementations the backlight  105  is supported by a backlight tray  352 . This may have a curved or rounded edge or end  352   a  to support and constrain an inner surface of the display stack around the bend  310 . In implementations an outer surface of the display stack may be protected by encapsulation e.g. epoxy and/or by a metal e.g. aluminium casing (not shown). 
     In implementations IDG circuitry  354  may be located behind the display/backlight and/or where the substrate again becomes planar e.g. partially or wholly overlapping the edge seal  125 . This helps to reduce stress on the TFTs and on any vias. Connections between the IDG circuitry  354  and the active area  150  of the display may be lengthened, as shown in  FIG. 4 . 
     In some implementations some of the electrical connections to control circuitry e.g. for pixels of the display may be multiplexed to reduce the number of electrical connections required, hence facilitating a reduced size border for the active display area. For example, source lines carrying the source drive signals may be multiplexed. In a similar manner connections e.g. source connections, to the LCD display panel may be multiplexed to reduce the number of connections required. 
     The display stack may be fastened to the rear of the display e.g. to the backlight  105  or backlight tray  352 , by a layer of adhesive  356 . This may also partially or wholly overlap the edge seal  125 . The adhesive layer may extend sufficiently far along the rear of the display to counter the force needed to pull the display stack around the bend. 
     As illustrated the bend is a 180 degree bend, but the bend may be shallower e.g. of order 150 degrees or less, to reduce stress on the LC cell. 
       FIG. 4 a    shows a close-up view of connections  362  between pixels  360  in the active area  150  of the display and the IDG circuitry  354 , here located beneath the edge seal  125  (with boundary  125 ′). As illustrated, the connections fan-out from the active area  150  and back at the IDG circuitry, so that each has multiple connections over the bend  310  to increase robustness and yield. The thickness of the individual connections may also be reduced. Also or instead, the interconnections  362  may include one or more meanders. 
       FIG. 4 b    shows a cross-sectional view through an example connection structure. This comprises a compliant layer  362   a  of metal e.g. aluminium, sandwiched by protective layers  362   b  of metal e.g. molybdenum to resist oxidation and cracking. 
     The connections  362  may be fabricated by photolithography. 
     Referring again to  FIG. 3 b   , light can leak out of the end of the backlight  105  into the backlight tray  352 . In implementations the LCD display stack may therefore be configured to block light from passing through. The red, green, and blue filters e.g. of a colour display stack may be surrounded by a black region. The LCD display stack may be configured to block light using the colour filter layer e.g. by extending the black region to be substantially continuous in the region of bend  310 . 
     A backlight may be attached to the display stack by a thin strip of light-blocking adhesive e.g. tape around the perimeter of the upper surface of the backlight. This may be omitted along the edge of the backlight  105  adjacent the bend  310 , but this can cause problems such as a bright strip of light at the edge of the display. Thus the rounded edge  352   a  of the backlight tray may be configured to absorb light e.g. by including a light absorbing (black) material. For example an opacity of the backlight tray may be tuned to absorb enough light to keep the lighting level consistent in the area above the light guide i.e. to attenuate or remove the bright strip e.g. so that the edge of the display is not substantially brighter than a central region of the display. Alternatively, an absorbing strip may be applied to the end of the waveguide. 
     As well or instead, the backlight tray or its rounded edge may be index matched to a refractive index of the backlight and/or a joint between the backlight tray or its rounded edge and the backlight may incorporate an index matching material e.g. adhesive. The refractive index may be matched to better than 0.2, 0.1 or 0.05. 
     In implementations the backlight, more specifically the light guide of the backlight, and the backlight tray may be integrally formed—in effect the light guide acts as the backlight tray. This can also reduce stray light leakage and may facilitate extending the active display area around the bend. 
     Whether or not the backlight tray and backlight are integrally formed, in implementations the rounded edge  352   a  of the backlight tray may have a physical relief pattern, e.g. formed by micro-embossing, to distribute light output evenly over the bend. This may be used to illuminate the LCD display stack over the bend e.g. to extend the active display area around the bend; and/or this may be used to achieve a more uniform illumination of the active display area e.g. by attenuating or removing the aforementioned bright strip. In some implementations the backlight diffuser may extend partially or wholly around the rounded edge; in other implementations the backlight diffuser may terminate where the rounded edge begins. 
       FIG. 5  shows an example of a display in which a radius of the bend  310  decreases around the bend from the active display area towards a rear of the display, eventually bending sharply so that it can be attached to the rear of the backlight or backlight tray, guided by the backlight/tray. 
