Method for operating a radiation emitting device

Abstract

A method for operating a radiation emitting device with the following steps is provided: - determining a temperature corrected forward voltage (VfTcor(0,y)) of an edge pixel (7) arranged in an edge region (8) of the radiation exit area (1), - determining a position and temperature corrected forward voltage (Vincrease(0,y)) of the edge pixel (7) from the temperature corrected forward voltage (VfTcor(0,y)), - determining a position and temperature corrected forward voltage (Vincrease(40,160)) of a hot spot pixel (16) being arranged in a hot spot region (17) of the radiation exit area (1) from the position and temperature corrected forward voltage of the edge pixel, - determining a temperature of the hot spot pixel (16) from the position and temperature corrected forward voltage (Vincrease(40,160)) of the hot spot pixel (16).

Description

[0001] 2023PF00442 July 22, 2024 P2023,0775 WO N - 1 – Description METHOD FOR OPERATING A RADIATION EMITTING DEVICE A method for operating a radiation emitting device is provided. It is an object of the present application to provide an improved method for operating a radiation emitting device having a plurality of pixels. Particularly, during the method the highest temperature of the pixels is to be determined. This object is achieved by a method having the steps of claim 1. Advantageous embodiments and developments of the method are given in the dependent claims. According to an embodiment, the method is configured for operating a radiation emitting device having a radiation exit area with a plurality of pixels. Particularly, the radiation exit area comprises or consists of the plurality of pixels. From the radiation exit area, the radiation emitting device emits electromagnetic radiation, particularly visible light, during operation. For example, each pixel comprises or consists of an epitaxial semiconductor layer stack with an active zone configured to generate electromagnetic radiation emitted from a radiation exit surface of the pixel. The epitaxial semiconductor layer stack is, particularly, epitaxially grown on a growth substrate, which ca be removed from the epitaxial semiconductor layer stack. For example, the radiation exit surfaces of the pixels form the radiation exit area of the 2023PF00442 July 22, 2024 P2023,0775 WO N - 2 – radiation emitting device. As an alternative, the pixels are comprised by the radiation exit area. When an electrical current is applied to a pixel of the plurality of pixels, a forward voltage is present at the active radiation generating zone of the pixel such that the pixel emits electromagnetic radiation, particularly visible light and appears bright. When no electrical current is applied to a pixel of the plurality of pixels, it does not emit electromagnetic radiation and appears dark. Particularly, the pixels of the plurality of pixels can be operated independently from each other. In other words, it is possible to supply a specific number of pixels with an electrical current while other pixels are shut off. Further, the electrical current applied to the pixels can be varied such that some pixels shine brighter than other pixels. Particularly, a temperature of a pixel is higher, if it shines brighter due to a higher electrical current. However, the electrical current to be applied to a pixel in order to achieve a specific forward voltage being present at the pixel in general decreases with temperature. Further, the forward voltage of a pixel depends on the position of the pixel within the radiation exit area of the radiation emitting device, since the electrical current applied to the pixel and the temperature of the pixel depends on its position. According to an embodiment of the method, a temperature corrected forward voltage of an edge pixel arranged in an edge region of the radiation exit area is determined. Particularly, the edge region of the radiation exit area comprises an edge of the radiation exit area or is limited by 2023PF00442 July 22, 2024 P2023,0775 WO N - 3 – the edge of the radiation exit area. Particularly, the edge region and / or the edge pixel are predetermined, For example, the plurality of pixels is arranged in rows and columns. For example, the rows and columns form regularly arranged cells, wherein each cell comprises a single pixel. For example, the cells are arranged in a cubic grid. If the pixels are arranged in rows and columns, the edge region comprises one or several rows of pixels, for example. For example, the edge region comprises between and including five and ten rows of pixels. If the pixels are arranged in rows and columns, the pixel of the rows are numbered in an x- direction with natural numbers, while the pixels of the columns are numbered in a y-direction with natural numbers, for example. According to a further embodiment of the method, a position and temperature corrected forward voltage of the edge pixel is determined from the temperature corrected forward voltage. If the pixels are arranged in rows and columns, the forward voltage of the edge pixel is, for example, increased by the serial resistance of the other pixels within the row of the edge pixel. By determining the position and temperature corrected forward voltage of the edge pixel from the temperature corrected forward voltage, this influence is removed. According to a further embodiment of the method, a position and temperature corrected forward voltage of a hot spot pixel being arranged in a hot spot region of the radiation exit area is determined from the position and temperature corrected forward voltage of the edge pixel. Particularly, the hot spot region of the radiation exit surface is the 2023PF00442 July 22, 2024 P2023,0775 WO N - 4 – region, wherein the pixels with the highest temperature are to be expected. For example, the hot spot region is the region of the radiation exit area provided with the highest voltage and / or the highest electrical current during operation. Particularly, the hot spot pixel is arranged within the hot spot region. The hot spot pixel is not