Color filter structures for electronic devices with color displays

A display may have a color filter layer and a thin-film transistor layer. A liquid crystal layer may be located between the color filter layer and the thin-film transistor layer. The color filter layer may have an array of color filter elements on a transparent substrate. The array of color filter elements may include more than three colors. Colored photoimageable polymer layers may be combined to form some of the color filter elements. The color filter may have cyan, magenta, and yellow color filter elements each formed from a respective single layer of cyan, magenta, and yellow polymer and may have blue elements formed by overlapping cyan and magenta polymer, green elements formed by overlapping cyan and yellow polymer, and red elements formed by overlapping magenta and yellow polymer. Filters with white elements may also be provided.

BACKGROUND

Electronic devices often include displays. For example, cellular telephones and portable computers may have displays for presenting information to a user.

Substrate layers such as color filter layers and thin-film transistor layers are used in liquid crystal displays. A thin-film transistor layer contains an array of the thin-film transistors that are used in controlling the electric fields in the liquid crystal layer. A color filter layer contains an array of color filter elements. The color filter layer provides the display with the ability to display color images. In an assembled display, the layer of liquid crystal material is sandwiched between the thin-film transistor layer and the color filter layer.

Other displays such as organic light-emitting diode displays may also have color filter layers. For example, an organic light-emitting diode display that has an array of white light diodes may use a color filter layer to impart colors to the light from the white light diodes.

Color filter layer arrays typically contain red, green, and blue color filter elements. The use of only three colors in a color filter layer restricts the color gamut that may be produced by the display. To enhance color gamut and enhance the overall transmittance of the color filter layer, additional colors may be incorporated into the color filter layer. For example, the color filter layer may be formed from color filter elements of six different colors.

Fabricating color filter layers with large numbers of color filter element colors can be challenging. Color filter elements are generally formed by depositing blanket layers of colored photoimageable polymer that are patterned photolithographically to form desired color filter element patterns. If care is not taken, an excessive number of processing steps may be needed to form the color filter elements in a color filter layer with more than three different colors.

It would therefore be desirable to be able to provide improved color filter layer arrangements for electronic devices with color displays.

SUMMARY

A display may have a color filter layer and a thin-film transistor layer. A liquid crystal layer may be located between the color filter layer and the thin-film transistor layer. The color filter layer may have an array of color filter elements on a transparent substrate. The array of color filter elements may include more than three colors formed using combinations of three colored polymers.

The color filter may, as an example, have six color filter elements such as red, green, blue, cyan, magenta, and yellow elements or red, green, blue, cyan, yellow, and white elements. Some of the color filter elements such as the cyan, yellow, and magenta elements may be formed from single layers of colored polymer. Other color filter elements such as the red, green, and blue color filter elements may be formed by overlapping two of the colored polymer layers. For example, blue color filter elements may be formed by overlapping cyan and magenta polymer layers, green color filter elements may be formed by overlapping cyan and yellow polymer layers, and red color filter elements may be formed by overlapping magenta and yellow polymer layers. Filters with white elements may be formed by omitting the magenta elements or other elements and forming clear elements that include only clear polymer and no non-clear polymer.

A black matrix for the color filter may have an array of openings in which the color filter elements are formed. The black matrix may be formed from a patterned opaque masking layer such as a layer of patterned black ink or other black masking material. If desired, the black matrix may be formed by overlapping portions of the cyan, magenta, and yellow polymer layers.

DETAILED DESCRIPTION

Electronic devices may include displays. The displays may be used to display images to a user. Illustrative electronic devices that may be provided with displays are shown inFIGS. 1, 2, 3, and 4.

Illustrative electronic device10ofFIG. 1has the shape of a laptop computer having upper housing12A and lower housing12B with components such as keyboard16and touchpad18. Device10may have hinge structures20that allow upper housing12A to rotate in directions22about rotational axis24relative to lower housing12B. Display14may be mounted in upper housing12A. Upper housing12A, which may sometimes be referred to as a display housing or lid, may be placed in a closed position by rotating upper housing12A towards lower housing12B about rotational axis24.

