Display configuration and method for operating the display configuration

Abstract

The present invention relates to a display arrangement comprising a pixel array having a plurality of pixels, wherein at least a portion of the plurality of pixels each comprises two μLEDs configured to emit light of the red spectrum, a first color filter having a high transmittance of the red spectrum and positioned on the first μLED of the two μLEDs, and a second color filter having a high transmittance of the green spectrum and positioned on the second μLED of the two μLEDs. A third μLED is configured to emit light of the blue spectrum, and a fourth μLED is configured to emit light of the green spectrum. The display arrangement is configured to operate at least a portion of the plurality of pixels during the emission mode, as a result of forward biasing the first, third, and fourth μLEDs, and during the sensing mode, the first, second, and third μLEDs are reverse biased.

Description

Technical Field

[0001] This application claims priority to German Patent Application DE102023124914 filed on September 14, 2023, the disclosure of which is incorporated herein by reference in its entirety. The present invention relates to a display arrangement having a plurality of pixels implemented by μLEDs and a method of operating the display arrangement. The present invention also relates to some applications of such a display.

Background Art

[0002] Modern mobile devices provide dynamic and intuitive display technology in terms of resolution, which not only presents information with extraordinary clarity but also facilitates interaction with users.

[0003] Today's advanced mobile displays offer unrivaled resolutions in the range of over 100 dots per inch, as well as high color accuracy, presenting images and text with sharp clarity and vivid details. They provide improved brightness, adaptive refresh rates, and power efficiency, all of which contribute to various environments such as shadows and different sunlight reflections. The display itself uses μLEDs, and each pixel includes at least three sub-pixels. Each sub-pixel includes at least one μLED that serves to emit light in one of the green, blue, and red portions of the visible spectrum, also known as green μLED, blue μLED, and red μLED. These μLEDs are often redundant so that damaged or non-functional μLEDs can be replaced.

[0004] The expression "μLED" refers to optoelectronic devices having a size less than 50 μm in diameter, particularly including sizes from 2 μm to 25 μm, although these specifications may vary. μLEDs are implemented in different material systems depending on the desired emission wavelength. For light in the blue and green portions of the visible spectrum, μLEDs are typically nitride-based, while for yellow / red and infrared, phosphide or arsenide material systems are used.

[0005] However, the capabilities of these displays extend far beyond merely presenting visual information. More specifically, it has been proposed to use the displays as sensor devices, such as fingerprint sensors. Further applications include sensors for reading vital sensory information, as well as scanners for photographs or other objects placed in front of the display.

[0006] Current technology is primarily based on fingerprint sensors, mainly using either capacitive or ultrasonic technology, capable of identifying and authenticating the unique patterns of a user's fingerprints. Capacitive fingerprint sensors are the more common type and work by measuring the difference in capacitance caused by the ridges and valleys of the fingerprint. Ultrasonic sensors, on the other hand, map the details of the fingerprint by contacting the finger and transmitting ultrasonic pulses. Both methods provide a secure, fast, and user-friendly way to unlock a device and authenticate an ID, thus adding an additional functional layer to the display. It has also been proposed to implement a photodetector in the display to enable scanning of the user's fingerprint by display placement.

[0007] One drawback lies in the fact that the sensor cannot be used in a μLED display. A μLED display typically has many layers with metal trays for routing driver signals to each radiator. This is an inherently opaque layer stack (in contrast to OLED displays), rendering all the technology behind the display unusable. Therefore, correctly identifying fingerprints, or more generally achieving the desired functionality, can be cumbersome. Current fingerprint applications require resolutions above 300 dpi, with a limit of around 500 dpi. Similarly, scanners and other devices offer similar high resolutions in the range of 300 dpi and above.

[0008] Therefore, the purpose of this application is to improve current display configurations and implement dual-use functionality that can meet the requirements of current state-of-the-art technology. [Overview of the Initiative] [Means for solving the problem]

[0009] This and other objectives are addressed by the gist of the present application in the independent claims. Features and further aspects of the proposed principle are outlined in the dependent claims.

[0010] The inventors propose a novel bidirectional display arrangement in which an optoelectronic device forms subpixels of multiple pixels, and the subpixels, implemented as μLEDs, have dual-use functionality. In this way, the pixels of the display arrangement and their respective subpixels operate in two different modes. The first mode, called the emission mode, is characterized by forward biasing the optoelectronic device so that it emits light. However, it has also been found that the μLEDs and optoelectronic devices can operate in reverse bias or zero bias, and when the generated photocurrent is read, they can function as photodetectors. As a result, when reverse biased, these μLEDs, subpixels, and pixels operate in detection mode or sensor mode. For the purposes of this application, the terms “reverse bias” or “reverse bias” also include zero bias and simply reading any photocurrent. Therefore, pixels, subpixels, or μLEDs that can be switched between zero bias and reverse bias are used as detectors.

[0011] The inventors hereby propose to implement individual subpixels of a display arrangement and pixels having their μLEDs in a specific manner, and to operate the pixels of the pixel arrangement in their two continuous modes. The proposed method enables an entirely new and different set of applications.

[0012] For example, a reverse-biased μLED can be used as a detector within the display, and a color filter can be used to obtain RGB color resolution. In practice, this can transform the display into a color image scanner that provides various scanning applications. In another application, a fingerprint or vital sign monitoring detector can be implemented by using μLEDs for green light emission from some pixels in light emission mode and operating μLEDs for red light from other pixels in sensing mode. By utilizing the RGBR scheme of each pixel, the current display resolution can be substantially doubled for such fingerprint and vital sign monitoring applications.

[0013] Various pixels (or their respective subpixels) can be addressed and set to one of the emission and detection modes, thereby generating specific emission and detection patterns. These patterns can provide compensation if there is dirt or dust on the display or on the object being scanned, i.e., on a fingerprint, iris scanner, or other object placed directly above or above the display.

[0014] In some embodiments, the inventors propose placing one additional μLED configured to emit light in the red portion of the visible spectrum at each pixel of the display. The μLED configured to emit light in the red portion is then covered by an additional color filter, which filters the spectral sensitivity of each μLED to photocurrent sensing when reverse-biased in sensing mode, without interfering with the display's emission performance.