necessarily the pixel with the highest temperature within the hot spot region, but, for example, is a pixel to be expected to have a very high temperature within the hot spot region. The hot spot pixel is particularly representative for the temperature of the pixels of the hot spot region. Particularly, the hot spot region and the edge region do not overlap. Rather, the hot spot region and the edge region are arranged in a distance to each other, for example. For example, the hot spot region and / or the hot spot pixel is predetermined, particularly based on an illumination pattern. Particularly, the radiation emitting device is configured to be driven in different operation modii, wherein in each operation modus a specific number of the plurality of pixels is switched on according to a predetermined illumination pattern, while the rest of the plurality of pixels is switched off. If the radiation emitting device is used as a light source in a front headlight of a motor vehicle, the radiation emitting device is configured, for example, to be operated in a low beam light operation modus, a high beam light operation modus or a bending light operation modus. In each of these operation modii, the plurality of pixels is switched on according to different illumination patterns. For example, it is possible to predict the hot spot region comprising the pixels with the highest temperatures from the illumination patterns of the different operation modii. 2023PF00442 July 22, 2024 P2023,0775 WO N - 5 – Particularly, the hot spot region corresponds to a region of the pixels with high forward voltage. Therefore, the hot spot region can be predicted from the predetermined illumination pattern. Also, the hot spot pixel can be predicted from the illumination patterns. According to an embodiment, the method for operating the radiation emitting device having the radiation exit area with the plurality of pixels comprises the steps: - determining the temperature corrected forward voltage of the edge pixel arranged in the edge region of the radiation exit area, - determining the position and temperature corrected forward voltage of the edge pixel from the temperature corrected forward voltage, - determining the position and temperature corrected forward voltage of the hot spot pixel being arranged in the hot spot region of the radiation exit area from the position and temperature corrected forward voltage of the edge pixel, - determining the temperature of the hot spot pixel from the position and temperature corrected forward voltage of the hot spot pixel. Preferably, the above-given steps are carried out in the given order. The forward voltage of a pixel is dependent on its temperature and also on its position within the radiation exit area. It is an idea of the present method to determine, for example by the help of a temperature sensor, the temperature of the edge pixel and to eliminate the influence of position and temperature on the forward voltage of the edge pixel. From this value a forward voltage of the hot spot 2023PF00442 July 22, 2024 P2023,0775 WO N - 6 – pixel corrected by the influence of temperature and position is determined and the presumably highest temperature within the pixel array, the hot spot temperature, is derived from this forward voltage. In particular, it is crucial to determine the hot spot temperature of the radiation emitting device in order to be able to operate the radiation emitting device with maximum power without damage. According to an embodiment of the method, the temperature corrected forward voltage is a forward voltage of the edge pixel corrected by a forward voltage value due to a temperature of the edge pixel differing from a temperature reference value. In other words, a temperature reference value is defined and a forward voltage value is determined resulting from a difference of the temperature of the edge pixel to the temperature reference value. For example, the temperature reference value is 25°. According to an embodiment of the method, the position and temperature corrected forward voltage of the edge pixel is the forward voltage of the edge pixel corrected by the forward voltage value due to the temperature of the edge pixel differing from the reference value and corrected by a voltage value due to the position of the edge pixel within the edge region of the radiation exit area. In other words, the position and temperature corrected forward voltage is corrected by both, the influence of the temperature and the influence of the position of the edge pixel within the radiation exit area. According to a further embodiment of the method, the position and temperature corrected forward voltage of the hot spot pixel is a forward voltage of the hot spot pixel corrected by 2023PF00442 July 22, 2024 P2023,0775 WO N - 7 – a voltage value due to a temperature of the hot spot pixel differing from the reference value and by a voltage value due to the position of the hot spot pixel within the hot spot region of the radiation exit area. In other words, the position and temperature corrected forward voltage of the hot spot pixel is corrected by both, the voltage value due to position and the voltage value due to temperature. According to a further embodiment of the method, the hot spot region is arranged in a center of the radiation exit area. In this case, the edge pixel is particularly arranged in a central region of the edge region of the radiation exit area. In the case that the pixels are arranged in rows and columns and the radiation exit surface has a rectangular area divided into regular cells, wherein each cell corresponds to a pixel, the hot spot region might be a region within the center of the radiation exit area. For example, the hot spot region has a round, for example elliptical, oval or a circle-shaped form. For example, a line connecting the hot spot pixel in the hot spot region with the edge pixel in the edge region is perpendicular to a side face of the radiation exit area. Particularly, the hot spot pixel and the edge pixel are arranged in a common column. The central region of the edge