FIG. 2shows how electronic device10may be a handheld device such as a cellular telephone, music player, gaming device, navigation unit, or other compact device. In this type of configuration for device10, housing12may have opposing front and rear surfaces. Display14may be mounted on a front face of housing12. Display14may, if desired, have openings for components such as button26. Openings may also be formed in display14to accommodate a speaker port (see, e.g., speaker port28ofFIG. 2).

FIG. 3shows how electronic device10may be a tablet computer. In electronic device10ofFIG. 3, housing12may have opposing planar front and rear surfaces. Display14may be mounted on the front surface of housing12. As shown inFIG. 3, display14may have an opening to accommodate button26(as an example).

FIG. 4shows how electronic device10may be a computer display, a computer that has been integrated into a computer display, or a display for other electronic equipment. With this type of arrangement, housing12for device10may be mounted on a support structure such as stand30or stand30may be omitted (e.g., stand30can be omitted when mounting device10on a wall). Display14may be mounted on a front face of housing12.

The illustrative configurations for device10that are shown inFIGS. 1, 2, 3, and 4are merely illustrative. In general, electronic device10may be a laptop computer, a computer monitor containing an embedded computer, a tablet computer, a cellular telephone, a media player, or other handheld or portable electronic device, a smaller device such as a wrist-watch device, a pendant device, a headphone or earpiece device, or other wearable or miniature device, a television, a computer display that does not contain an embedded computer, a gaming device, a navigation device, an embedded system such as a system in which electronic equipment with a display is mounted in a kiosk or automobile, equipment that implements the functionality of two or more of these devices, or other electronic equipment.

Housing12of device10, which is sometimes referred to as a case, may be formed of materials such as plastic, glass, ceramics, carbon-fiber composites and other fiber-based composites, metal (e.g., machined aluminum, stainless steel, or other metals), other materials, or a combination of these materials. Device10may be formed using a unibody construction in which most or all of housing12is formed from a single structural element (e.g., a piece of machined metal or a piece of molded plastic) or may be formed from multiple housing structures (e.g., outer housing structures that have been mounted to internal frame elements or other internal housing structures).

Display14may be a touch sensitive display that includes a touch sensor or may be insensitive to touch. Touch sensors for display14may be formed from an array of capacitive touch sensor electrodes, a resistive touch array, touch sensor structures based on acoustic touch, optical touch, or force-based touch technologies, or other suitable touch sensor components.

Display14for device10includes display pixels formed from liquid crystal display (LCD) components, organic light-emitting diode components, or other suitable image pixel structures.

A display cover layer may cover the surface of display14or a display layer such as a color filter layer, thin-film transistor layer, or other portion of a display may be used as the outermost (or nearly outermost) layer in display14. The outermost display layer may be formed from a transparent glass sheet, a clear plastic layer, or other transparent member.

A cross-sectional side view of an illustrative configuration for display14of device10(e.g., for display14of the devices ofFIG. 1,FIG. 2,FIG. 3,FIG. 4or other suitable electronic devices) is shown inFIG. 5. As shown inFIG. 5, display14may include backlight structures such as backlight unit42for producing backlight44. During operation, backlight44travels outwards (vertically upwards in dimension Z in the orientation ofFIG. 5) and passes through display pixel structures in display layers46. This illuminates any images that are being produced by the display pixels for viewing by a user. For example, backlight44may illuminate images on display layers46that are being viewed by viewer48in direction50.

Display layers46may be mounted in chassis structures such as a plastic chassis structure and/or a metal chassis structure to form a display module for mounting in housing12or display layers46may be mounted directly in housing12(e.g., by stacking display layers46into a recessed portion in housing12). Display layers46may form a liquid crystal display or may be used in forming displays of other types.

In a configuration in which display layers46are used in forming a liquid crystal display, display layers46may include a liquid crystal layer such a liquid crystal layer52. Liquid crystal layer52may be sandwiched between display layers such as display layers58and56. Layers56and58may be interposed between lower polarizer layer60and upper polarizer layer54.

Layers58and56may be formed from transparent substrate layers such as clear layers of glass or plastic. Layers56and58may be layers such as a thin-film transistor layer and/or a color filter layer. Conductive traces, color filter elements, transistors, and other circuits and structures may be formed on the substrates of layers58and56(e.g., to form a thin-film transistor layer and/or a color filter layer). Touch sensor electrodes may also be incorporated into layers such as layers58and56and/or touch sensor electrodes may be formed on other substrates.

