GB2548354A

GB2548354A - Display and method of manufacturing same

Info

Publication number: GB2548354A
Application number: GB1604320.0A
Authority: GB
Inventors: Banach Michael
Original assignee: FlexEnable Ltd
Current assignee: FlexEnable Ltd
Priority date: 2016-03-14
Filing date: 2016-03-14
Publication date: 2017-09-20
Also published as: WO2017158328A1; GB201604320D0

Abstract

A display device comprising a display surface which is viewed by a user. A wavelength adjusting layer 36 comprises a plurality of quantum dots which emit infrared radiation when excited. A light source 32 illuminates the wavelength adjusting layer of the display and excites the quantum dots to generate infrared radiation. A sensor 34 detects infrared radiation which is reflected by a user 20. The disclosed arrangement removes the need for IR LEDs to be incorporated into the backlight panel or around the bezel of the display, thereby allowing for thinner panels and bezels for touchscreen devices.

Description

Display and method of manufacturing same

Technical field

The invention relates to a display, particularly a liquid crystal display or a similar emissive display.

Background

Electronic displays are frequently combined with touch sensors to provide a touch sensitive display. Sensors which can recognise gestures, e.g. swipe, slide, pinch, scroll or similar gestures, are seen as an attractive replacement technology for touch sensors. Such gestures are defined by the system and when detected produce the defined functionality, e.g. a common gesture is to use two fingers in a downward or upwards motion to scroll the currently active page. A typical display has a matrix of pixels having a plurality of rows and columns of pixels. Typically, the pixel location on the display needs to be determined for the gesture to be correctly interpreted by the system. For sensors to be sensitive enough to provide pixel to pixel registration, the sensor typically needs to be an active matrix sensor, i.e. an array of sensors arranged in a matrix.

Various sensing technologies are known. Some touch sensors use capacitive or resistive touch sensing which requires the probing element (i.e. finger or stylus of a user) to be in direct contact or close proximity to the surface of the display. As an alternative, optical sensors can be used so as to allow the probing element (i.e. finger or stylus of a user) to be further away from the device. This enhances the 3D interactivity with the device.

When integrating an optical sensor with a display, it is important to consider the spectrum in which the optical sensor is operating. For example, sensors which are sensitive to ultraviolet or visible light will need to be positioned in front of a display which is itself emitting in this spectrum. Otherwise, the emission from the display will interfere with the sensor. However, if the sensor is sensitive to infra-red, the sensor may be positioned behind the display provided the display is transparent to the infrared radiation. Two examples of such integrated sensor and displays are illustrated in Figures 1a and 1b.

Figures la and 1b both show a display in the form of a liquid crystal display panel 10 together with its associated backlight panel 12. A sensor array 14 comprising a plurality of organic photodetectors and transistors arranged in a matrix is positioned behind (underneath) the display. The photodetectors detect infrared radiation which is reflected from a user’s finger to determine the gesture or touch and thus a source of infrared radiation is required for the optical touch sensor to be effective.

In Figure la, the sources of infrared radiation (IR) are a plurality of light emitting diodes 16 (LEDs) which are positioned around the edges of the LCD display 10. These LEDs could be held in a frame or bezel (not shown) which extends around the display. In an alternative arrangement (not shown), the IR LEDs could be at the edge of the device behind the display, for example, they could be incorporated into the backlight panel.

Alternatively, as shown in Figure 1 b, the sources of infrared radiation are a plurality of light emitting diodes 18 (LEDs) in an array positioned between the matrix sensor array 14 and the backlight unit. In both Figures la and 1b, infrared radiation is emitted from the LEDs and is reflected from a user’s finger 20. The reflected radiation passes through the LCD panel and its associated backlight panel which are transparent to infrared radiation and is detected by the photodetectors in the sensor array.

The arrangements of Figure la requires a bezel which may be considered to be unattractive as well as increasing the overall size of the device. The arrangement in Figure 1b may increase the depth of the device which may not be ideal. In the alternative arrangement in which the IR LEDs are incorporated into the backlight panel, this will add cost and complexity to the device. Accordingly, an improved integrated display and sensor is required.