[0015] Such a display arrangement may, in some embodiments, comprise a pixel array having multiple pixels arranged in rows and columns. At least a portion of the multiple pixels each include a tuned RGBR configuration. Such a configuration features two μLEDs configured to emit light in the red spectrum, with a first color filter having high transmittance in the red spectrum positioned above the first of the two μLEDs and a second color filter having high transmittance in the green spectrum positioned above the second of the two μLEDs; a third μLED configured to emit light in the blue spectrum; and a fourth μLED configured to emit light in the green spectrum. In this regard, an RGBR scheme is possible depending on the implementation. The pixels may include redundant μLEDs for red, green, or blue. Redundant μLEDs not typically used for light emission can be reused for sensing applications as described herein, even if the yield of the sensor portion (which is biased in the reverse direction) is reduced or the resolution is reduced.

[0016] According to the proposed principle, the display arrangement is configured to operate at least some of the pixels such that the first, third, and fourth μLEDs are forward-biased during the emission mode, and the first, second, and third μLEDs are reverse-biased during the sensing mode.

[0017] In this regard, it should be noted that not all pixels with such RGBR must operate in one of the above operating modes. Rather, some of those pixels can operate in sensing mode, while others can operate in emitting mode, or simply be turned off completely. As a result, in some embodiments, pixels in a display arrangement operating in sensing mode can detect ambient photons from objects positioned above each pixel. In some other embodiments, the arrangement is configured such that some pixels operate in emitting mode to form a radiation pattern on the display, while others operate in sensing mode. These patterns can change and move across the display so that stray light or other undesirable effects can be identified and compensated for.

[0018] Typically, this arrangement is configured to activate the RGB subpixels of pixels operating in emission mode simultaneously (while other pixels are operating in sensing mode). However, this is not mandatory. In some embodiments, the display arrangement is configured to operate a first subset of pixels in emission mode, so that only a portion of the subpixels of those pixels are activated, while a second subset of pixels operates in sensing mode. The subpixels of the first subset can then change over time. As a result, in such configurations, the color of the emitted light changes over time, so objects are not scanned with white light (although white light is used in conventional scanners, it is done with narrow-spectrum light, i.e., colored light). Therefore, objects that pass through the visible spectrum and are placed on the display can be scanned at different wavelengths. This can improve the signal-to-noise ratio.

[0019] Several configurations are possible. In some embodiments, the display arrangement is configured such that a first subset of at least some of the pixels operates during the emission mode and a second subset of at least some of the pixels operates during the sensing mode. In some other embodiments, the display arrangement is configured such that a first subset of at least some of the pixels operates during the emission mode and a second subset of at least some of the pixels operates during the subsequent sensing mode. In some further embodiments, the display arrangement is configured such that a first subset of at least some of the pixels operates alternately between the emission mode and the sensing mode.

[0020] It is possible to arrange pixels from a first subset of multiple pixels adjacent to pixels from a second subset of multiple pixels. However, the pixels may also be separated by one or more third subsets of pixels that are switched off. Nevertheless, the adjacent pixels (pixels that act for radiation) of the pixels in the first subset in this arrangement are the pixels in the second subset.

[0021] In some embodiments, the display arrangement may embed a control device, but the control device may also be a separate device coupled to the pixel array to operate at least some of the pixels.

[0022] In some embodiments, each μLED is uniformly distributed across the display arrangement area or a portion thereof. In some other embodiments, the μLEDs are at least equally distributed across the pixel area. As a result, they can be at equal distances from one another. In some embodiments, they are arranged along virtual lines. In some other embodiments, the μLEDs for each pixel are located at the edges of virtual rectangles. Similarly, in some embodiments, the μLEDs are arranged in a diamond pattern. Some applications can benefit from utilizing μLEDs configured to emit light in the red portion of the visible spectrum, so these μLEDs need to be spaced apart. As a result, these μLEDs are separated by at least one of the green and blue μLEDs. This distance can substantially increase the resolution of such μLEDs when operating in a sensing mode suitable for, for example, fingerprint or vital sign monitoring applications.

[0023] Some embodiments relate to the use of μLEDs as photoemitters and photodetectors. In some embodiments, the first and second μLEDs have an external quantum efficiency greater than 0.15 when reverse-biased for light with wavelengths between 500 nm and 535 nm and between 575 nm and 620 nm, and in particular greater than 0.2 for light with wavelengths between 500 nm and 535 nm and greater than 0.14 for light with wavelengths between 480 nm and 620 nm. Although such figures may not seem very large, they substantially enable the use of a μLED configured to emit light in the red spectrum as a photodetector for light in the green and red parts of the visible spectrum. Therefore, good results can be achieved when such a μLED is used as a photodetector.

[0024] In some embodiments, for example, a μLED configured to emit light in the red portion of the visible spectrum is also configured as a photodetector when operating in reverse bias towards light in the green portion of the spectrum. Thus, these μLEDs are dual-use and are suitable for capturing light reflected from fingers during fingerprint detection or monitoring of a user's vital signs, as described herein.

[0025] Some embodiments relate to color filters covering the surface of some μLEDs. These color filters can not only support the sensing mode by blocking undesirable portions of the visible spectrum, but can also provide a narrower, more directional light emission. In some embodiments, the transmittance of the first color filter is greater than 80% for light with wavelengths above 600 nm, greater than 90% for light with wavelengths above 620 nm in particular, and greater than 85% for light with wavelengths above 600 nm in particular. This color filter is transparent to red light in the spectrum and blocks light in the green and blue portions.

[0026] The second color filter may include a transmittance greater than 60% for light with wavelengths of 512nm to 565nm, a transmittance greater than 70% in particular for light with wavelengths of 520nm to 560nm, and a transmittance greater than 75% for light with wavelengths of 540nm. This color filter substantially blocks the red and blue portions of the visible spectrum and transmits the green portion. When placed on the radiating surface of a μLED configured to emit light with red portions of the visible spectrum, the μLED may be used as a green light detector when operating in reverse bias. Such applications as fingerprint detection, vital sign monitoring (both using green light to illuminate the user's fingers), and general object scanning become feasible by combining those μLEDs with a μLED that functions as a green light emitter.

