Display device for local brightness adjustment and methods of operating and manufacturing thereof

Abstract

A display device (1) comprises a substrate (10) comprising a main surface (12) and a plurality of emitters (20) configured to emit light during operation, the emitters (20) being arranged in pixels (2) on the main surface (12) of the substrate (10), wherein the pixels (2) form a display. It further comprises a plurality of sensors (30) distributed over the display, the sensors (30) being configured to sense ambient light during operation, and a control circuit (40) being configured to locally adjust a brightness of light emitted by the emitters (20) based on the ambient light sensed by the sensors (30). Methods of operating and manufacturing such a display device (1) are also provided. The emitters and sensors can be implemented as micro-LEDs.

Description

[0001] Description

[0002] DISPLAY DEVICE FOR LOCAL BRIGHTNESS ADJUSTMENT AND METHODS OF OPERATING AND MANUFACTURING THEREOF

[0003] A display device , a method of operating a display device and a method of manufacturing a display device are speci fied .

[0004] Ambient light directly reflecting on a display screen makes the proj ected images washed-out and hard to view . Systems may overcome this issue with a sensor cell placed somewhere around the display . Based on a measurement , a global correction may be applied on the display settings to improve image quality . The brightness may be lowered in dark locations and raised in bright locations . This correction may be done uni formly i f all display pixels undergo the same treatment .

[0005] At least one obj ect of particular embodiments is to provide in-display sensing . At least one further obj ect of particular embodiments is to provide local brightness adj ustment for a display .

[0006] This obj ect is achieved by the subj ect-matter and the methods according to the independent claims . Advantageous embodiments and developments of the subj ect-matter and the method are characteri zed in the dependent claims , and are also disclosed by the following description and the drawings .

[0007] According to at least one embodiment , a display device is provided . The display device comprises a display . For example , the display device is or is integrated in a touch screen, a smartwatch, a smartphone , a tablet , a dashboard, or an automotive dashboard .

[0008] According to at least one embodiment , the display device comprises a substrate comprising a main surface .

[0009] The substrate may also be called carrier or backplane . For example , the substrate is implemented as silicon backplane or as flex-plane . The substrate can be or can comprise a foil , for instance . Thus , the substrate can be rigid or flexible . The substrate has a main plane of extension . Here and in the following, lateral directions refer to directions that run parallel to the main plane of extension . The vertical direction refers to a direction that runs perpendicular to the main plane of extension . The main surface of the substrate is parallel to the main plane of extension of the substrate .

[0010] According to at least one embodiment , the display device comprises a plurality of emitters configured to emit light during operation, the emitters being arranged in pixels on the main surface of the substrate .

[0011] This can mean that the emitters are arranged in groups . The pixels may form rectangular or square regions on the main surface of the substrate , wherein said regions are adj acent to each other in lateral directions . The pixels form the display of the display device . Each pixel can comprise one or more emitters . Further, each pixel can comprise wirings to electrically connect the emitters . The pixels and / or the emitters in the pixels can be operated individually or in groups . That the emitters are arranged on the main surface of the substrate can mean that they are mounted on the main surface . This can mean that they are not integrated or embedded in the substrate . For example , they are attached to the substrate by means of a trans fer process , in particular a mass trans fer process , by which a plurality of emitters are attached to the substrate simultaneously . Here and in the following, light may refer to electromagnetic radiation in general . Each emitter is for example configured to emit electromagnetic radiation in a main emission direction during intended operation . The main emission direction is preferably oriented perpendicular to the main surface of the substrate , i . e . along the vertical direction . In particular, each emitter is configured to emit electromagnetic radiation having a main wavelength in the spectral region visible to the human eye , i . e . between 380 nm and 750 nm . Di f ferent emitters may emit light in di f ferent wavelength ranges . Each pixel may comprise one or more emitters . Each pixel may comprise at least three emitters that emit red, green and blue light , respectively, for covering the visible wavelength range . Each pixel may also comprise more than three emitters to provide a certain degree of redundancy and / or additional functionality .

[0012] According to at least one embodiment , the display device comprises a plurality of sensors distributed over the display, the sensors being configured to sense ambient light during operation .

[0013] This can mean that at least some of the pixels comprise a sensor . In a possible implementation, each pixel comprises at least one sensor . However, it is also possible that only a subset of pixels comprises at least one sensor . For example , each pixel or each second or each third pixel comprises a sensor . Preferably, the sensors are evenly distributed over the display . The pixels may comprise a respective sensor together with at least one emitter . However, it is also possible , that the display device comprises dedicated pixels with a sensor but no emitter . It is further possible , that more than one sensor is arranged in a single pixel . That the sensors are configured to sense ambient light during operation can mean that the sensors do not sense display light , i . e . light emitted by the emitters . The sensors can generate a detection signal based on the intensity of the detected ambient light . The sensors may be sensitive to a particular wavelength range in the visible spectrum . The sensors can be the same or di f ferent . That the sensors are di f ferent can mean that their sensitivities for particular wavelengths di f fer from each other . However, at least some of the sensors can have same or similar sensitivities for particular wavelength ranges . The sensor can have a viewing angle . In particular, the viewing angle includes the vertical direction, such that the sensor is a "top-looking" sensor . The field of illumination of the emitters and the field of view of the sensor may at least overlap .

[0014] According to at least one embodiment , the display device comprises a control circuit being configured to locally adj ust a brightness of light emitted by the emitters based on the ambient light sensed by the sensors .