Summary

According to a first aspect of the invention, there is provided a display device comprising a display having a display surface which is viewed by a user, a wavelength adjusting layer comprising a plurality of quantum dots which emit infrared radiation when excited; a light source to illuminate the wavelength adjusting layer to excite the plurality of quantum dots to generate infrared radiation, and a sensor for detecting infrared radiation which is reflected by a user.

The infrared radiation may be reflected by a user’s finger, hand or a stylus or similar instrument being used by the user. The distance and shape of the object which reflects the infrared radiation may be inferred by the sensor. Thus, greater flexibility is offered by the sensor which may be used to detect touches on the display device by a user or to detect gestures, e.g. swipe, slide, pinch, scroll or similar gestures.

Quantum dots can be tuned to emit light very efficiently at precise wavelengths. Each of the plurality of quantum dots which emit infrared radiation may have the same size so that a narrow bandwidth of infrared radiation is emitted. A typical suitable diameter for infrared radiation is 8mm. Alternatively, different sizes of quantum dots may be used to cover a broader spectrum of infrared radiation.

The display may be a liquid crystal display or other similar display, for example a display which requires a light source. Most liquid crystal displays have a light source which emits white light. Such a liquid crystal display typically has a colour filter which ensures that the light which is emitted from the light source produces red, green and blue light. The display may comprise a plurality of pixels each of which is split into three sub-pixels, one each for red, green and blue light. The colour filter may comprise a plurality of red, green and blue filters, one for each associated sub-pixel. The red colour filter on the red sub-pixel only allows the red light to pass and similarly for the green and blue filters respectively.

Whilst this technology is dominant in liquid crystal display, it is not efficient. As explained, for example in “Quantum Dot Displays: Giving LCDs a Competitive Edge through Colour” by Jian Chen et al, conventional LCDs face a ceiling in colour performance, at best reaching the sRGB colour gamut which is about 70% of an OLED’s capacity. The colour of each sub-pixel in an LCD display is determined by two factors: the spectral energy of the white light and the effectiveness of the colour filter at the subpixel. For a high quality red (or green or blue), the red (or green or blue) component in the white light must be narrow and tuned to the desired peak red colour wavelength in the filter. White LEDs are typically used as the light source. However, white LEDs do not produce the right spectrum to match colour filters and more importantly human eyes. The inefficiency of a typical LCD system is also discussed in “Quantum Dot Enhancement of Color for LCD systems” by Derlofske et al.

As explained in both of these papers, quantum dots can be used as a wavelength adjustment layer to tune the light produced by the light source (e.g. LED) to match the appropriate colour filter. The wavelength adjusting layer may further comprise a plurality of quantum dots which are tuned as necessary to emit red, green or blue light, respectively. In this way, a more efficient light source may be used and wavelengths which are perfectly matched for the colour filter and thus the human eyes are emitted. The light source may emit blue light or white light. For example, the light source may emit a short wavelength (e.g. 445nm)

The wavelength adjusting layer may thus further comprise a second plurality of quantum dots which emit red light when excited. Similarly, the wavelength adjusting layer may comprise a third plurality of quantum dots which emit green light when excited. Where a blue light source is used, no quantum dots are required to emit blue light but it will be appreciated that the wavelength adjusting layer may comprise a fourth plurality of quantum dots which emit blue light when excited. Indeed, quantum dots which are tuned to emit the colours which match the colour filters may be incorporated into the wavelength adjusting layer.

The size of the quantum dots determines the wavelength of light which is emitted. The diameter of each of the second plurality of quantum dots may be between 5nm to 7nm. The diameter of each of the second plurality of quantum dots may be between 2nm to 3nm. As before, each of the quantum dots may have the same size to produce narrow bandwidths of red or green (or blue if needed). Alternatively, different sizes may be used.

