Optoelectronic arrangement and method of processing the same

Abstract

The invention concerns an optoelectronic arrangement, comprising a top surface forming an emission surface of the arrangement, an array of optoelectronic devices, in particularly arranged in rows and columns, each optoelectronic device of the array of optoelectronic devices configured to emit light through the emission surface of the arrangement and a conductive grid structure arranged on the top surface, such that the conductive grid structure surrounds a subset optoelectronic devices of the array of optoelectronic devices when viewed from a direction onto the top surface. An optical element is arranged on the top surface in the area surrounded by the conductive grid structure and attached at least to sidewalls of the conductive grid structure. The conductive grid structure is covered at least in regions, on which the optical element is attached to, by a conductive oxide layer, in particular one of ITO or ZnO.

Description

[0001] OPTOELECTRONIC ARRANGEMENT AND METHOD OF PROCESSING THE SAME

[0002] The present application claims priority of German patent application DE 10 2024 108 044 . 2 dated March 20 , 2024 , the disclosure of which is incorporated herein by reference in its entirety . The present invention concerns and optoelectronic arrangement and a method for processing the same .

[0003] BACKGROUND

[0004] Optoelectronic devices are suitable for many light applications and can be distinguished between separate individual optoelectronic devices and optoelectronic devices arranged in an array of rows and columns . The latter are usually monolithically integrated and also referred to as pixelated LEDs or pixelated arrays , wherein -depending on the application- each LED or optoelectronic device corresponds to a pixel . In other applications , a pixel may comprise not only a single LED but a plurality of LEDs . In some aspects , for example each pixel may comprise three LEDs , wherein each LED is configured to emit light of a different wavelength, thereby generating a colored pixel .

[0005] Monolithically integrated pixelated optoelectronic devices or LEDs usually comprise a conductive grid structure arranged on the top and surrounding each pixel . This conductive grid structure serves the purpose of providing electrical current from a common contact area to the monolithically integrated pixelated LEDs . The grid structure is connected to a bond pad metal , often implemented as a single layer . The requirement for such a layer is a good contact to the doped semiconductor material , as well as a suitable material for wire bonding . For this purpose , a gold finish is usually used as such material , because it does not oxidize and is suitable for grid and the bond pad material .

[0006] A further requirement is the emission characteristics of such pixelated LEDs . It is required in some applications to emit light in a narrow angle cone . For this purpose , lenses may be arranged over the respective pixels and attached to the surface of the metal grid structure and the semiconductor material . It has now been found that lens material consisting of oxide layers show a poor adhesion to gold or similar bonding materials . This is especially true for lenses made of glass , Si02 , SiNx and Nb2O5 .

[0007] As a consequence , out-coupling structures that can collimate and direct the emitted light may not provide a sufficient adhesion to the grid structure . The ris k occurs that lens material is detached from the surface of the pixelated LEDs .

[0008] It is therefore an obj ect of the present invention, to improve the situation and provide a good adhesion between the surface layer of monolithically pixelated LED' and the lenses attached thereto .

[0009] SUMMARY OF THE INVENTION

[0010] This and other obj ects are addressed by the subj ect matter of the independent claims . Features and further aspects of the proposed principles are outlined in the dependent claims .

[0011] The inventors propose to change the material composition for the metal grid structure and particularly the finish of such metal grid structure . Instead of using a metal finish, wherein a metal forms the outermost surface of the grid, a conductive oxide layer like ZnO or ITO is used as a finish and outermost layer of the grid . This material provides a significant better adhesion to the lens material , other suitable materials may comprise Ti , Cr , Ni or Al and particularly its native oxides , as those provide a good adhesion properties compared to gold . The original metal structure is therefore either replaced completely by conductive oxide or at least partially covered by the conductive oxide layer . Gold will be deposited with a separate step to the bond pad area to achieve good wire bonding finish .

[0012] In addition, the conductive grid structure can be adapted to the needs and design choices to achieve an optimal out coupling results . It has been found that grids with conductive oxide layers can be made smaller due to the improved adhesion thereby reducing material consumption but also providing less shading and better light emission for the plurality of optoelectronic devices forming monolithically integrated pixelated LED array .

