Display pixel comprising light-emitting diodes and display screen having such display pixels

Abstract

The present description concerns a display pixel (12i, j) comprising at least first and second light-emitting diodes (LED), a first controllable current source (CS_B) supplying said first light-emitting diode (LED) with a first current, a second controllable current source (CS_R) supplying said second light- emitting diode (LED) with a second current, and an electronic circuit (40) comprising a storage circuit (48) for storing at least first and second color signals (R, B) and a driver circuit (50) configured to control the first controllable current source (CS_B) to supply the first current by pulse-width modulation based on the first color signal ((BB)) and configured to control the second controllable current source (CS_R) to supply the second current by a linear command based on the second color signal (R).

Description

DESCRIPTIONTITLE : Display pixel comprising light-emitting diodes and display screen having such display pixelsThis application claims the priority benefit of French patent application number 23 / 09903 , filed on 19 / 09 / 2023 , entitled "Display pixel comprising light-emitting diodes and display screen having such display pixel s" , which is hereby incorporated by reference to the maximum extent allowable by law .Technical background

[0001] The present disclosure concerns a display pixel comprising light-emitting diodes and a display screen having such display pixels .Prior art

[0002] A pixel of an image corresponds to the unit element of the image displayed by a display screen . For the display of color images , the display screen generally comprises , for the display of each pixel of the image , at least three components , also called display sub-pixels , which each emit a light radiation, called image pixel color component substantially in a single color ( for example , red, green, and blue ) . The superposition of the image pixel color components emitted by the three display sub-pixels provides the observer with the colored sensation corresponding to the pixel of the displayed image . In this case , the assembly formed by the three display sub-pixels used for the display of a pixel of an image is called display pixel of the display screen . Each display sub-pixel may comprise a light source , particularly a light-emitting diode .

[0003] The display pixels may be distributed in an array, each display pixel being located at the intersection of a row ( also called line ) and of a column of the array . Electrodes are provided along the rows and the columns to connect each display pixels to control circuits . Generally, each row of display pixels is successively selected by signal transmitted along the row electrodes , and the display pixels of the selected row are programmed to display the desired image pixels by signals transmitted along the column electrodes .

[0004] It is known to control a light emitting diode , by pulse-width modulation, also called PWM (English acronym for Pulse Width Modulation) . This type of control consists in circulating successive current pulses of constant intensity in the light-emitting diode , the pulses being repeated cyclically, the duty cycle determining the light intensity emitted by the light-emitting diode . Such a control advantageously makes it possible to operate the light-emitting diode at its optimum operating point where the ef ficiency of the light-emitting diode , equal to the ratio between the light power emitted by the light-emitting diode and the electrical power consumed by the lightemitting diode , is maximum . Moreover, a pulse-width modulation command allows the current density crossing the light-emitting diode to remain constant . This is advantageous since , for some types of light-emitting diodes , the central wavelength of the radiation emitted by the light-emitting diode may vary with the current density crossing the light-emitting diode .

[0005] Some of the display sub-pixels of the display pixel can comprise a photoluminescent block covering the lightemitting diode . The photoluminescent block comprises luminophores capable , when they are excited by the lightemitted by the associated light-emitting diode , of emitting light at a wavelength di f ferent from the wavelength of the light emitted by the associated light-emitting diode . The light conversion performances of some types of luminophores , for example quantum dots , can decrease in time according to the maximum light flux received by the quantum dots . Therefore , it can be desirable to command the light-emitting diode covered by such photoluminescent block so that the maximum light flux emitted by the lightemitting diode is reduced .Summary of the invention

[0006] An obj ect of an embodiment is to provide a display pixel comprising light-emitting diodes and a display screen comprising such display pixels overcoming all or part of the disadvantages of existing display pixels comprising light-emitting diodes and display screens comprising such display pixels .

[0007] An embodiment provides a display pixel comprising at least first and second light-emitting diodes , a first controllable current source supplying said first lightemitting diode with a first current , a second controllable current source supplying said second light-emitting diode with a second current , and an electronic circuit comprising a storage circuit for storing at least first and second color signals and a driver circuit configured to control the first controllable current source to supply the first current by pulse-width modulation based on the first color signal and configured to control the second controllable current source to supply the second current by a linear command based on the second color signal .

[0008] Such a control advantageously makes it possible to operate the first light-emitting diode at its optimumoperating point where the ef ficiency of the first lightemitting diode is maximum . Moreover, a pulse-width modulation command allows the current density crossing the first light-emitting diode to remain constant . This is advantageous since the central wavelength of the radiation emitted by first the light-emitting diode may vary with the current density crossing the first light-emitting diode . Moreover, the linear command of the second light-emitting diode is advantageous since it allows the second lightemitting diode not to always emit a radiation at the highest intensity, which could be damaging in particular when the second light-emitting diode is covered by a photoluminescent block comprising quantum dots .

[0009] According to an embodiment , the display pixel further comprises a third light-emitting diode , and a third controllable current source supplying said third lightemitting diode with a third current , the storage circuit being configured to store a third color signal and the driver circuit being configured to control the third controllable current source to supply the third current by a linear command based on the third color signal . The linear command of the third light-emitting diode is advantageous since it allows the third light-emitting diode not to always emit a radiation at the highest intensity, which could be damaging in particular when the third lightemitting diode is covered by a photoluminescent block comprising quantum dots .

[0010] According to an embodiment , the first color signal is a digital signal and the storage circuit comprises first memory cells for storing the bits of the first color signal .

[0011] According to an embodiment , the second color signal is a digital signal and the storage circuit comprisessecond memory cells for storing the bits of the second color signal .

[0012] According to an embodiment , the driver circuit comprises a digital-to-analog converter configured to convert the second color signal stored in the second memory cells into an analog control signal for controlling the second current source .

[0013] According to an embodiment , the first color signal is an analog signal and the storage circuit comprises a first capacitor for storing the first color signal .

[0014] According to an embodiment , the second color signal is an analog signal and the storage circuit comprises a second capacitor for storing the second color signal .

[0015] According to an embodiment , each of first and second light-emitting diodes comprises several elemental lightemitting diodes comprising each an active zone covering a three-dimensional semiconductor element corresponding to a wire , conical , f rustoconical or pyramidal element of nanometer or micrometer range . For such three-dimensional light-emitting diodes of the radial type , the central wavelength of the radiation emitted by the light-emitting diode can vary signi ficantly as a function of the current density passing through the light-emitting diode . A pulsewidth modulation command allows the current density crossing the first light-emitting diode to remain constant , which is advantageous when the first light-emitting diode is not covered by a photoluminescent block .

[0016] According to an embodiment , the second light-emitting diode is covered by a first photoluminescent block . According to an embodiment , the first light-emitting diode is configured to emit a first radiation at a first wavelength, the second light-emitting diode is configuredto emit a second radiation at a second wavelength, and the first photoluminescent block is configured to convert the second radiation into the third radiation at a third wavelength, di f ferent from the second wavelength . The first photoluminescent block absorbs the second radiation emitted by the second light-emitting diode and emits the third radiation at a central wavelength di f ferent from the central wavelength of the second radiation emitted by the second light-emitting diode . The linear command for the second light-emitting diode can lead to a variation of the current density supplied to the second light emitting diode , and, as a consequence , to a variation of the central wavelength of the second radiation emitted by the second light emitting diode . However, the first photoluminescent block can emit the third radiation with a fixed central wavelength even though the central wavelength of the second radiation emitted by the second light emitting diode shows a dispersion . Therefore , the central wavelength of the third radiation emitted by the first photoluminescent block remains fixed even with the variation of the central wavelength of the second radiation emitted by the second light emitting diode .