[0015] For example , the control circuit is integrated in the substrate . It is however also possible that the control circuit is arranged on the main surface of the substrate next to the pixels or in the pixels . The control circuit can also be arranged on an opposite rear surface of the substrate and can be electrically connected to the pixels by through- substrate-vias , TSVs . Further, the control circuit can be arranged in or on a further substrate that is electrically connected to the substrate by means of electrical interconnections . The control circuit can comprise circuitry for driving and biasing the emitters . Thus , the control circuit can comprise driving circuitry for the emitters and can be electrically connected to at least some of the emitters in the pixels . The display device can comprise more than one control circuit or the control circuit can be partitioned . For example , each control circuit or each partition is assigned to a group of pixels , e . g . to a group of 16 x 16 pixels . The respective control circuit or partition can drive the emitters in said group of pixels . The emitters and / or the pixels with the emitters can be controlled individually or at least in groups by the at least one control circuit . Thus , a brightness of the display light can be adj usted locally and dynamically . For example , a first area of the display can be controlled to have a larger brightness than a second area of the display, or vice versa . The brightness of the emitted light is adj usted based on the sensed ambient light . This can mean that the control circuit further comprises evaluation circuitry for the sensors and can be electrically connected to at least some of the sensors in the pixels . The control circuit receives respective detection signals from the sensors and can evaluate said signals individually and separately . For example , a sensor in a first display area generates a di f ferent detection signal than a sensor in a second display area, which can mean that the light conditions in said display areas are di f ferent . For example , ambient light is locally shadowed by an obj ect above the display or an external light source results in a non- uni form light distribution around the display . Consequently, the control circuit adj usts the brightness of the emitted light in the first display area in a di f ferent way than the brightness of the emitted light in the second display area .

[0016] According to at least one embodiment , a display device comprises a substrate comprising a main surface . It further comprises a plurality of emitters configured to emit light during operation, the emitters being arranged in pixels on the main surface of the substrate , wherein the pixels form a display . It further comprises a plurality of sensors distributed over the display, the sensors being configured to sense ambient light during operation . It further comprises a control circuit being configured to locally adj ust a brightness of light emitted by the emitters based on the ambient light sensed by the sensors .

[0017] The display device described here is based on the following considerations , among others .

[0018] Displays , in particular micro-LED displays , have many metal layers to fan out the driver signal to the emitters . They are therefore not very transparent and behind display sensing technologies cannot be used as in e . g . OLED displays . It is therefore beneficial to use in-display sensing technology, where the sensors are embedded and integrated into the display such that no display notch is needed . In other words , integrating the sensors into the display removes any notches from the display without the need to enable behind display sensing .

[0019] The sensors are distributed over the display . The display can be partially or entirely populated with the sensors , thus forming a distributed ambient light sensor . While a locali zed ambient light sensor does not work when it is covered, a distributed ( delocali zed) in-display sensor has redundancies and can also work when the display ( e . g . of a smartphone ) is partially covered .

[0020] Further, the distributed ambient light sensor exhibits a 2D spatial resolution, allowing local detection of ambient light . Based on local measurements , an intensity-based correction can be applied on the display settings of the corresponding pixel . Instead of a global brightness adj ustment , brightness correction is allowed to be done locally at a pixel scale . Thus , readability of the displayed content for a user is enhanced and image quality is improved . Screen readability and visibility are improved especially for outdoor application where the sun or external light sources can be very detrimental . Thus , the proposed display device can be used to prevent local disturbances such as sun' s brightness or shadows of ambient illumination on a display . In addition, the correction can be done in real-time .

[0021] With more sensors for sensing ambient light disturbance the correction can be done at the pixel scale , i . e . very locally, which paves the way for a better screen display . In-display ambient light sensing of fers various technical possibilities including static disturbance correction, dynamic disturbance correction and power saving . For example , direct arti ficial light on a TV screen causes a static disturbance . In this case , only one sensing frame is required to acquire the static disturbance . The control circuit can adj ust the display brightness with a high resolution to compensate for the static disturbance . As another example , shades from nearby trees while driving cause dynamic disturbances on the display . Here , compensation is doable thanks to real-time feedback loop correction . It is also possible to speed up the correction by decreasing the resolution, i . e . by binning of the acquired image and coarse correction . Speed and resolution adj ustment with respect to the correction mode also comes with a potential power saving . In addition, smart brightness balance by local brightness adj ustments instead of a brightness boost of the whole display also saves power .

[0022] According to at least one embodiment , each emitter comprises a light emitting diode , LED, in particular micro-LED .

[0023] As a broad definition, a micro-LED could be seen as any light emitting diode ( LED) - generally not a laser - with a particularly small si ze . As a rule - and this is a very important criterion in addition to si ze - a growth substrate is removed from micro-LEDs , so that typical heights of such micro-LEDs are in the range of 0 . 5 pm to 10 pm, for example . In principle , a micro-LED does not necessarily have to have a rectangular radiation emission surface . Generally, for example , an LED could have a radiation emission surface in which, in plan view of the layers of the layer stack, any lateral extent of the radiation emission surface is less than or equal to 100 pm or less than or equal to 70 pm .

[0024] For example , in the case of rectangular micro-LEDs , an edge length - especially in plan view of the layers of the layer stack - smaller than or equal to 70 pm or smaller than or equal to 50 pm is often cited as a criterion . Mostly, such micro-LEDs are provided on wafers with - for the pLED nondestructive^ - detachable holding structures . At present , micro-LEDs are mainly used in displays . The micro-LEDs form pixels or subpixels and emit light of a defined color . Small pixel si ze and a high density with close distances make micro-LEDs suitable , among others , for small monolithic displays for AR applications, especially data glasses. In addition, other applications are being developed, in particular regarding the use in data communication or pixelated lighting applications. Different ways of spelling micro-LED, e.g. pLED, p-LED, uLED, u-LED or micro light emitting diode can be found in the relevant literature.

