Optoelectronic Arrangement having a Radiation Conversion Element and Method for Producing a Radiation Conversion Element

Abstract

An optoelectronic arrangement having a radiation conversion element and a method for producing a radiation conversion element are disclosed. In an embodiment, an optoelectronic arrangement includes a semiconductor chip having an active region configured to generate radiation, a radiation conversion element arranged downstream of the semiconductor chip in an emission direction and a reflective polarization element arranged downstream of the radiation conversion element in the emission direction. The radiation conversion element has a plurality of conversion elements, each of which has an axis of symmetry, the spatial orientation of the axes of symmetry has a preferred direction and a radiation emitted by the radiation conversion element has a preferred polarization. The reflective polarization element largely allows radiation with the preferred polarization to pass through and largely reflects radiation polarized perpendicularly to the preferred polarization.

Claims

1-16. (canceled)

17. An optoelectronic arrangement comprising: a semiconductor chip comprising an active region configured to generate radiation; a radiation conversion element arranged downstream of the semiconductor chip in an emission direction, wherein the radiation conversion element comprises a plurality of conversion bodies each having an axis of symmetry, wherein a spatial orientation of the axes of symmetry comprises a preferred direction, and wherein a radiation emitted by the conversion bodies comprises a preferred polarization; and a reflective polarization element arranged downstream of the radiation conversion element in the emission direction, wherein the reflective polarization element largely allows the radiation with the preferred polarization to pass, and largely reflects radiation polarized perpendicular to the preferred polarization.

18. The optoelectronic arrangement according to claim 17, wherein the preferred direction of the conversion bodies and the preferred polarization are perpendicular to one another in a plane running perpendicularly to the emission direction.

19. The optoelectronic arrangement according to claim 17, wherein the conversion bodies contain quantum rods and have a maximum transversal extension perpendicularly to a longitudinal extension axis, and wherein a ratio of a longitudinal extension along the longitudinal extension axis to a maximum transversal extension is between 1.5:1 and 40:1, inclusive.

20. The optoelectronic arrangement according to claim 17, wherein the semiconductor chip is at least in places surrounded by a diffusely reflecting reflector.

21. The optoelectronic arrangement according to claim 17, wherein the radiation conversion element comprises a matrix material, in which the conversion bodies are embedded.

22. The optoelectronic arrangement according to claim 21, wherein the radiation conversion element is at least in places directly adjacent to the semiconductor chip.

23. The optoelectronic arrangement according to claim 21, wherein diffusers are embedded in the matrix material.

24. The optoelectronic arrangement according to claim 17, wherein the reflective polarization element comprises a plurality of layers having an anisotropic refractive index.

25. The optoelectronic arrangement according to claim 17, wherein the reflective polarization element has a higher reflectivity for primary radiation emitted by the semiconductor chip than for secondary radiation emitted by the radiation conversion element.

26. The optoelectronic arrangement according to claim 17, wherein the reflective polarization element is adjacent to the radiation conversion element or spaced from the radiation conversion element by no more than 200 μm.

27. The optoelectronic arrangement according to claim 17, wherein a main extension plane of the reflective polarization element and a main extension plane of the active region are parallel to one another.

28. The optoelectronic arrangement according to claim 17, wherein the optoelectronic arrangement is a surface-mounted semiconductor device.

29. The optoelectronic arrangement according to claim 17, wherein the optoelectronic arrangement is provided for backlighting of a liquid crystal display.

30. A method for producing a radiation conversion element, the method comprising: providing a basic material in liquid form, which is provided with conversion bodies each having an axis of symmetry; filling the basic material into a mold; at least partially orienting the axes of symmetry of the conversion bodies along a preferred direction; and curing the basic material.

31. The method according to claim 30, wherein the conversion bodies are oriented by an electrical field.

32. The method according to claim 30, wherein the mold is a cavity, in which at least one semiconductor chip is arranged.

33. An optoelectronic arrangement comprising: a semiconductor chip comprising an active region configured to generate radiation; a radiation conversion element arranged downstream of the semiconductor chip in an emission direction, wherein the radiation conversion element comprises a plurality of conversion bodies each having an axis of symmetry, wherein a spatial orientation of the axes of symmetry comprises a preferred direction, and wherein a radiation emitted by the conversion bodies comprises a preferred polarization; and a reflective polarization element arranged downstream of the radiation conversion element in the emission direction, wherein the reflective polarization element largely allows radiation with the preferred polarization to pass, and largely reflects radiation polarized perpendicular to the preferred polarization, wherein the optoelectronic arrangement is a surface mounted semiconductor device.