[0013] In one aspect , the inventors propose an optoelectronic arrangement , comprising a top surface forming an emission surface of the arrangement . An array of optoelectronic devices , in particularly arranged in rows and columns , are arranged on the carrier as a monolithically pixelated LED array . Each optoelectronic device of the array of optoelectronic devices is configured to emit light through the emission surface of the arrangement . A conductive grid structure is arranged on the top surface , such that the conductive grid structure surrounds a subset of optoelectronic devices of the array when viewed onto the top surface .

[0014] The subset of optoelectronic devices may comprise a single optoelectronic device of the array . In such embodiment , the grid structure therefore surrounds each of the optoelectronic devices of the array of optoelectronic devices when viewed from the top . Hence , a pixel of the array is formed by one optoelectronic device . In an alternative embodiment , the conductive grid structure may surround a triple of optoelectronic devices of the array, wherein the triple forms a single pixel of the array .

[0015] In accordance with the proposed principle , a lens is arranged on the top surface in the area surrounded by the conductive grid structure and attached at least to sidewalls of the conductive grid structure . For this purpose , the outermost layer of the conductive grid structure , at least in those regions in which the lenses attached to , comprises a conductive oxide layer, in particular one of ITO or ZnO . Other native oxides including Cr, Ti , Ni or Al , like for example TiOx or A12O3 may also be suited as outermost layer .

[0016] The present invention ensures that the lens is firmly attached to a conductive oxide layer and no longer directly to the metal , thereby increasing the adhesion between the lens material and the pixelated LED area . Risk of detachment is significantly reduced, particularly under high thermal stress . In some aspects , the lens material may also extend partially onto a top surface portion of the conductive grid structure . In some other aspects of the conductive oxide layer may also extend on the top surface of the arrangement , that is onto the top surface surrounded by the grid structure . This further increases the adhesion between the lens material and the arrangement . In this regard, the conductive oxide layer can also be chosen to adj ust the different refractive indices between the lens material and the semiconductor layer material forming the emission surface .

[0017] In some further aspects , the conductive grid structure comprises inclined sidewalls and a top surface portion that is substantially parallel to the top surface of the arrangement . The inclined sidewalls may provide an improved adhesion to the lens material . In some further aspects , the conductive grid structure comprises a metallic core particularly including at least one of gold, titan, platinum, copper , aluminum, germanium and silver . The metallic core is covered at least partially with the conductive oxide layer in accordance with the proposed principle the above-mentioned oxide layers can be used . This will allow a simpler processing , as application of the metallic core structure is a well-known process and regularly used when implementing such pixelated LED arrays . In some instances , the core may comprise Ge , ZnO or Ito and is covered with a different oxide material as outermost layer .

[0018] In some further aspects , the conductive oxide layer covers the conductive grid structure completely . In some further aspects , the conductive grid structure of the optoelectronic arrangement is arranged on an area of the top surface that separates two adj acent optoelectronic devices of the array optoelectronic devices . In this regard, the conductive grid structure may also be arranged in an area of the top surface , wherein the conductive grid structure separates three adj acent optoelectronic devices from another three adj acent optoelectronic devices of the array of optoelectronic devices . Depending on the design choice , the optoelectronic device or the three optoelectronic devices form a pixel of the array . In some further aspects , the conductive grid structure is arranged on an area of the top surface that is outside another area of the top surface forming an emission surface of the subset of optoelectronic devices of the array . Consequently, the conductive grid structure is arranged such that it does not cover an emission area of the optoelectronic devices , and thereby not reducing the overall emission efficiency .

[0019] In another aspect , the optoelectronic arrangement further comprises a transparent conductive layer covering the array of optoelectronic devices . The transparent conductive layer may correspond to the conductive oxide layer used to cover the grid structure . The transparent conductive layer may form a top surface of the arrangement and is also electrically connected to the conductive grid structure . The transparent conductive layer may also electrically connect the subset of optoelectronic devices of the array of optoelectronic devices . Consequently, the array of optoelectronic devices comprises a common contact implemented by the transparent conductive layer . The grid structure , in particular with a metal core , provides an overall low electrical resistance and therefore reduces the heat generation and power loss during operation of the arrangement .