[0025] According to at least one embodiment, each sensor is formed as a photodiode, wherein the photodiode is embedded in the substrate .

[0026] This can mean that the photodiode, RD, is integrated in the substrate and / or formed in the substrate. Thus, the photodiode is an embedded photodiode. In particular, if the substrate comprises silicon, the photodiode can be a silicon photodiode, but other material are also possible. For efficiency reasons, the silicon photodiode can have a larger size in lateral directions and can be thicker than the emitters. Silicon photodiodes are suitable to detect visible light. The substrate on which the emitters are arranged thus has additional sensing capabilities. The emitters can be arranged on regions of the substrate outside the photodiodes.

[0027] Alternatively, the photodiode is arranged on the main surface of the substrate next to the emitters.

[0028] Such a photodiode can form a separate detector chip. In particular, the photodiode can be a micro-PD. This can mean that the photodiode has a similar size as each of the emitters, in particular if they are formed as micro-LEDs. It is also possible that the photodiode has a larger size for efficiency reasons. If the photodiode is arranged on the substrate, its thickness can preferably be similar or equal to the thickness of the emitters . That the photodiode is arranged on the substrate can mean that it is mounted on the substrate , for example by means of a (mass- ) trans fer process . That the photodiode is arranged next to the emitters can mean that the photodiode and the emitters are arranged in a common pixel or in adj acent / near pixels .

[0029] According to at least one embodiment , each sensor is implemented as an LED, in particular micro-LED, that is arranged on the main surface of the substrate next to the emitters and configured to be biased for sensing a photocurrent .

[0030] That each sensor is implemented as (micro- ) LED can mean that the sensors and the emitters have a same or similar structure . In particular, the sensors and the emitters may be formed by a common semiconductor layer stack . Designed as an LED, the sensor can emit light when appropriately biased, in particular i f the sensor is forward biased . However, i f the sensor is zero biased or reverse biased, it is configured to sense a photocurrent depending on light hitting the sensor . It has been found that the external quantum ef ficiency, EQE , of micro-LEDs in reverse or zero bias can reach values above 20% depending on the wavelength to be detected . Thus , additional red and / or blue and / or green micro-LEDs can be placed in some or all pixels for sensing . As mentioned above , the pixels may comprise additional emitters like (micro- ) LEDs for redundancy reasons anyway . These additional emitters can be used as sensors , thus reducing complexity of the manufacturing process . The (micro- ) LEDs can be operated and biased depending on whether they are used as emitters or as sensors . Dynamic use as emitter and sensor is also possible . This means that an emitter can be used as sensor by dynamically changing its electrical bias , e . g . by integrating a multiplexer in the driving circuit . Biasing LEDs for sensing a photocurrent represents a simple and cost-ef ficient solution to provide sensing capabilities of a display device . By using reverse or zero biased micro-LEDs additional components other than display components are not required .

[0031] According to at least one embodiment , at least a subset of the plurality of sensors is implemented as red micro-LED that is configured to be biased for sensing a photocurrent .

[0032] A red micro-LED denotes a micro-LED that can emit red light i f properly biased . However, said red micro-LED is configured to be biased for sensing a photocurrent . It has been found that red micro-LEDs in reverse or zero bias can detect light in a main portion of the visible spectrum, in particular light at wavelengths between 400 nm and 700 nm . For wavelengths between 500 and 600 nm the EQE of red micro-LED even reaches values above 20% .

[0033] According to at least one embodiment , at least a further subset of the plurality of sensors is implemented as blue or green micro-LED that is configured to be biased for sensing a photocurrent .

[0034] A blue / green micro-LED denotes a micro-LED that can emit blue / green light i f properly biased . However, said blue / green micro-LED is configured to be biased for sensing a photocurrent . It has been found that the EQE of blue / green micro-LED is even larger than the EQE for red micro-LED for light in a wavelength range from about 350 nm to 500 nm and reaches values above 20% . Thus , red, green and blue light emitting micro-LEDs used in combination as sensors span the entire visible spectrum . In other words , the EQE curves of the blue or green and the red micro-LED match together to span the visible wavelength range . Thus , additional red or blue / green micro-LEDs can be placed in some or all pixels for sensing .

[0035] According to at least one embodiment , the emitters and the sensors are manufactured according to a common manufacturing process .

[0036] This can mean that at least some process steps for manufacturing the emitters are also used for manufacturing the sensors . This is in particular true i f both the emitters and the sensors are formed as (micro- ) LEDs . Thus , the emitters and the sensors can be fabricated on a common carrier substrate . They can simultaneously be trans ferred to the substrate of the display device . Therefore , fabrication of the display device is facilitated and costs are reduced . It is also possible to trans fer all display LEDs with double density for redundancy to avoid broken LED repair . LEDs that are not used for emitting light but are functional can be used for sensing . This would mean that the distributed ambient light sensor has a coverage of less than 100% but could still have a satis factory functionality .

[0037] According to at least one embodiment , the pixels are formed as RGB-pixels , in which a first emitter configured to emit red light , a second emitter configured to emit green light , and a third emitter configured to emit blue light are arranged .