With one illustrative configuration, layer58may be a thin-film transistor layer that includes an array of thin-film transistors and associated electrodes (display pixel electrodes) for applying electric fields to liquid crystal layer52and thereby displaying images on display14. Layer56may be a color filter layer that includes an array of color filter elements for providing display14with the ability to display color images. Configurations of this type in which the color filter layer is located above the thin-film transistor layer may sometimes be referred to as TFT-on-bottom configurations. If desired, lower layer58may be a color filter layer and upper layer56may be a thin-film transistor layer (i.e., a TFT-on-top configuration may be used for display14). Another illustrative configuration involves forming color filter elements and thin-film transistor circuits with associated pixel electrodes on a common substrate. This common substrate may be the upper substrate or may be the lower substrate and may be used in conjunction with an opposing glass or plastic layer (e.g., a layer with or without any color filter elements, thin-film transistors, etc.) to contain liquid crystal layer52.

During operation of display14in device10, control circuitry (e.g., one or more integrated circuits on a printed circuit) may be used to generate information to be displayed on display14(e.g., display data). The information to be displayed may be conveyed to a display driver integrated circuit such as circuit62A or62B using a signal path such as a signal path formed from conductive metal traces in a rigid or flexible printed circuit such as printed circuit64(as an example).

Backlight structures42may include a light guide plate such as light guide plate78. Light guide plate78may be formed from a transparent material such as clear glass or plastic. During operation of backlight structures42, a light source such as light source72may generate light74. Light source72may be, for example, an array of light-emitting diodes. If desired, light sources such as light source72may be located along multiple edges of light guide plate78.

Light74from light source72may be coupled into edge surface76of light guide plate78and may be distributed in dimensions X and Y throughout light guide plate78due to the principal of total internal reflection. Light guide plate78may include light-scattering features such as pits or bumps. The light-scattering features may be located on an upper surface and/or on an opposing lower surface of light guide plate78.

Light74that scatters upwards in direction Z from light guide plate78may serve as backlight44for display14. Light74that scatters downwards may be reflected back in the upwards direction by reflector80. Reflector80may be formed from a reflective material such as a layer of white plastic or other reflective materials.

To enhance backlight performance for backlight structures42, backlight structures42may include optical films70. Optical films70may include diffuser layers for helping to homogenize backlight44and thereby reduce hotspots, compensation films for enhancing off-axis viewing, and brightness enhancement films (also sometimes referred to as turning films or prism films) for collimating backlight44. Optical films70may overlap the other structures in backlight unit42such as light guide plate78and reflector80. For example, if light guide plate78has a rectangular footprint in the X-Y plane ofFIG. 5, optical films70and reflector80may have a matching rectangular footprint. If desired, optical films such as these may be incorporated into other portions of display14. For example, compensation films may be incorporated into polarizer layers, etc.

Display14may have a rectangular array of pixels. Vertical lines (sometimes referred to as data lines) may be used to supply data signals to columns of pixels. Horizontal control lines (sometimes referred to as gate lines) may be used in controlling rows of pixel circuits in the thin-film transistor layer. In response to the gate line signals and data signals, the pixel circuits of display14use electrodes to apply electric fields to corresponding pixel-sized portions of liquid crystal layer52and thereby control the brightness of the pixels in display14(i.e., the thin-film transistors control the emitted light for the pixels by controlling how much light44passes through each pixel).

Display14may be an organic light-emitting diode display. In an organic light-emitting diode display configuration, thin-film transistor layer58may have an array of organic light-emitting diodes that emit light to form images. The circuitry of the thin-film transistor is controlled to control the emitted light from the diodes, which form the pixels of the display. Each diode may have an anode and a cathode (e.g., a shared cathode) and a layer of electroluminescent organic material that is interposed between the anode and cathode. When current is applied to the diodes by thin-film transistor control circuitry in the thin-film transistor layer, the diodes emit light (e.g., white light in an array of white light organic light-emitting diodes). Because the diodes in the array emit light, liquid crystal layer52and backlight unit42may be omitted. The color filter elements of color filter layer56may be aligned with the diodes of the thin-film transistor layer.