[0017] According to an embodiment , the first wavelength is equal to the second wavelength within 10% . First lightemitting diode and second light-emitting diode can advantageously be light-emitting diodes manufactured by the same manufacturing method . The manufacturing method of the display pixel is therefore simpler .

[0018] According to an embodiment , the first photoluminescent block comprises first quantum dots . The light conversion performances of the first quantum dots tend to decrease in time according to the maximum light flux received by the first quantum dots . Linear command for the second light-emitting diode allows advantageously to limit the light flux on the first quantum dots compared to a pulse-width modulation command . Therefore , the first quantum dots do not always receive a second radiation from the second light-emitting diodes at the highest intensity . Therefore , the durability of light conversion performances of the first quantum dots is increased .

[0019] According to an embodiment , the third light-emitting diode is covered by a second photoluminescent block . According to an embodiment , the third light-emitting diode is configured to emit a fourth radiation at a fourth wavelength, and the second photoluminescent block is configured to convert the fourth radiation into a fi fth radiation at a fi fth wavelength, di f ferent from the fourth wavelength . The second photoluminescent block absorbs the fourth radiation emitted by the third light-emitting diode and emits the fi fth radiation at a central wavelength di f ferent from the central wavelength of the fourth radiation emitted by the third light-emitting diode . The linear command for the third light-emitting diode can lead to a variation of the current density supplied to the third light emitting diode , and, as a consequence , to a variation of the central wavelength of the fourth radiation emitted by the third light emitting diode . However, the second photoluminescent block can emit the fi fth radiation with a fixed central wavelength even though the central wavelength of the fourth radiation emitted by the third light emitting diode shows a dispersion . Therefore , the central wavelength of the fi fth radiation emitted by the second photoluminescent block remains fixed even with the variation of the central wavelength of the fourth radiation emitted by the third light emitting diode .

[0020] According to an embodiment , the fourth wavelength is equal to the first wavelength within 10% . First lightemitting diode and third light-emitting diode can advantageously be light-emitting diodes manufactured by the same manufacturing method . The manufacturing method of the display pixel is therefore simpler .

[0021] According to an embodiment , the second photoluminescent block comprises second quantum dots . The light conversion performances of the second quantum dots tend to decrease in time according to the maximum light flux received by the second quantum dots . Linear command for the third light-emitting diode allows advantageously to limit the light flux on the second quantum dots compared to a pulse-width modulation command . Therefore , the second quantum dots do not always receive a radiation from the second light-emitting diodes at the highest intensity . Therefore , the durability of light conversion performances of the second quantum dots is increased .

[0022] According to an embodiment , the display pixel comprises a first integrated circuit including the electronic circuit comprising said storage circuit and the driver circuit .

[0023] According to an embodiment , the display pixel comprises an optoelectronic circuit attached to the integrated circuit , the optoelectronic circuit comprising the first and second light-emitting diodes .

[0024] An embodiment also provides a display screen comprising : display pixels as previously defined; first electrodes coupled to the driver circuits of the display pixels ; a first circuit for delivering a selection signal on eachfirst electrode for the selection of the display pixels coupled to the first electrode; second electrodes coupled to the electronic circuits of the display pixels; and a second circuit for delivering data signals on the second electrodes .

[0025] According to an embodiment, the second circuit is configured to deliver the data signals on the second electrodes as analog signals.

[0026] According to an embodiment, the second circuit is configured to deliver the data signals on the second electrodes as digital signals.

[0027] According to an embodiment, the second circuit is configured to deliver the data signals on the second electrodes comprising alternating digital signals and analog signals.Brief description of the drawings

[0028] The foregoing features and advantages, as well as others, will be described in detail in the rest of the disclosure of specific embodiments given by way of illustration and not limitation with reference to the accompanying drawings, in which:

[0029] Figure 1 partially and schematically shows an embodiment of a display screen;

[0030] Figure 2 is a very simplified cross-section view of an embodiment of a display pixel;

[0031] Figure 3 shows a block diagram of an embodiment of a display pixel of the display screen of Figure 1;

[0032] Figure 4 shows a block diagram of an embodiment of a light-emitting circuit of the display pixel of Figure 3;

[0033] Figure 5 shows a block diagram of another embodiment of the light-emitting circuit of the display pixel of Figure 3;

[0034] Figure 6 shows a block diagram of an embodiment of a part the display pixel of Figure 3;

[0035] Figure 7 shows a block diagram of another embodiment of a part the display pixel of Figure 3;

[0036] Figure 8 shows examples of timing diagrams of signals of the display pixel of Figure 7 according to an embodiment of an operating method of the display screen;

[0037] Figure 9 shows a block diagram of another embodiment of a part the display pixel of Figure 3;

[0038] Figure 10 shows examples of timing diagrams of signals of the display pixel of Figure 9 according to another embodiment of an operating method of the display screen;

[0039] Figure 11 represents, partially and schematically, a more detailed embodiment of the display pixel represented in Figure 2;

[0040] Figure 12 represents an embodiment of a three- dimensional light-emitting diode; and

[0041] Figure 13 shows another embodiment of a three- dimensional light-emitting diode.Description of the embodiments

[0042] Like features have been designated by like references in the various figures. In particular, the structural and / or functional features that are common among the various embodiments may have the same references and may dispose identical structural, dimensional and material properties .

[0043] For the sake of clarity, only the operations and elements that are useful for an understanding of the embodiments described herein have been illustrated and described in detail.

[0044] In the following disclosure, unless indicated otherwise, when reference is made to absolute positional qualifiers, such as the terms "front", "back", "top", "bottom", "left", "right", etc., or to relative positional qualifiers, such as the terms "above", "below", "higher", "lower", etc., or to qualifiers of orientation, such as "horizontal", "vertical", etc., reference is made to the orientation shown in the figures.

[0045] Unless indicated otherwise, when reference is made to two elements connected together, this signifies a direct connection without any intermediate elements other than conductors, and when reference is made to two elements coupled together, this signifies that these two elements can be connected or they can be coupled via one or more other elements. Further, a signal which alternates between a first constant state, for example, a low logical state, noted "0", and a second constant state, for example, a high logical state, noted "1", is called a "binary signal". The high and low states of different binary signals of a same electronic circuit may be different. In practice, the binary signals may correspond to voltages or to currents which may not be perfectly constant in the high or low state .

[0046] Further, unless indicated otherwise, when it is spoken of a voltage at a conductive pad, the difference between the potential at said conductive pad and a reference potential, for example, the ground, taken as equal to 0 V, is considered. When a radiation presents a spectrum ofgeneral "bell" shape, for example of Gaussian shape, having a maximum, one calls wavelength of the radiation, or central or main wavelength of the radiation, the wavelength at which the maximum of the spectrum is reached.