[0027] In some embodiments, the transmittance of the first color filter is less than 40% for light with a wavelength less than 570 nm, particularly less than 30% for light with a wavelength less than 570 nm, and particularly less than 15% for light with a wavelength less than 570 nm. Similarly, the transmittance of the second color filter is less than 30% for light with wavelengths greater than 600 nm and less than 475 nm, and particularly less than 20% for light with wavelengths less than 450 nm.

[0028] Different embodiments for placing the color filters above their respective μLEDs are possible. In some embodiments, at least one of the first and second color filters is placed on the light emission surface of their respective first and second μLEDs. In some other embodiments, the display arrangement further comprises a transparent cover placed above the main emission surfaces of a plurality of pixels arranged in rows and columns. The transparent cover comprises a plurality of first color filters arranged opposite the emission regions of the first μLEDs and a plurality of second color filters arranged opposite the emission regions of the second μLEDs.

[0029] In some embodiments, the area of at least one of the first and second color filters is larger than the emission area of the μLED associated with the color filter. This prevents stray light from reaching the surface of the μLED when operating in the sensing mode. In this regard, the μLED may be embedded in a recess on the backplane surface. The transparent cover is placed on top of the recess, thereby forming a uniform surface. The backplane may comprise respective contact regions within the recesses that contact the μLEDs disposed therein.

[0030] Some other embodiments relate to a method for operating a display arrangement having multiple pixels. Each pixel comprises two μLEDs configured to emit light in the red spectrum, a first color filter having high transmittance in the red portion of the visible spectrum positioned on the first of the two μLEDs, and a second color filter having high transmittance in the green portion of the visible spectrum positioned on the second of the two μLEDs. Furthermore, the pixel also comprises a third μLED configured to emit light in the blue portion of the spectrum and a fourth μLED configured to emit light in the green portion of the visible spectrum.

[0031] The method here comprises the step of forward-biasing first, third, and fourth μLEDs of at least a first subset of a plurality of pixels during a first period. During the first period, the μLEDs are able to emit light. Biasing the μLEDs in the forward direction corresponds to the emission mode. During a second period, first, second, and third μLEDs of at least a second subset of the plurality of pixels are reverse-biased, corresponding to the sensing mode.

[0032] As a result, this method proposes two different operating modes. In the first operating mode, at least a portion of the μLEDs are biased forward and therefore emit light in each part of the visible spectrum. In the sensing mode, at least a portion of the μLEDs operate in reverse and function as a photodetector.

[0033] In some embodiments, the proposed method further includes the steps of: biasing first, second, and third μLEDs of at least a first subset of a plurality of pixels in the reverse direction within a third period; and biasing first, third, and fourth μLEDs of at least a second subset of a plurality of pixels in the forward direction within a fourth period.

[0034] This allows for an alternating pattern of emission and detection for each pixel. The pattern not only changes alternately, but also "moves" across the display, effectively scanning the entire area.

[0035] In some embodiments, forward biasing is performed sequentially, and only μLEDs of the same color are activated at specific times. Simultaneously, several corresponding μLEDs operate in sensing mode, and thus capture only the reflected light of the said color. By biasing only a subset of μLEDs of a particular color and detecting their reflected light portions with other μLEDs, the signal-to-noise ratio can be improved. For applications such as fingerprint detection or vital sign monitoring, μLEDs configured to emit light in the green portion of the spectrum are best suited for emission because such light has good transmission and scattering properties in human tissue (e.g., user's fingers and fingerprints).

[0036] In some embodiments, the first and second periods overlap at least partially, and the third and fourth periods overlap at least partially. In some further embodiments, the pixels of the first subset of the plurality of pixels are arranged adjacent to the pixels of the second subset of the plurality of pixels.

[0037] The proposed display configuration can be used for a variety of applications. For example, the proposed display configuration can be used as an in-display scanner where the object to be scanned is placed on the display configuration. Another application is provided by an in-display PPG sensor. Similarly, the proposed display configuration can be used as an in-display fingerprint sensor.

[0038] Further aspects and embodiments of the proposed principle will become apparent in connection with the various embodiments and examples described in detail with respect to the accompanying drawings. [Brief explanation of the drawing]

[0039] [Figure 1]This figure shows a first embodiment of a display arrangement according to several aspects of the proposed principle. [Figure 2] This figure shows a second embodiment of the display arrangement according to several aspects of the proposed principle. [Figure 3] This figure shows several third embodiments of the display arrangement according to some aspects of the proposed principle. [Figure 4] A diagram illustrating the wavelength efficiency of light in the green spectrum is provided to outline some aspects of the proposed principle. [Figure 5] A diagram illustrating the wavelength efficiency of light in the blue spectrum is provided to outline some aspects of the proposed principle. [Figure 6] This is a wavelength efficiency diagram to outline several aspects of the proposed principle. [Figure 7] This figure shows a first embodiment of a pixel in several aspects. [Figure 8] This figure shows a second embodiment of a pixel in several aspects. [Figure 9] Figures 9A to 9C show embodiments of pixels in display mode or sensing mode in several different ways. [Figure 10] This figure shows another embodiment of a pixel in display mode and sensing mode according to several aspects. [Figure 11] These are wavelength quantum efficiency diagrams of μLEDs covered with color filters in several configurations. [Figure 12] This figure shows a first embodiment of multiple pixels, including the arrangement of each μLED, in several different ways. [Figure 13] This figure shows further embodiments of multiple pixels, including the arrangement of each μLED, according to several aspects. [Figure 14] This figure shows further embodiments of multiple pixels, including the arrangement of each μLED, according to several aspects. [Figure 15]This figure shows further embodiments of multiple pixels, including the arrangement of each μLED, according to several aspects. [Figure 16] Wavelength transmittance diagrams of different color filters based on several embodiments of the proposed principle are shown. [Figure 17] Figure 17A shows one embodiment of a μLED embedded in a backplane substrate of a display arrangement according to several aspects of the proposed principle. Figures 17B and 17C are cross-sectional views of embodiments of the display arrangement according to several aspects of the proposed principle. [Modes for carrying out the invention]

[0040] The following embodiments and examples disclose various aspects and combinations thereof based on the proposed principle. The embodiments and examples are not necessarily to a constant scale. Similarly, different elements may be shown enlarged or reduced to emphasize individual aspects. It goes without saying that the individual aspects of the embodiments and examples shown in the drawings can be combined with each other without further difficulty without contradicting the principle of the present invention. Some aspects show regular structures or forms. It should be noted that in practice, slight differences and deviations from the ideal form may occur without contradicting the concept of the present invention.