[0020] In some aspects , the optoelectronic arrangement also comprises a contact area including a gold containing bond pad . The contact area is used for bonding a wire to the array and electrically contacts the conductive grid structure .

[0021] In order to individually control the subset of optoelectronic devices of the array of optoelectronic devices , it is proposed in some aspects to electrically connect the subset by a contact arranged on the side facing away from the top surface of the arrangement . In such embodiments , the subset of optoelectronic devices is implemented in so-called vertical devices , which provide the respective contacts on opposite sides .

[0022] In some further aspects , the subset of optoelectronic devices comprises inclined sidewalls opening towards the top emission surface . The inclined sidewalls may comprise a reflective layer material . In this regard, the inclined sidewalls may be mesa structured and can comprise further characteristics and features to improve the quantum efficiency of the subset of optoelectronic devices . For example , a regrowth layer or a quantum well intermixing can be used for this purpose . The inclined sidewalls extend at least across the active layer of the optoelectronic devices .

[0023] Another aspect concerns a method of processing an optoelectronic arrangement in accordance with the proposed principle . For this purpose , an array of optoelectronic devices is provided, each optoelectronic device comprising an active region . Each optoelectronic device of the array of optoelectronic devices is also configured to emit light through a continuous top surface . The expression "continuous top surface" in this regard corresponds to a non-interrupted surface . The optoelectronic devices are electrically and mechanically connected to each other by a semiconductor or another electrically conductive layer .

[0024] In accordance with the proposed principle , a conductive grid structure is formed on the continuous top surface , such that the conductive grid structure surrounds a subset of optoelectronic devices when viewed from a direction onto the continuous top surface . The continuous grid structure comprises a conductive oxide layer as its outermost layer , particularly one of ITO or ZnO on at least portions of the grid structure . A lens is formed in the area surrounded by the conductive grid structure attached to the conductive oxide layer on the portions of the conductive grid structure .

[0025] In some further aspects , the conductive oxide layer is deposited not only on the grid structure but also on the top surface of the plurality of optoelectronic devices and particularly on the top surface surrounded by the grid structure . Therefore , the lens material is not only attached to the conductive oxide layer on the portions of the grid structure but also on the top surface , improving the overall adhesion between the lens material and the array of optoelectronic devices .

[0026] In some further aspects , the method comprises the step of forming a contact area, comprising in particular a gold containing a bond pad . The contact area is electrically connected to the conductive grid structure .

[0027] In some aspects , the step of providing an array of optoelectronic devices also comprises the step of depositing a transparent conductive layer covering the array of optoelectronic devices and thereby forming the continuous top surface of the arrangement . The transparent conductive layer is electrically connected to the conductive grid structure and also electrically connects the subset of optoelectronic devices . In this regard, the transparent conductive layer may comprise the same material as the conductive oxide layer . In some aspects , both materials can be deposited in a single step .

[0028] The conductive grid structure is formed, in some aspects , by depositing a conductive oxide layer on the top surface and subsequently structuring the conductive oxide layer to form the conductive grid structure . In this embodiment , the conductive oxide layer completely forms the conductive grid structure . In some other aspects , the step of forming the conductive grid structure comprises the step of depositing a structured metallic layer on the top surface . The metallic layer may include gold or other material as stated above . Then, the conductive oxide layer, in particular one of ITO and ZnO is deposited on the structured metallic layer . In some aspects , the conductive oxide layer also extends onto the emission surface surrounded by the structured metallic layer .

[0029] SHORT DESCRIPTION OF THE DRAWINGS

[0030] Further aspects and embodiments in accordance with the proposed principle will become apparent in relation to the various embodiments and examples described in detail in connection with the accompanying drawings , in which

[0031] Figures 1A and IB show a side view and a top view of an optoelectronic device and an arrangement of optoelectronic devices , respectively, in accordance with some aspects of the proposed principle ; Figure 2 illustrates a side view of another embodiment of an optoelectronic device in an arrangement in accordance with some aspects of the proposed principle ;

[0032] Figures 3A to 3D shows some steps of a method of processing an optoelectronic arrangement in accordance with some aspects of the proposed principle ;

[0033] Figures 4A and 4B illustrate some alternative steps of a method of processing an optoelectronic arrangement in accordance with some aspects of the proposed principle .