[0047] Unless specified otherwise, the expressions "around", "approximately", "substantially" and "in the order of" signify within 10%, and preferably within 5%. Further the expression "substantially constant" means which varies by less than 10% over time with respect to a reference value.

[0048] A light-emitting diode is said to be a three- dimensional light-emitting diode when it comprises a three- dimensional semiconductor element of micrometric or nanometric size extending in a preferred direction, for example a microwire or a nanowire, covered with an active area. In particular, a three-dimensional light-emitting diode is said to be of the radial type when its active zone extends at least over the side walls of the three- dimensional semiconductor element.

[0049] Figure 1 partially and schematically shows a known example of a display screen 10. Display screen 10 comprises display pixels 12ifj , for example, arranged in M rows and in N columns, M being an integer varying from 1 to 8,000 and N being an integer varying from 1 to 16,000, i being an integer varying from 1 to M, and j being an integer varying from 1 to N. As an example, in Figure 1, M and N are equal to 6. Each display pixel 12ifj is coupled to a source of a low reference potential Gnd, for example, the ground, via an electrode 14±and to a source of a high reference potential Vcc via an electrode 16j . As an example, electrodes 14±are shown as being aligned along the rows in Figure 1 and electrodes 16j are shown as being aligned along the columns in Figure 1, the reverse layout being possible.The power supply voltage of the display screen corresponds to the voltage between high reference potential Vcc and low reference potential Gnd, and is noted Vcc like the high reference potential . Power supply voltage Vcc particularly depends on the arrangement of the light-emitting diodes and on the technology according to which the light-emitting diodes are manufactured . As an example , power supply voltage Vcc may be in the order of from 4 V to 5 V .

[0050] For each row, the display pixels 12i fj in the row are coupled to a row electrode 18i . For each column, the display pixels 12i fj in the column are coupled to a column electrode 20j . Display screen 10 comprises a selection circuit 22 coupled to row electrodes 18i and adapted to delivering a selection signal Comi on each row electrode 18i . Display screen 10 comprises a data delivery circuit 24 coupled to column electrodes 20j and adapted to delivering a data signal Dataj on each column electrode 20j . Selection circuit 22 and control circuit 24 are controlled by a circuit 26 , for example comprising a microprocessor .

[0051] Figure 2 is a very simpli fied cross-section view of a known example of display pixel 12i fj . Each display pixel 12i fj comprises a control circuit 30 covered with a display circuit 32 . Display circuit 32 comprises light-emitting diodes , preferably at least three light-emitting diodes LED . The display pixel comprises a lower surface 34 and an upper surface 35 opposite to lower surface 34 , surfaces 34 and 35 being preferably planar and parallel . Control circuit 30 further comprises conductive pads P_Gnd, P_Vcc, P_Col , P_Row on lower surface 34 . Control circuit 30 may correspond to an integrated circuit comprising electronic components , particularly insulated gate field ef fect transistors , also called MOS transistors , or thin film transistors , also called TFTs . Preferably, display circuit32 only comprises light-emitting diodes LED and the conductive elements of these light-emitting diodes LED, and control circuit 30 comprises all the electronic components necessary to the control of the light-emitting diodes LED of display circuit 32 . As a variant , display circuit 32 may also comprise other electronic components in addition to light-emitting diodes LED . According to an embodiment , each light-emitting diode LED comprises several elementary three-dimensional light-emitting diodes . In Figure 2 , the light-emitting diodes LED are shown as being connected with a common anode . It may however be desirable to arrange light-emitting diodes LED according to another configuration . As an example , the light-emitting diodes may be connected with a common cathode , or be connected independently from one another .

[0052] Each conductive pad P_Gnd, P_Vcc, P_Col , P_Row is intended to be connected to one of electrodes 14i , 16 j , 18i , 20j schematically shown in Figure 2 . The first conductive pad P_Gnd is coupled to the source of low reference potential Gnd . The second conductive pad P_Vcc is coupled to the source of high reference potential Vcc . The third conductive pad P_Row is coupled to row electrode 18i and receives selection signal Comi . The fourth conductive pad P_Col is coupled to column electrode 20j and receives data signal Dataj . The dimensions of conductive pads P_Gnd, P_Vcc, P_Col , P_Row and the layout of conductive pads P_Gnd, P_Vcc, P_Col , P_Row on surface 34 are particularly imposed by the rules of design of display pixel 12l fj and by the method of assembly of display pixels 12l fj in display screen 10 .

[0053] According to an embodiment , display pixel 12i rj comprises a first display sub-pixel emitting light at a first wavelength, a second display sub-pixel emitting lightat a second wavelength, and a third display sub-pixel emitting light at a third wavelength . According to an embodiment , the first wavelength corresponds to blue light and is within the range from 430 nm to 490 nm . The first display sub-pixel is then called blue display sub-pixel . According to an embodiment , the second wavelength corresponds to green light and is within the range from 510 nm to 570 nm . The second display sub-pixel is then called green display sub-pixel . According to an embodiment , the third wavelength corresponds to red light and is within the range from 600 nm to 720 nm . The third display subpixel is then called red display sub-pixel .

[0054] Figure 3 shows a block diagram of an embodiment of a display pixel 12i fj of display screen 10 . For a color di splay screen, display pixel 12i fj comprises at least three di splay sub-pixels SPix_R, SPix_G, SPix_B emitting radiations of di f ferent colors . For example , display sub-pixel SPix_B corresponds to the blue display sub-pixel defined previously, display sub-pixel SPix_G corresponds to the green display sub-pixel defined previously, and display sub-pixel SPix_R corresponds to the red display sub-pixel defined previously . Each sub-pixel SPix_R, SPix_G, SPix_B comprises at least one light-emitting diode LED . For each display sub-pixel SPix_R, SPix_G, SPix_B, light-emitting diode LED is series-coupled to a controllable current source CS_R, CS_G, CS_B . In the present example , for each light-emitting diode LED, the anode of light-emitting diode LED receives high reference potential Vcc, received at conductive pad P_Vcc of the display pixel 12l fj , and the cathode of light-emitting diode LED is for example coupled to a terminal of controllable current source CS_R, CS_G, CS_B, the other terminal of controllable current source CS_R, CS_G, CS_B receiving low reference potential Gnd,received at conductive pad P_Gnd of the display pixel 12i fj . As a variation, the cathode of light-emitting diode LED receives low reference potential Gnd and the anode of light-emitting diode LED is coupled to a terminal of controllable current source CS_R, CS_G, CS_B, the other terminal of controllable current source CS_R, CS_G, CS_B receiving high reference potential Vcc .

[0055] Display pixel 12l fj further comprises an electronic circuit 40 for driving controllable current source CS_R, CS_G, CS_B of each display sub-pixel SPix_R, SPix_G, SPix_B . Electronic circuit 40 may particularly comprise electronic components such as MOS transistors . It may be desirable to use a decreased power supply voltage , smaller than 4 V, for example in the order of 1 V or of 1 . 8 V, to power the electronic components of circuit 40 , this decreased power supply voltage for example corresponding to the voltage likely to be applied between the power terminals of the MOS transistors . For this purpose , display pixel 12i,j may comprise a circuit , not shown, for delivering, a decreased power supply voltage Vdd particularly used for the power supply of circuit 40 , for example from high reference potential Vcc or from selection signal Comi and data signal Dataj .

