EP2321699A1

EP2321699A1 - Led projector

Info

Publication number: EP2321699A1
Application number: EP09736803A
Authority: EP
Inventors: Stefan GRÖTSCH; Ewald Karl Michael GÜNTHER; Alexander Wilm; Siegfried Herrmann
Original assignee: Osram Opto Semiconductors GmbH
Current assignee: Ams Osram International GmbH
Priority date: 2008-09-11
Filing date: 2009-09-09
Publication date: 2011-05-18
Also published as: CN102047177A; JP2012502489A; DE102008046762B4; KR20110074841A; JP5713902B2; US8733950B2; CN102047177B; US20110176116A1; DE102008046762A1; WO2010028637A1

Abstract

The invention relates to an LED projector wherein every pixel (1) has a stacked epitaxial LED or at least two juxtaposed LEDs (2) as the light source. The LEDs can be addressed via strip conductors (3) for line addressing and strip conductors (4) for column addressing, the LED to be operated lying in the intersection of said strip conductors.

Description

LED projector

The following invention relates to a projection system whose imager comprises an array of light-emitting diodes.

Projection systems are usually implemented using discharge lamps that have a high power consumption and a short life. There are also known LED projectors with significantly longer life and more efficient operation. A disadvantage of the LED projectors, however, are the lower light output due to the light sources used here and losses in the optical system. In conventional projection systems, the light emanating from the light source is mixed, homogenized and divided into the colors red, green and blue by means of a color wheel. The light of each color is projected onto the imaging element. Typical imagers are an arrangement of LCDs (liquid crystal displays), LCoS (Liquid Crystal on Silicon) or DLP (Digital Light Processing) with an arrangement of small folding mirrors. Polarization based systems with LCDs or LCoS use only one direction of polarization. In systems with DLP, the images are superimposed sequentially so that each light source of a given color is turned on only intermittently. Therefore, even here, the light output of the light source is not fully utilized.

Basic principles of color mixing and contacting of layer stacks of substrateless diodes are z. B. in DE 10 2008 013030 and DE 10 2008 014094 described. Contacting substrateless diodes on or between Dielectric interlayers are described in DE 10 2008 008599, DE 10 2008 006757 and DE 10 2007 062042.

DE 199 25 318 C1 describes a color image projector with time-controlled LED light sources. WO 03/056876 A2 describes a lighting system with planar multilayer arrangements of LED light sources. US 2008/0211413 A1 describes a display device made of LEDs. DE 100 63 200 A1 describes a method and a device with LCD incident light modulators. EP 1 609 835 A1 describes a potting compound for LEDs.

Object of the present invention is to provide a projection system with high life and high efficiency despite low overall height.

This object is achieved with the LED projector with the features of claim 1. Embodiments emerge from the dependent claims.

As the light source, an array of LED chips is used, which are mounted on a support and interconnected. The carrier may preferably be silicon, since both data and power lines can be realized in a silicon carrier. Various contacting methods of silicon on printed circuit boards are already known. A pixel is preferably formed in color rendering from an array of red, green, and blue LED light sources. In the case of the LED projector, the LEDs are stacked epi-LEDs which have layers arranged one above another for different colors, or each pixel of the LED projector has a radiating surface in which at least two LEDs are arranged next to one another. Depending on the chip technology, the contacting can only take place from the underside of the carrier done or z. B. also partially from the bottom of a silicon substrate and partially from the top by means of a transparent glass plate with electrically conductive and optically transparent coating such. B. ITO (indium tin oxide). The number of pixels and thus the number of LEDs is determined by the desired resolution of the projector. A particularly high resolution with small dimensions is achieved with stacked Epi LEDs, in which the layers provided for the different colors are epitaxially grown one above the other. One pixel corresponds to a layer stack of a single LED, so that all colors of a respective pixel are emitted by the same emission surface of the relevant LED chip.

The following is a more detailed description of examples of the LED projector with reference to the attached figures.

FIG. 1 shows a plan view of an LED array.