34. The optoelectronic arrangement according to claim 33, wherein the radiation conversion element is an enclosure of the semiconductor chip, and wherein the reflective polarization element is adjacent to the radiation conversion element or spaced from the radiation conversion element by no more than 200 μm.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Further embodiments and developments result from the following exemplary embodiments described in conjunction with the figures.

[0041] The figures show in:

[0042] FIGS. 1A, 1B and C are exemplary embodiments for an optoelectronic arrangement in a schematic plan view (FIG. 1A) and in two associated sectional views (FIGS. 1B and 1C);

[0043] FIG. 1D is an exemplary embodiment for a display apparatus having an optoelectronic arrangement; and

[0044] FIGS. 2A and 2B are exemplary embodiments for a method for producing a radiation conversion element by means of intermediate steps schematically shown in a plan view.

[0045] Like, similar or equivalent elements are indicated with the same reference numerals throughout the figures. The figures and dimensional relations of the elements shown in the figures are not to be understood as being to scale. Rather, individual elements and in particular layer thicknesses can be illustrated in an exaggerated size for a better illustration and/or understanding.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

[0046] FIGS. 1A to 1C illustrate an exemplary embodiment for an optoelectronic arrangement 1 by means of a plan view and two sectional views, which are oriented perpendicularly to one another.

[0047] The optoelectronic arrangement 1 comprises a semiconductor chip 2 provided for the generation of radiation. For example, the semiconductor chip contains an active region on the basis of a nitride semiconductor compound material, such as Al.sub.xIn.sub.yGa.sub.1-x-yN with 0≦x≦1, 0≦y≦1 and x+y≦1, which is provided for the generation of radiation in the blue or ultraviolet spectral range. In particular, the radiation emitted by the semiconductor chip is unpolarised.

[0048] Furthermore, the optoelectronic arrangement 1 comprises a radiation conversion element 3, which is arranged downstream of the semiconductor chip 2 in an emission direction 21. Thus, the radiation conversion element 3 forms part of the optoelectronic arrangement. Thus, prior to the exit of the primary radiation, which is generated in operation of the optoelectronic arrangement, from a radiation output surface 10 of the optoelectronic arrangement, the radiation has to pass through the radiation conversion element 3.

[0049] The radiation conversion element 3 comprises a plurality of conversion bodies 4. The conversion bodies 4 each have an axis of symmetry 40. In the exemplary embodiment shown, the conversion bodies are elongated conversion bodies, e.g., inorganic quantum rods, in which a longitudinal extension axis forms the axis of symmetry. A longitudinal extension along the longitudinal extension axis is greater than a maximum transversal extension 42 running perpendicularly to the longitudinal extension direction.

[0050] The radiation conversion element 3 comprises a matrix material 35, with the conversion bodies 4 of the radiation conversion element 3 embedded therein. The matrix material in particular contains a polymeric material and/or an inorganic oxide. For example, PET, PE, PS, PMMA, an acrylate, an epoxy, a silicone, or an organic-inorganic polymer with at least one epoxy or a silicone, e.g., a silicon in which Al.sub.2O.sub.3 or SiO.sub.2 is linked, may be considered as the matrix material.

[0051] When the conversion bodies 4 are optically excited by means of a primary radiation 81, the conversion bodies emit a secondary radiation 82.

[0052] The individual conversion bodies 4 are oriented in the radiation conversion element 3 in such a way that the axes of symmetry 40 of the conversion bodies 4 have a preferred direction 45. The preferred direction in particular runs perpendicular to the emission direction 21 and parallel to the active region 20. In the exemplary embodiment shown, all axes of symmetry 40 run parallel to the preferred direction. Ideally, the secondary radiation generated in the radiation conversion element 3 by the conversion bodies 4 is fully polarized, with a preferred polarization 48 of the radiation emitted by the radiation conversion element running in a plane perpendicularly to the preferred direction 45. However, individual conversion bodies 4 may also have an orientation of the axis of symmetry different from the preferred direction 45, so that the secondary radiation 82 is partially polarized.

[0053] For example, the elongate conversion bodies 4 have a ratio of longitudinal extension to the maximum transversal extension between 1.5:1 and 40:1, inclusive.

[0054] The conversion bodies 4 may be phosphor particles or phosphor molecules, for example. The conversion bodies may furthermore contain an organic and/or inorganic material. In particular, the inorganic and organic materials indicated in the general part of the description are suitable for the conversion bodies.