[0038] In particular, each emitter of a pixel is intended to emit radiation of a di f ferent main wavelength . A main wavelength is to be understood as a wavelength in an emission spectrum where the intensity reaches a global maximum . For example , the first emitter is intended to emit radiation of a red color, the second emitter is intended to emit radiation of a green color, and the third emitter is intended to emit radiation of a blue color in its intended operation . Such a red, green, blue ( short : RGB ) arrangement is especially suitable for a pixel of a display device . Red light may refer to light in a wavelength range from 640 nm to 780 nm, for example . Green light may refer to light in a wavelength range from 490 nm to 570 nm, for example . Blue light may refer to light in a wavelength range from 430 nm to 490 nm . Thus , the entire visible spectrum is covered by additive color mixing of the three components R, G and B . As mentioned above , the emitters may be formed by respective LEDs , in particular micro-LEDs . Depending on the light color the LEDs can comprise di f ferent semiconductor materials , as for example gallium arsenide ( GaAs ) , gallium arsenide phosphide ( GaAsP ) , gallium phosphide ( GaP ) , aluminum indium gallium phosphide (Al InGaP ) , indium gallium nitrogen ( InGaN) and / or gallium nitride ( GaN) . In a possible implementation, each pixel is formed as an RGB-pixel comprising a red light emitter, a green light emitter and a blue light emitter . The pixel can also comprise more than one emitter for each color, for example to provide a certain degree of redundancy .

[0039] According to at least one embodiment , each sensor is arranged in a respective pixel of the display device together with at least one emitter of the plurality of emitters .

[0040] In other words , the pixels comprise emitters and sensors . In particular, each pixel may comprise at least one emitter and at least one sensor. Thus, the sensors are integrated in the display on a pixel-scale.

[0041] According to at least one embodiment, each sensor of the plurality of sensors is configured to locally sense ambient light .

[0042] In other words, the sensors may generate different detection signals dependent on their location within the display and the ambient light around the display. For example, a first location of the display is shadowed by an object above the display resulting in a different light distribution of ambient light over the display. As another example, a second location of the display is illuminated by an external artificial light source that produces a non-uniform light distribution over the display. As the sensors are distributed over the display, the distributed ambient light sensor has a 2D spatial resolution.

[0043] According to at least one embodiment, the control circuit is configured to adjust the brightness of light emitted by the emitters at a pixel scale.

[0044] This can mean that each pixel can be controlled individually with respect to its brightness. At least, small groups of neighboring pixels can be controlled with respect to their brightness. This is possible since the local light condition in known by means of the sensors that are distributed over the display. Thus, the brightness of the display light does not have to be adjusted as a whole over the entire display.

[0045] In addition, the brightness of light emitted by the emitters can be adjusted in real-time, i.e. based on a recent measurement frame of the sensors . Thus , a real-time feedback loop is provided for dynamic disturbance correction .

[0046] Further, an optoelectronic device comprising the display device is provided . This means that all features disclosed for the display device are also disclosed for the optoelectronic device and vice versa . In particular, the optoelectronic device can be a personal computer, a smartphone , a smart watch, a tablet , a laptop, a TV, or a dashboard . For example , the display device is integrated in a cockpit monitor or dashboard of a car, ferry, train, airplane or another vehicle , where direct sun light can be disturbing and can lead to potentially unsafe situations .

[0047] Further, a method of operating a display device is provided . The method of operating can preferably be carried out with the display device described above . This means that all features disclosed for the display device are also disclosed for the method of operating the display device and vice versa .

[0048] According to at least one embodiment , the method of operating the display device is carried out with a display device comprising a plurality of emitters being arranged in pixels on a main surface of a substrate , the pixels forming a display, a plurality of sensors distributed over the display, and a control circuit .

[0049] According to at least one embodiment , the method comprises emitting light by the emitters . In particular, light is emitted by the emitters in a main direction that runs perpendicular to the main surface of the substrate . Each emitter has a field of illumination . The light emitted by the emitters refers to display light . By emitting light content can be displayed on the display .

[0050] According to at least one embodiment , the method further comprises sensing ambient light by the sensors . Preferably, the emitters and the sensors are arranged such that display light is not sensed by the sensors . For example , light barriers are arranged between the emitters and the sensors and / or the sensors are outside the field of illumination of the emitters and / or the sensors are disabled when the emitters are on and enabled when the emitters are of f . Each sensor may provide a di f ferent detection signal depending on its location within the display and the ambient light around the display . Thus , ambient light is sensed locally .

[0051] According to at least one embodiment , the method further comprises locally adj usting, by the control circuit , a brightness of the emitted light based on the sensed ambient light . Since the intensity of the ambient light is known locally by means of the distributed sensors , the brightness of the display light can be controlled on a pixel scale in order to compensate for the di f ferent light conditions . For example , i f parts of the display are shadowed by an obj ect above the display, the local brightness of the display in that parts can be adj usted accordingly to ensure readability of the displayed content for a user .

[0052] According to at least one embodiment , the method of operating a display device , wherein the display device comprises a plurality of emitters being arranged in pixels on a main surface of a substrate , the pixels forming a display, a plurality of sensors distributed over the display, and a control circuit , comprises emitting light by the emitters ; sensing ambient light by the sensors, and adjusting locally, by the control circuit, a brightness of the emitted light based on the sensed ambient light.

[0053] By the operating method in-display sensing is enabled. The sensors form a distributed ambient light sensor enabling sensing even if some of the sensors are covered. Further, the distributed ambient light sensor allows local detection of ambient light, such that an intensity-based correction can be applied on the display settings of the corresponding pixel. Thus, instead of a global brightness adjustment, brightness correction is allowed to be done locally at a pixel scale. Thus, readability of the displayed content for a user is enhanced and image quality is improved. Potentially, display power is saved compared to current solutions that basically increase significantly the brightness of the full display area .

