Display device, method of operating a display device and method of manufacturing a display device

Abstract

A display device (1) comprises a substrate (10) comprising a main surface (12), and a plurality of emitters (20) arranged in pixels (2) on the main surface (12) of the substrate (10), wherein each emitter (20) comprises a light emitting diode LED, that is configured to emit light during operation. It further comprises a sensor (30) in at least one pixel (2), the sensor (30) being configured to sense light during operation. It further comprises at least one evaluation circuit (40) being configured to evaluate proximity of an object (100) above the display device (1) based on light sensed by the sensor (30). Further, a method of operating a display device (1) and a method of manufacturing a display device (1) is provided. The emitters and sensors can be implemented as micro-LEDs.

Description

[0001] Description

[0002] DISPLAY DEVICE, METHOD OF OPERATING A DISPLAY DEVICE AND METHOD OF MANUFACTURING A DISPLAY DEVICE

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

[0004] 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, so that behind display sensing technologies cannot be used as in e.g. OLED displays. A proximity sensor can be arranged outside the display, e.g. at a notch of the display.

[0005] At least one object of particular embodiments is to provide in-display sensing.

[0006] This object is achieved by the subject-matter and the methods according to the independent claims. Advantageous embodiments and developments of the subject-matter and the method are characterized 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 .

[0008] 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, an automotive dashboard. 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 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 . 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 .

[0012] According to at least one embodiment, each emitter comprises a light emitting diode, LED, that is configured to emit light during operation.

[0013] 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. 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. Different emitters may emit light in different wavelength ranges. Each pixel may comprise one or more emitters, thus, one or more LEDs. Each pixel may comprise at least three LEDs (e.g. red, green, blue) for covering the visible wavelength range. Each pixel may also comprise more than three LEDs to provide a certain degree of redundancy and / or additional functionality.

[0014] According to at least one embodiment, the display device comprises a sensor in at least one pixel, the sensor being configured to sense light during operation.

[0015] In other words, the display device comprises at least one sensor. In other words, at least one pixel of the plurality of pixels in the display device comprises a sensor. This can mean that said pixel comprises only the sensor or the sensor in addition to one or more emitters. In particular, said pixel comprises the sensor and at least three emitters to cover the visible wavelength range . That the sensor is configured to sense light during operation can mean that the sensor is configured to sense ambient light and / or to sense display light , for example after reflection at an obj ect . Display light refers to light emitted by the emitters of the display device . The sensor may be sensitive to a particular wavelength range in the visible spectrum . The sensor can have a viewing angle . In particular, the viewing angle includes the vertical direction, such that the sensor is a "toplooking" sensor . The field of illumination of the emitters and the field of view of the sensor may at least overlap . The display device may comprise more than one sensor that are distributed in respective pixels of the display device . It is also possible that more than one sensor is arranged in a single pixel . In case of two or more sensors in the display device the sensors can be sensitive to light in di f ferent wavelength ranges .

[0016] According to at least one embodiment , the display device comprises at least one evaluation circuit . The evaluation circuit is configured to evaluate proximity of an obj ect above the display device based on light sensed by the sensor .

[0017] For example , the evaluation circuit is integrated in the substrate . It is however also possible that the evaluation circuit is arranged on the main surface of the substrate next to the pixels or in the pixels . The evaluation 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 evaluation circuit can be arranged in or on a further substrate . That an obj ect is located above the display device can mean that the obj ect is located in the vertical direction above the display, in particular in a direction in which light is emitted by the emitters and in which the at least one sensor is looking . Thus , ambient light to be sensed by the sensor may be shadowed by the obj ect . Further, display light , i . e . light emitted by the emitters , may be reflected by the obj ect . By evaluating shadowed ambient light and / or reflected light proximity of an obj ect above the display can be determined . The evaluation circuit is electrically connected to the sensor or the plurality of sensors to evaluate the light intensity sensed by the sensor ( s ) . In addition, the evaluation circuit can comprise circuitry for driving and biasing the emitters . Thus , the evaluation 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 evaluation circuit . For example , each evaluation circuit is assigned to a group of pixels , e . g . to a group of 16 x 16 pixels . The respective evaluation circuit can drive the emitters and evaluate signals from sensors in said group of pixels .

[0018] According to at least one embodiment , a display device comprises a substrate comprising a main surface , and a plurality of emitters arranged in pixels on the main surface of the substrate , wherein each emitter comprises a light emitting diode , LED, that is configured to emit light during operation . The display device further comprises a sensor in at least one pixel , the sensor being configured to sense light during operation . The display device further comprises at least one evaluation circuit being configured to evaluate proximity of an obj ect above the display device based on light sensed by the sensor . The display device described here is based on the following considerations , among others .

[0019] 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 sensor is embedded and integrated into the display such that no display notch is needed . In other words , integrating the proximity sensor into the display removes any notches from the display without the need to enable behind display sensing .