[0041] Furthermore, individual figures and aspects are not necessarily shown in exact size, nor do the proportions between individual elements need to be inherently accurate. Some aspects are emphasized by showing them enlarged. However, terms such as "above," "up," "down," "below," "greater," and "smaller" are correctly represented with respect to the elements in the figures. Therefore, it is possible to infer such relationships between elements based on the drawings.

[0042] Figure 1 shows a display arrangement according to several embodiments of the proposed principle.

[0043] The display configuration 1 comprises an array of pixels 10 arranged in rows and columns on each substrate or backplane 12. Each pixel 10 comprises multiple μLEDs capable of generating light in various parts of the visible spectrum. For simplicity, a μLED or optoelectronic device configured to emit light in the red part of the visible spectrum is referred to as a red μLED. Similarly, a green μLED is an optoelectronic device configured to emit light in the green part of the visible spectrum, and a blue μLED is configured to emit blue light when in operation.

[0044] In this particular case, each pixel 10 comprises a μLED in an RGBR configuration according to the proposed principle. That is, two μLEDs are configured to emit red light, and each μLED is configured to emit green and blue light, respectively. The individual μLEDs may be integrated and combined on a backplane 12 using monolithic integration, or they may be mounted on the backplane 12 using a specific coupling technique. The backplane 12 comprises multiple integrated circuits, which are configured to individually control each of the μLEDs of each pixel 10 to function as a radiator and, in part, as a detector, according to the proposed principle.

[0045] Each pixel and μLED is connected to a control circuit 13 via a backplane 12. The control circuit 13 may also be integrated into the backplane 12. The control circuit 13 is configured to supply the current signals necessary to individually address the μLEDs, as well as voltage or current signals to them. In this respect, the embodiment shown in Figure 1 is similar to a conventional display arrangement, with multiple pixels arranged in rows and columns, and each pixel comprising multiple other pixels. As shown, various subpixels within a pixel 10 are positioned at specific locations to form a pattern. These positions may depend on various manufacturing techniques as well as individual functionalities, as will be further described below and in reference to some further figures below.

[0046] In this display arrangement, at least some of the pixels 10, their subpixels, and their respective μLEDs are used according to the proposed principles as photodetectors for various purposes. In some embodiments, as will be further described below, the pixels can be used to capture portions of the visible spectrum with varying wavelength sensitivities in order to scan an object placed directly in front of the display arrangement.

[0047] In another application, various pixels are used to illuminate an object, while other nearby pixels are used as photodetectors to detect and capture the light portion of the emitted light reflected from the object opposite the various pixels. Apart from scanning objects to create images, other use cases include fingerprint sensors, where the reflective portion corresponds to the structure of the user's finger placed on the display surface. Display configurations based on the proposed principle could also be used for PPG or vital sign monitoring. The latter can be combined with fingerprint sensor technology to ensure that fingerprints are obtained from living people, rather than from photographs or artificial models.

[0048] Regarding the function of the embodiment of Figure 1 according to the proposed principle, each pixel 10 contains a total of four different subpixels. Two of these pixels are configured to emit light in the red spectrum, a third pixel is configured to emit light in the green spectrum, and a fourth pixel is configured to emit light in the blue spectrum. According to the proposed principle, the surface of the μLED configured to emit light in the red spectrum is covered with a red color filter. Similarly, the second μLED configured to emit light in the red spectrum is covered with a green color filter. The red color filter transmits light in the red spectrum substantially above 650 nm, while the color filter covering the second μLED transmits light in the green spectrum. The transmission curves of each color filter are described in more detail below.

[0049] The functions of such pixel 10 are currently as follows: In the display arrangement's emission mode, the control circuit controls the μLEDs to emit light according to the desired color and brightness. In this respect, the emission mode corresponds to the operation of a conventional display arrangement. The red color filter does not interfere with the emission of light due to its very high transmittance of over 92% in the emission range. In this mode, the second μLED for red light is turned off. The control circuit 13 controls the mixing of light with each part and controls the on / off ratio of the μLEDs. By controlling each pixel 10 and the subpixels within each pixel, various photographs, signs, and other structures can be displayed on the display arrangement.

[0050] In the second operating mode, various μLEDs are reverse-biased and thereby act as photodetectors. More specifically, at least some μLEDs configured to emit blue light are reverse-biased here to act as photodetectors for detecting and capturing light in the blue spectrum. Some of the first μLEDs configured to emit red light, with a red color filter placed on the radiating surface, are also switched to reverse-bias mode to function as photodetectors. Due to the red color filter, these μLEDs detect only light in the red spectrum. Finally, some of the second μLEDs covered with a green color filter are switched to reverse-bias mode to act as green light photodetectors, as their quantum efficiency is large enough for them to capture green light. The green color filter absorbs or reflects light in the blue and red spectra, and therefore does not contribute significantly to the photocurrent. Third μLEDs configured to emit green light are turned off in sensing mode and are not used as photodetectors because their external quantum efficiency in that range is very small. As a result, the display here functions as a passive scanner, capturing the colors of objects such as photographs placed on the display arrangement.

[0051] In the above embodiment, the red color filter can substantially block the green light. In some alternative embodiments, the red color filter is omitted. Thus, the first μLED captures light within the green and red portions of the spectrum. Since the green portion is also captured by the second μLED, the undesirable signal portion of the first μLED (the sum of the red and green portions) can be corrected. In other words, a display with an RGBR configuration in which one μLED is covered with a green color filter can be dual-used as both a display and a fingerprint sensor. Furthermore, in some cases, the first μLED can be used as a detector in the reverse bias direction, and the green portion is later removed as noise in post-processing using photocurrent from the second μLED.

