Micro-led display emitting by active matrix

Abstract

The present invention relates to a display comprising a plurality of electronic chips (10) having μLEDs and an active matrix (40) for controlling the chips, the active matrix being mounted on a transparent slider (2). Each chip includes a plurality of light-emitting diodes (13), each chip including a substrate (11) including an electrode (12) common to the μLEDs, and including the μLEDs and electrical control contacts (14) of the μLEDs on its upper portion. The display includes: - one or more power planes (20) disposed on the upper surface of a support plate (1); - a plurality of electronic chips, a first conductive element (30) providing an electrical connection between the common electrode of each chip and the power plane; - a transparent slider (2) carrying the active matrix, a second conductive element (31) providing an electrical connection between the electrical contacts of the electronic chips and the electrical contacts (41) for controlling the active matrix.

Description

Background Technology

[0001] The field of this invention is flat panel displays. Currently, there are two main types of display technologies. The first technology involves realizing a liquid crystal matrix illuminated by light-emitting diodes, or "LEDs," with constant illumination. The liquid crystal cells act as spatial intensity modulators to form images.

[0002] The second technology involves creating a matrix of light-emitting diodes (LEDs) made of organic materials, or "OLEDs," to directly form an image. More precisely, the basic color pixels of an image consist of three diodes that emit light in three different colors, typically green, red, and blue. In this technology, the OLED acts as both the light source and the modulator.

[0003] OLEDs are primarily produced using a stack of thin layers with the functional characteristics of light-emitting diodes. These layers include, for example, n-type doped layers for providing electrons, p-type doped layers for providing holes, and intrinsic recombination layers for emitting photons. These layers are deposited in a vacuum or directly onto a transistor matrix via inkjet printing. The transistor matrix functions to control the current, and thus the intensity of the light emitted in the OLED at each point in the image. In the following description, this electron matrix will be referred to as the active matrix.

[0004] In recent years, a third very promising technology has emerged: μLED, or inorganic light-emitting diode. These diodes are called μLEDs because they are extremely small, approximately 100 micrometers in size.

[0005] In this latest technology, light-emitting diodes (LEDs) are no longer deposited in a thin layer on an active matrix. These LEDs, which are discrete components most commonly made of sapphire, silicon, or silicon carbide, are transferred and connected at the back to a glass plate supporting the active matrix. These μLEDs then act as a light source and modulator in the same way as OLEDs.

[0006] In display devices using organic or inorganic LEDs with an active matrix, it is preferable to emit light from the side opposite to the active matrix. This ensures that the rows, columns, and transistors of the active matrix constituting the LED control device do not obstruct light transmission. The entire surface of the emitter is then used to emit light.

[0007] However, this requires the LED's contacts to be located on the surface opposite to its light-emitting surface. This arrangement presents numerous challenges in its implementation.

[0008] In the case of a display device in which the LED is a discrete component transferred to an active matrix, the method for generating LEDs on a sapphire or silicon substrate provides a component in which the light-emitting surface is naturally located on the same side as the contacts.

[0009] In all cases, generating a colored component that includes light emission on the side opposite the electrical contact requires thinning or removing the initial substrate.

[0010] This removal or thinning is necessary to allow light transmission, for example when the substrate is made of silicon. It is also necessary to allow the creation of a color conversion layer on the emitting side, for example when the substrate is made of sapphire or silicon. This results in the LED being transferred multiple times to various substrates before obtaining the final component, whose contacts are located on one side of the active matrix and whose emitting area is located on the opposite side via the color conversion layer.

[0011] These multiple substrate thinning or transfer operations are expensive. They have random yields. They make components fragile and limit the temperature and pressure that can be used to bond and connect LEDs to the active matrix.