The display typically has a plurality of pixels. The sensor may be a sensor array and may for example comprise a plurality of photodetectors which detect infrared radiation. Each photodetector may be aligned with a pixel in the display. In this way, the gesture or touch may be sensed on a pixel-by-pixel registration. Furthermore, the use of an optical sensor rather than a capacitive or resistive sensor means that the user’s gesture can be further away from the device and still be detected.

The wavelength adjusting layer and the light source may be positioned between the sensor and the display. The infrared radiation emitted by the wavelength adjusting layer may be emitted through the display surface of the display. In other words, the light source and the wavelength adjusting layer may be behind or under the display (behind as viewed by the user). The sensor may be behind or under the light source. Thus, the infrared radiation which is emitted by the quantum dots passes through the display, which must be at least partially transparent to infrared radiation, and is incident on a user. The incident radiation is then reflected back through the display, the wavelength adjusting layer and the light source to the sensor. Thus, the wavelength adjusting layer and the light source must be at least partially transparent to infrared radiation.

Alternatively, different arrangements of the components are possible. For example, the sensor may be above or in front of the light source. Thus, the sensor may be positioned between the light source (with its wavelength adjusting layer) and the display. In this arrangement, the light source (e.g. backlight) need not be transparent to infrared radiation.

According to another aspect of the invention, there is provided a method of manufacturing a display device comprising providing a light source with a wavelength adjusting layer comprising a plurality of quantum dots which emit infrared radiation when excited by the light source, providing a display, providing a sensor for detecting infrared radiation and attaching the light source, display and sensor together.

The method may comprise mounting the light source under the wavelength adjusting layer, mounting the display on the wavelength adjusting layer and mounting the sensor under the light source. Alternatively, the method may comprise providing the light source under the wavelength adjusting layer, mounting the sensor on the wavelength adjusting layer and mounting the display on the sensor.

Each of the light source, display and sensor may be standard off-the-shelf components. Mounting or attaching may comprise any suitable method which laminates the various layers together. The wavelength adjusting layer may also be separately manufactured before being laminated with the other components. The wavelength adjusting layer may be formed by spin coating, spray-on or roll-printing a colloidal suspension comprising the quantum dots.

The first and second aspects of the invention may be combined as recognised by a skilled person. In other words, there is provided a method of manufacturing a display device as described above.

Brief description of the drawings

Figures 1a and 1b are schematic cross-sectional drawings of two integrated displays and infrared sensors;

Figures 2a and 2b are schematic cross-sectional drawings of two variations of an integrated display and infrared sensor according to a first aspect of the invention; Figures 3a and b are flowcharts showing the steps in manufacturing the device of Figures 2a and 2b respectively; and

Figure 4 is a schematic block diagram of a display according to the invention.

Detailed description of the drawings

Figures 2a and 2b both show an integrated display and infrared sensor with a different arrangement of components. Components having the same function have the same number for each of reference. The display is a liquid crystal display panel 30 together with its associated backlight panel 32. In this example, the backlight panel is emitting blue light at approximately 445nm but it will be appreciated that other suitable backlight panels may be used such as those which emit white light. The liquid crystal display panel is a standard display comprising a plurality of pixels. As is well known in the art, the liquid crystals within each pixel of the display panel 30 polarise the light emitted from the backlight panel 32. By controlling the voltage applied across the liquid crystal layer in each pixel, light can be allowed to pass through in varying amounts to generate different levels of grey from white through to black. The liquid crystal display panel may be a thin film transistor liquid crystal display panel, i.e. a matrix of thin film transistors may be used to control the voltage applied to the liquid crystal layer.

This is a colour display and a colour filter 38 is positioned in front of the backlight. For each pixel, the colour filter 38 comprises three sub-pixels which are found in all standard RGB filters, namely a sub-pixel for each of red, green and blue light. The colour filter thus separates its component red, green or blue colour from the light of the backlight unit. For example, the red colour filter on the red sub-pixels will cut off green and blue light and thus only red light of certain wavelengths pass through. By controlling the amount of light each sub-pixel allows to pass through, a broad range of colours is created by mixing the individual red, green and blue light. At common viewing distance, the separate red, green and blue sources are indistinguishable and thus a viewer sees a solid colour. The colour filter 38 also needs to be transparent to infrared radiation (which is not visible by the human eye) or comprise an additional subpixel for each pixel for infrared radiation. This sub-pixel operates in a similar manner to those for the visible red, green and blue light and thus only allows certain wavelengths of infrared radiation through.