region particularly preferably extends symmetrically to an x- position of the edge pixel in x-direction. For example, the edge pixel is arranged in a central position of the outermost row. According to a further embodiment of the method, determining the temperature corrected forward voltage of the edge pixel arranged in a central region of the edge region of the radiation exit area comprises the steps of measuring a temperature with a temperature sensor and determining the 2023PF00442 July 22, 2024 P2023,0775 WO N - 8 – voltage value due to the temperature of the edge pixel differing from a temperature reference value. Particularly, the voltage value due to the temperature of the edge pixel differing from the temperature reference value is determined on the basis of a temperature measured with the temperature sensor. Particularly, the dependency of the forward voltage from the temperature can be provided as a simulated or measured curve and the corresponding forward voltage value can be derived from the temperature measured by the temperature sensor. Particularly, the temperature sensor is arranged outside the radiation exit area. Therefore, the temperature sensor has a distance to the edge pixel. Preferably, the distance between the temperature sensor and the edge pixel is as small as possible. For example, the distance between the edge pixel and the temperature sensor is at most 200 micrometer. Particularly, if there is only little space within the radiation emitting device, it is an idea to position the temperature sensor outside the radiation exit area near to the edge pixel such that it can be assumed that the temperature measured by the temperature sensor is equal or very similar to the temperature of the pixel. Preferably, the temperature measured with the temperature sensor does not deviate from the temperature of the edge pixel by more than 5% or by more than 10%. According to a further embodiment of the method, the hot spot region is arranged offset to the center of the radiation exit area and the edge pixel is arranged offset to the central region of the edge region of the radiation exit area. In other words, the illumination pattern is not centred with 2023PF00442 July 22, 2024 P2023,0775 WO N - 9 – respect to the radiation exit area but is arranged offset to its center, for example for a bending light operation modus. If the hot spot region is arranged offset to the center of the radiation exit area, the hot spot pixel comprised by the hot spot region particularly has an x-position and a y- positon deviating from a center position of the radiation exit surface. According to a further embodiment of the method, determining the temperature corrected forward voltage of the edge pixel arranged in the edge region of the radiation exit area comprises measuring a first temperature with a first temperature sensor and measuring a second temperature with a second temperature sensor. Particularly, the first temperature sensor and the second temperature sensor are arranged outside of the radiation exit area near to the radiation exit area. For example, a distance of the first temperature sensor and / or the second temperature sensor to an outermost row of pixels does not exceed 200 micrometer. Particularly, the first temperature sensor and the second temperature sensor are arranged adjacent to a common edge of the radiation exit area. For example, the common edge extends along the x-direction. For example, in this embodiment of the method, the temperature of the edge pixel is determined, from the first temperature and the second temperature, particularly by interpolation. In other words, from the first temperature measured with the first temperature sensor and the second temperature measured with the second temperature sensor, the temperatures of the pixels between the first temperature sensor and the second temperature sensor are derived by interpolation, for example. By interpolation, an 2023PF00442 July 22, 2024 P2023,0775 WO N - 10 – interpolation curve is derived giving a dependency of the x- position of the pixel in the outermost row of the radiation exit area and the temperature, for example. Further, in this embodiment of the method, the voltage value due to the temperature of the edge pixel differing from the temperature reference value is determined, for example from the interpolated curve between the position of the first temperature sensor and the position of the second temperature sensor. According to a further embodiment of the method, determining the position and temperature corrected forward voltage of the edge pixel from the temperature corrected forward voltage comprises the step of forming the difference between a calibration value of the forward voltage of the edge pixel and the temperature corrected forward voltage of the edge pixel. Particularly, the calibration value represents the forward voltage of the edge pixel without influence of the position within the radiation exit area and particularly without any serial resistance due to the other surrounding pixels. According to a further embodiment of the method, the calibration value of the forward voltage of the edge pixel is the forward voltage of the edge pixel when the edge pixel is switched on and all other pixels are switched off. In other words, the calibration value of the forward voltage of the edge pixel is, for example, determined by only switching on the edge pixel, while all other pixels are switched off. In this way the position depending part of the forward voltage is eliminated. 