[0034] DETAILED DESCRIPTION

[0035] The following embodiments and examples disclose various aspects and their combinations according to the proposed principle . The embodiments and examples are not always to scale . Likewise , different elements can be displayed enlarged or reduced in size to emphasize individual aspects . It goes without saying that the individual aspects of the embodiments and examples shown in the figures can be combined with each other without further ado , without this contradicting the principle according to the invention . Some aspects show a regular structure or form . It should be noted that in practice slight differences and deviations from the ideal form may occur without , however , contradicting the inventive idea .

[0036] In addition, the individual figures and aspects are not necessarily shown in the correct size , nor do the proportions between individual elements have to be essentially correct . Some aspects are highlighted by showing them enlarged . However , terms such as "above" , "over" , "below" , "under" "larger" , "smaller" and the like are correctly represented with regard to the elements in the figures . So it is possible to deduce such relations between the elements based on the figures .

[0037] Figure 1A illustrates a side view of a portion of an array of optoelectronic devices in accordance with the proposed principle . The array 1 is arranged on the carrier 10 , which may also include different integrated circuitry for contacting the optoelectronic devices of the array and providing respective current and power to the optoelectronic devices . The surface of carrier 10 is covered by a filling material 11 , which provides a contact to the optoelectronic device . Filler material 11 can include an insulating material , but also a reflective layer, a metal or a plurality of sublayers depending on the design choice . It provides a contact between the contacts of the carrier 10 to the optoelectronic devices , such that each device can be individually addressed, for example .

[0038] The optoelectronic device shown in Figure 1A is Mesa structured and includes a p-doped semiconductor layer 15 , an active region 17 and an n-doped semiconductor layer 16 stacked on each other . The optoelectronic device includes inclined Mesa structured sidewalls , which are covered by a regrowth layer 14 and p-contact layer 13 , respectively . A small isolation layer 12 is covering the contact layer 13 and comprises a recess on the bottom side forming the contact to layer 11 . The design and structure of the optoelectronic device depicted herein can be adj usted to the needs and demands of the desired application .

[0039] The sidewalls in the upper part of the optoelectronic device close to the emission surface are covered by an isolation layer 12 ' . The material is the same is layer 12 . The top portion of the n-doped layer 16 extends outwards as semiconductor layer 18 , thus forming a common contact to the individual optoelectronic devices of the array . The n-doped semiconductor material 18 can also be replaced by another electrically conductive material forming a common contact .

[0040] In accordance with the proposed principle , a grid structure 19 is arranged on the top surface of the n-doped semiconductor layer 18 of array 1 and particularly surrounds the optoelectronic device and its emission surface . Grid structure 19 comprises a conductive oxide . A transparent lens 21 is attached to the top surface and the emission surface of the optoelectronic device , as well as on the sidewalls of the grid structure 19 as depicted herein . The conductive oxide material of grid 19 provides a good adhesion to the lens material 21 .

[0041] Figure IB illustrates a top view of the arrangement with the array of optoelectronic devices in accordance with the proposed principle . The arrangement includes a bonding area 110 and an array 100 with a plurality of optoelectronic devices , similar to the embodiment of Figure 1A . Each of the optoelectronic devices is surrounded by the grid structure 19 . Consequently, the area 100 comprises a plurality of optoelectronic devices and its surrounding structures 19 with the respective lenses 21 attached thereto . A thin gold layer is deposited on the bonding area 110 providing a good contact to a bonding wire for contacting the common contact of the array 100 . Bonding area 110 is also electrically connected to the grid structure 19 for distributing the current throughout the array .

[0042] Figure 2 illustrates a side view of a further embodiment of the proposed principle . The difference between the embodiments of Figure 1A and Figure 2 is given in the shape and structure of the conductive grid structure . In the embodiment of Figure 2 , the conductive grid structure comprises a metallic core 20 arranged on the top surface of layer 18 of the array . The metallic core 20 comprises gold or a similar metal with a low electrical resistance and good current spreading capacity . To improve the adhesion of the grid structure to the lens 21 , a conductive oxide layer 19 is applied to the metallic core , covering the metallic core completely . The conductive oxide layer thereby forms the outermost surface of the grid structure .