Below the colour filter 38 and above the light source 32, there is a wavelength adjusting layer 36 comprising a quantum dot film. As is known in the art, a quantum dot is excited by exciting light to emit fluorescence. Accordingly, each quantum dot changes the wavelength of the light emitted from the backlight to produce one of the desired red, green, blue and infrared light.

Quantum dots can be tuned to emit light very efficiently at precise wavelengths. For example, US8981207 describes a high efficiency quantum dot sensitized thin film solar cell. US8981207 describes how the bandgap of the quantum dots can cover infrared (IR), visible light and ultraviolet (UV) bands of solar spectrum. US2015/0330602 describes how quantum dots in an organic matrix can be used as a constituent member of a backlight unit of a liquid crystal display device. Three quantum dots. A, B and C can be used to provide red, green and blue light respectively. A paper entitled “Quantum Dot Displays: Giving LCDs a Competitive Edge through Colour” by Jian Chen et al also describes how a quantum dot layer can be used to provide red, green and blue light from a LCD panel. This paper explains how the spectral output of a quantum dot is determined by its size. Larger dots, e.g. 5 to 6nm, emit longer wavelengths, e.g. 620 to 630nm and smaller dots, e.g. 2 to 2.5nm emit shorter wavelengths, e.g. 500 to 550nm. The dots also have a narrow spectral distribution, e.g. 30 to 40nm at full width at half maximum and thus can be tuned to convert short-wavelength light (e.g. blue light such as that from the backlight) to nearly any colour in the visible spectrum.

In the described arrangement, the backlight is blue and thus the blue sub-pixel allows the blue light to pass unaltered. As described in for example, “Quantum Dot Displays: Giving LCDs a Competitive Edge through Colour” by Jian Chen et al, improving the performance on a LCD using quantum dots is known. Merely for illustration, some suitable examples of quantum dots for red, green and blue are given. Any known dots may be used. Red light typically has a wavelength of between 620 to 740nm. Accordingly, the red sub-pixels comprise a plurality of quantum dots which are tuned to emit red light, for example the quantum dots have a diameter of between 5nm to 6nm. Green light typically has a wavelength of between 495 to 570nm. Thus, the green sub-pixels comprise a plurality of quantum dots which are tuned to emit green light, for example the quantum dots have a diameter of between 2nm to 3nm. It will be appreciated that if the backlight does not emit blue light, quantum dots which have an appropriate size to generate blue light, e.g. below 2nm may be incorporated into the wavelength adjusting layer. Similarly, it will also be appreciated that the display may be monochrome and thus no red, green or blue emitting quantum dots are required. However, the wavelength adjusting layer may still incorporate the quantum dots to generate infrared light so as to combine the sensing with the display.

The infrared radiation may have a wavelength of between 630nm to 1mm through. A preferred range of wavelengths is between 630nm to 900nm, more particularly approximately 700nm. Accordingly, the size of the quantum dots which emit infrared light are typically above 6nm.

The material for the quantum dots may also depend on the light to be emitted. For example, quantum dots in the infrared range may be made from PbS, GaSb, InSb, InAs and CIS. Quantum dots in the visible range (i.e. red and green) may be made from InP or CdSe. In other words, the quantum dots for the visible range may be made from ll-VI elements or lll-V elements. The quantum dots (both visible and IR) may be suspended in materials such as epoxy, UV-curable adhesives and other polymers, e.g. to form a colloid. This layer of quantum dots may be sandwiched between two barrier films, e g. made of polyester, to retain the functionality of the quantum dots. The concentration of the quantum dots is dependent on the brightness of the target.