2023PF00442 July 22, 2024 P2023,0775 WO N - 11 – According to a further embodiment of the method, determining the position and temperature corrected forward voltage of the hot spot pixel comprises adding the product of a coefficient dependent on a sheet resistance of the radiation emitting device and an overall electrical current of all pixels to the position and temperature corrected forward voltage of the edge pixel. In other words, the influence of the position of the hot spot pixel within the radiation exit area is taken into account by a product of the coefficient dependent on the sheet resistance of the radiation emitting device and the overall electrical current of all pixels. In a first approximation, the coefficient is linearly dependent on the sheet resistance. According to a further embodiment of the method, determining the temperature of the hot spot pixel from the position and temperature corrected forward voltage of the hot spot pixel comprises determining a forward voltage of the hot spot pixel during operation of the radiation emitting device and subtracting the position and temperature corrected forward voltage of the hot spot pixel from the determined forward voltage of the hot spot pixel. In other words, the part of the forward voltage of the hot spot pixel which is due to its temperature above the reference value of the temperature is determined. Then, the temperature of the hot spot pixel is determined, for example, from the dependency of the voltage from the temperature. According to a further embodiment of the method, the pixels are comprised by a pixelated semiconductor chip. In other words, it is possible that the pixels are comprised by a common semiconductor chip. In this embodiment in particular, 2023PF00442 July 22, 2024 P2023,0775 WO N - 12 – the pixels are not manufactured separately from each other and then arranged, for example on a common carrier. Instead, the pixels are, for example, structured within a common epitaxial semiconductor layer sequence grown on a common growth substrate. According to a further embodiment of the method, the pixels are micro-LEDs. Particularly in this embodiment of the method, the pixels are first manufactured as micro-LEDs, for example connected to a common auxiliary carrier by small bridging elements and transferred from the common auxiliary carrier to a substrate, for example with the help of a stamp, in order to manufacture the radiation emitting device. As a broad definition, a micro-LED could be seen as any light emitting diode (LED short for “light emitting diode”) - generally not a laser - with a particularly small size. As a rule - and this is a very important criterion in addition to the small size - the growth substrate is removed from micro-LEDs, so that typical heights of such micro-LEDs are in the range of 1.5 micrometer to 10 micrometer, for example. In principle, a micro-LED does not necessarily have to have a rectangular radiation exit surface. Generally, for example, an LED could have a radiation exit surface in which, in plan view of the layers of the epitaxial layer stack, any lateral extent of the radiation exit surface is less than or equal to 100 micrometer or less than or equal to 70 micrometer. For example, in the case of rectangular micro-LEDs, an edge length - especially in plan view of the layers of the 2023PF00442 July 22, 2024 P2023,0775 WO N - 13 – epitaxial layer stack - smaller than or equal to 70 micrometer or smaller than or equal to 50 micrometer is often cited as a criterion. Mostly, such micro-LEDs are provided on wafers with - for the µLED non-destructively - detachable holding structures such as the bridging elements. For example, micro-LEDs are used in displays. The micro-LEDs form pixels or subpixels and emit light of a defined color, in particular. Small pixel size 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. µLED, µ-LED, uLED, u-LED or micro light emitting diode can be found in the relevant literature. According to a further embodiment of the method, the radiation emitting device is a light source of a headlight of a motor vehicle. The radiation emitting device finds, for example, application in automotive headlights, in illumination devices or in projectors, particularly as a light source. Further advantageous embodiments and developments of the method for operating a radiation emitting device result from the exemplary embodiment described below in connection with the Figures. 2023PF00442 July 22, 2024 P2023,0775 WO N - 14 – Figures 1 and 2 show schematically a radiation emitting device according to an exemplary embodiment to be operated with the method according to Figure 6. Figure 3 shows schematically a plan view on an electrical current distribution within the pixels of a radiation exit area of a radiation emitting device according to an exemplary embodiment. Figure 4 shows schematically a plan view on a radiation exit area of a radiation emitting device according to an exemplary embodiment. Figure 5 shows schematically the forward voltage of the pixels of different rows of the radiation exit area of Figure 4 dependent on the position x. Figure 6 shows schematically a flow chart of the method for operating a radiation emitting device according to an exemplary embodiment. Figures 7 to 12 show schematically plan views on electrical current distributions within the pixels of a radiation exit area of a radiation emitting device according to several exemplary embodiments. Figure 13 shows schematically a plan view on an electrical current distribution within the pixels of a radiation exit area of a radiation emitting device according to a further exemplary embodiment. 2023PF00442 July 22, 2024 P2023,0775 WO N - 15 – Figure 14 shows schematically a plan view on a radiation exit area of a radiation emitting device according to a further example. Figure 15 shows schematically the forward voltage of the pixels of different rows of the radiation exit area of Figure 14 dependent on the position x. Equal or similar elements as well as elements of equal function are designated with the same reference signs in the Figures. The Figures and the proportions of the elements shown in the Figures are not regarded as being shown to scale. Rather, single elements, in particular layers, can be shown exaggerated in magnitude for the sake of better presentation and / or better understanding. The radiation emitting device of Figures 1 and 2 is configured to be operated with the method according to the exemplary embodiment of Figure 6. Figure 1 shows a plan view on a radiation exit area of the radiation emitting device, while Figure 2 shows a backside surface of the radiation emitting