[0020] The sensor can be embedded into the display . The sensor is used to detect obj ects in the proximity of the display by detecting the backscattered display light and / or ambient light . I f several pixels comprise a respective sensor, the display can be partially or entirely populated with the additional sensors .

[0021] Sensing can be synchroni zed to the pulse width modulation ( PWM) of the LEDs allowing to distinguish between backscattered display light and ambient light . The di f ferential signal of both detection channels yields contours of the obj ects .

[0022] Thus , in-display depth and / or proximity sensing is provided . Possible applications for in-display depth and / or proximity sensing are smart surfaces , hover detection, predictive touch and distance measurements . According to at least one embodiment , each emitter is formed by a 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 . Di f ferent 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 . 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 .

[0025] In particular, each emitter is intended to emit radiation of a different 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, a first emitter is intended to emit radiation of a red color, a second emitter is intended to emit radiation of a green color, and a 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 different semiconductor materials, as for example gallium arsenide (GaAs) , gallium arsenide phosphide (GaAsP) , gallium phosphide (GaP) , aluminum indium gallium phosphide (AlInGaP) , 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. According to at least one embodiment, the sensor is formed as a photodiode, wherein the photodiode is embedded in the substrate .

[0026] This can mean that the photodiode, PD, 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 photodiode ( s ) .

[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-) transfer process. That the photodiode is arranged next to the emitters can mean that the photodiode and the emitters are arranged in a common pixel .

[0029] According to at least one embodiment , the 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 the sensor is implemented as (micro- ) LED can mean that the sensor and the emitters have a same or similar structure . In particular, the sensor 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 red, green and blue light emitting micro-LEDs in reverse or zero bias reach values above 20% depending on the wavelength to be detected . Hereby, red, green / 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 . As mentioned above , the pixels may comprise additional (micro- ) LEDs for redundancy reasons anyway . These additional emitters could 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 .

[0031] According to at least one embodiment , the emitters and the sensor are manufactured according to a common manufacturing process .

[0032] This can mean that at least some process steps for manufacturing the emitters are also used for manufacturing the sensor . This is in particular true i f both the emitters and the sensor are formed as (micro- ) LEDs . Thus , the emitters and the sensor 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 sensor has a coverage of less than 100% but could still have a satis factory functionality .

[0033] According to at least one embodiment , the display device comprises a plurality of sensors being configured to sense light during operation, wherein the sensors are distributed over the display in respective pixels of the display device .

[0034] All features disclosed for the sensor are also disclosed for the plurality of sensors . The above mentioned sensor can be one of the plurality of sensors . 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 second or each third pixel comprises a sensor. Preferably, the sensors are evenly distributed. The plurality of sensors arranged in respective pixels form a distributed proximity sensor that has more redundancies than a local sensor (e.g. at a notch of the display or a dedicated area behind the display) . Further, it is less sensitive to disturbances, e.g. covering the sensor by hairs, dirt or dust. Integrating the proximity sensor into the display removes any notches from the display without the need to be behind the display like e.g. behind OLED sensing. As the sensors are distributed over the display, the distributed proximity sensor has a 2D spatial resolution .

[0035] According to at least one embodiment, a viewing angle of at least one sensor is different from a viewing angle of at least another sensor within the display device.

[0036] This can mean that the fields of view of respective sensors of the plurality of sensors may be different. However, the fields of view may overlap. For example, some sensors of the plurality of sensors are configured to sense light coming from a first direction, while some other sensors of the plurality of sensors are configured to sense light coming from a second direction, wherein the first and the second direction are different. However, the first and second directions may have a common directional component. Different viewing angles can be implemented for additional spatial information . According to at least one embodiment , the display device further comprises an aperture and / or a light barrier and / or a micro-lens assigned to a respective sensor, the aperture , light barrier and the micro-lens being configured to define the viewing angle of the respective sensor .

[0037] A plurality of light barriers and / or apertures and / or microlenses can be provided . Each aperture / light barrier / microlens can be assigned to a respective sensor of the plurality of sensors . For example , the aperture and / or the light barrier comprises an opaque material like a metal layer or an opaque plastic material . The aperture and / or light barrier may prevent light from undesired direction from reaching the sensor . For example , the aperture is arranged in the vertical direction above the sensor, such that only light from the vertical direction can reach the sensor . The light barrier can be arranged of fset above the sensor or at a lateral side of the sensor, such that light coming from that side is blocked . The micro-lens can be positioned centrally above the sensor or shi fted in lateral directions . Thus , light from di f ferent directions can be focused onto the sensor surface . The micro-lens can be part of a micro-lens array . For example , the micro-lens array is formed by wafer level optics , WLO . By means of the aperture , the light barrier and the micro-lens the sensors can have di f ferent viewing angles . Di f ferent viewing angles can be implemented for additional spatial information . Shielding elements like apertures and light barriers allow for a 2D spatial resolution of the sensor . With micro-optical elements like micro-lenses it is furthermore possible to resolve depth information . With such a 3D in-display full area proximity sensor also hover detection is possible , which allows for predictive touch . Predictive touch means sensing of a close obj ect before touching which is an advantageous functionality for touch surfaces .