Although the description above makes references to red, green, blue and infrared subpixels, the quantum dots for each sub-pixel are not necessarily confined to specific areas. Quantum dots are much smaller than the pixel size. Accordingly, the quantum dots for each light type can be randomly dispersed throughout the layer provided there are a sufficient quantity to absorb the backlight. However, the LCD panel may have sub-pixels which are driven as described above to polarise the light through each subpixel to from the desired overall colour.

The infrared radiation which is emitted from the wavelength adjusting layer 36 is used to detect gestures or other touch impacts. Infrared is emitted as indicated by the arrows and is reflected back from a user’s finger 20 to the sensor 34. It will be appreciated that the reflection may also be from a stylus or another part of the user’s hand. The distance and shape of the object which reflects the infrared radiation is inferred by the optical sensor array 34 which in the Figure 2a arrangement is beneath (under) the backlight 32 and in the Figure 2b arrangement is above the backlight 32 and its associated wavelength adjusting layer. The optical sensor array 34 is any standard infrared sensor, for example the sensor may comprise an array of photodetectors, e.g. one for each pixel. The sensor take a 2D image of the infrared intensity reflected back to it and use this image to determine the gesture which is being made.

One suitable example of an optical sensor is a plastic image sensor developed by ISORG and FlexEnable, and described at http://www.isorg.fr/default.asp?cat_id=124. The sensor comprises a matrix of pixels, for example 220 x 192 pixels with a pixel spacing of 20μm. The infrared light reflected by a user, e.g. by their hand, is detected by an array of printed photodetectors. The photodetectors detect the proximity of the user’s hand as well as motion of the hand. The photodetectors are able to detect light in the spectrum of 380nm to 720nm. Thus, the infrared radiation is preferably focussed in the range 700nm to 720nm for such an optical sensor.

The infrared light is reflected from the user’s hand (or other associated object) through the display panel. Accordingly, the display panel must be at least partially transparent or wholly transparent to infrared light. Most standard LCD panels are at least partially transparent to infrared light.

Figures 3a and b shows a flowchart explaining how the devices in Figures 2a and 2b are assembled. As shown in Figure 3a, irst an active matrix infrared sensor is laminated (or mounted) behind a backlight unit S100. Both the sensor and the backlight unit are standard off-the-shelf components. A quantum dot film is then applied (or mounted) to the opposite face of the backlight unit to which the backlight unit is attached S102. It will also be appreciated that the backlight unit may be bought with the quantum dot film already integrated therein, perhaps in place of, or as well as, a standard diffuser.

The quantum dot film can be a preformed film in which the red, green and infrared quantum dots are dispersed. Quantum dots offer easy synthesis and preparation. As set out above, the quantum dots in the matrix form a colloid. This colloidal suspension can be easily handled throughout production. A fumehood is the most complex equipment which is needed. Quantum dots are typically synthesised in small batches but can be mass-produced. The dots can be distributed on a substrate by spin coating, spray-on or roll-printing of the colloidal suspension. Spin coating is typically for small scale production and can be done by hand or in an automated process. Spray-on or roll-printing is for large scale production and can dramatically reduce module construction costs. Barrier films can also be used to sandwich the layer of quantum dots. As evidenced in the publications above, quantum dot films that emit RGB are already known. The quantum dot film for the present invention can be manufactured in a similar manner to the known films with the addition of the infrared particles into the slurry (matrix). The final stage in the process is to laminate the liquid crystal display (e.g. a thin film transistor LCD) over the quantum dot film S104. Any suitable techniques for the lamination may be used, e.g. adhesives may be used to bond the various layers together. It will also be appreciated that the layers can be assembled in any suitable order. For example, the quantum dot layer may be first laminated to the backlight unit. The liquid crystal display may be added next and finally the sensor array.

Figure 3b shows an alternative method of bringing the three main layers: sensor, backlight unit and display together. The quantum dot film is applied (or mounted) to one face of the backlight unit S200. The sensor is then mounted on top of the backlight unit with its quantum dot film S202. The LCD panel is then mounted over the sensor S204. As with Figure 3a, any suitable techniques for the lamination may be used and the layers can be assembled in any suitable order. As shown in both Figures 2a and 2b, the methods of Figures 3a and 3b are used to form a multi-layer device, i.e. a device with several discrete layers.