device arranged opposite to the radiation exit area. The radiation emitting device according to Figures 1 and 2 comprises a radiation exit area 1 with a plurality of pixels 2. The plurality of pixels 2 is arranged on a carrier 3, for example on a silicon carrier. The carrier 3 has at present a larger surface than the radiation exit area 1. For example, the pixels 2 are part of a pixelated semiconductor chip or are micro-LEDs connected to a 2023PF00442 July 22, 2024 P2023,0775 WO N - 16 – substrate, for example by soldering. Particularly, the pixels 2 can be individually controlled. In other words, the pixels 2 are part of an active LED array. A cathode 4 connecting the pixels 2 to ground is arranged at opposite side edges 5 of the radiation exit area 1. Particularly, the cathode 4 is formed as strips along the opposite side edges 5 of the radiation exit area 1. Further, the pixels 2 are arranged in rows and columns forming cells 6, wherein each cell 6 comprises a pixel 2. The pixel 2 of the rows are numbered in an x-direction with natural numbers, while the pixels 2 of the columns are numbered in a y- direction with natural numbers. At present, only two rows and a few columns are shown exemplarily. However, the radiation emitting device comprises a plurality of pixels 2, for example about 25.000. Edge pixels 7 are arranged in central regions 9 of edge regions 8. At present, there are two edge pixels 7 defined in opposite edge regions 8 adjacent to opposite edges 10 of the radiation exit area 1. A temperature sensor 11 is arranged next to each edge pixel 7. For example, the temperature sensor 11 is based on silicon. Particularly, the temperature sensors 11 are arranged outside of the radiation exit area next to the edge pixels 7. At present, the temperature sensors 11 are fixed to the carrier 3 (Figure 1). A plurality of anode areas 12 are arranged on the backside surface of the radiation emitting device, which at present are of ring-shaped form (Figure 2). Surrounding the anode areas 12, cathode areas 13 are arranged which are electrically isolated against the anode areas 12. The cathode areas 13 shown in Figure 3 are connected to each other by 2023PF00442 July 22, 2024 P2023,0775 WO N - 17 – conductor tracks 14 and are electrically connected to the cathodes 4 shown in Figure 1. Each pixel 2 is provided by a separate anode area 12 with electrical current and is electrically connected by an anode area 12 and cathode areas 13 surrounding the anode area 12. Particularly, the anode areas 12 and cathode areas 13 shown in Figure 2 allows to control the pixels 2 separately from each other. It is also possible that pixels 2 have a common anode area 2 and separate cathode areas 13. Figure 3 shows values of an electrical current distribution I(x,y) applied to the pixels 2 of the radiation emitting device according to Figures 1 and 2. At present, the electrical current distribution I(x,y) is symmetrically with respect to a center 15 of the radiation exit area 1 of the radiation emitting device. Particularly, the electrical current is highest in the center 15 of the radiation emitting device. Figure 4 shows a plan view on a simulated forward voltage distribution V(x,y) present at the pixels 2 of the radiation emitting device of Figures 1 and 2 applied with the electrical current distribution I(x,y) of Figure 3. As can be seen in Figure 4, the forward voltage of the pixels 2 changes in the x-direction, while the forward voltage of the pixels 2 in the y-direction is nearly constant, since the strip-shaped cathodes 4 are continuously arranged at opposite side edges 5 of the radiation exit area 1 as shown in Figure 1. Figure 5 shows the forward voltage in dependence on the position x of Figure 4 for different rows. Curve r70 shows the forward voltage dependent on the x-position of row 70 at 2023PF00442 July 22, 2024 P2023,0775 WO N - 18 – y-position 70, curve r55 shows the forward voltage dependent on the x-position of row 55, and curve r40 shows the forward voltage dependent on the x-position of row 40. As can be seen, the forward voltages of different rows slightly differ from each other in the center 15. According to the method for operating a radiation emitting device having a radiation exit area 1 with a plurality of pixels 2 of the exemplary embodiment of Figure 6, a temperature corrected forward voltage VfTcor of an edge pixel 7 arranged in an edge region 8 of the radiation exit area 1 is determined in a first step S1. At present two edge regions 8 are defined and in each edge region 8 an edge pixel 7 is specified during step S1 (compare also, for example, Figures 1 and 4). The edge regions 8 are the first and the last row of the pixels 2 of the radiation exit area 1 arranged in rows and columns and the edge pixels 7 of the edge regions 8 are arranged within a central region 9 of the edge region 8. Particularly, the edge pixels 7 have the (x,y)-positions (0,160) and (80,160) Further, the edge pixels 7 are arranged in a common column at x-position 160. Near each edge pixel 7 a temperature sensor 11 is arranged on the carrier 3. During step S1, the temperatures are measured with the temperature sensors 11. Since the edge pixels 7 are located very close to the respective temperature sensor 11, it is estimated that the temperature measured by the temperature sensor 11 corresponds to the temperature of the adjacent edge pixel 7. Then, the voltage decrease ^V(T,(0,160), ^V(T,(80,160) of the forward voltage of the edge pixels 7 2023PF00442 July 22, 2024 P2023,0775 WO N - 19 – due to a temperature T of the edge pixels 7 above a temperature reference value Tref of 25°C is determined by using a curve V(T) with the information of the dependency of the forward voltage from the temperature (not shown). For example, the dependency of the forward voltage from the temperature is linear, at least in a first approximation. Further, the forward voltages of the edge pixels Vm(0,160), Vm(80,160) are measured when the electrical current according to the electrical current distribution I(x,y) of Figure 3 is applied to the radiation emitting