[0054] According to at least one embodiment, the method further comprises adjusting the brightness of the emitted light by pulse width modulation.

[0055] Pulse width modulation, PWM, for LEDs is a technique used to control the brightness of an LED by varying the duty cycle of a pulsating electrical signal. In PWM, the LED is rapidly turned on and off at a fixed frequency, and the average intensity of light perceived by the human eye depends on the ratio of time the LED is on (the on-state) to the time it is off (the off-state) during each cycle. PWM is an efficient and effective way to control LED brightness without changing the LED's forward current. According to at least one embodiment , sensing ambient light is performed when the emitters are in an of f-state during the pulse width modulation . Thus , sensing can be synchroni zed to the pulse width modulation of the LEDs . Thus , light emitted by emitters is prevented from being sensed by the sensors . This allows to distinguish between ambient light and display light . Thus , the surrounding light can be measured and disturbing crosstalk from the display light can be avoided .

[0056] According to at least one embodiment , sensing ambient light is performed continuously during the pulse width modulation and the sensed light is evaluated by filtering a detection signal in frequency space .

[0057] This can mean that light is sensed during the full PWM cycle , i . e . during the on- and the of f-state of the LEDs . Thus , the detection signal contains information about ambient light and (backscattered) display light . By knowing the PWM frequency post-processing is possible to filter the display light channel out of the detection signal and to obtain the pure ambient light channel .

[0058] Further, a method of manufacturing a display device is provided . All features disclosed for the display device are also disclosed for the method of manufacturing the display device and vice-versa .

[0059] The method of manufacturing the display device comprises providing a substrate . For example , the substrate is or is formed by a backplane or a flex-plane . For example , the substrate comprises silicon or a foil . The method of manufacturing the display device further comprises mounting a plurality of emitters on a main surface of the substrate , wherein the emitters are arranged in pixels forming a display and each emitter is configured to emit light during operation . In particular, the emitters can be formed by micro-LEDs and mounting the emitters on the substrate comprises a mass trans fer of said emitters from a carrier substrate to the substrate of the display device . For example , an elastomer stamp is used for the mass trans fer .

[0060] The method of manufacturing the display device further comprises forming a plurality of sensor, the sensors being configured to sense light during operation . It further comprises distributing the sensors over the display .

[0061] The method of manufacturing the display device further comprises providing a control circuit that is configured to locally adj ust a brightness of light emitted by the emitters based on the ambient light sensed by the sensors . The control circuit can be integrated in the substrate . It is also possible that the control circuit is arranged on the main surface of the substrate next to the pixels or in the pixels . The control circuit can also be arranged on an opposite rear surface of the substrate and can be electrically connected to the pixels by through-substrate-vias , TSVs . Further, the control circuit can be arranged in or on a further substrate that is electrically connected to the substrate by means of electrical interconnections .

[0062] Advantageously, a display device with in-display ambient light sensing can be manufactured . The sensors form a distributed ambient light sensor enabling sensing even i f some of the sensors are covered . Further, the distributed ambient light sensor allows local detection of ambient light , such that an intensity-based correction can be applied on the display settings of the corresponding pixel . Thus , instead of a global brightness adj ustment , brightness correction is allowed to be done locally at a pixel scale . Thus , readability of the displayed content for a user is enhanced and image quality is improved . Potentially, display power is saved compared to current solutions that basically increase signi ficantly the brightness of the full display area .

[0063] According to at least one embodiment , forming the sensors comprises embedding photodiodes in the substrate . Thus , forming the sensor may comprise embedding a photodiode in the substrate . This can mean, for example , that the substrate is semiconductor substrate and the photodiode is formed in the substrate by a semiconductor manufacturing process , e . g . a CMOS process . Thus , the photodiode is integrated in the substrate .

[0064] Alternatively, forming the sensors may comprise mounting photodiodes on the main surface of the substrate next to the emitters . This can mean that the photodiodes form single detector chips that are trans ferred onto the substrate and attached to it . For example , each photodiode is a microphotodiode and trans ferred to the substrate in a similar way as the emitters , in particular by means of a further mass trans fer .

[0065] As a further alternative , forming the sensors may comprise mounting LEDs , in particular micro-LED, on the main surface of the substrate next to the emitters , and biasing said LEDs for sensing a photocurrent . Said "sensor-LEDs" may have a similar or same structure as the "emitter-LEDs" . Thus , the sensors and the emitters may be formed by a common manufacturing process and they may be trans ferred simultaneously to the substrate . The sensors and the emitters may di f fer only in the way they are biased . For example , the sensors are reverse biased or zero biased (micro- ) LEDs . I f (micro- ) LEDs are used as sensors , fabrication can be facilitated, as both emitters and sensors can have the same structure and can be manufactured according to a common manufacturing process .

[0066] The following description of Figures may further illustrate and explain aspects of the display device , the operating method and the manufacturing method . Components and parts of the display device that are functionally identical or have an identical ef fect are denoted by identical reference symbols . Identical or ef fectively identical components and parts might be described only with respect to the Figures where they occur first . Their description is not necessarily repeated in successive Figures .

[0067] Figures 1 to 2 show display devices according to embodiments of the present invention .

[0068] Figure 3 shows the external quantum ef ficiency of micro-LEDs .

[0069] Figure 4 shows an optoelectronic device according to an embodiment .

[0070] Figure 5 shows a method of operating a display device according to an embodiment .