[0052] Figures 2 and 3 illustrate different operating modes in which the image or object to be scanned is placed directly on the top surface of the display arrangement.

[0053] The display configurations in Figures 2 and 3 both include arrays of multiple pixels 10 arranged in rows and columns. In this respect, the display configuration is the same as in the embodiment of Figure 1. However, the display configurations in Figures 2 and 3 operate in slightly different modes, with some of each pixel used for radiation to illuminate the object being scanned, while the other part of the pixel operates in sensing mode.

[0054] More specifically, Figure 2 shows the respective embodiments used for parallel illumination and sensing modes. In this configuration, the display arrangement comprises multiple pixels, with a first portion P1 of the pixels operating in sensing mode and a second portion P2 of the pixels operating in their respective emission modes. During emission, individual subpixels of the second portion P2 of the pixels operate in emission mode and are controlled to emit blue, green, and red light, respectively. The emitted light is reflected from an object located directly above the display arrangement and detected by subpixels (red and green μLEDs) of the first portion P1 of the pixels. The subpixels of portion P1 operate in inverse mode and act as their respective photodetectors.

[0055] Depending on the application, the shape, size, and position of different parts P1 and P2 of the pixel may change over time as the object is scanned sequentially. For example, the embodiment in Figure 2 shows the configuration of pixel parts P1 and P2 during a first period. In subsequent periods, parts P1 and P2 alternate, with subpixels within pixel part P2 being switched to sensing mode (i.e., biased in the reverse operation and acting as a photodetector), while part P1' of the pixel is switched to emission mode to emit light.

[0056] Such switching between emission and sensing modes for various pixel areas yields several advantages. Firstly, it enables more uniform illumination of the object being scanned. Furthermore, depending on the application, it is possible to recognize and subsequently correct for undesirable irregularities such as reflections and blemishes. In this embodiment, the total number of pixels operating during emission is small, about one-quarter of the number of pixels used for detection. This ratio is application-dependent but is also caused by a lower quantum efficiency for capturing photons. In addition, it is possible to detect stray light or average captured photocurrents to obtain a good scan of objects placed above the display. The pattern can change and "move across the display" as with conventional scanners.

[0057] Figure 3 shows another possibility for such a configuration. In this embodiment, a first portion P1 of a pixel is set to sensing mode. Each pixel immediately adjacent to such a pixel portion P1 is either turned off or similarly set to sensing mode. Pixel portion P2 is switched to emitting mode. As a result, row by row and column by column, pixel portions P1 and P2 alternate with one pixel in between. As in the previous embodiment, the emitting pixel portions and the pixel portions switched to sensing mode can also be alternated, but pixel portion P1 is then set to emitting mode and pixel portion P2 is switched to sensing mode. Similarly, the row and column pixel portions can be moved one pixel to the left / right or up / down so that the entire area of ​​the display arrangement is fully scanned. To accommodate the required applications, a variety of other options and possible emitting and sensing patterns are possible in the display arrangement according to the proposed principle.

[0058] In each embodiment shown in Figures 1 to 3, each subpixel of each pixel operating in emission mode (except for the μLED covered with a green color filter) is turned on to provide specific illumination. However, this is not mandatory. Rather, individual subpixels, which are subpixels configured to emit blue, green, and red light, can be sequentially activated and deactivated in each pixel operating in emission mode. In other words, to scan an object, the subpixels are sequentially activated so that the object being scanned is illuminated with substantially one color of light. Similarly, subpixels used in sensing mode may be sequentially turned on and off. This may be beneficial for improving the signal-to-noise ratio, although other photodetectors may be used to detect potential noise portions during the overall illumination of the object being scanned.

[0059] As mentioned above, the proposed principle involves dual-using the respective optoelectronic devices and μLEDs for both light emission and light detection. As a result, the μLED can be switched between a forward mode configured to emit light or a reverse-bias mode to function as a photodetector. Depending on the material system, the quantum efficiencies of emission and detection can vary. Figures 4 to 6 show the various external quantum efficiencies of each operating mode for gallium nitride-based μLEDs used for blue and green emission, and phosphide or arsenide-based μLEDs used for red emission.

[0060] Figure 4 shows the wavelength quantum efficiency diagram of a μLED configured to emit green light with wavelengths of 500 nm to 550 nm. This is given by the linear curve K1. The material system for such a μLED is typically gallium nitride based.

[0061] However, as shown in the figure, for phosphorus-based or arsenic-based μLEDs that switch in reverse bias mode, the dotted line K2 represents the external quantum efficiency for capturing photons and generating electron-hole pairs. These μLEDs are typically used for red light emission, but can be adapted as photodetectors for the green portion of the spectrum. As shown in the figure, the quantum efficiency of a μLED in reverse bias mode within its particular range of the spectrum is approximately 0.2, which is sufficient for it to function as a photodetector. Consequently, a μLED configured to emit light in the red spectrum can be used to operate in reverse bias mode and detect photons with wavelengths of 500 nm to 550 nm.

[0062] Figure 5 shows a similar example of a μLED configured to emit light in the blue range of the visible spectrum at approximately 450 nm. The linear curve K1 shows their emission spectra. However, a gallium nitride-based μLED, used to emit green light, has a quantum efficiency of detecting such photons at approximately 0.15, as shown by the dotted curve K2 in Figure 2, which is lower than that of a μLED configured to emit blue light. Nevertheless, this makes it possible to operate nitride-based μLEDs in reverse bias mode and use them to act as blue light photodetectors. The dotted curve K2 shows the respective quantum efficiencies over the presented wavelengths.

[0063] Figure 6 shows the final initial spectra of red, green, and blue light μLEDs, referencing the linear curves K1–K3 and the corresponding quantum efficiencies when switched to reverse bias mode. The dotted lines K4–K6 correspond to the quantum efficiencies in reverse bias mode when the μLED functions as a photodetector.

[0064] As illustrated, a phosphine-based μLED for red light emission may be used to detect photons in the red spectrum, the green spectrum, and the blue spectrum, although photons in the blue spectrum are not typically detected by such a μLED. A μLED configured to emit green light can be used in reverse bias mode to detect light in the blue spectrum, but each μLED for blue light is far more suitable for such an purpose because its external quantum efficiency is about 0.25 higher compared to 0.15 for green light. Consequently, a μLED configured to emit blue light is used in reverse bias mode as a photodetector for blue light according to the proposed principle.