device. Then, in step S1, the temperature corrected forward voltages VfTcor(0,160), VfTcor(80,160) of the edge pixels 7 is calculated as follows: VfTcor(0,160)=Vm(0,160)+ ^V(T,(0,160)), and VfTcor(80,160)=Vm(80,160)+ ^V(Temp (80,160)). In a second step S2, a position and temperature corrected forward voltage Vincrease(0,160), Vincrease(80,160) of the edge pixels is determined from the temperature corrected forward voltage VfTcor(0,160), VfTcor(80,160). During step 2, firstly a calibration value Vno_load(0,160), Vno_load(80,160) of the forward voltage of the edge pixels 7 is measured. The calibration value Vno_load(0,160), Vno_load(80,160) of the forward voltage of one of the edge pixels 7 is determined by switching off all other pixels 2 and only supplying the edge pixel 7 with an electrical current. From this calibration value Vno_load(0,160), Vno_load(80,160) of the forward voltage, the forward voltage corrected by temperature VfTcor(0,160), VfTcor(80,160) as 2023PF00442 July 22, 2024 P2023,0775 WO N - 20 – determined in step S1 is subtracted according to the following formulas: Vincrease(0,160)=Vno_load(0,160)-VfTcor(0,160), and Vincrease(80,160)=Vno_load(80,160)-VfTcor(80,160). In a third step S3, a position and temperature corrected forward voltage Vincrease(40,160) of a hot spot pixel 16 being arranged in a hot spot region 17 of the radiation exit area 1 is determined from the position and temperature corrected forward voltage of the edge pixels VfTcor(0,y). At present, the hot spot pixel 16 arranged within the hot spot region 17 in the center 15 of the radiation exit area 1 is located at the (x,y)-position (40,160). In step S3, the voltage increase of the hot spot pixel 16 due to its position within the hot spot region 17 located in the center 15 of the radiation exit area 1 is removed. For this, to the voltage increase Vincrease(0,160), Vincrease(80,160) determined in step S2, the product of a coefficient n being dependent on a sheet resistance and the overall current I running through all pixels 2 are added as follows: Vincrease(40,160)= Vincrease(0,160)+n*I Vincrease(40,160)= Vincrease(80,160)+n*I Here, the assumption is taken as a basis that the temperature T along the y-axis and thus the forward voltage is nearly constant, as can be seen in Figure 4. 2023PF00442 July 22, 2024 P2023,0775 WO N - 21 – In a further step S4, a temperature of the hot spot pixel 16 is determined from the position and temperature corrected forward voltage Vincrease(40,160) of the hot spot pixel 16 by using the dependency of the forward voltage from the temperature V(T). In the present embodiment, two temperature sensors 11 arranged at opposite edges 10 of the radiation exit area 1 are used and Vincrease(40,160) is determined using both values. For example, an average value of the two temperatures can be calculated in order to achieve a more exact value for the temperature of the hot spot pixel 16. It is also possible to calculate an average value from the two values for Vincrease(40,160) in step S3 and to proceed in step S4 with only one voltage value. Figures 7 to 12 show different electrical current distributions I(x,y) which are different from the electrical current distribution I(x,y) in Figure 3. The different electrical current distributions I(x,y) have different located hot spot pixels 16 and hot spot regions 17. In order to test the method for operating a radiation emitting semiconductor device, the temperature error due to inaccuracy of voltage increase determination was calculated. The calculated error is inserted within the figures and summarized in the table below. As can be seen from the table, the error lies between -0.38 K and 2.11 K. Figure showing electrical Calculated temperature error current distribution I(x.y) of the hot spot pixel 16 due to inaccuracy of the voltage increase determination [K] 2023PF00442 July 22, 2024 P2023,0775 WO N - 22 – Figure 7 -0.5 K Figure 8 1.42 K Figure 9 2.11 K Figure 10 -0.38 K Figure 11 -0.76 K Figure 12 -1.14 K Table During the method according to the exemplary embodiment of Figures 13 to 15, the pixels 2 of the radiation emitting device are provided with an off-centred electrical current distribution I(x,y) as shown in Figure 13. In other words, the hot spot region 17 comprising the hot spot pixel 16 is arranged offset to the center 15 of the radiation exit area 1. In order to determine a value of the temperature of the edge pixels 7, a first temperature sensor 11 and a second temperature sensor 11’ are arranged at edges 10 of the radiation exit area 1 along the x-axis (Figure 14). A first temperature of the first temperature sensor 11 and a second temperature of the second temperature sensor 11’ are measured. Then, a course of the temperature with the position y between the x-coordinate of the first temperature sensor 11 and the second temperature sensor 11’ is determined, for example by interpolation. The temperature of the edge pixel 7 arranged off-set to a central region 9 of an edge region 8 of the radiation exit area 1 is derived from the course of the temperature along the x-axis. Then, steps S1 to S4 are carried out as already explained in connection with the exemplary embodiment of Figure 6. 2023PF00442 July 22, 2024 P2023,0775 WO N - 23 – Figure 15 shows the forward voltage in dependence on the position x of Figure 14 for different rows. Curve r70 shows the forward voltage dependent on the x-position of row 70 at y-position 70, curve r55 shows the forward voltage dependent on the x-position of row 55, and curve r40 shows the forward voltage dependent on the x-position of row 40. The present application claims priority of the German application DE 102023122689.4, the disclosure content of which is incorporated herein by reference. The invention is not limited to the description of the exemplary embodiments. Rather, the invention comprises each new feature as well as each combination of features, particularly each combination of features of the claims, even if the feature or the combination of features itself is not explicitly given in the claims or the exemplary embodiments.