[0056] Circuit 40 comprises an interface circuit 46 ( Interface ) coupled to conductive pad P_Col receiving data signal Dataj and coupled to conductive pad P_Row receiving selection signal Comi and configured to deliver data signals Data to a storage circuit 48 ( Color Data Memory) . Storage circuit 48 is configured to store analog or digital color signals R, G, B based on received data signals Data . Color signals R, G, B are representative of the image pixel color components to be displayed by each display sub-pixel SPix_R, SPixjG, SPix_B .

[0057] Circuit 40 further comprises a driver circuit 50 ( LED driver ) for controlling the controllable current source CS_R, CS_G, CS_B associated of each display sub-pixel SPix_R, SPix_G, SPix_B . Driver circuit 50 ( LED driver ) is configured to control the controllable current sources CS_R, CS_G, CS_B coupled to light-emitting diodes LED with analog or digital signals I_red, I_green, and I_blue , obtained from color signals R, G, B . According to an embodiment , control circuit 30 can correspond to a single integrated circuit comprising circuit 40 for driving controllable current source CS_R, CS_G, CS_B of each display sub-pixel SPix_R, SPix_G, SPix_B . More generally, circuit 40 can be made by several integrated circuits .

[0058] According to an embodiment , a pulse-width modulation command is used to command current source CS_B of blue display sub-pixel SPix_B whereas a linear command is used to command current source CS_G of green display sub-pixel SPix_G and to command current source CS_R of red display sub-pixel SPix_R . Therefore , light emitting diode LED of blue display sub-pixel SPix_B is supplied with pulses of a current having a constant intensity, the durations of the pulses depending of the stored color signal B, whereas light emitting diode LED of green display sub-pixel SPix_G is supplied by a current having an intensity that varies according to stored color signal G and light emitting diode LED of red display sub-pixel SPix_R is supplied by a current having an intensity that varies according to stored color signal R .

[0059] The fact that the intensity of the current crossing the light-emitting diode LED of blue display sub-pixel SPix_B is constant is advantageous when it is important to obtain a reduced dispersion of the central wavelength of the radiation emitted by the light emitting diode LED ofblue display sub-pixel SPix_B in operation . Indeed, the central wavelength of the radiation emitted by the lightemitting diode usually varies as a function of the current density passing through the light-emitting diode , this variation being signi ficant for three-dimensional lightemitting diodes of the radial type . In the present embodiment , since the current density passing through each elementary light-emitting diode remains constant whatever the color signal B is , the central wavelength of the radiation emitted by the elementary light-emitting diodes does not vary in operation .

[0060] According to an embodiment , each of red and green display sub-pixels SPix_R and SPix_G comprises a photoluminescent block covering the light-emitting diode LED . The photoluminescent block absorbs the radiation emitted by light-emitting diode LED and emits a radiation at a central wavelength di f ferent from the central wavelength of the radiation emitted by light-emitting diode LED . The linear command for the red and green display subpixels SPix_R and SPix_G can lead to a variation of the current density supplied to the light emitting diode LED of red and green display sub-pixels SPix_R and SPix_G, and, as a consequence , to a variation of the central wavelength of the radiation emitted by the light emitting diode LED of red and green display sub-pixels SPix_R and SPix_G . However, a photoluminescent block can emit a radiation with a fixed central wavelength even though the central wavelength of the radiation emitted by light emitting diode LED shows a dispersion . Therefore , the central wavelength of the radiation emitted by the photoluminescent block remains fixed even with the variation of the central wavelength of the radiation emitted by the light emitting diode LED of red and green display sub-pixels SPix_R andSPix_G due to the linear command for the red and green display sub-pixels SPix_R and SPix_G .

[0061] The photoluminescent block may comprise quantum dots . The light conversion performances of quantum dots tend to decrease in time according to the maximum light flux received by the quantum dots . Linear command for the red and green display sub-pixels SPix_G and SPix_R allows advantageously to limit the light flux on quantum dots compared to a pulse-width modulation command . Therefore , the quantum dots do not always receive a radiation from the light-emitting diodes LED at the highest intensity . Therefore , the durability of light conversion performances of quantum dots is increased .

[0062] According to an embodiment , the pulse-width modulation command used to command current sources CS_B of blue display sub-pixel SPix_B is a digital pulse-width modulation command . In this case , signal I_blue is a binary signal and color signal B is a digital signal .

[0063] Figure 4 shows a block diagram of an embodiment of display-sub-pixel SPix_B . Controllable current source CS_B comprises a switch SW in series with an adj ustable current source VCS providing a current having a controllable intensity . Switch SW is controlled by signal I_blue . Adj ustable current source VCS is controlled by constant biasing signal Bias .

[0064] Figure 5 shows a block diagram of an embodiment of display sub-pixel SPix_R . Controllable current source CS_R comprises a MOS transistor . Signal I_red corresponds to an analog voltage that is applied on the gate of the transistor CS_R . Display sub-pixel SPix_G can have the same structure as display sub-pixel SPix_R .

[0065] According to an embodiment , data signal Dataj , received at conductive pad P_Col of each display pixel 12l fj , is a binary signal alternating between a low logical state " 0" and a high logical state " 1" , the low logical state corresponding to low reference potential Gnd and the high logical state " 1" corresponding to a low voltage , for example , approximately 1 V, smaller than decreased power supply voltage Vdd . In this embodiment , stored color signals R, G, and B are digital signals .

[0066] Figure 6 shows a block diagram of an embodiment of circuit 40 of display pixel 12i fj of Figure 3 when data signal Dataj is a binary signal and color signals R, G, and B are digital signals . Storage circuit 48 comprises three registers RR, GR, BR . The bits of digital color signal R are stored in memory cells of register RR, the bits of digital color signal G are stored in memory cells of register RG, and the bits of digital color signal B are stored in memory cells of register RB . Driver circuit 50 comprises a digital-to-analogic converter DAC_R configured to receive digital color signal R from register RR and to convert digital color signal R into an analog signal that corresponds to signal I_red . Driver circuit 50 also comprises a digital-to-analogic converter DAC_G configured to receive digital color signal G from register RG and to convert digital color signal G into an analog signal that corresponds to signal I_green .

[0067] According to another embodiment , stored color signal R and G are analog signals . Storage circuit 48 can comprise capacitors configured to store analog color signals R and G . According to an embodiment , circuit 48 is configured to convert the bits of data relative to color signal R into an analog voltage proportional to the data, the analog voltage being stored across a first capacitor . The voltageacross the first capacitor can then correspond to analog color signal R . Circuit 48 is configured to convert the bits of data relative to color signal G into an analog voltage proportional to the data, the analog voltage being stored across a second capacitor . The voltage across the first capacitor can then correspond to analog color signal G .

[0068] According to an embodiment , selection signal Comi , received at conductive pad P_Row of each display pixel 12i fj , is a binary signal alternating between a low logical state " 0" and a high logical state " 1" , the low logical state corresponding to low reference potential Gnd and the high logical state " 1" corresponding to a low voltage , for example , approximately 1 V, smaller than decreased power supply voltage Vdd .