The color filter in display14is used to impart color to the light that is passing through each pixel (i.e., backlight44from backlight unit42in a liquid crystal display or the light from the array of organic light-emitting diodes in an organic light-emitting diode display). The color filter (color filter layer) has a patterned array of color filter elements of different colors. Photoimageable polymers that include colored dyes may be photolithographically patterned to form the color filter elements. For example, a blanket layer of a photoimageable polymer of a particular color may be deposited on the surface of a glass substrate or other transparent substrate. Photolithography may then be used to pattern the deposited polymer layer. Multiple layers of photoimageable polymers of different colors may be deposited and patterned in this way.

To separate color filter material into discrete color filter elements corresponding to respective pixels, a black matrix may be formed as part of the color filter. The black matrix has an array of openings in which color filter elements of different colors are formed. For example, the black matrix may have a grid shape with rows and columns of rectangular openings. Configurations in which chevron-shaped openings or openings of other shapes are formed in the black matrix may also be used. Black matrix arrangements with rectangular openings are sometimes described herein as an example.

In some arrangements, a black masking layer (e.g., a layer of photoimageable polymer that contains a black additive such as carbon black or other opaque masking material) may be patterned to form the black matrix. In other configurations, overlapping portions of color filter element material of different colors may be used in forming the black matrix.

To enhance display performance (e.g., to increase color filter layer transmittance and to increase color gamut), it may be desirable to form the color filter in display14using more than three color filter element colors. Examples of colors that may be used in forming the color filter include red, green, blue, cyan, magenta, yellow, and clear. Different colors may be used, if desired. Six of these colors, four of these colors, or other suitable sets of these colors may be used in forming the color filter.

Color filter elements for the color filter may be organized in sets (tiles) with any suitable color filter element pattern (e.g., a repeating 1×6 array of six different colors may be used, a repeating 2×3 block of six different colors may be used, etc.).FIG. 6is a top view of a portion of a color filter104in which a repeating 2×3 block of color filter elements is used in forming a color filter array. Color filter elements100ofFIG. 6may include a red color filter element (R), a green color filter element (G), a blue color filter element (B), a yellow color filter element (Y), a cyan color filter element (C), and a magenta color filter element (M). Black matrix102may be formed from black photoimageable polymer (i.e., black masking material) or may be formed form overlapping color filter element layers (e.g., overlapping colors that block light and therefore serve as black matrix structures).

The 2×3 block of color filter elements100that is shown inFIG. 6and the sets of color filter elements100in the other FIGS. may cover the entire surface of display14in a tiled fashion. In the example ofFIG. 6, the upper row of the six-element set of color filter elements100contains red R, green G, and blue B color filter elements, whereas the lower row contains yellow Y, cyan C, and magenta M color filter elements. Other patterns may be used for the color filter elements that make up color filter104in display14. The configuration ofFIG. 6is merely illustrative.

To minimize the number of process steps that are used in forming color filter104, it may be desirable to form at least some of the colors for color filter elements100by overlapping multiple layers of color filter layer material. In this way, the total number of color filter element materials can be minimized. As an example, six different colors of color filter elements may be formed using just three different colored photoimageable polymer layers—a magenta layer, a cyan layer, and a yellow layer. The magenta layer may be used to produce magenta color filter elements. The cyan layer may be used to form cyan color filter elements. The yellow layer may be used to form yellow color filter elements. The cyan layer and magenta layer may be overlapped to form blue color filter elements. The cyan layer and the yellow layer may be used to form green color filter elements. The magenta and the yellow layer may be used to form red color filter elements.