[0012] Therefore, display solutions with LEDs that emit light through an active matrix have fewer manufacturing difficulties. Summary of the Invention

[0013] The μLED display according to the present invention falls within this context, that is, the context of a display emitting light through an active matrix. The present invention has three objectives:

[0014] - Limit the number of steps involved in producing the LED on its substrate. This eliminates the need for contacts on its light-emitting surface;

[0015] - Reduce the number of contacts between the active matrix and the LED;

[0016] - Reduce the number of power sources distributed above the glass plate that serves as the support plate for the active matrix. Specifically, power sources via the surface opposite the active matrix are preferentially moved through the conductive plane of that surface of the device.

[0017] Therefore, the subject of this invention is a μLED display, comprising a plurality of electronic chips having μLEDs and an active matrix for controlling the chips having μLEDs, the active matrix being mounted on a transparent slider, each chip having μLEDs comprising a plurality of light-emitting diodes, each chip having μLEDs comprising a substrate, the substrate comprising a conductive surface serving as a common electrode on its lower portion, and comprising μLEDs and electrical control contacts for the μLEDs on its upper portion, characterized in that the display comprises at least the following in the following order:

[0018] - Support plate, including a lower surface and an upper surface;

[0019] - One or more first power planes are arranged on the upper surface of the support plate;

[0020] - Multiple first conductive elements;

[0021] - Multiple electronic chips, wherein a first conductive element provides an electrical connection between a common electrode of each chip and a first power plane;

[0022] - Multiple second conductive elements, each of which is arranged on an electrical contact for controlling an electronic chip;

[0023] - A transparent slider carrying an active matrix, each second conductive element providing an electrical connection between the electrical contacts of the electronic chip and the electrical contacts used to control the active matrix.

[0024] Advantageously, the power plane is common to all electronic chips.

[0025] Advantageously, the second power supply plane is arranged on the lower surface of the support plate.

[0026] Advantageously, the second power plane is electrically connected to the upper surface of the support plate via a conductive via, which provides an electrical connection between the first power plane and the second power plane.

[0027] Advantageously, the heat dissipation element is attached to the underside of the support plate.

[0028] Advantageously, a third power plane is arranged on the lower surface of the support plate and is electrically connected to a metal connecting plate or conductive connecting plate via a conductive via. The metal connecting plate or conductive connecting plate is independent of the first or second power plane and is placed on the upper surface of the support plate. Multiple third conductive elements provide electrical connections between each via and an electrical contact for the power supply of the active matrix.

[0029] Advantageously, the support plate is a multilayer printed circuit comprising multiple electrically insulating conductive layers.

[0030] Advantageously, the support plate includes compartments into which electronic chips are inserted.

[0031] Advantageously, the support plate includes a first conductive pad disposed on each via, the height of which is equal to the height of the electronic chip.

[0032] Advantageously, the transparent slider includes a second conductive pad arranged facing each via, the height of which is equal to the height of the electronic chip.

[0033] Advantageously, the support plate is transparent, and the power plane is a grid that includes conductive pads arranged below the μLED.

[0034] Advantageously, the support plate is made of glass or polyethylene terephthalate.

[0035] Advantageously, the grid is covered with a light-absorbing material.

[0036] Advantageously, the space separating the first power plane from the transparent slider carrying the active matrix is ​​filled with a transparent or opaque insulating material.

[0037] Advantageously, the chips are all identical, each chip including at least three light-emitting diodes, each light-emitting diode emitting light in a spectral band different from the other two light-emitting diodes.

[0038] Advantageously, the chip is of at least three types, each type of chip including one or more identical light-emitting diodes, wherein the light-emitting diodes of one type of chip emit light in a spectral band different from the light-emitting diodes of the other two types of chips. Attached Figure Description

[0039] Other features, details, and advantages of the invention will become apparent from the description given with reference to the accompanying drawings, which are illustrated by way of example, wherein:

[0040] Figure 1 A cross-sectional view of an electronic chip with a light-emitting diode according to the present invention is shown.