[0071] Figure 6 shows a method of manufacturing a display device according to an embodiment . With Figure 1 a top-view of a display device 1 according to an embodiment is shown . The display device comprises a substrate 10 with a main surface 12 ( in Figure 1 only the main surface 12 is shown) . The display device 1 further comprises a plurality of emitters 20 configured to emit light during operation, the emitters 20 being arranged in pixels 2 on the main surface 12 of the substrate 10 . The pixels 2 form a display . The display device 1 further comprises a plurality of sensors 30 distributed over the display, the sensors 30 being configured to sense ambient light during operation . The display device 1 further comprises a control circuit 40 being configured to locally adj ust a brightness of light emitted by the emitters 20 based on the ambient light sensed by the sensors 30 .

[0072] The control circuit 40 is not shown in Figure 1 . For example , the control circuit 40 is arranged on an opposite rear surface of the substrate 10 or it is arranged on a separate substrate or it is arranged next to the pixels 2 . The control circuit 40 is electrically connected to the emitters 20 and the sensors 30 .

[0073] It can be seen that the pixels 2 form rectangular adj acent regions of the display, thereby forming an array . In the embodiment of Figure 1 the pixels 2 are implemented as RGB- pixels , in which a first emitter 20- 1 configured to emit red light , a second emitter 20-2 configured to emit green light , and a third emitter 20-3 configured to emit blue light are arranged . Thus , each pixel 2 can emit light of the entire visible spectrum by additive color mixing of the three components R, G and B . For example , the emitters 20 each comprise a light emitting diode , LED . In particular, each emitter 20 can comprise a micro-LED .

[0074] In the embodiment of Figure 1 each pixel 2 with the emitters 20 additionally comprises one sensor 30 . In other words , each sensor 30 is arranged in a respective pixel 2 of the display device 1 together with the three emitters 20- 1 , 20-2 , 20-3 of the plurality of emitters 20 . Thus , the sensors 30 are distributed over the display . In Figure 1 the emitters 20 and the sensor 30 are arranged along a diagonal of each pixel 2 . However, other arrangements are also possible . It is also possible that the sensors 30 are not integrated in the same pixels 2 as the emitters 20 but in separate sensor pixels next to or between the emitter pixels .

[0075] Each sensor 30 may be formed as a photodiode , wherein the photodiode is embedded in the substrate 10 . In particular, i f the substrate 10 is a semiconductor substrate , the sensors 30 can be integrated in the substrate 10 . That is , they can be part of the substrate 10 , while the emitters 20 are mounted on the substrate 10 . However, it is also possible that the sensors are formed as photodiodes , in particular microphotodiodes , that are arranged on the main surface 12 of the substrate 10 next to the emitters 20 . In other words , such photodiodes can form separate detector chips that are mounted on the main surface 12 of the substrate 10 .

[0076] In still another embodiment , the sensors 30 are implemented as LEDs , in particular micro-LEDs , that are arranged on the main surface 12 of the substrate 10 next to the emitters 20 and configured to be biased for sensing a photocurrent . In that case , the emitters 20 and the sensors 30 can be manufactured according to a common manufacturing process . Further, they can have the same or a similar structure . For example , each sensor 30 or at least a subset of sensors 30 can be implemented as red micro-LED that is configured to be biased for sensing a photocurrent . In forward bias , said red LED would emit red light . I f reverse or zero biased, however, said LED can detect light by sensing a photocurrent . It has been found that red micro-LEDs biased for sensing light cover a main portion of the visible wavelength range . As another example , each sensor 30 or at least a further subset of sensors 30 can be implemented as blue or green micro-LED that is configured to be biased for sensing a photocurrent . In forward bias , said blue or green LED would emit blue or green light , respectively . I f reverse or zero biased, however, said LED can detect light by sensing a photocurrent . It has been found that blue and green micro-LEDs have an even larger external quantum ef ficiency than red micro-LEDs in a wavelength range between 350 nm and 500 nm .

[0077] It should be noted that , since the sensors 30 are distributed over the display, they are configured to locally sense ambient light , i . e . on a pixel scale . This allows fluctuations in lighting conditions on the display to be detected . The sensors 30 sense the local intensity of the ambient light . In turn, the control circuit 40 is configured to adj ust the brightness of light emitted by the emitters 20 at a pixel scale . This means that the control circuit 40 can adj ust the brightness of each pixel 2 individually based on the ambient light sensed by the sensor 30 in said pixel 2 or by sensors 30 in the vicinity of said pixel 2 .

[0078] With Figure 2 a cross-sectional view of the display device 1 is shown . Figure 2 may show the cross-section of one pixel 2 . It can be seen that the emitters 20 and the sensor 30 are arranged on the main surface 12 of the substrate 10 . In the embodiment of Figure 2 the control circuit 40 is embedded in the substrate 10 . The display device 1 further comprises a transparent cover 60 . The cover 60 is arranged in a vertical direction above the main surface 12 of the substrate 10 , such that the emitters 20 and the sensor 30 are covered .

[0079] With Figure 3 the external quantum ef ficiency, EQE , of microLEDs as function of the wavelength X is shown . R- fw, G- fw and B- fw denote the EQE curves of forward biased red (R) , green ( G) and blue (B ) micro-LEDs , respectively . It can been seen that the micro-LEDs exhibit a narrow emission spectrum around their respective main emission wavelength . In addition, the EQE of a red micro-LED in reverse bias , R_rev, is shown . It can be seen that such a reverse biased micro-LED can cover a main portion of the visible spectrum for sensing light . Thus , the intensity of the ambient light can be detected by a sensor 30 that is implemented as reverse biased red micro- LED . As mentioned above , the display device 1 can also use blue and / or green micro-LEDs as sensors 30 to cover the full visible spectrum with a good EQE .