[0038] According to at least one embodiment , the display device further comprises a transparent cover covering the pixels .

[0039] The cover is transparent for visible light . For example , the cover comprises glass or a transparent plastic material . The cover can be arranged directly above the emitters and the sensor ( s ) . It is also possible that the cover has a distance to the emitters and the sensor ( s ) . The cover protects the emitter and the sensors ( s ) . Further, the cover may provide additional functionality, it may be formed as touch screen, for example .

[0040] According to at least one embodiment , the light barrier and / or the aperture and / or the micro-lens are structured on the cover .

[0041] This can mean that the light barrier and / or the aperture and / or the micro-lens are attached or mounted to the cover . It is also possible that these components are integrally formed with the cover . In particular, the micro-lenses can be monolithically integrated in the cover . Thus , it is possible to align the light barrier and / or the aperture and / or the micro-lens with the respective sensor on or in the substrate .

[0042] According to at least one embodiment , the light barrier is formed as a wall that is attached to the substrate next to the respective sensor .

[0043] As mentioned above , the light barrier can be arranged at a lateral side of the sensor, such that light coming from that side is blocked. The wall may be mounted to or integrally formed with the substrate. By attaching the wall to the substrate aligning with the respective sensor may be facilitated .

[0044] According to at least one embodiment, the evaluation circuit is configured to generate a first detection signal utilizing ambient light sensed by the sensor that is shadowed by the ob j ect .

[0045] Alternatively or additionally, the evaluation circuit is configured to generate a second detection signal utilizing light sensed by the sensor that is emitted by the emitter and reflected by the object.

[0046] The first and the second detection signal may be signals corresponding to the intensity of the sensed light. As mentioned above, the sensor may be configured to sense ambient light. If an object appears or moves above the display, the ambient light is shadowed by the object, wherein the light intensity drops. Thus, a shadow image can be generated. Further, the sensor may be configured to sense light that is emitted by the emitters and reflected by an object located above the display. The closer an object is, the higher the intensity of the backscattered display light. Thus, an image of backscattered display light can be generated. The evaluation circuit uses the measurement values of one or more sensors to determine that an object is located above the display. Further, by evaluating changes in size and shape of the generated images as well as the intensity of the sensed light, a distance of the object to the display can be determined. It is further possible that a movement of the object, e.g. a user's finger, is detected. Thus, the first and the second detection signal can be used for proximity, depth and gesture recognition .

[0047] According to at least one embodiment , the evaluation circuit is configured to calculate a di f ferential signal from the first detection signal and the second detection signal .

[0048] A di f ferential signal of the shadow image from the ambient light and the backscattered display light leads to a high contrast of the edges of the obj ect ( di f ferential lock-in detection) . For example , display light that is backscattered from a fingertip and ambient light that is shadowed from the fingertip is used for finger tracking detection .

[0049] Thus , hover detection is enabled . Hover detection means to detect an obj ect with 1 to about 20 mm distance to the display (not touching the display) . The tracking of hover movements can be used for "mouse over" ef fects and other display user interactions , where aiming without acting is essential (predictive touch) . State of the art hover detection is possible with a display-connected pencil via an electrical feedback . The present disclosure enables hover detection of one or multiple f ingertip ( s ) , as the display device enables short range 3D sensing with a high resolution to track the finger on top of the display . To detect the distance of the obj ect to the display, the sensors can be equipped with micro optics ( as mentioned above ) to reach left and right looking images and calculate the distance from the image shi ft . Relative distance changes in continuous tracking can also be derived from shape si ze changes and intensity changes in the backscattered display light . 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 .

[0050] 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 arranged in pixels on a main surface of a substrate , a sensor in at least one pixel , and at least one evaluation circuit .

[0051] According to at least one embodiment , the method comprises emitting light by the emitters , wherein each emitter comprises a light emitting diode , LED . In particular, light is emitted by the emitters in a main direction that runs perpendicular to the main surface of the substrate . Each emitter / LED has a field of illumination .

[0052] According to at least one embodiment , the method comprises sensing light by the sensor . The sensed light can be ambient light and / or light emitted by the emitters that is reflected by an obj ect above the display device . Preferably, the emitters and the sensor are arranged such that display light does not reach the sensor directly but only via reflection at an obj ect . For example , light barriers are arranged between the emitters and the sensor and / or the sensor is outside the field of illumination of the emitters .

[0053] According to at least one embodiment , the method comprises evaluating, by the evaluation circuit , proximity of an obj ect above the display device based on the sensed light . Proximity of the object can be determined by ambient light sensed by the sensor that is shadowed by the object. It is also possible that proximity of the object is determined by backscattered display light, i.e. light emitted by the emitters that is reflected by the object.