[0041] Figure 2 A partial cross-sectional view of a first embodiment of a μLED display including a power plane according to the present invention is shown;

[0042] Figure 3 A partial cross-sectional view of a second embodiment of a μLED display comprising two power planes according to the present invention is shown;

[0043] Figure 4 A partial top view of the power plane of the translucent display according to the present invention is shown. Detailed Implementation

[0044] The display according to the present invention is composed of a matrix or splicing of electronic chips having μLEDs. Figure 1 A cross-sectional view of an electronic chip 10 with μLEDs is shown. The chip includes a substrate 11, which includes a lower surface and a upper surface. Preferably, the substrate is conductive and naturally includes a conductive lower surface 12, which will serve as the common electrode for all diodes, provided that the back surface is not oxidized or the oxide layer can be treated to facilitate the formation of electrical contacts. The substrate is typically made of doped silicon. The upper surface carries the light-emitting μLEDs 13 and control contacts 14 of the light-emitting μLEDs 13, one contact associated with each diode. For each diode 13, the electrical control contact 14 is arranged next to the diode so as not to cover the surface of the diode. The emission of light from the diode is... Figure 1 And indicated by arrows in subsequent diagrams. They are located on the same side as the control contacts.

[0045] Depending on the associated light-emitting diodes (LEDs), various types of chips exist. The first type of chip consists of one or more diode triplets. Each triplet comprises three LEDs, each emitting light in a spectral band different from the other two. Typically, one diode emits red light, the second emits green light, and the third emits blue light. Each triplet corresponds to a color pixel in the imager.

[0046] The second type of chip consists only of diodes that emit light in the same spectral band. Depending on the color of the light emitted by the individual diodes in the chip, there are three types of chips. For example, the first type of chip includes diodes that emit red light, the second type includes diodes that emit green light, and the third type includes diodes that emit blue light. By appropriately juxtaposing different types of chips in a periodic stitching arrangement, pixels are created, each pixel consisting of a triplet of LEDs of a different color.

[0047] The size of electronic chips is on the same order of magnitude as the pixels of a display, that is, a few hundred micrometers. Chips typically have simple geometries (e.g., rectangles, squares, triangles, rhombuses, trapezoids, or hexagons) to allow for periodic splicing.

[0048] Figure 2 A partial cross-sectional view of a first embodiment of a μLED display A according to the present invention is shown. Two chips 10 are shown in this view. The display comprises at least the following components in the following order:

[0049] - Support plate 1, including a lower surface and an upper surface;

[0050] - One or more first power planes 20 are arranged on the upper surface of the support plate 1;

[0051] - Multiple first conductive elements 30;

[0052] - Multiple electronic chips 10 (as defined above), with a first conductive element 30 providing an electrical connection between a common electrode of each chip and a first power plane 20;

[0053] - Multiple second conductive elements 31, each second conductive element being arranged on an electrical contact for controlling an electronic chip;

[0054] - A transparent slider 2 carrying an active matrix 40, each second conductive element 31 providing an electrical connection between the electrical contacts of the electronic chip and the electrical contacts 41 used to control the active matrix 40.

[0055] The support plate 1 can be made of various materials suitable for carrying metallic conductors. Glass, epoxy resin, or polyethylene terephthalate (known as "PET") may be mentioned by way of non-limiting example. The material can be rigid or flexible (like PET) if it is thin enough. If the display is transparent, the support plate must be made of a transparent material (e.g., glass or PET). A transparent display can overlay images externally.

[0056] The power plane can be made of any type of conductive material. Metals with very low resistivity, such as copper or aluminum, are preferred.

[0057] If the display is opaque, it is preferable to darken the metal of the power plane outside the contact land where the electrodes contact, in order to reduce the display's reflection of ambient light. If the display is transparent, the area occupied by the power plane must be minimized as much as possible. For this purpose, such as Figure 4 As shown, the metal plane 20 can be a grid 21 organized into rows and columns, including mounting pads 22 located at the electrodes, allowing external light to pass through. Similarly, the grid can be darkened to reduce stray light.

[0058] To reduce access resistance relative to the center of the display, conductive planes can be placed on both surfaces of the support plate, with metal vias facing each μLED. These metal vias or through-holes serve two functions:

[0059] - Achieve a uniform and consistent voltage distribution over the entire surface of the display.