A cross-sectional side view of the upper row of color filter elements ofFIG. 6taken along line106and viewed in direction108in a configuration in which black matrix102is formed form black masking material110is shown inFIG. 7. As shown inFIG. 7, black masking material110can be deposited and patterned on transparent color filter substrate112to form black matrix102. Yellow Y color filter element material (e.g., a layer of yellow photoimageable polymer), magenta M color filter element material (e.g., a layer of magenta photoimageable polymer), and cyan C color filter element material (e.g. a layer of cyan photoimageable polymer) may then be deposited and patterned. Clear polymer overcoat layer OC may be deposited on top of the color filter element layers (e.g., to form a planarization layer that is adjacent to liquid crystal layer52when color filter layer104is assembled into a completed display14). In portions of color filter104in which yellow polymer overlaps magenta polymer, red color filter elements R are formed. In portions of color filter104in which yellow and cyan polymer layers overlap, green color filter elements G are formed. Blue color filter elements B are formed by overlapping cyan and magenta layers.

A cross-sectional side view of the lower row of color filter elements ofFIG. 6taken along line114and viewed in direction116is shown inFIG. 8. As shown inFIG. 8, black matrix102is formed from black masking material110. Black masking material110is patterned to form color filter element openings for respective color filter elements (e.g., rectangular openings, chevron-shaped openings, etc.). A color filter element100of a different color is formed in each black matrix opening. Yellow Y color filter element material (e.g., a single layer of the yellow photoimageable polymer), cyan C color filter element material (e.g. a single layer of cyan photoimageable polymer), and magenta M color filter element material (e.g., a single layer of magenta photoimageable polymer) may be deposited and patterned to form respective yellow color filter element Y, cyan color filter element C, and magenta color filter element M in the openings. Each color filter element100in ofFIG. 8is formed using a single layer of color filter element material. Because the same three colored polymer layers (yellow, cyan, and magenta) are used in forming the Y, C, and M color filter elements ofFIG. 8and the R, G, and B color filter elements ofFIG. 7, a complete six-color set of color filter elements (Y, C, M, R, G, and B) can be produced using only three layers of colored polymer. The use of a set of colored polymers having fewer colors than the total number of different colors in the color filter elements simplifies processing and reduces the cost and complexity of color filter104.

If desired, black matrix102may be formed by overlapping different polymer layers of different colors. Each polymer layer subtracts a different portion of the white spectrum and when multiple layers are overlapped, no white light can pass. The overlapping areas of the colored polymer layers therefore appear black and serve to form a grid-shaped black matrix102. Because the overlapping polymer layers (color filter element material layers) can be used to form black matrix102, it is not necessary to incorporate black masking material110into color filter104. Black masking material110can therefore be reduced or omitted with this approach.

A cross-sectional side view of the upper row of color filter elements100ofFIG. 6taken along line106and viewed in direction108in a configuration in which black masking material110has been omitted and in which black matrix102has been formed by overlapping portions of the colored photoimageable polymer layers that are used in forming color filter elements100is shown inFIG. 9. As shown inFIG. 9, yellow polymer layer Y and magenta polymer layer M may overlap to form red color filter element R. Cyan polymer layer C and yellow polymer layer Y overlap to form green color filter element G. Blue color filter element B is formed in the portion of color filter104in which magenta color filter element material M overlaps cyan color filter element material C. Black matrix102is formed in the portions of color filter104in which cyan polymer C overlaps magenta polymer layer M and yellow polymer Y. Little or no white light can pass through all three of these colors (C, M, and Y) in tandem, so the overlap of the C, M, and Y layers effectively forms portions of black matrix102without involving the extra process steps involved in depositing and patterning a separate black masking layer. A cross-sectional side view of the lower row of color filter elements100ofFIG. 6taken along line114and viewed in direction116in a configuration in which black matrix102is formed form overlapping color filter element materials of different (non-black) colors is shown inFIG. 10. As with the structures ofFIG. 9, black matrix102ofFIG. 10is formed from overlapped regions of cyan, magenta, and yellow polymer. Color filter elements100are formed from layers of yellow polymer Y (for yellow color filter element Y), cyan polymer C (for cyan color filter element C), and magenta polymer M (for magenta color filter element M).

FIG. 11is a top view of a portion of a color filter104in which two different 1×6 blocks of color filter elements are used in forming a color filter array. Color filter elements100ofFIG. 6may include a red color filter element (R), a green color filter element (G), a blue color filter element (B), a yellow color filter element (Y), a cyan color filter element (C), and a magenta color filter element (M). Black matrix102may be formed from black photoimageable polymer (i.e., black masking material) or may be formed form overlapping color filter element layers (e.g., overlapping colors that block light and therefore serve as black matrix structures).