[0054] According to at least one embodiment, the method of operating a display device, wherein the display device comprises a plurality of emitters arranged in pixels on a main surface of a substrate, a sensor in at least one pixel, and at least one evaluation circuit, comprises emitting light by the emitters, wherein each emitter comprises a light emitting diode, LED. It further comprises sensing light by the sensor. It further comprises evaluating, by the evaluation circuit, proximity of an object above the display device based on the sensed light.

[0055] Thus, in-display proximity sensing is enabled. The sensor is embedded into the display. The sensor is used to detect objects in the proximity of the display by detecting the backscattered display light and / or ambient light. Thus, indisplay depth and / or proximity sensing is enabled. If several pixels comprise a respective sensor, the display can be partially or entirely populated with the additional sensors, such that a certain spatial resolution is provided. Possible applications for in-display depth and / or proximity sensing are smart surfaces, fingerprint recognition, hover detection and distance measurements.

[0056] According to at least one embodiment, the method further comprises adjusting a brightness of the emitted light by pulse width modulation. 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.

[0057] According to at least one embodiment, sensing light comprises sensing ambient light when the emitters are in an off-state during the pulse width modulation, and / or sensing reflected light when the emitters are in an on-state during the pulse width modulation.

[0058] Thus, sensing can be synchronized to the pulse width modulation of the LEDs allowing to distinguish between backscattered display light and ambient light. Further, the differential signal of both detection channels yields contours of the objects.

[0059] According to at least one embodiment, light sensing is performed continuously during the pulse width modulation and the sensed light is evaluated by filtering a detection signal in frequency space.

[0060] This can mean that both display light and ambient light are sensed during the full PWM cycle, i.e. during the on- and the off-state of the LEDs. Thus, the detection signal contains information about ambient light and backscattered display light. By knowing the PWM frequency of the PWM postprocessing is possible to distinguish both channels. According to at least one embodiment, the method further comprises evaluating a distance between the object and the display device, wherein the distance is determined by evaluating an intensity of reflected light, and / or by evaluating an image shift captured by at least two groups of sensors with different viewing angles, and / or by evaluating a shape size change of an image captured by a plurality of sensors .

[0061] The distance of the object can be measured from the main surface of the substrate, the emitting surfaces of the emitters, the sensing surface of the sensor or from the cover of the display device. The distance of the object to the display device can be determined by evaluating an intensity of reflected light. The closer the object is to the display, the higher the intensity of the backscattered display light. In particular, relative distance changes in continuous tracking can be derived from intensity changes in the backscattered display light. In addition or alternatively, the distance of the object to the display can be determined by evaluating the image shift captured by at least two groups of sensors with different viewing angles. As mentioned above, the viewing angle of sensors can be modified by apertures, light barriers and / or micro-lenses. Thus, for example, left and right looking sensors can be implemented. Right and left looking pixels can be distributed equally over the entire display leading to a right and left looking image sensor. The right and left looking image sensors will see shifted shadow images of close objects (ambient light shadowed by the object) . The shift of the images depends on the distance of the object. By analyzing the two images, distance information can be extracted. This procedure may be similar to the phase auto focus in cameras . In addition or alternatively, relative distance changes in continuous tracking can also be derived from shape si ze changes of an image captured by a plurality of sensors .

[0062] 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 .

[0063] 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 .

[0064] 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 and each emitter comprises a light emitting diode , LED, configured to emit light during operation . In particular, the emitters are 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 .

[0065] The method of manufacturing the display device further comprises forming a sensor in at least one pixel , the sensor being configured to sense light during operation .

[0066] 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. Alternatively, forming the sensor may comprise mounting a photodiode on the main surface of the substrate next to the emitters. This can mean that the photodiode forms a single detector chip that is transferred onto the substrate and attached to it. For example, the photodiode is a microphotodiode and transferred to the substrate in a similar way as the emitters, in particular by means of a further mass transfer. As a further alternative, forming the sensor may comprise mounting an LED on the main surface of the substrate next to the emitters, and biasing said LED for sensing a photocurrent. Said "sensor-LED" may have a similar or same structure as the "emitter-LEDs" . Thus, the sensor and the emitters may be formed by a common manufacturing process and they may be transferred simultaneously to the substrate. The sensor and the emitters may differ only in the way they are biased. For example, the sensor is a reverse biased or zero biased (micro-) LED.

[0067] The method of manufacturing the display device further comprises providing at least one evaluation circuit that is configured to evaluate proximity of an object above the display device based on light sensed by the sensor. The evaluation circuit may be formed in the substrate. The evaluation circuit can be an integrated circuit, IC, and can provide additional functions. It is also possible that the evaluation circuit is attached to the substrate. In this case, the evaluation circuit can be implemented as micro-IC, i.e., an integrated circuit that can be separated and transferred as piece of silicon with a high density of integrated circuits. Alternatively, the evaluation circuit is attached to a further substrate and connected to the pixels via electrical connections, e.g. a flex connection. 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 .

[0068] Figures la to 1c show various examples of integrating sensors in a display device .

[0069] Figures 2 to 9 show display devices according to embodiments of the present invention .