[0069] Figure 7 shows a block diagram of another embodiment of a display pixel 12l fj of display screen 10 . Display pixel 12i fj shown in Figure 7 comprises all the elements of display pixel 12i fj shown in Figure 6 . Interface circuit 46 is configured to deliver a clock signal Clk from selection signal Comi or data signal Dataj and data signal Data from data signal Dataj to storage circuit 48 in a first phase Pl , also called programming phase , and to deliver a modulation timing signal PWM from selection signal Comi to driver circuit 50 for controlling the controllable current source CS_B of display sub-pixel SPix_B in a second phase P2 , also called display phase . Modulation timing signal PWM can be equal to selection signal Comi during each display phase P2 . Clock signal Clk can be equal to selection signal Comi during each programming phase Pl when it is generated from selection signal Comi . Storage circuit 48 is configured, when clocked by clock signal Clk, to storedigital color signals R, G, B based on received digital data Data.

[0070] Figure 8 shows a timing diagram of signals received by display pixels 12lfj having the structure shown in Figure 7 for an embodiment of a method of displaying an image on display screen 10.

[0071] Potentials Vcc and Gnd are substantially constant. The image pixels of a new image to be displayed are successively displayed from the row of rank 1 to the row of rank M. Call frame duration T the duration separating two successive selections of the same row of display screen 10. Timing diagrams of signals Com! and Datai will be detailed for the row of rank 1, knowing that the timing diagrams of signals Comi are similar to the timing diagram of signal Comi, although shifted in time. The display of a new image pixel by a display pixel 121rj , with j varying from 1 to N, of the row of rank 1 comprises first phase Pl followed by second phase P2 . During phase Pl, data signals Dataj are transmitted to each display pixel 12lrj of the row of rank 1, only signal Datai being shown in Figure 8. During second phase P2, the light-emitting diodes of each display pixel 12ifj are controlled from the R, G, B color signals, determined based on data signals Dataj .

[0072] During first phase Pl, selection signal Comi is set to state "1". The setting to state "1" of signal Comi for a long duration is detected by interface circuit 46 of each display pixel 12ifj of the row of rank 1 and thus enables to select the display pixels 12irj of this row, while the display pixels of the other rows are not selected. During first phase Pl, data signals Dataj are transmitted onto column electrodes 20j. For each display pixel 12ifj, interface circuit 46 determines a clock signal Clk and dataData based on the pulses of data signal Dataj . As an example , each pulse of data signal Dataj may have a first duration or a second duration, longer than the f irst duration . Signal Clk may correspond to a sequence of pulses of same durations having their rising edges coinciding, to within a possible constant of fset , with the rising edges of the pulses of data signal Dataj . Data Data may correspond to a binary signal at state " 0" when the pulse of signal Dataj has the first duration, and at state " 1" when the pulse of signal Dataj has the second duration . Interface circuit 46 , selected by signal Com! at state " 1" , delivers , at the rate of clock signal Clk, the data Data which are stored in circuit 48 in the form of R, G, B digital signals having their bits provided by the successive values of signal Data . The end of first period Pl for a row corresponds to the beginning of first period Pl for the next row .

[0073] According to an embodiment , the light-emitting diodes of display sub-pixel SPix_B are controlled by pulse-width modulation or PWM control . For this purpose , during second phase P2 , selection signal Comi exhibits the repetition of a succession of pulses at state " 1" which are transmitted by interface circuit 46 of each display pixel 12l rj of the row of rank 1 to circuit 50 ( PWM signal ) to clock the operation of circuit 50 for the control of light-emitting diodes LED of display sub-pixel SPix_B by pulse-width modulation . The number of pulses in the succession corresponds to the number of bits of each B digital signal . As an example , when current source CS_B is as shown in Figure 4 , switch SW is opened or closed, at the rate of the PWM pulses , according to the value " 0" or " 1" of each bit of B color signal , starting by the most signi ficant bit , this transistor being maintained on or of f until the nextpulse of signal Com! . The duration between two succes sive pulses of signal Comi is divided each time by two , so that the total duration for which the light-emitting diode is on depends on the value of the B color signal . The succession of pulses of signal Com! is repeated until the next first phase Pl of the row of rank 1 , a single repetition being illustrated as an example in Figure 8 .

[0074] According to another embodiment , data signal Dataj , received at conductive pad P_Col of each display pixel 12i fj , is an analog signal . Storage circuit 48 can comprise capacitors configured to store the analog color signals R, G, B .

[0075] Figure 9 shows a block diagram of another embodiment of a display pixel 12l fj of display screen 10 . Display pixel 12l fj shown in Figure 9 comprises all the elements of display pixel 12l fj shown in Figure 6 . According to an embodiment , selection signal Com! , received at conductive pads P_Row of each display pixel 12i rj , is an analog signal . Interface circuit 46 is configured to receive data signal Dataj and to deliver analog signal Data to storage circuit 48 in programming phase Pl and to provide an analog reference signal REF adapted for the performing of a PWM control in display phase P2 . Storage circuit 48 comprises a capacitor CR for storing analog color signal R . Analog color signal R can correspond to the voltage across capacitor CR . Storage circuit 48 comprises a capacitor CG for storing analog color signal G . Analog color signal G can correspond to the voltage across capacitor CG . Storage circuit 48 comprises a capacitor CB for storing analog color signal B . Analog color signal B can correspond to the voltage across capacitor CB . Driver circuit 50 is configured to command the controllable current sources CS_R, CS_G, CS_B coupled to light-emitting diodes LED with control signalsobtained from the analog control signals R, G, B and, for current source CS_B of display sub-pixel SPix_B, further from analog reference signal REF .

[0076] In an embodiment , signal Comi allows both the selection of display pixel 12l fj for the storage of a data signal Data and the delivery of the analog reference signal used for the PWM control of the light-emitting diodes of display sub-pixel SPix_B .

[0077] Figure 10 shows timing diagrams of signals received by display pixels 12i rj for an embodiment of a method of displaying an image on display screen 10 . For illustration purposes , in Figure 10 , there have only been shown signals associated with the row of rank 1 and the column of rank 1 of display screen 10 .

[0078] In the present embodiment , potentials Vcc and Gnd, not shown in Figure 10 , are substantially constant during the operation of display screen 10 . The image pixels of a new image to be displayed are successively displayed from the row of rank 1 to the row of rank M . There is called frame duration T the duration separating two successive selections of the same row of display screen 10 . The display of a new image pixel by a display pixel 12l fj , j varying from 1 to N, of the row of rank i comprises a first phase Pl followed by a second phase P2 . During phase Pl , analog data signals Dataj are transmitted to the display pixels 12l fj of the row of rank i , only signal Datai being shown in Figure 10 . Each display pixel 12i fj stores a new value of the R, G, or B analog color signal based on the received analog data signal Dataj . According to an embodiment , display pixel 12l fj can receive the data signals Dataj corresponding to the di f ferent colors successively during phase Pl . During second phase P2 , the light-emitting diodesof each display pixel 12lfj are controlled from the stored R, G, B color signals.