FIG. 2 shows an arrangement of stacked epi-LEDs on a carrier in a perspective view.

FIG. 3 shows a schematized view according to FIG. 2 for an embodiment with bonding wires.

FIG. 4 shows the underside of an embodiment with bottom-side terminal contact surfaces.

FIG. 5 shows a carrier with conductor tracks for row addressing in a perspective view. FIG. 6 shows a glass sheet with conductor tracks for row addressing and column addressing in a perspective top view.

FIG. 7 shows a glass sheet with strip conductors for column addressing in a perspective bottom view.

FIG. 8 shows a cross section through a multilayer arrangement of LED layers between transparent intermediate layers.

FIG. 9 shows an arrangement of LED chips of an embodiment according to FIG. 8 in a plan view.

1 shows a plan view of an embodiment with a grid-like arrangement of pixels 1, each of which has a Abstrahltlache, in each of which a plurality of LEDs are arranged side by side, in this example four LEDs 2. Each LED 2 can be arranged on a separate chip be. For any color mix, LEDs are sufficient for red, green and blue light. In the example shown in Figure 1, four square LEDs are provided in each pixel, two of which are for green light. The LED projector can be adapted to different applications, for example for monochrome images or for multi-color images, with suitably selected LEDs in the pixels. An addressing of a pixel for operating the LEDs or LEDs arranged therein is effected by the electrical control of an associated crossing point of a conductor track made of a plurality of conductor tracks for row addressing and a conductor track of a plurality of conductor tracks for column addressing. In the figure 1 are for a crossing point a conductor track 3 schematically indicated for row addressing and a track 4 for column addressing with dashed lines. The arrangement of the conductor tracks and the thus provided contacting the light-generating layers is not fixed in principle, but can be configured differently depending on the technology.

FIG. 2 shows a further exemplary embodiment in which the layers of the LEDs provided for the generation of light are arranged one above the other in each pixel 1 as a layer stack. The relevant LEDs may in particular be stacked epi-LEDs, in which the layers provided for the generation of light are epitaxially grown on top of each other and form a stack. On a support 5 is an array of layer stacks 6, d. h., A plurality of arranged in a grid layer stacks 6, each forming a pixel 1. The arrangement with stacked Epi LEDs has the particular advantage that the lateral dimensions can be kept low and thus a high resolution of the projector is achieved. For each color, the same radiating surface is used, which is formed by the top of the respective layer stack 6. For this purpose, different contacting methods in question; The electrical connections and addressing conductor tracks can be arranged at least partially on the upper side or completely within the carrier 5.

FIG. 3 shows a further embodiment in which LEDs 2 are arranged on the upper side of a carrier 5 in a grid of pixels, it being left open in the schematic representation of FIG. 3 whether these are layer stacks or monochromatic LEDs arranged next to one another , For the electrical connection to the outside are at the edges of the carrier 5 bonding wires 7 are provided, which are connected to associated, intersecting tracks for the row addressing and column addressing of the LEDs of the array. The conductor tracks are not shown in FIG. 3, since they are covered by the array of LEDs or arranged inside the carrier 5; the conductor tracks can be arranged on the upper side of the carrier 5 between the carrier 5 and the LEDs 2 or, in particular in the case of a carrier made of silicon, run inside the carrier. It can also strip conductors on the side facing away from the carrier 5 top of the LEDs 2 are arranged, if this is a transparent and electrically conductive material, for. B. ITO (indium tin oxide) is used.

FIG. 4 shows an alternative embodiment in which rear side contacts 8 for the electrical connection are provided on the rear side of the carrier 5. If transparent conductor tracks for the electrical connection are present on the front side, it is sufficient in each case one rear-side contact 8 for each LED; but it is also possible to provide the entire electrical contact on the back of the carrier 5 and to arrange for this purpose two or more backside contacts 8 for each pixel or for each LED or LED layer.