[0043] The lens 21 extends not only on the inner sidewalls of the grid structure in this embodiment , but also on its flat top surface , thereby increasing the adhesive area and improving the adhesion .

[0044] Figures 3A to 3D illustrate a method of processing an array of optoelectronic devices in accordance with the proposed principle .

[0045] The array comprises a plurality of optoelectronic devices arranged in rows and columns . The plurality of optoelectronic devices in this embodiment is implemented as a monolithically pixelated array . The array is epitaxially deposited on a growth substrate with different doped semiconductor layers having an active region 17 between . A Mesa structuring process is conducted to provide inclined sidewalls . More particularly, a first shallow Mesa etching process is performed followed by depositing a regrowth layer 14 and contact layerl3 . Then a subsequent deep Mesa etching process which removes material all the way up to a remaining common thin portion of an n-doped semiconductor layer 18 as depicted herein . Insulated layer material 12 is deposited on the surface , leaving a recess to gain a contact to the p— side of the layer stack . After the re-bonding process to carrier 10 , the growth substrate is removed, and the top surface processed to form the clean emission surface ( top surface of layer 18 ) as shown herein .

[0046] Following Figure 3B , a photo resist layer 30 is arranged on the top surface of layer 18 and subsequently structured to form a plurality of recesses . The structure of the recesses follows , when viewed from the top, the grid structure surrounding the optoelectronic devices . The recesses expose top surface portions of layer 18 . In a subsequent step , depicted in Figure 3C , a conductive oxide layer material 19 is deposited on the photo resist 30 as well as into the recesses forming the grid structure 19 as shown . Finally, the photo resist layer 30 is removed, leaving the conductive oxide layer grid structure 19 behind, which surrounds each of the optoelectronic devices . In subsequent steps not depicted herein, the lens material is applied and adhered to the semiconductor surface 18 and the grid structure 19 . A further process can then be conducted to provide a gold finish on a bonding area . Grid structure 19 is electrically connected to the bonding pad and the contact area .

[0047] Figure 4A to 4B illustrates a further embodiment of the proposed principle . In this particular embodiment , a metallic core 20 is deposited onto the exposed surface portions of layer 18 , that is in the respective recesses provided by the structured photo resist material 30 . Then, the residuals of the gold layer material and the photo resist layer 30 is removed and a thin conductive oxide layer 19 deposited . As shown herein, the conductive oxide layer 19 covers the core 20 completely and also extends on the top surface of layer 18 .

[0048] This will improve the adhesion to the lens material applied in subsequent process steps . Furthermore , the conductive oxide layer 19 may also act as an adj ustment layer for adj usting the refractive indices between the semiconductor layer material of layer 18 , and the lens material 21 , not shown herein .

[0049] The proposed principle improves the adhesion between a lens material , particularly made of SiO2 , SiNx and Nb2O5 and the surface of an array of optoelectronic devices . The form and size of the grid may also affect the shape of the lens . The improved adhesion is achieved by covering the grid structure with a conductive oxide layer, which provides an improved adhesion compared to a direct metal surface . In cases , in which the grid is formed completely of ITO and ZnO, one may also improve the overall light extraction as no shading does occur .

[0050] LIST OF REFERENCES arrangement carrier filling material , 12 ' insulating layer contact layer regrowth layer p-doped semiconductor layer n-doped semiconductor layer active region semiconductor layer grid structure metal core lens photoresist 0 array 0 bondpad