[0079] During first phase Pl, selection signal Comi is set to a high level, substantially constant, thus forming a voltage pulse. The pulse of signal Comi is detected by interface circuit 46 of each display pixel 12lfj of the row of rank i and thus enables to select the display pixels 12lfj of this row, while the display pixels of the other rows are not selected. According to an embodiment, the duration of each pulse is shorter than the duration of the frame divided by the number of rows to be selected, preferably shorter than 100 ps . During first phase Pl, data signals Dataj are transmitted onto column electrodes 20j . Each data signal Dataj may correspond to an analog signal capable of taking a constant value from a minimum value to a maximum value. Interface circuit 46 delivers signal Dataj which is stored in the circuit 50 of display pixel 12lfj in the form of an R, G, or B signal having its value depending on signal Dataj, the signal Ri,i stored by display pixel 12lfl, and the current ILEDlflcrossing the light-emitting diode of display sub-pixel SPix_B display pixel 12lflbeing shown as an example in Figure 10. The end of the first phase Pl for a row may correspond to the beginning of the first phase Pl for the next row.

[0080] According to an embodiment, the light-emitting diodes of display sub-pixel SPix_B of display pixel 12lfj are controlled by pulse-width modulation. For this purpose, during a first portion P2_ON of second phase P2, selection signal Comi periodically varies, exhibiting a succession of identical patterns which are detected by interface circuit 46 of each display pixel 12lfj of the row of rank i. Interface circuit 46 transmits the succession of patterns to circuit 50, as analog reference signal REF for thecontrol of light-emitting diodes LED of display sub-pixel SPix_B by pulse-width modulation. As an example, in Figure 10, each pattern comprises an ascending voltage ramp followed by a descending voltage ramp. According to another example, each pattern only comprises one ascending voltage ramp or only one descending voltage ramp. Generally, each pattern comprises a determined voltage variation curve, for example, an exponential growth curve, a sinusoidal curve, etc. The shape of the pattern may for example include eye sensitivity compensations, in particular a gamma correction. The pattern repetition frequency on each phase P2_OFF enables to have between 1 and 1,000 pattern cycles per phase P2_OFF.

[0081] The circuit 50 of display pixel 12ifj controls lightemitting diodes LED of display sub-pixel SPix_B based on the comparison between the stored B analog signal and analog reference signal REF. As an example, current source CS_B of display sub-pixel SPix_B is turned off when the stored B analog signal is greater than analog reference signal REF, which results in a zero current ILED powering the light-emitting diode, and current source CS_B of display sub-pixel SPix_B is turned on when the stored B analog signal is smaller than analog reference signal REF, which results in a current ILEDlflpowering the lightemitting diode at a constant non-zero value.

[0082] During a second portion P2_OFF of second phase P2, selection signal Comi is maintained at a constant level, for example, a low level, so that the light-emitting diodes LED of display sub-pixels SPix_B of the display pixels in the row are off. The duration of second portion P2_OFF may vary from 0% to 100% of the duration of second phase P2. In particular, second portion P2_OFF may not be present. According to an embodiment, the duration of each phase P2is equal to the duration of the frame Tframe decreased by the duration of phase Pl .

[0083] During display phase P2 , driver circuit 50 commands controllable current sources CS_R and CS_G coupled to light-emitting diodes LED of display sub-pixels SPix_R and SPix_B with control signals I_red and I_green obtained that can correspond to the analog control signals R and G .

[0084] According to another embodiment , data signal Dataj , received at conductive pad P_Col of each display pixel 121rj , is a digital signal for the transmission of color signal B and is an analog signal for the transmission of color signals G and R . Therefore , color signal B is a digital signal and storage circuit 48 can comprise a register for storing digital color signal B . Moreover, color signals R and G are each an analog signal . Storage circuit 48 can comprise capacitors configured to store the analog color signal R and G .

[0085] Figure 11 is a partial simpli fied cross-section view of an embodiment of a display pixel 12i rj compris ing microwires or nanowires . Display pixel 12i fj comprises , from bottom to top in Figure 11 :-a substrate 60 comprising opposite surface 62 and 64 , upper surface 62 being preferably planar at least at the level of the light-emitting diodes ;-a seed layer 66 made of a material favoring the growth of wires and arranged on surface 62 ;-an insulating layer 68 covering seed layer 66 and comprising openings 70 exposing portions of seed layer 66 ; -light-emitting diodes LED ( six light-emitting diodes being shown) , each light-emitting diode LED being in contact with seed layer 66 through one of openings 70 ;-an insulating layer 74 extending on the lateral sides ofa lower portion of light-emitting diode LED and extending on insulating layer 68 between light-emitting diodes LED; -a layer 76 forming an electrode covering each lightemitting diode LED and further extending on insulating layer 74 between light-emitting diodes LED;-a reflective conductive layer 78 , extending on layer 76 between light-emitting diodes LED, where conductive layer 78 may as a variant be interposed between electrode layer 76 and insulating layer 74 between light-emitting diodes LED;-a dielectric protection layer 80 extending on layers 76 and 78 ;-photoluminescent blocks 82 covering the assemblies of light-emitting diodes of display sub-pixels SPix_R and SPix_G;-blocks 84 transparent to the radiation emitted by the light-emitting diodes of display sub-pixels SPix_B, which transparent blocks 84 may be omitted;-walls 88 between blocks 82 , 84 , each wall 88 being opaque for the radiation emitted by the light-emitting diodes LED; and-one , two , or three color filters 90 for example , a single yellow filter, two filters , the first one being a yellow filter and the second one being a red filter, or three filters , the first one being a red filter, the second one being a green filter, and the third one being a blue filter, covering at least some of blocks 82 , 84 a single filter 90 covering two blocks being shown as an example .

[0086] According to one embodiment , each light-emitting diode can be a three-dimensional light-emitting diode . According to one embodiment , the light-emitting diodes LED comprise semiconductor layers made of I I I-V compounds , for exampleGaN, AIN, InN, InGaN, AlGaN or AlInGaN, or of II-VI compounds .

[0087] A three-dimensional light-emitting diode comprises a three-dimensional semiconductor element, for example a wire, conical, f rustoconical or pyramidal element, in particular a microwire or a nanowire, over which the active zone of the light-emitting diode extends. The term "microwire" or "nanowire" designates a three-dimensional structure of elongated shape in a preferred direction, of which at least two dimensions, called minor dimensions, are between 5 nm and 2.5 pm, preferably between 50 nm and 2.5 pm, the third dimension, called major dimension, being at least equal to 1 time, preferably at least 2 times, the largest of the minor dimensions. In certain embodiments, the minor dimensions can be less than or equal to about 3 pm, preferably between 100 nm and 3 pm, more preferably between 1 pm and 1.5 pm. In certain embodiments, the height of each microwire or nanowire can be greater than or equal to 500 nm, preferably between 1 pm and 50 pm.

[0088] Figure 12 is a partial and schematic sectional view of an embodiment of the light-emitting diodes LED of the display pixel 12ifj . According to one embodiment, each light-emitting diode LED comprises a wire 90 in contact with the seed layer 66 through one of the openings 70 and a shell 92 comprising a stack of semiconductor layers covering the side walls and the top of the wire 90. Such a configuration is called radial. The assembly formed by each wire 90 and the associated shell 92 constitutes the lightemitting diode LED.