[0080] Figure 4 shows an optoelectronic device 100 comprising the display device 1 . The display device 1 comprises a plurality of pixels 2 forming the display . The plurality of pixels 2 are arranged in an array on the main surface 12 of the substrate 10 , as indicated in Figure 4 . The display device 1 further comprises a control circuit 40 . Based on the light sensed by the one or more sensors 30 , the control circuit 40 is configured to evaluate ambient light around the display and to adj ust the brightness of the emitters 20 in the pixels

[0081] 2 . The control circuit 40 is electrically connected to the substrate 10 and the pixels 2 on the substrate 10 by means of electrical interconnections 45. The electrical interconnections 45 can be formed as flex connection, for example. The optoelectronic device 100 is, for example, a personal computer, a smartphone, a smart watch, a tablet, a laptop, a TV, or a dashboard.

[0082] Figure 5 shows a possible operating method for the display device 1. The method comprises emitting light by the emitters 20. In the shown example the emitters 20 comprise a first emitter 20-1 configured to emit red light, a second emitter 20-2 configured to emit green light and a third emitter 20-3 configured to emit blue light. The method further comprises sensing ambient light AL by the sensors 30. The method further comprises adjusting locally, by the control circuit 40, a brightness of the emitted light based on the sensed ambient light.

[0083] The brightness of the emitted light is adjusted by pulse width modulation, PWM, as shown in Figure 5. The brightness can be adjusted separately for each of the emitters 20, in particular the red LED 20-1, the green LED 20-2 and the blue LED 20-3. However, the on-states and off-states of the LEDs may be synchronized, such that there is a common on-state phase and a common off-state phase. In other words, a PWM frequency f may be the same for all emitters 20, as shown in Figure 5. To detect ambient light AL by means of the sensor 30, the detection is locked to time frames TA, in which the display is not on. The sensor 30 may be disabled when the emitters 20 are on. The on-states of the display are given by the pulse width modulation frequency and duty cycle. Having a dedicated ambient light sensing window TA may refer to a PWM lock-in detection mode of the display device 1. Alternatively, ambient light sensing is performed continuously during the pulse width modulation and the sensed light is evaluated by filtering a detection signal in frequency space. Thus, sensed ambient light AL can be distinguished from backscattered display light.

[0084] With Figure 6 a manufacturing process of the display device 1 is shown schematically. The method comprises the following steps that are not necessarily carried out in this order but can be carried out in this order.

[0085] In a first step SI, a substrate 10 is provided. For example, the substrate 10 is implemented as silicon backplane or as flex-plane .

[0086] In a second step S2, a plurality of emitters 20 are mounted on the main surface 12 of the substrate 10, wherein the emitters 20 are arranged in pixels 2 and each emitter 20 is configured to emit light during operation. The pixels 2 form a display. Mounting the emitters 20 can comprise a transfer process, in particular mass transfer process, by which a plurality of emitters 20 are attached to the substrate 10 simultaneously. For example, an elastomer stamp is used for the mass transfer.

[0087] In a third step S3, a plurality of sensors 30 is formed, the sensors being configured to sense ambient light during operation. Further, the sensors 30 are distributed over the display. Forming the sensors 30 may comprise embedding photodiodes in the substrate 10, in particular if the substrate 10 is a silicon substrate 10. This can be done by a semiconductor process, e.g. a CMOS process. In this case, forming the sensors 30 can be performed before mounting the emitters 20 on the substrate 10 . Forming the sensors 30 may also comprise mounting photodiodes on the main surface 12 of the substrate 10 next to the emitters 20 . In this case the photodiodes may be formed by separate detector chips that are trans ferred and attached to the substrate 10 . Forming the sensors 30 may also comprise mounting LEDs , in particular micro-LEDs , on the main surface 12 of the substrate 10 next to the emitters 20 , and biasing said LEDs for sensing a photocurrent . Said sensing (micro- ) LEDs can have the same structure as the emitters 20 . Thus , they can be formed in a same manufacturing process and they may be trans ferred to the substrate 10 in the same trans fer process as the emitters 20 . Biasing said LEDs for sensing a photocurrent can mean that these sensing LEDs are zero biased or reverse biased .

[0088] In a fourth step S4 , a control circuit 40 is provided that is configured to locally adj ust a brightness of light emitted by the emitters 20 based on the ambient light sensed by the sensors 30 . The control circuit 40 can be embedded in the substrate 10 . In this case , the control circuit 40 can be manufactured, e . g . by means of a ( CMOS- ) semiconductor process flow, before mounting the emitters 20 on the main surface 12 of the substrate 10 . However, the control circuit 40 can also be a separate chip that is attached to the substrate 10 or to a further substrate . Further, the control circuit 40 is electrically connected to the pixels 2 or a subset of pixels 2 . The control circuit 40 comprises driving circuitry for biasing the emitters 20 . The control circuit further comprises evaluation circuitry for receiving and evaluating detection signals from the sensors 30 .

[0089] The embodiments of the display device and the methods of operating and manufacturing the display device disclosed herein have been discussed for the purpose of familiari zing the reader with novel aspects of the idea . Although preferred embodiments have been shown and described, many changes , modi fications , equivalents and substitutions of the disclosed concepts may be made by one having skill in the art without unnecessarily departing from the scope of the claims .