Claims

CLAIMS1 . Optoelectronic arrangement , comprising :A top surface forming an emission surface of the arrangement ;An array of optoelectronic devices , in particularly arranged in rows and columns , each optoelectronic device of the array of optoelectronic devices configured to emit light through the emission surface of the arrangement ;A conductive grid structure arranged on the top surface , such that the conductive grid structure surrounds a subset optoelectronic devices of the array of optoelectronic devices when viewed from a direction onto the top surface ;An optical element arranged on the top surface in the area surrounded by the conductive grid structure and attached at least to sidewalls of the conductive grid structure ; wherein the conductive grid structure is covered at least in regions on which the optical element is attached to , by a conductive oxide layer, in particular one of ITO , ZnO or a native oxide comprising a metal selected from the group consisting of Ti , Cr, Ni and Al .2 . Optoelectronic arrangement according to claim 1 , wherein the optical element material also extends partially onto a top surface portion of the conductive grid structure .3 . Optoelectronic arrangement according to any of the preceding claims , wherein the conductive grid structure comprises inclined sidewalls and a top surface portion substantially parallel to the top surface ; and / or the conductive grid structure comprises a metallic core , particularly including at least one of Au, Ti , Pt , Cu, Al and Ag, said metallic core covered at least partially with the conductive oxide layer; and / or the conductive oxide layer covers the conductive grid structure completely .4 . Optoelectronic arrangement according to any of the preceding claims , wherein the conductive grid structure is arranged on an area of the top surface that separates two adj acent optoelectronic devices of the array of optoelectronic devices ; and / or the conductive grid structure is arranged on an area of the top surface that is outside of another area of the top surface forming an emission surface of the subset of optoelectronic devices of the array of optoelectronic devices .5 . Optoelectronic arrangement according to any of the preceding claims , further comprisingA transparent conductive layer covering the array of optoelectronic devices , thereby forming the top surface of the arrangement and electrically connected to the conductive grid structure , wherein the transparent conductive layer electrically connects the subset of optoelectronic devices of the array of optoelectronic devices ; and / orA contact area , comprising in particular a gold containing bond pad, said contact area electrically connected to the conductive grid structure .6 . Optoelectronic arrangement according to any of the preceding claims , wherein the subset optoelectronic devices of the array of optoelectronic devices is electrically connected by a contact arranged facing away from the top surface of the arrangement .7 . Optoelectronic arrangement according to any of the preceding claims , wherein the subset optoelectronic devices of the array of optoelectronic devices comprises inclined sidewalls opening towards the top emission surface , said inclined sidewalls comprising a reflective layer .8 . Optoelectronic arrangement according to any of the preceding claims , wherein the optical element comprises one of a lens , an anti- reflective coating , a DBR mirror, and a photonic crystal structure .9 . Method of processing an optoelectronic arrangement , comprisingProviding an array of optoelectronic devices , each comprising an active region, each optoelectronic device of the array of optoelectronic devices configured to emit light through a continuous top surface ;Forming a conductive grid structure on the continuous top surface , such that the conductive grid structure surrounds a subset optoelectronic devices of the array of optoelectronic devices when viewed from a direction onto the continuous top surface and wherein the conductive grid structure comprises a conductive oxide layer, in particular one of ITO ZnO or a native oxide comprising a metal selected from the group consisting of Ti , Cr , Ni and Al on a surface of at least portions of the conductive grid structure ;Forming an optical element in the area surrounded by conductive grid structure and attaching the optical element material to the conductive oxide layer on the portions of the conductive grid structure .10 . Method according to claim 9 , further comprising the step of forming a contact area, comprising in particular a gold containing bond pad, said contact area electrically connected to the conductive grid structure .11 . Method according to claim 9 or 10 , wherein the step of providing an array of optoelectronic devices comprises the step of :Depositing a transparent conductive layer covering the array of optoelectronic devices , thereby forming the continuous top surface of the arrangement and electrically connected to the conductive grid structure , wherein the transparent conductive layer electrically connects the subset of optoelectronic devices of the array of optoelectronic devices .12 . Method according to claim 9 to 11 , wherein the step of forming a conductive grid structure comprises the step ofDepositing a conductive oxide layer on the top surface ;Structuring the conductive oxide layer to form the conductive grid structure .13 . Method according to any of claims 9 to 12 , the step of forming a conductive grid structure comprises the step ofDepositing a structured metallic layer , in particularly including at least one of Au, Ti , Pt , Ni , Cu, Al and Ag on the top surface ; - Depositing a conductive oxide layer , in particular one of ITOZnO or a native oxide comprising a metal selected from the group consisting of Ti , Cr , Ni and Al on the structured metallic layer and optionally on the emission surface surrounded by the structured metallic layer .14 . Method according to any of claims 9 to 13 , wherein the step of forming an optical element in the area surrounded by conductive grid structure comprises the step of forming at least one of a lens , an anti-reflective coating, a DBR mirror, and a photonic crystal structure .

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