[0070] Figures 10 to 14 shows methods of operating a display device according to embodiments of the present invention .

[0071] Figure 15 shows the external quantum ef ficiency of micro-LEDs i f biased for sensing a photocurrent .

[0072] In Figures la to 1c di f ferent examples of integrating sensors 30 in a display device 1 are shown . The sensor 30 can be a proximity sensor or the like . Figure la shows a display device 1 in a top-view . The display device 1 comprise a display area . A sensor 30 is arranged outside the display area at a notch of the display . The disadvantages of such display device 1 are that the display area is reduced and that the sensor 30 is not a distributed sensor 30 but a single sensor that is prone to disturbances . For example , the sensor 30 could be covered by hairs , dust or other dirt .

[0073] Figure lb shows another example of a display device 1 comprising a sensor 30 . In that example the sensor 30 is arranged behind the display area, which is possible i f the display device 1 is or comprises a transparent display like an OLED display . However, also in this case the sensor 30 is restricted to a relatively small sensor area behind the display .

[0074] Figure 1c shows an embodiment of the present invention . The display device 1 comprises a substrate 10 with a main surface 12 ( shown in Figures 5a and 5b ) . A plurality of emitters 20 is arranged in pixels 2 on the main surface 12 of the substrate 10 , wherein each emitter 20 comprises a light emitting diode , LED, that is configured to emit light during operation ( see subsequent figures ) . Further, a sensor 30 is integrated in at least one of the pixels 2 , the sensor 30 being configured to sense light during operation ( see subsequent figures ) . The display device further comprises at least one evaluation circuit 40 ( shown in Figures 5a and 5b ) , the evaluation circuit being configured to evaluate proximity of an obj ect 100 ( see e . g . figures 12 and 13 ) above the display device 1 based on light sensed by the sensor 30 .

[0075] For example , each pixel 2 or at least a subset of the plurality of pixels 2 comprises a respective sensor 30 . Thus , the sensor area can be large and a distributed proximity sensor 30 can be formed . A distributed proximity sensor has more redundancies than a local sensor and is less sensitive to disturbances . Integrating the proximity sensor 30 into the display removes any notches from the display without the need to arrange the sensor behind the display like e . g . behind

[0076] OLED sensing . The display has not to be transparent .

[0077] Figures 2a and 2b show di f ferent embodiments of a respective pixel 2 within the display device 1 . According to Figures 2a and 2b the pixel 2 is formed as RGB-pixel 2 , 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 30-3 configured to emit blue light are arranged . The emitters 20 are formed as LEDs , in particular micro-LEDs . The emitters 20 are arranged along a diagonal of the pixel 2 . However, di f ferent arrangements are also possible . Further, the pixels 2 of Figures 2a and 2b comprise a respective sensor 30 arranged along the diagonal of the emitters 20 . The sensor 30- 1 of the pixel 2 according to Figure 2a is formed by an LED, in particular micro-LED, that can emit blue or green light in forward bias mode . However, said LED is configured to be biased for sensing a photocurrent . That is , said LED is configured to be reverse biased or zero biased . It has been found that blue or green micro-LEDs can generate a photocurrent in reverse bias with an external quantum ef ficiency of about 20% or more in a wavelength range between 350 nm and 500 nm . The sensor 30-2 of the pixel 2 according to Figure 2b is formed by an LED, in particular micro-LED, that can emit red light in forward bias mode . However, said LED is configured to be biased for sensing a photocurrent . That is , said LED is configured to be reverse biased or zero biased . It has been found that red micro-LEDs can generate a photocurrent in reverse bias with an external quantum ef ficiency of about 20% or more in a wavelength range between 500 nm and 650 nm . Thus , by means of reverse biased or zero biased (micro- ) LEDs for red and blue / green light the visible wavelength range is covered . The display device 1 may comprise di f ferent subsets of pixels 2 , wherein pixels 2 of a first subset comprise a blue / green LED used as sensor 30 , and wherein pixels 2 of a second subset comprise a red LED used as sensor 30 . It is also possible that blue / green LEDs and red LEDs used as sensors 30 are formed in the same pixel 2 . As both the emitters 20 and sensors 30 are implemented as

[0078] (micro- ) LEDs , they can be manufactured according to a common manufacturing process .

[0079] Figure 3 shows another embodiment of pixels 2 in a display device 1 . As in the embodiment of Figures 2a and 2b the pixels 2 are formed as RGB-pixels 2 . The pixels 2 are arranged adj acent to each other . The embodiment according to Figure 3 is di f ferent from the embodiments according to Figures 2a and 2b in that the sensor 30 is formed as photodiode , in particular micro-photodiode . The sensors 30 can be discrete micro-photodiodes that are manufactured to be mass trans ferred onto a display backplane or flex-plane similar to the emitters 20 . This means that the sensors are arranged on a main surface of a substrate 1 , on which also the emitters 20 are arranged .