[0089] The shell 92 may comprise a stack of several layers comprising in particular an active layer 94 and a connecting layer 96. The active layer 94 is the layer fromwhich the majority, preferably all, of the radiation supplied by the light-emitting diode LED. According to one example, the active layer 94 can include confinement means, such as a single quantum well or multiple quantum wells. Bonding layer 96 may comprise a stack of semiconductor layers of the same III-V material as wire 90 but of the opposite conductivity type to wire 90.

[0090] Figure 13 is a partial and schematic sectional view of another embodiment of the light-emitting diodes LED of the display pixel 12ifj . The light-emitting diode LED shown in Figure 13 comprises all the elements of the lightemitting diode LED represented in Figure 12 with the difference that the shell 92 is present only at the top of the wire 90. Such a configuration is said to be axial.

[0091] The formation of the light-emitting diodes LED as represented in Figures 12 and 13, that is to say the growth of the wires 90 in the openings 70, and the formation of the shells 92 covering the wires 90 can be carried out by for example by metal-organic chemical vapor deposition (MOCVD) or any other suitable method.

[0092] Substrate 60 can correspond to control circuit 30 previously disclosed.

[0093] Seed layer 66 is made of a material favoring the growth of wires. As an example, the material forming seed layer 66 may be a nitride, a carbide, or a boride of a transition metal from column TV, V, or VI of the periodic table of elements or a combination of these compounds. According to an embodiment, seed layer 66 may be omitted. According to another embodiment, seed layer 66 may be replaced with seed pads, for example, formed at the bottom of openings 70.

[0094] Each insulating layer 68, 74, 80 may be made of a dielectric material, for example, of silicon oxide (SiOg) ,of silicon nitride (SixNy, where x is approximately equal to 3 and y is approximately equal to 4, for example, Si N^ , of silicon oxynitride (particularly of general formula SiOxNy, for example, SigONg) , of aluminum oxide (AlgOg) , of hafnium oxide (HfOg) , of titanium dioxide (TiCt) , or of diamond. Insulating layer 68, 74, 80 may have a monolayer structure or may correspond to a stack of two layers or of more than two layers. When insulating layer 68 corresponds to a stack of at least two layers, the upper layer of the stack is of insulating type, for example, made of a dielectric material.

[0095] Conductive layer 78 preferably corresponds to a metal layer, for example, aluminum, silver, copper, gold, or zinc. The thickness of conductive layer 78 may be in the range from 0.01 pm to 1,000 pm.

[0096] Electrode layer 76 is capable of giving way to the electromagnetic radiation emitted by the light-emitting diodes. The material forming electrode layer 76 may be a transparent and conductive material such as indium tin oxide (ITO) , aluminum or gallium zinc oxide, or graphene. The thickness of electrode layer 76 may be in the range from 0.01 pm to 10 pm.

[0097] According to an embodiment, each photoluminescent block 82 is located opposite one of the light-emitting diodes or an assembly of light-emitting diodes. Each photoluminescent block 82 comprises luminophores capable, when they are excited by the light emitted by the associated light-emitting diode LED, of emitting light at a wavelength different from the wavelength of the light emitted by the associated light-emitting diode LED. According to an embodiment, display pixel 12lfj comprises at least two types of photoluminescent blocks 82. Each photoluminescent block82 of the first type is capable of converting the radiation supplied by the light-emitting diodes into a first radiation at a first wavelength, and each photoluminescent block 82 of the second type is capable of converting the radiation supplied by the light-emitting diodes that it covers into a second radiation at a second wavelength.

[0098] According to an embodiment, the light-emitting diodes are capable of emitting blue light, that is, a radiation having its wavelength in the range from 430 nm to 480 nm. According to an embodiment, the first wavelength corresponds to green light and is in the range from 510 nm to 570 nm. According to an embodiment, the second wavelength corresponds to red light and is in the range from 600 nm to 720 nm.

[0099] The aspect ratio of blocks 82, that is, the ratio of the height to the maximum width of the block, may be in the range from 0.01 to 10, preferably from 0.05 to 2.

[0100] According to an embodiment, each photoluminescent block 82 comprises particles of at least one photoluminescent material, for example, in a transparent matrix. An example of a photoluminescent material is yttrium aluminum garnet (YAG) activated by the trivalent cerium ion, also called YAG:Ce or YAG:Ce3+. The average size of the particles of conventional photoluminescent materials is generally greater than 5 pm.

[0101] According to an embodiment, each photoluminescent block 82 comprises a matrix having nanometer-range monocrystalline particles of a semiconductor material, also called semiconductor nanocrystals or nano-luminophore particles hereafter, dispersed therein. The internal quantum efficiency QYlntof a photoluminescent material is equal to the ratio of the number of emitted photons to thenumber of photons absorbed by the photoluminescent substance. The internal quantum efficiency QYintof the semiconductor nanocrystals is greater than 5%, preferably greater than 10%, more preferably greater than 20%.

[0102] According to an embodiment, the average size of the nanocrystals is in the range from 0.5 nm to 1, 000 nm, preferably from 0.5 nm to 500 nm, more preferably from 1 nm to 100 nm, particularly from 2 nm to 30 nm. For dimensions smaller than 50 nm, the photoconversion properties of semiconductor nanocrystals essentially depend on quantum confinement phenomena. The semiconductor nanocrystals then correspond to quantum dots.

[0103] According to an embodiment, the semiconductor material of the semiconductor crystals is selected from the group comprising cadmium selenide (CdSe) , indium phosphide (InP) , cadmium sulfide (CdS) , zinc sulfide (ZnS) , zinc selenide (ZnSe) , cadmium telluride (CdTe) , zinc telluride (ZnTe) , cadmium oxide (CdO) , zinc cadmium oxide (ZnCdO) , cadmium zinc sulfide (CdZnS) , cadmium zinc selenide (CdZnSe) , silver indium sulfide (AgInS2) , perovskites of PbScXg type where X is a halogen atom, particularly iodine (I) , bromine (Br) , or chlorine (Cl) , and a mixture of at least two of these compounds. According to an embodiment, the semiconductor material of the semiconductor nanocrystals is selected from the materials mentioned in Le Blevenec et al . ' s publication in Physica Status Solid! (RRL) - Rapid Research Letters Volume 8, No. 4, pages 349-352, April 2014.

[0104] According to an embodiment, the dimensions of the semiconductor nanocrystals are selected according to the desired wavelength of the radiation emitted by the semiconductor nanocrystals. As an example, CdSenanocrystals having an average size in the order of 3.6 nm are capable of converting blue light into red light and CdSe nanocrystals having an average size in the order of 1.3 nm are capable of converting blue light into green light. According to another embodiment, the composition of the semiconductor nanocrystals is selected according to the desired wavelength of the radiation emitted by the semiconductor nanocrystals.