[0002] 2023PF00442 July 22, 2024 P2023,0775 WO N - 24 – References 1 radiation exit area 2 pixel 3 carrier 4 cathode 5 side edge of the radiation exit area 6 cell 7 edge pixel 8 edge region 9 central region 10 edge of the radiation exit area 11, 11’ temperature sensor 12 anode area 13 cathode area 14 conductor track 15 center of the radiation exit area 16 hot spot pixel 17 hot spot region I(x,y) electrical current distribution V(x,y) forward voltage distribution VfTcor(0,y) temperature corrected forward voltage of edge pixels Tref temperature reference value ^V(T,(0,y) voltage decrease of edge pixels due to temperature above Tref Vm(0,y), measured forward voltages of the edge pixels Vincrease(0,y) position and temperature corrected forward voltage of the edge pixel Vno_load(0,y) calibration value 2023PF00442 July 22, 2024 P2023,0775 WO N - 25 – Vincrease(40,160) position and temperature corrected forward voltage of a hot spot pixel n coefficient S1 first step S2 second step S3 third step S4 fourth step

Claims

2023PF00442 July 22, 2024 P2023,0775 WO N - 26 – Claims 1. Method for operating a radiation emitting device having a radiation exit area (1) with a plurality of pixels (2), comprising the steps: - determining a temperature corrected forward voltage (VfTcor(0,y)) of an edge pixel (7) arranged in an edge region (8) of the radiation exit area (1), - determining a position and temperature corrected forward voltage (Vincrease(0,y)) of the edge pixel (7) from the temperature corrected forward voltage (VfTcor(0,y)), - determining a position and temperature corrected forward voltage (Vincrease(40,160)) of a hot spot pixel (16) being arranged in a hot spot region (17) of the radiation exit area (1) from the position and temperature corrected forward voltage of the edge pixel, - determining a temperature of the hot spot pixel (16) from the position and temperature corrected forward voltage (Vincrease(40,160)) of the hot spot pixel (16).