[0060] - Removes heat generated at each chip. In the latter case, the heatsink can be attached to the back surface. Vias then serve as heat pipes between the chip and the heatsink.

[0061] The first conductive element 30 and the second conductive element 31 are preferably made of a conductive adhesive. This can be isotropic or anisotropic. The conductive adhesive can be solid, in the form of an adhesive strip containing small-sized conductive elements laminated onto a conductive plane, or in the form of a paste containing small-sized conductive elements. The conductive elements can be metal sheets or metal spheres, or insulating spheres covered with a thin layer of metal. For example, the paste can be placed on the LED or on a conductive plane at a precise location on the LED by dispensing it with a syringe or by screen printing.

[0062] To reduce the risk of short circuits between the conductive plane and the metal tracks on the active matrix, it may be advantageous to fill the spaces between the LEDs with an insulating material (e.g., resin or adhesive). This material can be transparent or opaque black to optically isolate the chip from the μLEDs. This filling of spaces can be done before, during, or after the addition of the conductive plane.

[0063] As is well known, in order to power a diode, a positive power supply voltage (usually called VDD) and a negative power supply voltage (usually marked as ground GND or VSS) are required, and the current required to emit light flows through the positive and negative power supply voltages.

[0064] High access impedance in the power plane causes a voltage drop in the conductive plane. This voltage drop forces the use of a power supply voltage significantly higher than the minimum power supply voltage for the LED and transistor, and thus leads to excessive power consumption. The two power planes can be located on the top surface of the support plate, or they can be arranged on both surfaces of the support plate.

[0065] Figure 3 A partial cross-sectional view of an embodiment of a μLED display A employing this arrangement of power planes according to the present invention is shown. Two chips are shown in this view. Various reference numerals are... Figure 2 The views are the same.

[0066] In this configuration, the power plane 23 is arranged on the lower surface of the support plate 1. The power plane 23 is electrically connected to a metal connecting plate or conductive connecting plate through a conductive via 24. The metal connecting plate or conductive connecting plate is independent of the first or second power plane and is placed on the upper surface of the support plate. A plurality of third conductive elements 32 provide electrical connection between each via 24 and an electrical contact 42 for the power supply of the active matrix 40.

[0067] One voltage is then directly connected to the common electrode of all μLEDs on the same chip. The second voltage is connected to the drain or source of all control transistors of the μLEDs on the active matrix. Therefore, it is necessary to distribute two power supplies throughout the device.

[0068] However, when power planes are produced on active matrices in thin layers less than 1 μm thick, it is difficult to obtain power planes with low access impedance.

[0069] A support plate with the potential to support multiple electrically insulating metal layers (e.g., multilayer printed circuits) is preferred. The chips supporting the μLEDs also need to be significantly spaced apart on the active matrix to free up space in areas of the active matrix that contact the power plane.

[0070] The difficulty in performing contact operations stems from the fact that the contacts on the active matrix and the contacts on the silicon back surface of the chip are not at the same height, such as... Figure 3 As shown, conductive elements 31 and 32 have different heights. Four technical solutions can compensate for this height difference.

[0071] The first solution involves using isotropic conductive adhesive of varying volumes, depending on whether the adhesive is placed on the contact pads of the power plane for the active matrix or on the contact pads of the silicon power plane for the back surface of the LED.

[0072] The second solution involves using a printed circuit, which includes cavities formed at the locations of the LEDs and metal electrodes at the bottom of each cavity to accommodate conductive elements for contact on the silicon. The power contacts for the active matrix are placed on the upper surface of the printed circuit, such as... Figure 3 As shown. This allows the same conductive element to be used for two types of contacts or two power planes.

[0073] The third solution involves placing metal pads on the printed circuit board, which adds extra thickness relative to the surface of the printed circuit board. These pads are positioned facing the contact areas used for the active matrix.