Such a projector can also be built up by placing substrateless semi-transparent chips with LEDs on glass foils one above the other. The power supply in the provided for the different colors layer planes is preferably carried out by means of metal contacts, which are provided with conductor tracks, for. B. from ITO combined. Each pixel is located at the intersection of a column and a row of the array along which each transparent traces run, the arranged on the glass sheets of the stack or embedded in the glass sheets. To explain this structure, FIG. 5 shows, in a perspective top view, a carrier 5 on which strip conductors 3 for row addressing are applied. The respective LED chips are arranged on these strip conductors, and the respective terminal contact area of each LED chip is electrically conductively connected to the associated strip conductor 3.

About the LED chips on the tracks of the carrier 5, a glass sheet according to Figure 6 is arranged, which is provided on the underside with interconnects 4 for the column addressing and the top side with further interconnects 3 for the row addressing. The glass sheet 9, which is shown in FIG. 6 in a perspective view corresponding to FIG. 5, is placed over the array of LED chips on the support 5, the dashed arrows pointing downwards in FIGS. 5 and 6 pointing at points are, which come to lie vertically above each other. By means of these arrows, the relative orientation of the various levels of the arrangement can thus be recognized. The lower-side conductor tracks 4 for the column addressing are electrically conductively connected to the respective terminal contact surfaces of the LED chips on the carrier 5. On the upper side according to Figure 6 on the glass sheet 9 further existing interconnects 3 for row addressing further LED chips are arranged, which are provided for example with LEDs for a further color to be emitted. If a third color is still to be provided, a further glass foil 9 according to FIG. 6 can be applied on the upper side, whose upper-side conductor tracks are again provided with a further arrangement of LED chips. FIG. 7 shows, in a perspective bottom view, a further glass foil 9 which is arranged at the top in the stack, in such a way that the points marked with the dashed arrows pointing downwards in FIG. 7 are vertically aligned with those in FIG Marked points come to rest, so the points are aligned along the arrows. Due to the arrangement of the tracks 4 for the column addressing in the direction transverse to the tracks 3 for the row addressing direction, it is possible by selecting one track 3 for the row addressing and one track 4 for the column addressing an electrical voltage to exactly one LED chip apply and thereby cause a light emission of the LED in question, while the non-addressed LEDs remain dark. The line-by-line and column-by-column addressing of the different layers allows the desired color mixtures to be produced in each pixel.

FIG. 8 shows a cross-section of a preferred embodiment in which the electrical connection between the connection contacts of the LEDs and the conductor tracks takes place in each case via metal frame contacts 10. In the cross section of Figure 8, multiple layers of arrays of LED chips 14 are shown. On the carrier 5 is a first LED layer 11 for a first color. On it is a glass sheet 9, on which a second LED layer 12 is arranged for a second color. On a further glass sheet 9, a third LED layer 13 is arranged for a third color. This top third LED layer 13 is covered on the top side with a glass sheet 9. Between the glass sheets and the LED chips are thin strip conductors, which may for example be designed according to the illustrations in Figures 5, 6 and 7 and because of their small thickness in of Figure 8 are not shown. Metal frame contacts 10 are provided between these printed conductors and the electrical connections of the LEDs. In the longitudinal direction of the conductor tracks preferably metallic connections between the metal frame contacts 10 are provided, which may be formed, for example, by thin metal strips 16. In the cross-section of Figure 8 extending in the plane of interconnects 3 (row addressing) respectively on the carrier 5 facing the underside of the respective LED layer 11, 12, 13 are present, while the perpendicular thereto perpendicular to the plane of interconnects 4 (column addressing) each on the side facing away from the carrier 5 top of the respective LED layer 11, 12, 13 are present. The conductor tracks 3, 4 are connected via the metal frame contacts 10 with the connection contacts of the LEDs. The metal frame contacts 10 may be interconnected along the conductor tracks 3, 4 by means of metal strips 16. The metal strips 16 running along the conductor tracks can be seen in the cross section of FIG. 8 only in the case of the lower conductor tracks 3 running in the plane of the drawing. However, corresponding metal strips can also be provided for the upper conductor tracks 4 arranged on the respective upper sides of the LED chips and run between the upper metal frame contacts 10 parallel to the upper conductor tracks 4 perpendicular to the plane of the drawing. The metal frame contacts 10 on the upper sides of the LED chips are therefore separated from one another in the plane of the cross section of FIG.