[0105] The matrix is at least partly transparent to the radiation emitted by the photoluminescent particles and / or light-emitting diodes LED, preferably by more than 80%. The matrix is for example made of silica. The matrix is for example made of any at least partly transparent polymer, particularly of silicone, of acrylic resin or poly (methyl methacrylate) (PMMA) type or of polylactic acid (PLA) . The matrix may in particular be made of an at least partly transparent polymer used with three-dimensional printers. The matrix may correspond to photosensitive or nonphotosensitive glass deposited by centrifugation (SOG, Spin-On Glass) . According to an embodiment, the matrix contains from 2% to 90%, preferably from 10 wt . % to 60 wt.%, of nanocrystals, for example, approximately 30 wt . % of nanocrystals.

[0106] The thickness of photoluminescent blocks 82 depends on the nanocrystal concentration and on the type of nanocrystals used. The height of photoluminescent blocks 82 is preferably greater than the height of wires 71 and smaller than or equal to the height of walls 88. In top view, each photoluminescent block 82 may correspond to a square, a rectangle, an "L"-shaped polygon, etc. having an area that may be equal to the area of a square having a side length from 1 pm to 100 pm, preferably from 3 pm to 15 pm.

[0107] According to one embodiment , the opaque walls 88 are reflective for the radiation emitted by the light-emitting diodes LED . Walls 88 are at least partly made of at least one reflective material . The reflective material may be a metallic material , particularly iron, copper, aluminum, tungsten, silver titanium, hafnium, zirconium, or a combination of at least two of these compounds . Preferably, walls 88 are made of a material compatible with manufacturing methods implemented in microelectronics . Preferably, walls 88 are made of aluminum or of silver .

[0108] The height of walls 88 , measured along a direction perpendicular to surface 62 , is in the range from 300 nm to 200 pm, preferably from 3 pm to 15 pm . The thickness of walls 88 , measured along a direction parallel to surface 62 , is in the range from 100 nm to 50 pm, preferably from 0 . 5 pm to 10 pm .

[0109] According to an embodiment , walls 88 may be made of a reflective material or covered with a coating which is reflective at the wavelength of the radiation emitted by photoluminescent blocks 82 and / or the light-emitting diodes . Preferably, walls 88 surround photoluminescent blocks 82 . Walls 88 then decrease the crosstalk between adj acent photoluminescent blocks 82 .

[0110] Various embodiments and variants have been described . Those skilled in the art will understand that certain features of these various embodiments and variants may be combined, and other variants will occur to those skilled in the art .

[0111] Finally, the practical implementation of the described embodiments and variations is within the abilities of those skilled in the art based on the functional indications given hereabove .

Claims

CLAIMS1. A display pixel (12lfj) comprising at least first and second light-emitting diodes (LED) , a first controllable current source (CS_B) supplying said first light-emitting diode (LED) with a first current, a second controllable current source (CS_R) supplying said second light-emitting diode (LED) with a second current, and an electronic circuit (40) comprising a storage circuit (48) for storing at least first and second color signals (R, B) and a driver circuit (50) configured to control the first controllable current source (CS_B) to supply the first current by pulse-width modulation based on the first color signal (B) and configured to control the second controllable current source (CS_R) to supply the second current by a linear command based on the second color signal (R) .

2. The display pixel according to claim 1, further comprising a third light-emitting diode (LED) , and a third controllable current source (CS_G) supplying said third light-emitting diode (LED) with a third current, the storage circuit (48) being configured to store a third color signal (G) and the driver circuit (50) being configured to control the third controllable current source (CS_G) to supply the third current by a linear command based on the third color signal (G) .

3. The display pixel according to claim 1 or 2, wherein the first color signal (B) is a digital signal and the storage circuit (48) comprises first memory cells (RB) for storing the bits of the first color signal (B) .

4. The display pixel according to any one of claims 1 to 3, wherein the second color signal (R) is a digital signal and the storage circuit (48) comprises second memory cells (RR) for storing the bits of the second color signal (R) .

5. The display pixel according to claim 4, wherein the driver circuit (50) comprises a digital-to-analog converter (DAC_R) configured to convert the second color signal (R) stored in the second memory cells (RR) into an analog control signal (I_red) for controlling the second current source (CS_R) .

6. The display pixel according to claim 1 or 2, wherein the first color signal (B) is an analog signal and the storage circuit (48) comprises a first capacitor (CB) for storing the first color signal (B) .

7. The display pixel according to claim 1 or 2, wherein the second color signal (R) is an analog signal and the storage circuit (48) comprises a second capacitor (CR) for storing the second color signal (B) .

8. The display pixel according to any one of claims 1 to 7, wherein each of first and second light-emitting diodes (LED) comprises several elemental light-emitting diodes comprising each an active zone (94) covering a three- dimensional semiconductor element (90) corresponding to a wire, conical, f rustoconical or pyramidal element of nanometer or micrometer range.

9. The display pixel according to any one of claims 1 to 8, wherein the second light-emitting diode (LED) is covered by a first photoluminescent block (82) .

10. The display pixel according to claim 9, wherein the first light-emitting diode (LED) is configured to emit a first radiation at a first wavelength, wherein the second light-emitting diode (LED) is configured to emit a second radiation at a second wavelength, and wherein the first photoluminescent block (82) is configured to convert thesecond radiation into a third radiation at a third wavelength, different from the second wavelength.

11. The display pixel according to claim 10, wherein the first wavelength is equal to the second wavelength within10% .

12. The display pixel according to any of claims 9 to 11, wherein the first photoluminescent block (82) comprises first quantum dots.

13. The display pixel according to claim 2, wherein the third light-emitting diode (LED) is covered by a second photoluminescent block (82) .

14. The display pixel according to claims 10 and 13, wherein the third light-emitting diode (LED) is configured to emit a fourth radiation at a fourth wavelength, and wherein the second photoluminescent block (82) is configured to convert the fourth radiation into a fifth radiation at a fifth wavelength, different from the fourth wavelength .

15. The display pixel according to claim 14, wherein the fourth wavelength is equal to the first wavelength within10% .

16. The display pixel according to any of claims 13 to 15, wherein the second photoluminescent block (82) comprises second quantum dots.

17. The display pixel according to any one of claims 1 to16, comprising a single integrated circuit (30) including said electronic circuit (40) comprising said storage circuit (48) and said driver circuit (50) .

18. The display pixel according to claim 17, comprising an optoelectronic circuit (32) attached to the integrated circuit (30) , said optoelectronic circuit (32) comprising the first and second light-emitting diodes (LED) .

19. A display screen (10) comprising: display pixels (12ifj) according to any one of claims 1 to 18; first electrodes (18i) coupled to the driver circuits (50) of the display pixels (12ifj) ; a first circuit (22) for delivering a selection signal (Comi) on each first electrode for the selection of the display pixels (12ifj) coupled to the first electrode; second electrodes (20j) coupled to the electronic circuits (40) of the display pixels (12ifj) ; and a second circuit (24) for delivering data signals (Dataj) on the second electrodes.

20. The display screen according to claim 19, wherein the second circuit (24) is configured to deliver the data signals (Dataj) on the second electrodes (20j) as analog signals .

21. The display screen according to claim 19, wherein the second circuit (24) is configured to deliver the data signals (Dataj) on the second electrodes (20j ) as digital signals .

22. The display screen according to claim 19, wherein the second circuit (24) is configured to deliver the data signals (Dataj) on the second electrodes (20j ) comprising alternating digital signals and analog signals.

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