The upper and lower 1×6 sets of color filter elements100that are shown inFIG. 6may cover the entire surface of display14in a tiled fashion. In the example ofFIG. 6, the upper row of color filter elements100is arranged in a R, G, B, Y, C, and M pattern and the lower row of color filter elements100is arranged in a Y, C, M, R, G, B pattern. The use of different patterns for adjacent rows of color filter elements may help enhance display resolution by spatially separating pixels of identical colors.

A cross-sectional side view of color filter elements100ofFIG. 1taken along line120and viewed in direction122is shown inFIG. 12. As shown inFIG. 12, black matrix102may be formed by depositing and patterning black masking material110onto substrate112. If desired, overlapping color filter element material (e.g., overlapping yellow, cyan, and magenta polymer layers) may be used to form black matrix102. The configuration ofFIG. 12is merely illustrative.

Red color filter element R is formed by overlapping magenta polymer M and yellow polymer Y. Green color filter element G is formed by overlapping cyan polymer C with yellow polymer Y. Blue color filter element B is formed by overlapping cyan polymer C with magenta polymer M. Yellow color filter element Y is formed form a single layer of yellow polymer Y. Cyan color filter element C is formed from a single layer of cyan polymer C. Magenta color filter element M is formed from a single layer of magenta polymer. A clear planarization layer (overcoat layer OC) may cover color filter elements100.

If desired, white color filter elements100may be incorporated into color filter104. White color filter elements100are clear and do not impart any color to backlight44. White color filter elements can be formed by omitting colored polymer from openings in black matrix102. Consider, as an example, the illustrative color filter pattern ofFIG. 13. In the example ofFIG. 13, color filter104has color filter elements100that are arranged in a repeating 2×3 array that includes an upper row of red R, green G, and blue B color filter elements100and that includes a lower row of yellow Y, cyan C, and white W color filter elements100.

A cross-sectional side view of color filter elements100ofFIG. 13taken along line126and viewed in direction128is shown inFIG. 14. As shown inFIG. 14, black matrix102may be formed by depositing and patterning black masking material110onto substrate112. If desired, overlapping color filter element material (e.g., overlapping yellow, cyan, and magenta polymer layers) may be used to form black matrix102. The configuration ofFIG. 14is merely illustrative. As shown inFIG. 14, red color filter element R is formed by overlapping magenta polymer M and yellow polymer Y. Green color filter element G is formed by overlapping cyan polymer C with yellow polymer Y. Blue color filter element B is formed by overlapping cyan polymer C with magenta polymer M.

A cross-sectional side view of color filter elements100ofFIG. 13taken along line126and viewed in direction128is shown inFIG. 15. As shown inFIG. 15, yellow color filter element Y is formed from a single layer of yellow polymer Y. Cyan color filter element C is formed from a single layer of cyan polymer C. White color filter element W is formed by omitting colored polymer from opening134in black matrix102(i.e., opening134for white color filter element W contains only clear overcoat OC and does not contain any non-clear polymer).

In the example ofFIG. 13, a 2×3 filter element pattern was used in forming color filter104. If desired, a 1×6 arrangement of the type described in connection withFIG. 11may be used (e.g., an arrangement where each of the two sets of 1×6 color filter element groups in adjacent rows has a different pattern).

FIG. 16contains graphs in which transmission has been plotted as a function of wavelength λ for polymers of different colors such as yellow polymer (YCF), cyan polymer (CCF), and magenta polymer (MCF). The first column ofFIG. 16shows the transmission spectrum for a yellow layer, a cyan layer, and a magenta layer. The second column shows the transmission spectrum for three layers (magenta, yellow, and cyan, respectively) that may be combined with the first layers. The third column ofFIG. 16shows the resulting color filter elements that are produced when the colored layers of the first and second columns overlap. The first row ofFIG. 16shows how a red color filter RCF can be produced by overlapping yellow and magenta polymer layers. The second row ofFIG. 16shows how a green color filter element GCF can be produced by overlapping cyan and yellow polymer layers. The third row ofFIG. 16shows how blue color filter element BCF can be produced by overlapping magenta and cyan polymer layers.