[0080] Figure 4 shows an embodiment of pixels 2 in a display device 1 similar to that of Figure 3 . Here , the sensor 30 is formed as photodiode that is embedded in the substrate 10 on which the emitters 20 are arranged . For silicon backplanes as substrate , the sensors can be embedded directly into the backplane including the read out IC . The micro-photodiodes can be based on silicon, but also other materials are possible . The si ze of the photodiode sensors 30 can be similar to the si ze of the emitters 20 , as shown in Figures 3 and 4 . In Figures 5a and 5b further embodiments of the display device 1 are shown . The display device 1 comprises the substrate 10 . The emitters 20 and the sensor 30 are arranged on the main surface 12 of the substrate 10 . For example , Figures 5a and 5b show respective cross-sections of one pixel 2 , as for example the pixel 2 of Figure 2 . In the display devices 1 of Figures 5a and 5b the evaluation circuit 40 is integrated in the substrate 10 . However, it is also possible that the evaluation circuit 40 is arranged in or on a separate carrier which is electrically connected to the pixels 2 of the display device 1 . The display device 1 of Figures 5a and 5b further comprises a transparent cover 60 . The cover 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 . Figure 5a shows a light barrier 52 on a left lateral side of the sensor 30 , while Figure 5b shows a corresponding light barrier 52 on a right lateral side of the sensor 30 . The light barrier 52 is configured to define a viewing angle of the respective sensor 30 . Thus , the light barrier 52 of Figure 5a defines a rightwards directed viewing angle R of the sensor 30 , while the light barrier 52 of Figure 5b defines a leftwards directed viewing angle L of the sensor 30 . The light barriers 52 are formed as opaque walls that are attached to the substrate 10 next to the respective sensor 30 . They can also be attached to the cover 60 . The display device 1 can comprise di f ferent groups of pixels 2 , wherein pixels 2 of a first group comprise a sensor 30 with a rightwards directed viewing angle R, and pixels 2 of a second group comprise a sensor 30 with a leftwards directed viewing angle L . It is also possible that sensors with left- and rightwards directed viewing angle L, R are arranged in a common pixel 2 . Thus , a viewing angle of at least one sensor 30 is di f ferent from a viewing angle of at least another sensor 30 within the display device 1 . In this context , the terms rightwards and leftwards are to be understood only as directional indications in a certain orientation of the display device 1 . The directions can be switched or changed to upwards and downwards when the display device 1 is rotated .

[0081] Figure 6 shows a display device 1 similar to the one shown in Figure 5 . The substrate 10 and the evaluation circuit 40 are omitted for better illustration . In Figure 6 the light barrier 52 is formed as opaque layer structured on the cover 60 at a side of the cover 60 facing the sensor 30 . The light barrier 52 covers a portion of the sensor 30 . As shown in the example of Figure 6 , the light barrier 52 may cover a rightside sensor region of the sensor 30 , such that a leftwards directed viewing angle L is defined . Similarly, a rightwards directed viewing angle R can be defined by covering a leftside sensor region .

[0082] Figure 7 shows a similar display device 1 as Figure 6 . Here , the light barrier forms an aperture 50 structured on the cover 60 . The aperture 50 blocks light coming from lateral directions , such that a forward directed viewing angle C of the sensor 30 is defined . Thus , with blocking structures like light barriers 52 and apertures 50 the sensitivity of the sensors 30 can be guided into speci fic directions to allow spatial tracking of close obj ects 100 .

[0083] In the examples of Figures 8a to 8c di f ferent viewing angles L, R, C of sensors 30 are defined by means of micro-lenses 54 on the cover 60 or integrated in the cover 60 . That is , a micro-lens 54 is assigned to a respective sensor 30 , wherein in lateral directions the micro-lens 54 is aligned with the sensor 30. The micro-lens 54 can be arranged centrally above the sensor 30 to define a forward directed viewing angle C (see Figure 8a) . The micro-lens 54 can also be arranged offset above the sensor 30 to define a left- or rightwards directed viewing angle L, R (Figures 8b and 8c) . Micro-lenses 54 in the cover 60 can be formed as wafer level optics.

[0084] By means of the above-mentioned optical elements 50, 52, 54 the display device 1 may comprise an array of pixels 2, wherein, for example, each second pixel 2 comprise a left looking sensor 30, and each other pixel 2 comprise a right looking sensor 30 to form a checkerboard pattern, as shown in Figure 9. It is however also possible that pixels 2 comprise a forward or top looking sensor 30.

[0085] A display device 1 as shown above can be operated as follows: Light is emitted by the emitters 20. Further, light is sensed by the sensor 30. The sensed light can be ambient light and / or backscattered display light. Further, proximity of an object 100 above the display device 1 can be evaluated based on the sensed light.