[0065] As shown by the dotted curve K5, a μLED emitting red light is used to detect green light in the 500nm–550nm spectrum. A second phosphide-based μLED can also be used to detect red light according to the proposed principle. Thus, two μLEDs configured to emit red light can be provided within a pixel, one of which is covered with a transmissive color filter in the desired spectrum of 500nm–550nm to act as a photodetector for green light. The second μLED configured to emit red light may be used as both a red light emitter and detector, and this μLED is covered with a red light color filter. The second red color filter may not be necessary, as the optical signal obtained by the green-filtered μLED can correct the detection signal in those μLEDs.

[0066] In this regard, Figure 11 shows the wavelength quantum efficiency diagrams of a μLED used as a blue light photodetector, and two μLEDs used as red and green light detectors, respectively, the latter two having their respective color filters on top. The quantum efficiency in each case is between 0.15 and 0.2, which is sufficient for scanning applications. As a result, a pixel having four μLEDs as subpixels can be used either as a radiator for generating light of a desired color, or as a photodetector for detecting photons in the visible spectrum. Consequently, no additional photodetectors are required. Furthermore, as already shown in the first three embodiments, this arrangement enables a variety of different applications by operating each μLED within each pixel separately. The arrangement and structure of each pixel, including the μLEDs associated with the pixel, are shown in Figures 7 to 10.

[0067] Figure 7 shows the arrangement of μLEDs representing subpixels within diagonally arranged pixels 10. In total, each pixel 10 consists of five μLEDs, with two of the μLEDs 103 used as their respective photodetectors. More specifically, pixel 10 comprises a first μLED 100r configured to emit red light, a second μLED 100g configured to emit light in the green spectrum, and a μLED 100b configured to emit light in the blue spectrum.

[0068] Three μLEDs 100r, 100g, and 100b are arranged along a virtual line at a fixed distance apart. Another optoelectronic device 103 is placed between the red μLED and the green μLED, and between the green μLED and the blue μLED. Device 103 is configured to act as a photodetector for each, and is biased in reverse mode during device operation. Depending on the application, the three μLEDs can be used to emit light for display, as shown in Figure 7A. The photodetectors 103 are typically turned off during such operation. Depending on the application, the photodetectors 103 for adjacent or nearby pixels can operate in reverse bias mode, where the μLEDs 100r, 100g, and 100be are not operating. Thus, direct incident light is limited, and the photodetectors detect light reflected from the object.

[0069] Figure 7B shows a further embodiment in which an infrared emitter 102 is located within each pixel. This makes it possible to illuminate an object using infrared light, which can then be detected by a photodetector 103. For this purpose, the photodetector 103 may consist of respective color filters covering the main detection surface to allow only reflected light from the infrared emitter 102 to reach the detector.

[0070] Figure 8 shows two pixels, each containing three μLEDs 100r, 100g, and 100b configured to emit light of their respective colors, as well as three μ photodetectors 103. The photodetectors can be selectively activated or deactivated during the emission of the μLEDs to detect a portion of the emitted light reflected from an object. As in the embodiments described above, the photodetectors and μLEDs may be arranged along a virtual diagonal passing through each pixel 10.

[0071] Figure 9A shows a slightly different arrangement, with a dedicated μ-photodetector 104 positioned at each pixel. These individual μ-photodetectors may be positioned separately or embedded in the backplane of the main display during the manufacturing of the display arrangement. In some embodiments, the photodetectors are transferred in bulk to the backplane of the display, similar to the transfer process for μLEDs. The μ-photodetector 104 is primarily suited for detecting light within a specific range of the visible spectrum, for example, within the green range.

[0072] This makes it possible to implement specific applications such as high-resolution fingerprint detection. As a result, μ-photodetectors can be based on materials other than silicon, Si, arsenides, phosphides, or materials used in μLEDs.

[0073] Figures 9B and 9C show yet another example of fingerprint or bioparameter sensing, such as PPG measurement. Each pixel and μLED operates in the emission mode shown in Figure 9B. μLEDs 100r, 100g, and 100b are supplied in the forward direction, while a second μLED configured to emit red light 101r is turned off. Typically, no significant complexity is added due to the fact that such pixels require redundant μLEDs anyway.

[0074] Figure 9C shows a so-called sensing mode suitable for fingerprint detection, PPG measurement, or other applications. In this mode, the blue μLED 100b is switched off, and the green LED 100g operates in forward mode, emitting light of the green spectrum.

[0075] Light is reflected from an object, for example, a user's finger or any part of their skin, which is positioned on the display. A portion of the reflected light reaches μLEDs 100r and 101r. These μLEDs are switched in the reverse bias direction to act as photodetectors for the reflected green light portion. The fact that these μLEDs 100r and 101r operate in the same way at their respective pixels substantially doubles the overall resolution of the detector, and more specifically improves the signal-to-noise ratio.

[0076] In some cases, the detector μLED 101r may be equipped with a green color filter that transmits only green light. This makes it possible to compensate for specific noise or other undesirable signal portions by comparing the photocurrents provided by μLEDs 100r and 101r at each pixel and / or adjacent pixels. Using a pixel array with two μLEDs each configured to emit red light, and operating them in the reverse bias direction, a fingerprint detection resolution of more than 600 dots per inch can be obtained. At the same time, each pixel 100r (and even 101r) can be used for normal display of light.

[0077] Figure 10 shows a further example of such a configuration suitable for guiding light, where each μLED operates in the reverse bias direction and acts as a photodetector. In this configuration, μLED100r' is configured to emit red light and further comprises a red color filter covering the main emitting surface. The red color filter transmits red light but absorbs all reflected light from the rest of the visible spectrum.