[0074] The fourth solution involves placing metal components on a glass plate, with the same thickness as the silicon, and connecting them to a power plane for the active matrix. These metal components, distributed above the active matrix, are connected on one side to a power plane on the glass and on the other side to a contact area of ​​a power plane for the printed circuit. In this latter case, metal pads on the glass can be connected simultaneously and have the same contact solution as the chip supporting the μLED. They can be doped silicon pads with the same thickness as those used to support the μLED.

Claims

1. A μLED display comprising a plurality of electronic chips (10) having μLEDs and an active matrix (40) for controlling the chips having μLEDs, the active matrix being mounted on a transparent slider (2), each chip (10) having μLEDs comprising a plurality of light-emitting diodes (13), each chip having μLEDs comprising a substrate (11), the substrate (11) comprising a conductive surface (12) serving as a common electrode on its lower portion, and comprising the μLEDs (13) and respective electrical control contacts (14) of the μLEDs (13) on its upper portion, characterized in that, The display includes at least the following components in the following order: - Support plate (1), including a lower surface and an upper surface; - One or more first power planes (20) are arranged on the upper surface of the support plate; - Multiple first conductive elements (30); -The plurality of electronic chips (10) wherein a first conductive element provides an electrical connection between the common electrode of each chip and a first power plane; - Multiple second conductive elements (31), each second conductive element being arranged on an electrical contact for controlling an electronic chip; - The transparent slider (2) carrying the active matrix (40) provides an electrical connection between the electrical contacts of the electronic chip and the electrical contacts (41) for controlling the active matrix.

2. The μLED display according to claim 1, characterized in that, The first power plane is common to all the electronic chips.

3. The μLED display according to claim 1, characterized in that, The second power supply plane is arranged on the lower surface of the support plate.

4. The μLED display according to claim 3, characterized in that, The second power plane is electrically connected to the upper surface of the support plate via a conductive via, the conductive via providing an electrical connection between the first power plane and the second power plane.

5. The μLED display according to claim 3, characterized in that, The heat dissipation element is attached to the underside of the support plate.

6. The μLED display according to claim 3, characterized in that, A third power plane (23) is disposed on the lower surface of the support plate and is electrically connected to a metal connecting plate or a conductive connecting plate via a conductive via (24). The metal connecting plate or the conductive connecting plate is independent of the first power plane or the second power plane and is placed on the upper surface of the support plate. A plurality of third conductive elements (32) provide electrical connections between each via and an electrical contact for the power supply of the active matrix.

7. The μLED display according to claim 6, characterized in that, The support plate is a multilayer printed circuit comprising multiple electrically insulating conductive layers.

8. The μLED display according to claim 6, characterized in that, The support plate includes compartments into which the electronic chip is inserted.

9. The μLED display according to claim 6, characterized in that, The support plate includes a first conductive pad disposed on each via, the height of which is equal to the height of the electronic chip.

10. The μLED display according to claim 6, characterized in that, The transparent slider includes a second conductive pad arranged facing each via, the height of which is equal to the height of the electronic chip.

11. The μLED display according to claim 1, characterized in that, The support plate is transparent, and the first power plane is a grid (21) including conductive pads (22) arranged below the μLED.

12. The μLED display according to claim 11, characterized in that, The support plate is made of glass or polyethylene terephthalate.

13. The μLED display according to claim 11, characterized in that, The grid is covered with a light-absorbing material.

14. The μLED display according to any one of claims 1 to 13, characterized in that, The space separating the first power plane from the transparent slider carrying the active matrix is ​​filled with insulating material.

15. The μLED display according to claim 14, characterized in that, The insulating material is transparent.

16. The μLED display according to claim 14, characterized in that, The insulating material is opaque.

17. The μLED display according to any one of claims 1 to 13, characterized in that, The chips are all identical, and each chip includes at least three light-emitting diodes (LEDs), each LED emitting light in a spectral band different from the other two LEDs.

18. The μLED display according to any one of claims 1 to 13, characterized in that, The chip has at least three types, each type of chip including multiple identical light-emitting diodes, wherein the light-emitting diodes of one type of chip emit light in a spectral band different from the light-emitting diodes of the other two types of chips.

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