[0086] Figure 10 shows an exemplary operating method for evaluating the distance of an object 100, in particular if a plurality of right and left looking pixels 2 are distributed equally over the entire display leading to a right and left looking image sensor. If an object 100 is located above the display device 1, ambient light is shadowed by the object 100. Thus, the image sensor can generate a shadow image Im. By means of the left looking sensors 30 (leftwards directed viewing angle) a first instance ImLof the image, and by means of the right looking sensors 30 (rightwards directed viewing angle) a second instance ImRof the image is generated. There is a shift As between the first instance ImLand the second instance ImRof the image depending on the distance of the object 100 to the display device, for example the display cover 60. Figure 10 shows a situation for three different distances dl to d3 of an object 100. At a distance d3 (far distance) there is an image shift +As between the first instance ImLand the second instance ImR. At a distance d2 (medium distance) the image shift vanishes. At a distance dl (close distance) there is an image shift -As between the first instance ImLand the second instance ImR. Thus, by analyzing the two images, the distance information can be extracted. Thus, it is possible to equip the individual sensors 30 with micro-optical elements that split the plurality of sensors 30 in left and right looking elements. The image shift As that is detected between the right and left looking image can then be used to determine the distance of the object 100. This procedure is similar to the phase auto focus in cameras .

[0087] A brightness of the light emitted by the emitters 20 can be adjusted by pulse width modulation, PWM, as shown in Figure 11. 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 11. In order to detect the display light that is backscattered by a close object 100, the detection is locked to a window TD in the PWM cycle, in which the display is on. To detect ambient light that passes around the object 100 in proximity to the display, the detection is locked to time frames TA, in which the display is not on. The on-states of the display are given by the pulse width modulation frequency and duty cycle . Having a dedicated display light detection window TD and a dedicated ambient light sensing window TA may refer to a PWM lock-in detection mode of the display device 1 . Alternatively, 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 and sensed display light can be distinguished .

[0088] In Figures 12 and 13 sensing ambient light and sensing display light is illustrated . An obj ect 100 is located above the display device 1 , of which only the cover 60 is shown . On the left hand side of Figure 12 the display device 1 is in a mode in which ambient light AL is sensed, i . e . the display light is of f . The obj ect 100 shadows the ambient light 100 , such that a shadow image SH is generated by the sensors 30 . In other words , the sensors 30 sense an intensity drop due to the obj ect 100 shadowing the ambient light AL . In turn, a first detection signal of the evaluation circuit 40 using the sensor data indicates that the obj ect 100 is in proximity of the display device 1 . On the right hand side of Figure 12 the display device 1 is in a mode in which backscattered display light DL is sensed . The closer the obj ect 100 is , the higher the intensity of the backscattered display light DL . In turn, a second detection signal of the evaluation circuit 40 indicates that the obj ect 100 is in proximity of the display device 1 . The obj ect 100 can be , for example , a user' s hand or finger at a distance d to the display device , as shown in Figure 13 .

[0089] Possibly, the evaluation circuit 40 calculates a di f ferential signal from the first detection signal and the second detection signal which leads to a high contrast of the edges of the obj ect 100 . Such a di f ferential lock-in detection is shown in Figure 14 . Figure 14a shows a shadow image SH that may correspond to the fingertip in Figure 13 . Figure 14b shows an image of backscattered display light DL that may correspond to the fingertip in Figure 13 . Figure 14c shows a di f ferential image showing contours of the fingertip . By sensing the backscattered display light and shadowed ambient light it is therefore possible to detect a fingertip that is close ( 1mm to 20mm) to the display surface . This enables so called hover detection which is a touchless finger tracking of one or multiple fingers .

[0090] Apart from evaluating the distance of the obj ect 100 by evaluating an intensity of the sensed display light that is reflected by the obj ect 100 ( as in Figures 12 and 13 ) or by evaluating an image shi ft captured by at least two groups of sensors 30 with di f ferent viewing angles L, R, C ( as in Figure 10 ) , relative distance changes in continuous tracking can also be derived from evaluating a shape si ze change of the image captured by a plurality of sensors 30 .

[0091] As mentioned above , the at least one sensor ( 30 ) can be implemented as LED, in particular, micro-LED, that is biased for sensing a photocurrent . It has been found that the external quantum ef ficiency, EQE , of red, green and blue light emitting micro-LEDs in reverse or zero bias reach values above 20% depending on the wavelength to be detected . This is illustrated in Figure 15 showing the external quantum ef ficiency of micro-LEDs as function of the wavelength X . It can be seen that the blue (B ) and green ( G) micro-LEDs cover a wavelength range from about 350 nm to 500 nm, while red (R) micro-LEDs cover the wavelength range from about 450 nm to 650 nm . Thus , the display device 1 can use both red and blue / green micro-LEDs as sensors 30 to cover the full visible spectrum .

[0092] 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 .

[0093] 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 .

[0094] 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 .