[0055] In contrast to the described exemplary embodiment, the conversion bodies do not necessarily have to be formed elongate. For example, organic molecules, the transversal extension of which equals or substantially equals the extension along the axis of symmetry can be used.

[0056] Furthermore, the optoelectronic arrangement 1 comprises a reflective polarization element 5. The reflective polarization element is arranged downstream of the radiation conversion element 3 in the emission direction 21. The reflective polarization element largely allows radiation with the preferred polarization to pass and largely reflects radiation which is polarized perpendicular to the preferred polarization. In the exemplary embodiment shown, the reflective polarization element 5 forms the radiation output surface 10 of the optoelectronic arrangement 1.

[0057] Preferably, the reflective polarization element 5 allows at least 80% of the radiation with the preferred polarization 48 to pass. Furthermore, the reflective polarization element largely reflects radiation components which are polarized perpendicular to the preferred polarization. Radiation of which the polarization does not correspond to the preferred polarization, does thus at least largely not get lost by absorption at the reflective polarization element, but is reflected and thus returns into the radiation conversion element 3. Preferably, the reflectivity for this radiation component is at least 60%, particularly preferably at least 80%.

[0058] For example, the reflective polarization element 5 is formed as a prefabricated film, which is fixed to the radiation conversion element 3. In a plan view of the radiation output surface, the reflective polymerization element 5 completely covers the radiation conversion element 3. In the exemplary embodiment shown, the reflective polarization element 5 is adjacent to the radiation conversion element 3. In contrast, these elements may also be spaced from one another, for example, at a distance of 200 μm at the most.

[0059] In the exemplary embodiment shown, the reflective polarization element 5 comprises a plurality of layers 51 with an anisotropic refractive index. As a result, a polarization-dependent transmission and at the same time a high reflectivity for not-transmitted radiation components can be achieved in a simple and reliable manner. The reflectivity and/or transmission can also be wavelength-selective and be higher or lower for the primary radiation than for the secondary radiation, for example.

[0060] Preferably, the reflective polarization element 5 has a higher reflectivity for the primary radiation, which is generated in the active region 20 in a non-polarized manner, than for the secondary radiation. Radiation components having the non-suitable polarization can thereby be reflected back due to a high reflectivity. In contrast, the secondary radiation is generated to be partially-polarized already, so that absorption losses inside the optoelectronic arrangement can be reduced due to a lower reflectivity.

[0061] The optoelectronic arrangement 1 further comprises a reflector 7, which is formed to be diffusely reflecting for the primary radiation and for the secondary radiation. Preferably, the reflector has a reflectivity of at least 80%. The higher the reflectivity, the lower can be the absorption losses inside the optoelectronic arrangement. In the exemplary embodiment shown, the reflector is formed by a wall 26 of a cavity 250 of a housing body 25. The semiconductor chip 2 is arranged in the cavity 250 and surrounded by the reflector in a lateral direction, i.e., parallel to a main extension plane of the active region 20. Radiation not having the suitable polarization to be capable of exiting the reflective polarization element can be reflected at this polarization element. The polarization state of the radiation changes randomly along with every in particular diffuse reflection inside the optoelectronic arrangement 1, for example, at the reflector 7, so that at least a part of the radiation is capable of exiting the optoelectronic arrangement 1 at a subsequent impinge on the reflective polarization element 5. Optionally, diffusors 75 may be embedded in the matrix material 35 for increasing the outcoupling probability.

[0062] The radiation, which is generated by the optoelectronic arrangement 1 and exiting through the radiation output surface 10 of the optoelectronic arrangement is polarized or at least partially polarized. Thus, the optoelectronic arrangement 1 per se provides polarized or at least partially polarized radiation, so that losses at the polarization filter, which is arranged on the radiation input side of the liquid crystal display, are reduced when backlighting of a liquid crystal display. Furthermore, the secondary radiation in the radiation conversion element 3 is generated to have a preferred polarization already due to the generation mechanism by means of oriented conversion bodies, and efficiency of the optoelectronic arrangement is increased.

[0063] In the exemplary embodiment shown, the optoelectronic arrangement shown is a surface mounted semiconductor device. The connection conductors, via which the semiconductor chip 2 can be electrically contacted externally from outside the housing body 25 from the side facing away from the radiation output surface 10, are not shown in the figures for the sakes of clarity.

[0064] In the exemplary embodiment shown, the radiation conversion element 3 is adjacent with the semiconductor chip 2 and forms an enclosure 22 for the semiconductor chip 2. However, the radiation conversion element may also be a prefabricated element, which is fixed to the semiconductor chip. Furthermore, the radiation conversion element 3 can also be spaced from the semiconductor chip 2 and in particular be provided in addition to an enclosure.