[0078] A further μLED 100g is configured to emit green light, and another μLED 100b is configured to emit blue light. Furthermore, a fourth μLED 101r' is configured to emit red light. Similar to μLED 100r', this μLED 101r' features a color filter that transmits photons in the green range of the visible spectrum and covers the main emitting surface of each μLED. During the emission modes shown in the right-hand diagram of Figure 10, μLEDs 100r', 100g, and 100b operate in their normal forward bias direction, acting as radiators for their respective pixels. In such operation, the second μLED 101r' is typically turned off. In the sensing mode, where different colors of an object are scanned and detected, μLED 100g for the green mode is turned off, and the remaining μLEDs 100r', 101r', and 100b operate in the reverse bias direction. In such operation, each μLED detects light from its respective portion of the visible spectrum. In this regard, it should be noted that there is no need to illuminate the objects placed on the display arrangement being scanned. Rather, whether it is natural light or whether the objects emit light themselves can be detected by μLEDs 100b, 100r', and 101r'.

[0079] Depending on the application, the arrangement of μLEDs and subpixels within each pixel 10 can be optimized to suit each display and directional operating mode.

[0080] Figures 12 to 15 illustrate various configurations and arrangements of subpixels in such a display. In Figure 12, each pixel contains four μLEDs configured to emit light in the red spectrum, one μLED in each pixel configured to emit light in the blue spectrum, and one μLED configured to emit light in the green spectrum. These μLEDs are arranged along virtual lines, and the μLED configured to emit light in the red spectrum is separated by at least one of the green and blue LEDs. This configuration is also called an RGBR pixel. As shown herein, the pixel has a virtual parallelogram shape arranged on the display structure.

[0081] In the slightly different arrangement shown in Figure 13, each pixel has the shape of a rectangle of equal size. Each subpixel and μLED in each pixel is positioned on the virtual diagonal of each of those pixels. As in the previous embodiment, the red μLED is separated by a green or blue μLED opposite the pixel boundary. A different configuration is shown in Figure 14, where the subpixels and μLEDs are arranged in a rectangular shape, and the two μLEDs 100r and 101r are separated by a large distance. As in the previous embodiment, both the red μLEDs 100r and 101r are separated by their respective green or blue μLEDs.

[0082] Figure 15 shows the final rhombus-shaped configuration, where each μLED and subpixel within each pixel 10 forms a rhombus structure with μLEDs 100r and 101r positioned on a virtual horizontal line and pixels 100g and 100b alternately positioned on their respective virtual vertical lines.

[0083] Figure 16 shows the wavelength transmittance diagrams of several color filters F1, F2, and F3 that are usable and suitable for display configurations according to the proposed principle. Color filters F1, F2, and F3 have different transmittances within their respective ranges, but the transmittance outside the desired range drops significantly to less than 20%. This allows for the substantial blocking and absorption of light outside each high transmittance region, preventing the corresponding reaction of the photodetector.

[0084] Figures 17A to 17C show several possible mounting configurations of μLEDs and subpixels embedded in a silicon backplane or substrate. The silicon backplane 12 contains various functions and integrated circuits that control each subpixel and μLED 100 and provide the necessary voltage and current signals.

[0085] In the embodiment shown in Figure 17A, a plurality of recesses 121 are machined on the backplane 12, providing a contact area on the surface of each recess (not shown in Figure 17A). A vertical μLED 100 is placed in a recess, with one of its contacts in contact with the contact area of ​​the recess 121. The remaining space of the recess is then filled with a transparent material. The side walls 122 of the recess and the remaining surface of the recess can be covered with a corresponding reflective material to provide a reflective surface that increases radiation efficiency and detection probability. A transparent conductive contact 120 is placed on the upper surface of the transparent material 123 and the upper surface of the μLED 100. The transparent conductive material forms a second contact for supplying the respective control signal and supply signal to the μLED. The embodiment shown in Figure 17A provides a uniform and flat surface, which may be further machined as shown in Figures 17B and 17C.

[0086] Figure 17B shows a pixel having subpixels and μLEDs 100r', 100g, 101r', and 100b. All μLEDs are located within their respective recesses 121, and their transparent common contacts 120 are positioned above the recesses and the main radiating surfaces. The transparent conductive contact material 120 acts as a cover for the μLEDs and provides electrical contacts. Two color filters 200, 201 are provided above the transparent contacts 120. More specifically, color filter 200 provides high transmittance in the green region of the spectrum and is located above the main radiating surface of μLED 101r. Similarly, a second color filter with high transmittance in the red portion of the visible spectrum is positioned above μLED 100r and covers the main radiating surface. Both color filters have an area slightly exceeding the area of ​​their respective recesses 121, as shown in the figure, thereby completely covering the recesses. This prevents stray light from reaching each μLED during sensing mode.

[0087] During sensing mode, μLED100r, 101r, and 100b are switched to reverse bias mode, while μLED100g is turned off. The color filter then blocks photons outside of each portion of the spectrum, so that only the correct wavelength period reaches the photodetector and thus can generate a signal.

[0088] The red color filter 201 is removed in some alternative applications. During detection, detector 100r may detect not only photons in the red spectrum but also those in the green and blue spectra. However, such signal components can be compensated for at least some extent by taking into account the signals from photodetectors 101r and 100b, respectively. Similarly, emission can occur continuously, with only a single μLED per pixel emitting its respective light. For example, only the green μLED may emit some signal, and the blue and red μLEDs are turned off. During green light emission, the μLEDs 100r and 101r of the same pixel and adjacent subpixels are switched to sensing mode. A finger or any other object placed on a glass cover not shown herein may reflect some of the light. Depending on the reflection amplitude, it is then detected by the μLEDs 100r and 101r, which are positioned in reverse bias mode. This enables the detection of fingerprint structures. Since two μLEDs are used as photodetectors in such applications, the substantial resolution can be increased.