[0095] This patent application claims the priority of German patent application 102023125786 . 2 , the disclosure content of which is hereby incorporated by reference . References

[0096] 1 display device

[0097] 2 pixel

[0098] 10 substrate

[0099] 12 main surface

[0100] 20 emitter

[0101] 20- 1 first emitter

[0102] 20-2 second emitter

[0103] 20-3 third emitter

[0104] 30 sensor

[0105] 30- 1 sensor

[0106] 30-2 sensor

[0107] 40 evaluation circuit

[0108] 50 aperture

[0109] 52 light barrier

[0110] 54 micro-lens

[0111] 60 cover

[0112] 100 obj ect

[0113] AL ambient light

[0114] DL display light dl-d3 distance

[0115] L, R, C viewing angle

[0116] SH shadow image

[0117] TD display light detection window

[0118] TA ambient light detection window

[0119] As shi ft

Claims

Claims1. Display device (1) , comprising:- a substrate (10) comprising a main surface (12) ,- a plurality of emitters (20) arranged in pixels (2) on the main surface (12) of the substrate (10) , wherein each emitter (20) comprises a light emitting diode, LED, that is configured to emit light during operation,- a sensor (30) in at least one pixel (2) , the sensor (30) being configured to sense light during operation,- at least one evaluation circuit (40) being configured to evaluate proximity of an object (100) above the display device (1) and to determine a distance between the object (100) and the display device (1) based on light sensed by the sensor ( 30 ) .

2. Display device (1) according to the preceding claims, wherein each emitter (20) is formed by a micro-LED.

3. Display device (1) according to one of the preceding claims, wherein the pixels (2) are formed as RGB-pixels (2) , 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 (30-3) configured to emit blue light are arranged .

4. Display device (1) according to one of the preceding claims, wherein the 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) .

5. Display device (1) according to one of claims 1 to 3, wherein the 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.

6. Display device (1) according to the preceding claim, wherein the emitters (20) and the sensor (30) are manufactured according to a common manufacturing process.

7. Display device (1) according to one of the preceding claims, comprising a plurality of sensors (30) being configured to sense light during operation, wherein the sensors (30) are distributed over the display in respective pixels (2) of the display device (1) .

8. Display device (1) according to the preceding claim, wherein a viewing angle (L, R, C) of at least one sensor (30) is different from a viewing angle (L, R, C) of at least another sensor (30) within the display device (1) .

9. Display device (1) according to one of the preceding claims, further comprising an aperture (50) and / or a light barrier (52) and / or a micro-lens (54) assigned to a respective sensor (30) , the aperture (50) , the light barrier (52) and the micro-lens (54) being configured to define a viewing angle (L, R, C) of the respective sensor (30) .

10. Display device (1) according to the preceding claim, further comprising a transparent cover (60) covering the pixels (2) , wherein the light barrier (52) and / or the aperture (50) and / or the micro-lens (54) are structured on the cover ( 60 ) .

11. Display device (1) according to claim 9, wherein the light barrier (52) is formed as a wall that is attached to the substrate (10) next to the respective sensor (30) .

12. Display device (1) according to one of the preceding claims, wherein the evaluation circuit (40) is configured to generate a first detection signal utilizing ambient light sensed by the sensor (30) that is shadowed by the object (100) and / or a second detection signal utilizing light sensed by the sensor (30) that is emitted by the emitters (20) and reflected by the object (100) .

13. Display device (1) according to the preceding claim, wherein the evaluation circuit (40) is configured to calculate a differential signal from the first detection signal and the second detection signal.

14. Method of operating a display device (1) , wherein the display device (1) comprises a plurality of emitters (20) arranged in pixels (2) on a main surface (12) of a substrate (10) , a sensor (30) in at least one pixel (2) , and at least one evaluation circuit (40) , the method comprising:- emitting light by the emitters (20) , wherein each emitter(20) comprises a light emitting diode, LED,- sensing light by the sensor (30) ,- evaluating, by the evaluation circuit (40) , proximity of an object (100) above the display device (1) and determining a distance between the object (100) and the display device (1) based on the sensed light.

15. Method according to the preceding claim, further comprising adjusting a brightness of the emitted light by pulse width modulation.

16. Method according to the preceding claim, wherein sensing light comprises- sensing ambient light when the emitters (20) are in an off-state during the pulse width modulation, and / or- sensing reflected light when the emitters (20) are in an on-state during the pulse width modulation.

17. Method according to claim 15, wherein sensing light is performed continuously during the pulse width modulation and the sensed light is evaluated by filtering a detection signal in frequency space.

18. Method according to the preceding claim, further comprising evaluating a distance between the object (100) and the display device, wherein the distance is determined by- evaluating an intensity of the sensed light that is reflected by the object (100) , and / or- evaluating an image shift captured by at least two groups of sensors (30) with different viewing angles (L, R, C) , and / or- evaluating a shape size change of an image of the object (100) captured by a plurality of sensors (30) .

19. 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) , wherein the emitters (20) arearranged in pixels (2) and each emitter (20) comprises a light emitting diode, LED, configured to emit light during operation,- forming a sensor (30) in at least one pixel (2) , the sensor (30) being configured to sense light during operation,- providing at least one evaluation circuit (40) that is configured to evaluate proximity of an object (100) above the display device (1) and to determine a distance between the object (100) and the display device (1) based on light sensed by the sensor (30) .

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

Images