[0065] Furthermore, the radiation conversion element 3 may comprise conversion bodies 4, which generate secondary radiation components having different peak wavelengths.

[0066] For example, first conversion bodies generate radiation in the red spectral range, and second conversion bodies generate radiation in the green spectral range.

[0067] The optoelectronic arrangement 1 may of course also comprise more than one semiconductor chip 2 provided for the generation of radiation, wherein the semiconductor chips can each be arranged in a housing or multiple semiconductor chips can be arranged in a housing. Furthermore, as an alternative, multiple semiconductor chips can be arranged in a housing or be arranged in an un-housed fashion on a connection carrier, such as a circuit board, and be electrically contacted. The type of housing for the semiconductor chips 2 can be freely selected to a certain extent. For example, the housing body 25 may also be formed by a material, which is molded to the semiconductor chip 2 and in particular forms the reflector 7.

[0068] Furthermore, the optoelectronic arrangement 1 comprises an optical element 6. The optical element 6 is provided to deflect the radiation emitted by the radiation conversion element 3 and to deflect radiation exiting through the reflective polarization element in a manner so as to maintain polarization. To that end, the optical element comprises a plurality of longitudinal prisms in an exemplary manner, the longitudinal direction 610 of which is parallel to the preferred direction 45. In particular, the prisms are capable of collimating the radiation into a usable angular range. For example, the optical element 6 can be formed as a film, which is arranged on the reflective polarization element 5. The film may in particular be formed as a so-called brightness enhancement film (BEF). The optical element 6 and the reflective polarization element 5 can also be formed integrally in a film. Furthermore, the optical element may also be omitted.

[0069] One exemplary embodiment for a display apparatus 9 having the described arrangement 1 is schematically shown in FIG. 1D. The display apparatus comprises a light guide 91, into which the radiation emitted by the optoelectronic arrangement is coupled laterally. The optoelectronic arrangement 1 is arranged on a connection carrier 95, e.g., a circuit board. The radiation generated in the semiconductor chip 2 and the radiation emitted in the emission direction 21 pass the reflective polarization element 5 before being coupled into the light guide. Thus, the radiation coupled into the light guide is polarized or at least partially polarized. Expediently, the light guide is formed to maintain polarization. The radiation exiting from a main surface 910 of the light guide illuminates a liquid crystal display 92. Absorption losses on an input polarization filter 920 of the liquid crystal display are minimized due to the at least partially polarized emission of the optoelectronic arrangement 1. In particular, radiation components, which cannot be used for backlighting, e.g., due to unsuitable polarization, are already reduced when generating the radiation in the optoelectronic arrangement 1 in favor of an increase of the usable radiation.

[0070] In contrast to the exemplary embodiment shown, the optoelectronic arrangement 1 may also be provided for direct backlighting of the display apparatus.

[0071] A method for producing a radiation conversion element is shown in a schematic plan view in FIGS. 2A and 2B by means of two intermediate steps. Description is given in an exemplary manner for a radiation conversion element as described in conjunction with FIG. 1A to 1C.

[0072] A basic material 30 in the liquid form, which is interspersed with elongate conversion bodies 4 each having an axis of symmetry, is provided for forming the radiation conversion element. The basic material is filled in a mold 32, e.g., by molding, injection molding, or transfer molding. In the exemplary embodiment shown, a cavity 250 of a housing body 25 serves as a mold. As shown in FIG. 2A, the axes of symmetry 40 are initially randomly oriented and do not have a preferred direction.

[0073] Subsequently, the axes of symmetry of the conversion bodies are oriented at least partially along a preferred direction 45, as shown in FIG. 2B. This may be achieved by applying an electrical field, for example. After that, the basic material 30 is cured, wherein the electrical field is appropriately applied at least for as long as the basic material is sufficiently solidified, so that the orientation of the conversion bodies 4 is maintained even after switching-off the electrical field.

[0074] Thus, a radiation conversion element 3 can be generated in a simple manner, which emits an at least partially polarized secondary radiation when excited by primary radiation.

[0075] In contrast to the described exemplary embodiment, self-supporting conversion elements, e.g., in the form of plates, can be formed with the method. To that end, the mold can be removed after the curing step.

[0076] The invention is not limited to the exemplary embodiments by the description of these embodiments. The invention rather comprises each new feature as well as each combination of features, which in particular includes any combination of features in the patent claims, even if this feature or this combination per se is not explicitly indicated in the patent claims or exemplary embodiments.