The LED layers 11, 12, 13 may, for. B. be provided for red, green and blue light. It is instead also possible, for example, for the purpose of better color mixing, at least one further LED layer of a suitable color or to provide only a single LED layer for monochrome reproduction. The order of arrangement of the colors in the stack of LED layers and glass foils is basically arbitrary.

The sectional view marked in FIG. 8 is shown in FIG. FIG. 9 shows how the metal frame contacts 10 are arranged on the LED chips 14, which are separated from each other by narrow gaps 15. In the top view of FIG. 9, the conductor tracks 4 for the column addressing run from top to bottom. They are connected via the metal frame contacts 10 to the LED chips 14. Along the conductor tracks 4, the metal frame contacts 10 are connected to each other by metal strips 16. The existing on the undersides of the LED chips 14 strip conductors 3 for the row addressing are hidden by the LED chips. The lower metal strips 16 are shown in dashed lines in FIG. 9, which extend in the same direction as the line paths 3 for the row addressing.

A projector whose pixels are each formed by LEDs, also allows to improve the contrast of a generated image by the dark within the generated image LEDs are switched as photodetectors. This is done by applying a voltage in the reverse direction to the pn junction of the light-generating layer of the relevant LED. In this mode, the electron-hole pairs generated by the incident light are electrically isolated from each other and provide a photocurrent. The LED thus absorbs incident light and appears darker than a non-reverse operated LED. This patent application claims the priority of German Patent Application 102008046762.6, the disclosure of which is hereby incorporated by reference.

The invention is not limited by the description with reference to the embodiments. Rather, the invention encompasses any novel feature as well as any combination of features, including in particular any combination of features in the claims, even if this feature or combination itself is not explicitly stated in the patent claims or exemplary embodiments.

Claims

claims

1. LED projector with

- Light sources and

an imager comprising an array of pixels (1), wherein

- Each pixel (1) has at least one light source and

- The light sources LEDs (2), characterized in that

- The LEDs (2) are stacked Epi LEDs having superimposed layers for different colors, or each pixel (1) has a radiating surface and in the radiating surface at least two LEDs (2) are arranged side by side.

2. LED projector according to claim 1, wherein the LEDs (2) are stacked Epi LEDs having stacked layers for different colors.

3. LED projector according to claim 1, wherein each pixel (1) has a radiating surface and in the radiating surface in each case a plurality of LEDs ^' (2) are arranged side by side.

4. LED projector according to claim 3, wherein each pixel (1) comprises a LED (2) for red light, a LED (2) for blue light and two LEDs (2) for green light.

5. LED projector according to one of claims 1 to 4, wherein

- At least one with LEDs (2; 14) provided LED layer

(11, 12, 13) is present, a carrier (5) or a transparent glass film (9) with conductor tracks (3) is arranged below the LED layer (11, 12, 13), a transparent glass film (9) being arranged above the LED layer (11, 12, 13) is arranged with further conductor tracks (4) extending transversely to the conductor tracks (3) and the conductor tracks (3) and the further conductor tracks (4) are connected to terminal contacts of the LEDs (2, 14) such that each LED (2, 14) via a conductor track (3) and another conductor track (4) can be operated separately from the other LEDs.

LED projector according to claim 5, wherein a plurality of LED layers (11, 12, 13), which are separated from each other by transparent glass foils (9), are arranged one above the other and the LED layers (11, 12, 13) for different

Colors are provided.

LED projector according to one of claims 1 to 6, wherein the LEDs (2) are arranged on a support (5) made of silicon and the carrier (5) is provided with electrical conductors, by means of which the LEDs each independently of the other LEDs can be operated.

LED projector according to one of claims 1 to 7, wherein the LEDs (2) are provided with metal frame contacts (10) and the electrical connection of the LEDs (2) via the

Metal frame contacts (10) takes place.