Figure 4 shows a block diagram of the electronics of an LCD display panel. The device comprises a controller 1002 which includes a microprocessor, for example an ARM™ device, working memory and program memory coupled to one or more display interface integrated circuits 438 for driving the LCD 408. One or more optical sensors interface with optical sensor interface 414 to provide optical data which is processed to obtain touch and/or gesture data (as described above) to controller 1002.

The program memory in embodiments stores processor control code to implement functions including an operating system, various types of wireless and wired interface, document retrieval, storage, annotation (via the touch interface) and export from the device. The stored code also includes code 1003 to implement a document viewer/’printerless printing’ function, for example interfacing with corresponding driver code on a ‘host’ device.

The controller 1002 interfaces with non-volatile memory, for example Flash memory, for storing one or more documents for display and, optionally, other data such as user bookmark locations and the like. Optionally a mechanical user control 1004 may also be provided. A wireless interface 1010, for example a Bluetooth™ or WiFi interface is provided for interfacing with a consumer electronic device such as a phone 1014a, laptop 1014b or the like. The wireless interface 1010 may comprise a Bluetooth™ RF chip and antenna.

Inductive loop 432 is used to charge a rechargeable battery 430 which has associated circuitry to give one way for providing a regulated power supply to the system.

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

Claims

CLAIMS:

1. A display device comprising: a display having a display surface which is viewed by a user, a wavelength adjusting layer comprising a plurality of quantum dots which emit infrared radiation when excited; a light source to illuminate the wavelength adjusting layer to excite the plurality of quantum dots to generate infrared radiation, and a sensor for detecting infrared radiation which is reflected by a user.

2. The display device according to claim 1, wherein each of the plurality of quantum dots has the same size.

3. The display device according to claim 1 or claim 2, wherein the plurality of quantum dots each have a diameter of approximately 8nm.

4. The display device according to any one of the preceding claims, wherein the wavelength adjusting layer further comprises a second plurality of quantum dots which emit red light when excited and a third plurality of quantum dots which emit green light when excited.

5. The display device according to claim 4, wherein the diameter of each of the second plurality of quantum dots is between 5nm to 7nm.

6. The display device according to claim 4 or claim 5, wherein the diameter of each of the second plurality of quantum dots is between 2nm to 3nm.

7. The display device according to any one of the preceding claims wherein the display is a liquid crystal display.

8. The display device according to claim 7, wherein the light source is the backlight source for the liquid crystal display.

9. The display device according to any one of the preceding claims wherein the light source emits blue light.

10. The display device according to any one of the preceding claims wherein the wavelength adjusting layer and the light source are positioned between the sensor and the display.

11. The display device according to any one of the preceding claims wherein the display comprises a plurality of pixels and the sensor comprises a plurality of photodetectors which are aligned with the plurality of pixels to detect infrared radiation on a pixel-by-pixel registration.

12. The display device according to any one of the preceding claims wherein the sensor is capable of detecting gestures.

13. The display device according to any one of the preceding claims further comprising a colour filter.

14. The display device according to claim 13, when dependent on claim 4, wherein when excited the second plurality of quantum dots emit red light which matches a red filter in the colour filter and when excited the third plurality of quantum dots emit green light which matches a green filter in the colour filter.

15. A method of manufacturing a display device comprising providing a light source and a wavelength adjusting layer comprising a plurality of quantum dots which emit infrared radiation when excited by the light source, providing a display, providing a sensor for detecting infrared radiation and attaching the sensor, display and light source together to form a multi-layer device.

16. The method of claim 16, further comprising forming the wavelength adjusting layer by spin coating, spray-on or roll-printing a colloidal suspension comprising the quantum dots.

17. A display device substantially as hereinbefore described, with reference to and as illustrated in Figures 2a to 4.