[0090] It will be appreciated that the disclosure is not limited to the disclosed embodiments and to what has been particularly shown and described hereinabove . Rather, features recited in separate dependent claims or in the description may advantageously be combined . Furthermore , the scope of the disclosure includes those variations and modi fications , which will be apparent to those skilled in the art and fall within the scope of the appended claims .

[0091] The term " comprising" , insofar it was used in the claims or in the description, does not exclude other elements or steps of a corresponding feature or procedure . In case that the terms " a" or " an" were used in conj unction with features , they do not exclude a plurality of such features . Moreover, any reference signs in the claims should not be construed as limiting the scope .

[0092] This patent application claims the priority of German patent application 102023125785 . 4 , the disclosure content of which is hereby incorporated by reference . References

[0093] 1 display device

[0094] 2 pixel 10 substrate

[0095] 12 main surface

[0096] 20 emitter

[0097] 20- 1 first emitter

[0098] 20-2 second emitter 20-3 third emitter

[0099] 30 sensor

[0100] 40 control circuit

[0101] 45 electrical interconnection

[0102] 60 cover 100 optoelectronic device

[0103] AL ambient light

[0104] S I to S5 manufacturing steps

[0105] TA ambient light detection window

Claims

Claims1. Display device (1) , comprising:- a substrate (10) comprising a main surface (12) ,- a plurality of emitters (20) configured to emit light during operation, the emitters (20) being arranged in pixels (2) on the main surface (12) of the substrate (10) , wherein the pixels (2) form a display,- a plurality of sensors (30) distributed over the display, the sensors (30) being configured to sense ambient light during operation, and- a control circuit (40) being configured to locally adjust a brightness of light emitted by the emitters (20) based on the ambient light sensed by the sensors (30) .

2. Display device (1) according to claim 1, wherein each emitter (20) comprises a light emitting diode, LED, in particular micro-LED.

3. Display device (1) according to one of the preceding claims, wherein each sensor (30) is formed as a photodiode, wherein the photodiode is embedded in the substrate (10) or is arranged on the main surface (12) of the substrate (10) next to the emitters (20) .

4. Display device (1) according to one of claims 1 to 2, wherein each sensor (30) is implemented as an LED, in particular micro-LED, that is arranged on the main surface (12) of the substrate (10) next to the emitters (20) and configured to be biased for sensing a photocurrent.

5. Display device (1) according to the preceding claim, wherein at least a subset of the plurality of sensors (30) isimplemented as red micro-LED that is configured to be biased for sensing a photocurrent.

6. Display device (1) according to one of claims 4 to 5, wherein at least a further subset of the plurality of sensors(30) is implemented as blue or green micro-LED that is configured to be biased for sensing a photocurrent.

7. Display device (1) according to one of the preceding claims, wherein the emitters (20) and the sensors (30) are manufactured according to a common manufacturing process.

8. Display device (1) according to one of the preceding claims, wherein the pixels (2) are formed as RGB-pixels, in which a first emitter (20-1) configured to emit red light, a second emitter (20-2) configured to emit green light, and a third emitter (20-3) configured to emit blue light are arranged .

9. Display device (1) according to one of the preceding claims, wherein each sensor (30) is arranged in a respective pixel (2) of the display device (1) together with at least one emitter (20) of the plurality of emitters (20) .

10. Display device (1) according to one of the preceding claims, wherein each sensor (30) of the plurality of sensors (30) is configured to locally sense ambient light.

11. Display device (1) according to one of the preceding claims, wherein the control circuit (40) is configured to adjust the brightness of light emitted by the emitters (20) at a pixel scale.

12. Optoelectronic device (100) comprising the display device (1) according to one of the preceding claims, wherein the optoelectronic device is a personal computer, a smartphone, a smart watch, a tablet, a laptop, a TV, or a dashboard.

13. Method of operating a display device (1) , wherein the display device (1) comprises a plurality of emitters (20) being arranged in pixels (2) on a main surface (12) of a substrate (10) , the pixels (2) forming a display, a plurality of sensors (30) distributed over the display, and a control circuit (40) , the method comprising:- emitting light by the emitters (20) ,- sensing ambient light by the sensors (30) ,- adjusting locally, by the control circuit (40) , a brightness of the emitted light based on the sensed ambient light.

14. Method according to the preceding claim, wherein adjusting the brightness of the emitted light comprises pulse width modulation.

15. Method according to the preceding claim, wherein sensing ambient light is performed- when the emitters (20) are in an off-state during the pulse width modulation, or- continuously during the pulse width modulation and the sensed light is evaluated by filtering a detection signal in frequency space.

16. Method of manufacturing a display device (1) , the method comprising : providing a substrate (10) ,- mounting a plurality of emitters (20) on a main surface(12) of the substrate (10) , the emitters (20) being configured to emit light during operation, and wherein the emitters (20) are arranged in pixels (2) , the pixels (2) forming a display,- forming a plurality of sensors (30) , the sensors (30) being configured to sense ambient light during operation, and distributing the sensors (30) over the display,- providing a control circuit (40) that is configured to locally adjust a brightness of light emitted by the emitters (20) based on the ambient light sensed by the sensors ( 30 ) .

17. Method according to the preceding claim, wherein forming the sensors (30) comprises- embedding photodiodes in the substrate (10) , or- mounting photodiodes on the main surface (12) of the substrate (10) next to the emitters (20) , or- mounting LEDs, in particular micro-LED, on the main surface (12) of the substrate (10) next to the emitters (20) , and biasing said LEDs for sensing a photocurrent.

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