[0089] Figure 17C shows some variations of an embodiment in which an additional glass cover 300 is positioned over the transparent contact 120. Each color filter 200, 201 is positioned on the underside of the glass cover 300 facing the radiating surfaces of the μLEDs 100r, 101r and the recesses 121. The embodiment in Figure 17C shows a different manufacturing process, namely a glass cover 300 with a backplane 12 into which the μLEDs are embedded and a structured color filter. To compensate for the different thicknesses of the color filters, the color filters may be embedded between two thin glass covers 300 as shown herein, or embedded by an additional transparent material covering the color filters, forming a uniform surface to be attached to the upper transparent contact 120. [Explanation of Symbols]

[0090] 1. Display arrangement 10 pixels 10', 10" adjacent pixels 10" adjacent pixels 12 Backplane 13 Control Unit 100r subpixel, red μLED Red μLED with 100r' subpixel and color filter 100g subpixel, green μLED 100b subpixel, blue μLED 10¹r subpixel red μLED Subpixel red μLED using a 10¹r' color filter 102 subpixel infrared μLED 103 Photodetector 104 μ photodetector 121 Recess 122 Side wall 123 Transparent material 200 color filters 201 Color Filters 300 Glass Cover P1, P1' pixels P2, P2' pixels K1, K2 curve K3, K4 curve K5, K6 curve

Claims

1. Display arrangement, - A pixel array having a plurality of pixels arranged in rows and columns, wherein at least a portion of the plurality of pixels are, o Two μLEDs configured to emit light of the red spectrum, wherein a first color filter having a high transmittance of the red spectrum is placed on the first μLED of the two μLEDs, and a second color filter having a high transmittance of the green spectrum is placed on the second μLED of the two μLEDs, A third μLED configured to emit light in the blue spectrum, o comprising a fourth μLED configured to emit light of the green spectrum, - The display arrangement causes at least a portion of the plurality of pixels to operate, and as a result, During the emission mode, the first μLED, the third μLED, and the fourth μLED are forward-biased. During sensing mode, the first μLED, the second μLED, and the third μLED are biased in the reverse direction. A display arrangement configured as follows.

2. - The display arrangement is configured such that at least a first subset of the plurality of pixels operates during the emission mode, and at least a second subset of the plurality of pixels operates during the sensing mode, and / or - The display arrangement is configured such that at least a first subset of the plurality of pixels operates during the emission mode, and at least a first subset of the plurality of pixels operates during the subsequent sensing mode, and / or - The display arrangement is configured such that at least a first subset of the plurality of pixels alternate between emitting mode and sensing mode. The display arrangement according to claim 1.

3. The display arrangement according to claim 2, wherein the pixels of a first subset of the plurality of pixels are arranged adjacent to the pixels of a second subset of the plurality of pixels.

4. - Further comprising a control device coupled to the pixel array for operating at least a portion of the plurality of pixels, The display arrangement according to any one of claims 1 to 3.

5. The display arrangement according to any one of claims 1 to 4, wherein the first and second μLEDs in each of the plurality of pixels are separated by one of the third and fourth μLEDs.

6. The display arrangement according to any one of claims 1 to 5, wherein three μLEDs in each of the at least portion of the plurality of pixels are substantially arranged along a virtual line.

7. The first and second μLEDs have an external quantum efficiency greater than 0.15 in reverse bias for light with wavelengths between 500 nm and 535 nm and between 575 nm and 620 nm, and in particular, greater than 0.2 for light with wavelengths between 500 nm and 535 nm and greater than 0.14 for light with wavelengths between 480 nm and 620 nm. The display arrangement according to any one of claims 1 to 6.

8. The transmittance of the first color filter described above is greater than 80% for light with a wavelength greater than 600 nm, more particularly greater than 90% for light with a wavelength greater than 620 nm, more particularly greater than 85% for light with a wavelength greater than 600 nm, and / or The transmittance of the second color filter is greater than 60% for light with wavelengths between 512 nm and 565 nm, more particularly greater than 70% for light with wavelengths between 520 nm and 560 nm, and more particularly greater than 75% for light with a wavelength of 540 nm. The display arrangement according to any one of claims 1 to 7.

9. The transmittance of the first color filter is less than 40% for light with a wavelength less than 570 nm, in particular less than 30% for light with a wavelength less than 570 nm, in particular less than 15% for light with a wavelength less than 570 nm, and / or The transmittance of the second color filter is less than 30% for light with wavelengths greater than 600 nm and less than 475 nm, and in particular less than 20% for light with wavelengths less than 450 nm. The display arrangement according to any one of claims 1 to 8.

10. The display arrangement according to any one of claims 1 to 9, wherein at least one of the first and second color filters is placed on the light-emitting surface of each of the first and second μLEDs.

11. - Further comprising a transparent cover positioned above the main radiating surface of the plurality of pixels arranged in rows and columns, the transparent cover comprising a plurality of first color filters positioned opposite the radiating region of the first μLED and a second color filter positioned opposite the radiating region of the second μLED, The display arrangement according to any one of claims 1 to 10.

12. The display arrangement according to any one of claims 1 to 11, wherein the area of ​​at least one of the first and second color filters is larger than the radiating area of ​​the μLED associated with the color filter.

13. A method for operating a display arrangement having multiple pixels, wherein each pixel is - Two μLEDs configured to emit light of the red spectrum, wherein a first color filter having a high transmittance of the red spectrum is placed on the first of the two μLEDs, and a second color filter having a high transmittance of the green spectrum is placed on the second of the two μLEDs, - A third μLED configured to emit light in the blue spectrum, - comprising a fourth μLED configured to emit light of the green spectrum, The aforementioned method, - A step of biasing the first μLED, the third μLED, and the fourth μLED of at least a first subset of the plurality of pixels in the forward direction corresponding to the emission mode during a first period, A method comprising the step of biasing the first μLED, the second μLED, and the third μLED of at least a second subset of the plurality of pixels in the reverse direction corresponding to a sensing mode in a second period.

14. - A step of biasing the first μLED, the second μLED, and the third μLED of at least the first subset of the plurality of pixels in the reverse direction within a third period, - Further comprising the step of forward-biasing the first μLED, the third μLED, and the fourth μLED of at least the second subset of the plurality of pixels within a fourth period, The method according to claim 13.

15. The method according to any one of claims 13 or 14, wherein the first period and the second period overlap at least partially, and the third period and the fourth period overlap at least partially.

16. The method according to any one of claims 13 to 15, wherein the pixels of the first subset of the plurality of pixels are arranged adjacent to the pixels of the second subset of the plurality of pixels.

17. A display arrangement according to any one of claims 1 to 12, - An in-display scanner, wherein the object to be scanned is placed on the display arrangement, - In-display PPG sensor, - Used as one of the in-display fingerprint sensors.

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