       FIG. 6  shows a flexible active matrix LCD display stack  600  for a zero-bezel display. The active area  150  defines a rectangular display area  602  and extends beyond each of four fold lines  604   a - d . Depending upon the implementation the LCD display stack may extend beyond the active area on the flexible substrate  120 , as previously described. The flexible active matrix LCD display stack has a notch  620  at each corner of the flat rectangular display area. In the illustrated example, each notch defines a concave contour  622 . 
     The substrate  120  defines a first set of one or more tabs  606  on a first lateral edge of the display area  602  and a second set of one or more tabs  608  on a second, orthogonal lateral edge of the display area  602 . Each of the tabs is connected to a region of the flexible substrate  120  via a respective necked region  610  in which a lateral width of the tab diminishes. The tabs  606 ,  608  may have notches  612  where the necked region joins the flexible substrate. This is useful for stress relief, in particular when the display is curved. 
     In implementations the tabs  608 ,  610  may mount drive circuitry such as IGD circuitry, e.g. one or more driver integrated circuits  212 . These may be mounted directly onto the substrate, or may be mounted on a stiffer interconnect structure (not shown in  FIG. 6 ), which may also serve to make external electrical connections to the LCD display e.g. via an edge connector. 
       FIG. 7 a    shows a zero-bezel LCD display  700  with a flat rectangular display area, comprising the flexible active matrix LCD display stack  600  of  FIG. 6 . The tabs  606 ,  608  are folded behind the display, which incorporates a backlight (not shown). The inset figure shows details of a corner of the LCD display, illustrating how the active area extends around from a front of the display towards a rear of the display, repeated on all four edges to provide the appearance of an “infinity” display. 
       FIG. 7 b    shows an example configuration of a corner of the active area  150 . This shows a concave contour  622  defined by a notch, and in the illustrated example a further concave curve  624  defining an edge of the flexible active matrix LCD display stack. A convex curve  626  defines an edge of the active display area at each corner; this may be defined e.g. by an edge of the active matrix TFT circuitry. Such a configuration may also be used with a curved LCD display of the type described later. 
       FIG. 8 a    shows an example of a fabricated display with a structure as shown in  FIG. 3 b   .  FIG. 8 a    shows one edge of the display but the structure of  FIG. 3 b    may be replicated on more than one edge of the display. However, by using the flexible active matrix LCD display stack  600  of  FIG. 6 , as described with reference to  FIG. 7 , a “zero-bezel” display may be fabricated in which the active display area extends around each of the e.g. four edges of the display.  FIG. 8 b    shows an example of such a zero-bezel display as described with reference to  FIGS. 7 a  and 7 b   , by way of illustration incorporated into a laptop. 
       FIG. 9 a    shows a first example of a flexible LCD display  900  with a curved display area, comprising the flexible active matrix LCD display stack  600  of  FIG. 6 . In this example, the flexible LCD display stack  600  is curved about an axis parallel to the second lateral edge of the display. The necked region  610  of tab  606 , which in this example also includes a compliant structure  611 , e.g. a V- or U-shaped fold, facilitates curvature of the display, and the notches  612 , and where present, compliant structure, relieve stress. 
       FIG. 9 b    shows a second example of a flexible LCD display  950  with a curved display area, comprising the flexible active matrix LCD display stack  600  of  FIG. 6 . In this example the flexible LCD display stack  600  is curved about an axis parallel to the first lateral edge of the display. 
     Opposite edges of the display meet at a line  952 . In implementations the active display area is folded as previously described and extends around each of the two opposing edges. In this way the two opposite edges of the active display area may abut along line  952  to create a substantially seamless display. The use of multiple tabs  608 , each with a respective necked region  610 , in the example each including a compliant structure  611 , facilitates achieving sufficient bend radius for a cylindrical display. 
     The necked regions  610  carry interconnects from external electrical connections to the display; mounting the drive circuitry on the tabs reduces a number of connections each necked region carries. External electrical connections to the drive circuitry on the tabs may be made in any convenient manner. For example, depending upon the bend radius and number of connections, each tab may mount, directly or indirectly, an edge connector to a common printed circuit board which may be centrally located at one end of the cylindrical LCD display. 
       FIG. 9 c    shows a similar flexible LCD display  950  to that of  FIG. 9 b   , in which the driver circuitry is mounted on stiffer interconnect structures  210  which are themselves mounted on tabs  606 , and which may each carry a respective edge connector. 
     The arrangements if  FIGS. 9 b  and 9 c    may be used e.g. for a display on a smart speaker. 
     In general the zero-bezel and curved LCD displays described herein may be used e.g. in any consumer electronic device, or a land, sea, or air vehicle e.g. an automobile, or in equipment of any sort. 
     No doubt many other effective alternatives will occur to the skilled person. It will be understood that the invention is not limited to the described embodiments and encompasses modifications apparent to those skilled in the art lying within the spirit and scope of the claims appended hereto.