2. Method according to the previous claim, wherein the temperature corrected forward voltage (VfTcor(0,y)) of the edge pixel (7) is a forward voltage of the edge pixel (7) corrected by a voltage value due to a temperature of the edge pixel (7) differing from a temperature reference value (Tref).

3. Method according to any of the previous claims, wherein the position and temperature corrected forward voltage Vincrease(0,y) of the edge pixel (7) is the forward voltage of the edge pixel (7)corrected by the voltage value due to the temperature of the edge pixel (7) differing from the reference value (Tref) and corrected by a voltage value due2023PF00442 July 22, 2024 P2023,0775 WO N - 27 – to the position of the edge pixel (7) within the edge region (8) of the radiation exit area (1).

4. Method according to any of the previous claims, wherein the position and temperature corrected forward voltage (Vincrease(40,160)) of the hot spot pixel (16) is a forward voltage of the hot spot pixel (16) corrected by a voltage value due to a temperature of the hot spot pixel (16) differing from the temperature reference value (Tref) and by a voltage value due to the position of the hot spot pixel (16) within the hot spot region (17) of the radiation exit area (1).

5. Method according to any of the previous claims, wherein - the hot spot region (17) is arranged in a center (15) of the radiation exit area (1), and - the edge pixel (7) is arranged in a central region (9) of the edge region (8) of the radiation exit area (1).

6. Method according to the previous claim, wherein determining the temperature corrected forward voltage (VfTcor(0,y)) of the edge pixel (7) arranged in the central region (9) of the edge region (8) of the radiation exit area (1) comprises the steps: - measuring a temperature with a temperature sensor (11, 11’), and - determining the voltage value due to a temperature of the edge pixel (7) differing from a temperature reference value (Tref).

7. Method according to any of the claims 1 to 4, wherein - the hot spot region (17) is arranged offset to the center2023PF00442 July 22, 2024 P2023,0775 WO N - 28 – - the edge pixel (7) is arranged offset to the central region (9) of the edge region (8) of the radiation exit area (1).

8. Method according to the previous claim, wherein determining the temperature corrected forward voltage (VfTcor(0,y)) of the edge pixel (7) arranged in the edge region (8) of the radiation exit area (1) comprises the steps: - measuring a first temperature with a first temperature sensor (11), - measuring a second temperature with a second temperature sensor (11’), - determining the temperature of the edge pixel (7) from the first temperature and the second temperature, and - determining the voltage value due to the temperature of the edge pixel (7) differing from the temperature reference value (Tref).

9. Method according to any of the previous claims, wherein determining the position and temperature corrected forward voltage (Vincrease(0,y)) of the edge pixel (7) from the temperature corrected forward voltage (VfTcor(0,y)) comprises the step: forming the difference between a calibration value (Vno_load(0,y)) of the forward voltage of the edge pixel (7) and the temperature corrected forward voltage (Vincrease(0,y)) of the edge pixel (7).

10. Method according to the previous claim, wherein the calibration value (Vno_load(0,y)) of the forward voltage of the edge pixel (7) is the forward voltage of the edge pixel (7), when the edge pixel (7) is switched on and all other pixels (2) are switched off.2023PF00442 July 22, 2024 P2023,0775 WO N - 29 – 11. Method according to any of the previous claims, wherein determining the position and temperature corrected forward voltage Vincrease(40,160) of the hot spot (16) pixel comprises the step: adding the product of a coefficient (n) dependent on the sheet resistance of the radiation emitting device and an overall current of all pixels (2) to the position and temperature corrected forward voltage (Vincrease(0,y)) of the edge pixel (7).

12. Method according to any of the previous claims, wherein determining the temperature of the hot spot pixel (16) from the position and temperature corrected forward voltage (Vincrease(40,160)) of the hot spot pixel (16) comprises the steps: - determining a forward voltage of the hot spot pixel (16) during operation of the radiation emitting device, and - subtracting the position and temperature corrected forward voltage (Vincrease(40,160)) of the hot spot pixel (16) from the determined forward voltage of the hot spot pixel (16).

13. Method according to any of the previous claims, wherein the pixels (2) are comprised by a pixilated semiconductor chip.

14. Method according to any of claims 1 to 12, wherein the pixels (2) are micro-LEDs.

15. Method according to any of the previous claim, wherein the radiation emitting device is a light source of a head light of a motor vehicle.

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